Item

Abstract

Oxidative addition of CH₃I to (d^tbpe)Ni(C₂H₄) (d^tbpe = ^tBu₂PC₂H₄P^tBu₂) affords (d^tbpe)Ni(I)CH₃ (1). The reaction of (d^tbpe)NiCl₂ or 1 with the stoichiometric quantity of (tmeda)Mg(CH₃)₂ yields (d^tbpe)Ni(CH₃)₂ (2). (d^tbpe)Ni(I)CD₃ (1-d₃) and (d^tbpe)Ni(CD₃)₂ (2-d₆) have been prepared analogously. Thermolysis of 2 in benzene affords {(d^tbpe)Ni}₂(μ-η²:η²-C₆H₆) (4). The reaction of either 2 or 4 with hydrogen (H₂, HD, D₂) gives {(d^tbpe)Ni}₂(μ-H)₂ (3) and the isotopomers {(d^tbpe)Ni}₃(μ-H)(μ-D) (3-d) and {(d^tbpe)Ni}₂(μ-D)₂ (3-d₂). According to the NMR spectra, the structure of 3 is dynamic in solution. The crystal structures of 2 and 3 have been determined by X-ray crystallography. Solution thermolysis of 2 or reduction of (d^tbpe)NiCl₂ with Mg* in the presence of alkanes probably involves σ-complex-type intermediates [(d^tbpe)Ni(η²-R‘H)] (R‘ = e.g. C₂H₅, A). While the nonisolated [(d^tbpe)Ni⁰] σ-complexes A are exceedingly reactive intermediates, isolated 3 and 4 represent easy to handle starting complexes for [(d^tbpe)Ni⁰] reactions. Partial protolysis of 2 with CF₃SO₃H affords (d^tbpe)Ni(CH₃)(OSO₂CF₃) (5). Complex 5 reacts slowly with 2 equiv of ethene to give equimolar amounts of [(d^tbpe)Ni(C₂H₅)]⁺(OSO₂CF₃^-) (6) and propene. The reaction is thought to be initiated by an insertion of ethene into the Ni−CH₃ bond of 5 to form the intermediate [(d^tbpe)Ni(C₃H₇)(OSO₂CF₃)] (G), followed by elimination of propene to give the hydride intermediate [(d^tbpe)Ni(H)(OSO₂CF₃)] (H), which on insertion of ethene into the Ni−H bond affords 6.