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Studies on Group Ii Metal Alkyls Particularly Those of Beryllium

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Studies on Group Ii Metal Alkyls Particularly Those of Beryllium Durham E-Theses Studies on group ii metal alkyls particularly those of beryllium Robert, P.D. How to cite: Robert, P.D. (1968) Studies on group ii metal alkyls particularly those of beryllium, Durham theses, Durham University. Available at Durham E-Theses Online: http://etheses.dur.ac.uk/8717/ Use policy The full-text may be used and/or reproduced, and given to third parties in any format or medium, without prior permission or charge, for personal research or study, educational, or not-for-prot purposes provided that: • a full bibliographic reference is made to the original source • a link is made to the metadata record in Durham E-Theses • the full-text is not changed in any way The full-text must not be sold in any format or medium without the formal permission of the copyright holders. Please consult the full Durham E-Theses policy for further details. Academic Support Oce, Durham University, University Oce, Old Elvet, Durham DH1 3HP e-mail: [email protected] Tel: +44 0191 334 6107 http://etheses.dur.ac.uk STUDIES ON GROUP II METAL ALKYLS PARTICULARLY THOSE OF BERYLLIUM by P.D. ROBERTS, B.Sc. A thesis submitted for the Degree of Doctor of Philosophy in the University of Durham JULY 1968 Acknowledgements The author wishes to thank Professor G.E. Coates, M.A. , D.Sc, F.R.I.C., under whose supervision this research was carried out, for his constant encouragement and valuable advice. Thanks are also given to Dr. A.J. Downs, formerly of the University of Newcastle upon Tyne, for his help with vibrational spectroscopy and to members of this department, especially Dr. N.A. Bell, who have taken part in many valuable discussions. The author is indebted to the Scientific Research Council for a Research Studentship. Memorandum The work described in this thesis was carried out in the University of Durham between September 1965 and June 1968. The work has not been submitted for any other degree and is the original work of the author except where acknowledged by reference. Part of the work has been the subject of two publications in the Journal of the Chemical Society, [J.Chem.Soc.A, 1967, 1085; 1967, 1233]. Simimary Analysis of the vibrational spectrum of di-t-butylberyllium in conjunction with the infrared spectrum of the fully deuterated derivative and of di-t-butylzinc suggests that the molecules are monomeric with linear C-M-C skeletons. Assignment of the vibrational frequencies of the heavy atom skeleton has been carried out. Di-t- butylberyllium is monomeric in benzene solution and in the vapour phase. 1:1 Complexes between di-t-butylberyllium and MMe^ (M = N,P) are described. The p.m.r. spectrum of the N,N,N',N'-tetramethylethylene- diamine (TMED) complex, Pr''"2Be(TMED), does not change with temperature, in contrast to that of Bu*^2Se(TMED). The halides BuSeX,0Et2 (X = Cl,Br) are dimeric in benzene, and the chloride is monomeric in diethyl ether. Di-t-butylberylliirai reacts with N,N,N'-trimethylethylenediamine producing a monomeric compound, Bu''BeNMeC2H^NMe2• In contrast, di-n- propyl- and di-isopropyl-beryllium react with the same amine forming dimeric products. The p.m.r. spectrum of the latter is temperature dependent. The complexes BuSeOC2H^NMe2, BuSeSC2H^NMe2, and MeZnSC2H^NMe2 are dimeric in benzene solution. Ether-free beryllium dialkyls (R2Be, R = Et,Pr", Bu", Bu''') can be obtained by a process of prolonged boiling of the ether complexes under reflux at low pressure. All the above ether-free berylliim dialkyls are dimeric in benzene. The proton magnetic resonance spectra (p.m.r.) of some of the beryllium dialkyls are described. In several cases there is a marked temperature and solvent dependence. Pyrolysis of di-t-butylberyllium to the RBeH stage produced a mixture of t-butyl- and isobutyl-beryllium hydrides. Pyrolysis of di-isobutylberyllium resulted in the formation of isobutylberyllium hydride. Some co-ordination complexes of isobutylberyllium are described. A co-ordination complex of berylliim hydride, (H^Be2)TMED, has been prepared. Table of Contents Page Introduction 1-69 Group II Metal Alkyls and their Co-ordination Compounds 5-11 Berylliinn 5 Magnesium 8 Zinc, Cadmium, and Mercury 10 Reactions of Metal Alkyls with Acidic Hydrogen 12-38 Beryllium 13 Zinc 22 . Magnesium 30 Cadmium 37 Mercury 38 Anionic Complexes of the Group II Dialkyls 39 Organometal Halides of Group II 40-41 Hydride Chemistry of Beryllivmi 42-56 Hydride Chemistry of Magnesium 57-60 Hydride Chemistry of Zinc, Cadmium, and Mercury 61-64 Spectroscopic Studies on Organic and Hydride Derivatives of Group II 65-69 Page Experimental Apparatus and Techniques 70-72 Analyses 73-80 Preparation and Purification of Starting Materials 81-89 Reactions of dimethylzinc 90-92 Physical Properties and reactions of di-t-butylberyllium 