Stoichiometric and Catalytic Reactivity of Ni(6-Mes)(PPh3)2

The three-coordinate Ni(0) N-heterocyclic carbene complex Ni(6-Mes)(PPh3)(2) (1; 6-Mes = 1,3-bis(2,4,6-trimethylphen-yl)-3,4,5,6-tetrahydropyrimidin-2-ylidene) is formed in the reaction of Ni(cod)2 with a 1:2 mixture of 6-Mes and PPh3 or upon reduction of Ni(6-Mes)(PPh3)Br (2) with (KOBu)-Bu-t. Facile substitution of PPh3 in 1 gave a range of Ni(6-Mes)(PPh3)(L) products (L = PhGEECMe (3), PhCH=CH2 (4), Ph2CO (5), PhCHO (6)). Oxidative addition of C6F6 gave Ni(6-Mes)(PPh3)(C6F5)F (7), while 1 was also oxidized by 4-BrC6H4F to afford a mixture of 2 and Ni(6-Mes)(PPh3)(C6H4F)Br (8). Surprisingly, 1 was also oxidized upon reaction with the small 5-membered ring NHC IMe4 to give the terminal Ni(II) phosphido complex Ni(IMe4)(2)(PPh2)Ph (9). Compounds 1 and 5 proved to be active as a precursors for the catalytic transfer hydrogenation of ketones.