Effects of Spectator Ligands

The chemistry of Ru and Os compounds with metal-carbon bonds is extremely extensive and complicated. Much of this chemistry involves organic groups such as C5H5 and its substituted derivatives and arenes, effectively as spectator ligands, other groups being present as ligands. There is also an extensive chemistry of carbonyls like Ru3(CO)12 and other Ru and Os clusters. We can deal here only with some of the simpler compounds, especially those with M—C, M=C, MCp, and M(arene) bonds. 

While maintaining the spectator ligand L as CN, Nazeeruddin et al. traced the effect of cyclometalated ligands (8 in Fig. 10 42-45 in Fig. 18) in 2008 [85]. They found that introduction of 4-dimethylaminopyridine can destabilize LUMO and HOMO orbitals in parallel, leading to marginal changes in emission spectra, but it increased nomadiative rate constants, which in turn led to a reduction of overall quantum yield. They also found that introducing fluorine atoms on the phenyl... 

The steric environment of COP-X 46 and 47a around the catalytic palladium site mainly differs in a Ph (47a) and an i-Pr group (46) next to the coordinating N-site and the type and distance of the spectator ligand. While the distance of the two sandwich ligands differs only slightly between COP and 47a (3.4 A vs. 3.3 A), oxidation of the ferrocene to a ferrocenium species is expected to shorten this distance further. Overall, the steric hindrance to access the Pd-center is more distinct for 47a. These steric effects are capable to explain the higher ee obtained with 47a. 

There is an obvious and urgent need for more systematic kinetic evidence and isotope effect studies, especially for the less strai tforward processes, and even purely qualitative observations of relative reactivities, solvent and spectator ligand effects, selectivity, and the nature of minor products would be of the greatest value. 

In this article, we will compare the energetics of the conventional Halpern mechanism with that of the Brown mechanism. The basis functions used are the 3-21G for ethylene and hydrides, the ST0-2G for spectator ligands, PH and Cl, and valence double zeta basis functions for Rh with effective core potential replacing the core electrons (up to 4p) (5a.b.6). In addition, we carried out the MP2 calculations at selected, RHF-optimized structures with a larger basis set, which consists of uncontracted (3s,3p,4d) functions from the above valence DZ set for Rh, 4-31G for the ethyl group,... 

In the insertion reactions, isonitriles may serve as effective ligands on palladium ) for the activation of Si-Si bonds and, at the same time, they are involved as reactant. In contrast, ferf-alkyl isonitriles, which do not insert into Si-Si bonds at all, can exclusively serve as spectator ligands for highly effective activation of Si-Si bonds [46]. 

A very recent report moves forward significantly understanding the mechanism of reductive elimination reactions to form carbon-carbon bonds from platinum(IV) complexes.245 This report described the kinetics of reductive elimination from a cationic platinum(IV) complex as a function of solvent, of substituent character in a leaving group, of the potential effect of different spectator ligands and addressed whether there was a kinetic isotope effect. The reactions were studied also as a... 

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