Pyridyl‐Decorated Self‐Folding Heptaamide Cavitands as Ligands in the Rhodium‐Catalyzed Hydrogenation of Norbornadiene

Abstract

The different binding geometries exhibited in solution by the RhI cationic complexes of three regioisomeric self‐folding heptaamide cavitands, each decorated with one pyridyl group at the upper rim, are taken into account to explain the diverse distributions of products obtained when these complexes are employed as catalysts for the hydrogenation of norbornadiene.

Molecular Motion and Conformational Interconversion of IrI·COD Included in Rebek’s Self-Folding Octaamide Cavitand

“…As a result of our investigation, we reported the selective catalytic hydrogenation of norbornadiene to norbornene mediated by the inclusion complex of the self-folding octaamide cavitand 1 and rhodium­(I) bis-norbornadiene, Rh I ·(NBD) 2 , 2 + (Figure ). We also described a series of inclusion complexes prepared using pyridyl derivatives of self-folding cavitand 1 as containers of 2 + and showed that these too were able to facilitate the catalytic hydrogenation of norbornadiene …”

“…19 We also described a series of inclusion complexes prepared using pyridyl derivatives of self-folding cavitand 1 as containers of 2 + and showed that these too were able to facilitate the catalytic hydrogenation of norbornadiene. 20 We hypothesized that inclusion complexes of cavitand 1 21,22 with organometallic catalytically active species containing other metals than Rh I were also feasible. To this end, in light of the large number of monocationic iridium complexes available, we decided to pursue the inclusion of the iridium(I) bis-(cyclooctadiene) monocationic complex Ir I •(COD) 2 , 3 + , in the deep aromatic cavity of 1 (Figure 1).…”

Attachment of a RuII Complex to a Self-Folding Hexaamide Deep Cavitand

“…The chloro and aqua metallocavitands displayed an additional broad band at ≈3240 cm −1 assigned to the vibration of NHs in hydrogen-bonded amides. 8 The NN stretching frequency of the coordinated ancillary ligand was appreciably lower than for the free azpy ligand. This is consistent with backbonding donation from the metal.…”

“…We calculated an energy barrier of 16 kcal/mol for the cycloenantiomerization process. A total of 16 singlets are observed for the aromatic protons of the resorcin[4]­arene core and the bridging walls (red ● and H, , Figure ). The terpyridine substituent has five distinct proton signals owing to its free rotation through the connecting CC bond (H, − Figure ).…”

“…The synthetic availability of resorcin[4]­arene cavitands that are not symmetrically substituted allows the incorporation of functional groups at their upper rims that coordinate to catalytic metal centers. Examples of these structural modifications include oxazoline porphyrin, , salphen, , and pyridine substituted resorcin[4]­arene cavitands. All these molecular constructs feature a selective binding site in close proximity to an organometallic catalytic site.…”