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

Abstract Treatment of [Co 2 (CO) 6 (μ-η 2 -HOCH 2 C CCH 2 OH)] ( 1a ) with a catalytic quantity of HBF 4  · OEt 2 affords [{Co 2 (CO) 6 } 2 { cyclo -μ-η 2 :μ-η 2 -OCH 2 C CCH 2 OCH 2 C CCH 2 –}] ( 2 ) and [{Co 2 (CO) 6 } 3 { cyclo -μ-η 2 :μ-η 2 :μ-η 2 -OCH 2 C CCH 2 OCH 2 C CCH 2 OCH 2 C CCH 2 –}] ( 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 A ( 2 ) and 3.968–5.045 A ( 3 ). On the other hand, introduction of one equivalent of the cyclohexyl-substituted diyne-diol, (1-HO- cyclo -C 6 H 10 )C CC C(1-HO- cyclo -C 6 H 10 ), to the reaction furnishes the macrocyclic complexes [{Co 2 (CO) 6 } 2 { cyclo -μ-η 2 :μ-η 2 -OCH 2 C CCH 2 OCH 2 C CCH 2 O( cyclo -C 6 H 10 )C 2 C 2 ( cyclo -C 6 H 10 )–}] ( 4 ) and [{Co 2 (CO) 6 } 3 { cyclo -μ-η 2 :μ-η 2 :μ-η 2 -OCH 2 C CCH 2 OCH 2 C CCH 2 OCH 2 C CCH 2 O( cyclo -1-C 6 H 10 )C 2 C 2 ( cyclo -1-C 6 H 10 )–}] ( 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 [{Co 2 (CO) 6 } 2 (μ-η 2 :μ-η 2 -HOCH 2 C CCH 2 O( cyclo -1-C 6 H 10 )C 2 C 2 ( cyclo -1-C 6 H 10 )-OCH 2 C CCH 2 OH)] ( 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 A.