Organometallics 2009, 28, 2701–2706
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Synthesis and Characterization of Conjugated Diallenes and Their Binuclear Ruthenium η3-Allyl Complexes Jian-Long Xia, Xianghua Wu, Yinghui Lu, Gang Chen, Shan Jin, Guang-ao Yu, and Sheng Hua Liu* Key Laboratory of Pesticide and Chemical Biology, Ministry of Education, College of Chemistry, Central China Normal UniVersity, Wuhan 430079, People’s Republic of China ReceiVed December 17, 2008
A series of conjugated diallenes (CH2dCdCHRCHdCdCH2; R ) 1,4-C6H4, 4,4′-C6H4-C6H4, 4,4′C6H4CHdCHC6H4, 4,4′-C6H4NdNC6H4, 4,4′-C6H4CtCC6H4) have been prepared by copper-catalyzed reactions of the corresponding diacetylenes with paraformaldehyde and diisopropylamine. Treatment of these conjugated diallenes with [RuHCl(CO)(PPh3)3] produced the binuclear ruthenium η3-allyl complexes [(PPh3)2(CO)ClRu]2[(η3-CH2CHCH)2R], all of which have been characterized by elemental analysis, ESMS, 1H and 31P{1H} NMR spectrometry, IR spectroscopy, and UV/vis spectrophotometry, as well as by cyclic and square-wave voltammetry. These bimetallic complexes showed a remarkable absorption in the visible region (λmax: 380-451 nm), and the complex [(PPh3)2(CO)ClRu]2[(η3-CH2CHCH)2(C6H4Nd NC6H4)] (9) was found to undergo trans-to-cis isomerization under irradiation with UV light. Electrochemical study has shown that the two metal centers in complex [(PPh3)2(CO)ClRu]2[(η3CH2CHCH)2C6H4] (6) interact with each other. Introduction Complexes in which two redox-active transition metal moieties are linked together by an unsaturated conjugated bridging ligand have been a subject of great interest, first as a testing ground for all aspects related to intramolecular electron transfer and then as models for and principal constituents of possibly conducting molecule-based “wires”. Among the different approaches used to construct the wire-like organometallic entities, compounds with unsaturated carbon chains spanning two metal-containing components have received particular attention due to their facile accessibility and remarkable efficiency for electronic delocalization.1 These compounds have shown promising potential for the development of nanoscopic molecular devices. Particular efforts have been directed toward the preparation and characterization of polyynediyl arrays [M]-(CtC)m-[M] (m ) 1, 2, 3, etc.),2,3 polyylenediyl complexes [M]-(CHdCH)m-[M],4,5 and bimetallic molecular rods linked by π-conjugated carbon chains with both ethynyl and ethenyl * Corresponding author. E-mail:
