Ruthenium(II) Isocyanide Complexes Supported by ... - ACS Publications

May 5, 2009 - ... of Hong Kong, Tat Chee Avenue, Kowloon, Hong Kong SAR, People's Republic of China .... Siu-Chung Chan , Ho-Yuen Cheung , and Chun-Yu...
0 downloads 0 Views 719KB Size
Download PDF
Organometallics 2009, 28, 3537–3545

3537

Ruthenium(II) Isocyanide Complexes Supported by Triazacyclononane/Trithiacyclononane and Aromatic Diimine: Structural, Spectroscopic, and Theoretical Studies Chun-Yuen Wong,* Lo-Ming Lai, Hung-Fan Leung, and Sze-Ho Wong Department of Biology and Chemistry, City UniVersity of Hong Kong, Tat Chee AVenue, Kowloon, Hong Kong SAR, People’s Republic of China ReceiVed March 2, 2009

Ruthenium(II)-isocyanide complexes bearing cyclic tridentate amine/thioether (1,4,7-trimethyl-1,4,7triazacyclononane, Me3Tacn/1,4,7-trithiacyclononane, [9]aneS3) and aromatic diimine (1,10-phenanthroline, phen/2,2′-bipyridine, bpy) have been prepared. The molecular structures of [(Me3Tacn)(bpy)Ru(t-BuNC)]2+, [([9]aneS3)(phen)Ru(t-BuNC)]2+, and the nitrile-ligated congener [(Me3Tacn)(phen)Ru(CH3CN)]2+ show that the Ru-C distances in the isocyanide complexes are sensitive to the electron richness of the metal center, and isocyanide has a stronger trans influence than nitrile. The lowest-energy dipole-allowed absorptions for the isocyanide and nitrile complexes (λmax ) 330-405 and 417-458 nm, respectively, εmax ) (3-6) × 103 dm3 mol-1 cm-1) are assigned as dπ(RuII) f π*(diimine) metal-to-ligand charge transfer (MLCT) transitions. These complexes are emissive in glassy MeOH/EtOH at 77 K upon photoexcitation and give emission at λmax ) 477-601 nm. Density functional theory (DFT) calculations and charge decomposition analysis (CDA) have been used to compare the σ-donating and π-accepting abilities of nitrile and different organometallic ligands including isocyanide, methoxycarbene, and allenylidene. The molecular structure of the cofacial bioctahedral complex [(Me3Tacn)Ru(µCl)3Ru(Me3Tacn)]+ has also been determined, and the Ru · · · Ru distance has been found to be 3.1842(6) Å. Introduction 2+

Ruthenium(II)-diimine complexes such as [Ru(bpy)3] and its derivatives have received considerable attention because they exhibit rich photophysical and photochemical properties originating from the triplet [dπ(RuII) f π*(aromatic diimine)] metalto-ligand charge transfer (3MLCT) excited state. Due to the presence of the long-lived 3MLCT state, ruthenium(II)-diimine complexes have been a research focus in photochemistry,1 electron transfer reactions,2 luminescent sensing,3 light-emitting devices,4 and photosensitizers.5 In the meantime, the pursuit of [Ru(bpy)3]2+-related complexes exhibiting desirable photophysical properties continues unabated.6 For complexes with the general formula [Ru(diimine)x(L)y]n+, their photophysical properties can be modulated through simple * Corresponding author. E-mail: [email protected]. (1) (a) Kalyanasundaram, K. Coord. Chem. ReV. 1982, 46, 159. (b) Juris, A.; Balzani, V.; Barigelletti, F.; Campagna, S.; Belser, P.; von Zelewsky, A. Coord. Chem. ReV. 1988, 84, 85. (c) Balzani, V.; Barigelletti, F.; De Cola, L. Top. Curr. Chem. 1990, 158, 31. (d) Sauvage, J.-P.; Collin, J.-P.; Chambron, J.-C.; Guillerez, S.; Coudret, C.; Balzani, V.; Barigelletti, F.; De Cola, L.; Flamigni, L. Chem. ReV. 1994, 94, 993. (2) (a) Meyer, T. J. Acc. Chem. Res. 1989, 22, 163. (b) Balzani, V.; Juris, A.; Venturi, M.; Campagna, S.; Serroni, S. Chem. ReV. 1996, 96, 759. (c) De Cola, L.; Belser, P. Coord. Chem. ReV. 1998, 177, 301. (3) (a) Balzani, V.; Sabbatini, N.; Scandola, F. Chem. ReV. 1986, 86, 319. (b) de Silva, A. P.; Gunaratne, H. Q. N.; Gunnlaugsson, T.; Huxley, A. J. M.; McCoy, C. P.; Rademacher, J. T.; Rice, T. E. Chem. ReV. 1997, 97, 1515. (4) (a) Lee, J.-K.; Yoo, D. S.; Handy, E. S.; Rubner, M. F. Appl. Phys. Lett. 1996, 69, 1686. (b) Elliott, C. M.; Pichot, F.; Bloom, C. J.; Rider, L. S. J. Am. Chem. Soc. 1998, 120, 6781. (c) Handy, E. S.; Pal, A. J.; Rubner, M. F. J. Am. Chem. Soc. 1999, 121, 3525. (d) Buda, M.; Kalyuzhny, G.; Bard, A. J. J. Am. Chem. Soc. 2002, 124, 6090. (e) Bernhard, S.; Barron, J. A.; Houston, P. L.; Abruna, H. D.; Ruglovksy, J. L.; Gao, X.; Malliaras, G. G. J. Am. Chem. Soc. 2002, 124, 13624.

modifications of the degree of conjugation in the diimine ligands. Another approach would be tuning the energy of the dπ(RuII) level via manipulating the Ru-L interaction. In the interest of developing new luminophores based on transition metal complexes for luminescence-based technologies, we regard Ru(II)diimine complexes bearing organometallic ligands as an interesting class of compounds. Different organometallic ligands in (5) (a) O’Regan, B.; Gra¨tzel, M. Nature 1991, 353, 737. (b) Bignozzi, C. A.; Schoonover, J. R.; Scandola, F. Prog. Inorg. Chem. 1997, 44, 1. (c) Gerfin, T.; Gratzel, M.; Walder, L. Prog. Inorg. Chem. 1997, 44, 345. (d) Kalyanasundaram, K.; Gra¨tzel, M. Coord. Chem. ReV. 1998, 177, 347. (e) Bach, U.; Lupo, D.; Comte, P.; Moser, J. E.; Weisso¨rtel, F.; Salbeck, J.; Spreitzer, H.; Gra¨tzel, M. Nature 1998, 395, 583. (f) Hagfeldt, A.; Gra¨tzel, M. Acc. Chem. Res. 2000, 33, 269. (g) D’Alessandro, D. M.; Keene, F. R. Chem. ReV. 2006, 106, 2270. (6) (a) Sykora, M.; Kincaid, J. R. Nature 1997, 387, 162. (b) Beer, P. D.; Szemes, F.; Balzani, V.; Sala`, C. M.; Drew, M. G. B.; Dent, S. W.; Maestri, M. J. Am. Chem. Soc. 1997, 119, 11864. (c) Farzad, F.; Thompson, D. W.; Kelly, C. A.; Meyer, G. J. J. Am. Chem. Soc. 1999, 121, 5577. (d) Gao, F. G.; Bard, A. J. J. Am. Chem. Soc. 2000, 122, 7426. (e) Nazeeruddin, M. K.; Pe´chy, P.; Renouard, T.; Zakeeruddin, S. M.; Humphry-Baker, R.; Comte, P.; Liska, P.; Cevey, L.; Costa, E.; Shklover, V.; Spiccia, L.; Deacon, G. B.; Bignozzi, C. A.; Gra¨tzel, M. J. Am. Chem. Soc. 2001, 123, 1613. (f) Galoppini, E.; Guo, W.; Zhang, W.; Hoertz, P. G.; Qu, P.; Meyer, G. J. J. Am. Chem. Soc. 2002, 124, 7801. (g) Zhan, W.; Alvarez, J.; Crooks, R. M. J. Am. Chem. Soc. 2002, 124, 13265. (h) Potvin, P. G.; Luyen, P. U.; Bra¨ckow, J. J. Am. Chem. Soc. 2003, 125, 4894. (i) Kalyuzhny, G.; Buda, M.; McNeill, J.; Barbara, P.; Bard, A. J. J. Am. Chem. Soc. 2003, 125, 6272. (j) Welter, S.; Brunner, K.; Hofstraat, J. W.; De Cola, L. Nature 2003, 421, 54. (k) Dunn, A. R.; Belliston-Bittner, W.; Winkler, J. R.; Getzoff, E. D.; Stuehr, D. J.; Gray, H. B. J. Am. Chem. Soc. 2005, 127, 5169. (l) McFarland, S. A.; Lee, F. S.; Cheng, K. A. W. Y.; Cozens, F. L.; Schepp, N. P. J. Am. Chem. Soc. 2005, 127, 7065. (m) Soltzberg, L. J.; Slinker, J. D.; Flores-Torres, S.; Bernards, D. A.; Malliaras, G. G.; Abrun˜a, H. D.; Kim, J.-S.; Friend, R. H.; Kaplan, M. D.; Goldberg, V. J. Am. Chem. Soc. 2006, 128, 7761. (n) Johansson, E.; Zink, J. I. J. Am. Chem. Soc. 2007, 129, 14437. (o) McGee, K. A.; Veltkamp, D. J.; Marquardt, B. J.; Mann, K. R. J. Am. Chem. Soc. 2007, 129, 15092.

