13C NMR spectrum of crystalline [Rh(Acac) (CO)2]: A contribution to the discussion on [Rh(Acac) (CO)2] molecular structure in the solid state

13C MAS NMR spectrum of polycrystalline [Rh(Acac) (CO)2] (1) displays separate signals from all 7 carbon atoms: 2 doublets from CO ligand carbons along with 5 singlets from Acac carbons. GIPAW calculation of 13C shielding tensor values also revealed non-equivalence of all carbon atoms in molecule 1 in the anisotropic medium of the crystal lattice. Apparently, the C2v symmetry of molecule 1 is broken owing to the asymmetry of its contacts to the neighboring molecules. For example, the contacts O⋯HC of two CO ligands of molecule 1 to the CH group of the closest molecule in the adjacent stack are markedly different: the distances OH are 2.72 and 4.38 Å, the distances OC are 3.65 and 5.00 Å, the angles OHC are 164.9° and 126.4°

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

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-kappa N)bis(triphenylphosphine-kappa P)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 singlecrystal X-ray diffraction analysis and IR, H-1, C-13 and B-11 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 v(CO) and the carbonyl carbon (1)J(C-Rh) and (1)J(C-P) coupling constants of the C-ipso 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