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=(CRR2)-R-1}(2)] [(RR2)-R-1 = Me-2, (CH2)(4), (CH2)(5), (Me)C(Me)=NOH], [PtCl4{NH=C(Me)ONR2}(2)] (R = Me, Et, CH2Ph), [PtC4{N=C(Me)O-N(R-3)-C(R-1)(R-2}(2)] (R-1 = H; R-2 = Ph or C6H4Me; R-3 = Me) as well as anionic-type platinum(N) complexes (Ph3PCH2Ph)[PtCl5{NH=C(Me)ON=CR2}] [R-2 = Me-2, (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 Delta (4) 1,2,4-oxadiazoline complexes) were characterized by elemental analyses, FAB mass spectrometry, IR and H-1, C-13{H-1}, P-31{H-1}, and P-31{H-1} Pt-195 NMR spectroscopies, and X-ray single-crystal diffractometry, the latter for [PtCl2{NH=C(Me)ON=CMe2}(2)] [crystal system tetragonal, space group P4(2)/n (No. 86), a = b = 10.5050(10) Angstrom, c =15.915(3) Angstrom] and (Ph3PCH2CO2Me)[PtCl3(NCMe)] [crystal system orthorhombic, space group Pna2(1) (No. 33), a = 19.661(7) Angstrom, b = 12.486(4) Angstrom, c = 10.14(3) Angstrom]. 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.