Chelate and bridge complexes of metal carbonyl compounds with a ditertiary phosphine: A study of their formation and interconversion

Article abstract of DOI:10.1021/ic50035a007

The reactions of the compounds Co(NO)(CO)₃ and Fe(NO₂)(CO)₂ with a severalfold excess of the diphosphine 1,2-bis(diphenylphosphino)ethane (diphos, (C₆H₅)₂PCH₂CH₂P(C ₆H₅)₂) are shown to yield, in toluene or tetrahydrofuran solution, fairly long-lived intermediates Co(NO)(CO)₂(diphos) and Fe(NO)₂(CO)(diphos) in which the diphosphine is only attached to the metal by one phosphorus atom. These intermediates are slowly converted to the chelate complexes Co(NO)(CO)(diphos) and Fe(NO)₂(diphos) at rates which are independent of the free diphosphine concentration. Similar results have been obtained for CH₃Mn(CO)₅ which is converted, via an intermediate believed to be CH₃COMn(CO)₄(diphos), to the chelate complex CH₃COMn(CO)₃(diphos). Use of metal:diphosphine molar ratios of 2:1 yields complexes of the type [Co(NO)(CO)₂]₂(diphos), in which the diphosphine acts as a bridge between two metal atoms. These complexes can also be converted to the corresponding chelate complexes by reaction with excess diphosphine, but at a rate which is dependent on the free diphosphine concentration. The unsymmetrical bridge complex, Fe(NO)₂(CO)(diphos)Co(NO)(CO)₂, has been isolated and characterized.