The thorium metallacycle [(Me(3)Si)(2)N]Th-2[N(SiMe(2))(SiMe(2)CH(2))] (1) reacts with 4 equiv of 2,4-dimethylpentan-3-ol (diisopropylmethanol) in toluene at room temperature to produce dimeric Th-2(OR)(8) (2) (R = CH-i-Pr-2). H-1 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 Delta H degrees = 17 kcal mol(-1), Delta G degrees = 5 kcal mol(-1), Delta S 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 Me(3)SiI produces the monoiodide derivative TnI(OR)(3)(py)(2) (7). Compounds 2-7 have been characterized by H-1 NMR and IR spectroscopy, by elemental analysis, and, in the case of 2, 6, and 7, by single crystal X-ray diffraction studies. Th-2(OCH-i-Pr-2)(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 rage 2.154(11) Angstrom while bridging Th-O distances are significantly longer at 2.436(11) Angstrom (average).