Switching on the photochemical reactivity in heterodimetallic OsII–RuII bipyridyl complexes containing a bis(bidentate) phosphine

Available online at www.sciencedirect.com

Inorganic Chemistry Communications 10 (2007) 1510–1514 www.elsevier.com/locate/inoche

Switching on the photochemical reactivity in heterodimetallic Os –RuII bipyridyl complexes containing a bis(bidentate) phosphine II

Rene Gutmann a, Sylvia Eller a, Markus Fessler a, Wytze E. van der Veer b, Alexander Dumfort a, Holger Kopacka a, Thomas Mu¨ller c, Peter Bru¨ggeller a,* a

Institute of General, Inorganic and Theoretical Chemistry, University of Innsbruck, Innrain 52a, 6020 Innsbruck, Austria b Department of Chemistry, University of California, Irvine, CA 92697-2025, USA c Institute of Organic Chemistry, University of Innsbruck, Innrain 52a, 6020 Innsbruck, Austria Received 13 July 2007; accepted 15 September 2007 Available online 5 October 2007

Abstract For the first time the excited states of the RuP2N4 moiety belonging to a new heterodimetallic OsII–RuII bipyridyl complex are successfully designed in order to introduce photochemical reactivity. This dramatic effect is achieved via the use of the sterically demanding bis(bidentate) phosphine cis, trans, cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane (dppcb). Thus, the temperature dependence of the luminescence lifetimes ranging from 77 to 298 K for the novel homodimetallic species meso-(DK/KD)-[Os2(dppcb)(bpy)4](PF6)4 (1) and rac-(DD/KK)-[Os2(dppcb)(bpy)4](PF6)4 (2) clearly indicates that the d–d state responsible for photochemistry is not populated. By contrast, the analogous temperature dependence for the new heterodimetallic species DK/KD-[Os(bpy)2(dppcb)Ru(bpy)2](PF6)4 (3) and DD/ KK-[Os(bpy)2(dppcb)Ru(bpy)2](PF6)4 (4) unequivocally shows that as a consequence of the population of the d–d state the photochemical reactivity is switched on. Since single crystal X-ray structure analyses are a major clue to the understanding of photophysical and photochemical properties, also the X-ray structures of 1–3 are given.  2007 Elsevier B.V. All rights reserved. Keywords: Dinuclear Os and Ru complexes; Luminescence; Bis(bidentate) phosphine; Antenna effect; Energy transfer

In the development of molecular assemblies for studies in energy conversion, an important issue is the coupling of light absorption to electron transfer indirectly by the use of intervening energy transfer in an antenna array introduced by the combination of a [Ru(bpy)2]2+ ‘‘antenna’’ site and a [Os(bpy)2]2+ ‘‘trap’’ site [1]. The construction of useful photonic molecular devices via metal complexes as building blocks seems very flexible in terms of tailoring the energetics [2]. However, there are significant limitations in the preparation of molecular assemblies by sequential covalent bond formation [3]. This approach necessarily involves a stepwise sequence of reactions with penalties for yields of less than 100% at each step, which can greatly diminish overall yields in multistep syntheses [3]. Therefore, *

Corresponding author. Tel.: +43 512 507 5115; fax: +43 512 507 2934. E-mail address: [email protected] (P. Bru¨ggeller).

1387-7003/$ - see front matter  2007 Elsevier B.V. All rights reserved. doi:10.1016/j.inoche.2007.09.028

a photochemical approach would be very interesting, showing simultaneous covalent bond formation and regiospecific modification of chromophores in one step. The use of phosphines leading to enhanced ‘‘steric pressure’’ has made it possible to obtain long-lived excited RuP2N4 type units at ambient temperature [4]. The control of the energetic and geometric factors allows the mechanistic study of photoinduced processes, the manipulation of their rates, and finally the control of factors to build up photochemical molecular devices [2]. This is clearly revealed by the photochemical and photophysical differences between the new homodimetallic species meso-(DK/KD)-[Os2(dppcb)(bpy)4](PF6)4 (1) and rac-(DD/KK)-[Os2(dppcb)(bpy)4](PF6)4 (2) and the novel heterodimetallic complexes DK/ KD-[Os(bpy)2(dppcb)Ru(bpy)2](PF6)4 (3) and DD/KK[Os(bpy)2(dppcb)Ru(bpy)2](PF6)4 (4), where dppcb is cis, trans, cis-1,2,3,4-tetrakis(diphenylphosphino)cyclobutane

