Dihydroperimidine-Derived PNP Pincer Complexes as Intermediates en Route to N-Heterocyclic Carbene Pincer Complexes
作者:Anthony F. Hill、Caitlin M. A. McQueen
DOI:10.1021/om5000985
日期:2014.4.28
The reaction of N,N'-bis(dicyclohexylphosphinomethyl)-dihydroperimidine (H2C(NCH2PCy2)(2)C10H6-1,8, 1a) with [RuCl2(PPh3)(3)] in THF affords the perimidinylidene-based N-heterocyclic carbene (per-NHC) pincer complex [RuCl2(OC4H8)=C(NCH2PCy2)(2)C10H6}] (2) via chelate-assisted double C H activation. In contrast, the reactions of the tetraphenyl analogue H2C(NCH2PPh2)(2)C10H6 (1b) with [RuCl2(PPh3)(3)] and of la with [RuCl(R)(CO)(PPh3)(2)] (R = Ph, CH=CHPh) do not result in C-H activation but rather give the asymmetric, PNP-coordinated complexes [RuCl2(PPh3)kappa P-3,N,P'-CH2(NCH2PPh2)(2)C10H6}] (3) and [RuCl(R)(CO)-kappa(3) P,N,P'-CH2(NCH2PCY2)(2)C10H6}] (R = Ph (4), CH=CHPh (5)), respectively, in which the ruthenium migrates rapidly between nitrogen donors. This provides insight into the mechanistic pathway by which the proligands 1 undergo per-NHC formation, as demonstrated by the thermal conversion of 4 to [RuHCl(CO)=C(NCH2PCy2)(2)C10H6}] (6) and benzene.