Aerobically Stable and Substitutionally Labile α-Diimine Rhenium Dicarbonyl Complexes

20 January 2021, Version 1
This content is a preprint and has not undergone peer review at the time of posting.

Abstract

New synthetic routes to aerobically stable and substitutionally labile a-diimine rhenium(I) dicarbonyl complexes are described. The molecules are prepared in high yield from the cis-cis-trans-[Re(CO)2(tBu2bpy)Br2]- anion (2, where tBu2bpy 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 s-donor monodentate ligands (Ls) yields stable neutral 18-electron cis-cis-trans-[Re(CO)2(tBu2bpy)Br(L)] species. In coordinating solvents like methanol the halide is replaced giving the corresponding solvated cations. [Re(CO)2(tBu2bpy)Br(L)] species can be further reacted with Ls to prepare stable cis-cis-trans-[Re(CO)2(tBu2bpy)(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) enantiomers are also formed. In particular, cis-cis-trans-[Re(CO)2(tBu2bpy)(L)2]+ complexes establish an equilibrium with all cis enantiomers 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 a-diimine unit. [Re(CO)2(tBu2bpy)Br2]- and [Re(CO)2(tBu2bpy)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.

Keywords

Rhenium
Dicarbonyl Complexes

Comments

Comments are not moderated before they are posted, but they can be removed by the site moderators if they are found to be in contravention of our Commenting Policy [opens in a new tab] - please read this policy before you post. Comments should be used for scholarly discussion of the content in question. You can find more information about how to use the commenting feature here [opens in a new tab] .
This site is protected by reCAPTCHA and the Google Privacy Policy [opens in a new tab] and Terms of Service [opens in a new tab] apply.