Cyclooctatetraene complexes preparation

This quadruply bonded complex containing a bridging cyclooctatetraene is prepared in 20% yield. The molybdenum analogue can be prepared by a similar procedure in 35% yield d. 

It has recently been reported83 that di-n-cyclooctatetraene complexes of uranium, thorium, and plutonium can be prepared by the direct reaction of the finely divided metals with cyclooctatetraene. The finely divided metals were prepared by a procedure described by Seaborg and Katz.84 Several cycles of formation and descomposition of the hydride gave a finely divided reactive metal. However, treatment of the pyrophoric uranium with cyclopentadiene under the same conditions used to form uranocene failed to produce any detectable amounts of the known compounds U(CsH5)3 or U(C5H5)4. 

An analogous cyclooctatetraene complex can be prepared by displacement of hexadiene from a bis(i -allyl) complex with butadiene. The resulting allylic, CgHj -containing complex is a catalyst for the dimerization of butadiene to 1,3,6-trans,cis-octatriene ... 

It seems likely that in most of the cyclooctatetraene complexes so far prepared the olefin is in its usual tub conformation, the only notable exception being the iron tricarbonyl complexes 40, 41, 42). 

An interesting extension of the chemistry in this field is the preparation of mixed cyclopentadiene-cyclooctatetraene complexes (Jamerson et al., 1974) according to the reactions... 

CyclooctatetraenylCompounds. Sandwich-type complexes of cyclooctatetraene (COT), CgH g, are well known. The chemistry of thorium—COT complexes is similar to that of its Cp analogues in steric number and electronic configurations. Thorocene [12702-09-9], COT2Th, (16), the simplest of the COT derivatives, has been prepared by the interaction of ThCl [10026-08-1] and two equivalents of K CgHg. Thorocene derivatives with alkyl-, sdyl-, and aryl-substituted COT ligands have also been described. These compounds are thermally stable, air-sensitive, and appear to have substantial ionic character. 

The synthesis of bis(rj8-cyclooctatetraene)uranium(IV) (uranocene)J from uranium tetrachloride and (cyclooctatetraene)dipotassium was first published in 1968.1 The method reported here is a modification of that procedure and is suitable for a large variety of cyclooctatefraene complexes.2-4 BisO 8-cyclo-octatetraene)uranium(IV) has also been prepared by the reaction of uranium tetrafluoride with (cyclooctatetraene)magnesium in the absence of solvent.5 Direct reaction of finely divided uranium metal with cyclooctatetraene vapors at 150° also gives some uranocene.5 However, both methods give low yields. 

Another example concerns the initial electronic reduction of a-nitrostilbene (Todres, Dyusengaliev, Ustynyuck 1982 Todres, Dyusengaliev, Sevast yanov 1985 Todres Tsvetkova 1987 Charoenkwan and others, in preparation). The reduction develops as in process (a) in Scheme 2-7 if the mercury cathode as well as the cyclooctatetraene dianion are electron sources, and as in process (b) if the same stilbene enters the charge-transfer complexes with bis(pyridine)-tungsten tetra(carbonyl) or uranocene. For (b), the charge-transfer bands in the electronic spectra are fixed. So the mentioned data reveal a great difference in electrochemical and chemical reduction processes (a) and (b). 

The synthesis and reactivity of arene cyclooctatetraene osmium(O) complexes of type 216 (arene = benzene, mesitylene) (13,132) and arene dicyclopentadiene osmium(O) complexes 212 (arene = mesitylene) (102) have been discussed previously (Section III,A,2). Arene osmium(O) complexes of type Os( 7j6-C6H6)(PR3) (L) (230) have been prepared by reduction... 

The iron(O) complex [Fe(terpy)(CO)2] is readily prepared by the reaction of terpy with [Fe(cot)(CO)3] (cot, cyclooctatetraene) (41,46) in contrast, [Fe(terpy)2] may be obtained as an air-sensitive, paramagnetic solid from the reduction of [Fe(terpy)2]l2 with lithium benzophenone ketyl (240). 

