Synthesis and characterization of new paramagnetic nickel carbonyl clusters containing antimony atoms: X-ray structure of [NEt 3CH 2Ph] 2[Ni 15(μ 12-Sb)(CO) 24] and [NEt 4] 3[Ni 10Sb 2(μ 12-Ni)(CO) 18

Abstract

The reaction of the [Ni 6(CO) 12] 2− dianion with SbCl 3 in a 2.5:1 molar ratio leads to formation of the new [Ni 15(μ 12-Sb)(CO) 24] 2−, 1 2−, cluster with good selectivity. This has been conveniently separated from [Ni 9(CO) 18] 2−, [Ni 10(SbNi(CO) 3) 2(μ 12-Ni)(CO) 18] n− , 2 n− , ( n=2, 3) and other side-products by differential solubility of their [NEt 4] + salts and isolated in 50–60% yields. The corresponding [NEt 3CH 2Ph] 2[ 1] salt was obtained from [NEt 4] 2[ 1] by metathesis in acetonitrile with [NEt 3CH 2Ph]Cl and has been structurally characterized. The structure of 1 2− consists of a distorted Sb-centered Ni 12(μ 12-Sb) icosahedral moiety, capped by three Ni atoms on three adjacent triangular faces. The 1 2− dianion is moderately stable to oxidation and has been electrochemically reduced to the corresponding tri-, tetra- and penta-anion; these electrogenerated species are stable only on the timescale of cyclic voltammetry. The 1 2− dianion is readily degraded upon exposure to an atmosphere of carbon monoxide to a mixture of Ni(CO) 4 and a yet uncharacterized red–violet intermediate, which has been tentatively formulated as the [Ni 6Sb(CO) x ] 2− dianion on the basis of its spectroscopic features. The above mixture converts under nitrogen into the known 2 n− ( n=3, 4), through the intermediate formation of the new [Ni 10Sb 2(μ 12-Ni)(CO) 18] n− , 3 n− , ( n=3, 4) species. Pure 3 3− has been obtained by degradation of 2 3− with two equivalents of triphenylphosphine by elimination of two equivalents of Ni(CO) 3(PPh 3) and has been structurally characterized in its tetraethylammonium salt. The Ni-centered icosahedral 3 3− trianion shows a chemical and electrochemical redox propensity comparable to that of the parent 2 3− compound and is readily transformed in its corresponding 3 2− and 3 4− anions upon oxidation and reduction, respectively. Systematic observation of apparently exceptional electron counts and redox propensity by the above Ni-centered icosahedral clusters validate the previous attribution of these properties to the presence of interstitial nickel atoms and concomitant stabilization imparted by the peripheral antimony heteroatoms.