Synthesis and chemistry of bis(triisopropylphosphine) nickel(i) and nickel(0) precursors

Abstract

High yield syntheses of ((i)Pr(3)P)(2)NiX (3a-c), (where X = Cl, Br, I) were established by comproportionation of ((i)Pr(3)P)(2)NiX(2) (1a-c) with ((i)Pr(3)P)(2)Ni(η(2)-C(2)H(4)) (2). Reaction of 1a with either NaH or LiHBEt(3) provided ((i)Pr(3)P)(2)NiHCl (4), along with 3a as a side-product. Reduction of ((i)Pr(3)P)(2)NiCl (3a-c) with Mg in presence of nitrogen saturated THF solutions provided the dinitrogen complex [((i)Pr(3)P)(2)Ni](2)(μ-η(1):η(1)-N(2)) (5). In aromatic solvents such as benzene and toluene a thermal equilibrium exists between 5 and the previously reported monophosphine solvent adducts ((i)Pr(3)P)Ni(η(6)-arene) (6a,b). Reaction of 5 with carbon dioxide provided ((i)Pr(3)P)(2)Ni(η(2)-CO(2)) (7). Thermolysis of 9 at 60 °C provided a mixture of products that included the reduction product ((i)Pr(3)P)(2)Ni(CO)(2) (8) along with (i)Pr(3)P=O, as identified by NMR spectroscopy. Complex 8 was also prepared in high yield from the reaction of 5 with CO. Reaction of 5 with CS(2) gave the dimeric carbon disulfide complex [((i)Pr(3)P)Ni(μ-η(1):η(2)-CS(2))](2) (9). Diphenylphosphine reacts with 5 to form the dinuclear Ni(I) complex [((i)Pr(3)P)Ni(μ(2)-PPh(2))](2) (10). Complex 5 reacts with PhSH to form ((i)Pr(3)P)(2)Ni(SPh)(H) (11), which slowly loses H(2) and (i)Pr(3)P to form the dimeric Ni(I) complex [((i)Pr(3)P)Ni(μ(2)-SPh)](2) (12) at room temperature. Complex 12 was also accessed by salt metathesis from the reaction of ((i)Pr(3)P)(2)NiCl (3a) with PhSLi, which demonstrates the utility of 3a as a Ni(I) precursor. With the exception of 6a,b, all compounds were structurally characterized by single-crystal X-ray crystallography.