Diminished electron density in the Vaska-type rhodium(I) complextrans-[Rh(NCBH₃)(CO)(PPh₃)₂]

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 Rh(I) 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, (1)H, (13)C and (11)B NMR spectroscopy. The X-ray diffraction data indicate that the cyanotrihydridoborate ligand coordinates to the Rh(I) 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 (1)JC-Rh and (1)JC-P coupling constants of the Cipso atoms of the triphenylphosphine groups reflect the diminished electron density on the central Rh(I) atom compared to the parent trans-[RhCl(CO)(PPh3)2] complex.

Chloro-karboniel vastetoestand-wanordebepaling in Vaska tipe komplekse

“…Komplekse met die algemene formule trans-[Rh(CO)X(L) 2 ] (X = halied of pseudo-halied; L = ariel of alkiel gesubstitueerde tersiêre fosforligand) word in baie gevalle verwys na as Vaskatipe komplekse (Ohgomori & Watanabe, 1990, Galding et al, 2016, Smoleński et al, 2011, Roodt et al, 2003, 'n naam wat verband hou met die werk van Vaska & DiLuzio, 1961 op die oorspronklike trans-[Ir(CO)Cl(PPh 3 ) 2 ] kompleks. Die geskiedenis agter die benaming is ietwat omstrede, aangesien Angoletta, 1959 alreeds die kompleks twee jaar voor die werk van Vaska en DiLuzio berei het, en selfs die rhodium-analoog was alreeds gerapporteer (Vallarino, 1957) en is in 'n mate deur Chatt en mede-werkers ondersoek (Winterton & Leigh, 2002).…”