A family of group 4 metal alkoxo complexes with an M3(μ3-O) core relevant to Ziegler-Natta catalyst intermediates

Reactions of [Mg(thffo)(2)] (1) or [Ca(thffo)(2)] (2) with ZrCl4 or HfCl4 in a CH2Cl2/THF/CH3CN mixture give thermally stable neutral heterobimetallic tetranuclear complexes [M3M'(mu(x)-O)(mu, eta(2)-thffo)(6)(Cl)(6)] (thffo = tetrahydro-furfuroxide; M/M'/x: 3, Zr/Mg/3; 4, Hf/Mg/3; 5, Zr/Ca/4; 6, Hf/Ca/4) as colorless crystals in 75-82% yield. X-ray diffraction studies show complexes 3-5 to contain oxo-bridged M-3 triangles that are capped by an alkaline earth metal-containing moiety to form species of C, symmetry. Reactions of ZrCl4 and HfCl4 with pure tetrahydrofurfuryl alcohol in EtOH and MeOH provide ionic complexes [M-3(mu(3)-O)-(mu, eta(2)-thffo)(3)(L)(3)(Cl)(6)]Cl (M/L: 8, Zr/EtOH 9, Hf/EtOH; 10, Zr/MeOH) in 66 - 79% yield. Complexes 8 - 10 consist of M3 triangles that are analogous to those in 3-6 and possess similar overall symmetry, as shown by X-ray crystallography. Changes in the reaction conditions afforded the asymmetric neutral dimer [Zr-2(mu-thffo)(2)(thffoH)(Cl)(6)] (7) and the homometallic [Zr-3(mu(3)-O) (mu, eta(2)-thp)(3)(thf)(2)(Cl)(7)] (11).