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Organometallics 2010, 29, 1070–1078 DOI: 10.1021/om900661t
Fragmentation Pathways of [MX2(CO)2(dcbpy)] (M = Ru, Os; X = Cl, Br, I; dcbpy = 2,20 -bipyridine-4,40 -dicarboxylic acid) Complexes Janne J€ anis, Minna Jakonen, Larisa Oresmaa, Pipsa Hirva, Elina Laurila, Liubov Vlasova, Pirjo Vainiotalo, and Matti Haukka* Department of Chemistry, University of Eastern Finland, P.O. Box 111, FI-80101, Joensuu, Finland Received July 27, 2009
The gas-phase behavior and stability of [RuX2(CO)2(dcbpy)], [OsX2(CO)2(dcbpy)], and [OsI2(CO)2(mcbpy)] (X = Cl, Br, I; dcbpy = 2,20 -bipyridine-4,40 -dicarboxylic acid; mcbpy = 2,20 -bipyridine4-carboxylic acid) were studied by electrospray ionization (ESI) Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometry. Negative-ion ESI produced abundant singly and doubly deprotonated molecules for all of the compounds, without apparent changes in the metal atom oxidation state or the ligand coordination. The characteristic fragment ions resulting from the decarboxylation (loss of CO2) in one of the carboxylic acid substituents of the dcbpy ligand were also observed. The gas-phase fragmentation was investigated by means of collision-induced dissociation (CID) and infrared multiphoton dissociation (IRMPD) techniques. The most favored fragmentation pathway included the loss of CO2, followed by one or two decarbonylations. Fragmentation was observed to be both qualitatively and quantitatively dependent on the metal atom and the surrounding ligands. Generally, the compounds of osmium were considerably more stable than those of ruthenium, owing to the higher metal-carbonyl bond energies. On the basis of the ionic structures observed experimentally, the fragmentation processes were also investigated computationally at the DFT level of theory. The most likely fragmentation routes predicted by the calculations agreed well with the experimental findings. The computational structures of the different fragment anions provided additional information about the effect of the carboxylic acid substituents on the stability of the ruthenium and osmium complexes. Introduction Mass spectrometry (MS) represents not only a basic detection technique for organometallic compounds but also a versatile tool for the detailed characterization of their structures and properties.1-6 In particular, electrospray ionization (ESI),7 which is more frequently used in the field of biological chemistry, has been increasingly used in the field of organometallic chemistry. This is largely a result of its ability to transfer intact (quasi)molecular ions to the gas phase without fragmentation. In addition to analyzing their compound constitutions and purity using ESI-MS, their chemistry in both liquid and gas phase can be studied in *Corresponding author. Fax: þ358-13-251-3390. E-mail: matti.haukka@ uef.fi. (1) Traeger, J. C. Int. J. Mass. Spectrom. 2000, 200, 387. (2) Colton, R.; D’Agostino, A.; Traeger, J. C. Mass Spectrom. Rev. 1995, 14, 79. (3) Henderson, W.; Nicholson, B. K.; McCaffrey, L. J. Polyhedron 1998, 17, 4291. (4) Colton, R.; Traeger, J. C. Inorg. Chim. Acta 1992, 201, 153. (5) Henderson, W.; McIndoe, J. S.; Nicholson, B. K.; Dyson, P. J. J. Chem. Soc., Dalton Trans. 1998, 519. (6) Henderson, W.; McIndoe, J., Eds. Mass Spectrometry of Inorganic and Organometallic Compounds-Tools, Techniques, Tips, 1st ed.; Wiley Interscience, 2005 (7) Fenn, J. B.; Mann, M.; Meng, C. K.; Wong, S. F.; Whitehouse, C. M. Science 1989, 246, 64. (8) Dorcier, A.; Dyson, P. J.; Gossens, C.; Rothlisberger, U.; Scopelliti, R.; Tavernelli, I. Organometallics 2005, 24, 2114. (9) Qian, R.; Liao, Y.-X.; Guo, Y.-L.; Guo, H. J. Am. Soc. Mass Spectrom. 2006, 17, 1582. pubs.acs.org/Organometallics
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detail, providing valuable structural and thermochemical information.8-16 For instance, gas-phase fragmentation using the collision-induced dissociation (CID) technique has provided insights into the bonding characteristics that depend on the ligand structure or the metal center.9-16 In addition, the dissociation activation energies have been determined by infrared multiphoton dissociation (IRMPD)17-19 and blackbody infrared radiative dissociation (BIRD)20 techniques. The ability to detect transient reaction intermediates (10) Schalley, C. A.; M€ uller, T.; Linnartz, P.; Witt, M.; Sch€afer, M.; L€ utzen, A. Chem.;Eur. J. 2002, 8, 3538. (11) Moucheron, C.; Kirsch-De Mesmaeker, A. J. Am. Chem. Soc. 1996, 118, 12834. (12) Combariza, M. Y.; Fahey, A. M.; Milshteyn, A.; Vachet, R. W. Int. J. Mass Spectrom. 