title: The Distinctive Electronic Structures of Rhenium Tris(thiolate) Complexes, an Unexpected Contrast to the Valence Isoelectronic Ruthenium Tris(thiolate) Complexes.
abstract: The noninnocent 2-diphenylphosphino-benzenethiolate (DPPBT) ligand containing both phosphorus and sulfur donors delocalizes the electron density in a manner reminiscent of dithiolenes. The electronic structure of the [ReL3]n(L = DPPBT, n = 0, 1+, 2+) complexes was probed with density-functional theory (DFT) and high-level ab initio methods including complete active space self-consistent field (CASSCF and CASPT2) and coupled cluster (CCSD and CCSD(T)). DFT predicts a slight preference for a closed-shell (CS) singlet ground state for the neutral [ReL3]0and stronger preferences for low-spin ground states for the oxidized [ReL3]+and [ReL3]2+. High-level ab initio methods confirm a CS singlet with a Re(III) (d4, S = 0) center as the ground state of [ReL3]0. Thus, this neutral Re species has considerably less thiyl radical character than the valence isoelectronic [RuL3]+, which is mainly a Ru(III) (d5, S = 1/2) anti-ferromagnetically (AF) coupled to a thiyl radical (S = 1/2). However, the oxidized derivatives [ReL3]+and [ReL3]2+show significant metal-stabilized thiyl radical character like [RuL3]+. Both [ReL3]+and [ReL3]2+have major contributions from Re(III) (d4, S = 1) centers AF coupled to thiyl and dithiyl DPPBT ligands. These findings are consistent with the experimental chemistry as [RuL3]+, [ReL3]+, and [ReL3]2+can add ethylene to form the new C-S bonds, but [ReL3]0cannot. The thiyl radicals on the S2 position (the S trans to a P donor) serve as the intrinsic electron acceptors in the actual ethylene addition reactions with Ru and Re tris(thiolate) complexes.
authors.affiliation: Department of Chemistry, Texas A&M University , College Station, Texas 77845, United States.
authors.forename: Hao
authors.initials: H
authors.lastname: Tang
authors.affiliation: Science Program, Texas A&M University at Qatar , Doha, Qatar.
authors.forename: Edward N
authors.initials: EN
authors.lastname: Brothers
authors.affiliation: Department of Chemistry, Texas A&M University , College Station, Texas 77845, United States.
authors.forename: Michael B
authors.initials: MB
authors.lastname: Hall