A series of novel multifunctional carbenes of the type N-phosphine imide-substituted imidazolylidenes (Pi-mIms) has been synthesized and characterized. Substituents including (+)-10-camphorsulfonyl and pyroglutamate groups were introduced on the N-phosphinimidoyl moiety to diversify available structures of isolable carbenes. The impact that the rotation of the N-phosphinimidoyl groups has on the spatial environment surrounding the carbene carbon atoms was evaluated theoretically. This analysis suggested that the shape as well as the volume of the reaction field around the carbene carbon atoms varies drastically during this rotation.
Phosphine imides are ubiquitous nucleophiles/Lewis bases in modern organic chemistry. The introduction of unexplored substituents on the phosphine imidoyl nitrogen and/or phosphorus atoms should facilitate the discovery of unprecedented utility for phosphine imides. Herein, we have designed and prepared a novel class of phosphine imides known as N-borane-substituted cyclic phosphine imides (BCPIs). Experimental and theoretical analyses of the electronic structure of BCPIs demonstrate the existence of substantial negative hyperconjugation between the nitrogen and the phosphorus atoms. Given a characteristic nucleophilic/Lewis basic reactivity of BCPIs, we represent the first experimental demonstration that a 5-oxazaphosphetane species is a key intermediate in the transformation of CO2 using phosphine imides. Moreover, although it has been previously considered unlikely, the spontaneous heterolysis of a BCl bond in a BCPI-coordinated chloroborane has been directly observed, suggesting that such process is a plausible key step in the Lewis acid-promoted generation of borenium species from chloroboranes. These results thus provide evidence of two species that have been missing in contemporary organic chemistry.
Phosphine imides are ubiquitous nucleophiles/Lewis bases in modern organic chemistry. The introduction of unexplored substituents on the phosphine imidoyl nitrogen and/or phosphorus atoms should facilitate the discovery of unprecedented utility for phosphine imides. Herein, we have designed and prepared a novel class of phosphine imides known as N-borane-substituted cyclic phosphine imides (BCPIs). Experimental and theoretical analyses of the electronic structure of BCPIs demonstrate the existence of substantial negative hyperconjugation between the nitrogen and the phosphorus atoms. Given a characteristic nucleophilic/Lewis basic reactivity of BCPIs, we represent the first experimental demonstration that a 5-oxazaphosphetane species is a key intermediate in the transformation of CO2 using phosphine imides. Moreover, although it has been previously considered unlikely, the spontaneous heterolysis of a BCl bond in a BCPI-coordinated chloroborane has been directly observed, suggesting that such process is a plausible key step in the Lewis acid-promoted generation of borenium species from chloroboranes. These results thus provide evidence of two species that have been missing in contemporary organic chemistry.
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