R. Gutmann et al. / Inorganic Chemistry Communications 10 (2007) 1510–1514

(see Chart 1) [4e]. Especially the Os–Ru mixed-metal dinuclear complexes 3 and 4 are very interesting compounds for an investigation of intracomponent energy- and electrontransfer processes [5]. It is well-known that the two families of OsII- and RuII-polypyridine complexes nicely complement each other because the OsII complexes can be oxidized

4+

Ph Ph Ph P

Ph N N

P

P Ph Ph

Os

P

N

Ph

N

N N Os N N

Ph

1

4+

Ph Ph Ph Ph P N N

P

Os

P Ph Ph

Os

P

N

Ph

N

N

N

N N

Ph

2

Ph Ph Ph P

Ph N N

4+

P

N N Ru N

P Ph Ph

Os

P

N

Ph

N

N

Ph

3 4+ Ph Ph Ph P

Ph N N

Ru P

P Ph Ph

Os

P

N

Ph

N

N

N N N

Ph

4 Chart 1. Structure types: cation of 1; cation of 2; cation of 3 and cation of 4.

1511

at less positive potentials than the RuII analogues, which also implies that the luminescent 3MLCT level of an OsII complex lies lower in energy than that of an analogous RuII complex [5]. For the latter reason, only the OsII complexes are expected and found to be photochemically inactive. In this work it is shown that this is not only true for OsN6 and RuN6 complexes, but also for OsP2N4 and RuP2N4 moieties as soon as the latter are under ‘‘steric pressure’’. This is in agreement with the fact that the energy gap between 3MLCT and d–d excited states is much larger in the OsII complexes than in the RuII complexes and, as a consequence, the deactivation channel involving activated surface crossing to the upper lying d–d excited levels cannot enter into play [5]. Therefore, the photochemical reactivity is switched on in 3 and 4, whereas 1 and 2 are photochemically inert. However first, it is necessary to demonstrate that intramolecular energy transfer does indeed take place in 3 and 4, and this can be done most conveniently by the examination of absorption and emission spectra recorded for the dyads 3 and 4 and for relevant reference compounds like 1 and 2 [6]. The UV–vis absorption spectrum of a synthetically obtained 10:7 mixture of diastereoisomers 1 and 2 in CH3CN at 298 K shows a ligand-centred band at 276 nm, a MC band at 374 nm, and a low-energy MLCT (Os ! bpy) absorption at 473 nm (predominantly singlet in character) [7]. The analogous bands for a synthetically obtained 10:8 mixture of diastereoisomers 3 and 4 occur at 277, 374, and 479 nm, respectively. The low-energy absorptions are more pronounced for OsII because of the larger spin-orbit coupling constant compared with RuII [3], where this effect is clearly revealed by the e-values of 3478 M1 cm1 for 1/2 and 3083 M1 cm1 for 3/4. MLCT bands of OsP2N4 moieties like in 1–4 are blue-shifted from that observed for [Os(bpy)3](PF6)2 (kmax = 640 nm) because of the stabilization of the ground state by the enhanced d, p(Os)-r*,p(P) back-bonding and the destabilization of the excited state by the poorer r-donating phosphine ligands [7]. The emission centred at 600 nm for kex of 520 nm of 1/2 in CH3CN at 298 K stems from the 3MLCT state (see Fig. 1, S1) [4a,8]. The contour plot of this emission clearly demonstrates that only one state is involved (see Fig. 2, S2). It is shifted to 580 nm for kex of 480 nm in a 4:1:2 EtOH/ MeOH/CH3CN glass at 77 K, where also only one state is obvious (see Figs. 3 and 4, S3). Emission maxima of 600 nm at 298 K are typical for OsP2N4 chromophores [7]. Analogous emission bands of 3/4 occur at 600 nm for kex of 485 nm at 298 K and at 575 nm for kex of 485 nm at 77 K in the same solvents. For both temperatures the contour plots show emissions from single states also for 3/4 (see Figs. 5–8, S4, 5). The excitation maximum for a synthetically obtained 10:7 mixture of diastereoisomers meso-(DK/KD)-[Ru2(dppcb)(bpy)4](PF6)4 (5) and rac-(DD/ KK)-[Ru2(dppcb)(bpy)4](PF6)4 (6) is shifted to 465 nm in CH3CN at 298 K [4a]. This means that a shift to higher energy is typical for RuII compared with OsII (see above). It is a first hint that for 3/4 mainly the Ru-centre is involved

