Aminocarbyne and isocyanide complexes of rhenium. Crystal structures of trans-[ReCl(CNR)(Ph2PCH2CH2PPh2)2] (R = H or SiMe3)

Abstract

Treatment of a thf solution of trans-[ReCl(N₂)(dppe)₂] with an excess of NCSiMe₃ in sunlight led to the formation of trans-[ReCl(CNSiMe₃)(dppe)₂] 1 in which the trimethylsilyl isocyanide ligand undergoes desilylation by acid or MeOH to give the aminocarbyne trans-[ReCl(CNH₂)(dppe)₂]A 2 (A = BF₄ or Cl) upon treatment with an excess of HBF₄ or HCl or the isocyanide trans-[ReCl(CNH)(dppe)₂] 3 upon treatment with a stoichiometric amount of HCl or with MeOH. Complexes 2 convert into 3 by reaction with [NBu₄]OH or NEt₃ (a more convenient route for 3 than the above), and conversely are obtained from the reaction of 3 with HBF₄ or HCl. Anodic controlled potential electrolysis of a solution of 2 (A = BF₄) in 0.2 mol dm⁻³ [NBu₄][BF₄]–NCMe, until the consumption of 2 F mol⁻¹, resulted in complete deprotonation of the aminocarbyne ligand to give the cyano-complex trans-[ReCl(CN)(dppe)₂][BF₄] 4 which, upon hydrogen abstraction from the electrolytic medium, converts into the isocyanide compound 3⁺ isolated as trans-[ReCl(CNH)(dppe)₂][BF₄]·2[NBu₄][BF₄]. The detailed syntheses and spectroscopic properties of all these complexes are reported, as well as the crystal structures of 1 and 3, and are discussed in terms of electronic and stereochemical properties of the ligands and binding metal centres.