Acetylenes, dimerization

Vinylacetylene and Ghloroprene. In the presence of cuprous salt solutions, acetylene dimerizes to vinylacetylene [689-97-4], C H. Yields of 87% monovinylacetylene, together with 10% of divinylacetylene, have been described (6). 

Attempts to turn this acetylene dimerization reachon into a catalyhc polymeriza-hon process have failed thus far. In the presence of excess phenylacetylene, the iridium(I) complex 23 activates another Caikynyi—H bond and hansforms, after a hydrogen shift, to the stable (vinyl)(alkynyl) iridium(III) system 27 (Equahon 12.10). 

Saturated non-acetal dimers, such as 153 and 154, can be prepared from 151 via aluminium acetylide condensations or Friedel-Crafts reactions. Although the acetylenic dimer 153 is /3-linked to C-10 of the artemisinin skeleton, the aryl dimer 154 is a-linked <1999JME4275>. 

Another example of partial degradation of the Fe3(CO)i2 triangle is furnished by its reactions with phosphino-acetylenes which lead to complicated open Fe structures bridged by phosphido ligands and resulting acetylene dimers (79, 311). 

This C-H/olefin coupling can be extended to coupling with acetylenes [6], The reaction of aromatic ketones with internal acetylenes gives the ortho alkenylated product in high yield (Scheme 2), but reaction with terminal acetylenes does not afford the coupling product. With terminal acetylenes, dimerization of acetylenes occurs as a predominant reaction. 

An interesting aspect of acetylene dimerization was recently added by Haley s group [25]. The outcome of the cyclization of the precursor 60 depends strongly on the catalyst used for the coupling reaction. Cu-mediated coupling conditions [Cu(OAc)2, py] formed the macrocycle 61 as a sole product in 70 % yield whereas acetylene homocoupling with [PdCl2(dppe)] furnished 61a exclusively (84%) (Scheme 6.9). 

Ohshima, Y., Matsumoto, Y., Takami, M., and Kuchitsu, K., The structure and tunneling motion of acetylene dimer studied by free-iet infrared absorption spectroscopy in the 14um region, Chem. Phys. Lett. 147, 1-6 (1988). 

Muenter, J. S., An intermolecular potential function model applied to acetylene dimer, carbon dioxide dimer, and carbon dioxide acetylene, J. Chem. Phys. 94, 2781-2793 (1991). 

The 7t-type hydrogen bond with triple C-C bond acting as a proton-acceptor. A gradient-corrected hybrid HF-DFT and MP2 study of the phenol-acetylene dimer in the neutral S-0 ground state ... 

This T-shaped geometry is also identified in a microwave study of the C2H2.HF complexwhere the H—C=C midpoint distance is short at 2.19 A consistent with the higher acidity of HF by comparison with acetylene. Microwave and infrared studies of acetylene dimer also reveal a T-shape deviating by 27° from the fully perpendicular arrangementThe distance between the centres of mass of the two monomer units is given as 4.38 A. 

Terminal acetylenes dimerize to conjugated enynes in the presence of catalytic amounts of palladium(II) acetate and the hindered phosphine tris(2,6-dimethoxyphenyl)phosphine. 1-Octyne, for instance, affords the enyne 36 5. Palladium-catalysed condensations of 1-alkynes RC=CH (R=Ph or CH2OH) with vinyl bromide, ( )-2-bromostyrene, iodobenzene and 2-bromopyridine to yield 37, 38, 39, and 40, respectively (Scheme 1), have been reported (see also References 27 and 28). The palladium[tetrakis(triphenylphosphine)]-catalysed alkynylation of 1,1-dichloroethene with terminal alkynes 41 (R = pentyl, 3-chloropropyl, Ph or SiMes) results in the eneynes 42. ... 

HCN—acetylene dimer is formed when the monomers and a seed gas (typically in the ratio of 1 1 98 in order to avoid higher order clusters) are expanded through a small nozzle. The analysis of high-resolution IR spectra showed the presence of two conformations of the HCN-HCCH dimer (Block et al., 1989) ... 

Metallacycles have been suggested as intermediates in many transition-metal catalyzed reactions of olefins, acetylenes, and cyclopropanes. Metallacyclobutane complexes are invoked in olefin and cyclopropane isomerization schemes (Scheme as well as in olefin metathesis schemes. Metallacyclopentane, -pentene, and -pentadiene complexes can all be invoked in olefin and acetylene dimerization and polymerization (Scheme Many of these involve early transition metals and do not include phosphine ligands. 

Li G, Parr J, Fedorov I, Reisler H (2006) Imaging study of vibrational predissociation of the HCl-acetylene dimer pair-correlated distributions. Phys Chem Chem Phys 8 2915-2924... 

Butadiene is chlorinated in the gas phase to give mixtures of 1,2-dichlorobut-3-ene and l,4-dichlorobut-2-ene, which are interconvertible in the presence of copper catalysts. The former is dehydrochlorinated by contact with aqueous sodium hydroxide, to give chloroprene (2-chlorobuta-l, 3-diene) for polymer production (neoprene). The earlier acetylene-dimer route has been phased out. U.S. production of neoprene has fallen to about 120 kt per annum, of which over 40% is exported European production is somewhat lower. 

In 1869, Glaser found that copper(i) phenylacetylide prepared from phenylacetylene and a copper salt gave the acetylene dimer by air oxidation... 

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