1512

R. Gutmann et al. / Inorganic Chemistry Communications 10 (2007) 1510–1514

in excitation. This is in line with the more covalent character of the Os-P bonds, leading to greater p-back-bonding in Os complexes compared to Ru complexes and hence to a stabilization of the ground state of Os [5]. Nevertheless, the HOMO in 3 and 4 is located at the Os-centre as indicated by the E1/2-values for RuII/III of +1.25 V and OsII/III of +0.92 V in 3/4. Illumination of heterodyads containing OsN6 and RuN6 moieties at any wavelength gives rise to emission from the ‘‘Os-bpy’’ fragment without obvious contamination by luminescence from the ‘‘Ru-bpy’’ chromophore [6]. For 3/4 this means that their luminescence lifetimes should be similar to 1/2 at any wavelength and any temperature. Indeed, the luminescence lifetimes are 243(8) ns for 1/2 and 273(1) ns for 3/4 in CH3CN at 298 K, and 3.0(2) ls for 1/2 and 3.2(5) ls for 3/4 in the above glass at 77 K (see Fig. 9, S6). In comparison with these values, the corresponding parameters in the same solvents for 5/6 of 794(20) ns at 298 K and 6.2(4) ls at 77 K are significantly larger. Furthermore, the lifetime of 3/4 at 77 K is independent of excitation wavelength from 430 to 535 nm. These findings are in agreement with the fact that excitation at RuII in 3/4 is followed by rapid, efficient energy migration and transfer to give OsII . Typically, excitation at RuII leading to OsII is independent of excitation wavelength [1]. Also independent of excitation wavelength, single exponentials completely fit the signals in all cases. Therefore, proof positive is given that the RuII moiety in 3/4 acts as efficient ‘‘antenna’’ for collecting visible light and sensitizing the lower energy OsII site. In these experiments OsII* was formed within the instrument response of the apparatus used (fwhm < 500 ps). This results in ken P 2 · 109s1 for the energy transfer [1]. In 3/4 the Dexter (exchange) transfer is favored for which triplet-triplet transfer is allowed, since the MLCT excited states are largely triplet in character [1]. This requires overlap of the wavefunctions of the RuII energy donor and the OsII energy acceptor. It is ˚ throughwell-known that for Os  Ru-distances of 7 ± 2 A space mechanisms of energy transfer come into play [1], where the Os  Ru-distances in 3/4 are of comparable magnitude (see Fig. 1). In 3/4 a region of saturated carbons disrupts significant electronic wave function mixing through the cyclobutane backbone ‘‘bridge’’. Furthermore, the temperature dependence of the luminescence lifetimes of 3/4 clearly proves that at about 170 K in contrast to 1/2 the depopulation via the d–d state starts (see Figs. 10 and 11, S7, 8) [9]. The d–d state is accessed by thermal activation and barrier crossing from 3 MLCT states after they are formed by excitation. This introduces an additional temperature dependence into s [3]. Increasing temperature causes a decrease of the emission lifetime also for 1/2, but the Arrhenius plot between 77 and 298 K does not exhibit the highly activated decay processes characteristic of the 3MLCT ! d–d crossover. Below about 170 K the temperature dependence of the luminescence lifetimes of 1/2 and 3/4 can be related to repolarization rearrangements of the solvent molecules

