Sequential and Selective Hydrogenation of the Cα-Cb and M-Cα Double Bonds of an Allenylidene Ligand Coordinated to Osmium: New Reaction Patterns between an Allenylidene Complex and Alcohols
Autores: Tamara Bolaño, Ricardo Castarlenas, Miguel A. Esteruelas y Enrique Oñate
Ref. revista: Journal of the American Chemiscal Society, 129, 8850-8859, (2007)
Complex [OsH(dCdCdCPh2)(CH3CN)2(PiPr3)2]BF4 (1) reacts with primary and secondary alcohols to give the corresponding dehydrogenated alcohols and the hydride-carbene derivative [OsH(dCHCHdCPh2)(CH3CN)2(PiPr3)2]BF4 (2), as a result of hydrogen transfer reactions from the alcohols to the CR-Câ double bond of the allenylidene ligand of 1. The reactions with phenol and t-butanol, which do not contain any â-hydrogen, afford the alkoxy-hydride-carbyne complexes [OsH(OR)(tCCHdCPh2)(CH3CN)-(PiPr3)2]BF4 (R ) Ph (3), tBu (4)), as a consequence of the 1,3-addition of the O-H bond of the alcohols to the metallic center and the Câ atom of the allenylidene of 1. On the basis of the reactions of 1 with these tertiary alcohols, deuterium labeling experiments, and DFT calculations, the mechanism of the hydrogenation is proposed. In acetonitrile under reflux, the Os-C double bond of 2 undergoes hydrogenation to give 1,1-diphenylpropene and [Os{CH2CH(CH3)PiPr2(CH3CN)3(PiPr3)]BF4 (11), containing a metalated phosphine ligand. This reaction is a first-order process with activation parameters of ¢Hq ) 89.0 ( 6.3 kJ mol-1 and ¢Sq ) -43.5 ( 9.6 J mol-1 K-1. The X-ray structures of 2 and 3 are also reported.
Complex [OsH(dCdCdCPh2)(CH3CN)2(PiPr3)2]BF4 (1) reacts with primary and secondary alcohols to give the corresponding dehydrogenated alcohols and the hydride-carbene derivative [OsH(dCHCHdCPh2)(CH3CN)2(PiPr3)2]BF4 (2), as a result of hydrogen transfer reactions from the alcohols to the CR-Câ double bond of the allenylidene ligand of 1. The reactions with phenol and t-butanol, which do not contain any â-hydrogen, afford the alkoxy-hydride-carbyne complexes [OsH(OR)(tCCHdCPh2)(CH3CN)-(PiPr3)2]BF4 (R ) Ph (3), tBu (4)), as a consequence of the 1,3-addition of the O-H bond of the alcohols to the metallic center and the Câ atom of the allenylidene of 1. On the basis of the reactions of 1 with these tertiary alcohols, deuterium labeling experiments, and DFT calculations, the mechanism of the hydrogenation is proposed. In acetonitrile under reflux, the Os-C double bond of 2 undergoes hydrogenation to give 1,1-diphenylpropene and [Os{CH2CH(CH3)PiPr2(CH3CN)3(PiPr3)]BF4 (11), containing a metalated phosphine ligand. This reaction is a first-order process with activation parameters of ¢Hq ) 89.0 ( 6.3 kJ mol-1 and ¢Sq ) -43.5 ( 9.6 J mol-1 K-1. The X-ray structures of 2 and 3 are also reported.