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

Abstract

Platinum substrate [Pt 2Me 4(μ-SMe 2) 2] ( 1) reacts with chlorinated imines 3,5-Cl 2C 6H 3CHNCH 2C 6H 5 ( 2a) and 3-ClC 6H 4CHNCH 2C 6H 5 ( 2b) to yield cyclometallated platinum(II) compounds [PtMe(3,5-Cl 2C 6H 2CHNCH 2C 6H 5)(SMe 2)] ( 4a) and [PtMe(3-ClC 6H 3CHz.dbnd;NCH 2C 6H 5)(SMe 2)] ( 4b), arising from CH bond activation followed by loss of methane. A react intermediate [PtMe 2(3,5-Cl 2C 6H 3CHNCH 2C 6H 5)(SMe 2)] ( 3a) was detected by 1H NMR. The reaction of [Pt 2Me 4(μ-SMe 2) 2] ( 1) with chlorinated imine 2,4,-Cl 2C 6H 3CHNCH 2C 6H 5 ( 2c) produces a mixture of cyclometallated platinum(II) compound [PtMe(2,4- Cl 2C 6H 2CHNCH 2C 6H 5)(SMe 2)] ( 4c) and cyclometallated platinum(IV) compound [PtMe 2Cl(4-ClC 6H 3CHNCH 2C 6H 5)(SME 2)] ( 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-Cl 2C 6H 2CHNCH 2C 6H 5)PPh 3) 2] ( 5a) is formed with the imine acting as a [C −] unidentate ligand. 5a crystallizes in the monoclinic space group P2 1/ 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 PPh 3 to give cyclometallated compounds [PtMe(3-ClC 6H 3CHNCH 2 C 6H 5)(PPh 3)] ( 5b), [PtMe(2,4-Cl 2C 6H 2CHNCH 2C 6H 5)(PPh 3)] ( 5c), and [PtMe 2Cl(4-ClC 6H 3CHNCH 2C 6H 5)(PPh 3)]( 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.