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Free keywords:
ALKENES; NICKEL COMPLEXES; STANNENES; METAL-METAL BONDS
Abstract:
The coordinatively unsaturated (16e) (ethene)nickel(0) stannylene complex (C2H4)2Ni=Sn{CH(SiMe3)2}2 (1) reacts with 1,6-heptadiene with preservation of the Ni=Sn bond to yield quantitatively the 1,6-diene derivative (η2,η2-C7H12)Ni=Sn-{CH(SiMe3)2}2 (2). The alkene ligands of both 1 and 2 are readily displaceable. Compounds 1 and 2 react with butadiene at −50°C by a 4-e oxidation of the metal-metal pair Ni(0)/Sn(II) to Ni(II)/Sn(IV) and concomitant reduction of two butadiene molecules to butenediyl moieties to afford stereo-selectively the 16-e complex Ni-cis-{η3(Ni),η1(Sn)-anti-C3H4CH2}2Sn{CH(SiMe3)2}2 (3). Similarly, the reaction of 1 or 2 with isoprene yields regio- and stereoselectively the derivative Ni-cis-{η3(Ni,η1(Sn)-anti-C3(3-Me)H3CH2}2Sn{CH-(SiMe3)2}2 (4). These reactions imply the cleavage of one formal Ni-Sn bond and the formation of two new Sn-C bonds. Upon reaction of 3 with PMe3 the configuration of the allyl system changes and, again fully stereoselectively, the 18-e addition compound (Me3P)Ni-cis-{η3(Ni),η1(Sn)-syn-C3H4-CH2}2Sn{CH(SiMe3)2}2 (5) is formed. When 5 is treated with BPh3, the phosphane ligand is trapped and, kinetically controlled, Ni-cis-{η3(Ni),η1(Sn)-syn-C3H4CH2}2Sn{CH(SiMe3)2}2 (6) is obtained as a stereoisomer of 3. At 40°C 6 slowly rearranges into the thermodynamically stable stereoisomer Ni-trans-{η3(Ni),η1(Sn)-syn-C3H4CH2}2Sn{CH(SiMe3)2}2 (7). Mild protolysis of 3 with pyridine hydrochloride or hydrobromide affords region and stereoselectively (Me3Si)2CH}2(X)SnNi-(η3-1-MeC3H4)(NC5H5) (X = C1, 8a; Br, 8b). In the course of this protonation reaction one butadiene molecule is eliminated, accompanied by a 2-e reduction of the metal-metal pair Ni(II)/Sn(IV) to Ni(II)/Sn(II) and, at the expense of two Sn-C bonds, reformation of a Ni-Sn bond. All compounds are isolated in high yield and fully characterized by 1H-, 13C-, and 31P-NMR spectroscopy.
