Synthesis of ketonylplatinum(III) dinuclear complexes: Observation of the competitive radical vs electrophilic displacement in Pt(III)-promoted C-H bond activation of ketones

New ketonylplatinum(III) dinuclear complexes [Pt-2((CH3)(3)CCONH)(2)(NH3)(4 )(CH2COPh)] (NO3)(3) (4), [Pt-2((CH3)(3)CCONH)(2)(NH3)(4)(CH(CH3)COC2H5)](N O3)(3) (5), and [Pt-2((CH3)(3)CCONH)(2)(NH3)(4)(CH2COCH2COCH3)](NO3)(3) (6) were prepared by treatment of platinum blue complex [Pt-4(NH3)(8)((CH3)(3) CCONH)(4)](NO3)(5) (2) with acetophenone, 3-pentanone and acetylactone, res pectively, in the presence of concentrated HNO3 The structures of complexes 4; and 6 have been confirmed by X-ray diffraction analysis, which revealed that the C-H bonds of the methyl groups in acetophenone and acetylacetone have been cleaved and Pt(III)-C bonds are formed. Formation of diketonylpla tinum(III) complex 6 provides a novel example of the C-H bond activation no t at the central alpha -C-H but at the terminal methyl of acetylacetone. Re action with butanone having unsymmetrical alpha -H atoms led to two types o f ketonylplatinum(III) complexes [Pt-2((CH3)(3)CCONH)(2)(NH3)(4)(CH(CH3)COC H3)](NO3)(3) (7a) and [Pt-2((CH3)(3)CCONH)(2)(NH3)(4)(CH2COCH2CH3)] (NO3)(3 ) (7b) at a molar ratio of 1.7 to 1 corresponding to the C-H bond activatio n of methylene and methyl groups, respectively. Use of 3-methyl-2-butanone instead of butanone gave complex [Pt-2((CH3)(3)CCONH)(2)(NH3)(4)(CH2COCH(CH 3)(2))](NO3)(3) (8) as a sole product via C-H bond activation in the alpha -methyl group. The reactivity of the ketonylplatinum(III) dinuclear complex es toward nucleophiles, such as H2O and HNEt2, was examined. The alpha -hyd roxyl- and alpha -amino-substituted ketones were generated in the reactions of [Pt-2((CH3)(3)CCONH)(2)(NH3)(4)(CH2COCH3)](NO3)(3) (1), 5, and a mixtur e of 7a and 7b with water and amine, which indicates that the carbon atom i n the ketonyl group bound to the Pt(III) atom can receive a nucleophilic at tack. The high electrophilicity of the ketonylplatinum(III) complexes can b e accounted for by the high electron-withdrawing ability df the platinum(II I) atom. A competition between the radical and electrophilic displacement p athways was observed directly in the C-H bond activation reaction with buta none giving complexes 7a and 7b. Addition of a radical trapping agent suppr essed the radical pathway and gave complex 7b as the predominant product. O n the contrary, 7a was formed as the main product when the reaction solutio n was irradiated by mercury lamp light. These results together with ether m echanistic studies demonstrate that complex 7a was produced via a radical p rocess, whereas complex 7b is produced via electrophilic displacement of a proton;by the Pt(III) atom. The competitive processes were further observed in the reactions of platinum blue complex 2 with a mixture of,acetone and 3-pentanone in the presence of HNO3. The relative molar ratio of acetonyl complex 1 to pentanoyl complex 5 was 3 to 1 under room Light, whereas formation of complex 5 was almost suppresse d when the reaction was carried out in the dark with the addition of a radi cal trapping agent.