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

The three-coordinate Ni(0) N-heterocyclic carbene complex Ni(6-Mes)(PPh 3 ) 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 PPh 3 or upon reduction of Ni(6-Mes)(PPh 3 )Br ( 2 ) with KO t Bu. Facile substitution of PPh 3 in 1 gave a range of Ni(6-Mes)(PPh 3 )(L) products (L = PhC≡CMe ( 3 ), PhCH═CH 2 ( 4 ), Ph 2 CO ( 5 ), PhCHO ( 6 )). Oxidative addition of C 6 F 6 gave Ni(6-Mes)(PPh 3 )(C 6 F 5 )F ( 7 ), while 1 was also oxidized by 4-BrC 6 H 4 F to afford a mixture of 2 and Ni(6-Mes)(PPh 3 )(C 6 H 4 F)Br ( 8 ). Surprisingly, 1 was also oxidized upon reaction with the small 5-membered ring NHC IMe 4 to give the terminal Ni(II) phosphido complex Ni(IMe 4 ) 2 (PPh 2 )Ph ( 9 ). Compounds 1 and 5 proved to be active as a precursors for the catalytic transfer hydrogenation of ketones.