Fig. 1. (a) View of the cation of meso-(DK/KD)-[Os2(dppcb)(bpy)4](PF6)4 (1 0 ). (b) View of the cation of rac-(DD/KK)-[Os2(dppcb)(bpy)4](PF6)4 (2). (c) View of the cation of DK/KD-[Os(bpy)2(dppcb)Ru(bpy)2](PF6)4 (3 0 ). The atom labeling schemes are shown. Hydrogen atoms are omitted for ˚ ) and angles (): 1. Os1  Os1A 7.819(1), clarity. Selected bond lengths (A Os1–P1 2.305(1), Os1–P2 2.328(1), P1–Os1-P2 86.58(4); 1 0 . Os1  Os1A 7.812(1), Os1–P1 2.327(1), Os1–P2 2.305(1), P1–Os1-P2 86.58(4); 2. Os1  Os2 7.845(1), Os1–P1 2.313(1), Os1–P2 2.319(1), Os2–P3 2.319(1), Os2–P4 2.314(1), P1–Os1-P2 86.38(5), P3–Os2–P4 86.18(6); 3. Os1  Ru1 7.825(1), Os1–P1 2.330(2), Os1–P2 2.305(2), Ru1–P1 2.342(3), Ru1–P2 2.312(3), P1–Os1–P2 86.74(7), P1–Ru1–P2 86.32(10). 3 0 . Os1  Ru1 7.850(1), Os1–P1 2.303(3), Os1–P2 2.328(3), Ru1–P1 2.337(5), Ru1–P2 2.323(6), P1–Os1–P2 86.78(9), P1–Ru1–P2 86.11(18).

R. Gutmann et al. / Inorganic Chemistry Communications 10 (2007) 1510–1514

when the matrix begins to melt [5]. However, the steep linear behavior shown by the Arrhenius plot of 3/4 above about 170 K is also present in 5/6 [4a]. The retrieved parameters for 3/4: Ea = 377 cm1, A = 2.30 · 107 s1, k 0 = 3.73 · 106 s1 at 298 K (see Fig. 11, S8) compare very well with those obtained for 5/6: Ea = 444 cm1, A = 4.54 · 107s1, k 0 = 5.32 · 106 s1 at 298 K [4a]. As in the case of 5/6 the low values of the activation energy (Ea) and the corresponding high rate constants (k 0 ) for the population of the d–d states lead to the onset of photochemical reactivity also in 3/4 (see below) [4a,4b]. In order to completely understand the dynamical photophysical and photochemical events occurring in 3/4, also a comparison of the emission quantum yields (Ur) is necessary. In CH3CN at 298 K the Ur parameters are 1.9 · 102 for 1/2, 1.9 · 103 for 3/4, and 6.4 · 104 for 5/6 [4a], respectively. The value for 1/2 is typical of an OsP2N4 chromophore [7]. The reduction in Ur for 3/4 compared with 1/2 by one order of magnitude stems from the population of the d–d state in the case of 3/4 in contrast to 1/2. Thus, the ratio of the emission quantum yield and lifetime leads to radiative decay rate constants of 78200 s1 for 1/2 and 6960 s1 for 3/4. This nicely confirms the results obtained from the temperature dependence of the luminescence lifetimes above and means that a further channel of energy release is opened in 3/4. It is also in agreement with the Ur parameter for 5/6, where the d–d state is populated as in 3/4. On the basis of the whole analysis, it is evident that the dynamical events in 3/4 are complete by 273(1) ns and only the Ru-moiety of 3/4 is involved in photochemistry. If there were no interaction between the two bridged metal centres in the excited states of the dimetallic complexes 3/4, irradiation of the OsII chromophores should result in photophysical properties that are exactly the same as those for 1/2. However, proof positive has been presented that this is not the case. Only recently, it has been shown that long luminescence lifetimes at ambient temperature connected with photochemical reactivity for RuP2N4 chromophores occur as soon as these chromophores are under ‘‘steric pressure’’ [4a,4b]. Therefore, the full characterization of the new dimetallic complexes 1–4 [10] by X-ray structure analyses (see Fig. 1) [11] is very important. Even though the solidstate structures of 1, 3, and 5 [4b] containing CH2Cl2 are not isomorphous in the strict sense of the word [12] due to a slight polymorphism with respect to the number of solvent molecules, they are essentially the same regarding the conformations of the coordinated ligands, the packing of the cations and the relative positions of the PF 6 anions in the lattice. The shortest intramolecular contacts between ˚ in 1 and 2.284 A ˚ a bpy ligand and a phenyl ring are 2.293 A in 3. The analogous contacts between the phenyl rings ˚ in along a trans axis of the cyclobutane rings are 3.022 A ˚ 1 and 3.024 A in 3. These contact approaches are indicative of high ‘‘steric pressure’’ [4,13]. Interestingly, neither a different diastereoisomeric form nor different polymorphs essentially change this ‘‘steric pressure’’. Thus, the corre-

