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The Chemistry of Benzodisilacyclobutenes and Benzobis(disilacyclobutene)s: New Development of Transition-Metal-Catalyzed Reactions, Stereochemistry and Theoretical Studies
Abstract
The synthesis and reactions of 3,4-benzo-1,2-disilacyclobut-3-enes and benzo[1,2:4,5]bis(1,2-disilacyclobut-3-ene)s developed in our group are reported in this review. The palladium-, platinum- and nickel-catalyzed reactions of benzodisilacyclobutenes and benzobis(disilacyclobutene)s with unsaturated compounds afford various types of products. The structures of the products depend highly on the nature of transition metal used as a catalyst. The reactions of cis- and trans-benzodisilacyclobutene with alkenes and alkynes in the presence of a transition-metal catalyst proceed with high stereospecificity to give the respective adducts. The thermal reactions of cis- and trans-benzodisilacyclobutene with various substrates also proceed stereospecifically to give adducts. Results of theoretical calculations for the platinum-catalyzed reaction of disilacyclobutene with acetylene, the nickel-catalyzed reaction of benzodisilacyclobutene and thermal reaction of benzobis(disilacyclobutene) are discussed in this review.
... 9−11 On the other hand, platinumcatalyzed reactions of tetraisopropyl-substituted benzodisilacyclobutene with the same alkynes afford two types of products, benzodisilacyclohexadienes and benzodisilacyclopentenes. 12,13 Recently, we have demonstrated that the platinum-catalyzed reactions of 2,3-bis(diethylsilyl)thiophene with alkynes such as diphenylacetylene, 3-hexyne, and phenylacetylene afford the respective [1,4]disilino [2,3-b]thiophenes. 14 In these reactions, [1,2,5]platinadisilolo [3,4-b]thiophene derivatives would be formed as the reactive intermediates. ...
... Thus, when a mixture of 1 and mesitylacetylene in the presence of the same catalyst was heated to reflux in benzene for 4 h, a mixture of the regioisomers was obtained in an almost quantitative yield (Scheme 8). The regioisomers were separated using column choromatography and assigned as [2-(diisopropylsilyl)thiophen-3-yl]diisopropyl(mesitylethynyl)silane (12) and [3-(diisopropylsilyl)thiophen-2-yl]diisopropyl-(mesitylethynyl)silane (13) by MS and 1 H, 13 C, and 29 Si NMR spectroscopy. ...
... The solvent was evaporated, and the residue was distilled under reduced pressure to give 2.35 g (37% yield) of 2,3bis(diisopropylsilyl)thiophene 1: bp 77−80°C/2 torr; anal. calcd for C 16 13 ...
The reactions of 2,3-bis(diisopropylsilyl)thiophene (1) with diphenylacetylene, phenylacetylene, trimethylsilylacetylene, and mesitylacetylene have been reported. The reactions of 1 with diphenylacetylene and phenylacetylene in the presence of a catalytic amount of tetrakis(triphenylphosphine)platinum(0) at 80 °C gave [1,4]disilino[2,3-b]thiophene derivatives. With trimethylsilylacetylene, 1 afforded two types of products arising from sp-hybridized C–H bond activation of the acetylene, together with [1,3]disilolo[4,5-b]thiophene derivatives. A similar treatment of 1 with mesitylacetylene produced two regioisomers of products arising from the C–H bond activation of mesitylacetylene. Theoretical calculations for the intramolecular reactions of 10a and 10b are also discussed.
... Although the BDE difference between the strain-free C-C and Si-C bonds is small, strain could be more important in the SCB ring than in the all-carbon cyclobutene ring (vide infra). Here it can be noted that the cyclobutene and disilacyclobut-3-ene rings are less suitable than the SCB ring because the former opens only rarely upon photolysis (e.g., benzocyclobutene does not undergo photochemical ring-opening unless further derivatized) [14,49], while the latter is unstable and readily oxidized in air to 1,3-disila-2-oxacyclopentenes [50]. It should also be noted that strained four-membered rings with heteroatoms from Groups 15 and 16 are problematic in the context of excited state aromaticity indicators as these heteroatoms provide lone-pair electrons that will interact electronically with the π-conjugated annulene. ...
Baird’s rule tells that the electron counts for aromaticity and antiaromaticity in the first ππ* triplet and singlet excited states (T1 and S1) are opposite to those in the ground state (S0). Our hypothesis is that a silacyclobutene (SCB) ring fused with a [4n]annulene will remain closed in the T1 state so as to retain T1 aromaticity of the annulene while it will ring-open when fused to a [4n + 2]annulene in order to alleviate T1 antiaromaticity. This feature should allow the SCB ring to function as an indicator for triplet state aromaticity. Quantum chemical calculations of energy and (anti)aromaticity changes along the reaction paths in the T1 state support our hypothesis. The SCB ring should indicate T1 aromaticity of [4n]annulenes by being photoinert except when fused to cyclobutadiene, where it ring-opens due to ring-strain relief.
Organosilane compounds are widely used in both organic synthesis and materials science. Particularly, 1,2-disilylated and gem-disilylated alkenes, characterized by a carbon-carbon double bond and multiple silyl groups, exhibit significant potential for subsequently diverse transformations. The versatility of these compounds renders them highly promising for applications in materials, enabling them to be valuable and versatile building blocks in organic synthesis. This review provides a comprehensive summary of methods for the preparation of cis/trans-1,2-disilylated and gem-disilylated alkenes. Despite notable advancements in this field, certain limitations persist, including challenges related to regioselectivity in the incorporation and chemoselectivity in the transformation of two nearly identical silyl groups. The primary objective of this review is to outline synthetic methodologies for the generation of these alkenes through disilylation reactions, employing silicon reagents, specifically disilanes, hydrosilanes, and silylborane reagents. The review places particular emphasis on investigating the practical applications of the C-Si bond of disilylalkenes and delves into an in-depth discussion of reaction mechanisms, particularly those reactions involving the activation of Si-Si, Si-H, and Si-B bonds, as well as the C-Si bond formation.
The activation of the silicon-silicon bond in disilane Ph 2 Si(μ-Pz Me2 ) 2 SiPh 2 ( 1 ), which possesses two five-coordinate silicon centers, was achieved by a reaction with Pd(0) or Ni(0) precursors of modest steric demand...
A systematized survey of reviews and monographs published in 2016 on all aspects of heterocyclic chemistry is given.
Silylboronic esters bearing a N,N-dialkylaminomethyl group on the silicon atoms were synthesized and used in palladium-catalyzed reactions. Five silylboronic esters were synthesized through a reaction of the [(N,N-dialkylaminomethyl)diorganosilyl]lithiums with i-PrOB(pin). An addition reaction of the silylboronic ester to ethynylbenzene (silaboration) took place efficiently by a phosphine- and isocyanide-free palladium catalyst to give (E)-1-silyl-2-boryl-1-phenylethene in a regio- and stereoselective manner. On the other hand, the silylboronic esters underwent β-elimination reactions in the presence of a palladium catalyst and styrene to afford 1,3-disilacyclobutanes and aminoboranes in good yields. This may be due to the generation of silene intermediates during the reaction. It should be noted that use of styrene as a ligand was essential for the generation of the silene species.
