Organometallic Aggregates. 1. Structural Data Anne Harrison-Marchand*,† and Florence Mongin*,‡ †Laboratoire COBRA de l′Universite ́ de Rouen, INSA de Rouen, CNRS, UMR 6014 & FR 3038, IRCOF, Rue Tesnier̀e, 76821 Mont St Aignan Ced́ex, France ‡Équipe Chimie et Photonique Molećulaires, Institut des Sciences Chimiques de Rennes, UMR 6226 CNRS-Universite ́ de Rennes 1, Bat̂iment 10A, case 1003, Avenue du Geńeŕal Leclerc, 35042 Rennes Ced́ex, France

Mixed AggregAte (MAA): A Single Concept for All Dipolar Organometallic Aggregates. 1. Structural Data

Publisher Summary Since the metal alkoxidesM(OR), were first comprehensively reviewed in 1960 , considerable progress has been maintained and the next major review in 1967 quoted over three hundred references. The most significant advances have involved the chemistry of the transition metal alkoxides with the emphasis on the ligand field aspects of the alkoxo group (e.g., electronic spectra, magnetism, etc.) and on X-ray crystallographic and NMR structural determinations. Industrial applications have been concerned with metal alkoxides as components of soluble Ziegler-Natta catalysts for olefin polymerization and also as sources for the production of pure metal oxides. The metal dialkylamides M(NR,) are of special interest, in that they contain covalent metal-nitrogen bonds, and occupy a position between the metal alkoxides and the metal alkyls. The field has not been fully reviewed, hitherto. However, excellent reviews have recently appeared on titanium dialkylamides and the reactivity of metal-dialkylamido bonds.

Metal alkoxides and dialkylamides

An Approach to Pin Down the Solid-State Structure of the “Turbo Grignard”

In this chapter the focus is primarily on the recent structural work concerning carbanions of alkali and alkaline earth cations that are widely utilized in synthetic organic chemistry. In this context the year 1981 is significant because the first detailed X-ray diffraction analyses of two lithium enolates of simple ketones, i.e. 3,3-dimethyl-2-butanone and cyclopentanone, were published.1 Since 1981 a number of detailed X-ray diffraction analyses of synthetically useful enolate anions of alkali and alkaline earth cations have been described. Within this chapter, many recent structural characterizations will be examined with the overall goal of collating this new information especially as it pertains to increasing our knowledge and control over the reactivity of these most useful and important synthetic reagents. The chapter is organized by functional group because this classification is quite natural to synthetic chemists. The examples chosen have come to my attention while thinking about the role of these species in synthetic reactions. It is neither practical nor feasible to include in this chapter an exhaustive review of all structural characterizations of carbanions of alkali and alkaline earth cations.2 Should the complete list of all such structures be required, a comprehensive search of the Cambridge Structural Database (CSD) is recommended.3 Throughout this chapter structural references are given to six letter CSD reference codes as follows, (XXXXXX). These refcodes will assist in obtaining crystallographic coordinates directly from the CSD.

1.1 – Carbanions of Alkali and Alkaline Earth Cations: (i) Synthesis and Structural Characterization

4 – Magnesium, Calcium, Strontium and Barium

Several alkylmagnesium alkoxides have been prepared by alcoholysis of the dialkyls in diethyl ether, and can be obtained free from ether. In benzene, EtMgOPrn, PriMgOMe, and PriMgOEt are oligomers (degrees of association ca. 8), but those alkoxides we have studied in which there is chain-branching α to oxygen are tetramers, (EtMgOPri)4, (EtMgOBut)4, and (PriMgOPri)4. The 3-ethyl-pentan-3-ol derivative, from Et2Mg + Et2COor Et2Mg + Et3COH, crystallises as an ether complex (EtMgOCEt3,Et2O) which loses ether very readily: the tetrahydrofuran adduct is dimeric in benzene (EtMgOCEt3,THF)2. Some alkylmagnesium alkoxides are tetramers in diethyl ether, (EtMgOEt)4, (MeMgOBut)4, and (EtMgOBut)4, but two are dimers, (EtMgOCMeEt2)2 and (EtMgOCEt3)2. Methylmagnesium t-butoxide disproportionates in dilute solution in benzene. Both dimethyl-magnesium and ethylmagnesium ethoxide crystallise from diethyl ether at room temperature without solvent of crystallisation.The diethyl ether complex of t-butoxymagnesium bromide crystallises from the solution obtained when acetone is added to methylmagnesium bromide in ether. It is a dimer, (ButOMgBr,EtO)2, both in benzene and in ether and in the crystalline state. Several analogous products have been obtained by other similar reactions, and all those whose molecular weights were measured were also dimeric (solvent given) examples are (ButOMgBr,THF)2(benzene), (Et3COMgBr,THF)2(benzene), (Et2MeCOMgBr,Et2O)2(ether), (Et2MeCOMgl,Et2O)2(ether), (Me2PrnCOMgl,Et2O)2(ether), t-Butoxymagnesium bromide-diethyl ether complex has also been prepared from magnesium bromide and both Mg(OBut)2 and MeMgOBut. The 1H n.m.r. spectra of several of the compounds described are anomalous in unexplained ways.

D. Ridley

Papers

Some alkylmagnesium alkoxides and reaction products from Grignard reagents and carbonyl compounds