Formation of Four Conjugated Osmacyclic Species in a One-Pot Reaction

Treatment of HC≡CCH(OH)CH═CH 2 with OsCl 2 (PPh 3 ) 3 in THF produced the η 2 -allyl alcohol osmacycle OsCl 2 (PPh 3 ) 2 (CH═C(PPh 3 )CH(OH)CH═CH 2 ) ( 2 ) with poor solubility and low stability, which underwent a ligand substitution reaction with PMe 3 to give the more stable analogue [OsCl(PMe 3 ) 3 (CH═C(PPh 3 )CH(OH)CH═CH 2 )]Cl ( 3 ). Heating the suspension of 2 in CH 2 Cl 2 led to the formation of four interesting conjugated osmacycles in one pot, including the osmabenzene OsCl 2 (PPh 3 ) 2 (CHC(PPh 3 )CHCHCH) ( 4 ), the cyclic osmium η 2 -allene complex OsCl 2 (PPh 3 ) 2 (CH═C(PPh 3 )CH═C═CH 2 ) ( 5 ), the osmafuran OsCl 2 (PPh 3 ) 2 (CHC(PPh 3 )C(CH 2 CH 3 )O) ( 6 ), and the α,β-unsaturated ketone complex OsCl 2 (PPh 3 ) 2 (CH═C(PPh 3 )C(O)C═CH 2 ) ( 7 ). All of the four products could also be produced in higher yield under appropriate conditions.