Activation of Anisole by Organoplatinum(II) Complexes: Evidence for Rate-Determining C–H Activation

Abstract

A study of the basis of selectivity of C−H bond activation of anisole by electrophilic methylplatinum(II) complexes is reported. Anisole reacts with [PtXMe-(NN)] in trifluoroethanol solvent to give methane and [PtXAr(NN)], Ar = 2-, 3-, and 4-anisyl, in 90:8:2 ratio when X = HOB(C 6 F 5 ) 3 and NN = (2-C 5 H 4 N) 2 CO (DPK) but not when NN = 2,2′-bipyridine. Similar results are obtained when X = triflate or when NN = (2-C 5 H 4 N) 2 NH. Competition between reaction of anisole and anisole-d 8 with [PtXMe(NN)], X = HOB(C 6 F 5 ) 3 and NN = DPK, in trifluoroethanol gave an isotope effect k H /k D = 3.6. Several 4-anisyl complexes, [PtClAr(NN)], [PtAr 2 (NN)], and [PtMeAr(NN)], NN = DPK, DPA, or bipy, were prepared and reacted with HX [X = Cl, OTf, or HOB(C 6 F 5 ) 3 ]. Reaction of [PtMeAr(NN)], NN = DPK or bipy, with HX gave a detectable hydride [PtXHMeAr(NN)] when X = Cl, followed by loss of methane to give [PtClAr(NN)], but only [Pt(OTf)Ar(NN)] was detected when X = OTf. Reaction with more HOTf gave anisole and [PtX 2 (NN)], X = OTf, and no isomerization of the 4-anisyl group to the more favored 2-anisyl group was observed at any stage. The similar reaction of [PtMeAr(NN)] and HOTf in CD 3 OD/CD 2 Cl 2 gave CH n D 4−n (n = 0−4) and mostly 4-MeOC 6 H 4 D. It is argued that the anisole C−H bond cleavage step in anisole activation, or the anisyl−H bond forming step in protonolysis, is responsible for the observed selectivity in these reactions.

Selectivity in metal–carbon bond protonolysis in p-tolyl- (or methyl)-cycloplatinated(ii) complexes: kinetics and mechanism of the uncatalyzed isomerization of the resulting Pt(ii) products

“…[22][23][24][25][26][27][28][29][30][31][32][33] The reports in the literature indicate that usually in alkyl-arylplatinum(II) and methyl-cycloplatinated(II) complexes, the Pt-C(alkyl) bond, rather than the Pt-C(aryl) bond, is cleaved in Pt-R protonolysis. [34][35][36][37][38][39][40][41][42][43][44] However, there are a few other reports showing that quite different selectivity in Pt-C bond protonation is observed on changing the spectator ligands in alkyl-arylplatinum(II), and alkyl-(or aryl)-cycloplatinated(II) complexes. 45,46 We report here the synthesis of a number of new bis-chelate complexes of the type [Pt(C^N)(P^P)][CF 3 CO 2 ], 4, in which C^N = ppy or bhq and P^P = dppe or dppf, by the protonolysis of some proper p-tolyl-(or methyl)-cycloplatinated(II) precursors.…”

Theoretical Study on the Mechanism of Hydrogen Evolution Reaction Catalyzed by Platinum Subnanoclusters

“…38,39 The Pt-Oaqua distances (2.122 Å) in this species are roughly comparable to those in the standard squareplanar Pt(II) complexes (e.g., 2.04-2.13 Å for [Pt(OH2)2(bpy)] 2+ , trans-[PtCl2(PPh3)(OH2)], etc.). [46][47][48][49] It must be, however, noted that only a single filled bonding orbital contributes to the stabilization of the two Pt-Oaqua bonds (Figure S3), indicative of the 3-center 2-electron (3c-2e) bonding in this Oaqua-Pt-Oaqua geometry. This also reveals that S5; Figure S6, Tables S64 and S65).…”

Recent advances in the application of group-10 transition metal based catalysts in C–H activation and functionalization

“…To determine the basicity of selectivity of C−H bond activation of anisole by electrophilic methyl Pt(II) complexes, a study has been reported by Puddephatt and coworkers [83]. When the Pt(II) complex reacts with anisole in TFE, it produces methane as the major product (90%) with two minor anisyl complexes (10% collectively).…”