Bridging coordination involving M Lewis acid interactions

2 Bridging coordination involving M Lewis acid interactions 9.3.2.1 Concept of a-acceptor, Z-type ligand 

14 to 18). Lewis acids can also be varied broadly, from group 13 elements to heavier group 14-16 elements. It is not the purpose of this section to describe all the complexes featuring M LA interactions. Only representative examples will be presented and the key features of M LA interactions will be discussed. 

The corresponding Pd and Pt dichloro complexes adopt similar square-pyramidal stmctures, but the M B interaction weakens significantly from Rh to Pt and Pd, in line with the decrease of the Lewis basicity of the metal. Despite the presence of ortho-phenylene linkers, the bisphosphine-borane ligands are remarkably flexible. They can accommodate facial as well as meridional coordination and the two phosphine anchors support but do not impose M B interactions. 

Gold complexes 17 were used as models to vary the nature of the Lewis acid and study its influence on M LA interactions. Replacement of boron for heavier group 13 elements (A1 and Ga) leads to zwitterionic complexes as the result of chloride abstraction from Au (see Section 3.4). Heavier group 14-16 elements are significantly less Lewis acidic, but nevertheless, they are prone to coordinate Lewis bases and form thereby hypervalent compounds. Such a situation with metals (Au, Pd, Pt) acting as Lewis bases was illustrated with Si and Sn, Sb and Bi, ° = S as well as Te.  

4 M LA interactions supported by triphosphine-boranes and related ambiphilic ligands 

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