Alkyne complexes structures

Over the last decade, the chemistry of the carbon-carbon triple bond has experienced a vigorous resurgence [1]. Whereas construction of alkyne-con-taining systems had previously been a laborious process, the advent of new synthetic methodology based on organotransition metal complexes has revolutionized the field [2]. Specifically, palladium-catalyzed cross-coupling reactions between alkyne sp-carbon atoms and sp -carbon atoms of arenes and alkenes have allowed for rapid assembly of relatively complex structures [3]. In particular, the preparation of alkyne-rich macrocycles, the subject of this report, has benefited enormously from these recent advances. For the purpose of this review, we Emit the discussion to cychc systems which contain benzene and acetylene moieties only, henceforth referred to as phenylacetylene and phenyldiacetylene macrocycles (PAMs and PDMs, respectively). Not only have a wide... 

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 copper-alkoxo unit, which is usually synthesized in situ, plays a significant role in metal-promoted transformations of organic substrates by copper(I). To determine the reaction form of the Cu-OPh unit, Floriani and co-workers structurally characterized four complexes (772) (pseudotetrahedral Cu-Cu 3.223 AT (773) (pseudotetrahedral), (774) ( anion linear coordination) and (775) (planar trigonal).57 Using 3,3,6,6-tetramethyl-l-thia-4-cycloheptyne as terminal ligand the structural characterization of a copper(I)-alkyne complex (776) (Cu-Cu 2.940 A) was reported.573... 

The reaction of Ba[P(SiMe3)2]2(THF)2 with diphenylbutadiyne in toluene for 12 days induces a m-addition of the diyne to the phosphide, followed by a 1,3-silyl group shift and ring closure. The dinuclear complex 132 is then isolated in good yield.283 Its complex structure contains Ba-C a bonds (2.881(5), 2.899(5) A), side-on Ba-alkyne (3.003(6), 3.363(6) A) and arene interactions, and Ba-phospholide bonds (Ba-P = 3.487(2) A) (Figure 65). 

It is interesting to compare the structure of the species (1 ) (X-ray diffraction study for PR3 = PMePh2) with those of the isolobal bridged alkyne complexes (1 ) (L = PR3 or L2 = cyclo-... 

Terminal RCH—CH2 1-Hexene C4H9CH=CH2 is isomerized by complex 1 in accordance with the factors influencing the thermodynamic stability of cis- and trans-2 -hexene [15], At the end of the reaction, the alkyne complex 1 was recovered almost quantitatively. No alkene complexes or coupling products were obtained. The corresponding zirconocene complex 2a did not show any isomerization activity. Propene CH3CH=CH2 reacts with complex 6 with substitution of the alkyne and the formation of zirconacydopentanes as coupling products, the structures of which are non-uniform [16]. 

Complex condensation products are obtained by reaction of the alkyne complex with excess of 3,3-dimethyl-l-butyne, which yields two isomeric products of formulas Ru3(CO)6[HC2C(Me)3-COCH2CMe3][HC2CMe3]2 (125). The X-ray structure of one of those adducts (Fig. 19) shows that both dimerization of two alkyne molecules and the insertion of carbon monoxide into the alkyne metal bonds have occurred. The Ru-Ru distances of 2.820,2.828, and 2.686 A in the ring are of interest. The value of 2.686 A is one of the shortest found in a... 

In this review, well-defined metal-containing PAEs are described whose primary structure is represented by one of the schematic drawings A-C and E shown in Fig. 2. In contrast to the structures shown in the A-C systems, E has a conjugated phenyleneethynylene with metal chelates as end groups. PAEs containing metal complex as side groups (D) have, up to now, not been described in the literature. The classes of compounds such as metal-bridged alkynes, the poly(metallayne)s, and polymer carbyne complexes (structures G and H) do not in fact represent PAEs. 

The alkyne complex [MoI C(NHBu ) 2(CNBu )4]+ results from reductive coupling upon reduction of [MoI(CNBut)6]+ la The thiolate-isocyanide complex [Mo(SBu )2(CNBu,)4], prepared from [Mo(SBu )4] and CNBu, forms the adduct [Mo(CNBu )4(p-SBu )2CuBr]. All these compounds have been structurally characterized.73... 

If the alkyne is adsorbed as a di-jr-complex (structure L), the product olefin will be formed as an adsorbed species, which must, therefore, undergo desorption before appearing in the gas phase (see Fig. 4). Consequently, the selectivity defined as... 

Alternatively, if, as was originally envisaged [157] the alkyne is adsorbed as a di-a-bonded complex (structure J), hydrogenation will lead to the direct formation of olefin in the gas phase. 

The simplest alkyne complexes, the metal acetylenes, resemble those of ethylene. For example, there are analogues of Zeise s salt in which an acetylene molecule ts bound to platinum(l)) and occupies a position like that of ethylene in Zeise s salt. In addition, there are L,Pt(RC=CR) complexes that have structures paralleling that of LjWHjC CHj) (Fig. 15.24). For both of these PtfO) complexes, an approximate square planar arrangement around the metal is found. Alkynes are more electronegative than ulkenes and are therefore better it acceptors. Thus it is appropriate to view them as metal lacyclopropenes 79... 

Hexafluorobutyne-2 will add to platinum(II) complexes. The insoluble complex PtMe HB(pz)3 reacts with dissolution and the five-coordinate alkyne complexes can be isolated (equation 269).815 The coordination about platinum(II) is essentially trigonal bipyrami-dal. The C C triple bond is lengthened on coordination to 1.292(12) A and the alkyne bend-back angle is 34.4(4)°.816 These complexes have a -bonded alkyne ligand, and show different structural and reaction chemistry than platinum(II) acetylide complexes.817-821... 

Figure 8 The preparations and crystal structures of copper(I) alkene and alkyne complexes... 

An earlier review treated the organometallic derivatives, including alkyl, aryl, vinyl, alkynyl, carbonyl, carbene, alkene and alkyne complexes,16 and these will not be treated here (see Table 1 for other books and reviews on organogold chemistry). Two important articles dealing with [AuCl(CO)], including its structure and catalytic properties, have been published recently.97,381... 

As noted in the introduction, in contrast to attack by nucleophiles, attack of electrophiles on saturated alkene-, polyene- or polyenyl-metal complexes creates special problems in that normally unstable 16-electron, unsaturated species are formed. To be isolated, these species must be stabilized by intramolecular coordination or via intermolecular addition of a ligand. Nevertheless, as illustrated in this chapter, reactions of significant synthetic utility can be developed with attention to these points. It is likely that this area will see considerable development in the future. In addition to refinement of electrophilic reactions of metal-diene complexes, synthetic applications may evolve from the coupling of carbon electrophiles with electron-rich transition metal complexes of alkenes, alkynes and polyenes, as well as allyl- and dienyl-metal complexes. Sequential addition of electrophiles followed by nucleophiles is also viable to rapidly assemble complex structures. 

Alkenes (unsaturated hydrocarbons with double bonds) are the oldest and most studied carbon ligands, with interest in their study dating from around 1827 [3,185-189]. An important aspect is the structure of 71-alkene and similar n-alkyne complexes. Their structural data is summarized in reviews [186-189] and presented in... 

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