[email protected]. (1) (a) Paul, F.; Lapinte, C. Coord. Chem. ReV. 1998, 431, 178–180. (b) Long, N. J.; Williams, C. K. Angew. Chem., Int. Ed. 2003, 42, 2586. (c) Szafert, S.; Gladysz, J. A. Chem. ReV. 2003, 103, 4175. (d) Ren, T. Organometallics 2005, 24, 4854. (e) Bruce, M. I.; Low, P. J. AdV. Organomet. Chem. 2004, 50, 179. (f) Touchard, D.; Dixneuf, P. H. Coord. Chem. ReV. 1998, 409, 178–180. (g) Coe, B. J.; Fitzgerald, E. C.; Helliwell, M.; Brunschwig, B. S.; Fitch, A. G.; Harris, J. A.; Coles, S. J.; Horton, P. N.; Hursthouse, M. B. Organometallics 2008, 27, 2730. (2) (a) de Montigny, F.; Argouarch, G.; Costuas, K.; Halet, J.-F.; Roisnel, T.; Toupet, L.; Lapinte, C. Organometallics 2005, 24, 4558. (b) Hu, Q. Y.; Lu, W. X.; Tang, H. D.; Sung, H. H. Y.; Wen, T. B.; Williams, I. D.; Wong, G. K. L.; Lin, Z.; Jia, G. Organometallics 2005, 24, 3966. (c) Narvor, N. L.; Toupet, L.; Lapinte, C. J. Am. Chem. Soc. 1995, 117, 7129. (d) Courmarcel, J.; Gland, G. L.; Toupet, L.; Paul, F.; Lapinte, C. J. Organomet. Chem. 2003, 670, 108. (e) Rigaut, S.; Pichon, L. L.; Daran, J.-C.; Touchard, D.; Dixneuf, P. H. Chem. Commun. 2001, 1206. (f) Xu, G.-L.; Crutchley, R. J.; DeRosa, M. C.; Pan, Q.-J.; Zhang, H.-X.; Wang, X.; Ren, T. J. Am. Chem. Soc. 2005, 127, 13354. (g) Blum, A. S.; Ren, T.; Parish, D. A.; Trammell, S. A.; Moore, M. H.; Kushmerick, J. G.; Xu, G.-L.; Deschamps, J. R.; Pollack, S. K.; Shashidhar, R. J. Am. Chem. Soc. 2005, 127, 10010.
units.6 Very recently, another family of complexes has been described, in which the carbon chains contain both ethynyl and para-substituted phenylene units.7,8 In these systems, the π-conjugated molecular lengths are extended by successive insertion of 1,4-phenylene units, inducing a progressive transition from electron-delocalized class III mixed-valence behavior to weakly coupled class II mixed-valence systems, according (3) (a) Qi, H.; Gupta, A.; Noll, B. C.; Snider, G. L.; Lu, Y.; Lent, C.; Fehlner, T. P. J. Am. Chem. Soc. 2005, 127, 15218. (b) Stang, P. J.; Tykwinski, R. J. Am. Chem. Soc. 1992, 114, 4411. (c) Gil-Rubio, J.; Laubender, M.; Werner, H. Organometallics 2000, 19, 1365. (d) Gil-Rubio, J.; Laubender, M.; Werner, H. Organometallics 1998, 17, 1202. (e) Gevert, O.; Wolf, J.; Werner, H. Organometallics 1996, 15, 2806. (f) Field, L. D.; Turnbull, A. J.; Turner, P. J. Am. Chem. Soc. 2002, 124, 3692. (4) (a) Chung, M. C.; Gu, X.; Etzenhouser, B. A.; Spuches, A. M.; Rye, P. T.; Seetharaman, S. K.; Rose, D. J.; Zubieta, J.; Sponsler, M. B. Organometallics 2003, 22, 3485. (b) Etzenhouser, B. A.; Cavanaugh, M. D.; Spurgeon, H. N.; Sponsler, M. B. J. Am. Chem. Soc. 1994, 116, 2221. (c) Etzenhouser, B. A.; Chen, Q.; Sponsler, M. B. Organometallics 1994, 13, 4176. (d) Sponsler, M. B. Organometallics 1995, 14, 1920. (5) (a) Liu, S. H.; Chen, Y.; Wan, K. L.; Wen, T. B.; Zhou, Z.; Lo, M. F.; Williams, I. D.; Jai, G. Organometallics 2002, 21, 4984. (b) Liu, S. H.; Xia, H.; Wen, T. B.; Zhou, Z. Y.; Jia, G. Organometallics 2003, 22, 737. (c) Liu, S. H.; Hu, Q. Y.; Xue, P.; Wen, T. B.; Williams, I. D.; Jia, G. Organometallics 2005, 24, 769. (d) Yuan, P.; Wu, X.; Yu, G.; Du, D.; Liu, S. H. J. Organomet. Chem. 2007, 692, 3588. (6) (a) Shi, Y.; Yee, G. T.; Wang, G.; Ren, T. J. Am. Chem. Soc. 2004, 126, 10552. (b) Xia, H. P.; Ng, W. S.; Ye, J. S.; Li, X. Y.; Wong, W. T.; Lin, Z.; Yang, C.; Jia, G. Organometallics 1999, 18, 4552. (c) Xia, H. P.; Wu, W. F.; Ng, W. S.; Williams, I. D.; Jia, G. Organometallics 1997, 16, 2940. (d) Gao, L.