DALTON COMMUNICATION J. Chem. Soc., Dalton Trans., 1999, 1363–1364 1363 High-nuclearity cobaltadendrimers Edwin C. Constable,* Oliver Eich and Catherine E. Housecroft* Institut für Anorganische Chemie, Universität Basel, Spitalstrasse 51, CH-4056 Basel, Switzerland. E-mail: housecroft@ubaclu.unibas.ch Received 27th January 1999, Accepted 16th March 1999 New dendritic polyalkynes have been prepared and reacted with [Co2(CO)8] to give cobaltadendrimers containing up to 40 cobalt atoms.Metalladendrimers are of intrinsic structural and synthetic interest 1–3 and oVer potential applications as light-collecting devices, information storage devices and polyfunctional catalysts. We have prepared compounds in which the metals are part of the backbone dendritic connectivity,1 or in which they decorate the dendrimer.4 The generation of C2Co2(CO)6 clusters from alkynes is a facile method for the introduction of multiple metal centres which has not been widely used in metalladendrimer chemistry.5 We now report an extension of our previous work (which led to a starburst decorated with C2Co2- (CO)6 through to the third generation) 6 to genuinely dendritic systems. Our synthetic strategy involves the preparation of a starburst or dendritic polyalkyne and post-functionalization with [Co2- (CO)8].6 The doubly-protected compound 1 was prepared in 53% yield † by the sequential reaction of 1,3,5-tribromobenzene with two equivalents of (TIPS)C]] ] CH (TIPS = triisopropylsilyl) and a three-fold excess of (TMS)C]] ] CH (TMS = trimethylsilyl) in each case in the presence of [(Ph3P)2PdCl2], CuI and NEt3, followed by alkaline cleavage of the TMS group.The use of the base-stable TIPS protecting group is critical to the success of this strategy and allows the preparation of asymmetrically substituted derivatives. The reaction of C(p-C6H4I)4 7 with an excess of 1 under similar palladium(II)-catalysed coupling conditions followed by deprotection of 2 with [nBu4N]F in THF yielded the intensely luminescent (lmax 352 nm) dendritic dodecaalkyne 3 as white crystals.‡ Upon stirring 3 with [Co2(CO)8] in CH2Cl2, a dark coloured solution was obtained from which the dendritic tetracosacobalt complex 4 was isolated as deep red crystals in 28% yield.§ Linear extension of these systems proved to be facile.The reaction of the polyalkyne 3 with p-IC6H4C]] ] C(TMS) under standard Pd-coupling conditions yielded the protected dendritic icosaalkyne 5 as yellow crystals.Subsequent basic deprotection gave icosaalkyne 6, the reaction of which with an excess of [Co2(CO)8] produced the deep red crystalline tetracontacobalt compound 7 ¶ (Fig. 1). This latter compound and all others described were characterized by the normal spectroscopic and analytical methods adopted for ‘small molecules’ even though modelling indicates that 7 has a diameter of ª35 nm. We are currently investigating the chemical and structural aspects of these novel high-nuclearity species.Fig. 1 Proposed structure of compound 7.1364 J. Chem. Soc., Dalton Trans., 1999, 1363–1364 Acknowledgements This work was supported by the Schweizerischer Nationalfonds zur Förderung der wissenschaftlichen Forschung and the University of Basel. We thank Dr G. Scherer for assistance with the NMR spectroscopic experiments. Notes and references † 1: 1,3,5-Br3C6H3 (1.35 g, 4.28 mmol), (TIPS)C]] ] CH (1.64 g, 8.99 mmol), CuI (81.5 mg, 0.43 mmol) and [(PPh3)2PdCl2] (300 mg, 0.43 mmol) were stirred in NEt3 (50 ml) for 4 h at 35 8C.Treatment with (TMS)C]] ] CH (1.26 g, 12.8 mmol) under analogous conditions to those described above (reaction time 12 h), followed by chromatographic work-up gave the protected intermediate; this was dissolved in THF (120 ml) and 1 M NaOH (150 ml) added; the solution stirred for 3.5 h. After extraction, the residue was purified by column chromatography to give a colourless oil (1.06 g; 53%). 