Ancillary Ligand Effects on Carbon Dioxide-Ethylene Coupling at Zerovalent Molybdenum

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• 作者：Brian S. Hanna ; Alex D. MacIntosh ; Steven Ahn ; Brian T. Tyler ; G. Tayhas R. Palmore ; Paul G. Williard ; Wesley H. Bernskoetter
• 刊名：Organometallics
• 出版年：2014
• 出版时间：July 14, 2014
• 年：2014
• 卷：33
• 期：13
• 页码：3425-3432
• 全文大小：345K
• ISSN：1520-6041

文摘

A series of zerovalent molybdenum complexes bearing triphosphine ligands, [Ar₂PCH₂CH₂]₂PPh, have been synthesized and evaluated for reductive functionalization of CO₂ with ethylene. The ability to form dimeric triphosphine molybdenum(II) acrylate hydride species from CO₂-ethylene coupling was found to be highly sensitive to steric encumbrance on the phosphine aryl substituents. Trapping of triphosphine molybdenum(II) acrylate hydride species using triphenylphosphine afforded isolable monomeric CO₂ functionalization products with all ancillary ligands studied. Kinetic analysis of the acrylate formation reaction revealed a first-order dependence on molybdenum, but no influence from CO₂ pressure or the triphenylphosphine trap. Systematic attenuation of steric and electronic features of the triphosphine ligands showed a strong CO₂ functionalization rate influence for ligand size with [(3,5-^tBu-C₆H₃)₂PCH₂CH₂]₂PPh coupling nearly four times slower than with [(3,5-Me-C₆H₃)₂PCH₂CH₂]₂PPh. A considerably milder electronic effect was observed with complexes bearing [(4-F-C₆H₄)₂PCH₂CH₂]₂PPh reducing CO₂ at approximately half the rate as with [Ph₂PCH₂CH₂]₂PPh.