How frustrated Lewis acid/base systems pass through transition-state regions: H2 cleavage by [tBu3P/B(C6F5)3].

Chemphyschem

Department of Organic Chemistry, Arrhenius Laboratory, Stockholm University, Svante Arrhenius 16C, Stockholm, 10691 (Sweden).

Published: October 2014

We investigate the transition-state (TS) region of the potential energy surface (PES) of the reaction tBu3P + H2 + B(C6F5)3 → tBu3P-H(+) + (-)H-B(C6F5)3 and the dynamics of the TS passage at room temperature. Owing to the conformational inertia of the phosphane⋅⋅⋅borane pocket involving heavy tBu3P and B(C6F5)3 species and features of the PES E(P⋅⋅⋅H, B⋅⋅⋅H | B⋅⋅⋅P) as a function of P⋅⋅⋅H, B⋅⋅⋅H, and B⋅⋅⋅P distances, a typical reactive scenario for this reaction is a trajectory that is trapped in the TS region for a period of time (about 350 fs on average across all calculated trajectories) in a quasi-bound state (scattering resonance). The relationship between the timescale of the TS passage and the effective conformational inertia of the phosphane⋅⋅⋅borane pocket leads to a prediction that isotopically heavier Lewis base/Lewis acid pairs and normal counterparts could give measurably different reaction rates. Herein, the predicted quasi-bound state could be verified in molecular collision experiments involving femtosecond spectroscopy.

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http://dx.doi.org/10.1002/cphc.201402450DOI Listing

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