New C-tetrazolato complexes of rhodium(III), palladium(II) and gold(III)

The azido complexes [RhCp*(μ-N3)(N3)]2 (Cp*=η-C5Me5), trans-Rh(N3)(CO)(PPh3)2, Na2[Pd(N3)4], Na2[Pd2(μ-N3)2(N3)4] and Na[Au(N3)4], prepared in situ from metal halide precursors and a three- to ten-fold excess of NaN3 in water, react with aliphatic isocyanides to give a series of new metal–carbon bonded tetrazolato complexes. All azide ligands in the coordination sphere undergo this cycloaddition with isocyanides except on palladium(II) where only two tetrazol-5-ato groups are formed. In the neutral species HAu(CN4R)4 (R=tBu (2c), Cy (2d)) presumably one of the four tetrazol-5-ato groups has been protonated to afford a tetrazol-5-ylidene (carbene) ligand. The reactivities of the isocyanides decrease in the order CNtBu>CNCy>CN(CH2)4Cl>CN-allyl>CNCH2CO2Na; surprisingly, no reaction occurs with methylisocyanide. With tert-butyl isocyanide in the cold, [Ru(μ-N3)(N3)(η-C10H14)]2 (C10H14:4-isopropyltoluene) only reacts with cleavage of the azido bridges giving rise to [Ru(N3)2(η-C10H14)CNtBu] (5a), while heating of the same mixture affords a second azido-isocyanide complex, trans-[Ru(N3)2(CNtBu)4] (5b), of which an X-ray structure analysis has been carried out. In some cases the reactions proceed with N2 evolution, and rhodium complexes 6a–c are also formed probably containing cyanamido (N{R}CN) or carbodiimido (NCNR) ligands, respectively.