Allyl and carbonyl complexes of the groups VI and VII transition metals.

Abstract

The contents of this thesis fall naturally into four sections which form the subjects of Chapter 2-5- Chapter 1 comprises a general introduction and literature survey of the most relevant areas. In Chapter 2 the preparation and characterisation of a series of carbonylmetallate anions fac-[MX(CO)3L2]- where M = Mo or W, X = Cl, Br or I and L2 = 1, 10-phenanthroline or 2, 2'-bipyridine from the corresponding cis- [M(CO)4L2] complexes is described. Solution infrared studies indicated that these complexes do not isomerise to the mer-isomers as suggested previously, but are solvolysed in acetonitrile with the formation of fac-[M(CO)3L2(MeCN)]. Reaction of the anions with various allyl halides resulted in high yields of the n3-allyl complexes [(n3-RC3H4)MX(CO)2L2]. The significance of these observations for the mechanism of the allyl oxidative-addition reaction is discussed. Reactions between Mn(CO)5X and Et4NX (X = Cl, Br) in boiling chloroform and between Re(CO)5X and Et4 NK (X = Cl, Br, I) in boiling decalin are described in Chapter 3. The final products are the compounds Et4N[M2(CO)6(?-X)3]. Vibrational spectroscopic results indicate that the anions possess confacial bi-octahedral geometry with three bridging halogen atoms. The anions did not react with allyl halides to give n3-allyl derivatives. Details of the preparation of [(n1-C3H5)Re(CO)5] from [Re(CO)5]- and its photo-decarbonylation to [(n3-C3H5)Re(CO)4] are presented in Chapter 4. Both allyl complexes have been characterised using 1H NMR, mass spectrometry and particularly liquid-phase infrared and Raman spectroscopies. Although the vibrations of the Re(CO)5 unit in the n1-allyl compound can be assigned in terms of C4v symmetry, such a local symmetry approximation has been found to be invalid for the n3-allyl compound whose vibrational spectrum requires discussion in terms of the overall Cs symmetry. The n1- and n3- allyl internal modes are discussed in terms of Cs symmetry. For comparative purposes the methyl derivatives [MeRe(CO)5] (Me = 12CH3, 13CH3, 12CD3) have also been synthesised and their mass and vibrational spectra studied. In Chapter 5 some carbonyl substitution reactions of [(n3-C3H5)M(CO)4] (M = Mn, Re) are reported. The use of thermal or photolytic methods has allowed the synthesis of the complexes [(n3-C3H5)M(CO)3L], (M = Mn, L = PPh3, AsPh3, PCy3, PBun3, PMePh2); M = Re, L = PPh3) and [(n3-C3H5)M(CO)2L2], (M = Mn, L = PMePh2, P(OMe)3, P(OEt)3, 1/2Ph2PCH2PPh2; M = Re, L = PPh3). These complexes are considered to possess pseudo-octahedral structures, the carbonyl ligands being facial in the tricarbonyls and cis in the dicarbonyls. The 1H NMR spectra are characteristic of symmetrical n3-allyl species and show strong 1H-31P coupling. Mass spectra have been obtained and fragmentation pathways suggested mainly on the basis of observed metastable peaks. A single crystal X-ray structure determination has been carried out on the complex [(n3-C3H5)Mn(CO)2{lcub}P(OMe)3{rcub}2]. 1742 independent reflections above background have been collected and refined to R = 0.059. Considering the n3-allyl group to occupy two coordination sites, the metal has a distorted octahedral environment being bonded to two mutually trans- phosphorus atoms 2.175(5), 2.219(5) A, two cis- carbonyl groups 1.75(2), 1.83(2) A and a n3-allyl ligand with Mn-C 2.223(17), 2.114(14), 2.229(13) A. Appendices 1 - 5 contain details of experimental methods, starting materials, group theory, secular equations and computer programmes used in this work. Appendix 6 lists the structure factors and thermal parameters associated with the crystal structure determination.

Date of Award	1979
Original language	English
Awarding Institution	University of Bath