Issue 47, 2019

Interconversion and reactivity of manganese silyl, silylene, and silene complexes

Abstract

Manganese disilyl hydride complexes [(dmpe)2MnH(SiH2R)2] (4Ph: R = Ph, 4Bu: R = nBu) reacted with ethylene to form silene hydride complexes [(dmpe)2MnH(RHSi[double bond, length as m-dash]CHMe)] (6Ph,H: R = Ph, 6Bu,H: R = nBu). Compounds 6R,H reacted with a second equivalent of ethylene to generate [(dmpe)2MnH(REtSi[double bond, length as m-dash]CHMe)] (6Ph,Et: R = Ph, 6Bu,Et: R = nBu), resulting from apparent ethylene insertion into the silene Si–H bond. Furthermore, in the absence of ethylene, silene complex 6Bu,H slowly isomerized to the silylene hydride complex [(dmpe)2MnH([double bond, length as m-dash]SiEtnBu)] (3Bu,Et). Reactions of 4R with ethylene likely proceed via low-coordinate silyl {[(dmpe)2Mn(SiH2R)] (2Ph: R = Ph, 2Bu: R = nBu)} or silylene hydride {[(dmpe)2MnH([double bond, length as m-dash]SiHR)] (3Ph,H: R = Ph, 3Bu,H: R = nBu)} intermediates accessed from 4R by H3SiR elimination. DFT calculations and high temperature NMR spectra support the accessibility of these intermediates, and reactions of 4R with isonitriles or N-heterocyclic carbenes yielded the silyl isonitrile complexes [(dmpe)2Mn(SiH2R)(CNR′)] (7a–d: R = Ph or nBu; R′ = o-xylyl or tBu), and NHC-stabilized silylene hydride complexes [(dmpe)2MnH{[double bond, length as m-dash]SiHR(NHC)}] (8a–d: R = Ph or nBu; NHC = 1,3-diisopropylimidazolin-2-ylidene or 1,3,4,5-tetramethyl-4-imidazolin-2-ylidene), respectively, all of which were crystallographically characterized. Silyl, silylene and silene complexes in this work were accessed via reactions of [(dmpe)2MnH(C2H4)] (1) with hydrosilanes, in some cases followed by ethylene. Therefore, ethylene (C2H4 and C2D4) hydrosilylation was investigated using [(dmpe)2MnH(C2H4)] (1) as a pre-catalyst, resulting in stepwise conversion of primary to secondary to tertiary hydrosilanes. Various catalytically active manganese-containing species were observed during catalysis, including silylene and silene complexes, and a catalytic cycle is proposed.

Graphical abstract: Interconversion and reactivity of manganese silyl, silylene, and silene complexes

Supplementary files

Article information

Article type
Edge Article
Submitted
07 Sep 2019
Accepted
23 Oct 2019
First published
29 Oct 2019
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., 2019,10, 10853-10869

Interconversion and reactivity of manganese silyl, silylene, and silene complexes

J. S. Price and D. J. H. Emslie, Chem. Sci., 2019, 10, 10853 DOI: 10.1039/C9SC04513A

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