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 o f 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-el ectron cation Ru(NO)(CO)L-2(+), shown by X-ray diffraction to have a n onplanar structure symptomatic of greater back bonding than isoelectro nic Ru(CO)(2)L-2. Variable-temperature H-1 NMR studies of the Bu-t gro ups in [Ru(NO)(CO)L-2](BAr4F) show a Delta G double dagger (100 degree s 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 st ructure with apical bent NO. The IR frequencies of NO and CO are analy zed 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 line ar NO. RuX(CO)(NO)(PH3)(2)(+) (X = Cl-, BF4-, H-, no ligand, NCH, CO) was calculated with ab initio calculations at the Becke3LYP level. Dep ending on the nature of X, one minimum (square pyramid with bent NO) o r two minima (square pyramid with bent NO and trigonal bipyramid with linear NO) have been located. The difference in energy between these t wo 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.