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Published October 12, 2009 | Supplemental Material
Journal Article Open

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


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 C_(2+) compounds. The metal formyl complexes M(CO)_3(PPh_3)_2(CHO) (M = Mn, Re) are substantially stabilized by coordination of boranes BX_3 (X = F, C_6F_5) in the form of novel boroxycarbene complexes M(CO)_3(PPh_3)_2(CHOBX_3), 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)(PPh_3)_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(PPh_3)(CO)_4(C(O)CH_2OMe), can be alkylated to form the cationic carbene complex [Mn(PPh_3)(CO)_4(C(OR)CH_2OMe)]^+, 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(PPh_3)(CO)_4]^+. The acyl can also be protonated with HOTf to form a hydroxycarbene complex, which rearranges to Mn(PPh_3)(CO)_4(CH_2COOMe) and is protonolyzed to yield methyl acetate and [Mn(PPh_3)(CO)_4]^+; addition of L (L = PPh_3, CO) to the manganese cation regenerates [Mn(PPh_3)(CO)_4(L)]^+. Since the original formyl complex can be obtained by the reaction of [Mn(PPh_3)(CO)_5]^+ with [PtH(dmpe)_2]^+, which in turn can be generated from H_2, this set of transformations amounts to a stoichiometric cycle for selectively converting H_2 and CO into a C_2 compound under mild conditions.

Additional Information

© 2009 American Chemical Society. Received September 14, 2009. Wethank Prof.Arnold L.Rheingold for obtaining the X-ray structure of 4b, Lawrence M. Henling and Dr. Michael W. Day for help with the other X-ray structures, and Dr. Michael S. Malarek for assistance in obtaining ^(13)C NMR spectra. We thank Alexander Miller for helpful discussions. We are grateful to BP for generous financial support of this research through the Methane Conversion Cooperative (MC^2) program.

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Supplemental Material - om900804j_si_001.pdf

Supplemental Material - om900804j_si_002.cif


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August 19, 2023
October 19, 2023