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

Abstract

High yield syntheses of (ⁱPr₃P)₂NiX (3a–c), (where X = Cl, Br, I) were established by comproportionation of (ⁱPr₃P)₂NiX₂ (1a–c) with (ⁱPr₃P)₂Ni(η²-C₂H₄) (2). Reaction of 1a with either NaH or LiHBEt₃ provided (ⁱPr₃P)₂NiHCl (4), along with 3a as a side-product. Reduction of (ⁱPr₃P)₂NiCl (3a–c) with Mg in presence of nitrogen saturated THF solutions provided the dinitrogen complex [(ⁱPr₃P)₂Ni]₂(μ-η¹:η¹-N₂) (5). In aromatic solvents such as benzene and toluene a thermal equilibrium exists between 5 and the previously reported monophosphine solvent adducts (ⁱPr₃P)Ni(η⁶-arene) (6a,b). Reaction of 5 with carbon dioxide provided (ⁱPr₃P)₂Ni(η²-CO₂) (7). Thermolysis of 9 at 60 °C provided a mixture of products that included the reduction product (ⁱPr₃P)₂Ni(CO)₂ (8) along with ⁱPr₃PO, as identified by NMR spectroscopy. Complex 8 was also prepared in high yield from the reaction of 5 with CO. Reaction of 5 with CS₂ gave the dimeric carbon disulfide complex [(ⁱPr₃P)Ni(μ-η¹:η²-CS₂)]₂ (9). Diphenylphosphine reacts with 5 to form the dinuclear Ni(I) complex [(ⁱPr₃P)Ni(μ₂-PPh₂)]₂ (10). Complex 5 reacts with PhSH to form (ⁱPr₃P)₂Ni(SPh)(H) (11), which slowly loses H₂ and ⁱPr₃P to form the dimeric Ni(I) complex [(ⁱPr₃P)Ni(μ₂-SPh)]₂ (12) at room temperature. Complex 12 was also accessed by salt metathesis from the reaction of (ⁱPr₃P)₂NiCl (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.