Synthesis, single-crystal X-ray structures, and fluxional behaviour of 1,2-[Os3(CO)10(µ-dppe)] and its protonated derivative 1,2-[Os3(µ-H)(CO)10(µ-dppe)][PF6] where dppe = Ph2PCH2CH2PPh2

Abstract

The cluster 1,2-[Os₃(CO)₁₀(MeCN)₂] reacts with Ph₂PCH₂CH₂PPh₂(dppe) to give mainly 1,2-[Os₃(CO)₁₀(dppe)](1) but also some 1,2-[Os₃(CO)₁₀(dppe-P)₂]. Variable-temperature ¹³C-{¹H} and ¹H n.m.r. spectra for (1) were used to show that inversion of the [graphic omitted]s ring can easily be slowed to give frozen-out spectra below –40 °C. Single-crystal X-ray structures of (1) and its protonated derivative [Os₃H(CO)₁₀(dppe)][PF₆](2)(two independent but similar molecules in the unit cell) were determined. Although compounds (1) and (2) have closely related geometries, (1) has a much distorted structure in which the axial OC–Os–CO directions are not perpendicular to the Os₃ plane but are screwed with respect to each other. This screw distortion is not present in (2) because the µ-H ligand causes the two axial OC–Os–CO directions through adjacent Os atoms to be locked perpendicular to the Os–H directions and hence they are parallel. Ring inversion in (2) was also frozen out in the low-temperature n.m.r. spectra.