Fluorocarbon Complexes of the Transition Metals

Davidson, John L (1973) Fluorocarbon Complexes of the Transition Metals. PhD thesis, University of Glasgow.

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Abstract

Reactions of transition metal carbonyl and cyclopentadienyl complexes with disulphides and acetylenes bearing fluorocarbon substituents have been investigated. Photolytic reactions of disulphides RSSR, R = CF3, C6F5 are considered to proceed via RS radicals and with dimeric complexes monomers have been obtained e. g. [CpMo(CO)3]2 -RS→CpMo(CO)3SR Use of closed reaction systems has enabled the identification of thermally unstable compounds such as Mn(CO)5SCF3 and CpNi(CO)SR which decarbonylate readily in an open system to di-or polymeric mercapto bridged complexes e.g. 2Mn(CO)5SCF3→ [Mn(CO)4SCF3]2 + 2C0 The dimers in many cases exhibit isomerism due to inversion at sulphur and this has been studied by i.r. and n.m.r. spectroscopy. The photolytic reactions of disulphides and monomeric carbonyls e. g. Fe(CO)5, Mo(CO)6, gave dimeric mercapto-bridged compounds directly, e.g. [Fe(CO)3SCF3]2 [Mo(CO)4SCF3]2, but in the absence of u. v. light CpCo(CO)2 and C6F5SSC5F4 gave CpCo(CO)(SC6F5)2 which can be decarbonylated to [CpCoSC6F5]2, illustrating that monomeric carbonyls can react with disulphides to give sulphur bridged dimers via an oxidative addition reaction. Possible mechanisms of these reactions and steric and electronic effects of the substituent on sulphur are discussed. Reactions of these organothic derivatives with acetylenes CF3C=CCF3 and CF3C=CH gave a variety of novel complexes. Complexes CrMo(CO)3SCF3, M = Mo, W,were observed to undergo CO substitution by CF3C2CF3 to give CpM(C0)2(CF3C2CF3)SCF3, the variable temperature n.m.r. spectra of which have been interpreted in terms of restricted rotation of the SCF3, ligand. Similar complexes were obtained with CH3C=CCH3 and PhC=CPh. In contrast CpMo(CO)3SCF3 and CF3C=CH gave the cyclopentadienone derivative CpMo(CO)[ (CF3C2H)2CO]SCF3 which was photochemically decarbonylated to [CpMo[(CF3C2H)2CO]SCF3]2. Insertion of CF3C=CCF3 into the Mn-S bond of [Mn(CO)4SC6F5]2 gave Mn(CO)4C(CF3)=C(CF3)SC6F5 while CF3C=CH gave Mn(CO)4(CF3C2H)2SC6F5. With excess acetylene the former yielded Mn(CO)3[C4(CF3)4SC6F5] which has been shown by X-ray studies to contain a non-planar heterocyclic sulphonium ion [C4(CF3)4SC6F5] bonded to an Mn(CO)3 species. Several other examples of acetylene insertion into M-S bonds were observed but with [Fe(CO)3SR]2 insertion into the Fe-Fe bond gave complexes [Fe(CO)3SR]2CF3C2R' , R'= CF3, H. X-ray studies of [Fe(CO)3SCF3]2CF3C2CF3 have revealed that this results in a significant change in the Fe2S2 ring geometry which allows the formation of the syn (axial, axial) isomer not observed in the parent complexes. [CpCoSR]2 and CF3C=CCF3 in contrast gave CpCoC6(CF3)6 containing a tetrahapto hexakis(trifluoromethyl)benzene ligand. Attempts have been made to rationalise the various reaction types in terms of the properties of possible reaction intermediates. Reactions of certain cyclopentadienyl-nickel complexes with hexa-fluorobut-2-yne gave products resulting from condensation of the acetylene and a cyclopentadienyl ligand, e. g. Cp2Ni + CF3C=CCF3-->CpNi[(C5H5)C4(CF3)4] while in other cases cyclooligomerisation of the acetylene was observed. These reactions have been rationalised in terms of acetylene coordination promoting a pi-d rearrangement of a cyclopentadienyl ligand. Several complexes were isolated in which a pi-cyclopentadienyl ligand appears to have been replaced by a nickelacyclopentadiene ring, CpNiC4(CF3)4, e.g. Cp2Ni3C6(CF3)6, CpNi2[C4(CF3)4(C5H5)C2F3Cl] and [C5H5NiC2(CF3)2]4. The crystal structure of the last has been solved and suggests that the molecule is formed by a Diels-Alder addition of the nickelacyclopentadiene ring of a dinuclear intermediate [CpNiC2(CF3)2]2 to the 1,2 positions of a cyclopentadienyl ring of a second dimeric species. The reactions of CpMo(CO)3X, X = Cl, Br, I, with acetylenes . RC=CR, R = CF3, CH3, have been found to give sixteen electron molybdenum complexes CpMo(RC2R)2X and with R = CH3 tetramethylquinone was also obtained. Variable temperature n.m.r. studies suggest that the coordinated acetylenes undergo an intramolecular exchange reaction at temperatures above -25C, R = CF3, +15C, R = CH3 CpMo(CO)3X and PhC=CPh gave sixteen electron complexes CpMo(C0)(PhC2Ph)X at low temperatures (< 50 C) or on photolysis in pentane. At higher temperatures the tetraphenylcyclobutadiene derivatives CpMo(CO)(PhC)4X were obtained. Brief studies of reactions of acetylenes with transition metal trifluorophosphine complexes suggest that in certain cases the latter react in a similar manner to analogous carbonyl derivatives. CpCo(PF3)2 and CF3C=CCF3 gave CpCo[C4(CF3)4PF3] according to mass spectral evidence and this undergoes stepwise hydrolysis to [CpCoC4(CF3)4PO2H] via CpCo[C4(CF3)4POF]. An X-ray study of the terminal hydrolysis product has revealed a structure containing a heterocyclic P(v) ring pi-bonded to a cyclopentadienyl-cobalt moiety. This is analogous to CpCo[C4(CF3)4CO] obtained from the reaction of CpCo(CO)2 ana CF3C=CCF3.

Item Type: Thesis (PhD)
Qualification Level: Doctoral
Keywords: Organic chemistry
Date of Award: 1973
Depositing User: Enlighten Team
Unique ID: glathesis:1973-78642
Copyright: Copyright of this thesis is held by the author.
Date Deposited: 30 Jan 2020 15:06
Last Modified: 30 Jan 2020 15:06
URI: http://theses.gla.ac.uk/id/eprint/78642

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