Solution study of the ambient temperature monomer-dimer equilibrium Th2(OR)8 rightleftharpoons 2Th(OR)4 (R = CH-i-Pr2) and X-ray crystal structures of Th2(OCH-i-Pr2)8, Th(OCH-i-Pr2)4(quin), and ThI(OCH-i-Pr2)3(py)2

The thorium metallacycle [(Me3Si)2N]2Th[N(SiMe3)(SiMe2CH2)] (1) reacts with 4 equiv of 2,4-dimethylpentan-3-ol(diisopropylmenthanol) in toluene at room temperature to produce dimeric Th2(OR)8(2)(R=CH-i-Pr2). 1H NMR spectra of 2 in noncoordinating solvents indicate a monomer-dimer equilibrium in solution at ambient temperatures between 2 and its monomer Th(OR)4 (3). Thermodynamic parameters for the equilibrium process are δH degrees = 17 kcal mol-1, δG degrees = 5 kcal mol-1, δS degrees = 40 cal mol-1 K-1. Addition of Lewis bases such as DME (DME = 1,2-dimethoxyethane), pyridine or quinuclidine to solutions of 2 results in the formation of the five- and six-coordinate mononuclear adducts Th(OR)4(DME) (4), Th(OR)4(py)2(5), and Th(OR)4(quin) (6), respectively. Reaction of 5 with 1 equiv of Me3SiI produces the monoiodide derivative ThI(OR)3(py)2(7). Compounds 2-7 have been characterized by 1H NMR and IR spectroscopy, by elemental analysis, and, in the case of 2,6, and 7, by single crystal X-ray diffraction studies. Th2(OCH-i-Pr2)8(2) exhibits a dimeric structure in which the Th2O8 core can be viewed as two ThO5 trigonal bipyramids joined along a common axial-equatorial edge. Terminal Th-O distances average 2.154(11) Angstrom while bridging Th-O distances are significantly longer at 2.436(11) Angstrom (average)