The synthesis and platinum-catalyzed reactions of 2,3-bis(dimethylsilyl)furan (1) have been reported. The reactions of 1 with diphenylacetylene and phenyl(trimethylsilyl)acetylene in the presence of a platinum catalyst gave the corresponding six-membered ring compounds produced from dehydrogenative double silylation of alkynes. The similar reactions of 1 with mono-substituted acetylenes such as phenylacetylene and trimethylsilylacetylene proceeded to give the regioisomers of cyclic products. DFT calculations for the reaction mechanism of the platinum-catalyzed reaction of 1 with phenyl(trimethylsilyl)acetylene are also reported.
The reactions of 2,3-bis(diethylsilyl)thiophene 1 with alkynes such as diphenylacetylene, 3-hexyne and phenylacetylene in the presence of a catalytic amount of Pt(PPh3)4 in benzene at 80 °C proceeded to give products 2, 3, and 6a,b, respectively. Treatment of a mixture consisting of 1 and 1,4-diethynylbenzene with a Pt(PPh3)4 catalyst in refluxing benzene produced three types of isomers consisting of two di(silyl)thiophene units and a diethynylbenzene unit. Computational analyses for the reaction mechanism of the platinum-catalyzed reaction have also been reported.
The synthesis and palladium-catalyzed reactions of cis- and trans-3,4-benzo-1,2-diisopropyl- 1,2-dimethyl-1,2-disilacyclobut-3-ene (1a and 1b) are reported. Their reactions with diphenylacetylene in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium(0) proceeded with high stereospecificity to give cis- and trans-5,6-benzo-1,4-diisopropyl-1,4-dimethyl- 2,3-diphenyl-1,4-disilacyclohexa-2,5-diene, 2a and 2b, in 95% and 93% yield, respectively. Similar palladium-catalyzed reactions of 1a and 1b with monosubstituted acetylenes, such as 1-hexyne, tert-butylacetylene, phenylacetylene, and trimethylsilylacetylene, also proceeded stereospecifically to afford the respective cis- and trans-5,6-benzo-1,4-disilacyclohexa-2,5-dienes, 3a - 6a and 3b - 6b, in excellent yields and as the sole products. The palladium-catalyzed reaction of 1a with styrene gave a mixture consisting of two stereoisomers, cis-2- and trans-2-phenyl-substituted 5,6- benzo-(r-1),cis-4-diisopropyl-1,4-disilacyclohex-5-ene 7a and 8a in a ratio of 5 : 3 in 72% combined yield, while the reaction of styrene with 1b afforded two stereoisomers, 7b and 8b, in a ratio of 2 : 1 in 80% combined yield. With 1-hexene, 1a gave two stereoisomers, 5,6-benzo-cis-2-(nbutyl)-( r-1),cis-4-diisopropyl- and 5,6-benzo-trans-2-(n-butyl)-(r-1),cis-4-diisopropyl-1,4-dimethyl- 1,4-disilacyclohex-5-ene, 9a and 10a, in a ratio of 1 : 1 in 70% combined yield. A similar reaction of 1b with 1-hexene produced 5,6-benzo-cis-2-(n-butyl)-(r-1),trans-4-diisopropyl-1,4-dimethyl-1,4- disilacyclohex-5-ene in 81% yield and as a single isomer
The Wurtz type coupling of a mixture of meso- and dl-1,4-bis(chloromethylphenylsilyl)butanes with lithium metal in the presence of a catalytic amount of dimethylphenylsilyllithium afforded cis- and trans-1,2-disilacyclohexane (1a and 1b) in a ratio of 4:6. Pure 1a and 1b obtained by fractional distillation reacted with diphenylacetylene in the presence of a platinum catalyst at 200 °C to give stereospecifically the respective cis- and trans-1,4-dimethyl-1,2,3,4-tetraphenyl-1,4-disilacyclooct-2-ene (2a and 2b). Under identical conditions, the reactions of 1a and 1b with 1-phenyl-1-propyne, 3-hexyne, and phenylacetylene also proceeded with stereospecificity to form similar adducts.
The Wurtz type coupling of a mixture of meso- and dl-1,3-bis(chloromethylphenylsilyl)propanes with sodium metal afforded a mixture of cis- and trans-disilacyclopentanes (1a and 1b) in a ratio of 1:1. Pure 1a and 1b obtained by fractional distillation reacted with molecular oxygen in the presence of AIBN stereospecifically to give the respective cis- and trans-cyclic siloxanes (2a and 2b), with retention of configuration. The reactions of 1a and 1b with MCPBA produced cleanly 2a and 2b in high yields, respectively. The palladium-catalyzed reactions of 1a and 1b with phenylacetylene gave stereospecifically cis- and trans-1,4-dimethyl-1,2,4-triphenyl-1,4-disilacyclohept-2-enes (3a and 3b), in high yields. Similar treatment of 1a and 1b with diphenylacetylene also proceeded with high stereospecificity to give cis- and trans-1,4-dimethyl-1,2,3,4-tetraphenyl-1,4-disilacyclohept-2-enes (4a and 4b), respectively. The results of an X-ray crystallographic study for products 4a and 4b are described.
The organopolysilanes are those compounds containing at least one siliconsilicon bond and one silicon–carbon linkage. This review is mainly concerned with the chemistry of aliphatic derivatives of polysilanes. The reaction of concentrated sulfuric acid with hexamethyldisilane at room temperature proceeds in two distinct steps: first, a heterogeneous but fast step, and second, a homogeneous but slow one. The first step corresponds to cleavage of one methyl from one silicon, while the second step involves cleavage of the second methyl from another silicon. Demethylation by sulfuric acid can be successfully extended to certain organofunctional methyldisilanes. The chlorodemethylation with anhydrous hydrogen chloride or with acetyl (or benzoyl) chloride in the presence of anhydrous aluminum chloride affords another widely applicable method for preparation of methylchlorodisilanes and polysilanes. The organohalopolysilanes are capable of undergoing many of the reactions that are common to the related monosilane derivatives, with the silicon–silicon bond intact.
Vinylidene complexes can be prepared in the coordination sphere of rhodium with silylalkynes, RCCSiMe3 whereas such complexes were hitherto accessible only with 1-alkynes, RCCH. The synthesis proceeds via a [1,2]-SiMe3 migration along the alkyne CC bond, which is just as facile as [1,2]-H shifts. The corresponding alkyne complexes formed as intermediates can also be isolated.
The reaction of cis-3,4-benzo-1,2-diisopropyl-1,2-dimethyl-1,2-disilacyclobut-3-ene (1a) with ethylene in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium(0) in benzene at room temperature proceeded stereospecifically to give a 1:2 adduct, 3,4,9,10-dibenzo-1,2,5,8-tetrasilacyclodeca-3,9-diene (3a), consisting of two molecules of 1a and one molecule of ethylene, in 58% yield, along with a 1:1 adduct, cis-2,3-benzo-1,4-diisopropyl-1,4-dimethyl-1,4-disilacyclohex-2-ene (2a), in 7% yield. The reaction of trans isomer 1b with ethylene under the same conditions afforded two types of 1:2 adducts, 3b,c (64% combined yield), whose configurations at the silicon atoms were maintained, in a ratio of 1:1, together with the 1:1 adduct 2b (5% yield) with trans configuration. The reaction of a 1:1 mixture of 1a,b with ethylene in the presence of a catalytic amount of palladium(II) dichloride under the same conditions also gave the 1:2 adducts 3a–c (3a:3b:3c = 3:1:1) in 63% combined yield, together with 2a,b (2a:2b = 1:3) in 16% combined yield. The structures of 3a,b were determined by crystallographic analysis. Treatment of a mixture consisting of 1a and 2a with a tetrakis(triphenylphosphine)palladium(0) catalyst in benzene at room temperature did not produce 3a; instead, 1a and 2a were recovered unchanged.
