RC CH Research Articles

Metalsilicon bonded compounds : XV. The reactions of (LiSiMe 3) 6 and (LiSiMe 3) 2·(TMEDA) 3 with aromatic substrates

(LiSiMe 3) 6 (I) reacts with tetramethylethylenediamine (TMEDA) to yield the crystalline product (LiSiMe 3) 2 · (TMEDA) 3 (II). The reactions of I and II with simple aromatic and unsaturated compounds have been examined. I reacts with derivatives containing acidic protons including RCCH and fluorene in a fashion similar to organolithium derivatives, yielding simple metalated products and Me 3SiH. II also reacts with these derivatives to give the metalated products but with benzene it yields trimethylphenylsilyl and LiH quantitatively. With toluene and other methylated benzenes II attacks the methyl substituent and LiH and the trimethylsilylmethyl-substituted benzene derivatives are produced. A possible mechanism for this reaction has been proposed.

Investigation of the factors controlling the regioselectivity of the hydrosilylation of alkynes catalysed by trans-di-μ-hydridobis(tricylcohexylphosphine)bis(silyl)diplatinum complexes

The hydrosilylation of terminal and internal alkynes and also of some hydroxy-alkynes catalysed by trans-di-μ-hydridobis(tricyclohexylphosphine)bis(silyl)diplatinum complexes is described. These diplatinum complexes are very efficient catalysts for such hydrosilylations; high yields (80–98%) can be obtained under mild conditions with a catalysts/reactant ratio of 10 −4–10 −5/1. Addition of hydrosilanes X 3SiH to the alkynes RCCH, RCCR and RCCR′ proceeds in a cis fashion yielding trans-RCHCHSiX 3, cis-RC(SiX 3)CHR and mixtures of the regioisomers E-RC(SiX 3)CHR′ and E-RCHC(SiX 3)R′ respectively. In the case of terminal alkynes, minor amounts of internal adducts corresponding to Markownikow addition of the hydrosilanes are also formed. The effects of variation of the reaction conditions (concentration of reactants or catalyst and temperature) upon the rate and regioselectivity of the addition were assessed. The regioselectivity increases as the asymmetry of the electron density of the acetylenic π-bonds increases; the regioselectivity is explained in terms of a qualitative molecular orbital treatment of the transition state formed in the insertion step of the alkyne into the PtH bond.

Polymerization of acetylene and its monosubstitutes in the presence of halides and oxohalides of molybdenum and tungsten

AbstractMoCl5, WCl6, and OMoCl4 were found to be effective initiators for the polymerization of acetylene and its monosubstituted derivatives RCCH. The polymerization proceeded in homogeneous and heterogeneous media and was carried out in nonpolar (chloroalkanes, aromatic hydrocarbons) and polar (THF, acetone, dioxane, carboxylic acids) solvents to give a high yield of polymers.

Photochemical [2+2]-cycloaddition of cyclic α,β-enones to monosubstitüted acetylenes

The photo addition of cyclic α,β-enones to monosubstituted acetylenes gives substituted bicyclo [3,2,0]hept-6-en-2-ones and bicyclo[4,2,0]oct-7-en-2-ones. The addition of 2-cyclopentenone to different substrates of type RCCH (where R is alkyl, CH2X, OEt, COOMe and also Ph) and addition of 2-cyclohexenones to 1-hexyne show a linear correlation between the σ-constants of substituents and the rates of cycloaddition. The reaction can be qualified as a moderately electrophilic attack of the enone triplet on the acetylenic bond (¦ϱ¦~1.5). Temperature and solvent effects on the rates and regioselectivity were also studied. The regioselectivity of addition of these α, β,-unsaturated ketones to 1-alkynes does not correspond to what might be expected on the basis of Corey's orientation rule. The addition of 2-cyclopentenone to ethoxyacetylene 3g and to methyl propiolate3h proceeds with surprisingly low regioselectivity while phenylacetylene 3i undergoes only dimerization under photoannelation conditions.

Alcynes a partir de chlorures d'acide et de Na 2W(CO) 5

Na 2 reacts with acid chlorides RCH 2COCI to yield after hydrolysis noralkanes RCH 3 and alkynes RCCH.

