Protolytic Stability of (dfepe)Pt(Ph)O₂CCF₃:  Supporting Evidence for a Concerted S_E2 Protonolysis Mechanism

Abstract

An extension of prior protonolysis studies of platinum−carbon bonds to Pt−aryl bonds is reported. The protolytic stability of (dfepe)Pt(Ph)(O2CCF3) (dfepe = (C2F5)2PCH2CH2P(C2F5)2) in trifluoroacetic acid is found to be much less than (dfepe)Pt(Me)(O2CCF3), indicating that a concerted SE2 protonolysis mechanism is most likely operative in these electron-poor platinum systems. VT NMR experiments show that benzene coordination to the (dfepe)Pt2+ center in neat fluorosulfonic acid to form (dfepe)Pt(η6-C6H6)2+ at −80 °C is competitive with benzene dissociation in this weakly coordinating medium.

A T-shaped Ni[κ2-(CF2)4–] NHC complex: unusual Csp3–F and M–CFbond functionalization reactions

“…p K a ∼11). 31 With the bulkier trimethylbenzoic acid, kinetic acidity factors in the tighter 5-membered ring transition state could severely limit HF elimination. 32 …”

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

“…Mechanistic aspects of the protonolysis of M-R (R = alkyl or aryl) bonds, which is considered as the microscopic reverse reaction of selective activation and functionalization of saturated alkane C-H bonds, have been extensively investigated. [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.…”

Unusual [Pt{κ2(C,N)}]+ → [Pt{κ2(N,N)}]+ Coordination Mode Flip of the Guanidinate(1−) Ligand in Cationic N,N′,N″-Tris(3,5-xylyl)guanidinatoplatinum(II) Bis(phosphine) Complexes. Syntheses, Structural and Theoretical Studies

“…Protonation of the Pt–C bond in organoplatinum complexes and mechanistic aspects pertinent to this subject has been extensively discussed in the literature. Protonation of the Pt–C bond in organoplatinum complexes can occur via (i) a concerted S E 2 pathway and (ii) stepwise oxidative addition to the Pt­(II) atom followed by reductive elimination, an S E ox pathway. ,− Thus, the protonation of the intermediate E with trifluoroacetic acid can occur via oxidative addition to afford the cationic Pt IV -hydride species G , and this transformation was calculated to be more exergonic in nature by 63.8 kcal/mol; nevertheless, the formation of 16 ′ from G via H is not feasible (see Scheme ). Probably, the Pt­(II) atom in the model complex 22 ′ is much less crowded than that in 22 and thus protonation of the former complex becomes easier and as a result this step is more exergonic in our calculations.…”

“…The fact that we were able to isolate both 16 and 17 only when the platinated aryl ring in their respective precursors contains Me substituents in 4,6-positions and not in 3,5-, 3,6-, and 4,5-positions suggests the pathway illustrated in Scheme (see Figure ). The formations of a Wheland intermediate such as F and an agostic complex such as H have been invoked as intermediates in the protonation of organoplatinum­(II) phosphine complexes. , …”