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Products of the thermal reactions of μ-alkenyl complexes [Fe2(CO)6(μ-R1C=CHR 2)(μ-PPh2)] (1) (a, R1=R2=H; b, R1=EtO, R2=H; c, R1=H, R2=Ph; d, R1=Ph, R2=H; e, R1=R2=Ph; f, R1=CMe=CH2, R2=H), with bis(diphenylphosphino)methane (dppm) are substituent dependent. Complexes 1a-c afford simple substitution products trans-[Fe2(CO)4(μ-alkenyl)(μ-PPh 2)(μ-dppm)] (2a-c); while with 1d,e, α,β-unsaturated acyl complexes trans-[Fe2(CO)4(μ-O=C-C(Ph)=CH(R 2))(μ-PPh2)(μ-dppm)] (3d,e) are the major products formed via a migratory-insertion reaction. A minor product of the reaction with 1d is [Fe2(CO)5(μ-Ph2PC(Ph)=CH 2)(μ-dppm)] (4), the result of phosphorus-carbon bond formation. Reaction of 1f also leads to phosphorus-carbon bond formation together with a 1,4-proton shift giving the μ-alkylidene complex [Fe2(CO)4(μ-HC-C(Me)=C(Me)PPh2)(μ-dppm)] (5). Dppm addition to 1c has been followed in detail, allowing a complete reaction scheme to be developed. Initial carbonyl substitution affords the η1-dppm complex [Fe2(CO)5(η 1-dppm)(μ-HC=CHPh)(μ-PPh2)] (6). This subsequently isomerises to trans-[Fe2(CO)4(μ-O=C-CH=CHPh)(μ-PPh 2)(μ-dppm)] (3c) which then readily loses CO to give the μ-alkenyl 2c. Loss of CO from isomeric 3d occurs only upon prolonged thermolysis and also affords 2c, a result of α,β-alkenyl isomerisation. Further, heating 4 also yields 2c after CO loss, phosphorus-carbon bond cleavage, and alkenyl isomerisation. While the β-substituted phenylethenyl complex 2c is stable to prolonged reflux in toluene, heating isomeric cis-[Fe2(CO)4(μ-PhC=CH2)(μ-PPh 2)(μ-dppm)] (7) results in formation of the 5-electron μ-acyl complex [Fe2(CO)3(μ-O=C-C(Ph)=CH 2)(μ-dppm)(μ-PPh2)] ) (8); also prepared upon heating 4. Crystal structures have been carried out on 3e and 5. © 1999 Elsevier Science S.A.
Author(s): Hogarth G, Shukri K, Doherty S, Carty AJ, Enright GD
Publication type: Article
Publication status: Published
Journal: Inorganica Chimica Acta
Print publication date: 01/08/1999
ISSN (print): 0020-1693
ISSN (electronic): 1873-3255
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