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 [Ti(7)O(4)(OEt)(20)] (A). The octanuclear Ti(7)Co(II) cage [Ti(7)CoO(5)(OEt)(19)Cl] (1) (whose low-yielding synthesis we reported earlier) can be made in better yield, reproducibly by the reaction of a mixture of heptanuclear [Ti(7)O(4)(OEt)(20)] (A) and [KOEt] with [Co(II)Cl(2)] in toluene. A alone reacts with [Co(II)Cl(2)] and [Fe(II)Cl(2)] to form [Ti(7)Co(II)O(5)(OEt)(18)Cl(2)] (2) and [Ti(7)Fe(II)O(5)(OEt)(18)Cl(2)] (3), respectively. Like 1, compounds 2 and 3 retain the original Ti(7) fragment of A and the II-oxidation state of the transition metal ions (Tm). In contrast, from the reaction of [Ti(OEt)(4)] with [Cr(II)Cl(2)] it is possible to isolate [Ti(3)Cr(V)O(OEt)(14)Cl] (4) in low yield, containing a Ti(3)Cr(V) core in which oxidation of Cr from the II to V oxidation state has occurred. Reaction of [Mo(V)Cl(5)] with Ti(OEt) in [EtOH] gives the Ti(8)Mo(V)(4) cage [{Ti(4)Mo(2)O(8)(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.