A Stable P‐Heterocyclic Carbene

Abstract

A stable diphosphorus analogue of Enders' N‐heterocyclic carbene has been prepared by taking advantage of the inherent π‐donor capabilities of phosphorus, which are as good as, or better than, those of nitrogen. The P‐heterocyclic carbene (see figure; C gray, N blue, P red) behaves as a strong donor ligand and forms transition‐metal complexes that are thermally and air stable.

Bonding aspects of P-heterocyclic carbene transition metal complexes. A computational assessment

“…Ligand properties of phosphino carbenes have been investigated in a computational study and this new class of ligands displays a high degree of structural versatility when compared to aminocarbenes, which in turn might be utilized in tuning the properties and reactivity of carbene TM complexes [36]. A stable P-heterocyclic carbene (II) has lately been reported by Bertrand and co-workers [37]. The authors not only describe the synthesis and crystal structure of this new stable class of carbenes, but also discuss different rhodium complexes formed with this new type of heterocyclic carbene.…”

Dual Supermesityl Stabilization: A Room‐Temperature‐Stable 1,2,4‐Triphosphole Radical, Sigmatropic Hydrogen Rearrangements, and Tetraphospholide Anion

“…The introduction of two supermesityl groups has been recently shown to stabilize such intriguing diradicals as 5-7 and the diphosphorus analogue 8 of a cyclic carbene (Scheme 1). [3][4][5] …”

Heterocyclic Carbenes

“…However, these calculations also show that the nitrogen atoms of a hypothetical Nheterocyclic carbene 24 are in a perfectly planar environment, [33] whereas the phosphorus centers in a hypothetical Pheterocyclic carbene (PHC) 25 are, as expected, strongly pyramidalized, [34] thereby preventing efficient stabilization of the carbene center. Bertrand and co-workers have solved this problem elegantly and reported recently on the synthesis of the first stable PHC 29, [35] wherein pyramidalization of the phosphorus atoms [36] is prevented and the carbene center is stabilized by use of sterically demanding P substituents.…”