Nickel complexes hydrogenation

Some of these coupling reactions can be made catalytic if hydrogen is eliminated and combines with the anion, thus leaving the nickel complex in the zero-valent state. Allylation of alkynes or of strained olefins with allylic acetates and nickel complexes with phosphites has been achieved (example 38, Table III). 

Despite the fact that Nature uses nickel for the activation of dihydrogen, and that Raney-Ni is one of the oldest and the most important heterogeneous hydrogenation catalysts, very few nickel complexes are known to catalyze the homoge-... 

Table 5.1 Hydrogenation of several substrates in the presence of the nickel complex [N i (PPh3)2l2].a)...

Fig. 17 Optimized geometries at BP86/SVP of the nickel complexes N-Ni(CO)3 (N = 1-9). Experimental values are given in italics. Bond lengths in A, angles in degrees. Hydrogen atoms of the phenyl rings are omitted for clarity. Experimental values from X-ray analysis taken from [107]. Experimental values from X-ray analysis of a substituted analog taken from [111]...

Another example is butene dimerization catalyzed by nickel complexes in acidic chloroaluminates 14). This reaction has been performed on a continuous basis on the pilot scale by IFF (Difasol process). Relative to the industrial process involving homogeneous catalysis (Dimersol process), the overall yield in dimers is increased. Similarly, selective hydrogenation of diene can be performed in ionic liquids, because the solubility of dienes is higher than that of monoene, which is higher than that of paraffins. In the case of the Difasol process, a reduction of the volume of the reaction section by a factor of up to 40 can be achieved. This new Difasol technology enables lower dimer (e.g., octenes) production costs 14). 

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