title: Effect of intramolecular pi-pi and CH-pi interactions between ligands on structure, electrochemical and spectroscopic properties of fac-[Re(bpy)(CO)3(PR3)]+(bpy = 2,2'-bipyridine; PR3= trialkyl or triarylphosphines).
abstract: Intramolecular pi-pi and CH-pi interactions between the bpy and PR3 ligands of fac-[Re(bpy)(CO)3(PR3)]+ affect their structure, and electrochemical and spectroscopic properties. Intramolecular CH-pi interaction was observed between the alkyl groups on the phosphine ligand (R =nBu, Et) and the bpy ligand, and intramolecular pi-pi and CH-pi interactions were both observed between the aryl group(s) on the phosphorus ligand (R =p-MeOPh, p-MePh, Ph, p-FPh, OPh) and the bpy ligand, while no such interactions were found in the trialkylphosphite complexes (R = OiPr, OEt, OMe). The intramolecular interactions distort the pyridine rings of the bpy ligand as long as 3.7 x 10(-2)A in crystals. Molecular orbital calculations of the bpy ligand suggest that this distortion decreases the energy gap between its pi and pi* orbitals. An absorption band attributed to the pi-pi*(bpy) transition of the distorted rhenium complexes, measured in a KBr pellet, was red-shifted by 1-5 nm compared to the complexes without the distorted bpy ligand. Even in solution, similar red shifts of the pi-pi*(bpy) absorption were observed. The redox potential E1/2(bpy/bpy*-) of the complexes with the trialkylphosphine and triarylphosphine ligand are shifted positively by 110-120 mV and 60-80 mV respectively, compared with those derived from the electron-attracting property of the phosphorus ligand. In contrast with these properties, three nu(CO) IR bands, which are sensitive to the electron density on the central rhenium because of pi-back bonding, were shifted to higher energy, and a Re(I/II)-based oxidation wave was observed at a more positive potential according to the electron-attracting property of the phosphorus ligand.
authors.affiliation: Department of Chemistry, Graduate School of Science and Engineering, Tokyo Institute of Technology and CREST, Japan Science and Technology Agency, Okayama 2-12-1, Meguro-ku, Tokyo 152-8551, Japan.
authors.forename: Hideaki
authors.initials: H
authors.lastname: Tsubaki
authors.forename: Shigeki
authors.initials: S
authors.lastname: Tohyama
authors.forename: Kazuhide
authors.initials: K
authors.lastname: Koike
authors.forename: Hideki
authors.initials: H
authors.lastname: Saitoh
authors.forename: Osamu
authors.initials: O
authors.lastname: Ishitani
mesh_terms: D018360:Crystallography, X-Ray; D004563:Electrochemistry; D004583:Electrons; D008024:Ligands; D008968:Molecular Conformation; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry* / Q000378:metabolism; D010084:Oxidation-Reduction; D010720:Phosphines / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D010758:Phosphorus / Q000737:chemistry / Q000378:metabolism; D011725:Pyridines / Q000138:chemical synthesis / Q000737:chemistry / Q000378:metabolism; D012211:Rhenium / Q000737:chemistry* / Q000378:metabolism
chemical_list: D008024:Ligands; D009942:Organometallic Compounds; D010720:Phosphines; D011725:Pyridines; D010758:Phosphorus; D012211:Rhenium; C044646:phosphine; C023666:pyridine