Ligands dicarbene

Some bidentate bis(imidazolin-2-ylidene)s 18 have been used for the preparation of complexes with chelating dicarbene ligands [75-80]. The synthesis, properties, and coordination chemistry of tripodal tris(imidazolin-2-ylidene) ligands like 19... 

Bielawski et al. have developed Janus-head dicarbene ligands which are able to act as a bridge between two metal centers, thereby leading to dinuclear complexes of type 96 [58-60] (Fig. 32). More recently homonuclear bimetallic ruthenium(II) and iron(II) complexes 97 have been synthesized. It was hoped that the dicarbene ligand would interconnect the redox-active metal centers, but the... 

Figure 5.8 Five-coordinate nickel pincer complexes bearing a dicarbene ligand.

Figure 15.14 Trinuclear magnesium chloride adduct of an amino-bridged dicarbene ligand (R = 2,4,6-trimethylphenyl) [51].

Chelating dicarbene ligands were found very useful for stabilizing technetium(V) dioxo species, forming complexes of structure 51, which turned out to be stable to water, a potentially very useful feature for the application of these compounds as radiopharmaceuticals/ ... 

C—H activation/functionalization reactions represent one of the classes of chemical transformations that have been most intensively studied in recent years. Poly-NHC metal complexes have a long-standing tradition of involvement as catalysts in these processes, which can be tracked back to their stability under the relatively harsh reaction conditions that are often needed to drive such reactions to completion in a reasonable time. For example, the group of Strassner reported already in 2002 that paUadium(II) complexes with chelating dicarbene ligands can catalyze the... 

Direct arylation can be very efficiently catalyzed also by other metal centers besides paUadium(II), in particular rhodium(III) and ruthenium(II). In 2009, the groups of Ozdemir and Bruneau jointly reported on the catalytic activity of ruthenium(II) compounds with o-xylylene-bridged, chelating dicarbene ligands for the direct arylation of 2-phenylpyridine. Good catalytic efficiencies were observed even with aryl chlorides as substrates, so that the process resulted in the predominant formation ofbis-o-arylated products (Fig. 20). ... 

Another example was reported in 2012 by the group of Liu. Dinuclear iridium(I) complexes with a bridging saturated dicarbene ligand turned out to be efficient catalysts for the N,N -dialkylation of phenylenediamines with various alcohols (Fig. 24). Interestingly, with simple [Ir(COD)Cl]2 as catalyst, the intermediate imino—amino compound was predominantly formed. The authors claim the much higher selectivity for the diamino product... 

Finally, poly-NHC complexes of other metals have occasionally been employed as catalysts for hydrosilylations as well. The group of Hollis reported in 2012 on dinuclear rhodium(I) complexes with a bridging dicarbene ligand (structure 78, Fig. 26) as catalysts for the hydrosilylation of phenylacetylene with dimethylphenylsilane. Results were comparable to those previously obtained with platinum dicarbene complexes, which is in contrast to previous reports on Rh-catalyzed hydrosilylations, in which the Z-beta product is predominantly formed without production of the alpha isomer. 

Several metal complexes with CCC pincer-type dicarbene ligands have been investigated over the years by the group of Hollis as catalysts for the intramolecular hydroamination/cychzation of unactivated alkenylamines. Initial studies concerned rhodium(III) and iridium(III) complexes of type 75, but later investigations were extended to complexes of the same ligands with group 4 metals such as zirconium, hafnium, and tita-... 

A series of cyclometalated Ru(II) complexes, 91 and 92, with a CCC pincer dicarbene ligand have been also proposed in this regard. However, only complex 91b in acetonitrile solution at room temperature shows an emission band at 808 nm, although with a very low quantum yield (0en.[Pg.255]

Together with platinum(II) complexes, also complexes of group 11 metals have been intensively studied for their luminescence properties, in particular dinuclear complexes of M(I) (M = Cu, Ag, Au), in which one or two dicarbene ligands coordinate in a bridging fashion the two metal centers. The formula of this type of complexes is exemphfied in Fig. 38. 

A series of recent examples on photoluminescent dinuclear Au(I) complexes with bridging dicarbene ligands are shown in Fig. 40. 

In particular, in this case, a dicarbene ligand is used as bridging group between two cyclometalated gold(III) centers (134 and 135). In this case, the coordination environment of the gold(III) centers is different compared... 

In a similar study, Hemmert and coworkers have studied the in vitro activity of different dinuclear di-NHC silver(I) complexes against Plasmodium falciparum, the parasite responsible of malaiia. In their study, they identified two complexes, 142 and 143, characterized by a very low IC50 value, 1.2 and 1.5 pM respectively. Furthermore, no hemolytic properties have been shown by these two complexes, a problem that may affect this type of compounds. This case further underlines that the stabilizing effect of the dicarbene ligands and the possibihty of supporting metallophihc interactions impart good properties to the complexes. 

Biffis A, Cipani M, Tubaro C, et al. Dinuclear complexes of silver(I) and gold(I) with macrocycHc dicarbene ligands bearing a 2,6-lutidinyl bridge synthesis, structural analysis and dynamic behaviour in solution. New J Chem. 2013 37 4176-4184. 

Raynal M, Cazin CSJ, Vallee C, OKvier-Bourbigou H, Braunstein P. A new stable Cnhc CH—Cnhc N-heterocyclic dicarbene ligand its mono- and dinuclear Ir(I) and Ir(I)—Rh(I) complexes. Dalton Trans. 2009 3824—3832. 

Maity R, Rit A, Schulte to Brinke C, Kosters J, Hahn FE. Two different, metal-dependent coordination modes of a dicarbene ligand. Organometallks. 2013 32 6174-6177. 

Gd-Rubio J, Camara V, Bautista D, Vicente J. Dinuclear alkynyl gold(I) complexes containing bridging N-heterocycHc dicarbene ligands new synthetic routes and luminescence. Organometallics. 2012 31 5414-5426. 

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