Thermal reactions of benzodisilacyclobutene (1) and disilacyclobutene (2) with acetylene were investigated theoretically. The reactions are thought to proceed via the conventional Diels− Alder reaction of disilabutadiene, the conrotatory ring-opening product of disilacyclobutene, with acetylene. However, this mechanism is incompatible with the observed similar reactivities of 1 and 2 with acetylene and the retention of stereochemistry during the reaction. In our previous paper, we proposed an alternative [2 + 1] cycloaddition pathway that involved the direct addition of acetylene to the Si−Si σ−bond of 1 without ring opening. In this study, we extensively investigated the reaction pathways for both 1 and 2 on a theoretical basis. We found that charge transfer (CT) played a key role in the [2 + 1] cycloaddition pathway. On the basis of natural bond orbital (NBO) analysis, the interaction of the Si−Si σ-bond orbital (donor) with the π* orbital (acceptor) of the acetylene was attributed mainly to the CT process. Finally, an experiment to verify the [2 + 1] cycloaddition mechanism was proposed, in which the use of triacetylene as a terminal alkyne would allow the key intermediate in the pathway to be trapped. ■ INTRODUCTION This paper describes a theoretical mechanistic investigation of the reactions of benzodisilacyclobutenes (1) and disilacyclobu-tenes (2) with acetylene, which lead to benzodisilacyclohex-adienes (3) and disilacyclohexadienes (4), respectively. Recently, we proposed a new [2 + 1] addition mechanism for the reaction, 1 although a two-step mechanism is generally recognized for the reactions of 1 and 2 with terminal alkynes. 2
The thermal reaction of cis-3,4-benzo-1,2-diisopropyl-1,2-dimethyl-1,2-disilacyclobut-3-ene (1a) with tert-butyl alcohol at 300 °C for 24 h proceeded with high stereospecificity to give erythro-1-(tert-butoxyisopropyl-methylsilyl)-2-(isopropylmethylsilyl)benzene (2a) in 71% yield, as a single stereoisomer. A similar reaction of trans-benzodisilacyclobutene (1b) with tert-butyl alcohol produced the threo isomer 2b in 81% yield, as the sole product. The photolysis of 1a,b in the presence of tert-butyl alcohol afforded a mixture of two adducts formed by the reaction of 1-[2-(isopropylmethylsilyl)phenyl]-1-isopropylsilene with tert-butyl alcohol, respectively. The reaction of 1a with ethylene in an autoclave at 300 °C for 24 h gave 3,4,9,10-dibenzo(r-1)-trans-2,trans-5,cis-8-tetraisopropyl-1,2,5,8-tetrasilacyclododeca-3,9-diene (10a), as a single stereoisomer in 71% yield. The reaction of 1b with ethylene under the same conditions, however, produced poly[1,2-bis(isopropylmethylsilylene)phenylene−ethylene], whose molecular weight was determined to be 61000 (M w /M n = 2.32), relative to polystyrene standards. The reaction of 1a with 1-hexyne, tert-butylacetylene, phenylacetylene, and (trimethylsilyl)acetylene in benzene in a sealed degassed tube at 150 or 200 °C proceeded stereospecifically to give the respective cis-5,6-benzo-1,4-diisopropyl-1,4-dimethyl-1,4-disilacyclohexa-2,5-diene derivatives (11a−14a) in high yields as the sole products. The reaction of 1b with the alkynes under the same conditions afforded the respective trans-benzodisilacyclohexadienes (11b−14b), as the sole stereoisomers in high yields. Theoretical treatment for the reaction of 3,4-benzo-1,1,2,2-tetramethyl-1,2-disilacyclobut-3-ene (1c) with tert-butyl alcohol and acetylene indicated that the substrates react directly with 1c to give the respective adducts. For the reaction of 1c with acetylene, it has been shown that the acetylene molecule inserts directly into a silicon−silicon bond in 1c to give the benzodisilacyclohexadiene system. Such direct reactions of the substrates with 1c were shown to be energetically more advantageous than the reaction of o-quinodisilane, 1,2-bis(dimethylsilylene)cyclohexa-3,5-diene, arising from a conrotatory ring-opening reaction of 1c with substrates. ■ INTRODUCTION The chemistry of benzodisilacyclobutenes is interesting because of their high strain energy, which results in high reactivity. They show unique behavior in photochemical and thermal reactions and also in transition-metal-catalyzed reactions. 1−9 The thermal reaction of 3,4-benzo-1,1,2,2-tetramethyl-1,2-disilacyclobut-3-ene proceeds with ring opening to give poly[(o-tetramethyldisilanylene)phenylene] with high molecular weight. 7 The thermal reactions of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene with tert-butyl alcohol, aldehydes, and alkynes, however, afford the respective adducts. 8,11 With
Orbital symmetry controls in an easily discernible manner the feasibility and stereochemical consequences of every concerted reaction.
The thermolysis of hexamethylsilacyclopropane in the presence of 1,1-dimethyl-2,3-bis(trimethylsilyl)-1-silacyclopropene resulted in formation of octamethyl-1,2-disilacyclobutane and 1,1,2,2-tetramethyl-3,4-bis(trimethylsilyl)-1,2-disilacyclobut-3-ene via Me2Si insertion into the silacyclopropane and silacyclopropene rings. Thermolysis of hexamethylsilacyclopropane alone in benzene at 70° gave the former compound in 40% yield. Oxidation of these compounds with O2 gave the respective 1,3-disila-2-oxa-cyclopentane and 1,3-disila-2-oxa-cyclopent-4-ene compounds. Four new silacyclopropenes (VIIIa–d) have been prepared and characterized.
Fluorinated and angle-strained Si—Si compounds undergo palladium-catalyzed disilane metathesis and double silylation of acetylenes, the latter being stereospecific at silicon atoms.
This article provides an account of the group 10 transition-metal complexes with metal–silicon bonds formed by the reaction of hydrosilanes with group 10 transition-metal complexes, with particular emphasis on the unique chemistry of 1,2-disilylbenzene, 1-dimethylsilyl-2-silylbenzene and bis(2-silylphenyl)silane. These hydrosilanes provide sterically less congested bidentate and tridentate silyl ligands and make it possible to stabilize a number of unusual mono-, di- and trinuclear poly(silyl) group 10 metal complexes including those of high formal valence state.
The photochemical dimerization of 1,1,2,2-tetrafluoro-1,2-disilacyclobutene mediated by Group VI transition metal carbonyls generates (fluorosilyl)(trifluorosilyl)alkenes (5) by fluorine atom migration. The electronic properties (hardness) of the central metal influence the selection of the reaction pathway: F migration to give the dimer 5 or further oxidative addition to give the tetrasilyl transition metal compound 7 or 9.
