Rhenium(I) terpyridine pi-bases: Reversible eta(2)-coordination of ketones, aldehydes, and olefins in the terpyridine plane

The complex trans-[Re(terpy)(Br)(PPh3)(2)][OTf] (2) (terpy = 2,2':6',2"-ter pyridine) is a convenient precursor to the electron-rich pi-basic fragment {(terpy)(L)(2)Re}(+) (L = (BuNC)-Bu-t or PMe3). Reduction of 2 with activat ed magnesium in the presence of unsaturated organic molecules and an excess of either tBuNC or PMe3 yields complexes of the type trans-[(terpy)(L)(2)R e(eta(2)-pi)][OTf] (L = (BuNC)-Bu-t or PMe3; pi = olefin, aldehyde, or keto ne), The dihapto-coordinated organic moieties show a preference for binding in the plane of the terpy ligand. Reaction of trans- [Re(terpy)((BuNC)-Bu- t)(2)(eta(2)-acetone)][OTf] (9) with MeOTf yields an observable mu(2)-keton ium complex, The electronic environment of these complexes has been probed by cyclic voltammetry, and the details of ligand exchange for the eta(2)-ke tone complexes are presented. Geometric features determined from X-ray crys tal structure analyses of trans-[(terpy)((BuNC)-Bu-t)(2)Re(eta(2)-cyclopent ene)][OTf] (4) and trans-[(terpy)((BuNC)-Bu-t)(2)Re(eta(2)-acetophenone)][O Tf] (11) are reported.