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Carbon encapsulated NiFe nanoparticles (NiFe@C) have been prepared by high-temperature methane encapsulation of the bare bimetallic particles on alumina. High-resolution transmission electron microscopy pictures show that about 6-nm thick carbon layers encapsulate 10-20-nm diameter NiFe nanoparticles. The NiFe nanoparticles are shown to be single-crystalline and no carbide is found at the NiFe-C interface. This is confirmed by the electron energy-loss spectroscopy (EELS) measurements that in addition show that both Ni and Fe have a zero (metal) valence and that only graphite is present. EELS also shows that the nickel-to-iron ratio is exactly unity for all particles studied. Metallic Pd nanoparticles with a diameter of 1-2 nm can be anchored on the carbon layers, which creates a Pd/NiFe@C type of catalyst that could be used for liquid phase reactions. The EELS analysis reveals that part of the nanoparticles present are not Pd but other oxidic carbon encapsulated nanoparticles.

The potentially C,N,N′-chelating anionic aryldiamine ligand [C 6 H 4 (CH 2 N(Me)CH 2 CH 2-NMe 2)-2]-(CNN) has been employed in the preparation of six-coordinate Ta(V) alkylidene complexes. The new dichloro alkylidene complex [TaCl 2 (dCH-t-Bu)(CNN)], 2, prepared from [TaCl 3 (dCH-t-Bu)(THF) 2 ] and [Li(CNN)] 2 , 1, has been obtained as a mixture of three diastereoisomers (2a-c) in 51% yield. The molecular structure of the major isomer 2a, determined by X-ray methods, shows this to be a tetragonal bipyramidal complex in which the metal coordination sphere is comprised of the C,N,N′ facially bonded CNN, two cispositioned chlorides in the equatorial plane, and a neopentylidene group and the NMe 2 nitrogen donor mutually trans-positioned at the apices. The dialkoxide complexes [Ta-(dCHR)(CNN)(O-t-Bu) 2 ] (R) t-Bu (3a), CMe 2 Ph (3b)) have been obtained by transmetallation of [TaCl(dCHR)(O-t-Bu) 2 (PMe 3)] with 1. The neopentylidene complex 3a was isolated as an analytically pure orange solid in 47% yield, whereas the neophylidene complex 3b was isolated as an orange oil of (90% purity. Complex 3b reacts in pentane with ethene at room temperature to afford the tantalacyclobutane complex [Ta{(CH 2) 3-1,3}(CNN)(O-t-Bu) 2 ], 4, which was isolated as a white solid in 81% yield. An X-ray diffraction study of 4 shows it to be a heptacoordinate pentagonal bipyramidal tantalum species in which two mutually trans alkoxide groups are in the apical positions; the meridional ligation is comprised of the C,N,N′-coordination of CNN and the σ-bonded carbon atoms of the metallacyle. Reaction of 3b in hexane at 69°C with ethene gives a mixture of the new tantalum alkene complex [Ta(CNN)(O-t-Bu) 2 (H 2 CdCH 2)], 5, and 4 in a 5:2 ratio. Complex 5 can be isolated from this mixture as a yellow solid by recrystallization from diethyl ether at-30°C. The X-ray molecular structure of 5 shows it to be a pentagonal bipyramidal complex in which the array of atoms directly bonded to tantalum is like that in 4. However, in 5, the meridional ligation is comprised of the C,N,N′-coordination of CNN and the two C atoms of the ethene molecule. Complexes 3b and 4 initiate ring-opening metathesis polymerization with strained cyclic olefins; dicyclopentadiene produces cross-linked polymers, whereas norbornene produces polycyclopentamers with approximately 90% trans-vinylene bonds. In contrast, none of the isomers of alkylidene complex 2 show any reactivity toward either ethene or norbornene.