The use of trialkylsilyl metal carbonyl complexes as reagents for organometallic synthesis was investigated. In this communication it was reported that the metal silanes (CO)/sub 5/MnSi(CH/sub 3/)/sub 3/(1), (CO)/sub 4/Fe(SiCH/sub 3/)/sub 3/)/sub 2/(2), and (CO/sub 4/)FeSi(CH/sub 3/)/sub 2/(CH/sub 2/CH/sub 2/Si(CH/sub 3/)/sub 2/(3) undergo reactions with benzaldehyde which result, under appropriate conditions, in the formation of ..cap alpha..-silyloxybenzyl- and benzylidene-derived ligands. It was reported that a strongly oxygenophilic group must be present on manganese in order for a benzaldehyde adduct to be detectably formed. The catalytic hydrosilyation of aldehydes and ketones has been postulated to involve a similar carbonyl group addition by a catalytically active L/sb n/M(H)SiR/sub 3/ species. The presence of chelating disilane ligand enables the chemistry of 3 to dramaticaly diverge from that of 2. With aliphatic aldehydes and ketones, 1 and 2 react differently. (DP)
Benzo[1,2:4,5]bis(1,1,2,2-tetraisopropyldisilacyclobutene) (1) was synthesized. The X-ray crystal analysis shows that the benzene ring is deformed from the D6h symmetry. Compound 1 shows an intense 1Lb absorption band in the UV spectrum. In the emission spectrum, intense phosphorescence (Φp = 0.72) was observed at 77 K.
The metathesis of the Si–Si bonds of benzo[1,2∶4,5]-bis(1,1,2,2-tetramethyl-1,2-disilacyclobut-3-ene) with Pd(PPh3)4 gave 1,2,9,10,17,18,25,26,27,28,35,36,37,38,39,40- hexadecasila[28](1,2,4,5)cyclophane and its open-chain homologs, in which the σ–π conjugation is extended all over the molecule.
The thermolysis of 1,2-di(adamantoyl)tetrakis(trimethylsilyl)disilane (1a) with diphenylacetylene at 140 degrees C for 24 h afforded 1-[(E)-1,2-diadamantyl-2-(trimethylsiloxy)ethenyloxy]-2,3-diphenyl-1-[tris(trimethylsilyl)silyl]-1- silacycloprop-2-ene (2a) and 3,4-diadamantyl-2,2-bis(trimethylsiloxy)-1,1-bis(trimethylsilyl)1,2-disilacyclobut-3-ene (3a) in 43% and 41% yields, respectively. Similarly, the cothermolysis of 1,2-di(pivaloyl)tetrakis(trimethylsilyl)disilane (1b) with diphenylacetylene gave 1-[(E)-1,2-di(tert-butyl)2-(trimethylsiloxy)ethenyloxy]-2,3-diphenyl-1-[tris(trimethylsilyl)silyl]-1-silacycloprop-2-ene (2b) in 52% yield, along with a mixture of unidentified products. The reaction of 1a with bis(trimethylsilyl) acetylene under the same conditions produced 1-[(E)-1,2-diadamantyl-2-(trimethylsiloxy)ethenyloxy]-2,3-bis(trimethylsilyl)-1-[tris(trimethylsilyl)silyl]-1-silacycloprop-2-ene and 3a in 54% and 23% yield, while 1b with bis(trimethylsilyl) acetylene gave 1-[(E)-1,2-di(tert-butyl)-2-(trimethylsiloxy)ethenyloxy]-2,3-bis(trimethylsilyl)-1-[tris(trimethylsilyl)silyl]-1-silacycloprop-2-ene in 62% yield. The results of X-ray crystallographic analysis for the 1-silacycloprop-2-ene 2a are described. Computational analyses for successive isomerization of a simplified model, 1,2-di(acetyl) tetra(silyl) disilane to a silylene intermediate, [(E)-1,2-dimethyl-2-siloxyethenyloxy]tri(silyl)silylsilylene via trans-3,4-dimethyl-3,4-di(siloxy)-1,2-di(silyl)-1,2-disilacyclobut-1-ene, are described. The results of the calculations for the real models having the same substituents as 1b are also reported.
The reaction of cis- and trans-3,4-benzo-1,2-di(tert-butyl)-1,2-dimethyl-1,2-disilacyclobut-3-ene (1a and 1b) with chlorine gas in carbon tetrachloride proceeded stereospecifically to give meso- and rac-1,2-bis[(tert-butyl)chloromethylsilyl]benzene (2a and 2b, respectively). The condensation of 2a and 2b with lithium and sodium produced a mixture of cis- and trans-benzodisilacyclobutene 1a and 1b, respectively. The reaction of 1a and 1b with molecular oxygen proceeded with high stereospecificity to give the respective cis- and trans-4,5-benzo-2-oxa-1,3-disilacyclopent-4-ene. The palladium-catalyzed reactions of 1a and 1b with phenylacetylene, 1-hexyne, tert-butylacetylene, phenyl-1-propyne, and diphenylacetylene proceeded in a stereospecific fashion to give the corresponding 5,6-benzo-1,4-disilacyclohexa-2,5-diene derivatives. Similar reactions of 1a and 1b with trimethylsilylacetylene, dimethylphenylsilylacetylene, and mesitylacetylene gave stereospecifically the erythro- and threo-1,2-bis(silyl)benzene derivatives. The structure of trans-5,6-benzo-1,4-di(tert-butyl)-1,4-dimethyl-2-phenyl-1,4-disilacyclohexa-2,5-diene was determined by single-crystal X-ray crystallography.
The reactions of pure cis- and trans-3,4-benzo-1,2-di(tert-butyl)-1,2-dimethyl-1,2-disilacyclobut-3-ene (1a and 1b) with oxygen in the presence of AIBN in refluxing benzene proceeded stereospecifically to give the respective siloxanes, 4a and 4b. The palladium-catalyzed reactions of 1a and 1b with phenylacetylene and 1-hexyne produced stereospecifically cis- and trans-5,6-benzo-1,4-disilacyclohexa-2,5-dienes. The results obtained from computational analyses of the adduct of 1,1,2,2-tetramethyl-1,2-disilacyclobut-3-ene and CH3COO• using the Gaussian 98 program at the UB3LYP/6-311+G** level of density functional theory are also described.
Treatment of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobutene (1) with a catalytic amount of (eta2-ethylene)bis(triphenylphosphine)platinum(0) in refluxing benzene gave 1-(diethylphe-nylsilyl)-2-(diethylsilyl)benzene (2) and cis-4,5-benzo-1,1,3-triethyl-2-methyl-1,3-disilacyclopent-4-ene (3) in 10 % and 67 % yields. The platinum-catalyzed reaction of 1 with ethylene produced 5,6-benzo-1,1,4,4-tetraethyl-1,4-disilacyclohex-5-ene, while with styrene and 1-hexene, compound 1 afforded 4,5-benzo-1,3-disilacyclopent-4-ene derivatives. A similar reaction of 1 with a-methylstyrene produced an adduct arising from hydrosilylation of 3 to alpha-methylstyrene. The reaction of 1 with phenylacetylene, diphenylacetylene, phenyl(trimethylsilyl)acetylene, and 3-hexyne in the presence of a platinum catalyst yielded the respective 5,6-benzo-1,4-. disilacyclohexa-2,5-dienes. With benzaldehyde, 1 gave a 5,6-benzo-2-oxa-1,4-disilacyclohex-5-ene derivative.