10.1021/om9001654 CCC: $40.75  2009 American Chemical Society Publication on Web 05/05/2009

3538 Organometallics, Vol. 28, No. 12, 2009

principle perturb the energy of the dπ(RuII) level via different degrees of Ru-C σ/π-interactions, and modifying the Ru-C interactions through varying the substituent on the ligands may yield complexes with desirable photophysical properties. In this regard, it would be beneficial to probe the Ru-C bonding interactions in both the ground and the excited states. In a recent study, we have scrutinized the Ru-C bonding interactions in [(Me3Tacn)(phen)RudC(OMe)R]2+ and [(Me3Tacn)(phen)Rud CdCdCR2]2+ via structural, spectroscopic, and theoretical means.7 The Me3Tacn ligand has been chosen because (i) it is optically transparent in the UV-visible spectral region, which allows examination of the electronic transitions associated with the [(diimine)Ru(organometallic moiety)] core, and (ii) it is a pure σ-donor and does not compete with other ligands for π-bonding interactions. As an extension of our investigations to understand the effect of Ru-C interactions on the electronic and photophysical properties of a [Ru(diimine)] core, we now present the preparation and spectroscopic and theoretical investigations for a series of ruthenium(II)-isocyanide complexes bearing Me3Tacn and aromatic diimine 1,10-phenanthroline (phen)/2,2′-bipyridine (bpy). Isocyanide complex supported by 1,4,7-trithiacyclononane ([9]aneS3), [([9]aneS3)(phen)Ru(t-BuNC)]2+, and the nitrile derivatives [(Me3Tacn)(diimine)Ru(CH3CN)]2+ have also been synthesized for structural and spectroscopic comparisons. In addition, the structure of [(Me3Tacn)Ru(µ-Cl)3Ru(Me3Tacn)]+ has been determined. Our results illustrate that (1) σ-donating ability for CH3CN < t-BuNC < methoxycarbene and (2) the π-accepting ability for t-BuNC > :C(OMe)CH2Ph ≈ CH3CN > :CdCdCPh2. Thus the spectroscopic properties of [Ru(diimine)x(L)y]n+ can be systematically tuned by varying the Ru-C bonding interactions.

Results and Discussions Synthesis and Characterization. Isocyanide complexes [(Me3Tacn)(diimine)Ru-CNR]2+ (2, 2′, and 3) and [([9]aneS3)(phen)Ru(t-BuNC)]2+ (4) were prepared in ca. 80% yields by reacting isocyanide ligands with [(Me3Tacn)(diimine)Ru(OH2)]2+ and [([9]aneS3)(phen)RuCl]+, respectively, in methanol (Scheme 1). Slow diffusion of Et2O into an acetone or acetonitrile solution yielded analytically pure bright yellow or orange crystalline solids, which are sufficiently stable to be handled in air under ambient conditions in solution and solid forms. Acetonitrile-ligated complexes [(Me3Tacn)(diimine)Ru(CH3CN)]2+ (1 and 1′) were prepared for structural and spectroscopic comparisons. It is noted that (i) complexes 1-4 feature four sets of 1H signals for the phen or bpy ligands and (ii) the 13C NMR spectra for 1-3 contain five sets of signals corresponding to Me3Tacn, and those for 4 contains three sets of [9]aneS3 signals (Figure 1). These findings signify that complexes 1-4 possess a pseudo plane of symmetry in solution on the NMR time scale at room temperature. Moreover, the 1H NMR signal for the NMe trans to the L in [(Me3Tacn)(diimine)RuL]2+ is sensitive to the change of L. Taking the series [(Me3Tacn)(phen)Ru-L]2+ as an example, the 1H NMR signals for the NMe are 1.41-1.48, 2.07-2.09, and 2.52-2.59 ppm for L ) methoxycarbene [:C(OMe)R],7 isocyanide [:CNR], and allenylidene [:CdCdCAr2],7 respectively. As the concerned NMe groups are in the vicinity of the shielding location of phen, a possible explanation for the trend of the concerned chemical shift would be that the phen-Me distance in [(Me3Tacn)(phen)RuL]2+ decreases in the order L ) allenylidene > isocyanide > (7) Wong, C.-Y.; Lai, L.-M.; Lam, C.-Y.; Zhu, N. Organometallics 2008, 27, 5806.

Wong et al. Scheme 1

methoxycarbene. Significantly, this parallels the trend for the phen-Me distance calculated theoretically for [(Me3Tacn) (phen)Ru-L]2+ (see DFT Calculations section below). Defining the phen-Me distance as the distance between the centroid of the middle aromatic ring of phen and the C atom on NMe, the phen-Me distances are 4.469-4.535, 4.380, and 3.929-3.980 Å for L ) [:CdCdCAr2],7 [t-BuNC:], and [:C(OMe)R],7 respectively. The span in the phen-Me distance is correlated with the tilting of the phen toward the NMe groups as the ∠centroidphen-Ru-CMe are found to be in the order L ) allenylidene (74.97-76.51°) > isocyanide (73.20°) > methoxycarbene (63.66-64.59°). The νCtN values for the acetonitrile-ligated complexes 1 and 1′ are 2268-2270 cm-1, which are higher than those for the t-BuNC-ligated complexes 2 and 2′ (2114-2132 cm-1). This is consistent with the general understanding that isocyanide is a better π-acceptor compared with nitrile. The νCtN value for the (C6H4OMe-4)NC-ligated complex 3 (2096 cm-1) is lower than those for 2 and 2′, revealing that the phenyl ring on

Figure 1. 13C NMR spectra showing the signals for the Me3Tacn of 2′ and [9]aneS3 of 4. Signals for the tertiary carbon and methyl groups of t-BuNC are marked by * and +, respectively.