1513

sponding contacts between bpy and phenyl groups are ˚ in 2, and 2.350 A ˚ in 3 0 , where 1 0 ˚ in 1 0 , 2.213 A 2.325 A 0 and 3 are polymorphous forms of 1 and 3 containing DMF (1 0 ) and MeCN (3 0 ) instead of CH2Cl2 (1, 3), respectively [11]. The shortest approaches between the phenyl rings along a trans axis of the cyclobutane rings are ˚ in 1 0 , 2.982 A ˚ in 2, and 2.978 A ˚ in 3 0 . This clearly 2.791 A demonstrates that independent of crystal packing effects and diastereoisomeric forms large ‘‘steric pressures’’ are present in 1–4. Therefore, these ‘‘steric pressures’’ also occur in the solution structures of 1–4, as has already been shown for comparable compounds [13]. However, steric crowding reduces the non-radiative decay in 1–4 [4a] and hence a long-lived excited state of 273(1) ns becomes possible at ambient temperature also in the case of 3/4, where the d–d states are populated. This means that due to the presence of ‘‘steric pressure’’ in 3/4 their photochemistry is switched on, since it is well-known that RuP2N4 moieties containing simple diphosphines without ‘‘steric pressure’’ are photochemically inert [4b]. Thus, preliminary photochemical experiments using 3/4 in MeCN and a preliminary X-ray structure analysis indicate that [Os(bpy)2(dppcb)Ru(bpy)(MeCN)2](PF6)4 [14] is formed, showing that the osmium centre remains photochemically inactive. The enhanced rigidity of dppcb has the effect to decrease knr and to increase s, leading to ‘‘designer excited states’’ in which excited-state properties and photoreactivity are manipulated systematically by varying the ligands [3]. In the low-lying d–d excited states a dr* metal-ligand antibonding orbital is occupied in 3/4, which leads to metal-ligand bond breaking [3]. However, the lack of population of the d–d states in 1/2 makes these compounds photochemically inert. With respect to ‘‘artificial photosynthesis’’ it is important to note that in 3/4 a pathway is present in which single-photon, singleelectron activation leads to intermediates that are themselves photoactive, toward the release of a bpy ligand in this case [3]. The bridging ligand dppcb is not a trap for energy and electrons, and thus it appears a convenient bridge for polynuclear complexes which can exhibit photoinduced energy or electron migration. As a consequence of this it is possible to envisage a number of approaches to creating hierarchical assemblies for ‘‘artificial photosynthesis’’ based on polypyridyl complexes and dppcb or related phosphines. By the replacement of the simple sensitizer with molecular dyads, based on Ru-polypyridine complexes linked to phenothiazine or triarylamine, longlived photoinduced charge separation could be obtained for these assemblies [15]. Acknowledgements This research was financially supported by the Fonds zur Fo¨rderung der wissenschaftlichen Forschung, Vienna, Austria, the Tiroler Wissenschaftsfonds, Innsbruck, Austria, and the University of Innsbruck via the action D. Swarovski & Co.