The reactions of 3,4-benzo-1,1,2,2-tetra(isopropyl)-1,2-disilacyclobut-3-ene (1) with phenylacetylene and 1-hexyne in the presence of a catalytic amount of (η2-ethylene)bis(triphenylphosphine)platinum(0) at 200°C for 24 h gave two types of 1:1 adducts, 2-phenyl- and 2-butyl-substituted 5,6-benzo-1,1,4,4-tetra(isopropyl)-1,4-disilacyclohexa-2,5-diene and 2-benzylidene- and 2-pentylidene-substituted 4,5-benzo-1,1,3,3-tetra(isopropyl)-1,3-disilacyclopent-4-ene, respectively. With mesityl- and dimethylphenylsilylacetylene. 1 afforded 2-(mesityl)methylene- and 2-(dimethylphenylsilyl)methylene-4,5-benzo-1,1,3,3-tetra(isopropyl)-1,3-disilacylclopent-4-ene. A similar reaction of 1 with trimethylsilylacetylene produced an adduct arising from sp-hybridized CH bond activation of the acetylene, together with a benzodisilacyclopentene derivative. The reaction of 1 with diphenylacetylene yielded a 2,3-diphenyl-5,6-benzodisilacyclohexa-2,5-diene derivative, while with methylphenylacetylene and 2-hexyne, 1 gave 2-benzylidene- and 2-butylidene-5,6-benzo-1,4-disilacyclohex-5-ene, along with the benzodisilacyclohexa-2,5-diene derivatives. Similar treatment of 1 with methyl(trimethylsilyl)acetylene produced a 5,6-benzo-2-(trimethylsilyl)methylenedisilacyclohexene derivative.
The reactions of 3,4-benzo-1,1,2,2-tetra(isopropyl)-1,2-disilacyclobut-3-ene (2) with acetylene, phenylacetylene, 1-hexyne, and o-tolylacetylene in the presence of tetrakis(triphenylphosphine)palladium gave the respective 5,6-benzo-1,4-disilacyclohexa-2,5-dienes 3–6. Similar reactions of 2 with mesitylacetylene, trimethylsilylacetylene, and dimethylphenylsilylacetylene afforded 1-alkynyl(diisopropylsilyl)-2-(diisopropylsilyl)benzenes 7–9 arising from sp-hybridized CH bond activation of acetylenes. The reactions of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene with mesitylacetylene, trimethylsilylacetylene, and dimethylphenylsilylacetylene produced 5,6-benzo-1,4-disilacyclohexa-2,5-dienes 10–12 as the sole product. The stoichiometric reaction of 2 with tetrakis(triphenylphosphine)palladium gave a yield of 3,4-benzo-2,2,5,5-tetra(isopropyl)-1-pallada-2,5-disilacyclopent-3-ene (A), arising from insertion of a palladium species into a silicon-silicon bond in 2.
The reaction of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobutene (1) with benzene in the presence of a catalytic amount of Ni(PEt3)4 affo
Photolysis of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobutene gives a silene which can be trapped by t-butyl alcohol and acetone in high yields.
A new type of polymer, poly[o-(disilanylene)phenylene] was prepared via ring opening polymerization, at the SiSi bond, of 1,1,2,2-tetramethyl-1,2-disilabenzocyclobutene.
The palladium-catalyzed reaction of benzo[1,2:4,5]bis(1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene) (1) with styrene in refluxing benzene afforded two regioisomers of 1:2 adducts, benzo[1,2](1,1,4,4-tetraethyl-2-phenyl-1,4-disilacyclohex-4-ene)[4,5](1,1,4,4-tetraethyl-3-phenyl-1,4-disilacyclohex-4-ene) and benzo[1,2:4,5]bis(1,1,4,4-tetraethyl-2-phenyl-1,4-disilacyclohex-4-ene), whose isomers consist of cis and trans in a ratio of 1:1 in 91% combined yield. Similar reaction of 1 with 1-hexene gave two regioisomers involving cis and trans isomers in 89% combined yield. With ethylene, 1 produced benzo[1,2:4,5]bis(1,1,4,4-tetraethyl-1,4-disilacyclohex-5-ene) (8) in 70% yield, together with a 15% yield of a 2:3 adduct. The platinum-catalyzed reaction of 1 with styrene gave a 1:1 mixture of cis- and trans-benzo[1,2:4,5]bis(2-benzyl-1,1,3,3-tetraethyl-1,3-disilacyclopent-4-ene) in 90% yield. Similar treatment of 1 with 1-hexene produced cis- and trans-benzo[1,2:4,5]bis(1,1,3,3-tetraethyl-2-pentyl-1,3-disilacylopent-4-ene) in a ratio of 1:1 in 92% yield, while with ethylene, 1 afforded 8 as a main product, in addition to two types of 1:2 adduct as minor products.
The photolysis of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobutene (1) with a low-pressure mercury lamp bearing a Vycor filter in hexane gave 1,2-bis[(2-diethylsilyl)phenyl]tetraethyldisilane. Irradiation of 1 in the presence of tert-butyl alcohol gave 1-(tert-butoxydiethylsilyl)-2-(diethylsilyl)benzene, while in the presence of tert-butyl-d1 alcohol, compound 1 afforded 1-[tert-butoxy(1-deuterioethyl)ethylsilyl]-2-(diethylsilyl)benzene. The photolysis of 1 with acetone in hexane produced 2-(diethylsilyl)-1-[diethyl(isopropenyloxy)silyl]benzene. Irradiation of 1 with acetophenone gave 2-(diethylsilyl)-1-[diethyl[(1-phenylvinyl)oxy] silyl]benzene and 5,6-benzo-1,1,4,4-tetraethyl-3-methyl-3-phenyl-1,4-disila-2-oxacyclohexene (8). Similar irradiation of compound 1 with formaldehyde yielded 5,6-benzo-1,1,4,4-tetraethyl-1,4-disila-2-oxacyclohexene and 2-(diethylsilyl-1-[ethylmethoxyvinylsilyl]benzene in 12% and 27% yields, respectively. Irradiation of 1 with benzaldehyde gave 5,6-benzo-1,1,4,4-tetraethyl-3-phenyl-1,4-disila-2-oxacyclohexene (11). The photolysis of 1 with a high-pressure mercury lamp bearing a Pyrex filter in the presence of acetophenone and benzaldehyde gave compounds 8 and 11, respectively.
The thermolysis of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene (1) afforded 1,2-bis(diethylsilylene)cyclohexadiene (o-quinodisilane) as a reactive species, while its photolysis proceeded to give a silene, 1-ethyl-1-(2-diethylsilylphenyl)-1-silaprop-1-ene. Compound 1 reacted with a catalytic amount of tetrakis-(triethylphosphine)nickel(0) in benzene to give a benzene adduct. With a tetrakis(triphenylphosphine)palladium(0) catalyst, 1 produced a dimer. Similar reaction with an (η2-ethylene)bis(triphenylphosphine)platinum(0) catalyst afforded an isomerization product of 1. The transition-metal-catalyzed reactions of 1 in the presence of various trapping agents have also been described.
The nickel-catalyzed reactions of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene (1) with disubstituted acetylenes have been investigated. Treatment of 1 with 3-hexyne and diphenylacetylene at 150°C gave two types of adducts: 5,6-benzo-1,4-disilacyclohexa-2,5-diene and 5,6-benzo-1,2-disilacyclohexa-3,5-diene, together with a small amount of the other isomer. The reaction of 1 with phenyl(trimethylsilyl)acetylene produced 5,6-benzo-1,1,4,4-tetraethyl-3-phenyl-2-trimethylsilyl-1,4-disilacyclohexa-2,5-diene and 4,5-benzo-1,1,3,3-tetraethyl-2-[phenyl(trimethylsilyl)methylene]-1,3-disilacyclopent-4-ene (10). Similar reaction of 1 with 1-(trimethylsilyl)hexyne also afforded 5,6-benzo-3-butyl-1,1,4,4-tetraethyl-2-trimethylsilyl-1,4-disilacyclohexa-2,5-diene and 4,5-benzo-2-[butyl(trimethylsilyl)methylene]-1,1,3,3-tetraethyl-1,3-disilacyclopent-4-ene (12). A vinylidene carbene-nickel complex is proposed for the formation of 10 and 12, as a key intermediate.
