Reactions of sigma-pi alkenyl complexes [Fe-2(CO)(6)(mu-alkenyl)(mu-PPh2)]with bis(diphenylphosphino)methane (dppm); carbonyl substitution, migratory carbonyl insertion, phosphorus-carbon bond formation and cleavage, protonshift and alkenyl isomerisation reactions

Products of the thermal reactions of Ir-alkenyl complexes [Fe-2(CO)(6)(mu-( RC)-C-1=CHR2)(mu-PPh2)] (1) (a, R-1 = R-2 = H; b, R-1 = EtO, R-2=H; c, R-1= H, R-2=Ph; d, R-1=Ph, R-2=H; e, R-1=R-2=Ph; f, R-1=CMe-CH2, R-2=H), with bi s(diphenylphosphino)methane (dppm) are substituent dependent. Complexes 1a- e afford simple substitution products trans-[Fe-2(CO)(4)(mu-alkenyl)(mu-PPh 2)(mu-dppm)] (2a-c); while with 1d,e, alpha,beta-unsaturated acyl complexes trans-[Fe-2(CO)(4)(mu-O-C-C(Ph)= CH(R-2))(mu-PPh2)(mu-dppm)] (3d,e) are th e major products formed via a migratory-insertion reaction. A minor product of the reaction with Id is [Fe-2(CO)(5)(mu-Ph2PC(Ph)=CH2)(mu-dppm)] (4), t he result of phosphorus-carbon bond formation. Reaction of If also leads to phosphorus-carbon bond formation together with a 1,4-proton shift giving t he mu-alkylidene complex [Fe-2(CO)(4)(mu-HC-C(Me)=(Me)PPh2(mu-dppm)] (5). D ppm addition to Ic has been followed in detail, allowing a complete reactio n scheme to be developed. Initial carbonyl substitution affords the eta(1)- dppm complex [Fe-2(CO)(2)(eta(1)-dppm)(mu-HC=CHPh)(mu-PPh2)] (6). This subs equently isomerises to trans-[Fe-2(CO)(4)(mu-O=C-CH=CHPh)(mu-PPh2)(mu-dppm) ] (3c) which then readily loses CO to give the mu-alkenyl 2c. Loss of CO fr om isomeric 3d occurs only upon prolonged thermolysis and also affords 2c, a result of or,P-alkenyl isomerisation. Further. heating 4 also yields 2c a fter CO loss, phosphorus-carbon bond cleavage, and alkenyl isomerisation. W hile the P-substituted phenylethenyl complex 2c is stable to prolonged refl ux in toluene, heating isomeric cis-[Fe-2(CO)(4)(mu-PhC=CH2)(mu-PPh2)(mu-dp pm)] (7) results in formation of the 5-electron mu-acyl complex [Fe-2(CO)(3 )][(mu-O=C-C(Ph)-CH2)(mu-dppm)(mu-PPh2)]) (8); also prepared upon heating 3 . Crystal structures have been carried out on 3e and 5. (C) 1999 Elsevier S cience S.A. All rights reserved.