-B.; Liu, S.-H.; Zhang, L.-Y.; Shi, L.-X.; Chen, Z.-N. Organometallics 2006, 25, 506. (e) Gao, L.-B.; Kan, J.; Fan, Y.; Zhang, L.-Y.; Liu, S.-H.; Chen, Z.-N. Inorg. Chem. 2007, 46, 5651. (7) (a) Ghazala, S. I.; Paul, F.; Toupet, L.; Roisnel, T.; Hapiot, P.; Lapinte, C. J. Am. Chem. Soc. 2006, 128, 2463. (b) Klein, A.; Lavastre, O.; Fiedler, J. Organometallics 2006, 25, 635. (c) Medei, L.; Orian, L.; Semeikin, O. V.; Peterleitner, M. G.; Ustynyuk, N. A.; Santi, S.; Durante, C.; Ricci, A.; Sterzo, C. L. Eur. J. Inorg. Chem. 2006, 2582. (8) (a) Colbert, M. C. B.; Lewis, J.; Long, N. J.; Raithby, P. R.; Younus, M.; White, A. J. P.; Williams, D. J.; Payne, N. N.; Yellowlees, L.; Beljonne, D.; Chawdhury, N.; Friend, R. H. Organometallics 1998, 17, 3034. (b) Long, N. J.; Martin, A. J.; Biani, F. F.; Zanello, P. J. Chem. Soc., Dalton Trans. 1998, 2017. (c) Olivier, C.; Kim, B.; Touchard, D.; Rigaut, S. Organometallics 2008, 27, 509.
10.1021/om801191f CCC: $40.75 2009 American Chemical Society Publication on Web 04/10/2009
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Xia et al. Scheme 1
Scheme 2
to the Robin and Day classification.9 Ruthenium η3-allyl complexes have attracted much attention, as they can mediate organometallic and catalytic reactions.10 Recently, Jia11 reported in detail the insertion reactions of allenes with LnM-H and the isomerism of some monoruthenium η3-allyl complexes. In order to investigate how two metal centers in binuclear ruthenium complexes bridged by conjugated diallyl units interact with each other, a series of conjugated diallenes (1,12 2,13 3, 4, 5, Scheme 1) and their binuclear ruthenium η3-allyl complexes [(PPh3)2(CO)ClRu]2[(η3-CH2CHCH)2R] (Scheme 2) have been designed and synthesized. The electrochemical properties of the complexes have been investigated. (9) (a) Robin, M. B.; Day, P.; Hush, N. S. Prog. Inorg. Chem. 1967, 8, 357. (b) Hush, N. S. Prog. Inorg. Chem. 1967, 8, 391. (c) Robin, M. B.; Day, P. AdV. Inorg. Chem. Radiochem. 1967, 247. (10) See for example: (a) Yamamoto, Y.; Nakagai, Y.; Itoh, K. Chem.sEur. J. 2004, 10, 231. (b) Mbaye, M. D.; Demerseman, B.; Renaud, J. L.; Toupet, L.; Bruneau, C. Angew. Chem., Int. Ed. 2003, 42, 5066. (11) (a) Xue, P.; Bi, S.; Sung, H. H. Y.; Williams, I. D.; Lin, Z.; Jia, G. Organometallics 2004, 23, 4735. (b) Bai, T.; Zhu, J.; Xue, P.; Sung, H. H.Y.; Williams, I. D.; Ma, S.; Lin, Z.; Jia, G. Organometallic 2007, 26, 5581. (12) Sato, E.; Yokozawa, T.; Endo, T. Macromol. Rapid Commun. 1994, 15, 607. (13) Lee, K.; Seomoon, D.; Lee, P. H. Angew. Chem., Int. Ed. 2002, 41, 3901.
