The Unexpected Mechanism Underlying the High‐Valent Mono‐Oxo‐Rhenium(V) Hydride Catalyzed Hydrosilylation of CN Functionalities: Insights from a DFT Study

Abstract

In this study, we theoretically investigated the mechanism underlying the high-valent mono-oxo-rhenium(V) hydride Re(O)HCl2(PPh3)2 (1) catalyzed hydrosilylation of C=N functionalities. Our results suggest that an ionic S(N)2-Si outer-sphere pathway involving the heterolytic cleavage of the Si-H bond competes with the hydride pathway involving the C=N bond inserted into the Re-H bond for the rhenium hydride (1) catalyzed hydrosilylation of the less steric C=N functionalities (phenylmethanimine, PhCH=NH, and N-phenylbenzylideneimine, PhCH=NPh). The rate-determining free-energy barriers for the ionic outer-sphere pathway are calculated to be ∼28.1 and 27.6 kcal mol(-1), respectively. These values are slightly more favorable than those obtained for the hydride pathway (by ∼1-3 kcal mol(-1)), whereas for the large steric C=N functionality of N,1,1-tri(phenyl)methanimine (PhCPh=NPh), the ionic outer-sphere pathway (33.1 kcal mol(-1)) is more favorable than the hydride pathway by as much as 11.5 kcal mol(-1). Along the ionic outer-sphere pathway, neither the multiply bonded oxo ligand nor the inherent hydride moiety participate in the activation of the Si-H bond.

Hydrosilylation Reactions Catalyzed by Rhenium

“…The (CNbox)Re(V)-oxo complexes (C12) can be prepared by simply stirring L1 with Re(O)Cl3(OPPh3)(SMe2) (C11) in CH2Cl2 at r.t. and isolated as a green stable solid (Scheme 6a) or generated directly in situ. Similarly, a theoretical investigation of the mechanism for the high-valent mono-oxorhenium(V) hydride Re(O)HCl2(PPh3)2 (III-1) catalyzed hydrosilylation of C=N functionalities was performed by Wei and co-workers [40]. These results suggest that an ionic SN2-Si outer-sphere pathway proceeding via the heterolytic cleavage of the Si-H bond competes with the hydride pathway featuring the C=N bond inserted into the Re-H bond.…”

“…C14 (0.03 mol%, r.t.) is more reactive than C13 (0.1 mol%, 80 °C) for the hydrosilylation of aldehydes [42]. Excellent NMR yields (65-100%, 13 examples) were achieved at ambient Similarly, a theoretical investigation of the mechanism for the high-valent mono-oxorhenium(V) hydride Re(O)HCl 2 (PPh 3 ) 2 (III-1) catalyzed hydrosilylation of C=N functionalities was performed by Wei and co-workers [40]. These results suggest that an ionic S N 2-Si outer-sphere pathway proceeding via the heterolytic cleavage of the Si-H bond competes with the hydride pathway featuring the C=N bond inserted into the Re-H bond.…”

Technetium and rhenium schiff base complexes for nuclear medicine

“…[113][114][115][116][117][118] and hydrosilylation. 119,120 Schiff base complexes of methyltrixoxrhenium (MTO) have also been investigated as epoxidation catalysts. [121][122][123] Although technetium has been the subject of numerous catalytic studies [124][125][126][127][128][129][130] 99m Tc "Q-series", have been investigated for single-photon emission computed tomography (SPECT) imaging of both myocardial perfusion and multi-drug resistant (MDR) tumors.…”

“…They are useful for treatment of small tumor and neoadjuvant therapy due to their short range in tissue. Examples of Auger-emitting radionuclides include 119 Sb, 111 In, and 161 Ho.…”