[Show abstract][Hide abstract] ABSTRACT: The dipalladium(I) complex Pd(2)Cl(2)(dmpm)(2) (1a) [dmpm = bis(dimethylphosphino)methane] is known to react with elemental sulfur (S(8)) to give the bridged-sulfide complex Pd(2)Cl(2)(μ-S)(dmpm)(2) (2a) but, in the presence of excess S(8), PdCl(2)[P,S-dmpm(S)] (4a) and dmpm(S)(2) are generated. Treatment of 1a with elemental selenium (Se(8)), however, gives only Pd(2)Cl(2)(μ-Se)(dmpm)(2) (3a). Complex 4a is best made by reaction of trans-PdCl(2)(PhCN)(2) with dmpm(S). Complex 2a reacts with MeI to yield initially Pd(2)I(2)(μ-S)(dmpm)(2) and MeCl, and then Pd(2)I(2)(μ-I)(2)(dmpm)(2) and Me(2)S, whereas alkylation of 2a with MeOTf generates the cationic, bridged-methanethiolato complex [Pd(2)Cl(2)(μ-SMe)(dmpm)(2)]OTf (5). Oxidation of 2a with m-CPBA forms a mixture of Pd(2)Cl(2)(μ-SO)(dmpm)(2) and Pd(2)Cl(2)(μ-SO(2))(dmpm)(2), whereas Pd(2)Br(2)(μ-S)(dmpm)(2) reacts selectively to give Pd(2)Br(2)(μ-SO)(dmpm)(2) (6b). Treatment of the Pd(2)X(2)(μ-S)(dmpm)(2) complexes with X(2) (X = halogen) removes the bridged-sulfide as S(8), with co-production of Pd(II)(dmpm)-halide species. X-ray structures of 3a, 5 and 6b are presented. Reactions of dmpm with S(8) and Se(8) are clarified. Differences in the chemistry of the dmpm systems with that of the corresponding dppm systems [dppm = bis(diphenylphosphino)methane] are discussed.
[Show abstract][Hide abstract] ABSTRACT: The Pd(2)X(2)(dmpm)(2) complexes [X = Cl (1a), Br (1b), I (1c); dmpm = bis(dimethylphosphino)methane. In all the dipalladium complexes mentioned in this paper, the dmpm, depm, and dppm ligands (unless stated otherwise) are bridging, but for convenience the μ-symbol is omitted.] react with H(2)S to yield H(2) and the bridged-sulfido complexes Pd(2)X(2)(μ-S)(dmpm)(2) (2a-c), of which 2a and 2b are structurally characterized. With 1a, two rapid reversible equilibria are observed by NMR spectroscopy below -30 °C, and two reaction intermediates are detected; both are likely hydrido(mercapto) species. Reaction of 1a with 1 equiv of elemental sulfur also yields 2a. The reaction of 1a with COS results in the initial formation of Pd(2)Cl(2)(μ-COS)(dmpm)(2) (3) that undergoes decarbonylation to yield 2a and Pd(2)Cl(2)(μ-CO)(dmpm)(2) (4), which is also formed via reversible insertion of the CO into the Pd-Pd bond of 1a. The solid-state molecular structure of the previously reported complex Pd(2)Cl(2)(μ-CS(2))(dmpm)(2) (5), together with solution NMR data for 3 and 5, reveal that the bridging heterocumulene ligands coordinate in an η(2)-C,S fashion. Analogous findings were made for the corresponding Pd(2)X(2)(depm)(2) complexes [X = Cl (1a'), Br (1b'), I (1c'); depm = bis(diethylphosphino)methane], although no μ-COS species was detected. The Pd(2)X(2)(μ-S)(depm)(2) complex was structurally characterized. Differences in the chemistry of the previously studied, corresponding dppm systems (dppm = bis(diphenylphosphino)methane) are discussed.
[Show abstract][Hide abstract] ABSTRACT: Oxidative addition of H2S to MoRu(CO)6(µ-dppm)2 (1) at ~20 °C in toluene yields an isolable complex formulated as Mo(CO)3(µ-SH)(µ-CO)(µ-dppm)2RuH(CO) (2) via the possible intermediate Mo(CO)3(µ-H)(µ-CO)(µ-dppm)2Ru(SH)(CO) (4) (dppm = Ph2PCH2PPh2) that is detectable at lower temperatures. Over 2 days, species 2 in toluene loses H2 (and CO) to yield the bridged-sulfide product, Mo(CO)2(µ-CO)(µ-S)(µ-dppm)2Ru(CO) (5) that is also formed directly from the reaction of 1 with elemental sulfur. The solid-state molecular structure of 5 is determined by X-ray crystallography. A further hydrido-sulfhydryl species, possibly Mo(CO)3(µ-SH)(µ-H)(µ-dppm)2Ru(CO)2 (3), is in equilibrium with 2 at ambient temperature.Key words: molybdenum, ruthenium, bis(diphenylphosphino)methane, hydrogen sulfide, hydrido-sulfhydryl species, carbonyl complexes, bridged-sulfide complex.
