267238-07-3Relevant articles and documents
[2 + 3] Cycloaddition of nitrones to platinum-bound organonitriles: Effect of metal oxidation state and of nitrile substituent
Wagner,Haukka,Frausto da Silva,Pombeiro,Kukushkin
, p. 264 - 271 (2008/10/08)
The ligated benzonitriles in the platinum(II) complex [PtCl2(PhCN)2] undergo metal-mediated [2 + 3] cycloaddition with nitrones -ON+(R3)=C(R1)(R2) [R1/R2/R3 = H/Ph/Me, H/p-MeC6H4/Me, H/Ph/CH2Ph] to give Δ4-1,2,4-oxadiazoline complexes, [PtCl2{N=C(Ph)O-N(R3)-C(R1)(R2)} 2] (2a, 4a, 6a), as a 1:1 mixture of two diastereoisomers, in 60-75% yields, while [PtCl2(MeCN)2] is inactive toward the addition. However, a strong activation of acetonitrile was reached by application of the platinum(IV) complex [PtCl4(MeCN)2] and both [PtCl4-(RCN)2] (R = Me, Ph) react smoothly with various nitrones to give [PtCl4{N=C(R)O-N(R3)-C(R1)(R2)} 2] (1b-6b). The latter were reduced to the corresponding platinum(II) complexes [PtCl2{N=C(R)O-N(R3)-C-(R1)(R2)} 2] (1a-6a) by treatment with PhCH2NHOH, while the reverse reaction, i.e. conversion of 1a-6a to 1b-6b, was achieved by chlorination with Cl2. The diastereoisomers of [PtCl2{N=C(R)O-N(R3)-C(R1)(R2)} 2] (1a-6a) exhibit different kinetic labilities, and liberation of the Δ4-1,2,4-oxadiazolines by substitution with 1,2-bis(diphenylphosphino)ethane (dppe) in CDCl3 proceeds at different reaction rates to give free N=C(R)O-N(R3)-C(R1)(R2) and [PtCl2(dppe)] in almost quantitative NMR yield. All prepared compounds were characterized by elemental analyses, FAB mass spectrometry, and IR and 1H, 13C{1H}, and 195Pt (metal complexes) NMR spectroscopies; X-ray structure determination of the first (Δ4-1,2,4-oxadiazoline)Pt(II) complexes was performed for (S,S)/(R,R)-rac-[PtCl2{N=C(Me)O-N(Me)-C(H)Ph}2] (1a) (a = 9.3562(4), b = 9.8046(3), c = 13.1146(5) A; α = 76.155(2), β = 83.421(2), γ = 73.285(2)°; V = 1117.39(7) A3; triclinic, P1, Z = 2), (R,S)-meso-[PtCl2-(N=(Ph)O-N(Me)-C(H)Ph)2] (2a) (a = 8.9689(9), b = 9.1365(5), c = 10.1846(10) A; α = 64.328(6), β = 72.532(4), γ = 67.744(6)°; V = 686.82(11) A3; triclinic, P1, Z = 1), (S,S)/(R,R)-rac-[PtCl2(N=C(Me)O-N(Me)-C(H)(p-C6H 4Me))2] (3a) (a = 11.6378(2), b = 19.0767(7), c = 11.5782(4) A; β = 111.062(2)°; V = 2398.76(13) A3; monoclinic, P21/c, Z = 4), and (S,S)/(R,R)-rac-[PtCl2(N=C(Me)O-N(CH2Ph)-C(H)Ph 2] (5a) (a = 10.664(2), b = 10.879(2), c = 14.388(3) A; α = 73.11(3), β = 78.30(3), γ = 88.88(3)°; V = 1562.6(6) A3; triclinic, P1, Z = 2).
