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

Abstract

The complex trans- [Re(terpy)(Br)(PPh 3 ) 2 ][OTf] ( 2 ) (terpy = 2,2‘:6‘,2‘ ‘-terpyridine) is a convenient precursor to the electron-rich π-basic fragment {(terpy)(L) 2 Re} + (L = t BuNC or PMe 3 ). Reduction of 2 with activated magnesium in the presence of unsaturated organic molecules and an excess of either t BuNC or PMe 3 yields complexes of the type trans- [(terpy)(L) 2 Re(η 2 -π)][OTf] (L = t BuNC or PMe 3; 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 (η 2 -acetone)][OTf] ( 9 ) with MeOTf yields an observable η 2 -ketonium complex. The electronic environment of these complexes has been probed by cyclic voltammetry, and the details of ligand exchange for the η 2 -ketone complexes are presented. Geometric features determined from X-ray crystal structure analyses of trans- [(terpy)( t BuNC) 2 Re(η 2 -cyclopentene)][OTf] ( 4 ) and trans- [(terpy)( t BuNC) 2 Re(η 2 -acetophenone)][OTf] ( 11 ) are reported.