Results and Discussion Synthesis and Characterization of the Diallenes. The required diallenes were synthesized according to a coppercatalyzed one-pot procedure for the homologation of acetylenic compounds into monoallenes, developed by Crabbe´ in 1979 (Scheme 1).14 Although the yields of this organocoppercatalyzed process would seem to be generally lower, the reaction is more economical than those employing indium15 or palladium catalysts.13 All of the novel diallenes, except 1 and 2, which have been reported previously in the literature,12,13 have been characterized by NMR, MS, and elemental analysis. The 1H NMR spectra of all of the diallenes showed a doublet in the region δ ) 5.15-5.23 ppm and a triplet in the region δ ) 6.14-6.24 ppm, attributable to the CH2dCdCH protons. Their 13 C{1H} NMR spectra each feature three CH2dCdCH signals near δ ) 79, 93, and 210 ppm. The structure of diallene 4 was confirmed by an X-ray diffraction study. (14) (a) Crabbe´, P.; Fillion, H.; Andre´, D.; Luche, J.-L. J. Chem. Soc., Chem. Commun. 1979, 859. (b) Searles, S.; Li, Y.; Nassim, B.; Lopes, M.T.R.; Tran, P. T.; Crabbe´, P. J. Chem. Soc., Perkin Trans. 1 1984, 747. (15) (a) Nakamura, H.; Kamakura, T.; Onagi, S. Org. Lett. 2006, 8, 2095. (b) Nakamura, H.; Kamakura, T.; Ishikura, M.; Biellmann, J.-F. J. Am. Chem. Soc. 2004, 126, 5958.
Synthesis of Conjugated Diallenes
Organometallics, Vol. 28, No. 9, 2009 2703 Table 1. Crystal Data and Structure Refinement for 4
Figure 1. Molecular structure of 4. Selected bond lengths (Å) and angles (deg): C(1)-N(1), 1.423(2); C(4)-C(7), 1.467(3); C(7)-C(8), 1.302(2); C(8)-C(9), 1.283(3); N(1)-N(1a), 1.251(3); C(8)C(7)-C(4), 125.91(18); C(9)-C(8)-C(7), 179.4(2).
Synthesis and Characterization of the Binuclear Ruthenium η3-Allyl Complexes. The binuclear ruthenium η3allyl complexes [(PPh3)2(CO)ClRu]2[(η3-CH2CHCH)2R] (6, 7, 8, 9, 10) (Scheme 2) were readily prepared by reaction of [RuHCl(CO)(PPh3)3] with the corresponding diallene in CH2Cl2 at room temperature, adopting the same procedure as used for the mononuclear ruthenium η3-allyl complexes.11,16 All of the compounds have been characterized by elemental analysis, ESI mass spectrometry, 1H and 31P{1H} NMR spectrometry, and IR spectroscopy. The elemental analysis data were consistent with the calculated values. All of the complexes apparently have a structure similar to that of other reported mononuclear complexes 11 (Scheme 2), as inferred from the NMR data.11 The presence of the η3-allyl ligand was indicated by the 1H and 31 P{1H} NMR spectra. In the 1H NMR spectra, the allylic proton signals were observed in the regions δ ) 2.80-3.10 (CH2), 4.00-4.10 (CHAr), and 5.60-5.80 ppm (central CH), respectively. The 31P{1H} NMR spectra of each of the complexes showed two singlets in the regions δ ) 26.60-27.46 and 39.58-40.56 ppm, due to the unsymmetrical nature of the allyl ligand. The mononuclear ruthenium complex 11,11a prepared from phenylallene and [RuHCl(CO)(PPh3)3], was used as a reference for later discussion. Crystal Structure of Diallene 4. The molecular structure of diallene 4 is depicted in Figure 1. Crystallographic details and selected bond distances and angles are given in Table 1 and Figure 1, respectively. The crystal structure consists of discrete monomeric molecules of 4, which are in the trans configuration. The