An Electron-Excessive Nitrosyl Complex: Reactivity of a Ligand-Centered Radical Leading to Coordinated HNO Alexei V. Marchenko, Andrei N. Vedernikov, David F. Dye, Maren Pink, Jeffrey M. Zaleski,* and Kenneth G. Caulton* Department of Chemistry, Indiana UniVersity, Bloomington, Indiana 47405 Received May 7, 2002 The reaction of RuHCl(CO)L 2 (L ) P i Pr 3 ) with NO initially forms a 1:1 adduct, shown by DFT calculations and EPR spectroscopy (including the RuD isotopomer) to contain a bent (∠Ru-N-O ) 143.9°) nitrosyl where the majority of the spin density is on the nitrosyl nitrogen. This radical adduct transforms further to give equimolar RuCl(NO)(CO)L 2 and RuHCl(HNO)(CO)L 2 , the latter with hydride trans to the nitroxyl ligand HNdO. This is the first observation of the synthesis of coordinated HNO from NO itself. DFT calculations lead to the proposal that this H-atom transfer is effected by free NO, and the lifetime of RuHCl(HNO)(CO)L 2 is indeed qualitatively dependent on the presence of free NO. Nitric oxide 1,2 is a reagent that is not immediately compatible with a 16-valence electron complex; the radical character of NO would appear to lead to a radical coordina- tion complex, so the advantage of forming an adduct to the unsaturated reagent complex is not evident. In the event that an alkyl ligand is present, a single insertion into the M-R bond still leaves a radical product, the observed reaction for a metal alkyl often involves two NO molecules, and a biden- tate N-alkyl-N-nitrosohydroxylaminato ligand, N(O)(NO)R -1 , results. 3 For a hydride ligand, no NO insertion has ever been observed. We report here a 1:1 reaction of the type introduced above, together with mechanistic information on how the reaction may proceed from radicals to even-electron products. Reaction of RuHCl(CO)L 2 (L ) P i Pr 3 ) with excess NO in benzene proceeds over 10 min at 23 °C to one major product which was characterized by spectroscopic methods and single-crystal X-ray diffraction as Ru(NO)Cl(CO)L 2 (Figure 1a), 4 a square pyramidal complex with a bent nitrosyl ligand (∠Ru-N-O ) 138.8°) in the apical position. This 16- valence electron product gives the appearance of “replace- ment” of H by NO, which only raises the question of the fate of the lost H. The reaction (eq 1) was therefore carried out with a deficiency of NO (Ru/NO ) 2:1), and the reagents were combined below -70 °C in d 8 -toluene, followed by progressive warming in 10° increments and monitoring by 1 H and 31 P{ 1 H} NMR spectroscopy. At -60 °C, the strongest 31 P NMR signal is that of 1, but it is ∼1 ppm broad and shifted 1 ppm downfield from the chemical shift of pure 1. The hydride signal of 1 is also (∼0.4 ppm) broad (J PH is not resolved, which is not true of pure 1). This suggests some slow exchange, by adduct 2 formation, and that the (para- magnetic) adduct 2 is NMR silent. 5 Also present already at -60 °C are weak signals due to 4 and a 31 P{ 1 H} NMR singlet * To whom correspondence should be addressed. E-mail: caulton@ indiana.edu (K.G.C.); zaleski@indiana.edu (J.M.Z.). (1) Richter-Addo, G. R.; Legzdins, P. Metal Nitrosyls; Oxford University Press: New York 1992. (2) Hayton, T. W.; Legzdins, P.; Sharp, W. B. Chem. ReV. 2002, 102, 935. (3) Shortland, A. J.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1973, 872. (4) Crystallographic data for C 19H42ClNO2P2Ru at 120 K: a ) 21.7112- (5) Å, b ) 8.5601(2) Å, c ) 15.0871(4) Å, )118.9110(10)°, Z ) 4 in space group C2/c. R(F) ) 0.0236 for 6942 observed reflections I > 2σ(I). Figure 1. (a) ORTEP drawing (50% probability) of Ru(NO)Cl(CO)- (P i Pr3)2, omitting methyl carbon and hydrogen: Ru1 and N1 lie on a crystallographic C2 axis, so C11 and the carbonyl are disordered, as in O1. Selected data: Ru1-N1, 1.857(1) Å; Ru-C(11), 1.781(2) Å; Ru-Cl1, 2.4905(5) Å; Ru-P1, 2.4117(2) Å; N1-O1, 1.139(2) Å; Ru1-N1-O1, 138.8(1)°; Cl1-Ru1-C(11), 160.3(1)°; N1-Ru1-Cl1, 100.80(1)°; N1- Ru1-C(11), 98.9(1)°. (b) DFT geometry-optimized structure of RuHCl- (CO)(NO)[P( i Pr)3]2, with methyl hydrogens omitted. Selected structural parameters: Ru-H, 1.634 Å; Ru-N, 2.015 Å; N-O, 1.187 Å; H-Ru-N, 174.1°; Ru-N-O, 143.9°. This structure was confirmed as a true minimum by frequency analysis. Inorg. Chem. 2002, 41, 4087-4089 10.1021/ic025699j CCC: $22.00 © 2002 American Chemical Society Inorganic Chemistry, Vol. 41, No. 16, 2002 4087 Published on Web 07/10/2002