Prototypical Triplet Alkyl Phosphonatocarbenes

Abstract

The current case study focuses on the generation, identification, and characterization of two representative mono- and disubstituted alkyl phosphonatocarbenes by means of matrix isolation techniques in conjunction with density functional theory [B3LYP/6-311++G(d,p)] and coupled cluster [CCSD(T)/cc-pVXZ, X = D, T] computations. The EPR measurements identify both carbenes as triplet ground-state species with D values of 0.660 and 0.623 cm(-1), respectively, exhibiting persistency toward intramolecular reactions (the EPR signal observable in perfluoromethylcyclohexane up to around 70 K for the disubstituted molecule). While the reaction of the carbene center of the conformationally rich tetramethyl bisphosphonatocarbene with the CH bonds of the methyl groups leads to phosphaoxetane at room temperature, its fragmentation via a Wittig-type reaction during high vacuum flash pyrolysis (HVFP) results in dimethyl vinylphosphonate and methyl metaphosphate. The latter has been observed for the first time as an isolated entity.

Computational methods for contemporary carbene chemistry

“…These carbenes yet retain full spin density on the carbene carbon. Nemirowski et al138 put these new insights to use in a matrix isolation study of mono‐ and bis(alkylphosphonato)carbenes. The triplet character of these species could unequivocally be determined by EPR spectroscopy and their ability to form ketenes with carbon monoxide upon annealing of a CO‐doped matrix.…”