Formic Acid Modified Ti(OCHMe(2))(4). Syntheses, Characterization, and X-ray Structures of Ti(4)(&mgr;(4)-O)(&mgr;-O)(OFc)(2)(&mgr;-OR)(4)(OR)(6) and Ti(6)(&mgr;(3)-O)(6)(OFc)(6)(OR)(6) (OFc = O(2)CH; OR = OCHMe(2)).

Abstract

Novel structural arrangements for carboxylic acid modified titanium alkoxides were obtained from stoichiometric reactions between titanium isopropoxide (Ti(OPr(i))(4)) and formic acid (HOFc). The 1:1 reaction in toluene forms the tetranuclear species Ti(4)O(2)(OFc)(2)(OPr(i))(10), 1. The structure of 1 was solved in the triclinic space group P&onemacr; with a = 13.034(3) Å, b = 13.467(2) Å, c = 13.996(2) Å, alpha = 98.79(1) degrees, beta = 104.68(2) degrees, and gamma = 97.82(2) degrees for Z = 2. The general structure of 1 resembles two face-shared [Ti-O](4) cubes with one set of mirror-related titanium atoms removed. The oxygen atoms are represented by one &mgr;(4)-O, one &mgr;-O, and four &mgr;-OR ligands, with the remaining sites filled by two OFc ligands and six terminal alkoxides. Increasing the stoichiometry to 1:2 (Ti/HOFc) leads to the isolation of Ti(6)O(6)(OFc)(6)(OR)(6), 2. The structure of 2 was solved in the monoclinic space group P2(1)/c with a = 8.968(2) Å, b = 26.520(4) Å, c = 20.046(2) Å, and beta = 93.19(1) degrees for Z = 4. The structure of 2 consists of two offset six-membered [Ti-(&mgr;(3)-O)](3) rings joined through Ti-O bonds. The OFc ligands are arranged externally around the central hexagon-prism, oscillating between the top and bottom rings. Compound 1 adopts a very symmetrical arrangement in solution due to the labile OFc ligands and was found to undergo "aging" by a trans-esterification mechanism, the rate of which is enhanced by heating. Compound 2 maintains its solid-state structure in solution.