Migratory insertion and CO substitution reactions of the β,γ-unsaturated esters and amides [Fe2(CO)5(μ-PPh2)(μ-η1:η2-{NuC(O)CH2}CCH2}] (Nu=OMe, OEt, OPri, NHPh, NHBut): synthesis and characterisation of acyl-bridged [Fe2(CO)4L2(μ-PPh2)(μ-CO{CCH2}CH2C(O

Reaction of the β,γ-unsaturated esters and amides [Fe2(CO)5(μ-PPh2)(μ-η1(O):η1(C):η2(C)-{NuC(O)CH2}CCH2)] (Nu=OMe, 1a; R=OEt, 1b; R=OPri, 1c, R=NHPh, 1d, R=NHBut, 1e) with dppe and dppm results in displacement of the acyl carbonyl and migratory insertion to give the α,β,-unsaturated acyl derivatives [Fe2(CO)4(η2-dppe)(μ-PPh2)(μ-CO{CCH2}CH2C(O)Nu)] (Nu=OMe, 2a; R=OEt, 2b; R=OPri, 2c, R=NHPh, 2d, R=NHBut, 2e) and [Fe2(CO)4(μ-dppm)(μ-PPh2)(μ-CO{CCH2}CH2C(O)Nu)] (R=OMe, 3a; R=OEt, 3b; R=OPri, 3c, R=NHPh, 3d), respectively. Single-crystal X-ray analyses of 2a and 3a has revealed that the dppe ligand in the former chelates, with one arm binding trans and one cis to the phosphido bridge, while the dppm and phosphido group in the latter both bridge the iron-iron bond and are trans to one another. In contrast, reaction of 1a–c with trimethylphosphite results in displacement of the ester carbonyl oxygen to give [Fe2(CO)5{P(OMe)3}(μ-PPh2)(μ-η1(C):η2(C)-{NuC(O)CH2}CCH2}] (Nu=OMe, 4a; R=OEt, 4b; R=OPri, 4c) followed by CO substitution to give [Fe2(CO)4{P(OMe)3}2(μ-PPh2)(μ-η1(C):η2(C)-{Nu(O)CCH2}CCH2)] (Nu=OMe, 6a; R=OEt, 6b; R=OPri, 6c) with no evidence for the formation of the corresponding acyl-bridged derivative. Thermolysis of toluene solutions of 4a–c result in loss of CO and coordination of the oxygen atom of the ester carbonyl to give [Fe2(CO)4{P(OMe)3}(μ-PPh2)(μ-η1(O):η1(C):η2(C)-{NuC(O)CH2}CCH2)] (Nu=OMe, 5a; R=OEt, 5b; R=OPri, 5c), an intermediate in the formation of 6a–c. Complexes 5a and 6a have been characterised by single-crystal X-ray crystallography.