Cyclopentadienyl complexes crystal structure

The structure of the metallocene cation energy minimised with the Car-Parrinello method agrees well with the experimentally obtained crystal structures of related complexes. Typical features of the structure as obtained from X-ray diffraction on crystals of very similar neutral complexes (e.g., the dichlorides), such as small differences in distances between C atoms within a cyclopentadienyl (Cp) ring, as well as differences in distances between the C atoms of the Cp ring and the Zr atom, were revealed from the simulations. 

Reagent 7 is easily prepared from commercially available diacetone-D-glucose and trichloro(cyclopentadienyl)titanium35 (Section 1.3.3.3.8.1.). The monomeric structure of reagent 7 was confirmed by an X-ray crystal structure analysis1 7. Complex 9 is obtained36 analogously from (7 .7 )-tartaric acid derived (R,7 )-2,3-CMsopropylidene-l,l,4,4-tetraphenyl-1,2,3,4-butanetetrol. 

The crystal structure of a mono(cyclopentadienyl)zirconium complex containing a novel Me2Si-linked bis(amidinate) ligand was reported (Scheme 203). In this compound the central Zr atom is octahedrally coordinated with the bis(amidi-nate) acting as a tridentate ligand. ... 

Monomeric carbene complexes with 1 1 stoichiometry have now been isolated from the reaction of 4 (R = Bu, adamantyl or 2,4,6-trimethylphenyl R = H) with lithium l,2,4-tris(trimethylsilyl)cyclo-pentadienide (72). The crystal structure of one such complex (R = Bu) revealed that there is a single cr-interaction between the lithium and the carbene center (Li-C(carbene) 1.90 A) with the cyclopentadienyl ring coordinated in an if-fashion to the lithium center. A novel hyper-valent antimonide complex has also been reported (73). Thus, the nucleophilic addition of 4 (R = Mes R = Cl) to Sb(CF3)3 resulted in the isolation of the 1 1 complex with a pseudo-trigonal bipyramidal geometry at the antimony center. 

Vinylboronates are generally less reactive than vinylzirconocenes towards various electrophiles and hence selective reactions of the latter should be possible. It was found that selective cleavage of the carbon—zirconium bond in 45 by N-halosuccinimides provides (a-haloalkenyl)boronic esters 53 in excellent chemical yields and with complete re-gioselectivity (Scheme 7.17) [54], An X-ray crystal structure determination of 45 confirmed the configuration of the four-coordinate Zr complex, with two cyclopentadienyl rings, Cl, and C(sp2) as the four ligands (Fig. 7.5) [54,126]. 

Figure 7.8. Crystal structure of the novel zirconacyclopentadiene complex, 8,8-bis(cyclopentadienyl)-7,9-bis-(trimethylstannyl)-8-zirconabicyclo[4.3.0]nona-l (9),6(7)-die ne 109. Adapted by the authors.

Another complex involving the formation of a cyclopentadienyl unit is obtained from the interaction of ethyl or propyl acetylene with Fe3(CO)i2 117). The products contain the complexes Fe3(CO)7(HC2R)4 (R = Et, re-Pr), and the crystal structure of the ethyl derivative indicates the presence of the substituted 1,2,3-triethylcyclopentadienyl group bonded to one iron center with an ethylallyl group cr- and n-bonded to the three metal centers. The formation of adducts of this type must involve the fission of the C=C bond of the acetylene. 

The crystal structure of the bromide complex of [78] has been elucidated and clearly shows bromide anions hydrogen-bonded to the amide N—H groups and, interestingly, also to the cyclopentadienyl hydrogen atoms (Fig. 40). 

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. 

In a similar way Cp(Me)Mg(OEt2) is capable of deprotonating iV,Ai -bis(2,4,6-tri-methylphenyl)(ierr-butyl)amidine to form the corresponding cyclopentadienylmagnesium amidinate complex (226) (equation 17). An X-ray crystal-structure determination of 226, of which the structure is shown schematically (equation 17), showed that this compound also exists as a monomer in the solid state. Like in 225 the cyclopentadienyl group is /7 -bonded to magnesium while the amidinate anion is Ai,A -chelate bonded with almost equal Mg—N bond distances [Mg-N 2.090(2) and 2.097(2) A]. Furthermore, an additional... 

Early and late transition metal combinations were explored by Casey [71] and many others. Reaction of the bis(phosphinomethyl) complex Cp2Zr(CH2PPh2)2 (Cp = cyclopentadienyl) on Rh(H)(PPhj)4 gave the bimetallic hydride Cp2Zr (CH2PPh2)2Rh(H)(PPh3) (30), the crystal structure of which was determined [72],... 

There is a recent review of two-coordinate phosphorus complexes.306 Malisch et a/.307 observed the reversible reaction (86), in which a metal-arsenic(III) double bond is formed, i.e. the M—As a bond is augmented by the arsenic lone pair to form a n bond system (since the cyclopentadienyl coligand is not coplanar with the M=As, the arsenic double bond is isolated). Complex (58) undergoes reactions typical of double bond molecules (Scheme 14). Phosphorus analogues have also been prepared (Scheme 15) the crystal structure of product (c) in Scheme 15 has been solved (59a). The d(W—P) of 2.181 A is shorter than the predicted rf(W=P) of 2.26 A, and the trigonal planar coordination of phosphorus indicates sp2 hybridization.308... 

X-ray analysis of complex 9 shows two independent molecules in the unit cell. The Hf—Si bonds of 2.881(4) A and 2.888(4) A are longer than those found in other d° Zr—Si derivatives (Table 1), reflecting the steric hindrance in 9. The crystal structure of the mixed cyclopentadienyl complex CpCp Hf(SiH2Ph)Cl reveals a Hf—Si bond length of 2.729(3) A, which is shorter than in 9, presumably due to a lower steric interaction... 

The homoleptic lanthanide(III) benzamidinates 20-23 can be regarded as analogues of the well known tris(cyclopentadienyl)lanthanide complexes (C5H5)3Ln [7, 8]. One of the most characteristic reactions of the homoleptic cyclopentadienyls is the formation of 1 1 adducts with Lewis bases such as ethers, nitriles, esters etc. [7, 8], Recently it was discovered that the homoleptic lanthanide benzamidinates [PhC(NSiMe3)2]3Ln (20) form similar adducts with THF and nitrile ligands such as acetonitrile or benzonitrile [59]. The molecular and crystal structures of two benzonitrile adducts (26g, h) have been determined by X-ray diffraction. Figure 8 depicts the molecular structure of the europium... 

Diphenyl zirconocene complex 102 is unstable at room temperature and undergoes electrophilic substitution at the alkylated cyclopentadienyl ligand to produce the boratacycle 44 in high yield (Equation 10). The reaction involves loss of 1 equiv of benzene from the central zirconium, and the X-ray crystal structure of 44 (detailed in Section 7.14.3) clearly shows interaction between the zirconium and one of the perfluorophenyl ligands attached at boron <2004CC1020>. 

Note added in proof Very recent work by Schrock has extended this tantalum ylide chemistry very considerably and some cyclopentadienyl tantalum methylenes and benzylidenes could be isolated and fully characterized (82b). Among the new compounds the complex (C5H4CH3)2Ta(CH3)(CH2) is particularly noteworthy. Its crystal structure has been determined and the temperature dependence of its nmr spectra has been carefully investigated (17b). The ylidic carbon is in a trigonal planar configuration ... 

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