Reactivity of [TiM2] (M = Rh, Ir) and [TiIr3] early-late heterobimetallic sulfido-bridged clusters

Abstract

Treatment of heterobimetallic sulfido-bridged complexes [Cp(acac)Ti(μ3-S)2{M(cod)}2] (M = Rh (1), Ir (2)) with the organic acids CX3COOH (X = F, H) forms the corresponding acetate derivatives [Cp(CX3COO)Ti(μ3-S)2{M(cod)}2] (X = F, M = Rh (3), Ir (4); X = H, M = Rh (5), M = Ir (6)). While complex 3 was easily isolated, compounds 4–6 establish in solution the corresponding equilibria with the starting complexes 1 and 2. Treatment of 1 with a hydrochloric acid solution in THF generates the heterohexanuclear cationic cluster [{CpTi(μ3-S)2{Rh(cod)}2}2(μ-OH)][Cl] (7), which is deprotonated with weak bases affording the oxo derivative [{CpTi(μ3-S)2{Rh(cod)}2}2(μ2-O)] (8). Cluster 8, and the analogous with the ligand methylcyclopentadienyl [{(CpMe)Ti(μ3-S)2{Rh(cod)}2}2(μ2-O)] (9), can be synthesized from reaction of the respective complexes [Cp2Ti(SH)2] and [(CpMe)2Ti(SH)2] with the methoxo-bridged dinuclear complex [{Rh(μ-OMe)(cod)}2] in the presence of water. A preliminary study of the molecular structure of 9 confirmed the formation of an almost linear array of the “Ti–O–Ti” subunit, in which each titanium atom supports two “Rh(cod)” moieties through two sulfido bridges. Further, the heterotetranuclear cluster [CpTi(μ3-S)3Ir3(μ2-CO)(CO)3(PMe3)3] (10) reacts with alkynes at the triiridium metallic triangle. The reactions with activated alkynes, such as dimethyl acetylenedicarboxylate (or diethyl acetylenedicarboxylate) afford clusters [CpTi(μ3-S)3Ir3(μ2-η1-RO2CCCCO2R){C(O)RO2CCCCO2R}(CO)3(PMe3)3] (R = Me (11), Et (12)), which incorporate two molecules of alkyne. The X-ray molecular structure of 11 shows that one alkyne is cis-metallated to the metal–metal bonded iridium centres whereas the other is taking part of a iridacyclobutenone moiety resulting from the CO migratory insertion into a iridium–alkyne bond at the third iridium centre. However, reaction of 10 with phenylacetylene stops at the cluster [CpTi(μ3-S)3Ir3(μ2-η1-PhCCH)(CO)3(PMe3)3] (13), which contains only a cis-metallated olefin to two metal–metal bonded iridium atoms. The X-ray molecular structure of [CpTi(μ3-S)3Ir3(μ2-η1-PhCCH)(H)(CO)3(PMe3)3][BF4] (14), the product resulting from protonation of 13 with HBF4·OEt2 shows that the [TiIr3] core remains intact and that the olefin is indeed cis-metallated to the two metal–metal bonded iridium atoms, while the third iridium atom from the metallic triangle becomes protonated.