1H NMR (250 MHz, CDCl3) d 7.52– 7.50 (m, 3H, Ar), 3.08 (s, 1H, CCH), 1.12 (s, 42H, TIPS); 13C NMR (75 MHz, CDCl3) d 135.2, 124.2, 122.6, 105.1, 92.4, 82.0, 78.3, 18.7 (TIPS), 11.3 (TIPS); MS (MALDI-TOF) m/z 502 [M 1 K]1, 486 [M 1 Na]1. ‡ 3: compound 1 (0.37 g, 0.80 mmol), C(p-C6H4I)4 (0.16 g, 0.19 mmol), CuI (10.8 mg, 0.06 mmol) and [(Ph3P)2PdCl2] (40.0 mg, 0.06 mmol) were stirred in NEt3 (10 ml) and DMF (20 ml) for 70 h at 35 8C. Chromatographic work-up gave 2 as yellow crystals (0.35 g, 84.5%).Deprotection using [nBu4N]F (1.60 mmol) in THF (50 ml, room temperature, 4 h) yielded 3 as white crystals (62 mg, 42%). 1H NMR (300 MHz, CDCl3) d 7.61 (d, J 1.4 Hz, 8H), 7.56 (t, J 1.5 Hz, 4H), 7.45 (d, J 8.6 Hz, 8H), 7.21 (d, J 8.5 Hz, 8H), 3.11 (s, 8H, CCH); 13C NMR (75 MHz, CDCl3) d 146.2, 135.1, 131.3, 130.9, 124.0, 122.9, 120.8, 90.3, 87.9, 81.8, 78.5, 48.4; MS (MALDI-TOF) m/z 1828 [2M]1, 914 [M]1. § 4: alkyne 3 (54.3 mg, 0.06 mmol) and Co2(CO)8 (0.49 g, 1.43 mmol) were stirred in CH2Cl2 (10 ml) for 1.5 h at room temperature, the solvent removed, and the residue purified by column chromatography to give a deep red crystalline solid (71.9 mg, 28%).IR (KBr disc, cm21) nCO 2093 s, 2055 vs, 2020 vs; 1H NMR (250 MHz, CDCl3) d 7.67 (d, J 2.0 Hz, 8H), 7.57 (d, J 8.3 Hz, 8H), 7.50 (t, J 1.7 Hz, 4H), 7.18 (d, J 8.8 Hz, 8H), 6.37 (s, 8H, Hcluster); 13C NMR (101 MHz, CDCl3) d 199.0 (CO), 145.7, 140.4, 139.3, 135.9, 131.7, 130.4, 129.2, 128.3, 91.4, 90.3, 88.5, 72.8, 64.8; MS (MALDI-TOF) m/z 4317 [M 2 CO]1.¶ 6 and 7: alkyne 3 (62 mg, 68 mmol), p-IC6H4C]] ] C(TMS) (0.24 g, 0.82 mmol), CuI (10.4 mg, 0.05 mmol) and [(PPh3)2PdCl2] (38.1 mg, 0.05 mmol) were stirred in dry NEt3 (5 ml) for 100 h at 39 8C. Chromatographic work-up gave compound 5 as yellow crystals (67 mg, 43%); it was dissolved in THF (30 ml), and 1 M NaOH (30 ml) added; the solution was stirred for 4 h. Water was added and after extraction with CH2Cl2, the residue was purified by column chromatography to give 6 as white crystals (21.3 mg, 43%).Reaction of 6 (15.4 mg, 8.98 mmol) with [Co2(CO)8] under the same conditions as for 4 gave 7 as deep red crystals (27 mg, 41%). 6: 1H NMR (400 MHz, CDCl3) d 7.65 (br s, 12H), 7.48–7.46 (m, 40H), 7.24 (d, J 8.6 Hz, 8H), 3.19 (s, 8H, CCH); 13C NMR (75 MHz, CDCl3) d 146.2, 134.3, 132.1, 131.5, 131.3, 130.9, 124.0, 123.8, 123.1, 122.3, 120.9, 90.3, 90.1, 89.6, 88.1, 83.1, 79.2; MS (MALDI-TOF) m/z 1713 [M]1. 7: IR (KBr disc, cm21) nCO 2091 s, 2055 vs, 2020 vs; 1H NMR (400 MHz, CD2Cl2) d 7.79 (d, J 1.6 Hz, 8H), 7.72 (t, J 1.7 Hz, 4H), 7.62 (d, J 8.6 Hz, 8H), 7.56 (d, J 8.4 Hz, 16H), 7.48 (d, J 8.5 Hz, 16H), 7.24 (d, J 8.6 Hz, 8H), 6.46 (s, 8H, CCH); 13C NMR (101 MHz, CD2Cl2) d 199.8 (CO), 199.4 (CO), 199.2 (CO), 146.2, 140.9, 140.6, 138.4, 137.9, 136.3, 131.9, 131.2, 129.9, 129.4, 128.8, 91.8, 91.7, 90.9, 90.8, 89.6, 73.4, 69.5; MS (MALDI-TOF) m/z 7298 [M 2 5CO]1, 7144 [M 2 10 CO]1. 1 E. C. Constable, Chem. Commun., 1997, 1073. 2 G. R. Newkome, C. N. Moorefield and F. Vögtle, Dendritic Molecules, Wiley-VCH, Weinheim, 1996. 3 V. Balzani, A. Juris, M. Venturi, S. Campagna and S. Serroni, Chem. Rev., 1996, 96, 759. 4 E. C. Constable, C. E. Housecroft and L. A. Johnston, Inorg. Chem. Commun., 1998, 1, 68. 5 D. Seyferth, T. Kugita, A. L. Rheingold and G. A. P. Yap, Organometallics, 1995, 14, 5362. 6 E. C. Constable, O. Eich, C. E. Housecroft and L. A. Johnston, Chem. Commun., 1998, 2661. 7 M. Simard, D. Su and J. D. Wuest, J. Am. Chem. Soc., 1991, 113, 4696. Communication 9/02093D