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-trimethylphenyl)-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 KOtBu. Facile substitution of PPh3 in 1 gave a range of Ni­(6-Mes)­(PPh3)­(L) products (L = PhCCMe (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.