Mechanistic Investigation of Bis(imino)pyridine Manganese Catalyzed Carbonyl and Carboxylate Hydrosilylation

Tufan K. Mukhopadhyay, Christopher L. Rock, Mannkyu Hong, Daniel C. Ashley, Thomas L. Groy, Mu Hyun Baik, Ryan Trovitch

Research output: Contribution to journalArticle

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Abstract

We recently reported a bis(imino)pyridine (or pyridine diimine, PDI) manganese precatalyst, (Ph2PPrPDI)Mn (1), that is active for the hydrosilylation of ketones and dihydrosilylation of esters. In this contribution, we reveal an expanded scope for 1-mediated hydrosilylation and propose two different mechanisms through which catalysis is achieved. Aldehyde hydrosilylation turnover frequencies (TOFs) of up to 4900 min-1 have been realized, the highest reported for first row metal-catalyzed carbonyl hydrosilylation. Additionally, 1 has been shown to mediate formate dihydrosilylation with leading TOFs of up to 330 min-1. Under stoichiometric and catalytic conditions, addition of PhSiH3 to (Ph2PPrPDI)Mn was found to result in partial conversion to a new diamagnetic hydride compound. Independent preparation of (Ph2PPrPDI)MnH (2) was achieved upon adding NaEt3BH to (Ph2PPrPDI)MnCl2 and single-crystal X-ray diffraction analysis revealed this complex to possess a capped trigonal bipyramidal solid-state geometry. When 2,2,2-trifluoroacetophenone was added to 1, radical transfer yielded (Ph2PPrPDI·)Mn(OC·(Ph)(CF3)) (3), which undergoes intermolecular C-C bond formation to produce the respective Mn(II) dimer, [(μ-O,Npy-4-OC(CF3)(Ph)-4-H-Ph2PPrPDI)Mn]2 (4). Upon finding 3 to be inefficient and 4 to be inactive, kinetic trials were conducted to elucidate the mechanisms of 1- and 2-mediated hydrosilylation. Varying the concentration of 1, substrate, and PhSiH3 revealed a first order dependence on each reagent. Furthermore, a kinetic isotope effect (KIE) of 2.2 ± 0.1 was observed for 1-catalyzed hydrosilylation of diisopropyl ketone, while a KIE of 4.2 ± 0.6 was determined using 2, suggesting 1 and 2 operate through different mechanisms. Although kinetic trials reveal 1 to be the more active precatalyst for carbonyl hydrosilylation, a concurrent 2-mediated pathway is more efficient for carboxylate hydrosilylation. Considering these observations, 1-catalyzed hydrosilylation is believed to proceed through a modified Ojima mechanism, while 2-mediated hydrosilylation occurs via insertion.

Original languageEnglish (US)
Pages (from-to)4901-4915
Number of pages15
JournalJournal of the American Chemical Society
Volume139
Issue number13
DOIs
StatePublished - Apr 5 2017

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Hydrosilylation
Manganese
Pyridine
formic acid
Ketones
Isotopes
Catalysis
Aldehydes
Kinetics
X-Ray Diffraction
Esters
Metals
pyridine
Hydrides
Dimers
X ray diffraction analysis
Single crystals

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry

Cite this

Mechanistic Investigation of Bis(imino)pyridine Manganese Catalyzed Carbonyl and Carboxylate Hydrosilylation. / Mukhopadhyay, Tufan K.; Rock, Christopher L.; Hong, Mannkyu; Ashley, Daniel C.; Groy, Thomas L.; Baik, Mu Hyun; Trovitch, Ryan.

In: Journal of the American Chemical Society, Vol. 139, No. 13, 05.04.2017, p. 4901-4915.

Research output: Contribution to journalArticle

Mukhopadhyay, Tufan K. ; Rock, Christopher L. ; Hong, Mannkyu ; Ashley, Daniel C. ; Groy, Thomas L. ; Baik, Mu Hyun ; Trovitch, Ryan. / Mechanistic Investigation of Bis(imino)pyridine Manganese Catalyzed Carbonyl and Carboxylate Hydrosilylation. In: Journal of the American Chemical Society. 2017 ; Vol. 139, No. 13. pp. 4901-4915.
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AU - Hong, Mannkyu

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