Synthesis, Structure, and Electrochemistry of Di- and Zerovalent Nickel, Palladium, and Platinum Monomers and Dimers Derived from an Enantiopure (S,S)-Tetra(tertiary Phosphine)

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• 作者：Heather J. Kitto ; A. David Rae ; Richard D. Webster ; Anthony C. Willis ; S. Bruce Wild
• 刊名：Inorganic Chemistry
• 出版年：2007
• 出版时间：September 17, 2007
• 年：2007
• 卷：46
• 期：19
• 页码：8059 - 8070
• 全文大小：442K
• 年卷期：v.46,no.19(September 17, 2007)
• ISSN：1520-510X

文摘

The ligand (S,S)-1,1,4,7,10,10-hexaphenyl-1,4,7,10-tetraphosphadecane, (S,S)-tetraphos, reacts with hexa(aqua)nickel(II) chloride in the presence of trimethylsilyl triflate (TMSOTf) in dichloromethane to give the yellow square-planar complex [Ni{(R,R)-tetraphos}](OTf)₂, which has been crystallographically characterized as the square-pyramidal,acetonitrile adduct [Ni(NCMe){(R,R)-tetraphos}]OTf. Cyclic voltammograms of the nickel(II) complex in dichloromethane and acetonitrile at 20 C showed two reduction processes at negative potentials with oxidative (E_p^ox)and reductive (E_p^red) peak separations similar to those observed for ferrocene/ferrocenium under identical conditions,suggesting two one-electron steps. The cyclic voltammetric data for the divalent nickel complex in acetonitrile attemperatures below -20 C were interpreted according to reversible coordination of acetonitrile to the nickel(I) andnickel(0) complexes. The divalent palladium and platinum complexes [M{(R,R)-tetraphos}](PF₆)₂ and [M₂{(R,R)-tetraphos}₂](OTf)₄ have been prepared. The reduction potentials for the complexes [M{(R,R)-tetraphos}](PF₆)₂increase in the order nickel(II) < palladium(II) < platinum(II). The reaction of (S,S)-tetraphos with bis(cycloocta-1,5-diene)nickel(0) in benzene affords orange [Ni{(R,R)-tetraphos}], which slowly rearranges into the thermodynamically more stable, yellow, double-stranded helicate [Ni₂{(R,R)-tetraphos}₂]; the crystal structures of both complexeshave been determined. The reactions of (S,S)-tetraphos with [M(PPh₃)₄] in toluene (M = Pd) or benzene (M = Pt)furnish the double-stranded helicates [M₂{(R,R)-tetraphos}₂]; the palladium complex crystallizes from hot benzeneas the 2-benzene solvate and was structurally characterized by X-ray crystallography. In each of the three zerovalentcomplexes, the coordinated (R,R)-tetraphos stereospecifically generates tetrahedral M(PP)₂ stereocenters of Mconfiguration.