Intramolecular hydrogen bonding stabilizes the nuclearity of complexes. A comparative study based on the H-carborane and Me-carborane framework

Abstract

New dinuclear carboranylcarboxylate-bridged and mononuclear copper(II) compounds containing the 1-CO2H-2-H-1,2-closo-C2B10H10 carborane ligand (LH) have been synthesized from the previously synthesized dinuclear compound [Cu-2(mu-L)(4)(THF)(2)], 1. Reaction of LH with CuSO4 in THF leads to the dinuclear compound [CCu2(mu-L)(4)(THF)(2)], 1. The reaction of 1 with different terminal pyridyl ligands leads to the formation of a series of structurally analogous complexes by substitution of the terminal ligand THF (L-t = py, 2; p-CF3-py, 3; p-CH3-py, 4), which maintain the structural Cu-2(mu-O2CR)(4) core in most of the cases except for o-(CH3)(2)-py where a mononuclear compound (5) is exclusively obtained. In the case of 2 and 4, other dinuclear compounds [Cu-2(L)(4)(L-t)(4)], 2' and 4' are obtained in lower yield. These compounds have been characterized using analytical, spectroscopic (NMR, IR, UV-visible) and electrochemical techniques (CV, DPV). X-ray analysis revealed a paddle-wheel structure for the main dinuclear compounds with a square-pyramidal geometry around each copper ion and the carboranylcarboxylate ions bridging two copper atoms in syn-syn mode. In the case of 2' and 4' there are two carboranylcarboxylate ions bridging the copper atoms in syn-anti mode whereas the other two adopt a monodentate coordination mode. The mononuclear complex obtained with the o-(CH3)-py ligand presents a square-planar structure, in which the carboranylcarboxylate ligand adoptsmonodentate coordination. The effect of the substituent group on the cluster of the carboranylcarboxylate ligands on the reactivity of compound 1 is also discussed