Ruthenium(II) Isocyanide Complexes Scheme 2

(C6H4OMe-4)NC is effectively conjugated with the CtN moiety to give a lower π*(CNR) orbital. The higher νCtN value for complex 4 (2167 cm-1) compared with those for 2 and 2′ is in accordance with the stronger electron-donating capacity of Me3Tacn compared with [9]aneS3.8 The synthesis of [(Me3Tacn)Ru(µ-Cl)3Ru(Me3Tacn)]+ (5) was discovered in an attempt to prepare [Ru(Me3Tacn)(X)Cl]n+ where X ) bidentate cyclometalated ligand. Refluxing a mixture of [Ru(Me3Tacn)Cl3] and cyclometalated ligand X in ethylene glycol did not yield any [Ru(Me3Tacn)(X)Cl]n+ but a deep blue product that was analyzed to be the dicationic [(Me3Tacn)Ru(µCl)3Ru(Me3Tacn)]2+. It was then found out that the dicationic complex could be obtained by refluxing [Ru(Me3Tacn)Cl3] in ethylene glycol alone. In the literature, the oxidation states for the Ru centers in the mixed-valent complex [(Me3Tacn)Ru(µCl)3Ru(Me3Tacn)]2+ were assigned as +2.5.9,10 The reduction of the Ru centers from +3 to +2.5 upon the formation of [(Me3Tacn)Ru(µ-Cl)3Ru(Me3Tacn)]2+ should be due to the reducing power of ethylene glycol. However, the reducing power of ethylene glycol is not high enough to reduce both Ru centers to +2, and the monocationic complexes [(Me3Tacn)Ru(µCl)3Ru(Me3Tacn)]+ (5) have to be prepared by reducing [(Me3Tacn)Ru(µ-Cl)3Ru(Me3Tacn)]2+ by Zn powder (Scheme 2). Complex 5 is red in color and air-sensitive in both solution and solid forms; it will be oxidized to give [(Me3Tacn)Ru(µCl)3Ru(Me3Tacn)]2+ upon exposure to ambient air (Figure 2). The 1H and 13C NMR spectra for 5 feature two sets of signals corresponding to Me3Tacn, consistent with the fact that the cation in the crystal structure for 5(PF6) possesses a pseudoD3h symmetry (see Crystal Structures section below). Crystal Structures. The molecular structures of [1(PF6)2]2 · 3CH3CN, 2′(PF6)2, 4(PF6)2 · 3CH3CN, and 5(PF6) have been determined by X-ray crystallography. The perspective views of their cations are shown in Figures 3-5. Crystallographic data for these complexes are listed in Table 1. In each case, the Ru atom adopts a distorted octahedral geometry, with the Me3Tacn or [9]aneS3 facially coordinating to it. (A) Ru-C Bonding Interaction in Isocyanide Complexes. The Ru-C distance in [(Me3Tacn)(bpy)Ru(t-BuNC)]2+ (2′, 1.922(4) Å) is shorter than that in [([9]aneS3)(phen)Ru(t(8) Siclovan, O. P.; Angelici, R. J. Inorg. Chem. 1998, 37, 432. (9) Neubold, P.; Della Vedova, B. S. P. C.; Wieghardt, K.; Nuber, B.; Weiss, J. Inorg. Chem. 1990, 29, 3355. (10) Kaim, W.; Titze, C.; Klein, A.; Kno¨dler, A.; Zalis, S. Isr. J. Chem. 2001, 41, 145.

Organometallics, Vol. 28, No. 12, 2009 3539

BuNC)]2+ (4, 1.984(3) Å) by 0.062 Å. As the electronic and steric effects for bpy and phen are expected to be similar in these complexes, the difference in the Ru-C distance between 2′ and 4 should originate from the difference in the electrondonating effect of Me3Tacn and [9]aneS3. Since the bonding interaction of isocyanide complexes can be represented by the mesomeric structures [M--CtN+-R] T [MdCdN-R], the shorter Ru-C distance in 2′ compared with that in 4 is in accordance with the stronger electron-donating effect of Me3Tacn than [9]aneS3,8 which destabilizes the former mesomeric form to a greater extent and gives a stronger Ru-C π-interaction. Moreover, it is interesting to note that the Ru-C distance in 2′ is only slightly longer than those for the methoxycarbene complexes [(Me3Tacn)(phen)RudC(OMe)R]2+ (R ) CH2Ph, 1.917(3) Å; R ) CHdCPh2, 1.906(4) Å),7 of which the Ru-C bonds exhibit both σ-bonding and π-backbonding character. These findings reveal the presence of ruthenium-carbon multiple bonding character in 2′, presumably due to a dπ(RuII) f π*(CNR) π-back-bonding interaction. However, one should not jump to a conclusion that the mesomeric structure [MdCdN-R] is a better description for the bonding interaction in 2′. This is because the isocyanide ligand in 2′ is essentially linear (∠C-N-R ) 166.8(3)°), whereas [MdCdN-R] implies a bend at the nitrogen atom. In fact, significant bending in the isocyanide ligand was documented in Ru(0) complexes such as [Ru(t-BuNC)4(PPh3)] (∠C-N-R ) 130(2)°).11 Thus we still favor the [M-CtN+-R] description for the isocyanide complexes in this work. (B) Trans Influence of Isocyanide Ligand. Within the [(Me3Tacn)(diimine)Ru-L]2+ series, it is noted that the structural trans influences of nitrile, isocyanide, and methoxycarbene are significantly different: the Ru-NTacn-trans distance in 1 (2.108(5), 2.115(4) Å) < 2′ (2.170(3) Å) < [(Me3Tacn)(phen)Rud C(OMe)R]2+ (R ) CH2Ph, 2.237(2) Å; R ) CHdCPh2, 2.246(4) Å).7 The difference in the strength of the trans influence between these ligands can provide insight into their σ-donating ability. Considering the trans influence to be principally electrostatic in origin, the strength of the trans influence for a ligand is an interplay of metal-ligand σ- and π-interactions.12 Ligands (say L in the linear [L-M-X] system) with stronger σ-donating and poorer π-accepting ability have a stronger trans influence as they increase the electron density on the σ- and π-orbitals of M, respectively, leading to a stronger repulsive interaction between M and X. As the Me3Tacn ligand has no appreciable π-interaction with the Ru center, the Ru-NTacn-trans distance in [(Me3Tacn)(diimine)Ru-L]2+ should be affected only by the Ru-L σ-interaction (σ-trans influence) rather than the Ru-L π-interaction (π-trans influence). Thus the trend in Ru-NTacn-trans distance for [(Me3Tacn)(diimine)Ru-L]2+ reveals that the σ-donating ability for nitrile < isocyanide < methoxycarbene. It is also interesting to note that the Ru-S[9]aneS3-trans distance in [([9]aneS3)(phen)Ru(t-BuNC)]2+ (4) is 0.100 Å longer than that in [([9]aneS3)(phen)RuCl]+,13 even though the chloride ligand is charged, whereas isocyanide is a neutral ligand. (C) Cofacial Bioctahedral Complex [(Me3Tacn)Ru(µCl)3Ru(Me3Tacn)]+. An ideal cofacial bioctahedral complex of the type L3M(µ-X)3ML3 has ∠M-X-M and X-M-X of 70.5° (11) Barker, G. K.; Galas, A. M. R.; Green, M.; Howard, J. A. K.; Stone, F. G. A.; Turney, T. W.; Welch, A. J.; Woodward, P. J. Chem. Soc. Chem. Comm. 1977, 256. (12) Hartley, F. R. Chem. Soc. ReV. 1973, 2, 163. (13) Goodfellow, B. J.; Fe´lix, V.; Pacheco, S. M. D.; Pedrosa de Jesus, J.; Drew, M. G. B. Polyhedron 1997, 16, 393.

