Kinetico-Mechanistic Insight into the Platinum-Mediated C-C Coupling of Fluorinated Arenes

The reaction of compound CiS-[Pt(C6F5)(2)(SEt2)(2)] with the imine ligands ArCH=NCH2CH2NMe2 (Ar = 2-Br-C(6)H4 (1a) or 2,6-Cl2C6H3 (1b)) in toluene produces coordination compounds cis-[Pt(C6F5)(2)(ArCH=(N) under bar CH2CH2(N) under bar Me-2)] (2a, 2b) containing a bidentate [N,N'] ligand. No further reactivity has been observed from this point. Compound 2b has been characterized by single-crystal XRD. Under analogous conditions, ii-nine ligand 2-BrC6H4CH=NCH2(4'-C1C(6)H(4)) (1c) produced the Pt-II-metalated compound [PtBr{6-(C6F5)(2-(C) under bar )C5H3CH (N) under bar CH2(4'-ClC6H4)SEt2] (2c), which contains a five-membered metallacycle with a biaryl linkage involving a C6175 group. The derivative compounds [PtBr{6-(C6F5)(2-(C) under bar )C5H3CH (N) under bar CH2(4'-CIC6H4)L] (L = SMe2 (3c), L = PPh3 (4c)) were also prepared, and compound 4c has also been characterized by XRD. The kinetico-mechanistic study of the formation of compound 2c has also been Pursued in view of the previously published data, leading to seven-membered metallacycles. The time monitoring via UV-vis of the full process allowed the detection and NM R characterization of two intermediate species. An initial Pt-IV complex is present in steady-state low-concentration conditions, and formation of a non-cyclometalated intermediate Pt-II compound is also detected during the process. The latter already contains the C-C coupled ligand arising from a reductive elimination of the former. Intramolecular C-H activation from the latter produces the final characterized compound 2c along with C6F5H. The fill I process has been studied as a function of temperature and pressure as well as at varying nonstoichicimetric concentrations of SEt2 and free imine ligand. The results agree with the quenching of the process at important excesses of SEt2 (for stoichiometric reasons) or free imine (avoiding the formation of the final complex from the C-C reductively coupled intermediate). The thermal and pressure activation parameters measured indicate that the mechanism operating in this case lies out of the continuum existing for the series of C-H bond activations studied so far. The more than probable associative shift of the reactivity of the Pt-II complex containing the electron-withdrawing C6F5 ligands is held responsible for this fact.