Issue 39, 2018

A β-diketiminate manganese catalyst for alkene hydrosilylation: substrate scope, silicone preparation, and mechanistic insight

Abstract

The dimeric β-diketiminate manganese hydride compound, [(2,6-iPr2PhBDI)Mn(μ-H)]2, was prepared by treating [(2,6-iPr2PhBDI)Mn(μ-Cl)]2 with NaEt3BH. This compound was characterized by single crystal X-ray diffraction and found to feature high-spin Mn centres that exhibit strong magnetic coupling by EPR spectroscopy. Once characterized, [(2,6-iPr2PhBDI)Mn(μ-H)]2 was found to mediate the hydrosilylation of a broad scope of alkenes at elevated temperature. Aliphatic alkenes were found to undergo anti-Markovnikov hydrosilylation, while the hydrosilylation of styrenes using [(2,6-iPr2PhBDI)Mn(μ-H)]2 afforded Markovnikov's product. Importantly, this catalyst has also been employed for the cross-linking of industrially-relevant silicones derived from vinyl-terminated poly(dimethylsiloxane) and 1,2,4-trivinylcyclohexane with catalyst loadings as low as 0.05 mol%. To gain a mechanistic understanding of [(2,6-iPr2PhBDI)Mn(μ-H)]2-catalyzed olefin hydrosilylation, 4-tert-butylstyrene was added to [(2,6-iPr2PhBDI)Mn(μ-H)]2 and conversion to the monomeric Mn alkyl complex, (2,6-iPr2PhBDI)Mn(CH(CH3)(4-tBuPh)), was observed. Isolation of this secondary alkyl intermediate confirms that olefin insertion into the Mn–H bond dictates the observed regioselectivities. The importance of our mechanistic findings as they relate to recent advances in Mn hydrosilylation catalysis is described herein.

Graphical abstract: A β-diketiminate manganese catalyst for alkene hydrosilylation: substrate scope, silicone preparation, and mechanistic insight

Supplementary files

Article information

Article type
Edge Article
Submitted
23 Jun 2018
Accepted
14 Aug 2018
First published
15 Aug 2018
This article is Open Access

All publication charges for this article have been paid for by the Royal Society of Chemistry
Creative Commons BY-NC license

Chem. Sci., 2018,9, 7673-7680

A β-diketiminate manganese catalyst for alkene hydrosilylation: substrate scope, silicone preparation, and mechanistic insight

T. K. Mukhopadhyay, M. Flores, T. L. Groy and R. J. Trovitch, Chem. Sci., 2018, 9, 7673 DOI: 10.1039/C8SC02768D

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