two adjacent CdC bonds in the allenyl group have slightly different lengths [1.302(2) and 1.283(3) Å]. The NdN bond length (1.251(3) Å) is slightly longer than that reported in [(CH3)3SiCtCC6H4NdNC6H4CtCSi(CH3)3] (1.230(5) Å).17 The allenyl fragment is linear, with an angle of 179.4(2)° at the central C atom. UV/Vis Spectra. The UV/vis absorption spectral data for complexes 6-11 are summarized in Table 1. Complexes 6-10 all exhibit long-wavelength transitions of strong intensity at about 400 nm, which render them yellow or red. In the series of binuclear ruthenium complexes, the long-wavelength absorption energy decreases in the order 7 > 10 > 6 > 8 > 9. This absorption for the mononuclear ruthenium complex 11 is found at 294 nm. The absorptions of the diruthenium complexes are all quite red-shifted in comparison with 11. These findings agree (16) (a) Sasabe, H.; Kihara, N.; Mizuno, K.; Ogawa, A.; Takata, T. Chem. Lett. 2006, 35, 212. (b) Sasabe, H.; Nakanishi, S.; Takata, T. Inorg. Chem. Commun. 2003, 6, 1140. (c) Sasabe, H.; Nakanishi, S.; Takata, T. Inorg. Chem. Commun. 2002, 5, 177. (d) Nakanishi, S.; Sasabe, H.; Takata, T. Chem. Lett. 2000, 29, 1058. (e) Hill, A. F.; Ho, C. T.; Wilton-Ely, D. E. T. Chem. Commun. 1997, 2207. (17) Yin, J.; Yu, G.-A.; Guan, J. T.; Mei, F. S.; Liu, S. H. J. Organomet. Chem. 2005, 690, 4265.
empirical formula fw wavelength (Å) cryst syst space group a (Å) b (Å) c (Å) V (Å3) Z Dcalc (Mg/m3) abs coeff (mm-1) F(000) θ range (deg) reflns collected indep reflns cryst size (mm3) data/restraints/params goodness-of-fit on F2 final R indices (I > 2σ(I)) R indices (all data) largest diff peak and hole (e Å-3)
C36 H28 N4 516.62 0.71073 monoclinic P2(1)/c 7.2305(3) 6.3734(3) 15.1771(7) 699.31(5) 1 1.227 0.073 272 2.68-25.00 3991 1233 (R(int) ) 0.1188) 0.40 × 0.04 × 0.02 1233/0/91 0.910 R1 ) 0.0498, wR2 ) 0.1131 R1 ) 0.0793, wR2 ) 0.1220 0.199 and -0.143
with an assignment of these bands to a metal (dRu) to ligand (π*) charge-transfer transition (MLCT), within the bridging ligands. There are additional very strong, high-energy bands at around 240 nm that very probably correspond to intraligand (π-π* or IL) transitions. Compound 4 exhibits slight spectral changes after irradiation with UV light (Figure S1, Supporting Information). However, compound 9 exhibits obvious spectral changes after irradiation with UV light, as shown in Figure 2. Upon irradiation of a solution of compound 9 in CH2Cl2 from 0 to 9 min, spectral changes indicative of a trans-to-cis photoisomerization of the azobenzene moiety in the complex were observed. These changes were similar to those observed for photoactive azobenzene-type metal complexes (Ru,17 Au18). The “MLCT” absorption band for 9 is not obvious in Figure 2; it may be obscured by the azobenzene band. Electrochemistry. The redox chemistry of compounds 6-11 was investigated by cyclic and square-wave voltammetry (CV and SWV) using 0.1 M (Bu4N)(PF6) in dichloromethane as the supporting electrolyte. The electrochemical data are presented in Table 3. The cyclic voltammogram (CV) and the squarewave voltammogram (SWV) for compound 6 are depicted in Figure 3. As indicated in Table 3, mononuclear ruthenium
Figure 2. UV/vis absorption spectral change of compound 9 (1 × 10-5 mol/L) in CH2Cl2 upon UV light irradiation at 0, 0.5, 1, 2, 3, 4, 6, 8, and 9 min.
