Electrophilic Attack on a Cluster-Coordinated Nitrosyl Ligand: Crystal and Molecular Structure of Ru₃(NOCH₃)(CO)₁₀and Observation of an O-H to M-H Tautomerization

The reactions of the anionic cluster [Ru₃(CO)₁₀(NO)]~ with acids and CF₃SO₃CH₃are reported. O-Methylation of the µ₂-NO ligand gives high yields of Ru₃(NOCH₃)(CO)₁₀. A single-crystal X-ray crystallographic analysis of this new cluster [orthorhombic crystal system, Pnma space group, a = 14.775 (4) Å, b = 12.128 (2) Å, c = 9.987 (2) Å, Z = 4] revealed the presence of a triply bridging methoxyimido (NOCH₃) ligand and a triply bridging carbonyl ligand on opposite faces of an equilateral ruthenium triangle. O-Protonation with CF₃SO₃H gives an analogous structure; however, weaker acids, such as CF₃CO₂H, give only HRu₃(CO)₁₀(NO), where a Ru-Ru bond has been protonated. Addition of PPN(CF₃CO₂) to Ru₃(NOH)(CO)₁₀results in immediate O-H to M-H tautomerization. The PPN+ salts of 12 anions having differing basicities provide insight into the pK_aof Ru₃(NOH)(CO)₁₀and the relative kinetic acidity of the O-H vs the M-H group. Reactions of the substituted anions [Ru₃(CO)₉(L)(NO)]−, where L = PPh₃and P(OCH₃)₃, with acids reveal similar behavior.