Canadian Journal of Chemistry 02/2011; 84(2):330-336. DOI:10.1139/v06-002 · 1.06 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The room temperature reactions of RSH (R = Et, Ph) with (CO)(3)Mo(mu-dppm)(2)Ru(CO)(3) (1) in toluene yield (CO)(2)Mo(mu-SR)(mu-CO)(mu-dppm)(2)Ru(H)(CO) [R = Et (3); Ph (4)], which are characterized by elemental analysis, H-1 NMR and IR spectroscopies and, in the case of 3, by X-ray crystallography. The complexes contain a trans, trans-Mo(mu-dppm)(2)Ru unit with a bridging thiolate, a terminal hydride at the Ru, three terminal CO ligands (two at the Mo, and one at the Ru), and one semi-bridged CO closer to the Mo.
[Show abstract][Hide abstract] ABSTRACT: This report describes investigations that have elucidated the nature, extent, and mechanism of the cyclic-olefin oligomerization effected by a series of tungsten precatalysts, with particular focus on Cp*W(NO)(CH2CMe3)(2) (1) and Cp*W(NO)(CH2SiMe3)(eta(2)-CPhCH2) (2). Upon thermolysis, these precatalysts oligomerize simple cyclic olefins, from cyclopentene to cyclooctene, into ring-retaining oligomers as high as dodecamers (depending on the substrate) with remaining sites of unsaturation. Precatalyst initiation involves the coupling of one equivalent of the substrate with the reactive 16e intermediate thermally generated by the precatalyst (i.e., an alkylidene by 1 or an eta(2)-alkyne complex by 2), followed by rearrangement of the coupled ligand in the metal's coordination sphere either to an olefin or to a diene (with concomitant loss of two hydrogen atoms). The rearranged ligand is displaced from the metal center as two equivalents of substrate coordinate to form a putative bis-olefin complex, Cp*W(NO)(cyclic olefin)2, that represents the convergent entry point to the catalytic cycle for the precatalysts. The coordinated olefins undergo metal-mediated coupling to form a metallacyclopentane complex. The metallacycle then undergoes beta-hydrogen activation and reductive elimination to generate an eta(2)-cyclic-olefin dimer. Further incorporation of substrate leads to formation of trimers and higher oligomers. Alternatively, expulsion of any coordinated oligomer from the tungsten center regenerates the reactive bis-olefin complex. Finally, decomposition of the tungsten catalyst species is consistent with a bimetallic pathway. All new organometallic complexes have been characterized by conventional spectroscopic and analytical methods, and the solid-state molecular structures of several compounds have been established by X-ray crystallographic analyses.
[Show abstract][Hide abstract] ABSTRACT: Reactions of a variety of cyclic and acyclic olefins with the title alkylidene complex (formed spontaneously by loss of neopentane from Cp*Mo(NO)(CH2CMe3)2 under ambient conditions) result in the initial formation of molybdenacyclobutane complexes (Cp* = C5Me5). These molybdenacyclobutane complexes do not react via olefin metathesis or cyclopropanation pathways, but instead via C−H activation. Thus, when cyclopentene is the olefinic substrate, the direct result of C−H activation at the β-position of the metallacyclobutane affords a thermally stable allyl hydrido complex that can be isolated. Such an allyl hydride intermediate is not isolable for larger cyclic olefins (cyclohexene, cycloheptene, and cyclooctene) or acyclic olefins (allylbenzene and 1-hexene). Instead, those complexes react further, undergoing a second C−H activation at the allylic position to produce η4-trans-diene complexes concomitant with the loss of dihydrogen. Upon heating, these η4-trans-diene complexes liberate diene, thereby enabling the 14e Cp*Mo(NO) metal fragment to catalyze the oligomerization of cyclic olefins and dienes including cyclohexene and 1,4-cyclohexadiene. In the case of the acyclic olefin allylbenzene, the metal fragment catalyzes a dimerization to (E)-(4-methylpent-1-ene-1,5-diyl)dibenzene under ambient conditions.
