Design of sterically demanding, electron-rich carbene ligands with the perimidine scaffold

Abstract

A family of N,N′-disubstituted perimidinium cation salts were employed as precursors to persistent monomeric carbenes with novel molecular architectures and electronic structures. Depending on the substituents, reaction of these 1,3-disubstituted perimidinium cations with LiN(SiMe3)2 led either to deprotonation and generation of new carbenes or to enetetramines. In addition to spectroscopic characterization, crystallographic analysis of C 10H6(iPrN)2C (10), C 10H6(iPrN)(Me3CCH2N)C (11), {C10H6-[N(3,5-Me2C6H 3)]2C}2 (13), and C10H 6(iPrN)(3,5-Me2C6H3N)C (14) definitively confirmed the nature of these species. The mixed benzyl/cycloheptyl-substituted carbene C10H6(cyclo-C 7H13N)(p-MeC6H4CH2N)C (17) was observed to undergo dimerization upon heating to yield both cis and trans isomers of the enetetramine {C10H6(cyclo-C 7H13N)(p-MeC6H4CH 2N)C}2, (17)2. Rhodium complexes of these perimidinebased carbenes were accessed via reactions with either monomeric carbene or enetetramine. Spectroscopic and crystallographic analysis of these rhodium-carbene complexes revealed the sterically demanding nature of the carbene ligands, which is manifested in the observation of hindered Rh-C carbene bond rotation and through %Vbur measurements, and their exceptional electron-donating ability. © 2007 American Chemical Society.