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ABSTRACT: This paper reports the synthesis, structure, and properties of a series of PNP pincer complexes of osmium OsH(3)Cl[HN(C(2)H(4)P(i)Pr(2))(2)] (1), OsH(3)[N(C(2)H(4)P(i)Pr(2))(2)] (2), OsH(4)[HN(C(2)H(4)P(i)Pr(2))(2)] (3), and OsH(2)(PMe(3))[HN(C(2)H(4)P(i)Pr(2))(2)] (4). The tetrahydride 3 operates as an efficient catalyst at 0.1 mol% loading for the reactions of amination and dehydrogenative coupling of primary alcohols, producing secondary amines and symmetrical esters, respectively. The catalyst 3 is distinguished by outstanding stability, and it can be used in an aqueous environment at temperatures as high as 200 °C.
Dalton Transactions 04/2011; 40(35):8941-9. · 3.84 Impact Factor
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ABSTRACT: The ligand tBu2PC2H4NHC2H4NEt2 (PNHN) was synthesized starting from 2-(diethylamino)ethyl chloride hydrochloride and ethanolamine. Reaction of PNHN with [IrCl(COE)2]2 under H2 afforded the dihydride cis-IrH2Cl(κ3-PNHN) (1) in excellent yield. Treatment of 1 with tBuOK led to clean formation of the 16-electron amido complex IrH2(κ3-PNN) (2). Hydrogenation of 2 in toluene or ethyl acetate produced the trihydride mer-IrH3(κ3-PNHN) (3). This complex was unstable and dimerized to give [IrH2(κ2-PNHN)]2(μ-H)2 (4) with uncoordinated NEt2 groups. The structures of 1 and 4 were established by X-ray crystallography. Complex 2 demonstrated good catalytic activity for transfer hydrogenation of acetophenone, cyclohexanone, and butanone.
09/2007;
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ABSTRACT: The hydride complexes ReHBr(NO)[HN(C2H4PR2)2] (R = Pri, 1a; But, 1b) were synthesized by reactions of [NEt4]2[Re(NO)Br5] with the pincer-type ligands HN(C2H4PR2)2. Treatment of 1a and 1b with ButOK led to their dehydrobromination, resulting in the amido hydrides ReH(NO)[N(C2H4PR2)2] (2a,b), respectively. The dihydride trans-ReH2(NO)[HN(C2H4PPri2)2] (3a) was obtained by stirring an ether solution of 2a under hydrogen. Similarly, partial conversion of 2b was achieved under hydrogen to give trans-ReH2(NO)[HN(C2H4PBut2)2] (3b). The structure and properties of complexes 1−3 were studied by DFT calculations. Complexes 2a and 3a demonstrated low activity for transfer hydrogenation of acetophenone and cyclohexanone due to instability in 2-propanol.
05/2007;
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ABSTRACT: Bulky pincer complexes of ruthenium are capable of C-H activation and H-elimination from the pincer ligand backbone to produce mixtures of olefin and carbene products. To characterize the products and determine the mechanisms of the C-H cleavage, reactions of [RuCl(2)(p-cymene)](2) with N,N'-bis(di-tert-butylphosphino)-1,3-diaminopropane (L1) and 1,3-bis(di-tert-butylphosphinomethyl)cyclohexane (L2) were studied using a combination of X-ray crystallography, NMR spectroscopy, and DFT computational techniques. The reaction of L1 afforded a mixture of an alkylidene, a Fischer carbene, and two olefin isomers of the 16-e monohydride RuHCl[(t)Bu(2)PNHC(3)H(4)NHPBu(t)(2)] (2), whereas the reaction of L2 gave two olefin and two alkylidene isomers of 16-e RuHCl[2,6-(CH(2)PBu(t)(2))(2)C(6)H(8)] (3), all resulting from dehydrogenations of the ligand backbone of L1 and L2. The key intermediates implicated in the C-H activation reactions were identified as 14-electron paramagnetic species RuCl(PCP), where PCP = cyclometalated L1 or L2. Thus the alpha- and beta-H elimination reactions of RuCl(PCP) involved spin change and were formally spin-forbidden. Hydrogenation of 2 and 3 afforded 16-electron dihydrides RuH(2)Cl(PCP) distinguished by a large quantum exchange coupling between the hydrides.
Journal of the American Chemical Society 12/2006; 128(44):14388-96. · 9.91 Impact Factor
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ABSTRACT: Reactions of [RuCl2(p-cymene)]2 with (tBu2PCH2CH2)2O (POP-tBu) and (iPr2PCH2CH2)2O (POP-iPr) afforded RuCl2(POP-tBu) (1) and [Ru2(μ-Cl)3(POP-iPr)2]Cl (2·Cl), respectively. The POP ligand is coordinated in a mer fashion in complex 1, whose crystal structure revealed a γ-agostic C−H···Ru interaction of one tBu group. Spectroscopic evidence indicated that this agostic interaction is retained in 1 in solution. A related compound, [Ru(N2)Cl(POP-tBu)]BPh4 (4), which also showed agostic bonding of a tBu group, was obtained by substitution of N2 for Cl- in 1, in the presence of NaBPh4. Compound 2·Cl readily underwent ion exchange with LiBPh4 or LiPF6 to give 2·BPh4 or 2·PF6 salts, respectively. A crystallographic analysis of 2·PF6 established a co-facial bioctahedral geometry of the [Ru2(μ-Cl)3(POP-iPr)2]+ cation containing two POP ligands coordinated in a fac fashion. Reactions of 1 and 2 with H2 afforded the dihydrogen complexes cis,trans-Ru(H2)Cl2(POP-tBu) (3) and cis,cis-Ru(H2)Cl2(POP-iPr) (5), respectively. The H−H bond distances are very similar in both compounds, r(H−H) = 1.0 ± 0.1 Å, based on the T1min and JHD data and results of DFT calculations. Reaction of 2 with N2 gave the dinitrogen complex cis,cis-Ru(N2)Cl2(POP-iPr) (6), but solutions of 1 under a nitrogen atmosphere showed no evidence of an analogous compound. The different steric requirements of the phosphorus substituents of the POP ligands were identified as the source of the differences in the coordination properties of the POP-tBu and POP-iPr complexes 1−6.
