Ligand design has met with considerable success with both categories of hybrid ligands, which are characterized by chemically different donor groups, and of N-heterocyclic carbenes (NHCs). Their spectacular development and diversity are attracting worldwide interest and offers almost unlimited diversity and potential in e.g. coordination/organometallic main group and transition metal chemistry, catalysis, medicinal chemistry and materials science. This review aims at providing a comprehensive update on a specific class of ligands that has enjoyed much attention in the past few years, at the intersection between the two categories mentioned above, that of hybrid NHC ligands in which the functionality associated with the carbene donor is of the oxygen-donor type. For each type of oxygen-donor present in such chelating (Section 1) or bridging (Section 2) hybrid ligands, we will examine the synthesis, structures and reactivity of their metal complexes and their applications, with a special focus on homogeneous catalysis (Section 3). Thus, hydrogenation, C–H bond activation, C–C, C–N, C–O bond formation, hydrolysis of silanes, oligomerization, polymerization, metathesis, hydrosilylation, C–C bond cleavage, acceptorless dehydrogenation, dehalogenation/hydrogen transfer, oxidation and reduction reactions will be successively presented in a tabular manner, to facilitate an overview and a rapid identification of the relevant publications describing which metals associated with a given oxygen functionality are most suitable. The literature coverage includes the year 2015.

Metal complexes with oxygen-functionalized NHC ligands: synthesis and applications

Stereochemical and structural characteristics of single- and double-site Pd(II)–N-heterocyclic carbene complexes: Promising catalysts in organic syntheses ranging from CC coupling to olefin polymerizations

Direct dehydrogenative silylation of pyridyl and iminyl substrates with triethylsilane was achieved using (L)Ir(cod)(X) (1) (L = a perimidine-based carbene ligand, X = OAc and OCOPh) complexes as catalysts under toluene refluxing conditions in the presence of norbornene as a hydrogen scavenger, and the silylated products were obtained in good yields. The isolated bis(cyclometalated)iridium complexes, (C∧C:)(C∧N)IrOAc (2) (C∧C: = a cyclometalated perimidine-carbene ligand and C∧N = a cyclometalated pyridyl- and iminyl-ligated aromatic substrate), were key intermediates, where cyclometalated five-membered metallacycles of substrates such as phenylpyridine were selectively formed before yielding mono-ortho-silylation products. The bis(cyclometalated)iridium complex (XyC∧C:)(C∧N)IrOAc (2d) (XyC∧C: = a cyclometalated N-xylyl-N′-methylperimidine-carbene ligand and C∧N = a 2-pyridylphenyl ligand), reacted with 2 equiv of Et3SiH to give an iridium hydride complex, (L4)(C∧N)Ir(H)(SiEt3) (8d) (L4 = N-CH3, N-3,5-(CH...

Hemilabile N-Xylyl-N′-methylperimidine Carbene Iridium Complexes as Catalysts for C–H Activation and Dehydrogenative Silylation: Dual Role of N-Xylyl Moiety for ortho-C–H Bond Activation and Reductive Bond Cleavage

Current advances on ruthenium(II) N-heterocyclic carbenes in hydrogenation reactions

Amidinatogermylene Metal Complexes as Homogeneous Catalysts in Alcoholic Media

Synthesis of Ru(II) complexes containing N-heterocyclic carbenes functionalized with secondary donor groups: Catalytic activity toward enantioselective transfer hydrogenation

Synthesis and characterization of amide-functionalized N-heterocyclic carbene–Pd complexes

A series of new N-heterocyclic carbene (NHC)–Ru(II) complexes functionalized with additional hemilabile donor groups, such as a hydroxy-amide group, were successfully synthesized and structurally characterized. Preliminary studies indicated that the complexes acted as precatalysts with moderate activity in the asymmetric transfer hydrogenation at room temperature without temperature control. The investigation of the effect of varying the η 6 -arene ligands showed that these ligands appeared to significantly alter the activity of the complexes as precatalysts. Furthermore, it was revealed that the hydroxy functional group on the NHC ligand side-arm not only induced the stereoselectivity of the reaction but also enhanced the reaction rate.

Synthesis of Ru(II) Complexes Containing N-Heterocyclic Carbenes Functionalized with Secondary Donor Groups: Catalytic Activity Toward Enantioselective Transfer Hydrogenation.

Ryo Kamisue

Papers

Synthesis of Ru(II) complexes containing N-heterocyclic carbenes functionalized with secondary donor groups: Catalytic activity toward enantioselective transfer hydrogenation

Synthesis and characterization of amide-functionalized N-heterocyclic carbene–Pd complexes

Synthesis of Ru(II) Complexes Containing N-Heterocyclic Carbenes Functionalized with Secondary Donor Groups: Catalytic Activity Toward Enantioselective Transfer Hydrogenation.