The reactions between silicon difluoride and propyne, propyne-d1, 1-butyne, 2-butyne, and 3,3-dimethyl-1-butyne were studied. In each case products resulting from combining ratios (SiF2:alkyne) of 2:1 and 2:2 were isolated and identified. The 2:1 compounds were shown to be derivatives of disilacyclobutene, while three types of 2:2 compounds were identified. These either had an open chain structure, resulting from migration of either α (to C≡C)—CH or acetylenic H, or were derivatives of disilacyclohexadiene. Rationalizations of the types of products found and of the conditions which affect the reaction mechanism are discussed.
Two new 1,2-disilacyclobutenes have been prepared by the reaction of tetramethyldisilene with acetylenes. Several reactions of these new 1,2-disilacyclobutenes including oxidation, silylene insertion, iron carbonyl insertion, and addition to acetylenes and dienes are reported.
Heating a benzene solution of benzo[1,2:4,5]bis(1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene) (1) with a catalytic amount of tetrakis(triethylphosphine)nickel(0) gave two regioisomers, 2 and 3, arising from C−H bond activation of benzene in 81% combined yield. The reaction of 1 with diphenylacetylene in the presence of the nickel catalyst afforded benzo[1,2:4,5]bis(1,1,4,4-tetraethyl-2,3-diphenyl-1,4-disilacyclohexa-2,5-diene) in 91% yield, while with 3-hexyne, 1 yielded benzo[1,2:4,5]bis(1,1,2,3,4,4-hexaethyl-1,4-disilacyclohexa-2,5-diene) and its isomer (7) in 64% and 25% yields, respectively. The nickel-catalyzed reaction of 1 with benzophenone gave benzo[1,2](1,1,3,3-tetraethyl-2-oxa-1,3-disilacyclopent-4-ene)[4,5](1,1,3,3-tetraethyl-2,2-diphenyl-1,3-disilacyclopent-4-ene) and siloxane (8) in 40% and 50% yields. Similarly, with 4,4‘-dimethylbenzophenone, 1 produced benzo[1,2](1,1,3,3-tetraethyl-2-oxa-1,3-disilacyclopent-4-ene)[4,5](1,1,3,3-tetraethyl-2,2-(p-tolyl)-1,3-disilacyclopent-4-ene) in 19% yield, together with a 50% yield of 8. When the similar treatment of 1 with benzophenone was carried out in cyclohexene, 7,7-diphenylnorcarane was obtained in 14% yield, along with a 54% yield of 8.
The reaction pathways for the thermal additions of disilacyclobutenes and acetylene are discussed from B3LYP density-functional-theory computations. Butadiene is more stable in energy than cyclobutene, the corresponding ring compound, whereas disilabutadiene is less stable than disilacyclobutene. From detailed analyses of the potential energy surfaces, disilabutadienes formed by thermal ring opening of disilacyclobutenes are confirmed to play a central role in the addition reactions as intermediates in a manner similar to the Diels−Alder reaction. The activation energies for the symmetry-allowed conrotatory ring opening of 1,2-disilacyclobut-3-ene, 1,1,2,2-tetramethyl-1,2-disilacyclobut-3-ene, and 3,4-benzo-1,1,2,2-tetramethyl-1,2-disilacyclobutene are 41.5, 46.7, and 61.9 kcal/mol, respectively, and the activation energies for the Diels−Alder coupling reactions with acetylene are 1−4 kcal/mol when measured from the disilabutadiene intermediates at the B3LYP/6-31G** level of theory. Therefore the ring opening should be the rate-determining step in these reactions; once the four-membered ring of disilacyclobutene is opened by heat treatment, the addition reactions should readily take place, leading to six-membered ring products. The transition state for the addition of 1,4-disila-1,3-butadiene and acetylene is symmetrical with respect to the Si−C bonds being formed, whereas those of 1,1,4,4-tetramethyl-1,4-disila-1,3-butadiene and acetylene and of 1,2-bis(dimethylsilylene)cyclohexa-3,5-diene and acetylene are not symmetrical. There are good reasons that such asymmetrical transition states occur in these Diels−Alder reactions; one is the asymmetrical frontier orbitals in the methyl-substituted disilabutadienes, and the other is just a steric effect of the methyl groups.
Benzo[1,2:4,5]bis(1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene) (1) was synthesized in situ by the reaction of 1,2,4,5-tetrabromobenzene with magnesium in the presence of diethylfluorosilane in THF. The reaction of 1 with diphenylacetylene in the presence of a catalytic amount of (η2-ethylene)bis(triphenylphosphine)platinum(0) in refluxing benzene gave a 1:2 adduct, benzo[1,2:4,5]bis(1,1,4,4-tetraethyl-2,3-diphenyl-1,4-disilacyclohexa-2,5-diene) in 91% yield. Similar platinum(0)-catalyzed reaction of 1 with 3-hexyne and acetylene in refluxing benzene afforded the respective 1:2 adducts benzo[1,2:4,5]bis(disilacyclohexadiene) derivatives in excellent yields. Benzobis(disilacyclobutene) 1 also reacted with diphenylacetylene, 3-hexyne, and acetylene in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium(0) to give the corresponding 1:2 adducts in excellent yields. Computational analyses of benzo[1,2:4,5]bis(disilacyclobutene) and its 1:1 and 1:2 adducts with acetylene were carried out using the B3LYP density-functional-theory method; the structures of these compounds were shown to be planar. The Si−Si bond in the disilacyclobutene ring appeared from computations to be effectively cleaved by a platinum(0) complex.
Thermolysis of 1,1-dimethyl-2-phenyl-3-(trimethylsilyl)-1-silacyclopropene and 3-(ethyldimethylsilyl)-1,1-dimethyl-2-phenyl-1-silacyclopropene in a sealed glass tube at 250°C afforded the respective 1,4-disilacyclohexa-2,5-dienes consisting of two isomers in good yields. Under identical conditions 3-(tert-butyldimethylsilyl)-1,1-dimethyl-2-phenyl-1-silacyclopropene yielded 4-(tert-butyldimethylsilyl)-1,1,2,2-tetramethyl-3-phenyl-1,2-disilacyclobutene in high yield, while 1,1-dimethyl-2-phenyl-3-(phenyldimethylsilyl)-1-silacyclopropene gave two isomers of a 1-silacyclopenta-2,4-diene and 1,1,2,2-tetramethyl-3-phenyl-4-(phenyldimethylsilyl)-1,2-disilacyclobutene. From 1-methyl-1,2-diphenyl-3-(trimethylsilyl)-1-silacyclopropene, two isomers of the 1-silacyclopenta-2,4-diene and trans-1,4-dimethyl-1,2,4,5-tetraphenyl-3,6-bis(trimethylsilyl)-1,4- disilacyclohexa-2,5-diene were obtained. Similar thermolysis of 1,1,2-triphenyl-3-(trimethylsilyl)-1-silacyclopropene gave 1,1,3,4-tetraphenyl-2,5-bis(trimethylsilyl)-1-silacyclopenta-2,4-diene as a main product. A mechanism for dimerization of the silacyclopropenes is discussed on the basis of the molecular orbital calculations.
