A Trithiol Protio-Ligand and Its Fixation to the Periphery of a Carbosilane Dendrimer as Scaffolds for Polynuclear Rhodium and Iridium Complexes and Metallodendrimers

Tris(methylenethiol)methane derivatives containing an allyl or benzyl linker (ROCH 2 C(CH 2 SH) 3; R = Bn( 6a ), CH 2 CHCH 2 ( 6b )), which could allow their fixation to carbosilane dendrimers, were synthesized through a multistep synthesis. Grafting the periphery of the core dendrimer Si[(CH 2 ) 3 Si(Me) 2 H] 4 was achieved with the tosyl derivative CH 2 CHCH 2 OCH 2 C(CH 2 OTs) 3 by a hydrosilylation reaction to give selectively Si[(CH 2 ) 3 Si(Me) 2 (CH 2 ) 3 OCH 2 C(CH 2 OTs) 3 ] 4 ( G(0) OTs-12 ). This dendrimer was converted into the thiol-functionalized carbosilane dendrimer Si[(CH 2 ) 3 Si(Me) 2 (CH 2 ) 3 OCH 2 C(CH 2 SH) 3 ] 4 ( G(0) SH-12 ) by reduction of the thiocyanate intermediate Si[(CH 2 ) 3 Si(Me) 2 (CH 2 ) 3 OCH 2 C(CH 2 SCN) 3 ] 4 with LiAlH 4 . The trithiol compounds 6a and 6b protonated the complexes [Rh(μ-OMe)(cod)] 2 and [Rh(acac)diolefin] (M = Rh, diolefin = cod, nbd, tfb) to give the corresponding trinuclear complexes [Rh 3 {μ-ROCH 2 c(ch 2 s) 3 }(diolefin) 3 ] ( 7 − 9 ). Their structure can be described as an adamantane-like entity, in which the metals are held together by the thiolate arms of the ligand, with the sulfurs bridging the metal atoms in a μ 2 fashion, as shown for [Rh 3 {μ-BnOCH 2 C(CH 2 S) 3 }(nbd) 3 ] by X-ray diffraction methods. Carbonylation of 7 − 9 under atmospheric pressure gave the carbonyl complexes with the thiolate tripod ligands [M 3 {μ-ROCH 2 C(CH 2 S) 3 }(CO) 6 ] (M = Rh, Ir), which were reacted with phosphorus donor ligands (PR 3 = PPh 3, P(OMe) 3 ) to give [M 3 {μ-ROCH 2 C(CH 2 S) 3 }(CO) 3 (PR) 3 ] as a sole isomer of averaged C 3 v symmetry. The functional dendrimers were metalated by reaction of the core molecule Si[(CH 2 ) 3 Si(Me) 2 (CH 2 ) 3 OCH 2 C(CH 2 SH) 3 ] 4 ( G(0) SH-12 ) by applying the synthetic protocols above-described for trinuclear complexes. Thus, the reactions of G(0) SH-12 with the complexes [M(acac)(diolefin)] (M = Rh, Ir; diolefin = cod, nbd, tfb) gave the metallodendrimers Si[(CH 2 ) 3 Si(Me) 2 (CH 2 ) 3 OCH 2 C(CH 2 S) 3 {M(diolefin)} 3 ] 4 ( G(0) M(diolefin)-12 ) as insoluble solids. Soluble metallodendrimers, Si[(CH 2 ) 3 Si(Me) 2 (CH 2 ) 3 OCH 2 C(CH 2 S) 3 {Rh(CO) 2 } 3 ] 4 ( G(0) Rh(CO)2 - 12 ) and Si[(CH 2 ) 3 Si(Me) 2 (CH 2 ) 3 OCH 2 C(CH 2 S) 3 {M(CO)(PPh 3 )} 3 ] 4 ( G(0) M(CO)(PPh3)-12 ) were obtained either by carbonylation of the diolefin compounds or by the reaction of G(0) SH-12 with [M(acac)(CO) 2 ] (M = Rh, Ir), and by further reaction with PPh 3, respectively.