Uranium cyclopentadienyls preparation

A second example of a bis cyclopentadienyl uranium complex has resulted from the use of a bidentate, bridged bis(cyclopendadienyl) ligand to avoid further reaction to a tris species. It is prepared by the addition of the dianion of bis(cyclo-pentadienyl)methane to uranium tetrachloride in THE to give [CH2( — 5114)2]... 

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). 

A solution of [f/ -l,3-bis(trimethylsilyl)cyclopentadienyl]lithium is prepared in situ, using the procedure described in Section 33.A, from butyllithium (IS.OmL of a 1.5 M solution in C6H14, 29 mmol) and bis(trimethylsilyl)cyclo-pentadiene (5.89g, 28 mmol) in THF (lOOmL). This solution is added dropwise during h to a stirred, cooled (0°Q solution of uranium(IV) chloride (5.45g, 14mmol) in THF (lOOmL). The mixture is stirred at 25°C for 12h. Removal of the solvent at 25 °C and lOtorr affords a sticky brown residue this residue is warmed to 60°C at 10 torr. The brown involatile solid is extracted into warm toluene (100 mL), and the extract is filtered. The brown filtrate is concentrated (to 50mL), then cooled to — 30°C to yield large orange-brown crystals of [UCp"2 CI2 ] (2). Yield 6.1 g (60%). Two further crops of crystals are obtained from the mother liquor (total yield, 90%). For its characterization, see Table I. 

The tris(cyclopentadienyl)uranium(m) complexes Cp"3U and (GsMe4H)3U were prepared by synthetic routes that involve the reduction of the appropriate tetravalent uranium metallocene precursors with potassium metal and NaCioHg, respectively (Scheme 14). The molecular structure of (CsMe4H)3U shows a perfectly trigonal structure with a threefold axis (all Cp (centroid)-U-Cp (centroid) angles equal to 120°).46... 

X-ray analysis of complex 7 showed that two of the metal-chloride bonds are shorter than the other two Th(l) - Cl(l) = 2.770(2)A, Th(l) - Cl(2) = 2.661(2)A, Th (1) - Cl(3) = 2.950(2)A, and Th(l) - Cl(4) = 2.918(2)A. The longer Th-Cl distances are those belonging to the chlorine atoms encountered in the threefold bridging positions and connected to the lithium atoms. The other two chlorine atoms are coordinated only to one lithium atom. All the Th-Cl distances are longer than those observed for terminal Th-Cl distances (Th-Cl = 2.601 A for Cp2 ThCl2 or 2.65A for Cp2 Th(Cl)Me). Ansa-chelating bis(cyclopentadienyl) complexes of uranium have been prepared as presented in Scheme 1. Bums et al. have described an efficient high yield procedure for the required U(1V) complexes [44]. 

The preparation of two cyclo-octatetraene-gold complexes, (ct)AuCl and (cot)-AU2CI4, has been reported. The structures of biscyclo-octatetraenyl complexes of titanium, vanadium, thallium, and uranium, were deduced from their i.r. spectra. Protonation of (p-cyclo-octatetraene) (p-cyclopentadienyl) complexes has been studied. For the ruthenium and osmium complexes protonation occurs on the eight-membered ring to give CgH moiety co-ordinated to the metal atom via both an T -alkyl and an olefin-metal bond. For the cobalt and rhodium complexes a bicyclic cation (287) is produced which undergoes isomerization to the monocyclic (288). ... 

Cyclopentadienyl complexes of the trivalent uranium can be prepared most commonly from UCI3 (eqs. 53-54) or, and this... 

Ring-substituted tris(cyclopentadienyl)uranium(iv) complexes can be straightforwardly prepared from ring-substituted cyclopentadienylating reagents. Some examples are illustrated below [71, 72] ... 

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