Oxygen Atom Insertion into the Osmium–Carbon Bond via an Organometallic Oxido–Osmium(V) Intermediate

Abstract

A cyclometalated osmium­(III) complex, [OsIIICl­(phpy)­(tpy)]+ (OsIII(phpy); phpy = 2-C6H4-2′-C5H4N-κC,N) is synthesized from OsIIICl3(tpy) (tpy = 2,2′;6′,2″-terpyridine) and 2-phenylpyridine (H-phpy) in the presence of AgPF6, in which the metalated carbon atom is disposed trans to the chlorido ligand. Oxidation of OsIII(phpy) with oxygen atom transfer oxidants such as N-methylmorpholine N-oxide (NMO), N,N-dimethylaniline N-oxide (DMAO), H2O2, t-BuOOH, and m-chloroperoxybenzoic acid (m-CPBA) in CH3CN or electron transfer type oxidants such as (NH4)2S2O8 and ammonium hexanitratocerate (CAN) in H2O/acetone causes oxygen atom insertion between the osmium­(III)–carbon bond to give a phenoxido–osmium­(III) complex OsIII(O-phpy). Isotope labeling experiments using H2 18O and kinetic studies as well as calculation studies indicate formation of an organometallic oxido–osmium­(V) complex as the active intermediate.

Catalytic synthesis of phenols with nitrous oxide

“…However, regioselectivity issues arose, as the O atom was competitively transferred to the hydride ligand, thus also producing a Hf‒O‒H complex ( 3 ). Mechanistic studies on the O insertion step into various M‒C( sp 2 ) bonds using N 2 O, peroxides or oxygen suggest that an organometallic Baeyer–Villiger (OMBV)-type mechanism is operating, whereby the anionic carbon migrates to the coordinated O atom, forging the M‒O‒C bond 18 – 23 . On the basis of this reactivity, we aimed at unlocking the potential of N 2 O as an O-atom source in a fundamentally different catalytic synthesis of phenols.…”

“…These findings suggest that reduction of Ni(II) species to formal Ni(I) and the presence of iodide salts in the system are of importance to forge the desired C( sp 2 )‒O bond. Mechanistic investigations on M‒Ar oxy insertions for late transition metals (Pd, Ni and Fe) reveal that subtle changes in the ligand environment also lead to differences between the metal‒oxo/oxyl or concerted Baeyer-Villiger pathways for Ar‒O bond formation 18 – 23 . In this case, we suggest that in the continuum between the two extreme possibilities offered in the OMBV reaction, the oxy insertion of N 2 O in a d 9 complex lies towards the formation of the M‒O bond and N 2 , before Ar migration 39 .…”

Mechanism of Nitrous Oxide Activation in C(sp2)–O Bond Formation Reactions Catalyzed by Nickel Complexes

“…The relatively small difference between the activation free energies of concerted A and stepwise C mechanisms is a further confirmation that there is a continuum between the concerted Baeyer–Villiger and metal–oxo/oxyl concerted pathways. − This suggests that changes in the ligand environment may lead to different preferences among the viable pathways for C­(sp 2 )–O bond formation. These results are consistent with experimental reactivity studies of Cornella and co-workers …”

Structural, spectroscopic, luminescence sensing and TD–DFT theoretical studies of a CuP2N-type complex

“…In the CuP 2 N coordination triangle, the Cu-P and Cu-N bond lengths (Table 2) are comparable with those in analogous heteroleptic structures with BINAP or pyridine-type ligands (Ken et al, 2006;Nieto et al, 2008;Tan et al, 2012;Xu et al, 2014;Chai et al, 2015a;Hasegawa et al, 2017;Wang et al, 2020b). 2-PhPy is often used as a chelating ligand for Ir, Pd, Pt, Os, Au and other metal ions to produce complex functional materials Belviso et al, 2021;Sugimoto et al, 2021;Gukathasan et al, 2021). However, in I, the 2-PhPy ligand uses only the pyridine N atom in a terminal coordination mode, while its phenyl group is not used.…”