Self-cyclisation versus diynediol-promoted ring closure during the construction of coordinated crown-type macrocycles

Treatment of [Co2(CO)6(μ-η2-HOCH2CCCH2OH)] (1a) with a catalytic quantity of HBF4 · OEt2 affords [{Co2(CO)6}2{cyclo-μ-η2:μ-η2-OCH2CCCH2OCH2CCCH2–}] (2) and [{Co2(CO)6}3{cyclo-μ-η2:μ-η2:μ-η2-OCH2CCCH2OCH2CCCH2OCH2CCCH2–}] (3), in which cyclodimerisation and cyclotrimerisation of 1a has occurred, respectively. The molecular structures of 2 and 3 reveal non-bonding oxygen–oxygen separations within the macrocycles of 4.716 Å (2) and 3.968–5.045 Å (3). On the other hand, introduction of one equivalent of the cyclohexyl-substituted diyne-diol, (1-HO-cyclo-C6H10)CCCC(1-HO-cyclo-C6H10), to the reaction furnishes the macrocyclic complexes [{Co2(CO)6}2{cyclo-μ-η2:μ-η2-OCH2CCCH2OCH2CCCH2O(cyclo-C6H10)C2C2(cyclo-C6H10)–}] (4) and [{Co2(CO)6}3{cyclo-μ-η2:μ-η2:μ-η2-OCH2CCCH2OCH2CCCH2OCH2CCCH2O(cyclo-1-C6H10)C2C2(cyclo-1-C6H10)–}] (5), in which the chain ends of the rigid 1,3-diyne unit are linked by either di- or tri-merised derivatives of 1a. Also isolated in the reaction is the open-chain species [{Co2(CO)6}2(μ-η2:μ-η2-HOCH2CCCH2O(cyclo-1-C6H10)C2C2(cyclo-1-C6H10)-OCH2CCCH2OH)] (6). Inspection of the molecular structure of 4 reveals a 17-membered ring with the non-bonding oxygen–oxygen separations ranging from 4.958 to 7.257 Å.

The ability of butyne-1,4-diol-Co2(CO)6 (1a) to undergo self-cyclisation reactions under acidic conditions to give both dimeric and trimeric crown-type macrocycles has been demonstrated; incorporation of a rigid 1,3-diyne unit into the macrocycle formed during self-reaction of 1a is also reported.Figure optionsDownload as PowerPoint slide