title: Concurrent stabilization of π-donor and π-acceptor ligands in aromatized and dearomatized pincer [(PNN)Re(CO)(O)₂] complexes.
abstract: Aromatized cationic [(PNN)Re(π acid)(O)2](+) (1) and dearomatized neutral [(PNN*)Re(π acid)(O)2] (2) complexes (where π acid=CO (a), tBuNC (b), or (2,6-Me2)PhNC (c)), possessing both π-donor and π-acceptor ligands, have been synthesized and fully characterized. Reaction of [(PNN)Re(O)2](+) (4) with lithiumhexamethyldisilazide (LiHMDS) yield the dearomatized [(PNN*)Re(O)2] (3). Complexes 1 and 2 are prepared from the reaction of 4 and 3, respectively, with CO or isocyanides. Single-crystal X-ray structures of 1 a and 1 b show the expected trans-dioxo structure, in which the oxo ligands occupy the axial positions and the π-acidic ligand occupies the equatorial plane in an overall octahedral geometry about the rhenium(V) center. DFT studies revealed the stability of complexes 1 and 2 arises from a π-backbonding interaction between the d(xy) orbital of rhenium, the π orbital of the oxo ligands, and the π* orbital of CO/isocyanide.
authors.affiliation: Department of Chemistry, Purdue University, West Lafayette, IN 47907 (USA) http://www.chem.purdue.edu/abu-omar/
authors.forename: Michael G
authors.initials: MG
authors.lastname: Mazzotta
authors.forename: Kothanda Rama
authors.initials: KR
authors.lastname: Pichaandi
authors.forename: Phillip E
authors.initials: PE
authors.lastname: Fanwick
authors.forename: Mahdi M
authors.initials: MM
authors.lastname: Abu-Omar
keywords: carbon monoxide; isocyanide ligands; oxo ligands; pincer ligands; rhenium