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

Treatment of a thf solution of trans-[ReCl(N-2)(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 tran s-[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 obtaine d from the reaction of 3 with HBF4 or HCl. Anodic controlled potential elec trolysis of a solution of 2 (A=BF4) in 0.2 mol dm(-3) [NBu4][BF4]-NCMe, unt il the consumption of 2 F mol(-1), resulted in complete deprotonation of th e aminocarbyne ligand to give the cyano-complex trans-[ReCl(CN)(dppe)(2)][B F4] 4 which, upon hydrogen abstraction from the electrolytic medium, conver ts 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 a nd 3, and are discussed in terms of electronic and stereochemical propertie s of the ligands and binding metal centres.