Metal complexation different ligands variety

The majority of reports concerning the microwave-promoted synthesis of metal complexes describe ligand substitution reactions. A variety of ligands containing different numbers of donor atoms have been used, but ligands with nitrogen donor atoms are by far... 

Catalysis by Metals. Metals are among the most important and widely used industrial catalysts (69,70). They offer activities for a wide variety of reactions (Table 1). Atoms at the surfaces of bulk metals have reactivities and catalytic properties different from those of metals in metal complexes because they have different ligand surroundings. The surrounding bulk stabilizes surface metal atoms in a coordinatively unsaturated state that allows bonding of reactants. Thus metal surfaces offer an advantage over metal complexes, in which there is only restricted stabilization of coordinative... 

Metal-polysulfido complexes have been synthesized by a variety of methods using various reagents as sulfur sources, e.g., Ss, M2S (M=alkali metal), P2S5, H2S, organic polysulfanes, etc. The nature of the resulting polysulfido complexes often depends on the reaction conditions such as the ratio of starting materials, solvents, reaction temperature, and reaction time. In addition, the use of different ligands leads to the different results in most cases. This section shows typical synthetic methods for metal-polysulfido complexes based on recent reports on their syntheses. 

The survey on published methods for generating NHC metal complexes shows that a broad variety of different approaches exists. In general, the preparation by cleavage of dimeric metal precursors or exchange of other ligands with free NHC is the most convenient and general approach. In most examples the maximum number of NHC ligands on the metal is achieved by this method. Nevertheless, the necessity to prepare the free NHCs is a limitation. 

In accord with calculations performed by Cavell et al. [110], the oxidative addition of C2-X functionalized azolium cations (X = halogen) to metal centers proceeds faster and with a more favorable reaction enthalpy than the oxidative addition of the C2-H substimted imidazolium cations [118, 119]. The former reaction was applied successfully for the preparation of nickel and palladium complexes bearing a variety of different ylidene ligands [119]. 

Several groups have screened a variety of transition metal complexes for activity in the double silylation system, but only compounds of nickel, palladium, and platinum appear to be viable catalysts. The key factor appears to be the involvement of a M(0) species, although certain M(II) complexes can also be used, presumably with in situ reduction to M(0). Generalizations regarding the activity of the different transition metal complexes are difficult, as many variables exist in each system. However, the most active complexes seem to combine palladium metal centers with dba, small basic phosphine, or isocyanate ligands. 

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