[Show abstract][Hide abstract] ABSTRACT: trans-CP*W(NO)(CH2EMe3)(H)(PMe3) (E = C, Si) complexes can be prepared by the hydrogenation at 1 atm of the appropriate Cp*W(NO)(CH2EMe3)(2) precursor in the presence of a slight excess of PMe3. (Our designation of a particular geometrical isomer as cis or trans in this family of complexes indicates the relative positions of the hydrocarbyl and the hydrido ligands in the base of a four-legged piano-stool molecular structure.) The use of D-2 in place of H-2 during these syntheses affords the corresponding trans-Cp*W(NO)(CH2EMe3)(D)(PMe3) (E = C, Si) complexes. The cis-Cp*W(NO)(CH2EMe3)(H)(PMe3) isomers are obtainable by C-H bond-activation reactions of the trans precursors. Thus, activation of SiMe4 by trans-Cp*W(NO)(CH2CMe3)(H)(PMe3) under ambient conditions produces cis-Cp*W(NO)(CH2SiMe3)(H)(PMe3). Similarly, activations of C6H6 and C6D6 at 20-27 degreesC by the trans-Cp*W(NO)(CH2EMe3)(H)(PMe3) complexes produce cis-Cp*W(NO)(C6H5)(H)(PMe3) and cisCp*W(NO)(C6D5)(D)(PMe3), respectively, and the solid-state molecular structure of the latter complex has been established by a single-crystal X-ray crystallographic analysis. Kinetic, mechanistic, and theoretical investigations of these benzene C-H activation processes are consistent with initial trans to cis isomerization of the reactants followed by intramolecular reductive elimination of EMe4 to form the 16-electron Cp*W(NO)(PMe3) intermediate. Subsequent oxidative addition of the incoming benzene substrate to this coordinatively unsaturated intermediate produces the final cis hydrido phenyl complex. These single C-H activation processes are the requisite first steps in the development of these organometallic complexes as catalysts for the selective functionalization of hydrocarbons. All new complexes have been characterized by conventional spectroscopic methods.
[Show abstract][Hide abstract] ABSTRACT: Halogens oxidatively add to MoRu(CO)6(μ-dppm)2 (1) at ambient temperature to yield [(CO)2Mo(μ-X)(μ-CO)(μ-dppm)2Ru(CO)2]+[Mo(CO)4X3]−, where X=Cl (2) or I (3), dppm=Ph2PCH2PPh2, and the μ-CO is semi-bridging. Complexes 2 and 3 have been characterized by elemental analysis, conductivity, and NMR spectroscopy, while the molecular structure of 3 has been determined by X-ray crystallography. Ignoring a weak metal–metal bond interaction, the cation of 3 is most easily described as pseudo-octahedral at Ru(II) and Mo(0) centres; the anion is a monocapped octahedron that has been described previously.
[Show abstract][Hide abstract] ABSTRACT: The preparation of dipalladium complexes containing sterically nondemanding diphosphine (P-P) ligands of the type R(2)PCH(2)PR(2) where R = Me (dmpm) or Et (depm) is reported. Variable-temperature (1)H NMR spectra of the Pd(I)(2) complexes Pd(2)X(2)(dmpm)(2) (X = Cl, Br, or I; the P-P ligands in the Pd(2) complexes are always bridged, but for convenience, the micro -symbol is omitted) show the complexes to be fluxional in solution, the barriers to a ring-flipping process being DeltaG( double dagger ) = 37.9, 39.0, and 43.2 +/- 0.9 kJ mol(-)(1) for the chloro, bromo, and iodo complexes, respectively. Treatment of Pd(2)X(2)(P-P)(2) (X = Cl or Br) with X(2) generates the stable, face-to-face Pd(II)(2) derivatives trans-Pd(2)X(4)(P-P)(2), while oxidation of Pd(2)I(2)(P-P)(2) complexes with I(2) generates a new type of symmetrically di-iodo-bridged, five-coordinate complexes Pd(2)I(2)(micro -I)(2)(dmpm)(2) and Pd(2)I(2)(micro -I)(2)(depm)(2). The molecular crystal structures of four dipalladium(II) complexes are described: trans-Pd(2)Cl(4)(dmpm)(2).2CHCl(3), trans-Pd(2)Br(4)(dmpm)(2), trans-Pd(2)Cl(4)(depm)(2), and Pd(2)I(2)(micro -I)(2)(dmpm)(2). Solution NMR and UV-vis absorption spectra are consistent with the solid-state structures determined by X-ray diffraction. The stability of the dimeric Pd(II) complexes is attributed primarily to ligand steric factors.
