Electronic effects in the reaction of 1,3-diaryl-1,3-diketones with hydrazinopyridines

The regioselectivity of the condensation of electronically unsymmetrical 1,3-diaryl-1,3-diketones with 2-hydrazinopyridine and 2,6-bis-hydrazinopyridine to form N-(2-pyridyl)-3,5-diarylpyrazoles was studied. Significant electronic effects on regioselectivities were observed, and regioselectivities were opposite to those exhibited by perfluoroalkyl/alkyl 1,3-diketones. The electronic effects correlate well to the difference between the Hammett σ+ coefficients of the para substituents on the aryl rings. © 2008 Elsevier Ltd. All rights reserved

\u3cem\u3eAufbau\u3c/em\u3e Approach to Multimetallic Ensembles Based on Tetrathiooxalate: [Cp*\u3csub\u3e4\u3c/sub\u3eRh\u3csub\u3e4\u3c/sub\u3e(C\u3csub\u3e2\u3c/sub\u3eS\u3csub\u3e4\u3c/sub\u3e)\u3csub\u3e2\u3c/sub\u3e]\u3csup\u3e2+\u3c/sup\u3e, [Cp*\u3csub\u3e3\u3c/sub\u3eRh\u3csub\u3e2\u3c/sub\u3eRu(C\u3csub\u3e2\u3c/sub\u3eS\u3csub\u3e4\u3c/sub\u3e)]\u3csup\u3e+\u3c/sup\u3e, and [Cp*\u3csub\u3e6\u3c/sub\u3eRh\u3csub\u3e6\u3c/sub\u3e(C\u3csub\u3e2\u3c/sub\u3eS\u3csub\u3e4\u3c/sub\u3e)\u3csub\u3e2\u3c/sub\u3e]\u3csup\u3e4+\u3c/sup\u3e

Experiments aimed at the characterization of new coordination modes for tetrathiooxalate (TTO) are described. Cyclic voltammetric (CV) measurements on Cp*2Rh2(C2S4) (1) revealed an irreversible oxidation as part of an ECE process that results in the chemically reversible dimerization of 1+. Treatment of 1 with CpFe[C5H4C(O)Me]BF4 followed by anion exchange gave [Cp*4Rh4(C2S4)2](BPh4)2, the dication of which consists of a dimer of 1+ linked through two pairs of Rh−S bonds. A second new bonding mode for TTO was generated by treatment of 1 with [Cp*Ru(MeCN)3]PF6 to give [Cp*3Rh2Ru(C2S4)]+ (3) wherein Cp*Ru+ is η5-bonded to one RhS2C2 ring. A third new bonding mode for TTO is illustrated by [Cp*6Rh6(C2S4)2]4+, formed by the reaction of Cp*Rh(MeCN)32+ and 1. The structure can be viewed as a dimer of3, except that there are no M−M bonds:  the Cp*Rh2+ fragments are bonded via an η4-interaction to RhS2C2 rings. Furthermore, the [Cp*3Rh3(C2S4)]2+ subunits, which are otherwise isoelectronic with 3, dimerize, such that all eight sulfur atoms are triply bridging

Crystal structure of 2,6-bis-hydrazinopyridine dihydrate, its tosylate salt and 2,6-bis-(3,5-di-tert-butylpyrazolyl)pyridine

The crystal structures of the new compounds 2,6-bis-hydrazinopyridine dihydrate (2), its tosylate salt (3) and 2,6-bis-(3,5-di-tert-butylpyrazolyl) pyridine (4) were obtained by single-crystal X-ray diffraction. Crystallization of 2 occurs in the centrosymmetric monoclinic space group P21/c (No. 14) with a = 9.6218(18), b = 6.7331(12), c = 13.489(3); and β = 109.292(8)° and Z = 4. Crystallization of 3 occurs in the centrosymmetric monoclinic space group P21/c (No. 14) with a = 26.530(3), b = 16.6456(18), c = 9.9458(10) and β = 96.828(5) and Z = 8, while 4 crystallizes in P21/n (No. 14) with a = 15.0555(10), b = 10.4496(7), c = 16.9599(12) and β = 101.480(4) and Z = 4. These are the only structures for any bis-hydrazinopyridines reported to date. Details of the synthesis, structures and spectroscopic results are presented and discussed. © 2005 Springer Science+Business Media, Inc

Characterization of the Initial Intermediate Formed during Photoinduced Oxygenation of the Ruthenium(II) Bis(bipyridyl)flavonolate Complex

A ruthenium­(II) flavonolate complex, [Ru^II(bpy)₂fla]­[BF₄], was synthesized to model the reactivity of the flavonol dioxygenases. The treatment of dry CH₃CN solutions of [Ru^II(bpy)₂fla]­[BF₄] with dioxygen under light leads to the oxidative O-heterocyclic ring opening of the coordinated substrate flavonolate, resulting in the formation of [Ru^II(bpy)₂(carboxylate)]­[BF₄] (carboxylate = <i>O</i>-benzoylsalicylate or benzoate) species, as determined by electrospray ionization mass spectrometry. Moderation of the excitation and temperature allowed isolation and characterization of an intermediate, [Ru^II(bpy)₂bpg]­[BF₄] (bpg = 2-benzoyloxyphenylglyoxylate), generated by the 1,2-addition of dioxygen to the central flavonolate ring