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Table 2. UV-Vis Spectral Data for the Biallene Ruthenium Complexes 6-10 and Reference Mononuclear Complex 11 (1× 10-5 mol/L) in CH2Cl2 at 298 K compound
λmax (nm)
εmax (cm-1/M-1)
λmax (nm)
εmax (cm-1/M-1)
6 7 8 9 10 11
239 240 240 240 240 236
44 300 61 700 52 000 60 000 58 100 37 500
396 380 406 451 389 294
21 700 36 500 45 300 33 100 45 500 20 300
Table 3. Electrochemical Data for Compounds 6-11a complex
Ep.a1
Ep.a2
∆Eb
complex
Ep.ac
6 8
0.26 0.31
0.43 0.42
170 110
7 9 10 11
0.35 0.39 0.30 0.52
a From cyclic or square-wave voltammetry in 0.1 M CH2Cl2/ Bu4NPF6 solutions at a scan rate of 100 mV/s for CV and 10 Hz for SWV. Potentials Ep.a are in V vs Fc+/Fc. b Peak potential differences ∆E ) Ep.a2 - Ep.a1 are in mV. c Anodic peak potentials Ep,a are in V for a one-step two-electron processes.
n
complex 11 displays an irreversible oxidation wave at Ep.a ) 0.57 V. In comparison to that of complex 11, the anodic peak potentials Ep,a of the binuclear ruthenium complexes 6-10 are clearly decreased. As indicated in Figure 3, the CV and SWV of complex 6 show two separated one-electron oxidation waves, most likely originating from successive oxidation of RuII,II to RuII,III and RuII,III to RuIII,III, respectively. The separations of the two waves determined by square-wave voltammetry are consistent with the CV curves. It has been demonstrated that the wave separation or potential difference (∆E ) Ep.a2 - Ep.a1) is a critical measure for evaluating electronic delocalization along the molecular backbones in Ru2II,III mixed-valence species.1a The peak separa-
tion of the two oxidation waves, ∆E, for complex 6 is 170 mV, which indicates a moderate degree of electronic communication between the two metal centers. Successive insertion of phenyl, -NdN-C6H4-, and -CtC-C6H4- units between the two metal centers of complex 6 attenuates the electronic communication between the metal centers, as is reflected in the electrochemical data shown in Table 2. Complexes 7, 9, and 10 exhibit an irreversible oxidation wave, which can be ascribed to a one-step two-electron process for the ruthenium-centered oxidations. However, when a -CHdCH-C6H4- unit is inserted between the two metal centers of complex 6, a weak but appreciable electronic interaction between the metal centers is still observed in complex 8. The ∆E for complex 8 was found to be 110 mV, indicating a weaker interaction between the two metal centers than in 6. To our surprise, a metal-metal interaction was observed in complex 8, in which the distance between the two metal centers is longer than that in 7. We speculate that this outcome might be ascribed to rotation of two benzene rings in complex 7, which breaks the π-conjugated electronic communication. Recently, Winter et al. have reported a ∆E value of 250 mV for divinylphenylene-bridged diruthenium complexes [{(PiPr3)2(CO)ClRu}2 (µ-HCdCHC6H4CHdCH-1,4)].19 Such behaviors are also known from diethynylphenylene-bridged diruthenium complexes ([Ru]2[µ-CtCC6H4-CtC-1,4], [Ru] ) [Cl(dppe)2Ru], ∆E1/2 ) 341 mV;7b [Ru] ) [Cl(dppm)2Ru], ∆E1/2 ) 190 mV8a). On further comparison with the related