Thorium cyclopentadienyls

For the thorium cyclopentadienyls with R = CH3, photolysis in aromatic solvents produces 1 1 mixtures of alkene and alkanes and the trivalent thorium complex Th(C5E5)s. It was proposed that the reaction takes place by a photoinduced beta-elimination to give a hydrido complex and olefin followed by a bimolecular reductive elimination of the alkane. Schematically it can be represented by the following equations ... 

Allyl Complexes. Allyl complexes of thorium have been known since the 1960s and are usually stabilized by cyclopentadienyl ligands. AEyl complexes can be accessed via the interaction of a thorium haUde and an aHyl grignard. This synthetic method was utilized to obtain a rare example of a naked aHyl complex, Th(Tj -C2H )4 [144564-74-9] which decomposes at 0°C. This complex, when supported on dehydroxylated y-alumina, is an outstanding heterogeneous catalyst for arene hydrogenation and rivals the most active platinum metal catalysts in activity (17,18). 

This is remarkable, since the reduction potential of Th(IV) to Th(III) recently has been estimated as —3.7 volts 73) and direct reduction of U(C5H5)4 and Pu(C5Hs)3 with potassium metal produces the actinide metals. The ei/z for naphthalene in acetonitrile is —2.63 V (nearly the same as the aLkaJi metals). Since this is much smaller than the Th(IV) to Th(III) reduction potential, it would seem to imply substantial stabilization of the +3 state by cyclopentadienide. The observed room temperature magnetic moment of Th(C 5115)3 (0.403 BM) is consistent with the Th(III) (5/ ) assignment. Thorium triscyclopentaxhenide is similar in behavior to U(C5H5)3, forms adducts with both THF and cyclohexyhso-nitrile and has been shown to be isostructural with the other tris (cyclopentadienyl) actinides and lanthanides. 

The polymerization of ethylene was also qualitahvely inveshgated by pulse injec-hons of ethylene into helium flowing over thorium (67) and uranium (86) metallocene hydrocarbyl complexes supported on 7-AI2O3.950 at 25 °C, both revealing similar achvihes [171, 173]. Supported thorium half-sandwich complexes 65 exhibited higher achvity than surface species, resulhng from coordinatively more saturated tris(cyclopentadienyl) and metallocene U/Th-alkyl/hydride complexes, that is, 77, 79, 82, 90 and 91 [171]. C CP MAS NMR spectra revealed no clear evidence of ethylene insertion into [Th-CHs] or [AL5-CH3] moiehes of material... 

Cyclopentadienyl and Substituted Cyclopentadienyl Complexes. Thorium complexes containing cyclopentadienyl rings (Cp),... 

The tris(cyclopentadienyl)thorium-, -uranium- and -plutonium chlorides are best prepared from TlCp in dimethoxyethane Np(Cp- )3Cl is formed in the Be(Cp)2 melt reaction . Analogous complexes containing bromide, iodide and/or indenyl ligands are prepared from K[Cp] or K[indenyl] and the appropriate MX4 compound (see Table 2). 

The formation constants of an actinium isopropyltropolonate complex were determined. Thermochemically relevant studies of thorium enolates generally involve bis(pentamethyl-cyclopentadienyl)thorium derivatives. Cp 2Th(Cl)(C(0)CFl2Bu-f) with an anionic acyl group that readily rearranges to the isomeric enolate Cp 2Th(Cl)OCH=CHBu-t. The Z-isomer is formed upon heating and the -isomer upon catalysis with Cp 2ThH2. Is the E or Z enolate thermodynamically more stable For the simple alkyl enolates MeCH=CHOR, the equilibration reaction of the Z- and E-isomers is nearly thermo-neutral . Consider the two species Cp 2Th(H)OCH(Bu-t)2 and Cp 2Th(H)0-2,6-C6H3 (Bu-f)2. The reversible addition of CO yields the rp- formyl derivative in reactions that are 19 4 and 25 6 kJmoR exothermic. These formyl species dimerize to form the classical enediolate, Cp 2Th(OR)OCH=CHO(OR)ThCp 2. This product is formed as the Z-isomer, plausibly thermodynamically preferred over the -isomer, much as (Z)-MeOCH=CHOMe is preferred over its E-counterpart by 6.0 0.2 kJmoR. ... 

Chloro(/7-cyclopentadienyl)thorium(lV) is a white solid, less oxygen-sensitive than the uranium analog but considerably more moisture-sensitive. Exposure to air causes the appearance of an ocher color. The compound is less soluble in all organic solvents than the uranium analog solutions are extremely air-sensitive. The nmr spectrum in benzene-de exhibits a sharp singlet at t3.81. The infrared spectrum (Nujol mull) shows 7t-cyclopentadienyl bands at 1016 (m), 812 (sh), and 788 (s) cm i. 

Solid [ -l,3bis(trimethylsilyl)cyclopentadienyl]lithium (LiCp", 7.26g, 33.6 mmol, prepared as in Section 33A) is added via an addition tube to a stirred, cooled (0°C) slurry of anhydrous thorium(IV) chloride (Cerac) (6.27 g, 16.8 mmol) in diethyl ether (250 mL). The mixture is stirred at 25 °C for 15 h. Volatile substances are removed at 25 °C and 10 torr. The resultant off-white foam is extracted into warm (50 °C) hexane ( 150mL), and the extract is filtered. The filtrate is concentrated (to 75 mL), then cooled to — 30°C to yield colorless crystals of [ThCp"2Cl2] (1). Yield 4.45 g (40%). A further crop of crystals is obtained from the mother liquor (total yield, 60%). For its characterization, see Table I. 

Thiophenetetracarboxylic acid, tetra-methylestcr, 26 166 Thorium(IV), bis[Ti -l,3-bis(trimethyl-silyl)cyclopentadienyl]dichloro-,... 

Cl Si2ThC2jH42, Thorium(lV), bis(-n -l,3-bi (trimethylsilyl)-cyclopentadi-enyl]dichloro-, 27 173 CI,Si2UC22H42, Uranium(IV), bis(tt -l,3-bis(trimethylsilyl)- cyclopentadienyl]-dichloro-, 27 174... 

A remarkable achievement was the synthesis and characterization of tris(cyclopentadienyl)thorium(ni) complexes. The homoleptic dark blue, crystalline (disubstituted-cyclopentadienyl)thorium(m) complexes [C5H3(SiMe2R)2-l,3]3Th (R = Me, Buc) were obtained in good yield from the appropriate tris(cyclopentadienyl)thorium(iv) chloride by treatment with an excess of Na-K alloy in toluene at 20-35 °G with sonication (Scheme 16). The complex with R = Me is also accessible by a similar reduction of CpVThC. 50... 

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