C-H and C-Cl bond activation in the formation of cyclometallated platinumt(II) and platinum(IV) compounds with chlorinated N-benzylidenebenzylamines

Article abstract of DOI:10.1016/0022-328X(96)06221-3

Platinum substrate [Pt₂Me₄(μ-SMe₂)₂] (1) reacts with chlorinated imines 3,5-Cl₂C₆H₃CH=NCH₂C₆H₅ (2a) and 3-ClC₆H₄CH=NCH₂C₆H₅ (2b) to yield cyclometallated platinum(II) compounds [PtMe(3,5-Cl₂C₆H₂CH=NCH₂C₅H₅)(SMe₂)] (4a) and [PtMe(3-ClC₆H₃CH=NCH₂C₆H₅)(SMe₂)] (4b), arising from C-H bond activation followed by loss of methane. A reaction intermediate [PtMe₂(3,5-Cl₂C₆H₃CH=NCH₂C₆H₅)(SMe₂)] (3a) was detected by ¹H NMR. The reaction of [Pt₂Me₄(μ-SMe₂)₂] (1) with chlorinated imine 2,4-Cl₂C₆H₃CH=NCH₂C₆H₅ (2c) produces a mixture of cyclometallated platinum(II) compound [PtMe(2,4-Cl₂C₆H₂CH=NCH₂C₆H₅)(SMe₂)] (4c) and cyclometallated platinum(IV) compound [PtMe₂Cl(4-ClC₆H₃CH=NCH₂C₆H₅)(SMe₂)] (4c′) arising respectively from aryl C-H and aryl C-Cl bond activation. The reaction of complex 4a with triphenylphosphine produces metallacycle cleavage and [PtMe(3,5-Cl₂C₆H₂CH=NCH₂C₆H₅)(PPh₃)₂] (5a) is formed with the imine acting as a [C^-] unidentate ligand. 5a crystallizes in the monoclinic space group P2₁/n with a = 10.899(5) A, b = 22.953(5) A and c = 17.588(9) A, β = 95.14(5)° and Z = 4. Compounds 4b, 4c and 4c′ react with PPh₃ to give cyclometallated compounds [PtMe(3-ClC₆H₃CH=NCH₂C₆H₅)(PPh₃)] (5b), [PtMe(2,4-Cl₂C₆H₂CH=NCH₂C₆H₅)(PPh₃)] (5c), and [PtMe₂Cl(4-ClC₆H₃CH=NCH₂C₆H₅)(PPh₃)] (5c′) respectively. The stereo-electronic effect of chlorine substituents, as well as the NMR parameters, are discussed in relation to the observed reactivity of these compounds.