title: Diimine triscarbonyl Re(I) of isomeric pyridyl-fulvene ligands: an electrochemical, spectroscopic, and computational investigation.
abstract: The synthesis and characterization of a novel family of positively charged fac-[Re(bpy)(CO)(3)(L)]PF(6) (bpy = 2,2'-bipyridine) complexes are reported, where L is a pyridine functionalized in para or meta position with a fulvene moiety, namely, 4-fluoren-9-ylidenemethyl-pyridine (pFpy) and 3-fluoren-9-ylidenemethyl-pyridine (mFpy). The complexes were prepared in high yield (86%) by direct addition at room temperature of the corresponding pyridine to the tetrahydrofuran (THF) adduct fac-[Re(bpy)(CO)(3)(THF)][PF(6)] precursor. Both ligand and complex structures were fully characterized by a variety of techniques including X-ray crystallography. The complexes did not exhibit the expected triplet mixed metal-ligand-to-ligand charge transfer (MLLCT) emission, because of its deactivation by the non-emissive triplet excited state of fulvene. The absorption profile shows that the MLLCT is overshadowed by the fulvene centered π-π* transition of higher molar absorptivity as shown by time dependent density functional theory (TD-DFT) calculations. The position of the fulvene on the pyridyl ring has a large effect on this transition, the para position displaying a much higher absorption coefficient (21.3 × 10(3) M(-1) cm(-1)) at lower energy (364 nm) than the meta position (331 nm, 16.0 × 10(3) M(-1) cm(-1)).
authors.affiliation: Department of Chemistry, Université de Montréal, Montréal, Québec H3T 1J4, Canada.
authors.forename: Daniel
authors.initials: D
authors.lastname: Chartrand
authors.forename: Carlos A
authors.initials: CA
authors.lastname: Castro Ruiz
authors.forename: Garry S
authors.initials: GS
authors.lastname: Hanan
mesh_terms: D015082:2,2'-Dipyridyl / Q000737:chemistry*; D018360:Crystallography, X-Ray; D003517:Cyclopentanes / Q000737:chemistry*; D055664:Electrochemical Techniques; D007097:Imines / Q000737:chemistry*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011789:Quantum Theory; D012211:Rhenium / Q000737:chemistry*; D013056:Spectrophotometry, Ultraviolet
chemical_list: D003517:Cyclopentanes; D007097:Imines; D008024:Ligands; D009942:Organometallic Compounds; C017332:fulvene; D015082:2,2'-Dipyridyl; D012211:Rhenium