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]Cl2 (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-κC,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-κC,C,P)X] (X = Br (4), I (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-κC,C,P}Cl2] (6), obtained by reaction of [(p-FC6H4)3PCH2-(E)-C(Me)C(H)P(p-FC6H4)3]Cl2 (1f) 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-κC,C,P)(L)](ClO4) (L = NCMe
(8), PPh3 (9), pyridine (10), C⋮NtBu (11)) and [Pt(C6H3-3-Ph-2-PPh2-CC(Me)CH2PPh2-κC,C,P)(L−L-κP)](ClO4) (L−L = Ph2PCH2PPh2 (12)). Complex 3 reacts with excess X2 (Cl2,
I2) to give the expected Pt(IV) derivatives [Pt(C6H3-3-Ph-2-PPh2-CC(Me)CH2PPh2-κC,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.