A shape changing tandem Rh(CNC) catalyst: preparation of bicyclo[4.2.0]octa-1,5,7-trienes from terminal aryl alkynes

• Published in: Chemical science (Cambridge) Vol. 11; no. 8; pp. 251 - 257
• Main Authors: Storey, Caroline M, Kalpokas, Audrius, Gyton, Matthew R, Krämer, Tobias, Chaplin, Adrian B
• Format: Journal Article
• Language: English
• Published: CAMBRIDGE Royal Soc Chemistry 28.02.2020; Royal Society of Chemistry
• Subjects: Alkynes; Aromatic compounds; Cascade chemical reactions; Catalysts; Chemical reactions; Chemical synthesis; Chemistry; Chemistry, Multidisciplinary; Coordination; Crystallography; Ligands; NMR; Nuclear magnetic resonance; Physical Sciences; Rhodium; Science & Technology; Substrates; Trienes; RHODIUM; PNP; IRIDIUM; CYCLOADDITIONS; COMPLEXES; PINCER; DIMERIZATION
• ISSN: 2041-6520; 2041-6539
• DOI: 10.1039/c9sc06153c

The preparation of a range of tetraaryl-substituted bicyclo[4.2.0]octa-1,5,7-trienes using a one-pot procedure starting from terminal aryl alkynes and catalysed by a rhodium( i ) complex is reported. This synthesis proceeds by a reaction sequence involving head-to-tail homocoupling of the terminal alkyne and zipper annulation of the resulting gem -enyne. The rhodium catalyst employed is notable for the incorporation of a flexible NHC-based pincer ligand, which is suggested to interconvert between mer - and fac -coordination modes to fulfil the orthogonal mechanistic demands of the two transformations. Evidence for this interesting auto-tandem action of the catalyst is provided by reactions of the precatalyst with model substrates, corroborating proposed intermediates in both component cycles, and norbornadiene, which reversibly captures the change in pincer ligand coordination mode, along with a DFT-based computational analysis. Two catalysts for the price of one: a shape changing rhodium catalyst enables preparation of unusual isobenzenes using a one-pot procedure.