Changtao Qian

Synthesis and properties of new σ-bonded organolanthanide complexes and studies of their infrared spectra☆

Abstract Five new solvated organolanthanide complexes containing Ln-C σ-bonds (η5-CH3C5H4)2ErC6H4CH3-p · THF (I), (η5-C5H5)2LnC6H4X-p · THF, Ln  Er, X  CH3 (II); Ln  Er, X  Cl (III); Ln  Yb, X = CH3 (IV); Ln  Gd, X  CH3 (V) were synthesized by the reaction of appropriate aryllithium derivatives with (η5-C5H5)2LnCl or (η5-CH3C5H4)2LnCl in THF at low temperature (−78°C). The structures of these complexes were verified by elemental analyses, infrared spectra and mass spectra. Recrystallization of these complexes from non-polar solvents such as benzene-n-hexane or toluene-n-hexane led to removal of coordinated tetrahydrofuran resulting in unsolvated products. The thermal decomposition temperature and the variable temperature (77–291 K) magnetic susceptibilities of the five unsolvated complexes were measured. The relation between the structure and oxidative and thermal stability is also discussed. Two new “mixed ligand” tri-η5-cyclopentadienyllanthanide complexes Cp2YbCp′ (VI) and Cp′2ErCp (VII) where Cp  η5-cyclopentadienyl, Cp′ = η5-methylcyclopentadienyl were also prepared. They are relatively more stable to air and moisture and more thermally stable than the complexes with LnC σ bonds. The infrared spectra of fifteen organolanthanide complexes including those aforementioned compounds and eight known compounds, i.e. Cp2GdCl, Cp′2GdCl, Cp2HoCl, Cp2ErCl, Cp′2ErCl, Cp2YbCl, Cp3Yb and Cp3Er were measured from 4000 to 200 cm−1. The absorption peak at 250 cm−1 was assigned as the characteristic absorption of the π-bonded cyclopentadienyl group to metal.

Studies on organolanthanide complexes: XII. Synthesis, identification and reactivity of organolanthanide and -yttrium chlorides with the chelating 1,1′-(3-oxa-pentamethylene)dicyclopentadienyl ligand☆

Abstract Seven new 1,1′-(3-oxa-pentamethylene0dicyclopentadienyl lanthanide and yttrium chlorides, (C 5 H 4 CH 2 CH 2 OCH 2 CH 2 C 5 H 4 )LnCl(Ln = Nd, Gd, Ho, Er, Yb, Lu and Y) were synthesized by using 1,1′-(3-oxa-pentamethylene)biscyclopentadienyl as ligand. Disproportionation of xicyclopentadienyl neodymium chloride is thus succesfully prevented, and a stable early lanthanocene chloride is obtained. All seven complexes are unsolvated monomers, containing an intramolecular coordination bond. Their structures were verified by elemental analyses, and IR, MS, XPS, 1 H NMR and 13 C NMR spectroscopy. They are readily soluble in various solvents and more stable towards air and moisture than other related complexes without an intramolecular coordination bond. The complex/NaH system hydrogenates 1-hexane catalytically in hydrogen.

Studies on organolanthanide complexes: III. The stabilization of early lanthanocene chlorides by using a ring-bridged dicyclopentadiene ligand

Abstract THF-solvated early lanthanocene chlorides containing ring-bridged dicyclopentadiene as a ligand [C 5 H 4 (CH 2 ) 3 C 5 H 4 ]LnCl · THF (Ln = Nd, Pr) were synthesized. The disproportionation of dicyclopentadienyl lanthanide chlorides is thus successfully prevented and the stabilization of early lanthanocene chloride achieved. In order to further demonstrate that the products obtained are tetrahydrofuran-solvated, similar complexes of Gd, Dy, Ho, Er, Yb and Lu were also synthesized and characterized. The products obtained are without exception coordinated with one molecular tetrahydrofuran. When the tetrahydrofuran coordinated lanthanocene chlorides were allowed to react with 2,2′-bipyridyl, the coordinated tetrahydrofuran was replaced by 2,2′-bipyridyl in each case to form the 2,2′-bipyridyl complex. The latter are more stable towards air and moisture than the former ones. Fifteen new complexes were synthesized and their structures were verified by elemental analyses, infrared spectra, mass spectra and 31 H NMR. Moreover, the variable temperature (77–291 K) magnetic susceptibilities were also measured.

New dinuclear bis(cyclopentadienyl)lanthanoid chlorides containing η5-C5H4 ligands linked by a metal-coordinated 2,6-dimethylenepyridyl unit

The salts M2[2,6-(CH2C5H4)2C5H3N] (i.e. Na2L, Li2L) react under mild conditions with anhydrous LnCl3 in the molar ratio 1:1 to afford complexes of the type [(LLnCl)2] (Ln = Y, Pr, Nd, Sm, Dy, Er, Yb, or Lu; 1–8). The dinuclear nature of the products 1–8 has been confirmed by mass spectrometry. Extended B/E-linked scans of metastable transitions suggest that L is chelating and not metal-bridging. Direct coordination of the pyridine-N atom to the Ln ion has been deduced from XPS measurements. Reaction of PrCl·(THF)x, and Na2L in the molar ratio 2:3 leads to the compound [L3Pr2] (9) which has been characterized by elemental analysis, 1H NMR and mass spectrometry. Some preliminary results on the catalytic activity of 1–8 during hydrogenation of 1-hexene by LiAlH4 suggest the formation of catalytically active, intermediate hydrides.

