Ligand Effects in Carbon−Boron Coupling Processes Mediated by σ‐BH Platinum Complexes

Abstract

The reaction of tri-coordinated boranes (derived from dioxaborolanes and diazaborolanes) with cyclometalated low-electron count platinum complexes [Pt(NHC')(NHC)][BAr F ] (NHC = I t Bu i Pr, IMes, IMes*) led, at low temperature, to the formation of the corresponding σ-BH species. Some of these species have been characterized by X-Ray diffraction methods showing a rare η 1coordination mode. These compounds are thermally unstable and undergo a carbon-boron coupling process whose reversibility depends on the NHC ligand. DFT calculations indicate that the energy barriers required for CÀ B bond formation events (together with PtÀ H bonds) are lower than the competitive reactions leading to CÀ H bond formation (and PtÀ B bonds). However, the CÀ B coupling products appear to be formed under kinetic control with I t Bu i Pr ligands, whereas the relative low energy barrier leading to CÀ H bond formation is sufficiently low to form the thermodynamically more stable platinum boryl complexes at rt. The latter energy barrier is, nevertheless, too high for the systems bearing IMes and IMes* ligands.

Activation of Si–H and B–H bonds by Lewis acidic transition metals and p-block elements: same, but different

“…2). 22 In any case, the σ-BH complexes can be considered to some extent as arrested intermediates leading to B–H bond cleavage as for silanes (Fig. 1), by means of oxidative addition processes.…”

σ-GeH and Germyl Cationic Pt(II) Complexes

“…1h In a series of recent contributions by our group, we have been able to isolate and characterize, by spectroscopic means and X-ray diffraction studies, σ-EH cationic platinum complexes of dihydrogen, silanes, and boranes. 4 We have observed that these species are thermally unstable and evolve through E–H bond cleavage. Intriguingly, these processes result, in subsequent steps, in C–H/Pt–Si or C–Si/Pt–H coupling reactions for silanes (depending on the nature of the silane, Scheme 1 A) 4b and in reversible C–B/Pt–H coupling events (finally leading to the thermodynamically more stable C–H/Pt–B species, Scheme 1 B).…”