Rare earth metal complexes coupling

Tml2, Dyh and Ndh have also been used in an acetonitrile/amine coupling reaction, which produced amidines of general formula MeC (=NH)NR R R R2 = H, Me H, iPr H, fBu Et2). The reaction is sub-stoichiometric in rare-earth diiodide but not really catalytic since part of the produced amidine remained tightly held aroimd the rare-earth metal it could be liberated by heating a trivalent intermediate formulated as Rl2(amidine)4(amidinate) (R = Nd, Dy, Tm) imder vacuum, and the residue could be recycled to produce more amidine. This reaction is not specific of the divalent iodides since many rare-earth triiodides were also effective. In the case of dysprosium and diethylamine, an intermediate trivalent amidine complex has been isolated and structurally characterised in the form of the zwitterionic [Dy MeC(=NH)NEt2 4][(I)3] (Bochkarev et al., 2007) (Figure 9). 

Vibrational spectra of acetylacetonato complexes have been studied by many other workers. Only references are cited for the following Raman spectra of tris(acac) complexes, infrared spectra of acac complexes of rare-earth metals, relationships between CH and CH3 stretching frequencies and C—H spin-spin coupling constants, and relationships between p(C—O), p(C C), and C NMR shifts of CO groups. ... 

The isolated compounds (table 16) show identical infrared spectra with a characteristic band at 1195 cm for a methyl group attached to a rare earth metal. The single crystal X-ray analysis of the yttrium (table 18, fig. 25) and of the ytterbium derivative (table 18) show both compounds to be isostructural with an approximately tetrahedral metal environment and a R(ju-CH3)2R unit like the trimethyl aluminum dimer. The and NMR spectra of the diamagnetic yttrium complex were invariant between — 40°C and +40°C with a triplet for the bridging methyl protons due to the coupling with the two equivalent yttrium atoms (tables 17, 19). 

Half-sandwich rare earth metal alkyl complexes can act as catalyst precursors for the cross-coupling of various terminal alkynes with isocyanides selectively affording the (Z)-l-aza-l,3-enyne products (Scheme 20). The unprecedented Z selectivity could arise from the formation of an alkynide-bridged binuclear catalyst species, in which the crosscoupling reaction took place at the two metal centers in an intermolecular fashion. 

Rare earth metal NHC complexes have primarily been applied in polymerization reactions, addition of terminal alkynes and amines to carbodiimides, as well as catalytic C-N coupling. Although a relatively limited amount of research has been carried out in this area, these preliminary investigations have proven the utility of REM NHC complexes as catalysts. 

When aqueous solutions of rare earth salts are treated with solutions of ammonium carbonate in hydrazine hydrate (N2H5COON2H3), rare earth metal hydrazine carboxylate hydrate complexes are formed [15]. Initially, a precipitate forms that dissolves with the addition of excess reagent. On keeping the solution for a couple of days crystalline solids separate. The crystals are washed with alcohol and then diethyl ether and stored in a vacuum desiccator. The composition of the crystals determined by chemical analysis and infrared spectra has been found to be Ln(N2H3C00)3-3H20 ... 

An increase in the ion annihilation exergonicity AG to values comparable to the excited triplet-state energies (AG I LT < 0) opens an additional electron transfer channel (T-route). In the simplest case, only one excited triplet 3 A or 3 D becomes accessible. Triplet emission can be directly observed from the ECL systems involving rare earth and transition metal complexes with allowed (due to extensive spin-orbit coupling) triplet-singlet electronic transition. 

Raman spectroscopy metal in water complexes, 309 Rare earth complexes acetylacetone synthesis, 377 guanidinium, 282 hydroxamic acids, 506 Redox properties bipyridyl metal complexes, 90 Reductive coupling nitrile metal complexes, 265 Resorcinol, 2,4-dinitro-metal complexes, 273 Rhenium complexes acetylacetone, 376 synthesis, 375, 378... 

If this interaction is very weak, the zero-phonon line dominates in the spectrum (like in the rare earth ions). If the interaction is very strong, the spectra contain only broad bands from which not much information can be obtained. These situations are known as the weak- and strong-coupling case, respectively. Vibrational structure of any importance is usually only observed for the intermediate-coupling case. This is, for example, encountered for transition metal ions and uranate complexes. 

Studies of rare earth or transition metal complexes often necessitate use of multireference wave functions. Among the Coupled Cluster type methods one can distinguish two main lines of approach to incorporate multireference character in the reference wave function. In the Hilbert space method one computes a single wave function for a particular state, while in the Fock space method one tries to obtain a manifold of states simultaneously. Since the latter method [40] has recently been implemented and applied in conjunction with the relativistic Hamiltonian [48-50] we will focus on this approach. 

Electron paramagnetic resonance (EPR) spectroscopy [1-3] is the most selective, best resolved, and a highly sensitive spectroscopy for the characterization of species that contain unpaired electrons. After the first experiments by Zavoisky in 1944 [4] mainly continuous-wave (CW) techniques in the X-band frequency range (9-10 GHz) were developed and applied to organic free radicals, transition metal complexes, and rare earth ions. Many of these applications were related to reaction mechanisms and catalysis, as species with unpaired electrons are inherently unstable and thus reactive. This period culminated in the 1970s, when CW EPR had become a routine technique in these fields. The best resolution for the hyperfine couplings between the unaired electron and nuclei in the vicinity was obtained with CW electron nuclear double resonance (ENDOR) techniques [5]. 

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