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1,4 addition of electrophilic acetylenes to group VIII metal beta-ketoenolates.

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posted on 19.11.2015, 08:45 authored by Alan Charles. Jarvis
Chapter 1 presents a review on the structure and reactivity of Beta-diketonate metal chelates. In chapter 2 the reaction of various rhodium(I) and iridium(I) Beta-ketoenolates with the electrophilic acetylenes hexafluorobut-2-yne and dimethylacetylenedicarboxylate are described. Complexes of the type Rh(cod) (Beta-ketoenolate), which contain electron-donating substituents on the metal Beta-ketoenolate ring, react with C4F6 to give complexes in which the fluorocarbon adds 1,4 to the rhodium(I) (Beta-ketoenolate) ring. Also the hexafluorobut-2-yne is trimerised to hexakis (trifluoromethyl) benzene which remains co-ordinated to the rhodium so that the diene ligand is displaced. Similar 1,4 addition adducts are isolated from the reaction of C4F6 with complexes of the type Rh(olefin)2(Beta-ketoenolate), although Rh(C2H4)2(dpm) reacts with this acetylene to form a 1,4 addition adduct which contains a 1,2,3,4-tetrakistrifluoromethylcyclohexa-1,3-diene ligand. 3,3,3-trifluoropropyne is polymerised in similar reactions. Compounds of the type Rh(C2F4)(L)(dpm) where L = AsPh3 or SbPh3 react with the acetylenes hexafluorobut-2-yne, dimethylacetylenedicarboxylate and dimethylacetylenedicarboxylate to give metallocyclopentadienes of the type Rh(C4R4)(L)(dpm). Dipivaloylmethanatodicarbonylrhodium(I) reacts with hexafluoro- but-2-yne and dimethylacetylenedicarboxylate to give dinuclear adducts which contain two units formed by the acetylene adding 1,4 to the metal chelate ring, two carbonyl ligands and a bridging o-bonded acetylene ligand. Hexafluorobut-2-yne reacts with Ir(cod)(acac) and Ir(cod)(dpm) to give an iridiacyclopentene complex in which the acetylene has also added 1,4 to the iridium Beta-ketoenolate ring. In contrast, hexafluorobut-2-yne adds 1,4 to the co-ordinated cyclo-octa-1,5-diene in [Rh(cod)C1]2. Chapter 3 contains the results of some investigations into the reactivity of some palladium(II) Beta-ketoenolate complexes towards hexafluorobut-2-yne and dimethylacetylenedicarboxylate. Hexafluoro-but-2-yne reacts with bis(acetylacetonato)palladium(II) to give the complex Pd[-O=C(CH3)CH(COCH3)C(CF3)=C(CF3)]2 in which the acetylene links the y-CH of the Beta-diketonato ligands to the palladium. Similar reaction does not occur with dimethylacetylenedicarboxylate. The preparation and spectroscopic properties of some complexes of the type (N,N-dimethylbenzylamine-2C,N)palladium( B-ketoenolate) are described together with their reaction toward the acetylenes C4F6 and CH3O2CC=CCO2CH3. In general, complexes of the type Pd(dmba)(Beta-ketoenolate) containing electron-donating substituents on the metal Beta-ketoenolate ring react with these acetylenes to give square planar complexes in which the acetylene links the y-CH of the Beta-diketonate to the metal, whilst Beta-ketoenolates containing electron withdrawing substituents on the ring induce the acetylenes to insert into the palladium carbon bond of the orthometallated amine. The spectroscopic properties of these insertion products are discussed. Chapter 4 discusses the preparation of the fluoro-olefin complexes Rh(dpm)(C2H4)(CF2=CFX) where X = F, CF3, C1 or Br. Reaction of these complexes with triphenyl-phosphine, -arsine or -stibine results in displacement of ethylene and the formation of complexes of the type Rh(dpm)(CF2=CFX)L. 19F n.m.r. studies on these complexes are consistent with structures in which the substituent X in these compounds is in an outside position with respect to the ethylene or ligand L.


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University of Leicester

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