In the last few years, there has been a rapidly growing interest on metallocene-containing macromolecular materials in which metal atoms interact with one another. 1 On a different front, recent trends of research in dendrimers 2 have focused on the introduction of metal centers on the surface or within the dendritic structure. 3,4 We recently reported silicon 5 and aminebased 6 dendrimers in which ferrocenyl moieties behave as electronically isolated units, and the dendritic molecules undergo a simultaneous multielectron transfer at the same potential. A challenging target is the construction of well-defined dendrimers possessing redox-active organometallic units linked together in close proximity so that there is electronic communication between the metal sites in the dendritic structure. This would provide access to new multimetallic dendrimers with appreciable electron mobility and consequently with interesting electrical, redox, optical, and magnetic properties.We now report the convergent construction of novel dendrons and dendrimers possessing interacting ferrocenyl units. To our knowledge these are the first organometallic dendritic molecules displaying electronic interactions between transition metal atoms in the dendritic structure reported so far.The key dendritic wedge for the synthesis of the new dendrimers is the silicon-bridged biferrocene 1 (Chart 1), which is prepared by reaction of ferrocenyllithium with vinylmethyldichlorosilane, in THF at -20°C. After purification, the target vinyl-terminated 1 was obtained as an orange crystalline solid. The molecular structure of 1 (Figure 1) shows that the ferrocenyl groups are oriented at ca. 90°relative to one another, and the iron atoms are separated by 6.221 Å. 7 Further growth of this first-generation dendron was achieved by platinum-catalyzed hydrosilylation of 1 with phenylchlorosilane, resulting in the dendron ClSiPh(CH 2 CH 2 SiMeFc 2 ) 2 (2), which contains a reactive chlorosilane functionality available for an ensuing alkenylation step. Treatment of 2 with allylmagnesium bromide, followed by hydrolytic workup afforded the desired growth dendron (3), carrying four ferrocenyl units.The availability of the free carbon-carbon double bonds at the focal point of the dendritic wedges 1 and 3 enables the * Morán, M.; Losada, J.; Casado, C. M.; Pascual, C.; Alonso, B.; Lobete, F. Cuadrado, I.; Morán, M.; Casado, C. M.; Alonso, B.; Barranco, M. Anal. Chim. Acta 1996, 251, 5. (6) Cuadrado, I.; Morán, M.; Casado, C. M.; Alonso, B.; Lobete, F.; García, B.; Ibisate, M.; Losada, J. Organometallics 1996, 15, 5278. (7) Crystal data for 1: triclinic, P1 h, a ) 7.5540(10) Å, b ) 10.936(2) Å, c ) 12.442(2) Å, R ) 101.330(10)°, ) 84.580(10)°, γ ) 93.410-(10)°, V ) 1002.4(3) Å 3 , Z ) 2, µ ) 1.510 mm -1 , Mo kR radiation (λ ) 0.71073 Å), orange crystal (0.35 × 0.20 × 0.20 mm).Figure 1. Crystal structure of dendron 1.The methyl and vinyl groups are situated with statistic disorder (50% probability) around the silicon atom so that both C21 and C22 correspond to the diso...
Template condensation on iron(II) ion of dichloroglyoxime (H2C12Gm) with (C6H5O)3, n-C4H9B(O-n-C4H9)2, and BF3.O(C2H5)2 in CH3NO2 afforded reactive clathrochelate precursors Fe(C12Gm)3(BC6H5)2 (2), Fe(C12Gm)3(B-n-C4H9)2 (3), and Fe(C12Gm)3(BF)2 (4). A series of triribbed-functionalized clathrochelate dioximates have been synthesized. Reaction of 2 with C6H5SH/K2CO3 and CH3SH/t-C4H9OK in 1,4-dioxane and THF afforded Fe((C6H5S)2Gm)3(BC6H5)2 (5) and Fe((CH3S)2Gm)3(BC6H5)2 (6). Reaction of 3 with C6H5OK in THF afforded Fe((C6H5O)2Gm)3(B-n-C4H9)2 (7). Condensation of 3 with bis(2-(o-oxyphenoxy))diethyl ether in THF afforded di- and tricrown etheric Fe(CwGm)2(C12Gm)(Bn-C4H9)2 (8) and Fe(CwGm)3(B-n-C4H9)2 (9) clathrochelates. Condensation of 3 with 3,5-dithiaoctane-1,8-dithiol/Cs2CO3 in DMF afforded the thiocrown etheric Fe((12anS4)Gm)3(BC6H5)2 complex (10). Reaction of 2 with n-butylamine in DMF resulted in the tetrasubstituted Fe((n-C4H9NH)2Gm)2(C12Gm)(BC6H5)2 clathrochelate (11). The clathrochelates obtained have been characterized both on the basis of elemental analysis, FAB and PD mass spectrometry, IR, UV-vis, 57Fe Mössbauer, and NMR spectroscopies and crystallographically (compounds 3, 4, 6, 7, and 11). An encapsulated iron(II) ion in a distorted trigonal-prismatic environment of six nitrogen atoms of the macrobicyclic ligand was found to be in a low-spin state. The cyclic voltammograms for the complexes 2-11 show irreversible oxidation waves assignable to Fe3+/Fe2+ couples. The correlation of E1/2 for these couples with Hammet sigma para constants for substituents in dioximate fragments has been demonstrated.
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