“…The reaction has been carried out over a variety of supported (3,4,(18)(19)(20)28,30,31,37,38) and unsupported (1-3, l l , 2 8 , 2 9 , 32, 36) nickel systems, principally in the liquid phase (3,4, 11, 19,20,27-32, 34, 35, 37, 38), but gas phase transformations have also been reported (23,26,30,36). In attempting to define the nature of the surface sites that promote enantiodifferentiation, the effects of varying the modification conditions have been considered (1,3,4,18,24,25,27,28,32,33) and the reaction variables have also been altered to optimize the enantioselectivity process (1,4,10,12,14,17,34). Regardless, there is still no consensus of opinion regarding the actual source of the enantiocontrol and, to date, the efforts made to relate optical yield to the coverage of the catalyst surface by the modifier have been largely unsuccessful (20,27,33,35,36).…”