Regioselective Double Oxidative Addition of Bis-NHC Precursors

The 4,4'-dimethylenebiphenyl linked symmetric bis-(2-chlorobenzimidazole) 1 and the unsymmetric 2-chlorobenzimidazolium/2-chlorobenzimidazole 2(BF4) have been reacted with one equivalent [Pd(PPh3)(4)] in oxidative addition reactions. For the symmetric bis-NHC precursor 1, double metallation of both 2-chlorobenzimidazole sites to give the dinuclear bis-pNHC complex [3](BF4)(2) was observed. The unsymmetric compound 2(BF4) was only metallated at the 2-chlorobenz-imidazolium site with formation of the mononuclear NHC complex [4](BF4). The remaining 2-chlorobenzimidazole moiety was subsequently metallated in a second oxidative addition reaction with [M(PPh3)(4)] (M=Pd, Pt) to give the homobimetallic NHC/pNHC complex [5](BF4)(2) (M=Pd) and the heterobimetallic complex [6](BF4)(2) demonstrating the unique site-selective metallation of the bis-NHC precursor 2(BF4) by two consecutive oxidative additions.

Automated summary

Oxidative addition reactions of the symmetric bis-NHC precursor 1 with [Pd(PPh3)4] resulted in the formation of dinuclear bis-pNHC complex, while unsymmetric compound 2(BF4) only underwent metallation at the 2-chlorobenzimidazolium site. Subsequent metallation of the remaining 2-chlorobenzimidazole moiety with [M(PPh3)4] (M=Pd, Pt) led to the formation of homobimetallic NHC/pNHC complex and heterobimetallic complex, demonstrating unique site-selective metallation of the bis-NHC precursor 2(BF4) through two consecutive oxidative additions.