Weak donor, planar Chelating bitriazole N-heterocyclic carbene ligand for Ruthenium(II), Palladium(II), and Rhodium

The new ligand bitriazole-2-ylidene (bitz) has been successfully coordinated to Ru(II), Pd(II), Rh(l), Rh(II), and Rh(III), showing its wide chemical versatility. Reaction of the bitz ligand precursor salt, 1,1'-methyl-4,4'-bi-1,2,4-triazolium diiodide, with [RhCl(cod)](2) under mild conditions afforded chelate and bis-chelate Rh(III) complexes, as well as an unexpected metal-metal bounded di-Rh(II) species. The reaction of the precursor salt of bitz with [(eta(6)-p-cymene)RuCl2](2) and NaOAc afforded a mixture of chelate and dimetallic Ru(II)-arene complexes. The reaction of the salt with Pd(OAc)2 led to a chelate complex. In an unexpected, purely organic reaction, the precursor salt rearranges to a new C-C bound bitriazole on reaction with strong base in the absence of the metal. The electron-donor power of the bitz ligand, estimated by DFT computations, proved to be very low for an NHC and comparable with those of dmpe and dipy. Some of the new complexes proved to be catalytically active in hydrogen transfer from (PrOH)-Pr-i.