Strongly Nucleophilic RhI Centre in Square-Planar Complexes with Terdentate (κ3) 2,2′:6′,2′′-Terpyridine Ligands: Crystallographic, Electrochemical and Density Functional Theoretical Studies
✍ Scribed by Boke C. de Pater; Hans-Werner Frühauf; Kees Vrieze; René de Gelder; Evert J. Baerends; Drew McCormack; Martin Lutz; Anthony L. Spek; František Hartl
- Publisher
- John Wiley and Sons
- Year
- 2004
- Tongue
- English
- Weight
- 233 KB
- Volume
- 2004
- Category
- Article
- ISSN
- 1434-1948
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✦ Synopsis
Abstract
Rh^I^‐terpyridine complexes have been unambiguously formed for the first time. The 2,2′:6′,2′′‐terpyridine (tpy), 4′‐chloro‐2,2′:6′,2′′‐terpyridine (4′‐Cl‐tpy) and 4′‐(tert‐butyldimethylsilyl‐ortho‐carboranyl)‐2,2′:6′,2′′‐terpyridine (carboranyl‐tpy) ligands were used for successful syntheses and characterisation of the corresponding Rh^I^ complexes with halide co‐ligands, [Rh(X)(4′‐Y‐terpyridine)] (X = Cl, Y = H, Cl, carboranyl; X = Br, Y = H). All four neutral Rh‐tpy complexes are square planar, with Rh−X bonds in the plane of the 4′‐Y‐terpyridine ligands. Full characterisation of these dark blue, highly air‐sensitive compounds was hampered by their poor solubility in various organic solvents. This is mainly due to the formation of π‐stacked aggregates, as evidenced by the crystal structure of [Rh(Cl)(tpy)]; in addition, [Rh(Cl)(carboranyl‐tpy)] merely forms discrete dimers. The (bonding) properties of the novel Rh^I^‐terpyridine complexes have been studied with single‐crystal X‐ray diffraction, (time‐dependent) density functional theoretical (DFT) calculations, far‐infrared spectroscopy, electronic absorption spectroscopy and cyclic voltammetry. From DFT calculations, the HOMO of the studied Rh^I^‐terpyridine complexes involves predominantly the metal centre, while the LUMO resides on the terpyridine ligand. Absorption bands of the studied complexes in the visible region (400−900 nm) can be assigned to MLCT and MLCT/XLCT transitions. The relatively low oxidation potentials of [Rh(X)(tpy)] (X = Cl, Br) point to a high electron density on the metal centre. This makes the Rh^I^‐terpyridine complexes strongly nucleophilic and (potentially) highly reactive towards various (small) substrate molecules containing carbon−halide bonds. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)