Phosphinoalkylsilyl complexes. Part 7. Synthesis and reactivity of octahedral, bis(chelate)dicarbonyl complexes of ruthenium(II) and osmium(II). Conformational properties of the bis(chelate) framework and X-ray crystal structures of [M(PPh₂CH₂CH₂SiMe₂) ₂(CO)₂] (M = Ru or Os)

Reaction of the phosphinoethylsilanes Ph₂PCH₂CH₂SiR¹R²H (R¹ = R² = Me or Ph; R¹ = Me, R² = Ph) with [M₃(CO)₁₂] (M = Ru or Os) at 140 °C affords the octahedral complexes [M(PPh₂CH₂CH₂SiR¹R²) ₂(CO)₂] for which i.r. and n.m.r. data suggest a common structure with trans CO groups. The Ru complex in which R¹ = R² = Me is chemically inert, failing to undergo carbonyl displacement or to show evidence for either nucleophilic or electrophilic attack on co-ordinated CO [a characteristic which can be correlated with the low energy of ν(CO) (ca. 1 920 cm^-1) and which may result from inductive electron release from Si onto Ru], but reacting in boiling CCl₄ or with HCl gas or I₂ with cleavage of both Ru-Si bonds. The crystal and molecular structure of the Os complex in which R¹ = R² = Me has been determined by X-ray diffraction, showing that the chelate ligands adopt a cis relationship in the equatorial plane; in this structure two conformers coexist in the crystal, distinguished by the arrangement of the chelate ligand methylene backbones which are either parallel or skew with respect to one another. The crystals are triclinic, space group P1, with a = 12.598(3), b = 17.228(4), c = 18.501(4) Å, α = 119.96(2), β = 101.39(2), γ = 90.36(1)°, and Z = 4. Mean M-Si and M-P distances are ca. 2.48 and 2.38 Å respectively, the latter conspicuously long compared with related compounds and consistent with the strongly trans-influencing behaviour of Si.