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Schlagwörter:
CARBON-HYDROGEN-BONDS; BINUCLEAR PALLADIUM COMPLEXES; UNUSUAL COORDINATION BEHAVIOR; RAY CRYSTAL-STRUCTURE; NI-NI SYSTEM; C-H BONDS; REDUCTIVE ELIMINATION; METAL-COMPLEXES; MOLECULAR-HYDROGEN; BRIDGING HYDRIDES
Zusammenfassung:
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-d3) and (dtbpe)Ni(CD3)2 (2-d6) 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}3(μ-H)(μ-D) (3-d) and {(dtbpe)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 (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.
