Proton addition and hydrogen-bond formation in reactions of the dicyano-complex [NBu4][trans-Re(CN)2(dppe)2] with protic reagents

Abstract

[NBu₄][trans-Re(CN)₂(dppe)₂] (1, dppe = Ph₂PCH₂CH₂PPh₂) reacted with protic acids (HA = HBF₄, CH₃CO₂H or [Et₃NH][BPh₄], added in stoichiometric amounts) to give, on protonation of one of the cyano-ligands, the isocyanide complex trans-[Re(CN)(CNH)(dppe)₂] 3a, whereas the hydrogen-bonded cyano-adducts trans-[Re(CN·HO₂CCF₃)₂(dppe)₂] 4, trans-[Re(CN·HOMe)₂(dppe)₂] 5 and trans-[Re(CN·HNEt₃)₂(dppe)₂][BPh₄] 6 were obtained on treatment of 3a with an excess of CF₃CO₂H or of 1 with an excess of MeOH or [Et₃NH][BPh₄], respectively. However, solvent or other molecules can be trapped in the crystal lattice without hydrogen-bond interaction and trans-[Re(CN)₂(dppe)₂]·2L (L = MeOH 2a or Me₂CO 2b) or trans-[Re(CN)₂(dppe)₂]·NEt₃7 are formed on attempted recrystallization of 1 from MeOH or Me₂CO, or as a side product in the reaction of 1 with [Et₃NH][BPh₄], respectively. The crystal structures of 2b, 4, 5 and partially that of 2a were also determined and the anodic cyclic voltammetric behaviour (which is shown to distinguish between the CN–H and the hydrogen-bond CN⋯H formations) of the above complexes is described as well as an interpretative theoretical study (by extended Hückel and ab initio methods) of the CN and CNH complexes.