Much interest has been devoted to the related stable (f/ -bicyclo[5.1.0]octa-2,4-di-enylium)Fe(CO)3 cation complex, mainly in connection with the question of the possible homoaromaticity of these cations (equation 148) . The complex was first prepared by the formal electrocyclic ring closure of protonated (cyclooctatetraene)Fe(CO)3 at -60 (Scheme 7) and has later been proved by NMR studies in magic acid solutions... 

The first tris(arene)niobinm complex, [Nb(l-4-J7 -anthracene)3], prepared by the Na or K anthracene rednction of NbCL (THF)2, undergoes facile anthracene displacement in the presence of CO to afford [K(18-crown-6)(THF)2][Nb(CO)6]. Rednction of TaCls by sodinm naphthalene provides [Na(THF)][Ta(j7 -naphthalene)3], the first homoleptic naphthalene complex of a third row transition metal. This complex reacts with CO and anthracene to give [Ta(CO)6] and [Ta(l-4-jj -anthracene)3], respectively. The latter prodnct reacts with cyclooctatetraene (COT) to give [Ta(COT)3]... 

Mixed 5-8 titanium complexes have been prepared by reduction of Cp TiCb and CpTiCb with Mg in THF in the presence of cyclooctatetraene to give Cp ( ) -C8H8)Ti... 

One possible approach to the preparation of an all-hydrocarbon tripledecker compound, with the necessary 34-electron configuration, is to attempt to oxidize or reduce a near-miss complex (42), that is, one containing the correct number of ligands and metals but with an excess or deficiency of electrons. Two such attempts, involving complexes with bridging cyclooctatetraene (cot) ligands, have been reported. 

The first tris(pentamethylcyclopentadienyl) lanthanide complex was isolated accidentally from the reaction of a divalent samarium complex (CsMes )2Sm with cyclooctatetraene [9]. Following this discovery, two more convenient methods were developed for the preparation of the sterically crowded complexes (C5Mes)3Ln [10],... 

Cyclooctatetraene reacts with Co(CO)2(C5H5) to produce (CgHg)-Co(C5H5) 158, 268, 431) and (CsH, )[60(05115)]2 227). Preparation of the complexes by reaction of cyclooctatetraene with cobaltous acetyl-acetonate and ethoxydiethylaluminum has also been reported 611). Spectral data indicate that in the mononuclear complex the olefin is coordinated as a 1,5-diene with the tub conformation 158, 226, 227, 268). X-Ray data 220) show structure (169) for the binuclear complex. 

Haight and co-workers (269) have found that crystalline complexes can be readily obtained by reduction of CuCl2-2H20 or CuBr2 dissolved in ethanol with sulfur dioxide in the presence of the di- or oligoolefin. By this method they have prepared 1 1 complexes with norbomadiene, 1,5-cyclooctadiene, cyclooctatetraene, and dicyclopentadiene, 1 2 complexes with cis,trans,trans- and aW-complex with 1,3-cyclooctadiene. It was noted that rapid addition of SO2 to the system produced 1 2 complexes with norborna-diene and cyclooctatetraene. 

Upon the addition of CO or H2 in the presence of appropriate stabilizers, the controlled chemical decomposition of zerovalent transition metal complexes yields isolable products in multigram amounts [49]. The growth of metallic Ru particles from Ru(COT) (COD) (COT = cyclooctatetraene, COD = cycloocta-1,5-diene) with low-pressure dihydrogen was first reported by Ciardelli et al. [49a]. This material was, however, not well characterized, and the colloidal aspect of the ill-defined material seems to have been neglected in this work. Bradley and Chaudret [49b-l] have demonstrated the use of low-valent transition metal olefin complexes as a very clean source for the preparation of nanostructured mono- and bimetallic colloids. 

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