Lutetium-methyl complexes

Watson et al. reported a leading example of (3-carbon elimination observed with a well-defined metal complex [67]. Thermal decomposition of a lutetium-isobutyl complex having a vacant coordination site leads to the formation of a lutetium-methyl complex and propene by way of (3-methyl elimination, the microscopic reverse of olefin insertion. A concerted four-center transition state is proposed. This study demonstrated that (3-carbon elimination is an energetically accessible process, and provided a model for the chain transfer that occurs during propene oligomerization. 

Synthesis and Characterization of Lutetium- and Ytterbium-Methyl Complexes. The synthetic strategy outlined in Scheme 1... 

Polymerization of Ethylene by Methyl-Lutetium and -Ytterbium Complexes. Products. Ethylene (60 psi, 30-100 C) is polymerized rapidly by 10 to 10" M cyclohexane solutions of the methyl complexes 3, 4, 5, 6, and 8 (Table). Low Mw oligomers were not formed (analysis by GC) in experiments la or 3a, Table. At 160 C both the Lu and Yb etherates produced very little polyethylene ( lO of the Table yields at 40-100 ) reflecting thermal decomposition of the active species. 

A determination of the stability constants of aquo-complexes of Eu " in acetone showed that as the concentration of water in the solution of europium nitrate in acetone was increased, the first co-ordination sphere of europium(iii) became occupied by three water molecules which replaced three acetone molecules, and only then did the replacement of NO3 anions by water occur. An n.m.r. study of the hydration of lutetium(iii) nitrate in aqueous acetone showed the co-ordination number of lutetium to tend to six with increasing water concentration. The coexistence of several aquo(methyl sulphoxide)lutetium(iii) complexes were identified in the study of the complex formation between lutetium and dimethyl sulphoxide in acetone. 

The lanthanides and actinides are also active in electrophilic attack on arenes. Bis(pentamethylcyclopentadienyl)lutetium methyl or hydride complexes react readily with benzene to give phenyl complexes and methane or dihydrogen . Similar reactions are observed for Sc and Th In a remarkable reaction benzene can be dimetallated by Lu, yielding II ... 

For example, the exchange between a methyl complex of lutetium or yttrium and labeled methane proceeds as metathesis [21] ... 

The methane exchange reaction, T.3 and T.12, also should occur more easily for scandium-methyl than for lutetium-methyl. As seen from Table IV, Adduct I, Cl2LuCH3(CH4), is calculated to be only kinetically stable and lies 4.6 kcal/mol higher than reactants. The transition state separating reactants and the CH4 complex was not located. However, Adduct I for Sc, Cp2ScCH3(CH4), is thermodynamically stable by 6.0 kcal/mol relative to the reactants. The barrier for methane exchange is calculated to be 25.9 and 10.8 kcal/mol relative to the reactants, respectively, for the Lu and Sc compounds. In the transition state the distances of the two reacting CH bonds... 

NC,H, Benzene, 2-isocyano-l,3-dimethyl-, iron complexes, 26 53-57 NC Hu, Benzenemethanamine, N,N-di-methyl-, lithium complex, 26 152 palladium complex, 26 212 NCjHi, Benzenemethanamine, N,N-di-methyl-, lutetium complex, 27 153... 

OLuSiC,HH24, Lutetium, bis(T] -cyclopenta-dienyl)(tetrahydrofuran)[(trimethyl-silyl)methyl]-, 27 161 O, Oxide, gold complex, 26 326 ON, Nitrosyls, molybdenum and tungsten, 26 132, 133... 

The lutetium complex [(C5Me5)2LuMe] exists in solution as an equilibrium mixture of monomer and dimer, and crystallizes as the dimer [(C5H5)2Lu Me]2 103, in which the methyl group of one molecule coordinates (by C— H—Lu bonds) to vacant metal orbitals of the second molecule. 

Watson demonstrated alkane activation among /-block metals. Lutetium and ytterbium metals form complexes that are capable of inserting into C-H a bonds. The coordinatively unsaturated complexes (Cp )2M-CH3 (M = Yb, Lu) show a variety of interesting reactions (mainly of the Ziegler-Natta type). For example, the lutetium complex under solvent-free conditions exists as a dimer [Eq. (6.95) see Chapter 2, Section 2.10]. The crystal structure of the dimer indicates it to be unsymmetrical, in which a methyl group from one molecule coordinates to vacant metal orbitals of the second molecule. In cyclohexane solution, about 15% of this compound exists as a monomer and equilibration is rapid on the NMR timescale. For the dissociation of the dimer to monomers. A//= 12.6 kcal mol and A5 = 32.8eu in cyclohexane were reported. ... 

NMR data for half-sandwich rare-earth phthalocyanines are extremely rare. Ni et al. (1987) have measured the H and C NMR spectra of a series of R(Pc)(OAc)2H (R=Sm-Lu) and R(Pc)Cl (R=Er-Lu). Due to the intrinsic nature of the metal ions, the signals for the a and (3 protons of the phthalocyanine ring span a wide region. Figure 18 shows the variation of H NMR shift of the a protons and the OAc methyl protons in R(Pc)(OAc)2H (R=Sm-Yb) relative to those of the diamagnetic lutetium analog. It is noted that the A<5a/A<5(5 values remain almost constant for these complexes, showing that the shifts are mainly due to a dipolar contribution. 

Dicyclopentadienyl rare earth chlorides react with a variety of compounds containing other anions than Cl. Maginn et al. (1963) prepared some methoxides and one phenoxide, Schumann et al. (1982) isolated the dicyclopentadienyl samarium tert-butoxide, and Watson (1982) found bis(pentamethylcyclopentadienyl) lutetium ethoxide as one of the reaction products of the ethanolysis of bis(pentamethylcyclo-pentadienyl) methyl lutetium. These compounds are much more stable against oxidation. No X-ray structural determination of these complexes has been done. 

That even polynuclear methyl derivatives of the lanthanoides exist is demonstrated by a lutetium complex. In this compound pairs of methyl groups not only interconnect the lutetium atom with the lithixim atoms but also bridge the lutetium atoms (teed = tetraethylethylenediamine)... 

By replacing cyclopentadienyl by pentamethylcyclopentadienyl, steric compression at the metal centre is greatly increased, especially at lutetium, the smallest lanthanide. The complex Cp LuCHdOEt ) polymerizes ethene and oligomerizes propene. (Cp = / -C-MeJ. Its behaviour thus provides a good model for Ziegler-Natta catalysis. The insertion of propene into the Lu—CH bond and some further propagation steps have been followed by n.m.r. spectroscopy. Clear examples of such insertions are rare in d-block chemistry (p. 380). Termination can occur either by j -H transfer or by -methyl transfer the latter is a novel process which has yet to be observed for d-block elements. 

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