Organoplatinum Dendrimers Sudhir Achar, Jagadese J. Vittal, and Richard J. Puddephatt* Department of Chemistry, University of Western Ontario, London, Canada N6A 5B7 Received June 1, 1995 X A route to dendrimeric organoplatinum complexes is described by a strategy involving oxidative addition of the C-Br bonds of 4,4′-(BrCH 2 ) 2 -2,2′-(C 5 H 3 N) 2 , A, to [PtMe 2 (bu 2 bipy)], 1, bu 2 bipy ) 4,4′-di-tert-butyl-2,2′-bipyridine, to give 4,4′-{BrPtMe 2 (bu 2 bipy)CH 2 } 2 -2,2′- (C 5 H 3 N) 2 , 2, followed by regeneration of a [PtMe 2 (NN)] functionality by reaction of the free diimine group of 2 with [Pt 2 Me 4 (µ-SMe 2 ) 2 ], B, to give 4,4′-{BrPtMe 2 (bu 2 bipy)CH 2 } 2 -2,2′- (C 5 H 3 N) 2 PtMe 2 , 3. Repetition of this cycle has given dendrimers containing 6, 7, and 14 platinum atoms. The structure of 3 has been determined crystallographically. The above complexes containing 1, 3, or 7 platinum atoms react with the tetrafunctional core 1,2,4,5- (BrCH 2 ) 4 C 6 H 2 in a 4:1 ratio by oxidative addition of the C-Br bonds to the platinum(II) center to give dendrimers containing 4, 12, or 28 platinum atoms, respectively. An oligomeric dendrimer is prepared by reaction of A with B. Introduction There is much current interest in the synthesis and properties of molecular dendrimers. 1 Most such com- pounds are organic, 2 but routes to dendrimers contain- ing silicon, 3 phosphorus, 4 or transition metals 5,6 have also been developed recently. The synthesis of den- drimeric coordination compounds is usually based on ligand substitution with multifunctional ligands and often involves the need for protection/deprotection se- quences. 5 Most organotransition metal dendrimers have the metal either at the core only or at the periphery only, with the remainder based on organic chemistry. One major problem in devising routes to organometallic dendrimers with metals in each layer is that individual steps do not occur in sufficiently high yield to provide pure complexes directly and that separation procedures using chromatography are often not applicable. Since dendrimers must be built up layer-by-layer, usually with isolation and purification at each step, very high yields are imperative in every individual step if a multistep synthesis is to be accomplished without chromatographic purification steps. It has been shown that oxidative addition of primary alkyl or benzyl halides, RX, to [PtMe 2 (NN)] gives [PtXMe 2 R(NN)], NN ) diimine ligand such as 2,2′-bipyridine, 7 and that [PtMe 2 (NN) can be prepared from [Pt 2 Me 4 (µ-SMe 2 ) 2 ] and the ligand NN, 8 both in essentially quantitative yields (eqs 1 and 2). A strategy was then devised to prepare organoplatinum dendrimers by using a reagent containing both alkyl halide and diimine functionalities, and the resulting chemistry forms the basis of this paper. Preliminary accounts of the research 9 and of related chemistry 10 have been published. Results and Discussion First Synthetic Cycle. One key reagent in this work is 4,4′-bis(bromomethyl)-2,2′-bipyridine, A, which X Abstract published in Advance ACS Abstracts, November 15, 1995. (1) (a) Issberner, J.; Moors, R.; Vogtle, F. Angew. Chem., Int. Ed. Engl. 1995, 33, 2413. (b) Mekelburger, H. B.; Jaworek, W.; Vogtle, F. Angew. Chem., Int. Ed. Engl. 1992, 31, 1571. (2) (a) Xu, Z. F.; Kahr, M.; Walker, K. L.; Wilkins, C. L.; Moore, J. S. J. Am. Chem. Soc. 1994, 116, 4537. (b) Jansen, J. F. G. A.; Debrabandervandenberg, E. M. M.; Meijer, E. W. Science 1994, 266, 1226. (3) (a) Vandermade, A. W.; Vanleeuwen, P. W. N. M.; Dewilde, J. C.; Brandes, R. A. C. Adv. Mater. 1993, 5, 466. 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