3540 Organometallics, Vol. 28, No. 12, 2009

Wong et al.

Figure 2. (a, b) ESI mass spectrum (positive mode) and experimental isotopic distribution pattern of 5 in acetone. (c) Simulated isotopic distribution pattern of [(Me3Tacn)Ru(µ-Cl)3Ru(Me3Tacn)]+. Peaks corresponding to [(Me3Tacn)Ru(µ-Cl)3Ru(Me3Tacn)]2+ and {[(Me3Tacn)Ru(µCl)3Ru(Me3Tacn)]2+ + PF6-}+ (oxidized products of 5 formed during measurement) are marked by * and +, respectively.

Figure 3. Perspective views of the two crystallographically independent cations in [1(PF6)2]2 · 3CH3CN (thermal ellipsoids are drawn at 30% probability). Selected bond lengths (Å) and angles (deg): Ru(1)-N(6) 2.014(5), Ru(2)-N(12) 2.030(5), N(6)-C(22) 1.139(8),N(12)-C(45)1.131(8),C(22)-C(23)1.441(10),C(45)-C(46) 1.445(10), mean Ru(1)-Nphen 2.109, mean Ru(2)-Nphen 2.107, mean Ru(1)-NTacn-cis 2.151, mean Ru(2)-NTacn-cis 2.141, Ru(1)NTacn-trans 2.115(4), Ru(2)-NTacn-trans 2.108(5), Ru(1)-N(6)-C(22) 177.2(5), Ru(2)-N(12)-C(45) 173.0(5), N(6)-C(22)-C(23) 176.8(8), N(12)-C(45)-C(46) 178.6(7).

and 90°, respectively, and the existence of a metal-metal interaction (attractive or repulsive) would cause a deviation from the ideal geometry.14 In this work, the ∠Ru-Cl-Ru and ∠Cl-Ru-Cl of [(Me3Tacn)Ru(µ-Cl)3Ru(Me3Tacn)]+ (5) are 80.32(3)-80.81(4)° and 82.03(5)-83.02(4)°, respectively, revealing that the complex is elongated along the Ru-Ru axis. The Ru · · · Ru distance for the homovalent (RuIIRuII) complex 5 (3.1842(6) Å) is significantly longer than those for the corresponding mixed-valent congeners [(Me3Tacn)Ru(µ-Cl)3Ru(Me3Tacn)]2+ (2.8862(11), 2.8939(8) Å)10 and [(Tacn)Ru(µCl)3Ru(Tacn)]2+ (2.830(1) Å),15 of which metal-metal formal bond orders of 0.5 were proposed on the basis of a simple molecular orbital scheme for Ru2 complexes with D3h symmetry (Figure 6).16,17 Interestingly, the Ru · · · Ru distance in 5 is among (14) Summerville, R. H.; Hoffmann, R. J. Am. Chem. Soc. 1979, 101, 3821. (15) Clucas, W. A.; Armstrong, R. S.; Buys, I. E.; Hambley, T. W.; Nugent, K. W. Inorg. Chem. 1996, 35, 6789. (16) Trogler, W. C. Inorg. Chem. 1980, 19, 697.

the lowest reported for binuclear RuIIRuII complexes containing the [Ru(µ-Cl)3Ru] core. For example, the Ru · · · Ru distance in 5 is shorter than those in [(PMe3)3Ru(µ-Cl)3Ru(PMe3)3]+ (3.374(6) Å),18 [(η6-C6H6)Ru(µ-Cl)3Ru(η6-C6H6)]+ (3.287(1) Å),19 and [(AsMe3)3Ru(µ-Cl)3Ru(AsMe3)3]+ (3.263(1) Å)18 by 0.08-0.19 Å. Absorption and Emission Spectroscopies. The UV-visible spectral data of complexes 1-4 are summarized in Table 2, and representative absorption spectra are depicted in Figure 7. All complexes feature intense high-energy absorption at λmax < 300 nm (εmax g 104 dm3 mol-1 cm-1) and moderately intense bands at λmax > 300 nm (εmax ) (3-6) × 103 dm3 mol-1 cm-1) as their lowest-energy electronic transition. In the literature, ruthenium(II) complexes bearing aromatic diimine ligands such as [Ru(bpy)3]2+ and [Ru(phen)3]2+ feature two types of characteristic absorption bands: highly intense absorptions in the UV region, which are attributed to the diimine intraligand π f π* transitions, and moderately intense absorptions in the visible region, which are ascribed to dπ(RuII) f π*(diimine) metalto-ligand charge transfer (MLCT) transitions.1d In this work, the moderately intense bands at λmax > 300 nm for all the complexes are assigned as dπ(RuII) f π*(diimine) metal-toligand charge transfer (MLCT) transitions. This assignment is supported by the fact that the lowest-energy transitions for [(Me3Tacn)(diimine)Ru-L]2+ are sensitive to the nature of L. For example, the dπ(RuII) f π*(phen) transition energies for [(Me3Tacn)(phen)Ru-L]2+ follow the order L ) [:C(OMe)R] (22989-23041 cm-1)7 ≈ L ) CH3CN (1, 23981 cm-1) < L ) isocyanide (2 and 3, 26738-27174 cm-1). It is also noted that the MLCT transition energies for Me3Tacn-ligated complexes are smaller than that for the [9]aneS3-ligated congeners (e.g., 26 738 cm-1 for 2 and 30 303 cm-1 for 4). This is consistent with the fact that Me3Tacn is a better electron donor than [9]aneS3 and gives a lower dπ(RuII) f π*(diimine) transition energy via providing a higher dπ(RuII) level. Complexes 1-4 are emissive in glassy MeOH/EtOH (1:4, v/v; 77 K) solution. (17) Hush, N. S.; Beattie, J. K.; Ellis, V. M. Inorg. Chem. 1984, 23, 3339. (18) Yeomans, B. D.; Humphrey, D. G.; Heath, G. A. J. Chem. Soc., Dalton Trans. 1997, 4153. (19) Grepioni, F.; Braga, D.; Dyson, P. J.; Johnson, B. F. G.; Sanderson, F. M.; Calhorda, M. J.; Veiros, L. F. Organometallics 1995, 14, 121.

Ruthenium(II) Isocyanide Complexes

Organometallics, Vol. 28, No. 12, 2009 3541

Figure 4. Perspective views of the cation in 2′(PF6)2 (left) and 4(PF6)2 · 3CH3CN (right, thermal ellipsoids are drawn at 30% probability). Selected bond lengths (Å) and angles (deg): 2′: Ru(1)-C(20) 1.922(4), C(20)-N(6) 1.164(5), N(6)-C(21) 1.459(4), mean Ru(1)-Nbpy 2.101, mean Ru(1)-NTacn-cis 2.143, Ru(1)-NTacn-trans 2.170(3), Ru(1)-C(20)-N(6) 173.8(3), C(20)-N(6)-C(21) 166.8(3); 4: Ru(1)-C(19) 1.984(3), C(19)-N(3) 1.136(3), N(3)-C(20) 1.469(3), mean Ru(1)-Nphen 2.112, mean Ru(1)-S[9]aneS3-cis 2.312, Ru(1)-S[9]aneS3-trans 2.3723(7), Ru(1)-C(19)-N(3) 174.2(2), C(19)-N(3)-C(20) 175.9(3).

Figure 5. Perspective view of the cation in 5(PF6) (thermal ellipsoids are drawn at 30% probability). Selected bond lengths (Å) and angles (deg): Ru(1) · · · Ru(2) 3.1842(6), Ru(1)-Cl(1/2/3) 2.4575(11)-2.4721(11), Ru(2)-Cl(1/2/3) 2.4548(13)-2.4650(11), Ru(1)-N(1/2/3) 2.083(4)-2.085(4), Ru(2)-N(4/5/6) 2.095(4)2.101(4), Ru(1)-Cl(1/2/3)-Ru(2) 80.32(3)-80.81(4), Cl-Ru-Cl′ 82.03(5)-83.02(4), N-Ru-N′ 83.30(16)-84.06(15).

