Thermolysis of (tBu2PC2H4PtBu2)NiMe2 in benzene or reduction of (tBu2PC2H4PtBu2)NiCl2 with Mg* in THF/benzene affords a solution of mononuclear (tBu2PC2H4PtBu2)Ni(η2-C6H6) (1) and dinuclear {(tBu2PC2H4PtBu2)Ni}2(μ-η2:η2-C6H6) (2) in equilibrium. Complex 2 has been isolated; the X-ray structure analysis reveals an antifacial coordination of the [(tBu2PC2H4PtBu2)Ni0] moieties to adjacent CC bonds of a formal cyclohexatriene ligand. According to solid-state and solution NMR the structure of 2 is static in the solid and fluxional in solution. Displacement of the benzene ligand in 1 or 2 by C6F6 affords mononuclear (tBu2PC2H4PtBu2)Ni(η2-C6F6) (5) for which the molecular structure is also reported.

Reaction of (R2PC2H4PR2)Ni(C2H4) with COT gives the mononuclear complexes (R2PC2H4PR2)Ni(η2-C8H8) (R = iPr 1a, tBu 1b). The COT ligand in 1a,b is planar with alternating C−C and CC bonds, corresponding to a formal semiaromatic [C8H8]- ligand. Reactions of 1a with (iPr2PC2H4PiPr2)Ni(η2,η2-C6H10) and of 1b with stoichiometric amounts of {(tBu2PC2H4PtBu2)Ni}2(μ-C6H6) or lithium afford the dinuclear complexes {(iPr2PC2H4PiPr2)Ni}2{μ-η4(1,2,5,6):η4(3,4,7,8)-C8H8} (2a) and {(tBu2PC2H4PtBu2)Ni}2(μ-η2:η2-C8H8) (2b; two isomers). The COT ligand in 2a is tub-shaped and olefinic, whereas in 2b (as in 1a,b) it is planar and semiaromatic. The products are characterized by IR, solution and solid-state NMR spectroscopy, and by X-ray structure analysis.

Oxidative addition of CH3I to (dtbpe)Ni(C2H4) (dtbpe = tBu2PC2H4PtBu2) affords (dtbpe)Ni(I)CH3 (1). The reaction of (dtbpe)NiCl2 or 1 with the stoichiometric quantity of (tmeda)Mg(CH3)2 yields (dtbpe)Ni(CH3)2 (2). (dtbpe)Ni(I)CD3 (1-d 3) and (dtbpe)Ni(CD3)2 (2-d 6) have been prepared analogously. Thermolysis of 2 in benzene affords {(dtbpe)Ni}2(μ-η2:η2-C6H6) (4). The reaction of either 2 or 4 with hydrogen (H2, HD, D2) gives {(dtbpe)Ni}2(μ-H)2 (3) and the isotopomers {(dtbpe)Ni}2(μ-H)(μ-D) (3-d) and {(dtbpe)Ni}2(μ-D)2 (3-d 2). 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 (dtbpe)NiCl2 with Mg* in the presence of alkanes probably involves σ-complex-type intermediates [(dtbpe)Ni(η2-R‘H)] (R‘ = e.g. C2H5, A). While the nonisolated [(dtbpe)Ni0] σ-complexes A are exceedingly reactive intermediates, isolated 3 and 4 represent easy to handle starting complexes for [(dtbpe)Ni0] reactions. Partial protolysis of 2 with CF3SO3H affords (dtbpe)Ni(CH3)(OSO2CF3) (5). Complex 5 reacts slowly with 2 equiv of ethene to give equimolar amounts of [(dtbpe)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 [(dtbpe)Ni(C3H7)(OSO2CF3)] (G), followed by elimination of propene to give the hydride intermediate [(dtbpe)Ni(H)(OSO2CF3)] (H), which on insertion of ethene into the Ni−H bond affords 6.

No abstract