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The first X-ray crystal structure of an oxochromium(v) complex capable of effecting oxygen atom transfer t o alkenes in stoicheiometric and catalytic systems is reported.Oxygen atom transfer to effect the catalytic epoxidation of alkenes with oxometal species, i.e., equation (l), is currently of synthetic and theoretical intere~t.l-~ We report the first isolation and structure determination of a series of catalytically active oxochromium(v) complexes generated from various well-characterized chromium(m)salen [salen = N,N'-ethylenebis(salicylideneaminato)] comple~es.~ In a typical example, the treatment of Cr(salen)(H,O),+PF,-with iodosylbenzene in acetonitrile, followed a few minutes later by the slow addition of diethyl ether, led to the isolation of O=Cr(salen)+PF,-(1) in 87 % yield [equation ( 2)]. Careful recrystallization of the oxochromium(v) salt from an equimolar mixture of acetonitrile and chlorobenzene afforded dark brown crystals of sufficient quality for X-ray crystallographic determination.? The molecular structure of the oxochrom-

A novel series of substituted 3-phenyl benzoylpyrazoles were prepared and tested as potential grass herbicides. The targeted materials were prepared by three newly developed synthetic routes, which allowed a comprehensive study of the SAR (structure-activity relationships) of this series. The best combination of grass weed activity (Avena fatua L, Setaria viridis (L) Beauv and Alopecurus myosuroides Huds) and wheat selectivity was obtained with an alkoxy group in the 4-position of the phenyl ring. Activity was further enhanced by the presence of tert-butyl on the pyrazole and a methyl group at the C-2 position of the benzoyl moiety. The alkoxy-substituted 3-phenylbenzoylpyrazoles are a novel class of herbicides with potential utility for control of important grass weeds in cereals.

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