Peripheral SH-functionalisation of carbosilane dendrimers including the synthesis of the model compound dimethylbis(propanethiol)silane and their interaction with rhodium complexes

Abstract

Treatment of the allyl-containing compounds Me₂Si(CH₂CHCH₂)₂ and MeSi(CH₂CHCH₂)₃ with thioacetic acid in the presence of AIBN gave Me₂Si[(CH₂)₃SC(O)CH₃]₂ and MeSi[(CH₂)₃SC(O)CH₃]₃, respectively, which were reduced with LiAlH₄ to the dithiols Me₂Si[(CH₂)₃SH]₂ (3) and MeSi[(CH₂)₃SH]₃ (4). This protocol was applied to the first and second generations of the doubly and triply-branched carbosilane allyl dendrimers, Si[(CH₂)₃SiMe(CH₂CHCH₂)₂]₄ (G(1)_allyl-8), Si[(CH₂)₃SiMe{(CH₂)₃SiMe(CH₂CHCH₂)₂}₂]₄ (G(2)_allyl-16), Si[(CH₂)₃Si(CH₂CHCH₂)₃]₄ (G(1)_allyl-12), and Si[(CH₂)₃Si{(CH₂)₃Si(CH₂CHCH₂)₃}₃]₄ (G(2)_allyl-36) to give the corresponding SH functionalised surface dendrimers Si[(CH₂)₃SiMe(CH₂CH₂CH₂SH)₂]₄ (G(1)_SH-8), G(2)_SH-16, G(1)_SH-12, and G(2)_SH-36. Reactions of 3 with [M(acac)(diolefin)] (M = Rh, Ir; diolefin = 1,5-cyclooctadiene, 2,5-norbornadiene) gave the compounds of the type [M₂(µ-Me₂Si[(CH₂)₃S]₂)(diolefin)₂]_n. These diolefin complexes are octanuclear (n = 4) in solution while the complex [Rh₂(µ-Me₂Si[(CH₂)₃S]₂)(cod)₂]_n (5) is tetranuclear in the solid state. The structure of 5, solved by X-ray diffraction methods, consists of a 20-membered metallomacrocycle formed by two dimethylbis(propylthiolate)silane moieties bridging four fragments Rh(cod) in a µ₂ fashion through the sulfur atoms. Treatment of [Rh(acac)(CO)₂] with 3 gave [Rh₂(µ-Me₂Si[(CH₂)₃S]₂)(CO)₄]_n, which is a mixture of tetra (n = 2) and octanuclear (n = 4) complexes in a 2 : 1 ratio in solution, while the related complex [Rh₂(µ-Me₂Si[(CH₂)₃S]₂)(CO)₂(PPh₃)₂]₂ is tetranuclear. Reactions of [Rh(acac)(L–L)] (L–L = cod, (CO)₂, (CO)(PPh₃)) with 4 and the dendrimers G(1)_SH-8, G(2)_SH-16, and G(1)_SH-12, gave microcrystalline solids of formulae [Rh₃(MeSi[(CH₂)₃S]₃)(L–L)₃]_n, [Si[(CH₂)₃SiMe{(CH₂)₃SRh(cod)}₂]₄]_n ([G(1)_Rh(cod)-8]_n), [Si[(CH₂)₃Si{(CH₂)₃SRh(cod)}₃]₄]_n ([G(1)_Rh(cod)-12]_n), etc., which presumably are tridimensional coordination polymers.