Low-Temperature N-O Bond Cleavage of Nitrogen Monoxide in Heterometallic Carbonyl Complexes. An Experimental and Theoretical Study † M. Esther Garcı ´a, ‡ Sonia Melo ´n, ‡ Miguel A. Ruiz,* ,‡ Ramo ´n Lo ´ pez, § Toma ´s Sordo, § Luciano Marchio `, | and Antonio Tiripicchio | Departamento de Quı ´mica Orga ´nica e Inorga ´nica/IUQOEM, UniVersidad de OViedo, E-33071 OViedo, Spain, Departamento de Quı ´mica Fı ´sica y Analı ´tica, UniVersidad de OViedo, E-33071 OViedo, Spain, and Dipartimento di Chimica Generale ed Inorganica, Chimica Analitica, Chimica Fisica, UniVersita ` di Parma, Viale G. P. Usberti 17/A, I-43100 Parma, Italy Received July 19, 2008 The reaction of Na[RuCp(CO) 2 ] with [MnCp′(CO) 2 (NO)]BF 4 gives the corresponding heterometallic derivative [MnRuCpCp′(µ-CO) 2 (CO)(NO)] (Cp ) η 5 -C 5 H 5 ; Cp′ ) η 5 -C 5 H 4 Me). In contrast, the group 6 metal carbonyl anions [MCp(CO) 2 L] - (M ) Mo, W; L ) CO, P(OMe) 3 , PPh 3 ) react with the Mn and Re complexes [M′Cp′(CO) 2 (NO)]BF 4 to give the heterometallic derivatives [MM′CpCp′(µ-N)(CO) 3 L] having a nitride ligand linearly bridging the metal centers (W-N ) 1.81(3) Å, N-Re ) 1.97(3) Å, W-N-Re ) 179(1) o , in [WReCpCp′(µ-N)(CO) 3 {P(OMe) 3 }]). Density-functional theory calculations on the reactions of [WCp(CO) 3 ] - and [RuCp(CO) 2 ] - with [MnCp(CO) 2 (NO)] + revealed a comparable qualitative behavior. Thus, two similar and thermodynamically allowed reaction pathways were found in each case, one implying the displacement of CO from the cation and formation of a metal-metal bond, the other implying the cleavage of the N-O bond of the nitrosyl ligand and release of a carbonyl from the anion as CO 2 . The second pathway is more exoergonic and is initiated through an orbitally controlled attack of the anion on the N atom of the NO ligand in the cation. In contrast, the first pathway is initiated through a charge- controlled attack of the anion to the C atom of a CO ligand in the cation. The CO 2 -elimination pathway requires at the intermediate stages a close approach of the NO and CO ligands, which is more difficult for the Ru compound because of its lower coordination number (compared to W). This effect, when combined with a stronger stabilization of the initial intermediate in the Ru reaction, makes the CO 2 -elimination pathway slower in that case. Introduction Nitrogen monoxide is a remarkable molecule able to strongly bind to transition metal atoms both in high and low oxidation states, thus giving rise to a wide variety of co- ordination and organometallic complexes exhibiting a rich chemistry. 1,2 Further interest in this molecule stems from its biological activity, also related in many cases to its ability to bind to metal centers. 1,3 In addition, nitrogen monoxide is of great relevance from an environmental point of view, since this substance is released to some extent in all combustion processes, from both stationary and mobile power sources (vehicle engines, power stations, domestic heating, etc.), as well as in some specialized chemical processes (nitric acid production, nitration plants, etc.), thus † This paper is dedicated to Prof. E. Carmona on the occasion of his 60th birthday. * To whom correspondence should be addressed. E-mail: mara@ uniovi.es. ‡ Departamento de Quı ´mica Orga ´nica e Inorga ´nica/IUQOEM, Univer- sidad de Oviedo. § Departamento de Quı ´mica Fı ´sica y Analı ´tica, Universidad de Oviedo. | Universita ` di Parma. (1) Ritcher-Addo, G. B.; Legzdins, P. Metal Nitrosyls; Oxford University Press: Oxford, U.K., 1992. (2) (a) Hayton, T. W.; Legzdins, P.; Sharp, W. B. Chem. ReV. 2002, 102, 935. (b) Ford, P. C.; Lorkovic, I. M. Chem. ReV. 2002, 102, 993. (c) Mingos, D. M. P.; Sherman, D. J. AdV. Inorg. Chem. 1989, 34, 293. (d) Gladfelter, W. L. AdV. Organomet. Chem. 1985, 24, 41. (3) (a) Franke, A.; Roncaroli, F.; Rudi, v. E. Eur. J. Inorg. Chem. 2007, 773. (b) Ghosh, A. Acc. Chem. Res. 2005, 38, 943. (c) Ford, P. C.; Laverman, L.; Lorkovic, I. M. AdV. Inorg. Chem. 2003, 54, 203. (d) Wang, P. G.; Xian, M.; Tang, X.; Wu, X.; Wen, Z.; Cai, T.; Janczuk, A. J. Chem. ReV. 2002, 102, 1091. (e) Butler, A. R.; Megson, I. L. Chem. ReV. 2002, 102, 1155. (f) Williams, R. J. P. Chem. Soc. ReV. 1996, 77. (g) Clarke, M. J.; Gaul, J. B. Struct. Bonding (Berlin) 1993, 81, 147. Inorg. Chem. 2008, 47, 10644-10655 10644 Inorganic Chemistry, Vol. 47, No. 22, 2008 10.1021/ic801356m CCC: $40.75  2008 American Chemical Society Published on Web 10/18/2008