1514

R. Gutmann et al. / Inorganic Chemistry Communications 10 (2007) 1510–1514 3

Appendix A. Supplementary material CCDC 653525-653529 contain the supplementary crystallographic data for this paper. These data can be obtained free of charge from The Cambridge Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/cif. Supplementary data associated with this article can be found, in the online version, at doi:10.1016/ j.inoche.2007.09.028. References [1] C.N. Fleming, L.M. Dupray, J.M. Papanikolas, T.J. Meyer, J. Phys. Chem. A 106 (2002) 2328–2334. [2] L. De Cola, P. Belser, Coord. Chem. Rev. 177 (1998) 301–346. [3] J.H. Alstrum-Acevedo, M.K. Brennaman, T.J. Meyer, Inorg. Chem. 44 (2005) 6802–6827. [4] (a) R. Gutmann, G. Czermak, A. Dumfort, W.E. van der Veer, B. Hong, H. Kopacka, K.-H. Ongania, T. Bechtold, P. Bru¨ggeller, Inorg. Chem. Commun. 8 (2005) 319–322; (b) R. Haid, R. Gutmann, T. Stampfl, C. Langes, G. Czermak, H. Kopacka, K.-H. Ongania, P. Bru¨ggeller, Inorg. Chem. 40 (2001) 7099–7104; (c) H.A. Mayer, W.C. Kaska, Chem. Rev. 94 (1994) 1239–1272; (d) In this context the expression ‘‘steric pressure’’ is appropriate, since intramolecular forces are applied to certain areas like phenyl rings.; (e) W. Oberhauser, C. Bachmann, T. Stampfl, R. Haid, C. Langes, H. Kopacka, A. Rieder, P. Bru¨ggeller, Inorg. Chim. Acta 290 (1999) 167–179. [5] F. Barigelletti, L. De Cola, V. Balzani, R. Hage, J.G. Haasnot, J. Reedijk, J.G. Vos, Inorg. Chem. 30 (1991) 641–645. [6] A. Harriman, F.M. Romero, R. Ziessel, A.C. Benniston, J. Phys. Chem. A 103 (1999) 5399–5408. [7] P.-W. Wang, M.A. Fox, Inorg. Chem. 34 (1995) 36–41. [8] Though the diastereoisomers 1/2 or 3/4 can be separated by partial crystallization, this is not necessary, since in both cases the diastereoisomers show the same absorption and emission properties. Furthermore, the luminescence lifetimes of 1/2 or 3/4 can be fitted by single exponential decay functions in the whole temperature range 77–298 K. [9] J.V. Caspar, T.J. Meyer, Inorg. Chem. 22 (1983) 2444–2453. [10] The details of the preparation of 1–4 will be reported elsewhere. In the case of 1/2 a 10:7 mixture of diastereoisomers was obtained. FAB mass spectrum: m/z (m/zcalcd) 2232.8 (2232.9) [M+PF6], 2087.6 (2087.9) [M+2PF6], 1942.7 (1943.0) [M+3PF6]. UV–vis absorption: kmax = 473 nm (4 · 103 M in CH3CN, e = 3478 M1 cm1). Anal. Calcd. for C92H76F24N8Os2 P8 (2377.872): C, 46.47; H, 3.22; N, 4.71. Found: C, 46.33; H, 3.31; N, 4.60. E1/2 values versus SCE (DE, DEp [mV]): OsII/III +0.94 V [110], first bpy0/ 1.72 V [100], second bpy0/ 2.07 V [100]. Compounds 1 and 2 were separated by partial crystallization (see Ref. [4b]). Compound 1: m.p.: >360 C. 31P{1H} NMR (CH3CN): d 39.2 (t), 35.6 (t), 2JP,P + 3JP,Pcis = 3JP,Ptrans 1 1 = 7.4 Hz, 143.2 (septet, PF 6 ), JP,F = 709 Hz. H NMR (CD3CN): 3 3 d (bpy) 9.17 (d, JH,H = 5.3 Hz, 4H), 8.13 (t, JH,H = 5.9 Hz, 4H), 8.10 (d, 3JH,H = 7.9 Hz, 4H), 7.99 (d, 3JH,H = 7.9 Hz, 4H), 7.91 (t, 3 JH,H = 7.9 Hz, 4H), 7.84 (d, 3JH,H = 8.6 Hz, 4H), 7.74 (t, 3 JH,H = 7.4 Hz, 4H), 7.68 (d, 3JH,H = 7.6 Hz, 4H); 5.7–7.6 (m, 40H, Ph); 4.17 (br. m, 4H, P–CH). Compound 2: m.p.: >360 C. 31P{1H} NMR (CH3CN): d 35.3 (t), 34.6 (t), 2JP,P + 3JP,Pcis = 3JP,Ptrans 1 1 = 8.9 Hz, 143.2 (septet, PF 6 ), JP,F = 709 Hz. H NMR (CD3CN): d (bpy) 9.29 (d, 3JH,H = 5.6 Hz, 4H), 8.31 (d, 3JH,H = 8.3 Hz, 4H), 8.25 (t, 3JH,H = 7.9 Hz, 4H), 8.18 (d, 3JH,H = 8.3 Hz, 4H), 7.85 (d,

