Alkynyl complexes association

The complex Re(CO)3(Bu/-bpy) 2((i-C=CC=C) undergoes three irreversible oxidations and a Buj-bpy-centered reduction (—1.62 V). Oxidation processes near + 1.8 V are also observed in related alkynyl complexes, and suggests that this redox event is associated with the Re(I/II) couple. The remaining redox events were tentatively assigned to oxidation of the carbon chain.253... 

The history of routinely interpreting the structures and spectra of metal-carbonyl and -cyano complexes from a rr-backbonding perspective tempts one to carry this approach over to metal-alkynyl complexes as well. But however successful this may appear to be for individual or limited series of metal-alkynyl compounds, consideration of the whole body of metrical and vibrational-frequency data associated with the M—C=C—R linkage makes it clear that, rather than a particular datum or series of data demonstrating the presence of 7r-backbonding, they are... 

Alkynyl complexes Cp2LnC R are associated even in donating solvents [148, 154, 169, 170]. In most cases association degree is equal 2 except the lanthanum and cerium complexes obtained by Tsutsui and coworkers [151, 152], in which Cp-rings are bonded by the trimethylene bridge... 

In summary, [Au(alkynyl)(CNR)j complexes also show mesomorphic behavior but, in contrast to the halide-isocyanide derivatives, they are thermally less stable and usually decompose before or at the clearing temperatures. This thermal instability is thought to be associated with the gold-(alkynyl) bond and makes these compounds... 

Dimeric association (71) can be obtained by an acid-base reaction between alkyl zirconocene and a terminal alkynyl ruthenium complex (equation 32). Surprisingly, the same reaction was observed with an iron acetylide opposed to Schwartz s reagent see Schwartz s Reagent) (equation 33). ... 

This concept was extended to an asymmetric conjugate aUcynylation of enones [59]. In this case, -alkynyl ehmination from the rhodium-alkoxide complex 101 (Scheme 22), delivers not only alkynyl-rhodium species 103 but simultaneously also reveals the reacting substrate, a, -unsaturated ketones 102. Subsequent conjugate addition gives rise to -alkynylketones 105 in high yields and enantioselec-tivities. This on-demand release and generation of the alkynyl-rhodium and the enone substrate bypasses the common dimerization issues associated with the formation of alkynyl-rhodium species from terminal alkynes. 

The relative ease of depolymerization of the alkynyl gold complexes may be associated with the reluctance of gold(I) to raise its co-ordination number above 2 [270]. 

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