Extending the Family of Titanium Heterometallic–oxo–alkoxy Cages

Here we investigate the synthesis of high-nuclearity heterometallic titanium oxo–alkoxy cages using the reactions of metal chlorides with [Ti(OEt)4] or the pre-formed homometallic titanium–oxo–alkoxy cage [Ti7O4(OEt)20] (A). The octanuclear Ti7CoII cage [Ti7CoO5(OEt)19Cl] (1) (whose low-yielding synthesis we reported earlier) can be made in better yield, reproducibly by the reaction of a mixture of heptanuclear [Ti7O4(OEt)20] (A) and [KOEt] with [CoIICl2] in toluene. A alone reacts with [CoIICl2] and [FeIICl2] to form [Ti7CoIIO5(OEt)18Cl2] (2) and [Ti7FeIIO5(OEt)18Cl2] (3), respectively. Like 1, compounds 2 and 3 retain the original Ti7 fragment of A and the II-oxidation state of the transition metal ions (Tm). In contrast, from the reaction of [Ti(OEt)4] with [CrIICl2] it is possible to isolate [Ti3CrVO(OEt)14Cl] (4) in low yield, containing a Ti3CrV core in which oxidation of Cr from the II to V oxidation state has occurred. Reaction of [MoVCl5] with [Ti(OEt)]4 in [EtOH] gives the Ti8MoV4 cage [{Ti4Mo2O8(OEt)10}2] (5). The single-crystal X-ray structures of the new cages 2, 3, 4, and 5 are reported. The results show that the size of the heterometallic cage formed can be influenced by the nuclearity of the precursor. In the case of 5, the presence of homometallic Mo–Mo bonding also appears to be a significant factor in the final structure.