JH,H = 6.0 Hz, 4H), 7.74 (t, 3JH,H = 6.3 Hz, 4H), 7.66 (t, JH,H = 8.9 Hz, 4H), 7.56 (t, 3JH,H = 6.6 Hz, 4H); 5.7–7.5 (m, 40H, Ph); 4.55 (br. m, 2H, P–CHax), 4.05 (br. m, 2H, P–CHeq). In the case of 3/4 a 10:8 mixture of diastereoisomers was obtained. ESI mass spectrum: m/z (m/zcalcd) 427.0 (427.2) [M4+4PF6]. UV–vis absorption: kmax = 479 nm (4 · 103 M in CH3CN, e = 3083 M1 cm1). Anal. Calcd. for C92H76F24N8OsP8Ru (2288.712): C, 48.28; H, 3.35; N, 4.90. Found: C, 48.23; H, 3.41; N, 4.80. E1/2 values versus SCE (DE, DEp [mV]): RuII/III + 1.25 V [50], OsII/III + 0.92 V [80], first bpy0/ 1.98 V [160], second bpy0/ 2.17 V [150]. Compounds 3 and 4 were separated by partial crystallization (see Ref. [4b]). Compound 3: m.p.: >360 C. 31P{1H} NMR (CH3CN): d 80.1 (dt, PRu), 75.2 (dt, PRu), 2JP,P + 3JP,Pcis = 3JP,Ptrans = 8.9 Hz, 4JP,P = 3.0 Hz, 38.8 (dt, POs), 35.4 (dt, POs), 2JP,P + 3JP,Pcis = 3JP,Ptrans 1 1 = 8.9 Hz, 4JP,P = 3.0 Hz, 143.9 (septet, PF 6 ), JP,F = 708 Hz. H 3 NMR (CD3CN): d (bpy) 9.08 (d, JH,H = 5.5 Hz, 4H), 8.94 (d, 3 JH,H = 5.5 Hz, 4H), 8.33 (d, 3JH,H = 5.0 Hz, 4H), 8.21 (t, 3 JH,H = 7.0 Hz, 4H), 8.19 (d, 3JH,H = 4.5 Hz, 4H), 8.18 (t, 3JH,H = 4.0 Hz, 4H), 8.17 (d, 3JH,H = 4.0 Hz, 4 H), 8.12 (t, 3JH,H = 7.0 Hz, 4H); 5.8–8.2 (m, 40H, Ph); 4.18 (br. m, 4H, P–CH). Compound 4: m.p.: >360 C. 31P{1H} NMR (CH3CN): d 77.3 (dt, PRu), 76.4 (dt, PRu), 2JP,P + 3JP,Pcis = 3JP,Ptrans = 8.9 Hz, 4JP,P = 5.9 Hz, 35.6 (dt, POs), 34.9 (dt, POs), 2JP,P + 3JP,Pcis = 3JP,Ptrans = 8.9 Hz, 4JP,P = 5.9 1 1 Hz, 143.9 (septet, PF 6 ), JP,F = 708 Hz. H NMR (CD3CN): d (bpy) 9.29 (d, 3JH,H = 5.0 Hz, 4H), 9.14 (d, 3JH,H = 5.0 Hz, 4H), 8.84 (d, 3JH,H = 5.5 Hz, 4H), 8.34 (d, 3JH,H = 7.0 Hz, 4H), 8.30 (t, 3 JH,H = 7.5 Hz, 4H), 8.26 (d, 3JH,H = 6.5 Hz, 4H), 8.20 (t, 3 JH,H = 8.0 Hz, 4H), 8.18 (d, 3JH,H = 7.5 Hz, 4H); 5.8–8.0 (m, 40H, Ph); 4.55 (br. m, 2H, P–CHax), 4.05 (br. m, 2H, P–CHeq). ˚ ): for both cases 1 and Crystal structure analyses of 1–3 (k = 0.71073 A 3 two polymorphs have been obtained; however, despite numerous attempts it was impossible to produce single crystals of 4 suitable for an X-ray