Organometallic compound: functional

Regioselectivity of C—C double bond formation can also be achieved in the reductiv or oxidative elimination of two functional groups from adjacent carbon atoms. Well estab llshed methods in synthesis include the reductive cleavage of cyclic thionocarbonates derivec from glycols (E.J. Corey, 1968 C W. Hartmann, 1972), the reduction of epoxides with Zn/Nal or of dihalides with metals, organometallic compounds, or Nal/acetone (seep.lS6f), and the oxidative decarboxylation of 1,2-dicarboxylic acids (C.A. Grob, 1958 S. Masamune, 1966 R.A. Sheldon, 1972) or their r-butyl peresters (E.N. Cain, 1969). 

For reviews of the addition of organometallic compounds to carbonyl groups, see Eicher, T. in Patai, Ref. 2, p. 621 Kharasch, M.S. Reinmuth, O. Grignard Reactions of Nonmetallic Substances, Prentice-Hall Englewood Cliffs, NJ, 1954, p. 138. For a review of reagents that extend carbon chains by three carbons, with some functionality at the new terminus, see Stowell, J.C. Chem. Rev., 1984, 84, 409. 

Indeed, these reactions proceed at 25 °C in ethanol-aqueous media in the absence of transition metal catalysts. The ease with which P-H bonds in primary phosphines can be converted to P-C bonds, as shown in Schemes 9 and 10, demonstrates the importance of primary phosphines in the design and development of novel organophosphorus compounds. In particular, functionalized hydroxymethyl phosphines have become ubiquitous in the development of water-soluble transition metal/organometallic compounds for potential applications in biphasic aqueous-organic catalysis and also in transition metal based pharmaceutical development [53-62]. Extensive investigations on the coordination chemistry of hydroxymethyl phosphines have demonstrated unique stereospe-cific and kinetic propensity of this class of water-soluble phosphines [53-62]. Representative examples outlined in Fig. 4, depict bidentate and multidentate coordination modes and the unique kinetic propensity to stabilize various oxidation states of metal centers, such as Re( V), Rh(III), Pt(II) and Au(I), in aqueous media [53 - 62]. Therefore, the importance of functionalized primary phosphines in the development of multidentate water-soluble phosphines cannot be overemphasized. 

Studies of the effects of low frequency ultrasonic waves on a broad range of synthetically useful reactions are summarized. Discussion is centered on the results obtained in our laboratory where we have concentrated on the reactions of metals with functionalized organic and organometallic compounds. Special emphasis is on lithium and zinc with organic and organosilicon halides. 

The chemistry of coordination compounds comprises an area of chemistry that spans the entire spectrum from theoretical work on bonding to the synthesis of organometallic compounds. The essential feature of coordination compounds is that they involve coordinate bonds between Lewis acids and bases. Metal atoms or ions function as the Lewis acids, and the range of Lewis bases (electron pair donors) can include almost any species that has one or more unshared pairs of electrons. Electron pair donors include neutral molecules such as H20, NH3, CO, phosphines, pyridine, N2, 02, H2, and ethyl-enediamine, (H2NCH2CH2NH2). Most anions, such as OH-, Cl-, C2042-, and 11, contain unshared pairs of electrons that can be donated to Lewis acids to form coordinate bonds. The scope of coordination chemistry is indeed very broad and interdisciplinary. 

The main purpose of these final comments is to show a few general trends in the thermochemistry of Group 14 organometallic compounds, helped by some (hopefully) reliable values. And one of the trends is revealed by a rather usual plot1,2, in which the mean bond dissociation enthalpies of the species MR4 (i.e. one-fourth of the enthalpy required to break all the M—R bonds) are represented as a function of the enthalpy of formation of M in the gaseous state. As observed in Figure 4, for R = H and Me, D(M—H) and D(M—Me) increase with the enthalpy of formation (or sublimation) of M. It is noted, on the other hand, that the differences D(M—H) — D(M—Me) vary from 47.7 kJmol-1... 

As was the case with the volume The chemistry of organic arsenic, antimony and bismuth compounds, published in 1994, it was clear that the set of five volumes describing organometallic compounds (edited by Professor Frank R. Hartley) did not deal in sufficient depth with organic compounds of germanium, tin and lead. Hence we decided to publish the present volume, which we hope will be a useful and worthwhile addition to the series The Chemistry of Functional Groups. In this volume the authors literature search extended in most cases up to the end of 1994. 

The first chemical transformations carried out with Cjq were reductions. After the pronounced electrophilicity of the fullerenes was recognized, electron transfer reactions with electropositive metals, organometallic compounds, strong organic donor molecules as well as electrochemical and photochemical reductions have been used to prepare fulleride salts respectively fulleride anions. Functionalized fulleride anions and salts have been mostly prepared by reactions with carbanions or by removing the proton from hydrofullerenes. Some of these systems, either functionalized or derived from pristine Cjq, exhibit extraordinary solid-state properties such as superconductivity and molecular ferromagnetism. Fullerides are promising candidates for nonlinear optical materials and may be used for enhanced photoluminescence material. 

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