CLUSTERS AS LIGANDS - COMPARISON OF THE REACTIVITY OF (CO)9CO3(MU-3-CR) (R = COOH, P-C6H4(CH2)2COOH) LEADING TO THE FORMATION OF ZN[P-C6H4(CH2)2CO2]2 VS MII4O[(CO)9CO3CCO2]6(M=ZN,CO)

In order to explore the notion of cluster-substituted ligands as a route to large cluster assemblies, the gram-scale synthesis and purification along with spectroscopic and crystallographic characterization of two cluster-substituted carboxylate ligand precursors, (CO)9Co3{mu3-C[1,4-C6H4(CH2)2COOH]}, I, and (CO)9Co3(mu3-CCOOH), II, were carried out [1-toluene, space group triclinic P1BAR, a = 9.348(1) angstrom, b = 11.954(1) angstrom, c = 13.862(1) angstrom, a = 92.83(2)-degrees, beta = 100.67(2)-degrees, gamma = 109.51 (1)-degrees, V = 1424.3 angstrom3, d(calcd) = 1.59 g/cm3, Z = 2; II, space group triclinic P1BAR, a = 7.906(1) angstrom, b = 8.673(1) angstrom, c = 12.915(4) angstrom, alpha = 83.73(2)-degrees, beta = 86.94(2)-degrees, gamma = 68.30(1)-degrees, V = 817.8 angstrom3, d(calcd) = 1.98 g/cm3, d(obs) = 1.97 g/cm3, Z = 2]. Although the spectroscopic characterization of 11 has been previously reported, its instability in solution at room temperature has not been recognized. Thus, we report its spontaneous conversion to Co4O[(CO)9Co3CCO2]6, III, which is a metal cluster analogue of classical MII4O[RCO2]6 ''basic'' metal carboxylates normally formed by sublimation of MII[RCO2]2. The reaction of 1, which is stable in solution, with 1/2 ZnEt2 yields Zn[(CO)9Co3CC6H4(CH2)2CO2]2, which is analogous to the product formed from either acetic acid or C6H5(CH2)2COOH with the same reaction stoichiometry. In contrast, the reaction of 11 with ZnEt2 in a 1:1 stoichiometry forms Zn4O[(CO)9Co3CCO2]6, IV, in high yield at room temperature. The differing chemistry of II is attributed to the direct electronic interaction of the tricobalt cluster with the carboxylate fragment in II. IR spectra and cyclic voltammetry are used to detail the nature of this electronic coupling. Although both III and IV undergo quasi-reversible cluster ligand dissociation in THF, the reaction is more extensive for the former compound and ultimately leads to degradation of the tricobalt cluster.