This article reviews recent advances in late-transition-metal complexes with chelating Si and Ge ligands. Compounds with two Si−H bonds, such as bis(silyl)alkanes, bis(silyl)arenes, and tetramethyldisiloxanes, react with Re, Rh, Ir, Pd, and Pt complexes to form disilametallacycles with five- or six-membered chelate rings. Four- and five-membered disilacycloalkanes and disilanyldiylcarboranes undergo Si−Si bond cleavage promoted by Pd(0) and Pt(0) complexes to produce the corresponding disilametallacycles. High reactivity of the Si−Si bond toward oxidative addition facilitates the above ring enlargement, even for compounds with stable five-membered rings. Platinum complexes with a η2-silene ligand react with small molecules having electronegative atoms, such as O2 and NH3, to produce metallacycles formed via addition of the electronegative atom to the Si−Si bond. The above disilametallacycles undergo insertion of alkynes and carbonyl compounds into the M−Si bonds of the disilametallacycles. The persilyl metallacycle [Pt(SiPh2SiPh2SiPh2SiPh2)(PPh3)2] is obtained by the double oxidative addition of tetrakis(diphenylsilane) with two Si−H groups and via a metathesis reaction of its dilithio derivative with [PtCl2(PPh3)2]. Reactions of H2GeAr2 with Pd(II) and Pt(II) complexes having diphenylgermyl ligands yield the tetragerampalladacyclopentane and its Pt analogue. Trigermaplatinacyclobutane reacts with Ph2GeH2 to produce the tetragermaplatinacyclopentane via formal insertion of GePh2 into a Pt−Ge bond.
The mechanism and energetics of the Pt(PPh3)2-catalyzed reaction between disilacyclobutene and acetylene are considered from density functional theory calculations at the B3LYP/6-31G**+LanL2DZ level using reasonable models. The catalytic cycle involves the following elementary processes: (1) oxidative addition of the Si−Si bond of disilacyclobutene to Pt, (2) release of one phosphine ligand, (3) coordination of acetylene to form a π-complex, (4) migratory insertion of acetylene into a Pt−Si bond leading to an Si−C bond, (5) coordination of acetylene, and (6) elimination of product disilacyclohexadiene. The rate-determining step is the insertion of acetylene into a Pt−Si bond. Its activation energy of 23.0 kcal/mol is lower than that of the ring opening of disilacyclobutene, 41.5 kcal/mol, in the thermal reaction between disilacyclobutene and acetylene, which occurs at 250 °C (Yoshizawa, K.; Kang, S.-Y.; Yamabe, T.; Naka, A.; Ishikawa, M. Organometallics 1999, 18, 4637). Therefore this Pt-catalyzed reaction should proceed under milder conditions. There are two possible reaction pathways in the initial stages of this catalytic cycle; one is the addition of disilacyclobutene, and the other is the addition of acetylene, the former being energetically more preferred than the latter in the initial stages of this reaction. Our calculations demonstrate that this Pt-catalyzed reaction should proceed stereospecifically.
The reaction of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobutene (1) with benzene in the presence of Ni(PEt3)4 gave 1-(diethylphenylsilyl)-2-(diethylsilyl)benzene (4a) in high yield. Similar reaction of 1 with toluene gave 1-[diethyl(3-methylphenyl)silyl]- and 1-[diethyl(4-methylphenyl)silyl]-2-(diethylsilyl)benzene (5a,b). The reaction of 1 with isopropylbenzene also produced the corresponding two regioisomers. With m-xylene, 1 afforded 1-[diethyl(3,5-dimethylphenyl)silyl]- and 1-[diethyl(2,4-dimethylphenyl)silyl]-2-(diethylsilyl)benzene, while the reaction of 1 with p-xylene gave 1-[diethyl(2,5-dimethylphenyl)silyl]-2-(diethylsilyl)benzene as a main product, in addition to 1-[diethyl(4-methylbenzyl)silyl]-2-(diethylsilyl)benzene as a minor product. Similar reaction of 1 with mesitylene gave 1-[diethyl(3,5-dimethylbenzyl)silyl]-2-(diethylsilyl)benzene. The nickel-catalyzed reaction of 1 with a 1:1 mixture of benzene and toluene afforded 4a, 5a, and 5b in 56, 22, and 9 % yields, while, with a 1:1 mixture of benzene and mesitylene, 4a was produced as the sole product.
Thermolysis of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobutene (1) at 250-degrees-C gave 4,5,7,8-dibenzo-1,1,2,2,3,3,6,6-octaethyl-1,2,3,6-tetrasilacycloocta-4,7-diene (4). Similar thermolysis of 1 with tert-butyl alcohol produced 1-(tert-butoxydiethylsilyl)-2-tau(diethylsilyl)benzene. The reaction of compound 1 with phenylacetylene, 1-hexyne, and dimethyl acetylenedicarboxylate afforded the respective [4 + 21 cycloadducts arising from o-quinodisilane and the acetylenes. Similarly, heating 1 with benzaldehyde and formaldehyde yielded the corresponding [4 + 2] cycloadducts, while with methyl vinyl ketone 1 gave an eight-membered cyclic compound, 7,8-benzo-1,1,6,6-tetraethyl-3-methyl-2-oxa-1,6-disilacycloocta-3,7-diene.
The reactions of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene (1) in the presence of a catalytic amount of tetrakis(triphenylphosphine)palladium(0) have been investigated. Heating 1 in the presence of tetrakis(triphenylphosphine)palladium(0) in benzene at 150 degrees C gave 4,5,7,8-dibenzo-1,1,2,2,3,3,6,6-octaethyl-1,2,3,6-tetrasilacycloocta-4,7-diene (3) in 79% yield. The palladium-catalyzed reaction of 1 with benzaldehyde in refluxing benzene afforded 5,6-benzo-1,1,4,4-tetraethyl-2-oxa-3-phenyl-1,4-disilacyclohex-5-ene in 90% yield. The reaction of 1 with acetylene, phenylacetylene and diphenylacetylene in benzene at room temperature produced the respective 5,6-benzodisilacyclohexa-2,5-diene derivatives in high yields. The reaction of 1 with styrene and l-hexene in the presence of the palladium catalyst in benzene yielded 2,3-benzodisilacyclohex-2-enes 8 and 9a, respectively, while the reaction of 1 with 1-hexene at 150 degrees C, 1 gave 9a and (E)-1-[diethyl(2-hexenyl)silyl]-2-(diethylsilyl)- benzene in 39% and 41% yields. The palladium-catalyzed reaction of 1 with 1,1-deuterio-1-hexene at 150 degrees C produced (E)-1-[diethyl(1,1-dideuterio-2-hexenyl)silyl]-2-(diethylsilyl)- benzene in 35% yield, together with a 43% yield of 2,3-benzo-5-butyl-1,1,4,4-tetraethyl-6,6 dideuterio-1,4-disilacyclohex-1-ene. With triethylsilane at 150 degrees C, 1 gave 2-diethysilyl-1-(pentaethyldisilanyl) benzene and 3 in 31% and 41% yields. Similar reaction of 1 with ethylene in benzene at room temperature afforded 2,3-benzo-1,1,4,4-tetraethyl-1,4-disilacyclohex-2-ene and 3,4,9,10-dibenzo-1,1,2,2,5,5,8,8-octaethyl-1,2,5,8-tetrasilacyclodeca-3,9- diene in 28% and 40% yields, respectively. Reinvestigation of the thermolysis of 1 in the absence of a trapping agent indicated the formation of a mixture of 4,5-benzo-1,1,2,2,3,3-hexaethyl-1,2,3-trisilacyclopent-4-ene and 2,3,5,6-dibenzo-1,1,4,4-tetraethyl-1,4-disilacyclo- hex-2,5-diene.
