Alkyne complexes thermal decomposition

The stepwise coupling of two cis ligands as depicted in Scheme 3 has been verified as involving a sequence of three discrete steps at low temperatures, allowing the isolation of the relevant intermediates as individual compounds [18]. When a chelated tetracarbonyl amino-vinyl carbene complex (chelated analogue of intermediate B in Scheme 3) was reacted with an electron-deficient alkyne under controlled conditions, a l,4,5- 3-dienylcarbene tetracarbonyl chromium complex (corresponding to intermediate D in Scheme 3) was formed. It underwent thermal decomposition to give phenol derivatives as the final products. 

An interesting carbene-alkyne intermediate was postulated for the conversion of carbene complexes to chrysene derivatives, which again illustrates the potential of cr,Tr-activation of bridging ligands by metal centers [Eq. (32)] (225). The thermal decomposition of the carbene complex Cr-... 

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. 

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