Alkynes : derivatives structure

The diamagnetic ylide complexes 34 have been obtained from the reaction of electron-deficient complexes [MoH(SR)3(PMePh2)] and alkynes (HC=CTol for the scheme), via the formal insertion of the latter into the Mo-P bond. The structural data show that 34 corresponds to two different resonance-stabilized ylides forms 34a (a-vinyl form) and 34b (carbene ylide form) (Scheme 17) [73]. Concerning the group 7 recent examples of cis ylide rhenium complexes 36 cis-Me-Re-Me) have been reported from the reaction of the corresponding trans cationic alkyne derivatives 35 with PR" via a nucleophilic attack of this phosphine at the alkyne carbon. 

Liquid crystals based on aliphatic isocyanides and aromatic alkynyls (compounds 16) show enantiotropic nematic phases between 110 and 160 °C. Important reductions in the transition temperatures, mainly in clearing points (<100 °C), areobtained when a branched octyl isocyanide is used. The nematic phase stability is also reduced and the complexes are thermally more stable than derivatives of aliphatic alkynes. Other structural variations such as the introduction of a lateral chlorine atom on one ring of the phenyl benzoate moiety or the use of a branched terminal alkyl chain produce a decrease of the transition temperatures enhancing the formation of enantiotropic nematic phases without decomposition. 

The cytotoxicity of the Co2(CO)6 alkyne derivative of enkephalin described in Sect. 2.1 was investigated by our group, and IC50 values between 15 and 50 pM were obtained, depending on the cell line [31]. This is about one order of magnitude worse than the activity an Co2(CO)6 alkyne derivative of acetyl salicylic acid, which is the lead structure of this class of compounds [116-118]. 

Alt has prepared a cationic cis-carbene alkyne derivative, CpW(CO)-(HC=CH)[C(OEt)Me] + (77), but the presence of both an alkyne ligand and a carbonyl ligand in the d4 coordination sphere as well as a heteroatom on the carbene complicates orientational predictions relative to W(CHPh)-(RC=CR)L2X2. No structural data are yet available for this cationic carbene alkyne complex. 

This article is concerned with one specific aspect of cluster organometallic chemistry, and describes the synthesis, characterization, structure, and reactivity of transition metal clusters containing alkyne, or alkyne-derived ligands. Alkynes display a diverse reactivity in their reactions with carbonyl clusters, and exhibit a wider range of coordination modes than any other simple, unsaturated molecule. It is this compelling diversity that has prompted the authors to undertake this review. 

Structural Parameters for Clusters Which Contain Alkyne-Derived Ligands Adopting Bonding Mode M17... 

A characteristically different mechanism appears to operate in alkyne trimerization systems based on PdCb." Cationic metal complexes are involved in which initial halide transfer to an alkyne carbon is followed by sequential linear insertion of two more alkyne moieties. Metallacyclopentadiene intermediates are not involved in this sequence. Unique to this mechanism is the subsequent ring-closure to a cy-clopentadienylmethyl metal derivative, which, via halide transfer back to the metal, eventually leads to benzene via a bicyclo[3.1.0] system (Scheme 27). Support for this mechanism comes in part from the isolation of methylcyclopentadienyl-derived structures in several cases, including pentalene derivatives from further alkyne insertion followed by a second ring-closure." ... 

As already mentioned in the introduction, anionic early transition metallocene complexes of the type [Cp2Zr(R1)(R2)(R3)] with R, R2, R3 = alkyl, alkenyl, or alkynyl, are unstable. Most of them exhibit electrostatic anion-cation pairing resulting in dimer, trimer, oligomer, or polymeric structures [21-25]. In marked contrast, stable 18 electron-zirconate complexes were prepared via a formal [3 + 2] cycloaddition reaction between 2-phosphino-zirconaindene 16a and alkyne derivatives (Scheme 5) [26,27]. 

Figure 12.3 X-ray crystal structure of alkynes derived from cinchona alkaloids. Torsion angles defining twist sense, cf. Scheme 12.19.

Such structures are not made from the phospholes as reactants but are prepared indirectly by condensation reactions of alkynic derivatives with trialkyl phosphites <8ICC420,8ITL3523>, whereupon a cyclization process occurs that gives the phosphole ring. In the reaction of dimethyl ethynedicarboxylate with trialkyl phosphites, an intermediate has been detected at — 50°C that has structure (227) <84JCS(P1)1627>. 

The Stone group continues to be prolific, and, in this review, the metallacarbaboranes reported since last year s survey have been organised by metal. Group 6 chemistry includes alkyne derivatives, and the preparation and structure of [3,3,3-(CO)3-8,3- a,Ti2-CH=CHSiMe3 -... 

Alkenes and alkynes are similar in structure to the alkanes except the alkenes contain a carbon-to-carbon double bond (C=C) and the alkynes contain a carbon-to-carbon triple bond (C=C). The name prefixes are exactly the same as for the alkanes with the same number of carbons, but the endings are -one for compounds with double bonds and their derivatives and -yne for compounds with triple bonds... 

The alkynylation of estrone methyl ether with the lithium, sodium and potassium derivatives of propargyl alcohol, 3-butyn-l-ol, and propargyl aldehyde diethyl acetal in pyridine and dioxane has been studied by Miller. Every combination of alkali metal and alkyne tried, but one, gives the 17a-alkylated products (65a), (65c) and (65d). The exception is alkynylation with the potassium derivative of propargyl aldehyde diethyl acetal in pyridine at room temperature, which produces a mixture of epimeric 17-(3, 3 -diethoxy-T-propynyl) derivatives. The rate of alkynylation of estrone methyl ether depends on the structure of the alkyne and proceeds in the order propar-gylaldehyde diethyl acetal > 3-butyn-l-ol > propargyl alcohol. The reactivity of the alkali metal salts is in the order potassium > sodium > lithium. 

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