Synthesis and characterisation of triosmium nitrite clusters containing phosphine ligands

Abstract

The nitrite cluster [Os₃(µ-H)(CO)₁₀(µ-η²-NO₂)] 1 reacted with trimethylamine N-oxide in CH₂Cl₂ to give a pair of isomers with formula [Os₃(µ-H)(CO)₉(µ-η²-NO₂)(NMe₃)] 2a and 2b in moderate yields. Reaction of 1 with PPh₃ and Me₃NO in CH₂Cl₂ gave a pair of isomers [Os₃(µ-H)(CO)₉(µ-η²-NO₂)(PPh₃)] 3a and 3b and [Os₃(µ-H)(CO)₈(µ-η²-NO₂)(PPh₃)₂] 4. With cis-1,2-bis(diphenylphosphino)ethylene (dppen) and Me₃NO in CH₂Cl₂, 1 gave a pair of isomers [Os₃(µ-H)(CO)₈(µ-η²-NO₂)(dppen)] 5a and 5b, and [Os₃(µ-H)(CO)₆(µ-η²-NO₂)(dppen)₂] 6. Reaction of 1 with bis(diphenylphosphino)acetylene (dppa) and Me₃NO in CH₂Cl₂ gave [Os₃(µ-H)(CO)₈(µ-η²-NO₂)(dppa)] 7 in good yield. The dppa co-ordinates to two Os atoms to form a six-membered ring suffering from severe angle strain in which the carbon–carbon triple bond is maintained. All the products were characterised by IR, NMR and FAB mass spectroscopies. All these clusters contain an asymmetrically bridging NO₂^– ligand along one Os–Os edge of the triosmium metal framework, as is evident from structural determinations of 2a, 2b, 3b, 4, 5a, 6 and 7.