RuX(CO)(NO)L-2 and Ru(CO)(NO)L-2(+): Ru(0) or Ru(II) or in between?

The synthesis of RuCl(CO)(NO)L-2 (L = (PBu2Me)-Bu-t) and replacement of Cl- by BF4-, CO, CH3CN, H2O F-, and H- are reported. NaBAr4F (Ar-F = 3,5-(CF3)(2)C6H3) removes halide to produce the four-coordinate 16-electron cation Ru(NO)(CO)L-2(+), shown by X-ray diffraction to have a nonplanar structure symptomatic of greater back bonding than isoelectronic Ru(CO)(2)L-2. Variable-temperature H-1 NMR studies of the Bu-t groups in [Ru(NO)(CO)L-2](BAr4F) show a Delta G double dagger (100 degrees C) for inversion through planar Ru of 19.1 kcal/mol. Ru(eta(1)-BF4)(CO)(NO)L-2 is shown by X-ray diffraction to have a square-pyramidal structure with apical bent NO. The IR frequencies of NO and CO are analyzed to conclude that all five-coordinate species except Ru(NO)(CO)(2)L-2(+) and RuH(NO)(CO)L-2 have bent nitrosyls; these last two have linear NO. RuX(CO)(NO)(PH3)(2)(+) (X = Cl-, BF4-, H-, no ligand, NCH, CO) was calculated with ab initio calculations at the Becke3LYP level. Depending on the nature of X, one minimum (square pyramid with bent NO) or two minima (square pyramid with bent NO and trigonal bipyramid with linear NO) have been located. The difference in energy between these two structures follows closely the NO vibrational frequency. While the frontier between bent and linear NO is indistinct, the results clearly show that pi-donor ligands stabilize 16-electron unsaturated species.