AbstractThe acid‐catalysed reaction of [{Co2(CO)6(μ‐η2‐HOCH2C2‐)}2] (1a) with a range of alkyl diols has been examined as means of preparing large crown‐type macrocycles (up to twenty eight‐membered) containing at least one coordinated 1,3‐diyne unit, multiple oxygen atoms and a variety of soft donor units. Thus, interaction of 1a with HOCH2(CH2)nCH2OH, allows access to the monomeric cyclised complexes [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2OCH2(CH2)nCH2O}] (3a: n = 2, 3b: n = 3, 3c: n = 4) along with the dimeric cyclised species [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2OCH2(CH2)nCH2O}]2 (4a: n = 2, 4b: n = 3, 4c: n = 4). Introduction of additional oxygen donor atoms into the macrocycle can be achieved by reaction of 1a with the glycols, HO(CH2CH2O)nH, to afford exclusively monomeric [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2O(CH2CH2O)n}] (5a: n = 3, 5b: n = 4). On the other hand, treatment of 1a with the 1,3‐diyne‐linked alkyl diols, HOCR2C≡CC≡CCR2OH, furnishes the more rigid monomeric [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2OCR2C2C2CR2O}] [6a: R = H, 6b: R = Me] and dimeric macrocycles [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2OCR2C2C2CR2O}]2 [7a: R = H, 7b: R = Me], whereas the use of the alkynyl‐ or aryl‐linked alkyl diols, HOCH2(L)CH2OH, affords the unsymmetrical dimeric [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2}2O{OCH2(L)CH2O}] [8a: L = –C≡C–, 8b: L = 1,4‐C6H4] and symmetrical dimeric species [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2OCH2(L)CH2O}]2 [9a: L = –C≡C–, 9b: L = 1,4‐C6H4]. Also isolated as a by‐product from all the above reactions is the self‐dimerised macrocycle [{Co2(CO)6}2{cyclo‐μ‐η2:μ‐η2‐CH2C2C2CH2O}]2 (2) which can itself be synthesised more directly by treating 1a with catalytic quantities of HBF4·OEt2. Single crystal X‐ray diffraction studies have been performed on 2, 3a, 5a, 7a, 8a, 8b and 9a. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)