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Alkynyldicobalt Derivatives of Dibenzosuberenol and Dibenzocyclooctatrien‐5‐ol: Ring Conformations, Ease of Carbonyl Elimination and Relevance to Pauson–Khand Cyclization
Author(s) -
Brusey Sarah A.,
Shen Wen,
MüllerBunz Helge,
Ortin Yannick,
Evans Paul,
McGlinchey Michael J.
Publication year - 2017
Publication title -
european journal of inorganic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 1434-1948
DOI - 10.1002/ejic.201601538
Subject(s) - chemistry , alkyne , alkene , moiety , ring (chemistry) , substituent , stereochemistry , isopropyl , ligand (biochemistry) , carbon monoxide , methylene , medicinal chemistry , molecule , phenyl group , crystallography , organic chemistry , alkyl , catalysis , biochemistry , receptor , halogen
Under very mild conditions, (5‐alkynyl‐5 H ‐dibenzo[ a,d ]cycloheptatrien‐5‐ol)Co 2 (CO) 6 clusters 1 lose a carbon monoxide ligand and form the corresponding η 2 ‐alkene‐µ‐alkyne‐Co 2 (CO) 5 complexes 2 (the first isolated examples of the initial phase of the Pauson–Khand reaction). This behaviour is not paralleled by the homologue in which an additional methylene group has been inserted within the seven‐membered ring, as in the [5‐alkynyl‐6 H ‐dibenzo[ a,e ]cyclooctatrienol]Co 2 (CO) 6 system 8 , for which several X‐ray crystal structures are reported. The apparent additional flexibility of this molecular framework does not translate into conformations appropriate for the formation of η 2 ‐alkene‐µ‐alkyne‐Co 2 (CO) 5 complexes. The relative inertness of the ethynyl complex 1a , compared with the ease of carbonyl loss in the trimethylsilylethynyl‐ and the tri(isopropyl)silylethynyl‐substituted hexacarbonyldicobalt clusters, 1b and 11 , respectively, is discussed in terms of out‐of‐plane angle strain within the dibenzo[ a,d ]cycloheptatrienyl moiety. Comparison of the changing conformations of the seven‐membered ring in a series of free and complexed molecules reveals a marked flattening of the organic framework, as bulkier substituents are incorporated at C5. The possibility of η 2 ‐alkene‐µ‐alkyne‐Co 2 (CO) 5 clusters functioning as hemilabile systems was explored by monitoring the ease of carbonyl substitution by triphenylphosphine in 2b (alkynyl substituent C≡CSiMe 3 ).