Reduction of (imine)Pt(IV) to (imine)Pt(II) Complexes with Carbonyl-Stabilized Phosphorus Ylides

A novel method is reported for generation of the difficult-to-obtain (imine)Pt(II) compounds that involves reduction
of the corresponding readily available Pt(IV)-based imines by carbonyl-stabilized phosphorus ylides, Ph3PCHCO2R, in nonaqueous media. The reaction between neutral (imino)Pt(IV) compounds [PtCl4{NHC(Me)ONCR1R2}2] [R1R2 = Me2, (CH2)4, (CH2)5, (Me)C(Me)NOH], [PtCl4{NHC(Me)ONR2}2] (R = Me, Et,
CH2Ph), (R1 = H; R2 = Ph or C6H4Me; R3 = Me) as well as anionic-type platinum(IV) complexes (Ph3PCH2Ph)[PtCl5{NHC(Me)ONCR2}] [R2 = Me2, (CH2)4, (CH2)5] and 1
equiv of Ph3PCHCO2R (R = Me, Et) proceeds under mild conditions (ca. 4 h, room temperature) to give
selectively the platinum(II) products (in good to excellent isolated yields) without further reduction of the platinum
center. All thus prepared compounds (excluding previously described Δ4-1,2,4-oxadiazoline complexes) were
characterized by elemental analyses, FAB mass spectrometry, IR and 1H, 13C{1H}, 31P{1H} and 195Pt NMR
spectroscopies, and X-ray single-crystal diffractometry, the latter for [PtCl2{NHC(Me)ONCMe2}2] [crystal
system tetragonal, space group P42/n (No. 86), a = b = 10.5050(10) Å, c = 15.916(3) Å] and (Ph3PCH2CO2Me)[PtCl3(NCMe)] [crystal system orthorhombic, space group Pna21 (No. 33), a = 19.661(7) Å, b = 12.486(4)
Å, c = 10.149(3) Å]. The reaction is also extended to a variety of other Pt(II)/Pt(IV) couples, and the ylides
Ph3PCHCO2R are introduced as mild and selective reducing agents of wide applicability for the conversion of
Pt(IV) to Pt(II) species in nonaqueous media, a route that is especially useful in the case of compounds that
cannot be prepared directly from Pt(II) precursors, and for the generation of systematic series of Pt(II)/Pt(IV)
complexes for biological studies.