Rhenium(I) Terpyridine π-Bases:  Reversible η²-Coordination of Ketones, Aldehydes, and Olefins in the Terpyridine Plane

Abstract

The complex trans-[Re(terpy)(Br)(PPh3)2][OTf] (2) (terpy = 2,2‘:6‘,2‘ ‘-terpyridine) is a convenient precursor to the electron-rich π-basic fragment {(terpy)(L)2Re}+ (L = t BuNC or PMe3). Reduction of 2 with activated magnesium in the presence of unsaturated organic molecules and an excess of either t BuNC or PMe3 yields complexes of the type trans-[(terpy)(L)2Re(η2-π)][OTf] (L = t BuNC or PMe3; π = olefin, aldehyde, or ketone). The dihapto-coordinated organic moieties show a preference for binding in the plane of the terpy ligand. Reaction of trans-[Re(terpy)( t BuNC)2(η2-acetone)][OTf] (9) with MeOTf yields an observable η2-ketonium complex. The electronic environment of these complexes has been probed by cyclic voltammetry, and the details of ligand exchange for the η2-ketone complexes are presented. Geometric features determined from X-ray crystal structure analyses of trans-[(terpy)( t BuNC)2Re(η2-cyclopentene)][OTf] (4) and trans-[(terpy)( t BuNC)2Re(η2-acetophenone)][OTf] (11) are reported.

Stereoselective Dihapto-Binding of Prochiral Aromatic Compounds by {TpRe(CO)(PMe3)}: Synthesis, Characterization, Stability, and Enantiofacial Discrimination (Tp = Hydrido(tris)pyrazolylborate)

“…As a consequence of η 2 -coordination, the ketone carbonyl resonates at 84.2 ppm in the 13 C NMR spectrum. 56 Numerous dihapto-bound ketone complexes have been reported, 57-80 but most of these examples are with electron-deficient ketones. The irreversible oxidation wave (irreversible up to 500 mV/s; E p,a ) 0.26 V vs NHE 100 mV/s) is likely a consequence of the ability of the acetone ligand to access an η 1 -oxygen bound coordination isomer.…”

Synthesis of Re(I) complexes bearing tridentate 2,6-bis(7′-azaindolyl)phenyl ligand with green emission properties

“…Among them, the Re(CO) 3 (N^N)X type complexes (N^N: a bidentate N ; N 0 -chelating ligand such as 2,2 0 -bipyridine or 1,10-phenanthroline, and X ¼ Cl, Br) have been used in a variety of processes including photochemical reduction of CO 2 [6], chemoluminescence [7], electrochemiluminescence [8], exciplex emission [9], and luminescent probe in curing of epoxy resins [10]. Despite a number of studies on the complexes bearing bidentate N ; N 0 -chelating ligands, only few papers on the tridentate counterparts have been reported [11]. Surprisingly, to the best of our knowledge, only one report appeared on Re complexes containing a Re-carbon bond with a tridentate ligand [12].…”

A novel terpyridyl rhenium(II) complex – Synthesis, spectroscopic characterization and X-ray structure

“…Surprisingly, the rhenium complexes with 2,2 0 :6 0 ,2 00 -terpyridine ligands have been studied relatively little [9][10][11][12][13][14].…”