Computational Hammett analysis of redox based oxy-insertion by Pt(ii) complexes

Abstract

A computational Hammett analysis of oxy-insertion into platinum-aryl bonds is performed. Modeled transformations involve the two-step conversion of [((X)bpy)Pt(R)(OY)](+) (R = p- or m-X-C(6)H(4); Y = 4- or 3-X-pyridine; (X)bpy = 4,4'- or 5,5'-X-bpy; X = NO(2), H, OMe, NMe(2)) proceeding through a Pt-oxo intermediate to form aryloxide [((X)bpy)Pt(OR)(Y)](+), which contrasts a one-step non-redox (Baeyer-Villiger) oxy-insertion. A structural connection is proposed between redox and non-redox transition states, linked to, among other parameters, oxidant identity. The electronic impact of the catalytic components is compared to previous Hammett studies on OMBV transformations. The Hammett sensitivity for aryl migration is diminished for the migrating group (R) and leaving group (Y), components as compared to OMBV transitions, while the bipyridine supporting ligand (L(n)) has an increased impact. The Hammett impact of R, Y and L(n) upon the aryl migration transition state is small in a global sense, ca. 5 kcal mol(-1); therefore, we conclude that the metal and oxidant are the most important factors in controlling oxy-insertion kinetics for these late metal systems. These results also point to a possible mechanistic advantage for redox over non-redox functionalization of hydrocarbons to alcohols.

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

“…1−16 With respect to the mechanism of the C−O bond formation, the oxygen atom of an oxidant (XO) is considered to be inserted into the M−C bonds in a concerted manner (Scheme 1a). 17,18 Cyclometalated complexes comprising group 8 elements and phpy have also been synthesized so far. 19−23 However, most of the research interests have been focused on effects of the strongly electron donating nature of the carbanion to the metal center on photochemical and electrochemical properties or cancer cell cytotoxicity, but little attention has been paid to the detailed reaction mechanism of the C−O bond formation.…”

“…It was confirmed that the oxygen atom of NMO (17 μmol) is not replaced with the labeled one by the reaction with H 2 18 O (100 μL, 5.0 mmol) in acetone (50 μL) at 25 °C for at least 5 h of reaction (Figure S6). If the oxido−osmium(V) species (Os V (O)(phpy)) is formed by the oxygen atom transfer from NMO to Os III (phpy), the oxido group can partially be replaced with the labeled oxygen atom of H 2 18O to form 18 Olabeled (Os V ( 18 O)(phpy)). If so, the labeled Os III ( 18 O-phpy) ([Os III Cl( 18 O-phpy)(tpy)] + ) will be produced from Os V ( 18 O)-(phpy).…”

“…If so, the labeled Os III ( 18 O-phpy) ([Os III Cl( 18 O-phpy)(tpy)] + ) will be produced from Os V ( 18 O)-(phpy). This actually happened in the present reaction (5 h; 25 °C; Os III (phpy), 3.3 μmol; NMO, 17 μmol; H 2 18 O, 65 μL, 3.3 mmol; acetone, 100 μL). The positive ESI mass spectrum of the reaction solution exhibited a peak cluster at m/z = 632.1, the observed peak positions as well as the isotope distribution pattern of which well matched the mixture of [Os III Cl( 16 Ophpy)(tpy)] + :[Os III Cl( 18 O-phpy)(tpy)] + in a 95:5 ratio, as shown in Figure S7.…”

“…-labeled complex Os III ( 18 O-phpy) must be generated via [Os V ( 18 O)Cl(phpy)(tpy)] + that is formed by exchanging the16 O atom of [Os V ( 16 O)Cl(phpy)(tpy)] + formed from [Os III (NMO)Cl(phpy)(tpy)] + with18 O atom of the solvent H 2 . The low ratio (∼ 5%) of Os III ( 18 O-phpy) against Os III ( 16 O-phpy) indicates that the oxygen atom exchange reaction between Os V ( 16 O)(phpy) and H 2 18…”

“…Development of organometallic compounds that have a reactive metal–carbon bond is one of the most advanced areas in the fields of organic synthesis and catalysis. − The cyclometalated compounds have been synthesized to examine fundamental reactivities of the metal–carbon bonds against oxene, nitrene, and carbene sources to produce C–O, C–N, and C–C bonds. − 2-Phenylpyridines (H-phpys) are one of the typical substrates to form such complexes. As a result, many chemically active, especially toward C–O bond formation, cyclometalated complexes consisting of Rh, Ir, Pd, and Pt in group 9 and 10 elements and phpys have been synthesized and characterized. − With respect to the mechanism of the C–O bond formation, the oxygen atom of an oxidant (XO) is considered to be inserted into the M–C bonds in a concerted manner (Scheme a). , …”