Reaction of BX(2)-BX(2) (X=H or OH) with M(PH3)(2) (M=Pd or Pt). A theoretical study of the characteristic features

The insertion of M(PH3)(2) (Nd = Pd or Pt) into BX(2)-BX(2) (X = H or OH) was theoretically investigated with the ab initio MO/MP4SDQ, SD-CI, and coupled cluster with double substitutions (CCD) methods, The MP4SDQ method provides an activation energy (E(a)) and an exothermicity (E(exo)) similar to those of the SD-CI and CCD methods (the MP4SDQ values are given here). This reaction proceeds with a moderate E(a) of similar to 15 kcal/mol and a considerable E(exo) of similar to 20 kcal/mol for X = OH and M = Pt and a higher E(a) of 20 kcal/mol and a higher E(exo) of 33 kcal/mol for X = H and M = Pt, II should be noted that the 8-B bond, as well as the Si-Si bond, undergoes the insertion reaction of Pt(PH3)2 much more easily than does the C-C bond, However, the insertion of Pd(PH3)(2) into B(OH)(2)-B(OH)(2) is difficult, unlike the insertion into the Si-Si bond, The Pt-BH2 and Pt-B(OH)(2) bond energies were estimated to be similar to 60 kcal/mol, being similar to the Pt-SiH3 bond energy and much greater than the Pt-CH3 bond energy, while the Pd-B(OH)(2) bond energy (49 kcal/mol) was calculated to be much smaller than the Pt-B(OH)(2) bond energy. The reaction of BX(2)-BX(2) exhibits interesting features; around the transition state (TS), not only the sigma* orbital of the B-B bond but also the unoccupied pi and pi* orbitals can form the charge-transfer interaction with the occupied d(sigma) and d(pi) orbitals of Pt, which stabilizes the TS, This is the reason that although the B-B bond is much stronger than the Si-Si bond, the insertion of Pt(PH3)(2) into BX(2)-BX(2) easily occurs.