From Clusters to Ionic Complexes:  Structurally Characterized Thallium Titanium Double Alkoxides

A series of sterically varied titanium alkoxides {[Ti(OR)4] n , n = 4, OR = OCH2CH3 (OEt); n = 1, OCH(CH3)2 (OPri); n = 2, OCH2C(CH3)3 (ONep); n = 1, OC6H3(CH3)2-2,6 (DMP)} were reacted with a series of thallium alkoxides {[Tl(OR)] x (x = 4, OR = OEt, ONep; n = ∞, DMP)}. The resultant products of the [Tl(μ3-OEt)]4-modified [Ti(OR)4] n (OR = OEt, OPri, ONep) were found by X-ray analysis to be Tl4Ti2(μ-O)(μ3-OEt)8(OEt)2 (1), Tl4Ti2(μ-O)(μ3-OPri)5(μ3-OEt)3(OEt)2 (2), and TlTi2(μ3-OEt)2(μ-OEt)(μ-ONep)2(ONep)4 (3), respectively. The reaction of [Tl(μ3-OEt)]4, 12HOEt, and 4[Ti(μ-ONep)ONep)3]2 to generate 3 in a higher yield resulted in the isolation of TlTi2(μ3-OEt)(μ3-ONep)(μ-OEt)(μ-ONep)2(ONep)4 (4). Compounds 1 and 2 possess an octahedral (Oh) arrangement of two Ti and four Tl metal atoms around a μ-O central oxide atom (the Tl−O distance is too long to be considered a bond). For both compounds, each Ti atom adopts a distorted Oh geometry with one terminal OEt ligand. The Tl atoms are formally 4-coordinated, adopting a distorted pyramidal geometry using four μ3-OR (OR = OEt or OPri) ligands to complete their coordination sphere. The Tl atoms reside ∼1.4 Å below the basal plane of oxygens. In contrast to these structures, both 3 and 4 utilize ONep ligands and display reduced oligomerization yielding trinuclear complexes without oxo formation. The two Ti cations are Oh, and the single Tl cation is in a formal distorted pyramidal (PYD) arrangement. If the lone pair of the Tl cations are considered in the geometry, each Tl adopts a square base pyramidal geometry. Two terminal ONep ligands are bound to each Ti with the remainder of the molecule consisting of μ3- and μ-ONep ligands. The reaction of [Tl(μ3-ONep)]4 with two equivalents of [Ti(μ-ONep)(ONep)3]2 also led to the isolation of the homoleptic trinuclear complex TlTi2(μ3-ONep)2(μ-ONep)3(ONep)4 (5) which is analogous in structure to the mixed ligand species of 3 and 4. Each Ti is Oh coordinated with six ONep ligands, and the single Tl is PYD bound by ONep ligands. A further increase in the steric bulk of the pendant ligands, using [Tl(μ-DMP)]∞ and [Ti(μ-ONep)(ONep)3]2, resulted in a further decrease in the nuclearity yielding the dinuclear species TlTi(μ-DMP)(μ-ONep)(DMP)(ONep)2 (6). For 6, the two metals are bound by a μ-ONep and a μ-DMP ligand. The Tl metal center was solved in a bent geometry while the Ti adopted a distorted trigonal bipyramidal (TBP) geometry using three ONep and two DMP ligands to fill i