Alkyne quinuclidines

From a variety of X-ray crystal studies (e.g., didehydro-QCI/QCD and didehydro-quinidine), we have established that alkyne quinuclidines are twisted consistently less than the vinyl and ethyl analogues. Overall torsion angles, that is, the sum of the three torsion angles, vary from 26 to 49° compared with up to 65° for ethyl and 60° for ethenyl derivatives, respectively (Figure 12.3). Fine-tuning of nitrogen polarity (and basicity), which may be important for catalysis and perhaps pharmacological activity, is thus possible ([28] R. Wartchow, personal communication). 

Co arene chemistry has been expanded by the preparation of a number of (arene)Co(j7" -diene)+ and (arene)Co( , -enyl) complexes starting from (10). Hydrogenation of (10) in the presence of an arene and a base (piperidine or quinuclidine for obvious stabilization of coordinatively unsaturated cobalt intermediates) gives cyclooctenyl complexes (37) (equation 53). This reaction occurs with a large niunber of arenes even CeFg gives an j -arene complex. The resulting complexes (37) are moderately active catalysts in the pyridine synthesis from alkynes and nitriles (Section 5.1.4). 

Although the metathesis of terminal alkynes also proceeds rapidly, polymerization of the terminal alkynes displaces the carbyne exchange reactions towards the wrong side towards the starting terminal alkyne that polymerizes except if suitable parameters are ad usted such as temperature, solvent diethyl ether and especially the presence of the potential ligand quinuclidine together with the... 

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