Aerobically stable and substitutionally labile α-diimine rhenium dicarbonyl complexes

• Published in: RSC advances 2021-02, Vol.11 (13), p.7511-752
• Main Authors: Schindler, Kevin, Crochet, Aurélien, Zobi, Fabio
• Format: Article
• Language: English
• Subjects: Carbon monoxide; Chemistry; Coordination compounds; Crystal structure; Crystallography; Diamagnetism; Diimide; Electrons; Isomers; Ligands; Molecular structure; Oxygen; Rhenium; Solid state
• ISSN: 2046-2069; 2046-2069
• DOI: 10.1039/d1ra00514f

New synthetic routes to aerobically stable and substitutionally labile α-diimine rhenium( i ) dicarbonyl complexes are described. The molecules are prepared in high yield from the cis - cis - trans -[Re(CO) 2 ( t Bu 2 bpy)Br 2 ] − anion ( 2 , where t Bu 2 bpy is 4,4′-di- tert -butyl-2,2′-bipyridine), which can be isolated from the one electron reduction of the corresponding 17-electron complex ( 1 ). Compound 2 is stable in the solid state, but in solution it is oxidized by molecular oxygen back to 1 . Replacement of a single bromide of 2 by σ-donor monodentate ligands (Ls) yields stable neutral 18-electron cis - cis - trans -[Re(CO) 2 ( t Bu 2 bpy)Br(L)] species. In coordinating solvents like methanol the halide is replaced giving the corresponding solvated cations. [Re(CO) 2 ( t Bu 2 bpy)Br(L)] species can be further reacted with Ls to prepare stable cis - cis - trans -[Re(CO) 2 ( t Bu 2 bpy)(L) 2 ] + complexes in good yield. Ligand substitution of Re( i ) complexes proceeds via pentacoordinate intermediates capable of Berry pseudorotation. In addition to the cis - cis - trans -complexes, cis - cis - cis - (all cis ) isomers are also formed. In particular, cis - cis - trans -[Re(CO) 2 ( t Bu 2 bpy)(L) 2 ] + complexes establish an equilibrium with all cis isomers in solution. The solid state crystal structure of nearly all molecules presented could be elucidated. The molecules adopt a slightly distorted octahedral geometry. In comparison to similar fac -[Re(CO) 3 ] + complexes, Re( i ) diacarbonyl species are characterized by a bend ( ca. 7°) of the axial ligands towards the α-diimine unit. [Re(CO) 2 ( t Bu 2 bpy)Br 2 ] − and [Re(CO) 2 ( t Bu 2 bpy)Br(L)] complexes may be considered as synthons for the preparation of a variety of new stable diamagnetic dicarbonyl rhenium cis -[Re(CO) 2 ] + complexes, offering a convenient entry in the chemistry of the core. New synthetic routes to aerobically stable and substitutionally labile α-diimine rhenium( i ) dicarbonyl complexes offer a convenient entry in the chemistry of the cis -[Re(CO) 2 ] + core.