The reactions of 3,4-benzo-1,1,2,2-tetraethyl-1,2-disilacyclobut-3-ene (1) with alkenes in the presence of a catalytic amount of tetrakis(triethylphosphine)nickel(0) at 150 degrees C have been investigated. With 1,1-diphenylethylene, 1 afforded 1,2-bis(diethylsilyl)benzene (2), 4,5-benzo-1,1,3,3-tetraethyl-2-diphenylmethylene-1,3-disilacyclopent-4-ene, and 1-[diethyl(2, 2-diphenylethenyl)silyl]-2-diethylsilylbenzene in 4%, 55%, and 7% yields. The reaction of 1 with styrene gave 4,5-benzo-1,1,3,3-tetraethyl-2-phenylmethylene-1,3-disilacyclopent-4-ene and (E)-1-tetraethyl(2-phenyl)disilanyl-2-phenylethene in 12% and 47% yields, while with 1- and 2-hexene, 1 produced 4,5-benzo-1,1,3,3-tetraethyl-2-(n-pentylidene)-1,3-disilacyclopent-4-ene, together with a product arising from hydrosilation of 2 and 1-hexene. Similar treatment of 1 with ethylene in an autoclave afforded 4,5-benzo-1,1,3,3-tetraethyl-2-methylene-1 ,3-disilacyclopent-4-ene, tetraethyl-1-phenyl-2-vinyldisilane, and 2,3-benzo-1,1,4,4-tetraethyl-1,4-disilacyclohex-2-ene in 7%, 34%, and 10% yields. Similarly, the nickel-catalyzed reaction of 1 with 2,3-dimethylbutadiene yielded 4,5-benzo-1,1,3,3-tetraethyl-2-(1,2,2-trimethylethenyl)-1,3-disilacyclopent-4-ene and 2,3-benzo-1,1,4,4-tetraethyl-6,7-dimethyl-1 ,4-disilacycloocta-2,6-diene in 33% and 30% yields, while with 1,3- and 1,4-cyclohexadiene, 1 afforded 5,5,10,10-tetraethyl-8,9,13,14-tetrahydrosilanthrene, as the sole product. The results of MO calculations for 1-nickela-2,5-disilacydopent-3-ene are also reported.
3-tert-Butyl-1,1,2,2-tetrafluoro-1,2-disilacyclobut-3-ene (1), one of the products from the reaction between (CH3)3CC≡CH and SiF2, is shown to undergo further cycloaddition to (CH3)3CC≡CH in the presence of Ni(CO)4. The apparent function of Ni(CO)4 is to assist the cleavage of Si-Si bonds through d → d back π bonding to form chelate intermediates which react readily to form new cycloaddition products. These intermediates were isolated by reacting 1 directly with Ni(CO)4. An oxidative addition of the Si-Si bond to nickel resulted in the first well-characterized metal cheiate with two silicon atoms bound to a metal atom. A reaction mechanism is proposed and is compared with those of other related catalytic systems.
The photolysis of 1-(trimethylsilylethynyl)-1,1-diphenyl-2,2,2-trimethyldisilane in the absence of a trapping agent afforded 1,1,2,2-tetraphenyl-3,4-bis[bis(trimethylsilyl)methylene]-1,2-disilacyclobutane (6). This compound could be transformed photochemically or thermally into 1,1,2,24etraphenyl-3-[bis(trimethylsilyl)ethenylidene]-4,4-bis(trimethylsilyl)- 1,2-disilacyclobutane (8). 1,2-Disilacyclobutanes 6 and 8 reacted with m-chloroperoxybenzoic acid to give the corresponding 1-oxa-2,5-disilacyclopentane derivatives. Thermolysis of 8 gave 1,1,3,3-tetraphenyl-2-[bis(trimethylsilyl)ethenylidene]-4,4-bis(trimethylsilyl)- 1,3-disilacyclobutane (10) and 1,1-dimethyl-2-[bis(trimethylsilyl)ethenylidene]-3,3-diphenyl-4,4- bis(phenyldimethylsilyl)-1,3-disilacyclobutane (11) in a ratio of 1:1. Thermolysis of 8 in the presence of anthracene afforded a 1:1 adduct of anthracene and 1,1-diphenyl-4,4-bis(trimethylsilyl)-1-silabutatriene in addition to 1,3-disilacyclobutane 10. When 8 was thermolyzed in the presence of a small excess of methanol, both 1,1-diphenyl-4,4-bis(trimethylsilyl)-1-silabutatriene and 1,1-diphenyl-2,2-bis-(trimethylsilyl)-1-silaethene were trapped by methanol. On heating 8 with elemental sulfur, a 1-thia-2,5-disilacyclopentane was produced. Preliminary results of an X-ray diffraction study of 11 are also described.
Two stable disilacyclopropanes, 1,1,2,2-tetramesityl-3-[phenyl(trimethylsilyl)methylene]- and 1,1,2,2-tetramesityl-3-[bis(trimethylsilyl)methylene]-1,2-disilacyclopropane (3 and 8), have been prepared by addition of dimesitylsilylene to 1,1-dimesityl-3-phenyl-3-(trimethylsilyl)-1-silapropadiene and 1,1-dimesityl-3,3-bis(trimethylsilyl)-1-silapropadiene, respectively. Thermolysis of 3 at 200°C gave 1,1,2,2-tetramesityl-4-(trimethylsilyl)-5,6-benzo-1,2-disilacyclohex-3-ene, quantitatively, while 8 at 170°C afforded 1,1,2,2-tetramesityl-3,4-bis(trimethylsilyl)-1,2-disilacyclobut-3-ene (11) in quantitative yield. The reaction of 3 with trimethylamine oxide dihydrate yielded 1,1,3,3-tetramesityl-4-[phenyl(trimethylsilyl)methylene]-2-oxa-1,3- disilacyclobutane as the sole product. Similar reaction of 8 with anhydrous trimethylamine oxide gave 1,1,3,3-tetramesityl-4,5-bis(trimethylsilyl)-2-oxa-1,3-disilacyclopent-4-ene, along with 3-(hydroxydimesitylsilyl)-1,1-dimesityl-2,2-bis(trimethylsilyl)-1- silacyclopropane (14). Some of the chemical behavior of 11 and preliminary results of an X-ray study of 14 are also described. The crystals of 14 belong to the monoclinic space group P2 1/n with cell dimensions a = 18.146 (1) Å, b = 14.631 (1) Å, c = 16.029 (1) Å, β = 91.05 (1)°, V = 4255.1 (5) Å 3, and D(calcd) = 1.126 Mg m -3 (Z = 4).
Lorsque la reaction est conduite photochimiquement en presence de Fe(CO) 5 on obtient des derives du disila-1,4 naphtalene. Mise en evidence d'un complexe de Fe carbonyle comme intermediaire de la reaction