Tris cyclopentadienyl

Reaction of ammonium hexanitrocerate and cyclopentadienylsodium under inert conditions gives tris(cyclopentadienyl)cerium and sodium nitrate, removed by filtration before evaporation of solvent [1]. When the filtration step was omitted, and the evaporated solid mixture was heated to 75°C, a violent explosion occurred. This may have involved complexes of the type Ce(N03)Cp2.NaN03[2], but a direct redox reaction between the reactive CeCp3and the oxidant is also possible. 

Several tri(cyclopentadienyl)tin(ll) and lead(ll) complexes have been prepared with alkali metal cations. The arrangement of Cp rings around the metal is in a paddle wheel configuration the alkali cation is bound to Cp and not Sn or Pb, further supporting the view of a weak alkali metal group 14 bond. Representative examples of these compounds include (77S-Cp)2E(/r-Cp)-Na(PMDTA) (E = Sn 230, Pb 231).239 240... 

Tricyclopentadienyluranium tetrahydroalmninate, 3688 N. /V.4-Trilithioanilinc. 2180 Triphenylmethylpotassium, 3781 Tris(cyclopentadienyl)cerium, 3683 Tris(cyclopentadienyl)plutonium, 3 684 Tris(cyclopentadienyl)uranium, 3685... 

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. 

One other structure of a tricyclopentadienide has appeared (57) and it provides a further demonstration of the correlation between ionic size and coordination. Neodymium tris(methylcyclopentadienide) crystallizes as a tetramer (Fig. 10). The Nd + ion (which is slightly larger than Sm3+) is pentahapto bound to three cyclopentadienyl rings and monohapto bound to a fourth ring. This fourth ring is in turn j -bonded to another Nd + ion, until the tetramer is generated. The distances between tetramers are those expected for van der Waals contact. The crystal and molecular parameters are compared with the other tris cyclopentadienyl complexes in Table 5. 

Fig. 15. The structure of tris(cyclopentadienyl) (2-methylallyl)uranium(IV), from Ref. (75)...

From the relative stabilities of the actinide homoalkyls or -allyls and the tris(cyclopentadienyl) actinide alkyls, it appears that a coordinatively saturated metal center is necessary for kinetic stability. In contrast to f-transition metal alkyls, the absence of hydrogens appears to be of minor importance. In the case of the lanthanide alkyls and the tetrabenzylthorium, where the formal coordination number is only four, the steric bulkiness of the Hgands must be responsible for their observed thermal stability. 

The ground state geometries in these complexes are often determined by a subtle balance of the energy released by an increase in coordination number and the energy lost by intramolecular repulsion. The question of versus bonding in the tris(cyclopentadienyl)uranium aUyls is one molecular example. The structures of the lanthanide tiicyclopentadienides represent another example in extended crystalline arrays. 

The Lu—C sigma bond is about 0.2 A shorter than the pentahapto coordinated Sm—C bond in tris-cyclopentadienyl complex (Sm—C =2.76 A) taking account of the difference of ionic radii of 0.11 A between Sm and Lu (Table 1). 

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... 

Tris(aminomethyl)ethane, 2044 1,1, l-Tris(bromomethyl)methane, 1550 Tris(cyclopentadienyl)cerium, 3683 Tris(hydroxymethyl)methylamine, 1731 Tungsten hexamethoxide, 2604... 

The addition of NaC5H5 to Sn(C5H5)2 in the presence of PMDTA gives the tris(cyclopentadienyl)stannate Na(/x-T)5, i 5"C3H5)Sn(T75-C5H5)2. PMDTA, 3977 (Fig. 23). The tin center is almost planar. The sodium is... 

See Sodium nitrate Tris(cyclopentadienyl)cerium See other ORGANOMETALLICS... 

Tris(bromomethyl)ethanol, 1916 Tris(cyclopentadienyl)cerium, 3676 Tris(cyclopentadienyl)plutonium, 3677 Tris(cyclopentadienyl)uranium, 3678 Tris(2,3-diaminobutane)nickel(II) nitrate, 3583 Tris(l,2-diaminoethane)chromium(III) perchlorate, 2615 Tris(l,2-diaminoethane)cobalt(III) nitrate, 2618 Tris(l,2-diammoethane)ruthenium(III) perchlorate, 2617 Tris(difluoroamino)fluoromethane, 0363 Tris(dimethylamino)antimony, 2594... 

Tris(2,4-pentanedionato)molybdenum(III), 3683 Tris(cyclopentadienyl)cerium, 3676 Tris(cyclopentadienyl)plutonium, 3677 Tris(cyclopentadienyl)uranium, 3678... 

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