2- -6-arylpyridine ligands

It is important to note that the electronic effects in this system are complicated by the fact that there are two different carboxylate ligands and two different arylpyridine ligands, each of which plays a different role in the C-O bond-forming process. However, overall, the data are consistent with a transition state like 21 or 22 for this transformation (Eq. 21). Notably, reductive elimination could also occur with the other (inequivalent) phenylpyridine ligand. 

Photoinduced and chemical oxidation of coordinated imines to amides in isomeric osmium(II) complexes of AT-arylpyridine-2-carboxaldimines has been studied by Ghosh and coworkers [34]. The complexes [Os(Br)2(Rimpy)2] (Scheme 1) were prepared and characterized structurally, indicating the pyridines of the two Rimpy ligands are trans to one another and the bromides are cis. Broadband photolysis of the complex in aerated acetonitrile resulted in oxidation of one Rimpy ligand to yield the RimOpy ligand and oxidation of the osmium to Os(III). The overall yield of the photochemical process is reported to be greater than 95%. The authors propose a mech-... 

A unique cyclometallation process was utilized to synthesize zirconium dibenzyl complex 229 involving the reaction of 2-(2 -phenol)-6-arylpyridine with Zr(CH2Ph)4185 (Equation (16)). This complex is supported by an unsymmetric tridentate, phenolate-pyridine-carbanion [CT,N,0 ]-typs ligand. Both the solution NMR data and... 

A series of iridium(III) complexes of the type Ir(L-L)3 have been prepared by reaction of a glycerol solution of Ir(acac)3 and L-L (2-arylpyridine or 2-aryl-l-qui-noline) in an open vessel equipped with a reflux condenser. 5 This represented an improvement on the analogous methodology using a domestic microwave oven as less ligand was required, but YIFs were only 0.82-1.2. In the case of 2-phenyl-l-quin-oline, a 10% yield of the Ir complex was obtained in 20 min, while only trace amounts were produced after 10 h of conventional reflux. Cyclometallated platinum(II) complexes of the type PtCl(L-L)L where L-L = 2-phenylpyridine, 2-(2 -thienyl)pyridine, or benzoquinoline have also been prepared but not with any enhancement in yield (YIF = 0.58-1.0). 55... 

The 2-Arylpyridines and Analogues Versatile Cyclometallating Ligands for Colour Tuning of Platinum(H) Complexes... 

In contrast to C-O bond-forming reactions, C-S and C-Se coupling are rare in oxidative Pd catalysis. However, a recent report by Dong and coworkers demcmstrated the Pd-catalyzed ligand-directed sulfonylation of arylpyridine, aiylpyrazole, and aryloxime ether derivatives with ArS02Cl (Eq. 6) [30]. The authors speculated that a Pd mechanism (involving oxidative addition into the S-Cl braid and subsequent C-S bond-forming reductive elimination from Pd ) was potentially operative. 

More recently, Yoshikai [135] developed a cobalt-catalyzed chelation-assisted C-H bond alkylation with alkenes. The reaction was initially developed with 2-arylpyridines (Scheme 19.92) [136], The authors demonstrated the influence of the ligand on the reaction, leading selectively to the formation of the linear or the branched product. 

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