Abstract: | Vaska‐type complexes, i.e. trans‐RhX(CO)(PPh3)2] (X is a halogen or pseudohalogen), undergo a range of reactions and exhibit considerable catalytic activity. The electron density on the RhI atom in these complexes plays an important role in their reactivity. Many cyanotrihydridoborate (BH3CN?) complexes of Group 6–8 transition metals have been synthesized and structurally characterized, an exception being the rhodium(I) complex. Carbonyl(cyanotrihydridoborato‐κN)bis(triphenylphosphine‐κP)rhodium(I), Rh(NCBH3)(CO)(C18H15P)2], was prepared by the metathesis reaction of sodium cyanotrihydridoborate with trans‐RhCl(CO)(PPh3)2], and was characterized by single‐crystal X‐ray diffraction analysis and IR, 1H, 13C and 11B NMR spectroscopy. The X‐ray diffraction data indicate that the cyanotrihydridoborate ligand coordinates to the RhI atom through the N atom in a trans position with respect to the carbonyl ligand; this was also confirmed by the IR and NMR data. The carbonyl stretching frequency ν(CO) and the carbonyl carbon 1JC–Rh and 1JC–P coupling constants of the Cipso atoms of the triphenylphosphine groups reflect the diminished electron density on the central RhI atom compared to the parent trans‐RhCl(CO)(PPh3)2] complex. |