The reaction of [Os3(µ-H)2(CO)9L](L = CO or PEt3) with dimethylcyanamide, Me2NCN: X-ray crystal structure of [Os3(µ-H)(µ-NCHNMe2)(CO)10] and the reactions of this complex with acids

Abstract

The reaction of [Os₃H₂(CO)₁₀] with Me₂NCN gives a 1 : 1 adduct, [Os₃H(µ-H)(NCNMe₂)(CO)₁₀](1), which, on reflux in hexane solution, rearranges to give [OS₃(µ-H)(µ-NCHNMe₂)(CO)₁₀](2). The complex [Os₃H₂(CO)₉(PEt₃)] reacts similarly to give [OS₃(µ-H)(µ-NCHNMe₂)(CO)₉(PEt₃)](3) which exists in solution as a mixture of two isomers which could not be separated by t.I.c. An X-ray diffraction study of complex (2) shows that both the NCHNMe₂ group and the hydride bridge the short edge [OS–OS 2.795(1)Å] of an isosceles OS₃ triangle. The ten carbonyl groups are all terminal, four bonded to the unique OS, and three to each of the OS atoms which are also co-ordinated to the bridging ligands. Complex (2) reacts with strong acids, HX (X = CF₃CO₂ or Cl), and, in the presence of HBF₄·R₂O (R = Me or Et), with weak acids (X = CH₃CO₂, MeO, HO, or HOCH₂CH₂O) to give complexes of the type [OS₃(µ-H)(µ-X)(CO)₁₀]. The mechanism of this reaction is discussed in the light of a study by ¹H n.m.r. spectroscopy of the protonation of (2) at low temperatures. Results of the thermolysis and attempted hydrogenation of complex (2) are also reported.