The cationic vanadium complexes [CpzVCH3(CH3CN)lf and [Cp2V(THF)I+ with [BPLIas counterion are obtained from CpzVMez and [NHMezPhlBPL in CH3CN or THF, respectively; in CHzClz, chloride abstraction from the solvent occurs via a redox decomposition, evidenced by the X-ray crystal structure of [N(CHzCl)MezPh]BPL and the formation of Cp2VCl. In presence of the phosphine PMezPh, [Cp2VCH3(CH&N)l+ affords the intermediate species [ C~Z V C H~( P M~Z P~) I + (characterized by the EPR spectrum with resolved methyl hyperfine interaction) followed by a disproportionation and a redox reaction with [BPLI-, giving CpzVMez and [CpzV(PMe2Ph)l+. Preliminary studies show that [CpzVCH3]+ is unreactive toward ethylene polymerization.The chemistry of cationic transition metals of group 4 has challenged both experimentalists and theoricians due to its importance with regard to Ziegler-Natta or Kaminsky cata1ysts.l The extreme reactivity of the 14electron species [CpzMRI+ (M = Ti, Zr) allowed only occasional isolation of such compounds, stabilized by trapping with a donor. The synthesis of these stable 16-electron species is now well documented.2 In contrast to the well-developed field of cationic dicyclopentadienyl-Ti and -Zr c~mplexes,~ the chemistry of cationic vanadium complexes has attracted much less a t t e n t i~n .~ In order to extend the cationic chemistry already described for Ti and Zr to V, we studied the protonolysis of CpzVMez (1) with [NHMezPhIBPb. Results and DiscussionThe general procedure used in the synthesis of the 16-electron compounds [CpzMR(L)]+ and base-free 14electron compounds [CpzMR]+ (M = Ti, Zr) was used @ Abstract published in Advance ACS Abstracts, September 1,1995. (1) For leading references to cationic group 4 metal alkyl complexes see: (a) Dyachkovskii, F. Kuber, F.; Winter, A.; Rohrmann, J.; Bachmann, B.; Anterg, M.; Dolle, V.; Paulus, E. F. Organometallics 1994, 13, 954 and references cited therein. (e) Stehling, U.; Diebold, J.; Kirsten, R.; Rol, W.; Brintzinger, H.; Jungling, S.; Mulhaupt, R.; Langhauser, F. Organometallics 1994, 13, 964 and references cited therein. (0 Andersen, A.; Cordes, H. G.; Herwig, J.; Kaminski, W.; Merck, A.; Mottweiler, R.; Pein, J.; Sinn, H.; Vollmer, H. of CpzVMez (1) with [NHMezPh]BPh4 in CH3CN at room temperature afforded a nearly quantitative precipitate of pale violet [C~~VCH~(CH~CN)IBP~U (2). The presence of the methyl group in 2 was confirmed by evolution of CHI (characterized by IR and mass spectra) on adding HC1 to a suspension of 2 in THF. The adduct is paramagnetic, with one unpaired electron and a formal oxidation state of IV for the vanadium 01 = 1.88 pg).The IR spectrum showed bands due to CH3CN at 2308 and 2279 cm-' (free CH&N bands at 2287 and 2251 cm-l).When the reaction was carried out in THF at room temperature or at -80 "C, 1 equiv of methane was evolved and a blue-violet precipitate of [Cp2V(THF)I-BPh4 (3) was obtained, identified by elemental analysis, magnetism (u = 2.75 pg, indicating two unpaired electrons), and IH NMR spectroscopy. The filtra...

Metal-free O-arylation and [3, 3]-rearrangement have been shown as an efficient strategy to construct new C-O and C-N bonds in one-pot reactions. The method was used to prepare N-aryl benzo[1,2,3]triazin-4(1H)-one derivatives in good yields from N-hydroxy benzo[1,2,3]triazin-4(3H)-one and diaryliodonium salts. The reaction was tolerated a variety of sensitive functional groups such as iodine, nitro, ester, and aldehyde groups. A rational mechanism was proposed based on the experimental results, and the reaction was easily up to gram scale.

Efficient access to α,α'-diacetoxy ketones has been developed from ethynylcarbinols and PhI(OAc)2. A plausible mechanism for this was proposed on the basis of experimental studies. The usefulness of α,α'-diacetoxy ketone products has been documented, and glycerol derivatives can be easily synthesized in good yields via a one-pot reaction.

A copper-catalyzed selective cross-coupling reaction of 3-(hydroxyimino)indolin-2-ones with alkenyl boronic acids to access (E)-N-vinyl oxindole nitrones has been achieved under mild conditions. The studies showed that catalytic copper salt selectively gave mono N-vinylation products, while 2.0 equiv of copper salt provided double N-vinylation products. The control experiments revealed that the carbonyl group in 3-(hydroxyimino)indolin-2-one played important roles on N-vinylation. Furthermore, the prepared N-vinyl oxindole nitrones could be converted to spirooxindoles in good yields under thermal conditions.

An efficient transition-metal-free method for the preparation of α,β-unsaturated N-aryl ketonitrones under mild conditions has been developed. This reaction shows good functional group tolerance for both electron-rich and electrondeficient substituents on both oximes and diaryliodonium salts. Two examples of gram-scale preparations have been realized in good yields. Further transformations of these nitrones to different N-heterocycles have been demonstrated. DFT calculations suggest that N-arylation products are formed by [1,3]-phenyl migration of an O-coordinated oximate complex via a four-centered transition state, while the O-arylation products are formed by [1,3]-phenyl migration of a N-coordinated oximate complex.