Excitation of 1-3 at λ ) 430 nm and 4 at 400 nm gives emission at λmax ) 477-601 nm (Figure 8, Table 3). As the trend in emission maxima for 1-4 parallels the corresponding dπ(RuII) f π*(diimine) 1MLCT absorption maxima, these emissions are tentatively ascribed as dπ(RuII) f π*(diimine) 3 MLCT in nature. The nonemissive nature of 1-4 in solution at room temperature suggests the presence of nonradiative pathways of deactivation of the lowest-lying dπ(RuII) f π*(diimine) 3MLCT excited state in solution. DFT Calculations. The ground-state structures of complexes 1, 2, 2′, 4, and 5 were optimized at the DFT level (PBE1PBE).20 The PBE1PBE functional was employed because it had been used to calculate ruthenium-acetylide,21 -allenylidene,7 and -alkoxycarbene7,22 systems, and satisfactory results had been obtained. Frequency calculations were also performed on all the optimized complexes. As no imaginary vibrational frequencies were encountered, the optimized stationary points were confirmed to be local minima. Detailed optimized structural data are summarized in the Supporting Information. Table 4 sum(20) (a) Perdew, J. P.; Burke, K.; Ernzerhof, M. Phys. ReV. Lett. 1996, 77, 3865. (b) Adamo, C.; Barone, V. J. Chem. Phys. 1999, 110, 6158. (21) Wong, C.-Y.; Che, C.-M.; Chan, M. C. W.; Han, J.; Leung, K.-H.; Phillips, D. L.; Wong, K.-Y.; Zhu, N. J. Am. Chem. Soc. 2005, 127, 13997. (22) Wong, C.-Y.; Man, W.-L.; Wang, C.; Kwong, H.-L.; Wong, W.Y.; Lau, T.-C. Organometallics 2008, 27, 324.

marizes the compositions of the highest-occupied molecular orbitals (HOMOs) and the lowest-unoccupied molecular orbitals (LUMOs) for complexes 1, 2, 2′, and 4. Figure 9 depicts the plots of the HOMOs and LUMOs for 1 and 2, which illustrate that the HOMOs and LUMOs for these complexes are localized on the Ru and diimine, respectively. It is noted that the energies of the frontier orbitals for these complexes are sensitive to the nature of Ru-isocyanide/nitrile bonding interactions and the cyclic tridentate ligands. For example, (1) the HOMO-LUMO gap for isocyanide-ligated complex 2 is larger than that for nitrile-ligated complex 1 by about 0.2 eV, although isocyanides are isoelectronic with nitriles; (2) the HOMO-LUMO gap for the Me3Tacn-supported complex 2 is smaller than that for the [9]aneS3-supported complex 4 by about 0.3 eV. Such sensitivity is important, as it provides a way to manipulate their photophysical properties. On the other hand, the HOMO of complex 5 is also depicted in Figure 9. In agreement with the simple bonding model depicted in Figure 6, the HOMO of 5 is derived from the antisymmetric combination of the dz2 orbitals of both Ru centers in a σ-fashion, suggesting the metal-metal formal bond order in 5 to be 0. A simple approach to compare the π-accepting ability of different organometallic ligands and nitrile is to evaluate their ability to stabilize/destabilize the dπ orbitals of the ruthenium center. Defining the direction along the Ru-L as the z-axis and the Ru-Ndiimine as the x- and y-directions, the dπ orbitals are linear combinations of dxz and dyz orbitals. Figure 10 depicts the plots of the energies of the dπ orbitals for 1, 2, and their corresponding frozen [(Me3Tacn)(phen)Ru]2+ fragments. Similar plots for [(Me3Tacn)(phen)RudC(OMe)CH2Ph]2+ and [(Me3Tacn)(phen)RudCdCdCPh2]2+ are also depicted on the same figure for comparison. Since the energies of the dπ orbitals for [(Me3Tacn)(phen)Ru-L]2+ are in the order :CdCdCPh2 > CH3CN ≈ :C(OMe)CH2Ph > t-BuNC, the π-accepting ability for these ligands go in reverse order. This also parallels the trend for the dπ(RuII) f π*(diimine) MLCT transition energies: 22 989-23 041 cm-1 for L ) [:C(OMe)R],7 23 981 cm-1 for 1 (L ) CH3CN), and 26 738-27 174 cm-1 for L ) isocyanide (2 and 3). Charge decomposition analysis (CDA) for the interactions between the closed-shell fragment [metal core]2+ and isocyanide/ nitrile have been performed (Table 5). As the residue terms (∆) are essentially zero, the Ru-isocyanide/nitrile complexes in this

3542 Organometallics, Vol. 28, No. 12, 2009

Wong et al.

Table 1. X-ray Crystallographic Data for 1, 2′, 4, and 5 formula fw space group a, Å b, Å c, Å R, deg β, deg γ, deg V, Å3 Z T, K λ, Å Dc, g cm-3 µ, cm-1 R, Rwa a

[1(PF6)2]2 · 3CH3CN

2′(PF6)2

4(PF6)2 · 3CH3CN

5(PF6)

C52H73N15Ru2P4F24 1690.27 P1j 12.0416(5) 15.8303(6) 18.8685(7) 85.705(3) 78.584(3) 85.926(3) 3509.9(2) 2 298(2) 0.71073 1.599 0.0632 0.0684, 0.1861

C24H38N6RuP2F12 801.61 Pbcn 11.6445(1) 21.8319(2) 24.5405(2) 90 90 90 6238.72(9) 8 100(2) 1.54178 1.707 0.5957 0.0427, 0.1115

C29H38N6RuS3P2F12 957.84 P21/n 11.1419(1) 22.9481(3) 15.4446(2) 90 92.172(1) 90 3946.12(8) 4 100(2) 0.71073 1.612 0.0725 0.0370, 0.0681

C18H42N6Ru2Cl3PF6 796.04 P2/c 15.141(3) 13.854(3) 13.565(3) 90 90.00(3) 90 2845.4(10) 4 100(2) 0.71073 1.858 0.1460 0.0372, 0.0871

R ) ∑|Fo| - |Fc|/∑|Fo|, wR ) {∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]}1/2.

Figure 6. Molecular orbital diagrams showing the metal-metal interactions in dimeric ruthenium complexes [L3Ru(µ-X)3RuL3]n+ with D3h symmetry. Defining the metal-metal axis as the z-axis, orbitals a′1 and a′2 originate from the symmetric and antisymmetric combinations of t2g0 (dz2) orbitals, and e′ and e′′ orbitals are derived from similar combinations of t2g+ (linear combinations of dx2-y2 and dxz) and t2g- (linear combinations of dxy and dyz) orbitals.16,17 Table 2. UV-Visible Absorption Data for Complexes 1-4 in CH3CN at 298 Ka complex

λmax/nm (εmax/dm3 mol-1 cm-1)

1

268 (33 220), 289 (sh, 11 780), 317 (sh, 1960), 417 (6160), 453 (sh, 5040) 295 (26 020), 333 (sh, 3510), 458 (4130) 263 (37 250), 292 (sh, 9680), 374 (5450), 410 (sh, 4000) 286 (21 260), 328 (sh, 2850), 405 (3460) 263 (46 200), 290 (sh, 25450), 368 (4730), 401 (sh, 4040) 251 (21 380), 273 (21 590), 292 (sh, 11 080), 330 (5590), 388 (sh, 2610)

1′ 2 2′ 3 4 a

sh ) shoulder.

