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Transformations of Group 7 Carbonyl Complexes: Possible Intermediates in a Homogeneous Syngas Conversion Scheme.

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Title: Transformations of Group 7 Carbonyl Complexes: Possible Intermediates in a Homogeneous Syngas Conversion Scheme.
Authors: Paul R. Elowe1, Nathan M. West1, Jay A. Labinger1, John E. Bercaw1
Source: Organometallics. Nov2009, Vol. 28 Issue 21, p6218-6227. 10p.
Subjects: Metal complexes, Carbonyl compounds, Intermediates (Chemistry), Chemical bonds, Synthesis gas, Metal catalysts, Boranes, Organomanganese compounds
Abstract: A variety of C−H and C−C bond forming reactions of group 7 carbonyl complexes have been studied as potential steps in a homogeneously catalyzed conversion of syngas to C2犉ꦢ. The metal formyl complexes M(CO)3(PPh3)2(CHO) (M = Mn, Re) are substantially stabilized by coordination of boranes BX3(X = F, C6F5) in the form of novel boroxycarbene complexes M(CO)3(PPh3)2(CHOBX3), but these boron-stabilized carbenes do not react with hydride sources to undergo further reduction to metal alkyls. The related manganese methoxycarbene cations [Mn(CO)5−x(PPh3)x(CHOMe)](x= 1 or 2), obtained by methylation of the formyls, do react with hydrides to form methoxymethyl complexes, which undergo further migratory insertion under an atmosphere of CO. The resulting acyls, cis- and trans-Mn(PPh3)(CO)4(C(O)CH2OMe), can be alkylated to form the cationic carbene complex [Mn(PPh3)(CO)4(C(OR)CH2OMe)], which undergoes a 1,2 hydride shift to form 1,2-dialkoxyethylene, which is displaced from the metal, releasing triflate or diethyl ether adducts of [Mn(PPh3)(CO)4]. The acyl can also be protonated with HOTf to form a hydroxycarbene complex, which rearranges to Mn(PPh3)(CO)4(CH2COOMe) and is protonolyzed to yield methyl acetate and [Mn(PPh3)(CO)4]; addition of L (L = PPh3, CO) to the manganese cation regenerates [Mn(PPh3)(CO)4(L)]. Since the original formyl complex can be obtained by the reaction of [Mn(PPh3)(CO)5]숫 [PtH(dmpe)2], which in turn can be generated from H2, this set of transformations amounts to a stoichiometric cycle for selectively converting H2and CO into a C2compound under mild conditions. [ABSTRACT FROM AUTHOR]
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Abstract:A variety of C−H and C−C bond forming reactions of group 7 carbonyl complexes have been studied as potential steps in a homogeneously catalyzed conversion of syngas to C2犉ꦢ. The metal formyl complexes M(CO)3(PPh3)2(CHO) (M = Mn, Re) are substantially stabilized by coordination of boranes BX3(X = F, C6F5) in the form of novel boroxycarbene complexes M(CO)3(PPh3)2(CHOBX3), but these boron-stabilized carbenes do not react with hydride sources to undergo further reduction to metal alkyls. The related manganese methoxycarbene cations [Mn(CO)5−x(PPh3)x(CHOMe)](x= 1 or 2), obtained by methylation of the formyls, do react with hydrides to form methoxymethyl complexes, which undergo further migratory insertion under an atmosphere of CO. The resulting acyls, cis- and trans-Mn(PPh3)(CO)4(C(O)CH2OMe), can be alkylated to form the cationic carbene complex [Mn(PPh3)(CO)4(C(OR)CH2OMe)], which undergoes a 1,2 hydride shift to form 1,2-dialkoxyethylene, which is displaced from the metal, releasing triflate or diethyl ether adducts of [Mn(PPh3)(CO)4]. The acyl can also be protonated with HOTf to form a hydroxycarbene complex, which rearranges to Mn(PPh3)(CO)4(CH2COOMe) and is protonolyzed to yield methyl acetate and [Mn(PPh3)(CO)4]; addition of L (L = PPh3, CO) to the manganese cation regenerates [Mn(PPh3)(CO)4(L)]. Since the original formyl complex can be obtained by the reaction of [Mn(PPh3)(CO)5]숫 [PtH(dmpe)2], which in turn can be generated from H2, this set of transformations amounts to a stoichiometric cycle for selectively converting H2and CO into a C2compound under mild conditions. [ABSTRACT FROM AUTHOR]
ISSN:02767333
DOI:10.1021/om900804j