Details

Autor(en) / Beteiligte

• Varela-Álvarez, Adrián
• Yang, Tzuhsiung
• Jennings, Heather
• Kornecki, Katherine P
• Macmillan, Samantha N
• Lancaster, Kyle M
• Mack, James B. C
• Du Bois, J
• Berry, John F
• Musaev, Djamaladdin G

Titel

Rh2(II,III) Catalysts with Chelating Carboxylate and Carboxamidate Supports: Electronic Structure and Nitrene Transfer Reactivity

Ist Teil von

• Journal of the American Chemical Society, 2016-02, Vol.138 (7), p.2327-2341

Ort / Verlag

United States: American Chemical Society

Erscheinungsjahr

2016

Quelle

MEDLINE

Beschreibungen/Notizen

• Dirhodium-catalyzed C–H amination is hypothesized to proceed via Rh2-nitrene intermediates in either the Rh2(II,II) or Rh2(II,III) redox state. Herein, we report joint theoretical and experimental studies of the ground electronic state (GES), redox potentials, and C–H amination of [Rh2 II,III(O2CCH3)4(L) n ]+ (1_L) (L = none, Cl–, and H2O), [Rh2(esp)2]+ (2), and Rh2(espn)2Cl (3) (esp = α,α,α′,α′-tetramethyl-1,3-benzenedipro­panoate and espn = α,α,α′,α′-tetramethyl-1,3-benzenedipro­panamidate). CASSCF calculations on 1_L yield a wave function with two closely weighted configurations, (δ*)2(π1*)2(π2*)1 and (δ*)2(π1*)1(π2*)2, consistent with reported EPR g values [ Chem. Phys. Lett. 1986, 130, 20−23 ]. In contrast, EPR spectra of 2 show g values consistent with the DFT-computed (π*)4(δ*)1 GES. EPR spectra and Cl K-edge XAS for 3 are consistent with a (π*)4(δ*)1 GES, as supported by DFT. Nitrene intermediates 2N_L and 3N_L are also examined by DFT (the nitrene is an NSO3R species). DFT calculations suggest a doublet GES for 2N_L and a quartet GES for 3N_L. CASSCF calculations describe the GES of 2N as Rh2(II,II) with a coordinated nitrene radical cation, (π*)4(δ*)2(πnitrene,1)1(πnitrene,2)0. Conversely, the GES of 3N is Rh2(II,III) with a coordinated triplet nitrene, (π*)4(δ*)1(πnitrene,1)1(πnitrene,2)1. Quartet transition states (4TSs) are found to react via a stepwise radical mechanism, whereas 2TSs are found to react via a concerted mechanism that is lower in energy compared to 4TSs for both 2N_L and 3N_L. The experimental (determined by intramolecular competition) and 2TS-calculated kinetic isotopic effect (KIE) shows a KIE ∼ 3 for both 2N and 3N, which is consistent with a concerted mechanism.