Figure 8. Glass emission spectra of 1, 2, and 4 in MeOH/EtOH (1:4, v/v; 77 K; λex ) 430 nm for 1 and 2, 400 nm for 4). Table 3. Emission Data for Complexes 1-4 in MeOH/EtOH (1:4, v/v) at 77 Ka,b λmax/nm

complex 1 1′ 2 2′ 3 4 a

601, 601, 551, 555, 540, 477,

653 (sh), 717 651 (sh), 710 590 (sh), 655 593 (sh), 660 584 (sh), 675 508, 551 (sh)

(sh) (sh) (sh) (sh) (sh)

λex ) 430 nm for 1-3 and 400 nm for 4. b sh ) shoulder.

donation (d), b/d, would reflect the relative weighting of these two bonding modes: the b/d ratios are 0.399 and 0.341-0.344 for 1 and 2/2′, respectively. Since isocyanide is a better π-acceptor compared with nitrile, the smaller b/d ratio for isocyanide-ligated complexes compared with their acetonitrile analogues reveals that the isocyanide complexes have stronger L f [(Me3Tacn)(phen)Ru]2+ donation compared with that in nitrile-ligated complexes. This is consistent with the structural studies that isocyanide is a stronger donor (σ-donor) than acetonitrile and exerts greater trans influence than acetonitrile. The smaller b/d ratio for 4 (0.246) compared with 2 (0.344) is consistent with the fact that [9]aneS3 is a weaker donor and gives weaker [metal core] f L back-donation compared with Me3Tacn.

Figure 7. UV-visible absorption spectra of 1, 2, and 4 in CH3CN at 298 K.

Conclusions

work can be discussed within the framework of the DewarChatt-Duncanson donor-acceptor model. The ratio of the values for [(Me3Tacn)(phen)Ru]2+ f RNtC or RCtN backdonation (b) and RNtC or RCtN f [(Me3Tacn)(phen)Ru]2+

A series of ruthenium(II)-isocyanide complexes supported by Me3Tacn/[9]aneS3 and phen/bpy have been synthesized, and the Ru-C bonding interactions have been probed by structural, spectroscopic, and theoretical methods. The molecular structures

Ruthenium(II) Isocyanide Complexes

Organometallics, Vol. 28, No. 12, 2009 3543

Table 4. HOMO and LUMO Compositions of Complexes 1, 2, 2′, and 4 % composition complex

HOMO-LUMO gap/eV

molecular orbital

1, [(Me3Tacn)(phen)Ru(NtCCH3)]2+

4.090

2, [(Me3Tacn)(phen)Ru(t-BuNtC)]2+

4.297

2′, [(Me3Tacn)(bpy)Ru(t-BuNtC)]2+

4.213

4, [([9]aneS3)(phen)Ru(t-BuNtC)]2+

4.623

HOMO LUMO HOMO LUMO HOMO LUMO HOMO LUMO

of [(Me3Tacn)(bpy)Ru(t-BuNC)]2+, [([9]aneS3)(phen)Ru(tBuNC)]2+, and [(Me3Tacn)(phen)Ru(CH3CN)]2+ show that isocyanide has a stronger trans influence than nitrile, suggesting that isocyanide is a better σ-donor than nitrile. Moreover, the Ru-C distances in the isocyanide complexes are sensitive to the electron richness of the metal center. The lowest-energy dipole-allowed absorptions for the isocyanide complexes are assigned as dπ(RuII) f π*(diimine) MLCT transitions. The emissions of the isocyanide and nitrile complexes at λmax ) 477-601 nm are tentatively assigned as dπ(RuII) f π*(diimine) 3 MLCT in nature. Theoretical calculations suggest that the π-accepting ability for t-BuNC > :C(OMe)CH2Ph ≈ CH3CN > :CdCdCPh2. This study demonstrates that the Ru-L bonding interaction has a dramatic effect on the optical properties of [Ru(diimine)x(L)y]n+ (L ) carbon-rich organic moieties), and functional emissive materials may be devised by tuning the Ru-L interaction.

Experimental Section General Procedures. All reactions were performed under an argon atmosphere using standard Schlenk techniques unless otherwise stated. All reagents were used as received, and solvents were purified by standard methods. [(Me3Tacn)(diimine)Ru(OH2)](PF6)2 and [([9]aneS3)(phen)RuCl](PF6) were prepared according to literature procedures.7,13 1H and 13C{1H} NMR spectra were recorded on Bruker 400 DRX FT-NMR spectrometers. Peak positions were calibrated with solvent residue peaks as internal

Figure 9. Optimized structures and frontier orbital surfaces for complexes 1, 2, and 5 (hydrogens are omitted for clarity, surface isovalue ) 0.03 au).

Ru

CH3CN/ t-BuNtC

diimine

Me3Tacn/ [9]aneS3

81.94 31.04 75.16 16.81 75.58 18.87 48.37 25.96

6.17 0.51 11.25 0.66 11.15 0.66 4.94 0.74

6.42 58.62 7.67 77.30 7.40 75.96 30.94 68.67

5.47 9.84 5.92 5.23 5.86 4.51 15.76 4.64

standard. Electrospray mass spectrometry was performed on a PESCIEX API 3000 triple quadrupole mass spectrometer. Infrared spectra were recorded as KBr plates on a Perkin-Elmer FTIR-1600 spectrophotometer. UV-visible spectra were recorded on a HewlettPackard HP8452A diode array spectrophotometer interfaced with an IBM-compatible PC. Elemental analyses were done on an Elementar Vario EL analyzer. [(Me3Tacn)(diimine)RuCtNR](PF6)2, 2,3(PF6)2. Excess CtNR (1 mmol) was added to a methanolic solution (20 mL) containing [(Me3Tacn)(diimine)Ru(OH2)](PF6)2 (0.20 mmol). After refluxing for 12 h, the reaction mixture was concentrated to about 5 mL and filtered off. The yellow or orange precipitates were washed with diethyl ether and dried under vacuum. The solid was then recrystallized by slow diffusion of Et2O into an acetone solution to give bright yellow or orange crystals. Complex 2(PF6)2 (diimine ) phen, R ) t-Bu): yield 0.15 g, 91%. Anal. Calcd for C26H38N6RuP2F12: C, 37.77; H, 4.64; N, 10.17. Found: C, 37.83; H, 4.54; N, 10.35. 1H NMR (400 MHz, (CD3)2CO): δ 1.07 (s, 9H, t-Bu), 2.07 (s, 3H, CH3 in Me3Tacn), 3.18-3.54, 3.63-3.75 (m, 12H, CH2 in Me3Tacn), 3.55 (s, 6H, CH3 in Me3Tacn), 8.21 (dd, 2H, J ) 8.3, 5.3 Hz, phen), 8.38 (s, 2H, phen), 8.93 (d, 2H, J ) 8.3 Hz, phen), 9.88 (d, 2H, J ) 5.3 Hz, phen). 13C NMR (100 MHz, (CD3)2CO): δ 30.56 (CH3 of t-Bu); 49.70, 56.40, 60.22, 60.48, 62.88 (Me3Tacn); 58.45 (C-CH3 of t-Bu); 126.43, 128.77, 131.54, 138.70, 148.96, 155.15 (phen), CN of isocyanide not resolved. IR (KBr, cm-1): νCtN ) 2114, νP-F ) 841. ESI-MS: m/z 680 [M2+ + PF6-]. Complex 2′(PF6)2 (diimine ) bpy, R ) t-Bu): yield 0.14 g, 87%. Anal. Calcd for C24H38N6RuP2F12: C, 35.90; H, 4.77; N, 10.47. Found: C, 36.05; H, 4.45; N, 10.58. 1H NMR (400 MHz, (CD3)2CO): δ 1.27 (s, 9H, t-Bu), 2.25 (s, 3H, CH3 in Me3Tacn), 3.07-3.41, 3.45-3.64 (m, 12H, CH2 in Me3Tacn), 3.43 (s, 6H, CH3 in Me3Tacn), 7.87 (dd, 2H, J ) 8.0, 5.8 Hz, bpy), 8.32 (t, 2H, J ) 8.0 Hz, bpy), 8.73 (d, 2H, J ) 8.0 Hz, bpy), 9.45 (d, 2H, J )

Figure 10. Plot of the energies of the dπ orbitals for the calculated complexes 1, 2, [(Me3Tacn)(phen)RudC(OMe)CH2Ph]2+, [(Me3Tacn)(phen)RudCdCdCPh2]2+, and their corresponding frozen [(Me3Tacn)(phen)Ru]2+ fragments (H ) HOMO).

