Isocyanide ligands acetylenes

Special Ligands. As discussed in Sect 2.5.3, the substitution of carbonyl ligands in the cluster often enhances the liability of the clusters. This property has also been used in catalytic processes. Thus for instance, the nickel cluster with isocyanide ligands Ni4(CNR)7 is an efficient catalyst precursor in the hydrogenation of acetylenes. Actually, Ni4(CNR)7 reacts with acetylenes yielding the adduct Ni4(CNR)4 (acetylene)3 which in turn is able to catalyze, under rather mild conditions, the hydrogenation of diaryl and dialkylacetylenes at rates of ca. one turnover per minute. Mononuclear complexes do not catalyze this reaction under the same conditions. 

Bis(l, 5-cyclooctadiene)nickel(0) (Ni(cod)2) prepared in eq (1) is a versatile precursor to Ni(0) complexes. The cod ligand is readily replaced by group 15 donors and/or unsaturated organic molecules such as olefins, acetylenes, and isocyanides to give a wide variety of Ni(0) complexes (eq (3)) [9,10]. 

Reactant ligands for this series of reactions appear to be limited so far to carbon monoxide and sulfur dioxide. It would be interesting to learn what othfer potential ligands (isocyanides, acetylenes, etc.) can also be added to the A-frame and face-to-face reactants in this fashion. 

Silylboration and borylstannation of acetylenes have also been achieved easily in the presence of a catalyst of palladium complexes. In contrast, palladium complexes such as Pd(PPh3)4 or Pd(OAc)2-isocyanide were ineffective for diboration of alkynes. However, the development of another new ligand will solve this difficulty in the future. 

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