A Pentacoordinate Mn(II) Precatalyst That Exhibits Notable Aldehyde and Ketone Hydrosilylation Turnover Frequencies
School of Molecular Sciences, Arizona State University, Tempe, Arizona 85287, United States
Inorg. Chem., Article ASAP
DOI: 10.1021/acs.inorgchem.5b01825
Publication Date (Web): October 19, 2015
Copyright © 2015 American Chemical Society
*E-mail: ryan.trovitch@asu.edu. Phone: (480) 727-8930.
Abstract
Heating (THF)2MnCl2 in the presence of the pyridine-substituted bis(imino)pyridine ligand,PyEtPDI, allowed preparation of the respective dihalide complex, (PyEtPDI)MnCl2. Reduction of this precursor using excess Na/Hg resulted in deprotonation of the chelate methyl groups to yield the bis(enamide)tris(pyridine)-supported product, (κ5-N,N,N,N,N-PyEtPDEA)Mn. This complex was characterized by single-crystal X-ray diffraction and found to possess an intermediate-spin (S = 3/2) Mn(II) center by the Evans method and electron paramagnetic resonance spectroscopy. Furthermore, (κ5-N,N,N,N,N-PyEtPDEA)Mn was determined to be an effective precatalyst for the hydrosilylation of aldehydes and ketones, exhibiting turnover frequencies of up to 2475 min–1 when employed under solvent-free conditions. This optimization allowed for isolation of the respective alcohols and, in two cases, the partially reacted silyl ethers, PhSiH(OR)2 [R = Cy and CH(Me)(nBu)]. The aldehyde hydrosilylation activity observed for (κ5-N,N,N,N,N-PyEtPDEA)Mn renders it one of the most efficient first-row transition metal catalysts for this transformation reported to date.
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