1,2,3-Triazol-5-ylidenes (tzNHC) have become a popular class of NHC ligands in homogeneous catalysis. Herein, we introduce chelate monovalent Rh- and Ir(cod) complexes bearing bidentate ligands that combine this tzNHC and an Arduengo-type NHC motif. The reactivity of these complexes with H2 and CO gas has been investigated, leading to an interesting octahedral [Ir(tzNHC-CH2-NHC)(CO)2(H)2]OTf complex and [M(tzNHC-CH2-NHC)(CO)2]OTf complexes. The carbonyl stretching frequencies of the latter indicate that the ligand has stronger electron-donating properties than classic di-NHC ligands. The square planar rhodium and iridium NHC-tzNHC complexes have been applied in transfer hydrogenation employing isopropyl alcohol as the hydrogen donor, in which they show moderate activity (Ir > Rh) toward a range of ketones as well as for an aldehyde, an imine, and a diene. The new dicarbene complexes proved to be more active for this reaction than the analogues in which the triazolyl moiety coordinates through a nitrogen donor.

A transmetallation route, using silver(I) precursors, to several zero-and di-valent palladium complexes with chelating bis(N-heterocyclic carbene) ligands bearing various N-substituents has been established.The resulting complexes have been characterized by NMR and mass spectroscopy. In addition, the structure of a representative compound, [Pd 0 (bis-(Mes)NHC)(η 2 -ma)] (3a), was confirmed by X-ray crystal structure determination. In contrast to the transfer semihydrogenation, in which only low activity was observed, complex 3a showed activity (TOF = 49 mol sub mol cat −1 h −1 ) and selectivity comparable to its monodentate counterparts in the semihydrogenation of 1-phenyl-1-propyne with molecular hydrogen.

Despite the prolific use of (di-)NHC complexes in homogeneous catalysis, there are relatively few reports on their successful application in asymmetric transformations. In this work the atropisomeric binaphthyl backbone was combined with readily obtainable 1,2,3-triazolylidenes to develop a strongly electron-donating C 2 -symmetric ligand. The ligand was efficiently synthesized in a three-step procedure in an overall yield of 91 % starting from commercially available[a] Van 'Scheme 1. Synthesis of the chiral ditriazolium salt 3.

Mechanistic insights into catalytic carboxylic ester hydrogenation with cooperative Ru(II)-bis1,2,3-triazolylidene pyridine pincer complexes Sluijter, S.N.; Korstanje, T.J.; van der Vlugt, J.I.; Elsevier, C.J.