Activation of Strong Boron-Fluorine and Silicon-Fluorine σ-Bonds: Theoretical Understanding and Prediction.

The oxidative addition of BF3 to a platinum(0) bis(phosphine) complex [Pt(PMe3)2] (1) was investigated by density functional calculations. Both the cis and trans pathways for the oxidative addition of BF3 to 1 are endergonic (ΔG°=26.8 and 35.7 kcal mol(-1), respectively) and require large Gibbs activation energies (ΔG°(≠)=56.3 and 38.9 kcal mol(-1), respectively). A second borane plays crucial roles in accelerating the activation; the trans oxidative addition of BF3 to 1 in the presence of a second BF3 molecule occurs with ΔG°(≠) and ΔG° values of 10.1 and -4.7 kcal mol(-1), respectively. ΔG°(≠) becomes very small and ΔG° becomes negative. A charge transfer (CT), F→BF3, occurs from the dissociating fluoride to the second non-coordinated BF3. This CT interaction stabilizes both the transition state and the product. The B-F σ-bond cleavage of BF2Ar(F) (Ar(F)=3,5-bis(trifluoromethyl)phenyl) and the B-Cl σ-bond cleavage of BCl3 by 1 are accelerated by the participation of the second borane. The calculations predict that trans oxidative addition of SiF4 to 1 easily occurs in the presence of a second SiF4 molecule via the formation of a hypervalent Si species.