C-P and C-H bond activations and C-C coupling in bis-phosphonium salts induced by platinum(II) complexes

The reaction of [Ph3PCH2-(E)-C(Me)=C(H)PPh3]Cl-2 (1b) with PtCl2(NCPh)(2) (1:1 molar ratio) in refluxing 2-methoxyethanol gives the ortho-metalated complex [Pt(C6H3-3-Ph-2-PPh2-C=C(Me)CH2PPh2-kappaC,C,P)Cl] (3). The synthesis of complex 3 formally involves three C-H and one C-P bond activation and one C-C bond coupling. Complex 3 reacts with excess KBr or NaI to give, after halide metathesis, the complexes [Pt(C6H3-3-Ph-2-PPh2-C=C(Me)CH2PPh2-kappaC,C,P)X] (X = Br (4), 1 (5)). Complex 5 has been characterized by X-ray diffraction methods. The influences of several factors, such as the solvent, the platinum starting complex, and the bis-phosphonium salt, in the synthesis of 3 have been examined, and a plausible reaction mechanism for the synthesis of 3 is proposed. This mechanism is supported by the isolation of the Pt(IV) derivative [Pt(C6H4-4-F){C6H3-5-F-2-P(p-FC6H4)(2)-C=C(Me)CH2P(p-FC6H4)(2)-kappaC,C,P}Cl-2] (6), obtained by reaction of [(p-FC6H4)(3)PCH2-(E)-C(Me)=C(H)P(p-FC6H4)(3)]Cl-2 (If) with PtCl2(NCPh)(2) in refluxing 2-methoxyethanol. Complex 3 reacts with AgClO4 and neutral monodentate (L) and bidentate (L-L) ligands, giving the cationic derivatives [Pt(C6H3-3-Ph-2-PPh2-C=C(Me)CH2PPh2-kappaC,C,P)(L)](ClO4) (L = NCMe (8), PPh3 (9), pyridine (10), C=(NBu)-Bu-t (11)) and [Pt(C6H3-3-Ph-2-PPh2-C=C(Me)CH2PPh2-kappaC,C,P)(L-L-kappaP)](ClO4) (L-L = Ph2PCH2PPh2 (12)). Complex 3 reacts with excess X-2 (Cl-2, 12) to give the expected Pt(IV) derivatives [Pt(C6H3-3-Ph-2-PPh2-C=C(Me)CH2PPh2-kappaC,C,P)-(Cl)(X)(2)] ((X)(2) = (Cl)(2) (13), (I)(2) (14)) through a typical oxidative addition process. Complex 14 has also been characterized by X-ray diffraction methods.