Phosphorus–oxygen bond formation on organo-capped tricobalt centres via phosphorus–hydrogen or phosphorus–phosphorus bond scission

Abstract

Chromatographic work-up of the initial products of the reaction of the secondary phosphine PPh₂H with [Co₃(µ₃-CR)(CO)₉] (R = Me 1a or CO₂Me 1b) at 308 K in heptane gave the mono- and bis-substituted complexes [Co₃(µ₃-CR)(CO)₈(PPh₂H)] (R = Me 2a or CO₂Me 2b) and [Co₃(µ₃-CR)(CO)₇(PPh₂H)₂] (R  Me 3a or CO₂Me 3b) and, in addition, when R = Me, the complex [Co₃(µ₃-CMe)(µ-Ph₂POPPh₂)(CO)₆(PPh₂H)] 4a, in which phosphorus–oxygen bond formation has occurred. Thermolysis of complex 2a at 343 K in heptane gave 1a and [Co₃(µ₃-CMe)(µ-H)(µ-PPh₂)(CO)₇] 5a, while thermolysis of 3a under the same conditions afforded 4a, a trace of 5a and [Co₃(µ₃-CMe)(µ-H)(µ-PPh₂)(CO)₆(PPh₂H)] 6a. Similar reactions with the µ₃-CCO₂Me capped species 2b and 3b resulted in unstable non-isolable species. Treatment of complexes 3a, 3b with CO at 343 K causes the replacement of first one and then the other PPh₂H ligand by CO to give 2a, 2b and then 1a, 1b respectively, while reformation of a phosphorus–hydrogen bond to give initially 2a or 3a can be achieved on carbonylation of either complex 5a or 6a. Substitution of a PPh₂H group in 4a can be achieved by purging with CO to give [Co₃(µ₃-CMe)(µ-Ph₂POPPh₂)(CO)₇] 7a. Complex 7a can also be prepared directly by the reaction of 1a with the diphosphane P₂Ph₄ as can the analogue [Co₃(µ₃-CCO₂Me)(µ-Ph₂POPPh₂)(CO)₇] 7b on reaction of 1b. The intermediates [Co₃(µ₃-CR)(CO)₈(P₂Ph₄)] (R = Me 8a or CO₂Me 8b) and [Co₃(µ₃-CR)(µ-P₂Ph₄)(CO)₇] (R = Me 9a or CO₂Me 9b) isolated in the reactions can be converted under the same reaction conditions into 7a and 7b respectively. Complex [Co₃(µ₃-CMe)(µ-Ph₂POPPh₂)(CO)₆(PPhMe₂)] 4a′, the tertiary phosphine analogue of 4a, has been prepared from the reaction of 7a with PPhMe₂. The structures of complexes 4a′ and 5a have been determined by single crystal X-ray diffraction studies.