Migratory insertion and CO substitution reactions of the beta,gamma-unsaturated esters and amides [Fe-2(CO)(5)(mu-PPh2)(mu-eta(1):eta(2)-{NuC(O)CH2}C=CH2}] (Nu = OMe, OEt, OPri,NHPh, NHBut): synthesis and characterisation ofacyl-bridged [Fe-2(CO)(4)L-2(mu-PPh2)(mu-C=O{C=CH2}CH2C(O)Nu)](L-2 = dppm,dppe) and alkenyl-bridged [Fe-2(CO)(4){P(Ome)(3)}(2)(mu-eta(1):eta(2)-{NuC(O)CH2}C=CH2)]

Reaction of the beta,gamma -unsaturated esters and amides [Fe-2(CO)(5)(mu - PPh2)(mu-eta (1)(O):eta (1)(C):eta (2)(C)-{NuC(O)CH2}C=CH2)] (Nu = OMe, la; R = Oft, Ib; R = OPri, Ic, R = NHPh, Id, R = NHBut, le) with dppe and dppm results in displacement of the acyl carbonyl and migratory insertion to gi ve the alpha,beta -unsaturated acyl derivatives [Fe-2(CO)(4)(eta (2)-dppe)( mu -PPh2)(mu -C=O{C=CH2}CH2C(O)Nu)] (Nu = OMe, 2a; R = OEt, 2b; R = OPri, 2 c, R = NHPh, 2d, R = NHBut, 2e) and [Fe-2(CO)(4)(mu -dppm)(mu -PPh2)(mu -C= O{C=CH2}CH2C(O)Nu)] (R = OMe, 3a; R = Oft, 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 lat ter both bridge the iron-iron bond and are ti ans to one another. In contra st, reaction of la-e with trimethylphosphite results in displacement of the ester carbonyl oxygen to give [Fe-2(CO)(5){P(OMe)(3)}(mu -PPh2)(mu-eta (1) (C):eta (2)(C)-{NuC(O)CH2}C=CH2)] (Nu = OMe, 4a; R = OEt, 4b; R = OPri, 4c) followed by CO substitution to give [Fe-2(CO)(4){P(OMe)(3)}(2)(mu -PPh2)(m u-eta (1)(C):eta (2)(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-brid ged 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 [Fe-2( CO)(4){P(OMe)(3)}(mu -PPh2)(mu-eta (1)(O):eta (1)(C):eta (2)(C)-{NuC(O)CH2} C=CH2)] (Nu = OMe, 5a; R = OEt, 5b; R = OPri, 5c), an intermediate in the f ormation of 6a-c. Complexes 5a and 6a have been characterised by single-cry stal X-ray crystallography. (C) 2001 Elsevier Science B.V. All rights reser ved.