diethynylphenylene-bridged complex, in which the bridge is bound to the Cp coligand (Fc-CtCC6H4-CtC-Fc), no ∆E1/2 was observed.20 As we can see from the above comparisons, electronic communication between the two metal centers of the complex 6 is weaker than that of σ (alkenyl, alkynyl) bound complexes. We speculated that this outcome might be expected if the η3allyl coordination in 6 disfavors a coplanar arrangement of allyl and the benzene ring and, consequently, reduces π-overlap. The crystal structure of Os(η3-CH2CHCHPh)Cl(CO)(PPh3)2 reported shows that η3-allyl and the benzene ring are not a coplanar arrangement with a dihedral angle of 31.6°.11
Conclusion A series of conjugated diallenes and their binuclear ruthenium η3-allyl complexes have been designed and synthesized. These bimetallic complexes show a remarkable absorption in the visible region (λmax: 380-451 nm), and complex 9 has been found to undergo trans-to-cis isomerization under irradiation with UV light. Electrochemical studies have shown that 6 displays a moderate electronic communication between the two metal centers. It maybe ascribed to a class II mixed-valence compound according to Robin and Day classification.9 This new η3-allyl coordination mode may be applied as a new model to test intramolecular electron transfer in mixed-valence metal complexes.
Experimental Section All manipulations were carried out under a nitrogen atmosphere using standard Schlenk techniques, unless otherwise stated. Solvents were distilled under nitrogen from sodium benzophenone (hexane,
Figure 3. Cyclic and square-wave (CV and SWV) voltammograms of compounds 6 in a 0.1 M dichloromethane solution of (Bu4N)(PF6). The scan rate is 100 mV/s-1 for CV and 10 Hz for SWV.
(18) Tang, H.-S.; Zhu, N. Y.; Yam, V. W.-W. Organometallics 2007, 26, 22. (19) Maurer, J.; Sarkar, B.; Schwederski, B.; Kaim, W.; Winter, R. F.; Za´lisˇ, S. Organometallics 2006, 25, 3701. (20) Lavastre, O.; Plass, J.; Bachmann, P.; Guesmi, S.; Moinet, C.; Dixneuf, P. H. Organometallics 1997, 16, 184.
Synthesis of Conjugated Diallenes diethyl ether, dioxane) or calcium hydride (dichloromethane). The starting materials RuHCl(CO)(PPh3)3,21 1,4-diethynylbenzene,22 HCtCC6H4C6H4CtCH,23 HCtCC6H4CHdCHC6H4CtCH,24 HCtCC6H4NdNC6H4CtCH,17 and HCtCC6H4CtCC6H4Ct CH25 were prepared according to literature methods. All other reagents were commercially available. Elemental analyses (C,H, N) were performed by the Microanalytical Services, College of Chemistry, CCNU. The electrospray mass spectra (ES-MS) were recorded on a Finnigan LCQ mass spectrometer using dichloromethane-methanol as mobile phase. 1H, 13C{1H}, and 31P{1H} NMR spectra were collected on an American Varian Mercury Plus 400 spectrometer (400 MHz) or 600 spectrometer (600 MHz). 1H and 13C{1H} NMR chemical shifts are relative to TMS, and 31P{1H} NMR chemical shifts are relative to 85% H3PO4. Infrared spectra were obtained on a Nicolet AVATAR 360 FTIR instrument using KBr Pellets. UV/vis spectra were obtained on a S-3100 PDA UV-vis spectrometer (SCINCO CO., Ltd.). Photoisomerizatoin measurements were carried out under a HPK 125 W mercury lamp as an irradiation source. UV light (