Preparation and properties of methylbis[1,2-bis(diphenylphosphino)ethane]cobalt(I)

Reaction of cobalt(III) acetylacetonate with dimethylaluminum monoethoxide in the presence of 1,2-bis(diphenylphosphino)ethane (dpe) gives methylbis[1,2-bis(diphenylphosphino)ethane]cobalt(I), CoCH 3(dpe) 2 (I), which was characterized by elemental analysis, chemical reactions, IR and NMR spectra. The cobalt—carbon bond in I is cleaved by a protic acid with liberation of methane. The reaction of I with D 2 liberated CH 3D as a sole gaseous product and afforded CoD(dpe) 2. Insertion of carbon monoxide into the cobalt—carbon bond under mild conditions gave an acetylcobalt complex, Co(COCH 3)(CO) 2(dpe). sol1 2 Et 2O. Cobalt(I) acetylides, RCCCo(dpe) 2 (R = Me, Ph) were obtained by the reaction of I with RCCH.

The synthesis of binuclear iron carbonyl complexes with dimethylaminoallyl ligand

Binuclear iron carbonyl complexes with a common aminoallyl ligand were obtained by reaction of iminoester salts [RCH=CHC(OEt)NMe 2] +BF − 4, or their tetracarbonyliron π-complexes [π-RCH=CHC(OEt)NMe 2Fe(CO) 4] +BF 4 −, with Fe 3(CO) 12. Apart from these unsaturated amides, β-aminovinylketone ethylation products [RC(OEt)CH=CHNMe 2] +BF 4 − or a mixture of the β-aminovinylketone with an alkylating agent may also be used.

Synthese nouvelle d'alcynes α-silicies

In the presence of catalytic amounts of copper(I) chloride, and at 150° in an autoclave methylchlorosilanes Me 4 SiCl 4- n ( n = 1,2,3) react with terminal alkynes RCCH (R = n-Bu, Ph) leading to the corresponding alkynylmethyl-chlorosilanes, RCCSiMe 4 Cl 3- n , in good yields.

Homogeneous catalysis : II. ziegler systems as catalysts for hydrosilylation

Ziegler type systems, e.g., M(acac) n —AlEt 3 (M = Ni, Co, or Fe) catalyse the hydrosilylation of 1,3-dienes or terminal acetylenes. With isoprene or 1,3-pentadiene the 1,4-adducts CH 3CHC(CH 3)CH 2SiX 3 or CH 3 CH 2 CH 2 CHCHCH 2SiX 3 are the major products, and Ni salts [NiCl 2 or Ni(acac) 2] provide the best catalysts. For 1,3-pentadiene and HSi(OR) 3 a significant by-product is CH 3 CH CHCH(SiX 3)CH 3, the formation of which is suppressed by addition of phosphines. A chain-reaction mechanism consistent with these results involves the formation successively of a Ni o complex, its oxidative adduct L(diene)Ni(H)SiX 3, a π-allyl complex L(π-allyl)NiSiX 3, isomeric σ-pentenyl derivatives, and (I)-(III) + the Ni o complex. Terminal acetylenes RC yield the products in which linear dimerisation accompanies hydrosilylation. The head-to-head adduct H 2 CC(R)C(R)(SiX 3 preponderates over the head-to-tail isomer R(H)C C(H)C(R)CH(SiX 3); structures of the former were established by IR and NMR studies and examination of the Diels—Alder adducts with tetracyanoethylene, including comparisons with results on RCCD. The catalytic cycle is believed to be similar to that proposed for 1,3-dienes; the linear dimerisaiton arising from successive insertion of RCCH into the Ni and NiC [in NiC(R) Ch 2] bond. Competition experiments demonstrate that hydrosilylation is favoured by electronegative substituents X at Si, and that terminal acetylenes are more reactive than 1,3-dienes. Bis(π-1,5-cyclooctadiene)nickel(O) is also shown to be an effective hydrosilylation catalyst for 1,3-pentadiene.

Étude par rmn de l'influence des solvants et de la température sur l'équilibre cis-trans d'énaminocétones et d'énaminothiones. marquage à l'azote-15

The enaminoketone-enolimine tautomeric equilibrium is studied by nmr spectroscopy in RC(A)CHCHNHR' (A = O, S). Chemical shifts and spin coupling considerations in 15 N-labelled compounds speak in favour of the existence of a major chelated enaminoketone or -thione structure. Basic solvents with high dielectric constant induce breaking of the chelated bridge and promote a second form for which the olefinic two-proton double bond is trans.