Synthesis of cobalt-containing cyclophanes, and the formation of an unprecedented seven-membered cyclic diyne

The acid-catalysed Nicholas reaction of the bis-propargyl complex [{Co2(CO)6(μ-η2-HOMe2CCC–)}2] 1 in the presence of a variety of nucleophiles leads in each case to [{Co2(CO)6}2{cyclo-μ-η2:μ-η2-C(CH2)CH2CMe2CC–CC}], a complex which contains an unprecedented seven-membered macrocyclic diyne ligand. The reactivity of 1 is compared to that of [{Co2(CO)6}2{μ-η2:μ-η2-1,4-C6H4(CCCMe2OH)2}] which does not cyclise on treatment with nucleophiles but instead gives the expected substitution products.