Oxidorhenium(V) and Rhenium(III) Complexes with m-Terphenyl Isocyanides

Reactions of the sterically encumbered m-terphenyl isocyanides CNArDipp2 (Dipp = 2,6-diisopropylphenyl) and CNArMes2 (Mes = 2,4,6-trimethylphenyl) with (NBu4)[ReOCl4] in CH2Cl2 form stable complexes of the composition (NBu4)[ReOCl3(CNAr(R))] or [ReOCl3(CNAr(R))(2)] depending on the amount of isocyanide added. In the [ReOCl3(CNAr(R))(2)] complexes, cis coordination of the two isocyanides is observed for CNArMes2, while the sterically more demanding CNArDIPP2 ligands are found in trans positions. The rhenium(III) species [ReCl3(PPh3)(CNArMes2)(2)] was obtained from the reaction of [ReOCl3(PPh3)(2)] and CNArMes2. The nu(CN) IR frequencies measured for the Re-V complexes appear at higher wavenumbers than for the uncoordinated isocyanides, which suggests a low degree of backdonation into anti-bonding orbitals of these ligands.