[Rh10As(CO)22]3-. Example of encapsulation of arsenic by transition-metal carbonyl clusters as illustrated by the structural study of the benzyltriethylammonium salt

Article abstract of DOI:10.1021/ic50215a048

The reaction of Rh(CO)₂acac and alkali carboxylates in a glyme solvent with Ph₃As under ～300 atm of carbon monoxide and hydrogen resulted in the isolation of [PhCH₂N(C₂H₅)₃]₃[Rh ₁₀As(CO)₂₂]·C₄H₈O. The complex has been characterized via a complete three-dimensional X-ray diffraction study. The complex crystallizes in the primitive monoclinic space group P2₁/n, with a = 14.785 (2) A?, b = 22.495 (7) A?, c = 23.083 (5) A?, β = 95.45 (1)°, V = 7642.3 A?³, and δ(calcd) = 2.059 g/cm³. The structure was solved by direct methods and refined by difference-Fourier and least-squares techniques. All nonhydrogen atoms have been located and refined; final discrepancy indices are R_F = 5.4% and R_wF = 6.0% for all 3093 symmetry-independent reflections in the range of 0.5° ≤ 20 ≤ 45°. The structure consists of a bicapped square antiprism of rhodium atoms with the arsenic atom in its center. Rhodium-rhodium contacts are in the range 2.869-3.120 A? with arsenic-rhodium contacts of 2.502 and 3.008 A? for the metal atoms on the prism and the capped corner, respectively. Average values for the rhodium-carbon and carbon-oxygen distances are in the normal range, 1.83 and 1.16 A?, respectively, for the terminal carbonyls. There are one set of symmetrical and another of asymmetrical bridging carbonyls with Rh-C = 1.99 A? and C-O = 1.21 A? for the former set and Rh-C = 2.222 and 1.95 A? and C-O = 1.20 A? for the latter one, as is usual in this situation. High-pressure infrared studies show the cluster is stable under 537 atm of CO-H₂ (1:1 ratio) up to 150°C, but it reacts under 1000 atm, yielding [Rh(CO)₄]^- and [Rh₉As(CO)₂₁]^2-. The reaction of these two anions to form the initial anion has also been established.