Alkynyldicobalt Derivatives of Dibenzosuberenol and Dibenzocyclooctatrien‐5‐ol: Ring Conformations, Ease of Carbonyl Elimination and Relevance to Pauson–Khand Cyclization. Issue 13 (7th April 2017)

• Record Type: Journal Article
• Authors: Brusey, Sarah A.; Shen, Wen; Müller‐Bunz, Helge; Ortin, Yannick; Evans, Paul; McGlinchey, Michael J.
• Is Part Of: European journal of inorganic chemistry. Issue 13(2017)
• Page Start: 2048
• Page End: 2057
• Publication Date: 2017-04-07
• Subjects: Ring conformations -- Steric hindrance -- Silyl ligands -- Alkynes -- Cobalt; Chemistry, Inorganic -- Periodicals; Organometallic chemistry -- Periodicals; Bioinorganic chemistry -- Periodicals; Solid state chemistry -- Periodicals; 546
• DOI: 10.1002/ejic.201601538
• Languages: English
• ISSNs: 1434-1948

Abstract

Abstract : Under very mild conditions, (5‐alkynyl‐5 H ‐dibenzo[ a, d ]cycloheptatrien‐5‐ol)Co2 (CO)6 clusters1 lose a carbon monoxide ligand and form the corresponding η 2 ‐alkene‐µ‐alkyne‐Co2 (CO)5 complexes2 (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]Co2 (CO)6 system8, 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‐Co2 (CO)5 complexes. The relative inertness of the ethynyl complex1a, compared with the ease of carbonyl loss in the trimethylsilylethynyl‐ and the tri(isopropyl)silylethynyl‐substituted hexacarbonyldicobalt clusters, 1b and11, 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‐Co2 (CO)5 clusters functioning as hemilabile systems was explored by monitoring the ease of carbonyl substitution by triphenylphosphine in2b (alkynyl substituent C≡CSiMe3 ). Abstract : (5‐Alkynyl‐5 H ‐dibenzo[ a, d ]cycloheptatrien‐5‐ol)Co2 (CO)6 clusters lose a carbon monoxide ligand and form the corresponding η 2 ‐alkene‐µ‐alkyne‐Co2 (CO)5 complexes under very mild conditions. However, the ease of carbonyl loss depends on the size and conformation of the central ring.