Preparative and electrochemical investigations on the electron sponge behavior of cobalt telluride clusters: CO substitution in [Co11Te7(CO)10]n- ions (n=1, 2) by PMe2Ph and crystal structure of [Co11Te7(CO)5(PMe2Ph)5].

The reaction of the cluster salts [CpNb(CO)2]n[Co11Te7(CO)10] (Cp*=C5Me5; n=1, 2) with excess PMe2Ph gave the neutral, dark brown clusters [Co11Te7(CO)6(PMe2Ph)4] (5) and [Co11Te7(CO)5(PMe2Ph)5] (6) with 147 metal valence electrons. The new compounds were characterized by IR spectroscopy, elemental analyses, and mass spectrometry. The molecular structure of 6 was determined by X-ray crystallography. Like its precursor anion, it consists of a pentagonal-prismatic [Co11Te7] core, but with a ligand sphere composed of five CO and five PMe2Ph ligands. Detailed electrochemical studies of both reactions reveal that a stepwise substitution of CO ligands in the initial cluster anions takes place leading to intermediate [Co11Te7(CO)10−m(PMe2Ph)m]n− ions (m=1–5; n=1, 2). Each of these intermediates is distinguished by at least one oxidation and two reduction waves, giving rise to a total of 21 redox couples and 27 electroactive species. The electron sponge character of the new compounds is particularly pronounced in 5, which exhibits charges n between +1 and −4 corresponding to metal valence electron counts of between 146 and 151.