TY - JOUR
T1 - A β-diketiminate manganese catalyst for alkene hydrosilylation
T2 - Substrate scope, silicone preparation, and mechanistic insight
AU - Mukhopadhyay, Tufan K.
AU - Flores, Marco
AU - Groy, Thomas L.
AU - Trovitch, Ryan J.
N1 - Funding Information:
This material is based upon work supported by the National Science Foundation under Grant No. 1651686.
Publisher Copyright:
© The Royal Society of Chemistry 2018.
PY - 2018
Y1 - 2018
N2 - 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.
AB - 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.
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U2 - 10.1039/c8sc02768d
DO - 10.1039/c8sc02768d
M3 - Article
AN - SCOPUS:85054364023
VL - 9
SP - 7673
EP - 7680
JO - Chemical Science
JF - Chemical Science
SN - 2041-6520
IS - 39
ER -