Rhodium complexes, with triaryl

Several examples of poly- and oligomerization of acetylenes are also quite typical. Water-soluble rhodium complexes with hydrophilic phosphine ligands catalyze the polymerization of arylacetylenes into stereoregular cis-oriented poly(arylacetylenes), which can further be selectively depolymerized on heating to provide a convenient method for the preparation of triaryl-benzenes [194]. Different types of product formed by regioselective di- and trimerization can be obtained by the reaction of such catalysts with other kinds of terminal acetylenes [195]. 

The trialkyl or triaryl phosphite complexes are more accessible than those of tertiary phosphines. The phosphite ligands complex strongly to rhodium, and easily displace alkene, alkadiene and even carbonyF ligands from [RhCl(CO)2]2 (equations 41 and 42), a displacement that cannot be achieved by tertiary phosphines. Indeed, even tertiary phosphine ligands themselves can be displaced by the phosphite ligands (equation 43).The phosphite complexes can also be prepared by cleaving [RhX(P(OR)3 2]2 complexes with additional ligand (equation 26). 

Rhodium and nickel have been by far the most common metals aside from palladium employed in Suzuki-Miyaura carbon-carbon bond-forming reactions. Platinum has been used on several occasions, for example Bedford and Hazelwood showed that platinum complexes with n-acidic, ortfto-metalated triaryl phosphite and phosphinite ligands exhibited what they termed unexpectedly good activity in Suzuki biaryl coupling reactions with aryl bromide substrates (Scheme 13.22). Application to aryl chlorides resulted in low conversion to the desired biaryl products. 

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