Relating the Radical Stabilization Energy and Steric Bulk of a Hydrocarbyl Group to the Strength of its Bonds with Metals and Hydrogen. A Theoretical Study

Abstract

We have analyzed the strength of the XR bond for a number of hydrocarbyl groups (R) attached to X = hydrogen, X = (CNCH3)(H)(Tp)Rh [Tp = H-B(pyrazolyl)3], and X = (OSi(CH3)3)(OSi(CH3)3)(NH-Si(CH3)3)Ti with the help of a density functional theory (DFT) based energy decomposition scheme (EDA). The hydrocarbyl groups included had a radical sp3 carbon with unsaturated aromatic or olefinic bonds (R1 = Ph-CH2, mesityl, Me-allyl, allyl) or saturated alkyl substituents (R2 = Me, Et, Pe, i-Pr, t-Bu), a radical carbon as part of a saturated ring (R3 = c-Pr, c-Bu, c-Pe, c-He), or a radical sp2 carbon (R4 = Ph, t-Bu-vinyl, Me-vinyl, vinyl). The EDA scheme was used to rationalize the relative order of the X−Ri bond energies between groups (i = 1,4), within groups (same i), and between metals X = Rh, Ti, and hydrogen (X = H). It was found that the average bond energy within each group increases as R4 > R3 ∼ R2 > R1 for the two metals as well as H. This trend correlates with the radical stabilization energy of Ri that d...