2005, 244, 109. (13) Bossio, R. E.; Hoffman, N. W.; Cundari, T. R.; Marshall, A. G. Organometallics 2004, 23, 144. (14) Butcher, C. P. G.; Dinca, A.; Dyson, P. J.; Johnson, B. F. G.; Langridge-Smith, P. R. R.; McIndoe, J. S. Angew. Chem., Int. Ed. 2003, 42, 5752. (15) Trage, C.; Diefenbach, M.; Schr€ oder, D.; Schwarz, H. Chem.; Eur. J. 2006, 12, 2454. (16) Mullen, G. E. D.; F€assler, T. F.; Went, M. J.; Howland, K.; Stein, B.; Blower, P. J. J. Chem. Soc., Dalton Trans. 1999, 3759. (17) Freitas, M. A.; Hendrickson, C. L.; Marshall, A. G. J. Am. Chem. Soc. 2000, 172, 7768. (18) Pires de Matos, A.; Freitas, M. A.; Marshall, A. G.; Marques, N.; Carvalho, A.; Isolani, P. C.; Vicentini, G. J. Alloys Comp. 2001, 323, 147. (19) Leslie, A. D.; Daneshfar, R.; Vomer, D. A. J. Am. Soc. Mass Spectrom. 2007, 18, 632. (20) Stevens, S. M., Jr.; Dunbar, R. C.; Price, W. D.; Sena, M.; Watson, C. H.; Nichols, L. S.; Riveros, J. M.; Richardson, D. E.; Eyler, J. R. J. Phys. Chem. A 2004, 108, 9892. r 2010 American Chemical Society
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by ESI-MS provides an additional benefit for reaction mechanism studies.1,21 Almost all types of organometallic compounds can be analyzed using ESI-MS.1 Intrinsically ionic compounds are readily ionized in solution and are easiest to study because of their high ionization efficiencies and energetically gentle phase transfer. Compounds with basic or acidic functionalities ionize readily via protonation/deprotonation under typical ESI conditions. More difficult to analyze are neutral, less polar compounds. Neutral metal carbonyls may be ionized by simple cationization or alkoxide anion derivatization.5 As a result of the electrolytic nature of the ESI process, electrochemical oxidation or reduction of the metal atom may also occur in the ion source, providing means for ionization. For example, one of the first organometallic compounds studied by ESI-MS, cis-[Cr(CO)2(dpe)2] (dpe = Ph2PCH2CH2PPh2), forms an abundant trans-[Cr(CO)2(dpe)2]þ cation via one-electron oxidation, Cr(0) f Cr(I).22 Another good example is metallocenes [M(C5H5)2], where M=Fe, Ru, or Os, for instance.4,23 However, any changes in the metal atom oxidation state may also affect the ligand coordination, resulting in ionic structures that are significantly different from those found in solution. This does not necessarily present a problem when ESI-MS is used for the basic characterization purposes, but it impairs studies significantly if one is seeking information about the intrinsic nature of complexes, especially conformational properties or ion thermochemistry. Matrix-assisted laser desorption ionization (MALDI), although less frequently used, can also be used to ionize organometallic compounds. For example, Eelman recently showed that MALDI-TOF performed under inert atmosphere can effectively be used to ionize air- and water-sensitive and highly reactive organometallics.24 However, intrinsic photon excitation and unintended ion/molecule reactions in the ion source tend to limit the use of MALDI for organometallic compounds. Ruthenium and osmium complexes with polypyridine ligands have been studied actively because of their optical properties and catalytic activity. Although the nature of a given complex is determined largely by the metal atom, ligands may also play a crucial role. As an example, when substituents of different nature are attached to a ligated bipyridine (bpy) ring, it results in considerable changes in the electrochemical and photochemical behavior of the corresponding metal bipyridine complexes.25 The electronic effects of the substituents originate from changes in the electron distribution caused by the electron-donating or -withdrawing nature of the substituent. The possible steric effects of the substituents or their chemical reactivity may also be important. For example, reduction of [RuX2(CO)2(NNbpy)], NNbpy being 2,20 -bipyridine or 4,40 -substituted 2,20 -bipyridine and X = halide, follows a different path depending on the substituents on the bipyridine rings. While complexes with no substituents or with substituents such as (21) Guo, H.; Qian, R.; Liao, Y.; Ma, S.; Guo, Y. J. Am. Chem. Soc. 2005, 127, 13060. (22) Colton, R.; Traeger, J. C. Inorg. Chim. Acta 1992, 153, 201. (23) Xu, X.; Nolan, S. P.; Cole, R. B. Anal. Chem. 1994, 66, 119. (24) Eelman, M. D.; Blacquiere, J. M.; Moriarty, M. M.; Fogg, D. E. Angew. Chem., Int. Ed. 2008, 47, 303. (25) (a) Kinnunen, T. J. J.; Haukka, M.; Nousiainen, M.; Patrikka, A.; Pakkanen, T. A. Dalton Trans. 2001, 2649. (b) Eskelinen, E.; Haukka, M.; Kinnunen, T. J. J.; Pakkanen, T. A. J. Electroanal. Chem. 2003, 556, 103. (c) Jakonen, M.; Hirva, P.; Haukka, M.; Chardon-Noblat, S.; Lafolet, F.; Chauvin, J.; Deronzier., A. Dalton Trans. 2007, 3314.
