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.