structure analysis. The data collections were performed with a Nonius Kappa CCD diffractometer with the use of combined /–x scans. Final refinements on F2 were carried out with anisotropic thermal parameters for all non-hydrogen atoms in all cases. Compound 1: C92H76F24N8Os2P8 Æ 4CH2Cl2, fw = 2717.53, 203 K, triclinic, ˚ , b = 13.1306(3) A ˚ , c = 17.7641(4) A ˚, space group P 1, a = 12.3283(2) A ˚ 3, a = 94.904(1), b = 92.683(1), c = 114.737(1), U = 2591.33(10) A Z = 1, Dc = 1.741 g/cm3, R(F) = 0.0371, R(wF2) = 0.0991. Compound 1 0 : C92H76F24N8Os2P8 Æ 3.4DMF, fw = 2602.34, 243 K, mono˚ , b = 35.0131(5) A ˚, clinic, space group P21/n, a = 12.4608 (2) A ˚ , b = 115.6692(7), U = 5206.45(12) A ˚ 3, Z = 2, Dc c = 13.2401(1) A = 1.660 g/cm3, R(F) = 0.0350, R(wF2) = 0.0824. Compound 2: C92H76F24N8Os2P8 Æ 6.4CH2Cl2, fw = 2914.505, 203 K, triclinic, space ˚ , b = 18.1035(1) A ˚ , c = 22.0316(2) A ˚, a= group P 1, a = 14.6920(1) A ˚ 3, 87.5223(5), b = 72.4689(4), c = 89.5350(4), U = 5582.42(7) A Z = 2, Dc = 1.734 g/cm3,R(F) = 0.0469, R(wF2) = 0.1206. Compound 3: C92H76F24N8OsP8Ru Æ 3.7CH2Cl2, fw = 2595.44, 203 K, triclinic, ˚ , b = 13.1641(5) A ˚ , c = 17.7248(6) A ˚, space group P 1, a = 12.3449(3) A ˚ 3, a = 95.286 (2), b = 92.507(2), c = 114.822(2), U = 2592.38(15) A Z = 1, Dc = 1.663 g/cm3, R(F) = 0.0486, R(wF2) = 0.1301. Compound 3 0 : C92H76F24N8OsP8Ru Æ 2MeCN, fw = 2370.78, 243 K, ˚ , b = 23.6418(1) A ˚, monoclinic, space group P21/c, a = 13.8576(1) A ˚ , b = 106.0264(4), U = 4689.09(7)A ˚ 3, Z = 2, c = 14.8914 (2) A Dc = 1.679 g/cm3, R(F) = 0.0339, R(wF2) = 0.0978. H.S. Chow, E.C. Constable, C.E. Housecroft, M. Neuburger, S. Schaffner, Dalton Trans. (2006) 2881–2890. C. Bachmann, R. Gutmann, G. Czermak, A. Dumfort, S. Eller, M. Fessler, H. Kopacka, K.-H. Ongania, P. Bru¨ggeller, Eur. J. Inorg. Chem. (2007) 3227–3239. A full description of this photoproduct will be given elsewhere. H. Wolpher, S. Sinha, J. Pan, A. Johansson, M.J. Lundqvist, P. Perrson, R. Lomoth, J. Bergquist, L. Sun, V. Sundstro¨m, B. ˚ kermark, T. Polı´vka, Inorg. Chem. 46 (2007) 638–651. A 3

[11]

[12] [13]

[14] [15]