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Figure 1. The compounds studied.
methyl can be polymerized electrochemically26 or chemically27 into catalytically highly active28 zerovalent [Ru(CO)2(NNbpy)]n, complexes with 2,20 -bipyridine-4,40 -dicarboxylic acid substituents (dcbpy) cannot be polymerized by electrochemical methods. It has been suggested that the electrochemical reduction of the metal centers and any subsequent polymerization are prevented because of the redox processes on the carboxylic acid substituents rather than on the ruthenium center.29 Ruthenium complexes with the dcbpy ligand are of special interest because of their applications in photochemistry, especially in the dyes used in dye-sensitized solar cells. One of the most effective dyes discovered so far is Ru(dcbpy)2(SCN)2.30,31 On the other hand, the catalytic activities of corresponding carbonyl complexes depend on reactivity and stability of the ligands, especially the active carbonyl ligands. In order to investigate the effect of the metal and the dcbpy ligand on the properties of the complexes, we studied [MX2(CO)2(dcbpy)] (M = Ru, Os; X = Cl, Br, or I) (1-6) and [OsI2(CO)2(mcbpy)] (mcbpy = monocarboxylic acid2,20 -bipyridine) (7) compounds (Figure 1) using a highresolution Fourier transform ion cyclotron resonance (FTICR) mass spectrometry employing negative-ion ESI. The general gas-phase fragmentation behavior was examined using in-source CID and IRMPD techniques. The observed ionic structures and potential fragmentation pathways were also investigated computationally at the DFT level of theory.
Results and Discussion Complexes 1-3 and 7 were prepared from Os3(CO)12 in acidic conditions using a method similar to that used for (26) See for instance: (a) Chardon-Noblat, S.; Deronzier, A.; Ziessel, R. Collect. Czech. Chem. Commun. 2001, 66, 207. (b) Chardon-Noblat, S.; Pellissier, A.; Cripps, G.; Deronzier, A. J. Electroanal. Chem. 2006, 597, 28. (c) Chardon-Noblat, S.; Deronzier, A.; Ziessel, R.; Zsoldos, D. J. Electroanal. Chem. 1998, 444, 253. (27) Luukkanen, S.; Haukka, M.; Laine, O.; Ven€al€ainen, T.; Vainiotalo, P.; Pakkanen, T. A. Inorg. Chim. Acta 2002, 332, 25. (28) (a) Chardon-Noblat, S.; Collomb-Dunand-Sauthier, M.-N.; Deronzier, A.; Ziessel, R.; Zsoldos, D. Inorg. Chem. 1994, 33, 4410. (b) Chardon-Noblat, S.; Deronzier, A.; Ziessel, R.; Zsoldos, D. Inorg. Chem. 1997, 36, 5384. (c) Luukkanen, S.; Homanen, P.; Haukka, M.; Pakkanen, T. A.; Deronzier, A.; Chardon-Noblat, S.; Zsoldos, D.; Ziessel, R. Appl. Catal., A 1995, 185, 157. (d) Haukka, M.; Ven€al€ainen, T.; Kallinen, M.; Pakkanen, T. A. J. Mol. Catal. A 1998, 136, 127–134. (e) Moreno, M. A.; Haukka, M.; Ven€al€ainen, T.; Pakkanen, T. A. Catal. Lett. 2004, 96, 153. (29) Eskelinen, E.; Luukkanen, S.; Haukka, M.; Ahlgren, M.; Pakkanen, T. A. Dalton Trans. 2000, 16, 2745. (30) Nazeeruddin, M. K.; Kay, A.; Rodicio, I.; Humphry-Baker, R.; Mueller, E.; Liska, P.; Vlachopoulos, N.; Graetzel, M. J. Am. Chem. Soc. 1993, 93, 6382. (31) Robertson, N. Angew. Chem., Int. Ed. 2006, 45, 2338.
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Figure 2. Thermal ellipsoid view of complex 3 with atomic numbering scheme. Thermal ellipsoids are drawn at 50% probability. Hydrogen bonds: O6-H6: 0.88 A˚, H6 3 3 3 O7: 1.57, O6 3 3 3 O7: 2.556(6) A˚, O6-H6 3 3 3 O7: 168.2°. The structures of complexes 1 and 2 are similar, except that the crystal structure of complex 1 does not contain water of crystallization.
[RuX2(CO)2(dcbpy)] 4-6 complexes reported earlier,29,32 although some optimizations of the synthesis reactions were needed for the osmium compounds. For example, the reaction conditions used in the synthesis of [RuI2(CO)2(dcbpy)] (1:1 HI/H2O, 200 °C, 20 h) produced only a few isolated crystals in the corresponding synthesis of osmium complex 3. With a lower acid concentration (HI