92-104 Reactions of di-t-butylzinc 104-107 Reactions of di-isopropylberyllium 107-109 Reactions of di-n-propylberyllium 109-112 Ether free diethylberyllium 112 P.m.r. spectra of beryllixm dialkyls 113 Pyrolysis of [2-dimethylaminoethyl(methyl)amino t-butylberyllium] 114 Pyrolysis of di-t-butylberyllium 114-118 Preparation of di-isobutylberyllium 119-122 Pyrolysis of di-isobutylberyllium 122-125 Co-ordination compounds of isobutylberyllium hydride 126-128 Decomposition of di-t-butylberyllium 128-130 Co-ordination compounds of beryllium hydride 130-133 Reactions of isobutylberyllitnn hydride with olefins 133-134 Page Discussion 135-177 The vibrational spectra and molecular structures of di-t- butyl-beryllium and -zinc 135-146 Reactions of di-t-butylberylliinn with bases and weak acids 147-152 Ether free beryllium di-alkyls 153-156 Reactions of zinc dialkyls with weak acids 157-159 P.m.r. spectra of beryllitrai dialkyls 160-164 Hydride chemistry 165- Tables Index INTRODUCTION This thesis is concerned with preparative and structural studies on organic and hydride derivatives of beryllivmi and zinc. The organic compounds of beryllium, calcium, strontium, and barium have been reviewed''' (covering the literature to early 1961), and the co-ordination chemistry of beryllium, zinc and cadmium, and mercury 2 was reviewed in 1966. Organoberyllium compounds have been the subject of a very recent review by Fetter, covering the literature to early 3 1967. This review includes a catalogue of all known organoberyllixim compounds together.with physical properties and preparative details. Organometallic compounds of the main group elements have been the 4 5 subject of a recent book, as have metal hydrogen compounds. This introduction will be concerned with organic and hydride derivatives of beryllium, magnesium, zinc, cadmiimi, and mercury together with relevant work on boron and aluminium. The structural problems of Grignard reagents will not be discussed in this thesis; they have been discussed in two reviews.^The organic derivatives of calcium, strontium, and barium will not be discussed as their organic chemistry, so far as it is known, is more akin to that of the heavier elements of Group I. Preparative methods in organometallic chemistry of these elements are covered in detail in books, earlier theses, and review articles^'^'^ and the relevant literature references can be obtained from them. -2- Preparative aspects are not, therefore, discussed in detail in this introduction. Both beryllium and magnesiim form 'electron-deficient' compounds, these are compounds in which an atom makes use of more orbitals than the number of available valence electrons, resulting in a structure in which the total nimiber of valence electrons is less than twice the number of conventional electron pair bonds. This type of bonding is found in dimethyIberyllitmi and dimethyImagnesium, both of which are poljmieric solids. H3 H3 \ .a / ^3 V H3 H3 M = Be or Mg The crystal structures have been determined by X-ray diffraction and the relevant data are tabulated: Me2Be''"^ Me2Mg^^ M-M 2*09 + O'OIA 2*73 + 0'02A M-C 1*93 + 0*02A 2*24 + 0'03A A CMC 114 + 1 O 10,^r5- +, 2o O MCM 66 +1° 75 + 2° The bonding can be explained in terms of 'three centre' molecular 13 3 3 orbitals formed from metal sp hybrid orbitals and the remaining sp orbital of carbon. The organic compounds of zinc, cadmium, and mercury do not show the same tendency to form electron deficient compounds. The increased size of the metal atom resulting in the non-existence or poor overlap of the relevant orbitals. Hence dimethylzinc, -cadmiian, and -mercury • T -J £ 1 1 . 14,15,16,17 are monomeric liquids of normal covalent structure. Berylliimi compounds are known in which the co-ordination nimber of the metal atom is two, three, or four. Two co-ordinate beryllium is relatively rare. It had been suggested that ether-free di-tert-butyl• beryllium is monomeric on vapour pressure grounds and hence would, be 4 the first example of two-co-ordinate beryllium at room temperature. The only other example of a compound in which two-co-ordinate beryllium is present at room temperature is the silazane derivative, [(Me3Si)2N]2Be, which has been shown, by vibrational and p.m.r. 18 spectroscopy, to have a linear N-Be-N skeleton and planar BeNSi2 groups. -4- Three-co-ordinate beryllium occurs in the dimeric metal alkyls, (R2Be)2, and in the aminoberyllium alkyls, (RBeNR'2)j^ where n = 2 or 3 19 depending on steric considerations. Four-co-ordinate beryllium is most common and is found, for example, in solid dimethylberyllium'''^ and is likely to be present in the tetrameric alkylberyllivmi alkoxides.^^ No organomagnesium compounds are known in which the co-ordination number of the metal is two: generally organomagnesium compounds contain 3 four-co-ordinate magnesium in the sp hybridised state. This co• ordination nimiber is attained either by polymerisation e.g.
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