THIOXOPHOSPHANE (HP=S) AND SELENOXOPHOSPHANE (HP=SE) COMPLEXES OF OS(0) - SYNTHESIS, STRUCTURE, REACTIVITY, AND THEORETICAL-STUDIES OF OS(ETA-2-PH=S)(CO)2(PPH3)2, OS(ETA-2-PME=S)(CO)2(PPH3)2, OS(ETA-2-PH=SE)(CO)2(PPH3)2

The thioxophosphane and selenoxophosphane complexes Os(η2-PH═E)(CO)2(PPh3)2 (E = S, 2a; E = Se, 2b) are prepared by the sequential addition of triflic acid and base to Os(O2CCH3)(PH2═E)(CO)2(PPh3)2 (E = S, 1a; E = Se, 1b). The31P{1H} NMR spectra of 2a,b have strongly coupled inequivalent trans triphenylphosphine ligands. Compound 2a crystallizes in the triclinic space group P1 with a = 10.524 (4) Å, b = 18.010 (3) Å, c = 10.389 (5) Å, α = 103.26 (3)°, β = 115.63 (3)°, γ = 76.11 (2)°, V = 1705.6 Å3, and ρ(calcd) = 1.62 g cm-3. The crystal structure of 2a indicates that both phosphorus and sulfur of HPS lie in the same plane as the osmium and the carbon monoxide ligands. These structural features are interpreted as arising from the binding of HP═S as a π-accepting ligand with a lone pair localized on the phosphorus. Electrophiles such as H+, Me+, and AuI add to this lone pair to give the adducts 3, 7, and 8, respectively. In a reversible reaction, acid in the presence of alcohol cleaves the P‒S bond in 2a to give [Os-(PH2OR)(SH)(CO)2(PPh3)2]+ (4‒6). Deprotonation of the cationic complex containing η2-PHMe═S, 7a, returns the neutral complex Os(η2-PMe═S)(CO)2(PPh3)2 (9), which readily isomerizes to a complex (10) with cis triphenylphosphine ligands. A similar fluxionality is also found for the products of the reaction of 10 with acid and methyl triflate. Ab initio SCF calculations for RP═X (R = H, Me; X = CH2, NH, O, S, Se) at the 6-311+G* level, with and without the second-order Møller‒Plesset correction (MP2), are used to determine the structure and the order of frontier orbitals of these species and to rationalize the reactivity of 2a,b and 10. © 1990, American Chemical Society. All rights reserved.