Bernard J. L. Henner

Mechanism of nucleophilic substitution at silicon: kinetic evidence on the slow formation of a pentacoordinate silicon intermediate

Abstract Kinetic studies of various coupling reactions between silicon derivatives (SiF, SiCl, SiOMe, SiH) and organometallic reagents (RMgX, RLi) were performed for systems involving retention and inversion of configuration. The results show that for both stereochemical courses, the rupture of the SiX bond is not the rate determining step. Results are in good agreement with the rate determining formation of a pentacoordinate silicon intermediate.

A general route to five-coordinate hydridosilicates

Abstract Five-coodinate potassium hydridosilicates, [HSi(OR) 4 ] − K + (R  Et, i-Pr, Ph), have been obtained in good yield from the reaction of a trialkoxy- or triarylox-silane with the corresponding potassium alkoxide or aryloxide, and characterized spectroscopically. Reaction of the hydrosilicates with an excess of Grignard reagent gives the corresponding triorganosilanes.

Pentavalent hydridosilicates: some aspects of the reactivity of potassium tetraethoxyhydridosilicate

Abstract Some reactions of the pentacoordinate tetraethoxyhydridosilicate, [HSi(OEt) 4 ] − , are reported. The ready reduction of ketones and aldehydes in the absence of a catalyst indicates the high reactivity of the SiH bond in this compound which also readily shows good one electron transfers to an appropriate substrate.

An organometallic route to zinc phosphonates and their intercalates

An organometallic non-aqueous route to zinc phosphonates and to their intercalates has been studied. Various phosphonic acids react with dimethylzinc in THF media to afford the corresponding layered zinc phosphonates Zn(O 3 PR 1 ) (R 1 = Me, Ph, 2- and 3-thienyl, thiophen-3-ylmethyl) with evolution of methane. The presence of a primary n-alkylamine in the reaction mixture allows the one-pot formation of 2D-layered intercalated phases of general formula Zn(O 3 PR 1 )·RNH 2 [R 2 = Bu n , Pen n (= n-pentyl)] whereas a more bulky amine such as cyclohexylamine (Hex c NH 2 ) lead to the formation of 1D polymeric chains of formula Zn(O 3 PPh)·2Hex c NH 2 .

Five-coordinate potassium dihydridosilicates: synthesis and some aspects of their reactivity

Abstract Five-coordinate potassium dihydridosilicates, K+[H2Si(OR)3]− (R = Et, i-Pr) have been obtained by reaction of a trialkoxysilane with potassium hydride. Reaction of the dihydridosilicate with an excess of a Grignard reagent gives the corresponding diorganosilane. The ease of reduction of carbonyl compounds by the dihydridosilicate in the absence of a catalyst is indicative of the high reactivity of the SiH bond in such species.

The mechanism of nucleophilic substitution at silicon: solvent influence on the rates of organometallicorganosilane coupling reactions

Kinetic studies of coupling reactions of Grignard reagents with organosilane derivatives (SiF, SiOMe) in ether, tetrahydrofuran and dimethoxyethane show that the rate increases in the order Et2O < THF < DME. The retention of configuration at silicon in these reactions cannot be explained by the SNiSi mechanism involving electrophilic assistance at silicon.

Synthesis and crystal structure of chiral chlorotris(carbonylmetallato)tin(IV) complexes

Abstract The complexes [Cp(CO) 2 Fe][Cp(CO)Mo[(CO) 4 Co]SnCl (I) (Cp  η 5 -C 5 H 5 ) and [Cp(CO) 3 Mo][Cp(CO) 2 Fe][(CO) 4 Co]SnCl (II) were prepared by the reaction of [Cp(CO) 2 Fe][Cp(CO)Ni]SnCl 2 , or [Cp(CO) 3 Mo][Cp(CO) 2 Fe]SnCl 2 with Co 2 (CO) 8 or TICo(CO) 4 . A single crystal X-ray structural determination shows I to have an almost perfect tetrahedral-geometrahedral around the Sn atom.

Poly[(silylene)diacetylene]/fine metal oxide powder dispersions : Use as precursors to silicon-based composite ceramics

A synthetic route to silicon-based composite ceramics that employs organosilicon polymer/metal oxide precursors is described. The precursor materials were obtained by dispersing metal oxides in the poly[(silylene)diacetylenes] 1. Subsequent pyrolysis of the dispersions above 1400 °C under various experimental conditions afforded β-SiC-based metal carbides and metal nitrides, metal silicides and Si3N4-based composites of defined compositions, in high ceramic yields. Under atmospheres of argon or of nitrogen, the precursor-to-ceramic conversion involved two critical transformations: i) the thermal cross-linking of 1 leading to an irreversible encapsulation of the oxide particle inside the polymeric matrix and ii) the carbothermal reduction of the oxide constituents by the carbon resulting from the degradation of polymer 1 to produce either the final carbide or the final nitride under the pyrolysis conditions. Moreover, it is shown that the encapsulation of the oxide particles inside a reactive matrix led to the formation of particle-tailored micro-scale reactors in which the reduction process took place with high efficiency.

Electrochemical reduction of transition metal-substituted silicon, germanium and tin derivatives: II. Iron derivatives. Synthesis of distannanes containing Cpc(CO)2Fe groups☆

Abstract The electrochemical reduction of the complexes Cp(CO)2FeER3 (E = Si, Ge, Sn; R = alkyl, aryl) have been studied. The radical anion is formed, followed by rupture of the FeE bond with formation of the Cp2(CO)2Fe− anion. As expected, the relative ease of reduction of these derivatives was in the order Sn > Ge > Si. Some other complexes having SnFe and SnCl bonds have been studied: i.e. [Cp(CO)2Fe]nPh−nSnCl (n = 0–3), [Cp(CO)2Fe]2SnCl2. The exhaustive electrolysis of these derivatives provided the synthesis of four new distannanes, substituted with Cp(CO)2Fe groups.

Methylidyne tricobalt nonacarbonyl clusters; optically active silicon and germanium derivatives, and substitutions at silicon

Abstract The preparation and alcoholysis of chiral chlorosilanes containing the nonacarbonyltricobaltcarbon cluster, RR′Si(Cl)CCo3(CO)9, is described. The alkoxy derivatives react with i-Bu2AlH or BF3 · Et2O to give the corresponding silicon hydride or fluoride. Reaction of methylidynetricobalt nonacarbonyl with optically active silanes of germane gave the optically active cluster complexes R1R2R3M*CCo3(CO)9 (M* = Si, Ge). These compounds react with phosphine to give the monosubstituted R1R2R3M*CCo3(CO)8(PR3 (M* = Si, Ge). The diastereomers have been resolved in the case of the MePhSi (Obornyl) CCo3(CO)9 complex.