[Show abstract][Hide abstract] ABSTRACT: Cp*Mo(NO)(CH2CMe3)2 (1), a complex with α-agostic CH···Mo interactions, evolves neopentane in neat hydrocarbon solutions at room temperature and forms the transient 16-electron alkylidene complex, Cp*Mo(NO)(CHCMe3), which subsequently activates solvent CH bonds. Thus, it reacts with tetramethylsilane or mesitylene to form Cp*Mo(NO)(CH2CMe3)(CH2SiMe3) (2) or Cp*Mo(NO)(CH2CMe3)(η2-CH2C6H3-3,5-Me2) (3), respectively, in nearly quantitative yields. Under identical conditions, 1 in p-xylene generates a mixture of sp2 and sp3 CH bond activation products, namely Cp*Mo(NO)(CH2CMe3)(C6H3-2,5-Me2) (4, 73%) and Cp*Mo(NO)(CH2CMe3)(η2-CH2C6H4-4-Me) (5, 27%). In benzene at room temperature, 1 transforms to a mixture of Cp*Mo(NO)(CH2CMe3)(C6H5) (6) and Cp*Mo(NO)(C6H5)2 (7) in a sequential manner. Most interestingly, the thermal activation of 6 at ambient temperatures gives rise to two parallel modes of reactivity involving either the elimination of benzene and formation of Cp*Mo(NO)(CHCMe3) or the elimination of neopentane and formation of the benzyne complex, Cp*Mo(NO)(η2-C6H4). In pyridine, these intermediates are trapped as the isolable 18-electron adducts, Cp*Mo(NO)(CHCMe3)(NC5H5) (8) and Cp*Mo(NO)(η2-C6H4)(NC5H5) (9), and, in hydrocarbon solvents, they effect the intermolecular activation of aliphatic CH bonds at room temperature to generate mixtures of neopentyl- and phenyl-containing derivatives. However, the distribution of products resulting from the hydrocarbon activations is dependent on the nature of the solvent, probably due to solvation effects and the presence of σ- or π-hydrocarbon complexes on the reaction coordinates of the alkylidene and the benzyne intermediates. The results of DFT calculations on these processes in the gas phase support the existence of such hydrocarbon complexes and indicate that better agreement with experimental observations is obtained when the actual neopentyl ligand rather than the simpler methyl ligand is used in the model complexes.
Journal of the American Chemical Society 07/2003; 125(23):7035-48. DOI:10.1021/ja0349094 · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: Gentle thermolysis of appropriate CpM(NO)(hydrocarbyl)(2) complexes (Cp = eta(5)-C(5)Me(5)) of molybdenum and tungsten results in loss of hydrocarbon and the transient formation of 16-electron CpM(NO)-containing complexes such as CpM(NO)(alkylidene), CpM(NO)(eta(2)-benzyne), CpM(NO)(eta(2)-acetylene), and CpM(NO)(eta(2)-allene) (M = Mo, W). These intermediates effect the single, double, or triple activation of hydrocarbon C-H bonds intermolecularly, the first step of these activations being the reverse of the transformations by which they were generated. This Account summarizes the various types of C-H activations that have been effected with these nitrosyl complexes and also describes the results of kinetic, mechanistic, and theoretical investigations of these processes.
Accounts of Chemical Research 05/2003; 36(4):223-33. DOI:10.1021/ar0202215 · 22.32 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: The molybdenum nitrosyl complex Cp*Mo(NO)(CH2CMe3)(C6H5) reacts at room temperature via elimination of neopentane or benzene to form the transient species Cp*Mo(NO)(=CHCMe3) and Cp*Mo(NO)(eta2-C6H4). These reactive intermediates effect the intermolecular activation of hydrocarbon C-H bonds via the reverse of the transformations by which they are generated. Thermolysis of Cp*Mo(NO)(CH2CMe3)(C6H5) in pyridine yields the adducts Cp*Mo(NO)(=CHCMe3)(NC5H5) and Cp*Mo(NO)(eta2-C6H4)(NC5H5), and the benzyne complex has been characterized by X-ray diffraction.
Journal of the American Chemical Society 09/2002; 124(33):9680-1. DOI:10.1021/ja027080m · 12.11 Impact Factor
[Show abstract][Hide abstract] ABSTRACT: From a mixture of cis- and trans-Ru(SH)(2)(dppm)(2) (4), formed from reaction of H2S with trans-Ru(H)Cl(dppm)(2) (2), a crystal of cis-4 has been isolated and its structure determined by X-ray analysis. The mercapto protons are located within the centrosymmetric structure, although the S-atoms are partially disordered (S - H similar to 1.06 Angstrom). The thiolate complexes, trans-Ru(H)SR(dppm)(2) (R = Ph, 5a; C6F5, 5b), have been isolated from reaction of trans-2 with 1 equiv. of RSH. trans-Ru(H)SH(dppm)(2) (3) has been isolated from reaction of H2S with a mixture of cis- and trans-Ru(H)(2)(dppm)(2) (1). An improved synthetic route for 1 is presented.