3544 Organometallics, Vol. 28, No. 12, 2009

Wong et al.

Table 5. Charge Decomposition Analysis (CDA) for the [Metal Core]2+-L Interaction [metal core], L 2+

[(Me3Tacn)(phen)Ru] , CH3CN (1) [(Me3Tacn)(phen)Ru]2+, t-BuNC (2) [(Me3Tacn)(bpy)Ru]2+, t-BuNC (2′) [([9]aneS3)(phen)Ru]2+, t-BuNC (4)

LfM donation (d)

MfL back-donation (b)

b/d

repulsion (r)

residue (∆)

0.544 1.379 1.376 1.287

0.217 0.474 0.469 0.316

0.399 0.344 0.341 0.246

-0.516 -0.526 -0.527 -0.609

-0.042 -0.031 -0.030 -0.017

5.8 Hz, bpy). 13C NMR (100 MHz, (CD3)2CO): δ 30.73 (CH3 of t-Bu); 49.83, 56.27, 60.22, 60.39, 62.77 (Me3Tacn); 58.64 (C-CH3 of t-Bu); 124.68, 127.84, 139.40, 154.07, 158.61 (bpy); CN of isocyanide not resolved. IR (KBr, cm-1): νCtN ) 2132, νP-F ) 840. ESI-MS: m/z 657 [M2+ + PF6-]. Complex 3(PF6)2 (diimine ) phen, R ) C6H4OMe-4): yield 0.14 g, 80%. Anal. Calcd for C29H36N6ORuP2F12: C, 39.72; H, 4.14; N, 9.59. Found: C, 39.67; H, 4.24; N, 9.46. 1H NMR (400 MHz, (CD3)2CO): δ 2.09 (s, 3H, CH3 in Me3Tacn), 3.34-3.63, 3.73-3.80 (m, 12H, CH2 in Me3Tacn), 3.69 (s, 6H, CH3 in Me3Tacn), 3.72 (s, 3H, OMe), 6.79 (d, 2H, J ) 9.0 Hz, C6H4), 7.04 (d, 2H, J ) 9.0 Hz, C6H4), 8.24 (dd, 2H, J ) 8.0, 5.4 Hz, phen), 8.39 (s, 2H, phen), 8.97 (d, 2H, J ) 8.0 Hz, phen), 9.94 (d, 2H, J ) 5.4 Hz, phen). 13 C NMR (100 MHz, (CD3)2CO): δ 49.59, 56.10, 60.50, 60.89, 63.39 (Me3Tacn); 57.01 (OMe); 115.48, 122.61, 126.90, 128.57, 129.18, 132.00, 139.41, 149.16, 155.49, 160.44 (phen + C6H4), CN of isocyanide not resolved. IR (KBr, cm-1): νCtN ) 2096, νP-F ) 841. ESI-MS: m/z 730 [M2+ + PF6-]. [([9]aneS3)(phen)Ru(t-BuNC)](PF6)2, 4(PF6)2. The complexes were prepared analogously as described for complexes 2 and 3 except [([9]aneS3)(phen)RuCl](PF6) was used instead of [(Me3Tacn)(diimine)Ru(OH2)](PF6)2. The products were then recrystallized by slow diffusion of Et2O into an acetonitrile solution to give bright yellow crystals. Yield: 0.16 g, 96%. Anal. Calcd for C23H29N3S3RuP2F12 · 3CH3CN: C, 36.32; H, 4.00; N, 8.77. Found: C, 36.50; H, 4.13; N, 8.56. 1H NMR (400 MHz, CD3CN): δ 1.19 (s, 9H, t-Bu), 2.57-2.71, 2.84-3.03, 3.12-3.23 (m, 12H, [9]andS3), 7.99 (dd, 2H, J ) 8.0, 4.8 Hz, phen), 8.24 (s, 2H, phen), 8.78 (dd, 2H, J ) 8.0, 1.2 Hz, phen), 9.11 (dd, 2H, J ) 4.8, 1.2 Hz, phen). 13 C NMR (100 MHz, CD3CN): δ 30.27 (CH3 of t-Bu); 32.33, 33.79, 36.55 ([9]aneS3); 59.66 (C-CH3 of t-Bu); 127.42, 128.84, 132.03, 139.52, 147.83, 154.88 (phen); CN of isocyanide not resolved. IR (KBr, cm-1): νCtN ) 2167, νP-F ) 840. ESI-MS: m/z 689 [M2+ + PF6-]. [(Me3Tacn)(diimine)RuNtCCH3](PF6)2, 1(PF6)2. An acetonitrile solution (20 mL) containing [(Me3Tacn)(diimine)Ru(OH2)](PF6)2 (0.20 mmol) was refluxed for 12 h and then concentrated to about 5 mL. Slow diffusion of Et2O into the acetonitrile solution gave analytically pure red crystals. Complex 1(PF6)2 (diimine ) phen): yield 0.14 g, 89%. Anal. Calcd for C23H32N6RuP2F12: C, 35.20; H, 4.11; N, 10.72. Found: C, 35.13; H, 4.26; N, 10.55. 1H NMR (400 MHz, CD3CN): δ 1.74 (s, 3H, CH3 in Me3Tacn), 1.91 (s, 3H, CH3 in CH3CN), 2.93-3.19, 3.36-3.45 (m, 12H, CH2 in Me3Tacn), 3.25 (s, 6H, CH3 in Me3Tacn), 8.00 (dd, 2H, J ) 8.1, 5.5 Hz, phen), 8.18 (s, 2H, phen), 8.64 (dd, 2H, J ) 8.1, 1.1 Hz, phen), 9.64 (dd, 2H, J ) 5.5, 1.1 Hz, phen). 13C NMR (100 MHz, CD3CN): δ 4.25 (CH3 of CH3CN); 52.35, 54.22, 59.98, 61.74, 61.98 (Me3Tacn); 125.71, 128.71, 131.67, 137.61, 150.24, 155.48 (phen); CN of CH3CN not resolved. IR (KBr, cm-1): νCtN ) 2270, νP-F ) 840. ESI-MS: m/z 639 [M2+ + PF6-]. Complex 1′(PF6)2 (diimine ) bpy): yield 0.13 g, 86%. Anal. Calcd for C21H32N6RuP2F12: C, 33.15; H, 4.24; N, 11.05. Found: C, 33.02; H, 4.22; N, 11.12. 1H NMR (400 MHz, CD3CN): δ 2.07 (s, 3H, CH3 in CH3CN), 2.18 (s, 3H, CH3 in Me3Tacn), 2.85-3.12, 3.26-3.36 (m, 12H, CH2 in Me3Tacn), 3.26 (s, 6H, CH3 in Me3Tacn), 7.67 (dd, 2H, J ) 7.6, 7.0 Hz, bpy), 8.09 (dd, 2H, J ) 7.0, 5.6 Hz, bpy), 8.41 (d, 2H, J ) 7.6 Hz, bpy), 9.25 (d, 2H, J ) 5.6 Hz, bpy). 13C NMR (100 MHz, CD3CN): δ 4.33 (CH3 of CH3CN); 52.80, 54.15, 59.82, 61.67, 62.04 (Me3Tacn); 124.64,

