Catalytic Deuteration of C(sp²)–H Bonds of Substituted (Hetero)arenes in a Pt(II) CNN-Pincer Complex/2,2,2-Trifluoroethanol-d₁ System: Effect of Substituents on the Reaction Rate and Selectivity

Abstract

Thirty four (hetero)­arene derivatives have been tested in catalytic H/D exchange reactions involving their C­(sp2)–H bonds and 2,2,2-trifluoroethanol-d 1 (TFE-d 1) in the presence of the homogeneous Pt­(II) complex 1 supported by a sulfonated CNN-pincer ligand at 80 °C. The 18 substrates, including one pharmaceutical (naproxen), that are stable in the presence of 1 and are active in the H/D exchange reaction have been characterized by their position-specific extent of deuteration and, in a number of cases, the reaction kinetic selectivity. For the most reactive substrates the extent of deuteration approaches the expected statistical distribution of the exchangeable H and D atoms: e.g., 67–69% for phenol after 23 h and 88% for indole β-CH bonds after 45 min. For a few substrates (N,N-dimethylaniline, indole, nitrobenzene) the H/D exchange is highly position selective. No satisfactory correlation was found between the position-specific (meta, para) H/D exchange rate constants for X-monosubstituted benzenes and Hammett σX constants. This observation was proposed to be related to the concerted nature of the CH bond activation, the rate-determining CH bond oxidative addition at a Pt­(II) center. A novel scale of Hammett σM X constants was introduced to characterize the reactivity of C­(sp2)–H bonds in transition-metal-mediated reactions. The experimentally determined position-specific Gibbs energies of activation of the H/D exchange in substituted benzenes (meta and para positions) as well as in thiophene (α and β positions) were matched satisfactorily using DFT calculations.

Recent Developments for the Deuterium and Tritium Labeling of Organic Molecules

“…Very high deuterium incorporation of unfunctionalized arenes can simply be achieved by prolonged heating in the presence of catalytic amounts of strong acid in deuterated benzene (Scheme b) . The deuteration of similar substrates with a platinum CNN pincer complex and a mixture of monodeuterated trifluoroethanol and deuterium oxide resulted in moderate to low deuterium incorporation levels for noncoordinating or weakly coordinating substrates, whereas only catalyst decomposition was observed in the presence of coordinating groups (Scheme c) …”

Oxidative Addition of a Hypervalent Iodine Compound to Cycloplatinated(II) Complexes for the C–O Bond Construction: Effect of Cyclometalated Ligands

“…The appearance of a broad singlet signal at 9.62 ppm was attributed to the hydrogen atoms of the H 2 O ligand bound to Pt. This chemical shift is somewhat unusual for aqua ligands in the platinum complexes, − and it is suggesting the existence of notable hydrogen bonding in the molecular packing. , This bonding is observed in the crystal structure of 2a between the hydrogen of H 2 O and oxygen of N -oxide group (Figure ), while this signal and the interaction were not detected in its analogue Pt­(IV) complex [PtMe­(ppy)­(OAc) 2 (H 2 O)], 2b . Also, this signal does not have any cross-peaks with carbon atoms in the HSQC experiment (Figure S7).…”

Oxidation of Methylplatinum(II) Complexes K[(L)PtIIMe] with O2 and C(sp3)-X (X = O and C) Reductive Elimination Reactivity of Methylplatinum(IV) Products (L)PtIVMe(OH): The Effect of Structure of Sulfonated CNN-Pincer Ligands L

“…These complexes are the active catalysts of H/D exchange between various arenes and TFE-d 1 /D 2 O (TFE = 2,2,2trifluoroethanol) mixtures (compare with step a, Scheme 1). 10,14,15 Remarkably, when reacted with arenes ArH under an O 2 atmosphere, 1 produced arylplatinum(IV) derivatives 2 (compare with steps a and b, Scheme 1), along with formal products of their C−C coupling, 3. 11 On the downside, similar to arylplatinum(IV) complex (dpms)Pt IV Ph(OH), 16 4 (Scheme 2, b), supported by an earlier generation of sulfonated dipyridine ligands such as di(2pyridyl)methanesulfonate (dpms), the resulting Pt(IV) aryl hydroxo complexes (L1)Pt IV Ar(OH), 2, are inert in C−O reductive elimination (compare with step c, Scheme 1).…”

“…These complexes are the active catalysts of H/D exchange between various arenes and TFE- d 1 /D 2 O (TFE = 2,2,2-trifluoroethanol) mixtures (compare with step a , Scheme ). ,, Remarkably, when reacted with arenes ArH under an O 2 atmosphere, 1 produced arylplatinum­(IV) derivatives 2 (compare with steps a and b , Scheme ), along with formal products of their C–C coupling, 3 …”