Timothy C. Johnstone

Electrophilic phenoxy-substituted phosphonium cations

A family of electrophilic phenoxy-substituted phosphonium salts [(RO)P(C6F5)3][B(C6F5)4] (R = C6H5, 4-FC6H4, 2,4-F2C6H3, C6F5) have been synthesized and their air stability was evaluated. Computations of the fluoride ion affinity and global electrophilicity index have been used to compare the electrophilicity of these phosphonium salts. The Lewis acidity of these phosphonium salts was probed computationally and experimentally in a Friedel-Crafts-type dimerization, hydrodefluorination, hydrosilylation, hydrodeoxygenation, and dehydrocoupling reactions.

1,1-Hydroboration and a Borane Adduct of Diphenyldiazomethane: A Potential Prelude to FLP-N2 Chemistry

Diphenyldiazomethane reacts with HB(C6 F5 )2 and B(C6 F5 )3 , resulting in 1,1-hydroboration and adduct formation, respectively. The hydroboration proceeds via a concerted reaction involving initial formation of the Lewis adduct Ph2 CN2 BH(C6 F5 )2 . The highly sensitive adduct Ph2 CN2 (B(C6 F5 )3 ) liberates N2 and generates Ph2 CB(C6 F5 )3 . DFT computations reveal that formation of Ph2 CN2 B(C6 F5 )3 from carbene, N2 , and borane is thermodynamically favourable, suggesting steric frustration could preclude carbene-borane adduct formation and affect FLP-N2 capture.

Accessing Frustrated Lewis Pair Chemistry from a Spectroscopically Stable and Classical Lewis Acid‐Base Adduct

B(C6 F5 )3 and P(MeNCH2 CH2 )3 N form a classical Lewis adduct, (C6 F5 )3 BP(MeNCH2 CH2 )3 N. Although (C6 F5 )3 BP(MeNCH2 CH2 )3 N does not exhibit spectroscopic evidence of dissociation into its constituent acid and base, products of frustrated Lewis pair (FLP) addition reactions are seen with PhNCO, PhCH2 N3 , PhNSO, and CO2 . Computational studies show that thermal access to the dissociated acid and base permits FLP reactivity to proceed. These results demonstrate that FLP reactivity extends across the entire continuum of equilibria governing Lewis acid-base adducts.