Metal-coordinated bridging ligands

Metal-Coordinated Bridging Ligands for Self-Supported Catalysts... 

This last class, which is the subject of the present Chapter, is essentially constituted by metal complexes in which the formation of extended metal-metal bonds is favoured by the presence of coordinating bridging ligands which hold the metal centres in close proximity. 

Figure 27-10 Anhydrous acetates of Pd" and Pt" (a) trimeric [Pd(02CMe)2h involving square-planar coordinated Pd but no metal-metal bonding (average Pd -Pd = 315pm), and (b) tetrameric [Pt(02CMc)2]4 involving octahedrally coordinated Pt and metal-metal bonds (average Pt-Pi = 249.5 pm). llie four bridging ligands in the Pt,j plane are much more labile than the others.

AT-Heteroaryl ring systems are well-known as bridging functions between transition metal centers [12, 40, 41]. The pyridyl substituent is one of the representative examples of such systems that has been a widely used ligand in transition metal coordination chemistry [42]. However, the interest in group 13 metal chemistry of these ligands is of recent interest. Stalke et al. [43] have reported the synthesis and structure of the aluminum adduct Me3Al(/r-Py)PPy2 10. 

The finding of preparatively available iminoboranes RB = NR some years ago opened exciting new possibilities not only in B—N chemistry, but also in coordination chemistry. The first examples of iminoborane-transition-metal complexes have now been published. The structurally completely characterized t-BuB = NBu-t adds, like its alkyne analog, to the 03(00)5 fragment as a bridging ligand. When Co2(CO)g and t-BuB = NBu-t are dissolved in pentane at 0°C, warming to RT and evaporation of unreacted iminoborane yields (t-BuBNBu-t)Co2(CO)5 (86%) as a black solid, which can be recrystallized from ether-nitromethane (1 3) ... 

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