Chemistry of metallacyclobutanones. Part I . Synthesis and ring inversion of some highly puckered metallacyclobutan-3-one (slipped oxodimethylenemethane) complexes of platinum ; crystal structure of 2,4-bis(methoxycarbony1)-1,1-bis(triphenylphosphine)platinacyclobutan-3-one monohydrate

Abstract

The reactions of the carbonato-complexes [ Pt (CO2) L2] with esters of 3-oxopentanedioic acid, RCH2COCH2R, in warm ethanol afford, in high yield, the formally platinacyclobutan-3-one compounds [Pt(CHRCOCHR)L,] (R = C02Me, L = PPh,, AsPh,, PMePh, or PMe2Ph; 2L = Ph2PCH2CH2PPh2; - R = C02Et, L = PPh,, or AsPh,; R = C02Prn, L = PPh,, or AsPh,). The compounds [Pk(CHRCOCHR)- L2] (R = C02Me, L = PPh,, AsPh,, PMePh,, or PMe2Ph; R = C02Et, L = PPh, or AsPh,) are also formed upon treatment of benzene solutions of [PtL,] with RCH2COCH2R in the presence of air. Using the latter method, the triphenylphosphine derivative [ Pi{CH ( C02Me)COCH ( C02Me) I( PPh3)2] is often contaminated with the peroxo-ring compound [P~{OOC(CH2C02Me)20)( PPh,),] which is the major product if the reaction is carried out in diethyl ether. The reaction of [Pt(02)(PPh3)2] with Me02CCH2COCH2C02Me in diethyl ether also gives the peroxo-ring compound. Treatment of Me02CCH2COCH2C02Me with either [Pt(trans-PhCHZCHPh) ( PPh3)2] in benzene in the presence of air, [PtOOC(O)O(PPh,),] in ethanol, ~is-[Pt(OC0Ph)~(PPh,)~l in ethanol, or cis-[PtC12( PPh3)2] and - silver oxide in dichloromethane also affords [Pt{CH(C02Me)COCH(C02Me)}(PPh,),l. A single-crystal X-ray diffraction study has been carried out on [Pt(CH(CO,Me)COkH(CO,Me))( PPh3)2]*H20 (3a). The crystals are triclinic, space group P I , Z = 2, in a unit cell with a = 17.59(1), b = 12.736(6), c = 10.27(1) A, ac = 118.2(1), p = 94.7(1), and y = 74.0(1)'. The structure has been refined to R 0.035 (R' 0.036) for 7 263 reflections with / 2 30(/). It can be considered to be based either upon a highly puckered platina- cyclobutan-3-one ring [fold angle = 50.4(4)'] with a weak transannular Pt-C bond of 2.416(5) A, or as a slipped q3-oxodimethylenemethane compound. N.m.r. data ( H, I3C-{ H}, and 31 P-(H}) are reported and variable-temperature H n.m.r. data for the compounds [Pi( CH RCOCH R) L2] (R = C02Me, L = PPh, or AsPh,) are interpreted in terms of inversion of the platinacyclobutan-3-one ring through a planar transition state. The magnitude of the platinum-I95 coupling to the axial and equatorial ring hydrogens of the platinacyclobutan-3-one ring is dependent upon the orientation of of the CH bonds with respect to the square planar platinum function and the magnitudes of 3J(cis- PPtCH) are controlled by the dihedral angle.