Marked changes in relative nucleophilicity in comparing S(N)2Ar reactions of free arenes and coordinated arenes. Kinetic studies of reactions of (eta(6)-chlorobenzene)(eta(5)-cyclopentadienyl)iron(II) tetrafluoroborate with anionic and neutral nucleophiles

Quantitative kinetic studies have be en made of reactions of the (eta(6)-chlorobenzene)(eta(5)-cyclopentadienyl)iron(II) cation, (C6H5Cl)Fe(C5H5)(+) (1), With methoxide, phenoxide, methanethiolate, benzenethiolate, and azide ions in methanol, piperidine, morpholine, aniline, and thiourea in methanol, and guanidine in ethanol. The results were compared with the same nucleophile-solvent combinations in reactions with 1-chloro-2,4-dinitrobenzene, C6H3(NO2)(2)Cl (2). In general, the reactivity decreases on passing from 2 to 1. The decrease is small (less than or equal to 10(-1)) for phenoxide (PhO(-)), methanethiolate (MeS(-)), and guanidine (gua) and large (ca. 10(-5)) for benzenethiolate (PhS(-)), azide (N-3(-)), piperidine (pip), morpholine (morph), aniline (anil), and thiourea (thiou). The differences in reactivity when comparing the S(N)2Ar reactions of 1 and 2 is discussed in terms of the different location of the negative charge generated in the transition state by the electrons displaced from the reaction center by the entering groups (arenide electrons).15143198320

Exfoliation and Raman Spectroscopic Fingerprint of Few-Layer NiPS3 Van der Waals Crystals

The range of mechanically cleavable Van der Waals crystals covers materials with diverse physical and chemical properties. However, very few of these materials exhibit magnetism or magnetic order, and thus the provision of cleavable magnetic compounds would supply invaluable building blocks for the design of heterostructures assembled from Van der Waals crystals. Here we report the first successful isolation of monolayer and few-layer samples of the compound nickel phosphorus trisulfide (NiPS(3)) by mechanical exfoliation. This material belongs to the class of transition metal phosphorus trisulfides (MPS(3)), several of which exhibit antiferromagnetic order at low temperature, and which have not been reported in the form of ultrathin sheets so far. We establish layer numbers by optical bright field microscopy and atomic force microscopy, and perform a detailed Raman spectroscopic characterization of bilayer and thicker NiPS(3) flakes. Raman spectral features are strong functions of excitation wavelength and sample thickness, highlighting the important role of interlayer coupling. Furthermore, our observations provide a spectral fingerprint for distinct layer numbers, allowing us to establish a sensitive and convenient means for layer number determination