Welcome to the new version of CaltechAUTHORS. Login is currently restricted to library staff. If you notice any issues, please email coda@library.caltech.edu
Published October 7, 2017 | Supplemental Material
Journal Article Open

The mechanism for catalytic hydrosilylation by bis(imino)pyridine iron olefin complexes supported by broken symmetry density functional theory


Density functional theory (DFT, B3LYP-D3 with implicit solvation in toluene) was used to investigate the mechanisms of olefin hydrosilylation catalyzed by PDI(Fe) (bis(imino)pyridine iron) complexes, where PDI = 2,6-(ArN CMe)_2(C_5H_3N) with Ar = 2,6-R_2-C_6H_3. We find that the rate-determining step for hydrosilylation is hydride migration from Et3SiH onto the Fe-bound olefin to form (PDI)Fe(alkyl)(SiEt_3). This differs from the mechanism for the Pt Karstedt catalyst in that there is no prior Si–H oxidative addition onto the Fe center. (PDI)Fe(alkyl)(SiEt_3) then undergoes C–Si reductive elimination to form (PDI)Fe, which coordinates an olefin ligand to regenerate the resting state (PDI)Fe(olefin). In agreement with experimental observations, we found that anti-Markovnikov hydride migration has a 5.1 kcal mol−1 lower activation enthalpy than Markovnikov migration. This system has an unusual anti-ferromagnetic coupling between high spin electrons on the Fe center and the unpaired spin in the pi system of the non-innocent redox-active PDI ligand. To describe this with DFT, we used the "broken-symmetry" approach to establish the ground electronic and spin state of intermediates and transition states over the proposed catalytic cycles.

Additional Information

© 2017 The Royal Society of Chemistry. The article was received on 25 Jun 2017, accepted on 04 Sep 2017 and first published on 05 Sep 2017. Dr Robert J. Nielsen and Prof. William A. Goddard III, gratefully acknowledge financial support from The Dow Chemical Company. Dr Yan Choi Lam was supported by the National Science Foundation (NSF) through the Centers for Chemical Innovation (CCI): Solar Fuels grant CHE-1305124. There are no conflicts of interest to declare.

Attached Files

Supplemental Material - c7dt02300f1_si.pdf


Files (186.2 kB)
Name Size Download all
186.2 kB Preview Download

Additional details

August 19, 2023
October 17, 2023