126.91, 138.24, 154.61, 159.88 (bpy); 125.70 (CN of CH3CN). IR (KBr, cm-1): νCtN ) 2268, νP-F ) 839. ESI-MS: m/z 614 [M2+ + PF6-]. [(Me3Tacn)Ru(µ-Cl)3Ru(Me3Tacn)](PF6), 5(PF6). [Ru(Me3Tacn)Cl3] (0.10 g, 0.26 mmol) was refluxed in ethylene glycol (15 mL) for 1 h. Upon cooling to room temperature, the resultant deep blue solution was added to an aqueous solution of NaPF6 (2 g, 11.9 mmol, in 3 mL of H2O) to afford a blue precipitate, which was characterized to be [(Me3Tacn)Ru(µ-Cl)3Ru(Me3Tacn)](PF6)2 (yield: 0.22 g, 90%). This blue precipitate was used for the synthesis of complex 1 without further purification. A mixture of [(Me3Tacn)Ru(µCl)3Ru(Me3Tacn)](PF6)2 (0.2 g, 0.21 mmol), zinc powder (0.4 g, 6.15 mmol), and methanol (25 mL) was refluxed for 1 h, during which an orange precipitate formed. Upon cooling to room temperature, the mixture was filtered off under argon, and the orange precipitate was recrystallized by slow diffusion of Et2O into an acetone solution to give bright red crystals. Yield: 0.14 g, 84%. Anal. Calcd for C18H42N6Ru2Cl3P1F6: C, 27.13; H, 5.32; N, 10.55. Found: C, 27.10; H, 5.28; N, 10.62. 1H NMR (400 MHz, (CD3)2CO): δ 2.83-2.96 (m, 24H, CH2 in Me3Tacn), 3.04 (s, 18H, CH3 in Me3Tacn). 13C NMR (100 MHz, (CD3)2CO): δ 55.91 (CH3 of Me3Tacn); 62.48 (CH2 of Me3Tacn); assignment confirmed by DEPT-135 NMR experiment. ESI-MS: m/z 651 [M+]. X-ray Crystallography. X-ray diffraction data for [1(PF6)2]2 · 3CH3CN, 2′(PF6)2, 4(PF6)2 · 3CH3CN, and 5(PF6) were collected on an Oxford Diffraction Gemini S Ultra X-ray single-crystal diffractometer with Cu KR radiation (λ ) 1.54178 Å) or Mo KR radiation (λ ) 0.71073 Å). The data were processed using the program CrysAlis.23 The structure was solved and refined using full-matrix least-squares based on F2 with the programs SHELXS97 and SHELXL-9724 within WinGX.25 The Ru and many non-H atoms were located according to the direct methods. The positions of the other non-hydrogen atoms were found after successful refinement by full-matrix least-squares using the program SHELXL97. In the final stage of least-squares refinement, all non-hydrogen atoms were refined anisotropically. In each case, the positions of (23) CrysAlis, Oxford Diffraction Ltd., Version 1.171.31.8, 2007. (24) Sheldrick, G. M. SHELXS-97 and SHELXL-97, Program for Crystal Structure Solution and Refinements; University of Go¨ttingen: Germany, 1997. (25) Farrugia, L. J. J. Appl. Crystallogr. 1999, 32, 837. (26) Andrae, D.; Haeussermann, U.; Dolg, M.; Stoll, H.; Preuss, H. Theor. Chim. Acta 1990, 77, 123. (27) Hehre, W. J.; Ditchfield, R.; Pople, J. A. J. Chem. Phys. 1972, 56, 2257. (28) (a) Frenking, G.; Fro¨hlich, N. Chem. ReV. 2000, 100, 717. (b) Dapprich, S.; Frenking, G. J. Phys. Chem. 1995, 99, 9352. (29) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.; Robb, M. A.; Cheeseman, J. R.; Montgomery, J. A.; Jr., Vreven, T.; Kudin, K. N.; Burant, J. C.; Millam, J. M.; Iyengar, S. S.; Tomasi, J.; Barone, V.; Mennucci, B.; Cossi, M.; Scalmani, G.; Rega, N.; Petersson, G. A.; Nakatsuji, H.; Hada, M.; Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima, T.; Honda, Y.; Kitao, O.; Nakai, H.; Klene, M.; Li, X.; Knox, J. E.; Hratchian, H. P.; Cross, J. B.; Bakken, V.; Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.; Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Ayala, P. Y.; Morokuma, K.; Voth, G. A.; Salvador, P.; Dannenberg, J. J.; Zakrzewski, V. G.; Dapprich, S.; Daniels, A. D.; Strain, M. C.; Farkas, O.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.; Foresman, J. B.; Ortiz, J. V.; Cui, Q.; Baboul, A. G.; Clifford, S.; Cioslowski, J.; Stefanov, B. B.; Liu, G.; Liashenko, A.; Piskorz, P.; Komaromi, I.; Martin, R. L.; Fox, D. J.; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.; Challacombe, M.; Gill, P. M. W.; Johnson, B.; Chen, W.; Wong, M. W.; Gonzalez, C.; Pople, J. A. Gaussian 03, reVision D.01; Gaussian, Inc.: Wallingford, CT, 2004.

Ruthenium(II) Isocyanide Complexes H atoms were calculated on the basis of the riding mode with thermal parameters equal to 1.2 times that of the associated C atoms. Disorders were observed in the PF6- anions for all complexes and in the Me3Tacn ligand for complex 5, and split-atom models were used to model the disorder behaviors. Computational Methodology. Density functional theory (DFT) calculations were performed on complexes 1, 2, 2′, 4, and 5. Their electronic ground states were optimized without symmetry constraints using the density functional PBE1PBE,20 which is a hybrid of the Perdew, Burke, and Ernzerhof exchange and correlation functional and 25% HF exchange. The Stuttgart small-core relativistic effective core potentials were employed for Ru atoms with their accompanying basis sets.26 The 6-31+G* basis set was employed for N, 6-31G* for CR, and 6-31G for O and other C and H atoms.27 Tight SCF convergence (10-8 au) was used for all calculations. As no imaginary vibrational frequencies were encountered, the optimized stationary points were confirmed to be local minima. The nature of the Ru-C bonds was examined using charge decomposition analysis.28 All the DFT calculations were performed

Organometallics, Vol. 28, No. 12, 2009 3545 using the Gaussian 03 program package (revision D.01),29 while CDA analysis was performed with the QMForge program.30

Acknowledgment. The work described in this paper was supported by grants from the Hong Kong Research Grants Council (Project No. CityU 102708) and City University of Hong Kong (Project No. 7002302). We are grateful to Dr. Shek-Man Yiu for X-ray diffraction data collection. Supporting Information Available: Crystallographic information files (CIF) for [1(PF6)2]2 · 3CH3CN, 2′(PF6)2, 4(PF6)2 · 3CH3CN, and 5(PF6); optimized geometries for 1, 2, 2′, 4, and 5. This material is available free of charge via the Internet at http://pubs.acs.org. OM9001654 (30) (a) Tenderholt, A. L. QMForge, Version 2.1, http://qmforge. sourceforge.net. QMForge depends heavily on cclib, which does all the parsing and analysis. (b) O’Boyle, N. M.; Tenderholt, A. L.; Langner, K. M. J. Comput. Chem. 2008, 29, 839.