M. R. Momeni, E. Rivard, and A. Brown*
Organometallics 32 6201-6208.
Publication year: 2013

The stability of a variety of borane (BH3 and BH2NHMe) and silane (SiHnPh4–n, n = 0–4) adducts with diamino (NHC) and aminoalkyl (CAAC) carbenes has been carefully examined using M06-2X/cc-pVDZ computations, including natural bond orbital and atoms-in-molecules analyses. Moreover a potential mechanism for the hydride-mediated ring expansion of the carbene donors is reported. While the NHC adducts can undergo thermally induced ring-expansion chemistry, the CAAC adducts show increased stability due to a large energetic barrier for the insertion of boron (or silicon) atoms into the CAAC heterocycle. A series of substituted NHCs were investigated to further explore the roles of both electronic and steric effects on adduct stabilities and on their propensities for undergoing ring-expansion transformations.