The formation and X-ray crystal structure of (η5-C5H5)2LuCl•OC4H8

LuCl 3 reacts with two equivalents of sodium cyclopentadienide in THF followed by crystallization from this solvent at 5°C to afford (C 5 H 5 ) 2 LuCl · OC 4 H 8 . The product has been characterized by its proton NMR and mass spectra, elemental analysis and by single crystal X-ray diffraction studies. The complex (C 5 H 5 ) 2 LuCl · OC 4 H 8 crystallizes in the monoclinic space group P 2 1 / n with the unit cell parameters, a 8.116(2), b 12.670(2), c 14.376(1) A, β 105.61(1)°, V 1423.7 A 3 , Z = 4, D c 1.925 g cm −3 . The structure was solved by heavy-atom Patterson techniques and the least-squares refinement has led to a final R value of 0.097 based on 2253 independent observed reflections. The THF molecule is coordinated to the lutetium atom at a LuO bond length of 2.27(1) A. The LuC(η5) bond distances average 2.56 A. The compound (η 5 -C 5 H 5 ) 2 LuCl · OC 4 H 8 is a neutral monomer.

Studies on organolanthanide complexes: XVIII. The reduction and isomerization of olefins with tricylopentadienyllanthanides/sodium hydride

Abstract Reduction of 1-hexene with Cp 3 Ln/NaH (Cp = cyclopentadienyl, Ln = rare earth metals) in THF at 45°C, after hydrolysis, gives hexane. The reducing activity of Cp 3 Ln depends strongly upon the ionic radius of the trivalent rare earth ion. The activity and selectivity of early rare earths for 1-hexane reduction are higher than those of heavy rare earths. The Cp 3 Ln/NaH systems can be used to regioselectively reduce dienes which contain a terminal carboncarbon double bond as well as an internal one with high yield. Selectivity is 100%. Moreover, the Cp 3 Ln/NaH systems are able to catalyze the hydrogenation of olefins. When Cp 3 Ln/Nah is used as catalyst, 1-hexene was isomerized at 45°C to cis -2-hexene and to trans -2-hexene in excellent yields. In contrast to reducing activity, the catalytic activity of heavy rare earths in the isomerization reaction is higher than that of the early earths. Hence, Cp 3 Sm/NaH and Cp 3 Y/NaH are new reducing agents and catalysts for 1-hexene reduction and isomerization, respectively.

STUDIES ON ORGANOLANTHANIDE COMPLEXES. XXIII, REACTION OF ORGANIC HALIDES WITH TRICYCLOPENTADIENYLLANTHANIDES/SODIUM HYDRIDE

Abstract The reductive dehalogenation of aryl and vinyl halides with tricyclopentadienyllanthanide / sodium hydride systems affords, respectively, the corresponding aromatics and alkenes in excellent yields under mild conditions. However, the reaction with alkyl halides generates alkylated products, which yield alkyl cyclopentadienes after hydrolysis. The reaction mechanism has been briefly investigated.

Studies on organolanthanide complexes: XXXVIII. New organolanthanide hydrides: synthesis and reactivity towards alkenes, alkynes and organic halides☆

Abstract The reaction of [O(CH 2 CH 2 C 5 H 4 ) 2 ]LnCl with NaH in THF at 45°C generates the dimeric organolanthanide hydridges, [O(CH 2 CH 2 C 5 H 4 ) 2 LnH] 2 (Ln = Gd, Er, Yb, Lu, Y), in good yield. These new complexes have been fully characterized by elemental analyses, mass spectrometry, IR and NMR spectroscopy. The hydrides cn react with alknes and alkynes. A more active system, organolanthanide hydride/NaH, is able not only to reduce specifically the terminal carboncarbon double bond but also to catalyse dehalogenation of organic halides.

Studies on organolanthanide complexes: XXXVII. Reaction of dicyclopentadienylyttrium chloride with acyl chlorides in tetrahydrofuran. Acylative cleavage of the CpY π-bond and tetrahydrofuran ring☆

Abstract Dicyclopentadienylyttrium chloride reacts with aromatic and aliphatic acid chlorides in tetrahydrofuran at room temperature, resulting in cleavage of the CpY π-bond to produce 1,5-diacylcyclopentadienes, and the acylative ring-opening of tetrahydrofuran. A possible reaction mechanism is proposed.

Studies on organolanthanide complexes: XLIV. Synthesis of bis(2-methoxyethylcyclopentadienyl) divalent organolanthanides (Ln = Sm, Yb) and molecular structure of solvated (MeOCH2CH2C5H4)2Yb·OC4H8☆

Abstract Bis(2-methoxyethylcyclopentadienyl) divalent solvent-free organolanthanide complexes (MeOCH 2 CH 2 C 5 H 4 ) 2 SM ( 1 ) and (MeOCH 2 CH 2 C 5 H 4 ) 2 Yb ( 2 ) have been synthesized by the interaction of (MeOCH 2 CH 2 C 5 H 4 )K with LnI 2 (Ln = Sm, Yb). Recrystallization of 2 from THF produced the solvated single crystal (MeOCH 2 CH 2 C 5 H 4 ) 2 Yb·OC 4 H 8 ( 3 ) which has the coordination number of nine, the highest yet reported for this class of compound. The two ring centroids of the 2-methoxyethylcyclopentadienyl rings, the two oxygen atoms of ether-substituted groups on the rings and the oxygen atom of the THF form a distorted trigonal bipyramid around the central ion of ytterbium.