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In toluene at 100°C the dimetallacyclopentenone complex [Fe2(CO)5{μ-σ:η3-C(O)CHCH}(μ-dppm)] (1a) isomerises to the μ-vinyl complex [Fe2(CO)6{μ-C(CH2)P(Ph2)CH2PPh2}] (2) via intramolecular nucleophilic attack of phosphorus on a carbon of the metallacycle, with an associated 1,2-hydrogen shift and CC bond cleavage. On further heating to 110°C, 2 in turn is transformed to isomeric [Fe2(CO)6−{μ-C(CH2Ph)P(Ph2)CH2PPh}] (3), arising from transfer of a phenyl group from phosphorus to carbon, and the complex [Fe2(CO)5−{μ-Ph2PCH2P(Ph)C6H4C(CH3)}] (4a), resulting from more complex rearrangement. Heating the complexes [Fe(CO)5−{μ-σ:η3(C(O)CRCH}(μ- dppm)] (R = Me (1b), Ph (1c)) gave only [Fe2(CO)2{μ-Ph2PCH2P(Ph)C6H4C(CH2R)}] (4b, 4c), the likely intermediates analogous to 2 and 3 not being detectable. The structures of 2, 3 and 4c were established by X-ray diffraction, providing an insight into the molecular manoeuvres involved in the rearrangements. In contrast to the ready thermolysis of 1a-c, in which the diphosphine and organic moieties lie cis to one another, the analogous trans complexes [Fe(CO)5{μ-σ:C(O)CRCR}(μ-dp pm)] (R = Me (1d), Ph (1e)) are stable in refluxing toluene, partly attributable to the inability of phosphorus to attack the distant metallacycle. |
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