J. CHEM. SOC. PERKIN TRANS. I 1990 Synthesis of Unsymmetrical 4,4-Disu bstituted 22'-Bipyridines containing Benzo Crown Ether and Ferrocene Moieties Oldrich Kocian," Roger J. Mortimerb and Paul D. Beer"" Department of Chemistry, University of Birmingham, PO Box 363, Birmingham B 15 211,UK Department of Chemistry, University of Technology, Loughborough, Leicestershire L El 7 3TU, UK A simple one-pot synthesis of unsymmetrical 4,4'-disubstituted 2,2'-bipyridine ligands containing benzo crown ether and redox-active ferrocene moieties is described. Ruthenium,'.' o~mium,~ and rhenium4,' polypyridyl complexes exhibit properties of importance to redox electrocatalysis and solar energy With respect to the latter, although simple transition metal 2,2'-bipyridyl (bpy) co-ordination compounds are known to be effective photosensitisers Gratzel and co-workers * have shown that unsymmetric 4,4'-dialkyl- 2,2'-bipyridineruthenium(11)complexes can substantially im- prove the efficiency of visible light photocatalytic cleavage of water.Surprisingly, very few reports 9-1 have subsequently described the syntheses of these desired unsymmetrical bi- pyridyl ligands. We present here a simple one-pot synthesis of unsymmetrical 4,4'-disubstituted 2,2'-bipyridine compounds using step-by-step lithiation of the commercially available 4,4'-dimethyL2,2'-bipyridine 1. Monolithiation of 1 using 1 equiv. of lithium diisopropyl- amide (LDA) in tetrahydrofuran is known to produce 2." Reaction of 2 with the appropriate aldehyde (R'CHO) gave the intermediate 3a-e (X = Li) the corresponding alcohol 3a-e (X = H) can be isolated in excellent yield (Table l), and in situ this lithium salt can be further lithiated with 1 equiv.of LDA to give 4. Subsequent addition of a different aldehyde (R2CHO) followed by quenching of the reaction mixture with water gave the crude product which after purification by flash chromato- graphy produced the respective unsymmetrical diol 5a-e (Scheme 1, Table 1). Dehydration of the diols 5a-e with pyridinium toluene-p- sulphonate (PTPS)in boiling toluene afforded the respective E,E-dienes 6a,b,d,ein very good yields (Table 1). The structures of all these new compounds were characterised on the basis of spectroscopic and analytical evidence.? Interestingly with 5c complete dehydration could not be achieved and only the mixed vinyl-alcohol compound 7 was isolated.The new unsymmetrical bipyridyl ligands are all polytopic in design and contain recognition sites for binding transition metal and Group IA/IIA metal guest cations. For example, preliminary t All new compounds gave spectroscopic and analytical data in accordance with assigned structures. Data are quoted for compounds 5b and 6b. For 5b m.p. 71-72deg;C (Found: C, 62.3; H, 6.3; N, 4.0. C,,-,H,,FeN,0,~2H20 requires C, 62.46; H, 6.34; N, 3.83); 6,(270 MHz,CDCI3)2.37(1 H,b~,OH),2.77(1 H,b~,OH),2.98-3.10(4H, m, CH,), 3.74 (8 H, s, OCH,), 3.85-3.90 (4 H, m, OCH,), 4.09-4.14 (4 H, m, ArOCH,), 4.17-4.26 (9 H, m, Fc-H), 4.69 (1 H, t, J 6.4 Hz, CH-Fc), 4.93 (1 H, t, 6.7 Hz, CH-Ar), 6.78-6.88 (3 H, m,ArH), 7.05 (1 H, d, J4.9 Hz, 5-PyH), 7.12 (1 H, d, J4.8 Hz, 5'-PyH), 8.25 (1 H, S, 3-PyH), 8.26 (1H, S, 3'-PyH), 8.49 (1 H, d, J4.9 Hz, 6-PyH), 8.50 (1 H, d, J4.9 Hz, 6'- PyH); m/z (FAB) 695 (M+ H+,75).For 6b,m.p. 83-85OC (decomp.) (Found C, 65.6; H, 5.8; N, 4.0. C3,H38FeN,05-2H ,O requires C, 65.71; H, 6.09; N, 4.03); 6,(270 MHz, CDCl,) 3.77 (8 H, s, OCH,), 3.94-3.97 (4 H, m, OCH,), 4.16 (5 H, s, unsubst. Fc ring), 4.16-4.21 (4 H,m, OCH,), 4.36 (2 H, t, J 1.8 Hz, P,P'-FcH), 4.52 (2 H, t, J 1.8 Hz, a,a'-FCH), 6.72 (1 H, d, J 16.1 Hz, =CH-Fc), 6.86-6.89 (1 H, m, ArH), 6.98 (I H, d, J 16.3 Hz, =CH-Ar), 7.10-7.12 (2 H, m, ArH), 7.25-7.38 (3 H, m, 5,5'-PyH and =CH-Fc), 7.39 (1 H, d, J 16.3 Hz,=CH-Ar), 8.47 (1 H, s, 3'-PyH), 8.52 (1 H, s, 3-PyH), 8.62 (1 H, d, J 5.1 Hz, 6'-PyH) and 8.66 (1 H, d, 6.1 Hz, 6-PyH); m/z (FAB) 659 (M + H+, 100).iTH3-CH3 2 3a-e (X = Li, H) iii1 vi I iv. v I 6a-e 5 4 For 3,5 and 6 For 5 and 6 R' R2 C +NO2 -Scheme 1. Reagents and conditions: i, LDA (1 equiv.), -78 OC in THF; ii, R'CHO, -78 to 0 "C; iii, X = Li LDA (1 equiv.), -78 to 0 OC in THF; iv, R'CHO, 0 "C to room temp.; H,O, PTPS/toluene, reflux. co-ordination studies reveal ligand 5b to form the heter- opolymetalhc ruthenium(i1)-ferrocene-sodium cation complex 8.