04/2005;
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Angewandte Chemie International Edition 02/2003; 42(2):216-9. · 13.45 Impact Factor
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ABSTRACT: This communication reports the preparation of a novel trans-chelating diphosphine, 1,5-bis(di-tert-butylphosphino)-2-(S)-dimethylaminopentane, that undergoes triple C-H activation in reaction with [RuCl2(p-cymene)]2 to give a chiral square-pyramidal 16-electron carbene complex of ruthenium.
Chemical Communications 11/2002; · 6.17 Impact Factor
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ABSTRACT: Addition of pyridine to the syn and anti isomers of cis-RuHCl[tBu2PCH2CH2((E)-CHCH)CH2PBut2] (1) afforded a single isomer of trans,cis,anti-RuHCl(Py)[tBu2PCH2CH2((E)-CHCH)CH2PBut2] (2), where the anti α-HC-RuH configuration was established by a difference NOE experiment. The carbonyl complex RuCl(CO)[CH(C2H4PBut2)2] (3) was obtained from 2 under CO, and two hydride complexes, RuH(CO)[CH(C2H4PBut2)2] (4) and RuH(N2)[CH(C2H4PBut2)2] (5), were prepared from 3 and 1, respectively, using Li[HBEt3] as the hydride source. Decarbonylation of isoamyl alcohol with polymeric [RuCl2(COD)]n in the presence of 1,5-bis(di-tert-butylphosphino)pentane (DtBPP) resulted in isolation of the 16-atom-ring binuclear species [RuHCl(CO)(DtBPP)]2 (6). New products 3−5 were characterized by single-crystal X-ray analysis. In the computational study, we successfully modeled complexes 1−4 using the ONIOM methodology. It was established that the bulky PBut2 groups are responsible for the electronically unfavorable cis arrangement of the CO and Cl ligands in 3. B3PW91 calculations of the transition state structures for the intramolecular olefin insertion into the Ru−H bond in anti-1, trans,cis-2, and cis,trans-2 gave barrier heights of 28.3, 27.1, and 17.7 kcal/mol, respectively.
10/2002;
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ABSTRACT: Cyclometalation of bis(di-tert-butylphosphino)pentane (DtBPP) and subsequent product dehydrogenation take place in reactions of DtBPP with [OsCl6]2- and [RuCl2(p-cymene)]2 to give the M(IV) dihydrides, MH2Cl[CH(C2H4PBut2)2], and the (alkylidene)osmium and (olefin)ruthenium complexes OsHCl[C(C2H4PBut2)2] and RuHCl[But2PCH2CH2((E)-CHCH)CH2PBut2].
05/2002;
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ABSTRACT: The transition metal halides Re(H2)Br2(NO)(PiPr3)2 and MHCl(CO)(PiPr3)2, M = Ru, Os afforded the hydrido(tertiary phosphine)metalates [ReH3(NO)(PiPr3)2]- and [MH3(CO)(PiPr3)2]-, M Ru, Os in reactions with KH in the presence of crown ethers (2.2.2-crypt, 18-crown-6, 1-aza-18-crown-6) under H2. The anionic hydrides [RuH3(PPh3)3]- and [MH5(PiPr3)2]-, M = Ru, Os were also efficiently prepared by this method. The trihydrides [K(18-crown-6)][OsH3(CO)(PiPr3)2] and [K(1-aza-18-crown-6)][OsH3(CO)(PiPr3)2] were characterized by single-crystal X-ray diffraction and possess the mer structure with two trans hydride ligands. Unlike the former structure, the latter is chain polymeric via CO···K+ links and NH···HOs hydrogen bonds; this is the first one-dimensional network to be held together by proton−hydride bonding. The [K(1-aza-18-crown-6)]+ N−H IR band shift (Δν) indicates the increasing strength of hydrogen bonding with the following hydrides: [ReH3(NO)(PiPr3)2]- (102 cm-1) < [OsH3(CO)(PiPr3)2]- (116 cm-1) < [RuH3(CO)(PiPr3)2]- (136 cm-1). The order of acidity of the conjugate acid forms follows a different trend: Os(H2)(H)2(CO)(PiPr3)2 > Re(H)4(NO)(PiPr3)2 > Ru(H2)(H)2(CO)(PiPr3)2. The crypt-containing cations interact weakly with the anions in [K(2.2.2-crypt)][OsH3(CO)(PiPr3)2] and [K(2.2.2-crypt)][RuH3(CO)(PiPr3)2] in toluene or tetrahydrofuran (THF). This results in the formation of only the mer isomers. Substantial ion-pairing between [K(18-crown-6)]+ and the trihydrides results in the stabilization of the fac isomers to a greater degree in toluene than in polar THF. Use of [K(1-aza-18-crown-6)]+ results in even greater stabilization of the fac isomers both in THF and toluene. Nuclear Overhauser effect (NOE) experiments reveal that NH···HM hydrogen bonds cause tighter ion pairing in this case.
12/1998;
