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Free keywords:
ALKENES; ETHYNE; NICKEL(O); PHOSPHANE; X-RAY
Abstract:
Ni(cdt) reacts with tBu2PC2H4PtBu2 in pentane at 20-degrees-C to yield brownish crystals of (tBu2PC2H4PtBu2)Ni(η2-C12H18) (1). The molecular structure of 1, as established by X-ray crystallography, exhibits a trigonal-planar coordination geometry of the nickel center with a η2-bonded cdt ligand. In the crystal 1 exists as two enantiomers, which are determined by the left- or right-handed screw axis of the cdt ligand. The cdt ligand in 1 resists most typical displacement reactions but 1 reacts with CO at -78-degrees-C to afford the colorless 18e complex (tBu2PC2H4PtBu2)Ni(CO)2 (2). From the reaction of Ni(cod)2 with tBu2PC2H4PtBu2 yellow needles of (tBu2PC2H4PtBu2)Ni(η2-cod) (3) are obtained. Low temperature NMR spectroscopy established that only one diene C=C bond is coordinated to nickel(0). At higher temperatures a rapid exchange of the coordinated and unbound C=C bonds is induced. When solutions of 3 are kept at 20-degrees-C for several days the dinuclear, almost insoluble yellow complex {(tBu2PC2H4PtBu2)Ni} 2(µ-η2,η2-cod) (4) precipitates. The reaction of Ni(C2H4)3 and tBu2PC2H4PtBu2 affords orange (tBu2PC2H4PtBu2)Ni(C2H4) (5). From Ni(1,5-hexadiene)2 and tBu2PC2H4PtBu2 in 1,5-hexadiene the yellow-greenish complex (tBu2PC2H4PtBu2)Ni(η2-C6H10) (6) is obtained. As for 3, only one diene C=C bond is coordinated to nickel(0), but the structure is fluxional with exchange of the coordinated and unbound C=C bonds (NMR at 20-degrees-C). From a solution of 6 in pentane the dinuclear, diastereomeric compounds rac/meso-{(tBu2PC2H4PtBu2)Ni}2(µ-η2,η2-C6H10) (7 a, b) separate in large yellow crystals. In similar reactions the 1,6-heptadiene complexes (tBu2PC2H4PtBu2)Ni(η2-C7H12) (8) and rac/meso-{(tBu2PC2H4PtBu2)Ni}2(µ-η2,η2-C7H12) (9a,b) are also obtained. In 6, 7a,b, 8, and 9a,b the open-chain diene ligands can easily be displaced, e.g., by ethene to afford 5. Thus, complexes 6, 7a,b, 8, 9a,b are the most reactive. These complexes react readily (the ethene derivative 5 also reacts but very slowly) with butadiene to yield large yellow cubes of (tBu2PC2H4PtBu2)Ni(η2-C4H6) (10), which is also fluxional. The alkene complexes 5, 6, 7a, b, 8, 9a,b, 10 react with ethyne to yield yellow-brownish crystalline (tBu2PC2H4PtBu2)Ni(C2H2) (11).