* * Characterised by elemental analysis of the isolated heteropolymetallic hexafluorophosphate complex. (Found: C, 45.1; H, 3.7; N, 5.2.8-3PF6 requires C, 45.5; H, 3.5; N, 5.5). J. CHEM. SOC. PERKIN TRANS. 1 1990 7 8 Table 1. Yields ("A)of 3 (X = H), 5 and 6 Compd. 30 = H) 5 6 a 95 52 88 b 77 59 86 C 77 30 -* d 76 58 90 e 73 54 85 * Identified as 7,46 yield. The photo- and electro-chemical properties of 8 and other heteropolymetallic transition metal complexes of ligands 5 and 6 are under current investigation. Experimental Typical Procedure using the Preparation of 4-2-Hydroxy-2-(2,3,5,6,8,9,11,12-octahydrobenzo-1,4,7,10,13-pentaoxapenta-decin-1 5-yl)ethyll-4'-2-hydroxy-2-(ferrocenyl)ethyl-2,2'-bipyridine 5b.-A solution of compound 1 (2.5 g, 13.6mmol) in anhydrous THF (75 ml) was added under a nitrogen atmosphere to a stirred solution of lithium diisopropylamide (LDA), prepared from diisopropylamine (2.0 ml, 14.3 mmol) and butyllithium (1.6~solution in hexane; 8.8ml, 14.1mmol) at -78"C.The resulting dark orange-red mixture was allowed to warm to 0 *C and stirred for 1 h at this temperature. A solution of ferrocenecarbaldehyde (3.0g, 14.0mmol) in anhydrous THF (20 ml) was added dropwise during 5 min and stirring was continued at 0deg;C until the reaction was completed (2 h, monitored by TLC). The reaction mixture was then cooled to -78 "Cand treated successively with diisopropylamine (2.0 ml, 14.3mmol) and butyllithium (1.6~solution in hexane; 8.8 ml, 14.1mmol). After being stirred at -78 "C for 20 min and at 0 "C for 1 h, 2,3,5,6,8,9,11,12-octahydrobenzo-1,4,7,10,13-pentaoxa-pentadecine- 15-carbaldehyde (4.15g, 14.0 mmol) in THF (50 ml) was added dropwise and the resulting mixture stirred at 0deg;C for 2 h and then at room temperature overnight.The reaction mixture was poured into ice-water and extracted with dichloromethane and the extracts were dried (MgSOJ and evaporated. The crude product was then purified by flash chromatography on silica gel with dichloromethane-methanol-ammonium hydroxide (100:5:1)as the eluant to afford the diol5b (5.57g, 59). J. CHEM. SOC. PERKIN TRANS. 1 1990 Typical Dehydration Procedure using Preparation of 6b.-A solution of 5b (1 g, 1.44 mmol) and PTPS (0.25 g) in dry toluene (150 ml) was refluxed overnight using a Dean-Stark trap.The cooled solution was washed with water and dried (MgS0.J. The solvent was removed under reduced pressure and the resulting crude product purified by flash chromatography on silica gel with dichloromethane-methanol-ammonium hydroxide (100:5: 1) as the eluant to afford 6b (0.82 g, 86). AcknowledgementsWe thank the SERC for a postdoctoral research fellowship to 0. K. and for the use of the highfield NMR service at the University of Warwick and the Mass Spectrometry service of University College Swansea. References 1 E. A. Seddon and K. R. Seddon, The Chemistry of Ruthenium, Elsevier, Amsterdam, 1984 2 A. Juris, F.. Barigelletti, S. Campagna, V. Balzani, P. Belser and A. von Zelewsky, Coord. Chem. Rev., 1988,84,85. 3 M.E. Kober, J. V. Caspar, R. S. Lumpkin and T. J. Meyer, J. Phys. Chem., 1986,90,3722. 4 J. V. Caspar and T. J. Meyer, J.Phys. Chem., 1983,87,952. 5 A. Juris, S. Campagna, I. Bidd, J. M. Lehn and R. Zeissel, Inorg. Chem., 1988,27,4007. 6 T. J. Meyer, Acc. Chem. Res., 1989,22, 163. 7 J. S. Connolly, Photochemical Conversion and Storage of Solar Energy, Academic Press, New York, 1981. 8 E. Borgarello, J. Kiwi, E. Pelizzetti, M. Visca, and M. Gratzel, Nature, 1981,289, 158. 9 D. K. Ellison and R. T. Iwamoto, Terrahedron Lett., 1983,24,31. 10 C. G. Griggs and D. J. H. Smith, J. Chem. SOC.,Perkin Trans. I, 1982, 3041. 11 P. K. Ghosh and T. G. Spiro, J. Am. Chem. Soc., 1980,102,5543. Paper 0/03065A Received 9th Jury 1990 Accepted 13th August 1990
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