Diverse ligand substitution behavior in the reaction of H₄Os₄(CO)₁₂ with 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) and Me₃NO: Spectroscopic characterization of the diphosphine chelating and bridging isomers H₄Os₄(CO)₁₀(bpcd) and the X-ray diffraction structures of the tetraosmium clusters H₄Os₄(CO)₁₁(NMe₃) and 1,2-H₄Os₄(CO)₁₀(NMe₃)($\eta^{1}$-bpcd)

Abstract

The reaction between the tetraosmium cluster H$_{4}\hbox{Os}_{4}$(CO)$_{12}$ and the unsaturated diphosphine ligand 4,5-bis(diphenylphosphino)-4-cyclopenten-1,3-dione (bpcd) has been examined in CH$_{2}\hbox{Cl}_{2}$ solvent and in the presence of the oxidative-decarbonylation reagent Me$_{3}$NO. Rapid ligand substitution is observed and the four products H$_{4}\hbox{Os}_{4}$(CO)$_{11}$(NMe$_{3}$), 1,1-H$_{4}\hbox{Os}_{4}$(CO)$_{10}$(bpcd), 1,2-H$_{4}\hbox{Os}_{4}$(CO)$_{10}$(bpcd), and 1,2-H$_{4}\hbox{Os}_{4}$(CO)$_{10}$(NMe$_{3}$) ($\eta^{1}$-bpcd) have been isolated and characterized in solution by IR and NMR spectroscopies. The molecular structures of H$_{4}\hbox{Os}_{4}$(CO)$_{11}$(NMe$_{3}$) and 1,2-H$_{4}\hbox{Os}_{4}$(CO)$_{10}$(NMe$_{3}$)($\eta^{1}$-bpcd) have been crystallographically determined. H$_{4}\hbox{Os}_{4}$(CO)$_{11}$(NMe$_{3}$) crystallizes in the orthorhombic space group $\hbox{\it Pca}2_{1}, a=19.907(3)$ Å, $b = 8.137(1)$ Å, $c = 13.796(2)$ Å, $V=2234.6(6)$ ų, Z=4, and $d_{\rm calc} = 3.353$ mg/m³; $R=0.0418, R_{\rm w} = 0.1071$ for 4997 reflections with $I>2 \sigma(I)$. 1,2-H$_{4}\hbox{Os}_{4}$(CO)$_{10}$(NMe$_{3}$)($\eta^{1}$-bpcd) crystallizes in the monoclinic space group $P2_{1}/c, a = 21.0173(3)$ Å, $b = 10.755(2)$ Å, $c = 23.135(4)$ Å, $V = 4950.5(1)$ ų, Z=4, and $d_{\rm calc} = 2.099$ mg/m³; $R = 0.0591, R_{\rm w} = 0.1046$ for 10,766 reflections with $I>2\sigma(I)$. The monodentate coordination of the bpcd ligand in 1,2-H$_{4}\hbox{Os}_{4}$(CO)$_{10}$(NMe$_{3}$)($\eta^{1}$-bpcd) and the disposition of the NMe$_{3}$ and bpcd ligands across one of the Os–Os bonds are crystallographically verified.