Ytterbium-methyl complexes

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. 

Dicyclopentadienyl erbium methyl and dicyclopentadienyl ytterbium methyl react with alkynes like HC CC(CH3)3 with formation of dimeric alkynide-bridged complexes of the type [Cp2RC=CC(CH3)3]2 (Atwood et al., 1981). 

The compounds Ln(C5H5)2Cl also have been made only with the lanthanides above samarium (772). These compounds are stable in the absence of air and moisture, sublime near 200 °C, are insoluble in non-polar solvents, and exhibit room temperature magnetic moments near the free ion values (772, 113). The chloride ion may be replaced by a variety of anions including methoxide, phenoxide, amide and carboxylate. Some of these derivatives are considerably more air-stable than the chloride — the phenoxide is reported to be stable for days in dry air. Despite their apparent stability, little is known about the physical properties of these materials. The methyl-substituted cyclopentadiene complexes are much more soluble in non-polar solvents than the unsubstituted species. Ebulliometric measurements on the bis(methylcyclopentadienyl)lanthanide(III) chlorides indicated the complexes are dimeric in non-coordinating solvents (772). A structmre analysis of the ytterbium member of this series has been completed (714). The crystal and molecular parameters of this and related complexes are compared in Table 5. 

CjHjS, Thiophene, tetrahydro-gold complexes, 26 85-87 C4H,NO, 2-Propenamide, 2-methyl-nickel complex, 26 205 C4H1()02, Ethane, 1,2-dimethoxy-solvates of chromium, molybdenum, and tungsten carbonyl cyclopentadienyl complexes, 6 343 tungsten complex, 26 50 ytterbium complex, 26 22 C4H i02.NaC5H5, Ethane, 1,2-dimethoxy-compd. with cyclopentadienylsodium, 26 341... 

P2RhC2jH47, Rhodium(I), carbonylphen-oxobis(triisopropylphosphine)-, 27 292 02SC,H, Benzenesulfonic acid, 4-methyl-, rhodium complex, 27 292 02SmCa,H4t, Samarium(II), bis(T) -penta-methylcyclopentadienyl)bis-(tetrahydrofuran)-, 27 155 OjYbCMHM, Ytterbium(H), bis(Ti -cyclo-pentadienyl)( 1,2-dimethoxyethane)-, 26 22... 

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. ... 

Structural studies by Baker, Brown, and Raymond (42) have shown the dimeric nature of lanthanide dicyclopentadienyl halides. They reported that the molecular structure of [Y (C H CH ) Cl] consists of two ytterbium atoms, each with two n -bound methyl-cyclopentadienyl rings, which are nearly symmetrically bridged by the two chlorine atoms. The crystal structure of Yb(C(.H Me was reported by Halton et al. (43). The complex actually nas a dimeric structure, Cp2YbMe2YbCp2, remarkably similar to Me2ALMe2 AlMe2 The overall molecular geometry is identical with that or the chloride analogue Yb(C H CH )2CI. 

A recent exhaustive review [1] presents the known and well characterised lanthanide hydrides. Recently, a few additional original complexes have been synthesised. These include phospholyl [7] and indenyl derivatives [8], a bimetallic metallocenic structure (Scheme 1) [4], a samarium hydride supported by a calix-tetrapyrrolyl ring, with a triply bonded hydride ligand (Scheme 2) [9], metallocenes with chiral groups which has been used for the asymmetric hydrogenation [10], a tris(pyrazolyl)borate ytterbium(II) hydride [11], Cp amido-[12] and bis(amido)yttrium hydrides [13]. The latter was not isolated but obtained in situ from the methyl derivative (Scheme 2). 

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). 

Carboranyl derivatives of lanthanum, thulium and ytterbium are formed when the C-mercuro derivatives of methyl- and phenylcarboranes react with the rare earth metals in tetrahydrofuran at 20°C (Suleimanov et al., 1982a), or from the lithium derivatives of methyl- and phenylcarboranes with the rare earth trichlorides in benzene-ether at 20°C (Bregadze et al., 1983) as complexes with THF. A carboranyl derivative with a thulium-boron bond is also described. The reaction (eq. 62) may proceed via the formation of B-Tm-C derivatives, followed by disproportionation. 

C10H15N, Benzenemethanamine, N,N,4-trimethyl-, lithium complex, 26 152 C10H15P, Phosphine, diethylphenyl-, nickel complex, 28 101 platinum complex, 28 135 CioHigAsi, Arsine, 1,2-phenylenebis(dimethyl-, gold complex, 26 89 nickel complex, 28 103 CioHie, 1,3-Cyclopentadiene, 1,2,3,4,5-pen-tamethyl-, 28 317 chromium complex, 27 69 cobalt complexes, 28 273, 275 iridium complex, 27 19 samarium complex, 27 155 titanium complex, 27 62 ytterbium complex, 27 148 CioH,gBrN04S, Bicyclo[2.2.1]heptane-7-methanesulfonate, 3-bromo-1,7-di-methyl-2-oxo-, U.IRHENDO, ANTPi]-, ammonium, 26 24... 

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