Cycloheptatrienyl complexes structure

Only one cycloheptatrienyl complex of the lanthanides is known until now. Reaction of Nd(BFl4)3(TFIF)2 with K(C7Hg) yields (THF)(BH4)2Nd(/x- ] )] -C7H7)Nd (BH4)(THF)3 (Figure 76). The X-ray structure determination shows a unique reverse-sandwich structure with both Nd atoms r] coordinated to the planar ligand. 

Some nucleophiles react with cationic cycloheptatrienyl complexes to give addition products. Addition of H, CN , OMe , and Ph leads to the formation of complexes possessing exo structures (11.17). 

Actinides. Unique examples of cycloheptatrienyl complexes with f elements are reported (Arliguie et al. 1994b) with the anions [(X3U)2(tt-C7H7)] (X = NEt2, BH4), synthesized from UX4 and K[C7H9]. An inverse sandwich structure has been... 

Finally, consider the complex C7H7Co(CO)3 whose structure is unknown but may be predicted using the 18-electron rule. At first sight the complex appears to be a 7 -f 9 -f 6 = 22 electron complex. It is therefore proposed that the C7H7 ring only contributes three electrons to the cobalt, rather than seven, and that instead of being the jr-cycloheptatrienyl complex, I.l, it is the Ti-enyl complex 1.2 ... 

The structures of two jr-cycloheptatrienyl complexes have been determined by X-ray analysis and are given in Figure 45. 

The mixed cyclopentadienyl-cycloheptatrienyl ( 5-7 ) titanium complex Cp( -C7H7)Ti has been prepared in 33 -40% yield by the reduction of CpTiCb with isopropylmag-nesium bromide or Mg in the presence of cycloheptatriene. Reduction of Cp TiCb in THF with Mg in the presence of cycloheptatriene gives Cp ( -C7H7)Ti in 68% yield. Titanium 5-7 complexes exhibit sandwich structures see Sandwich Compound) with the five-membered and seven-membered rings nearly parallel to each other. 

The synthesis and structural characterization of the first example of an titanium complex (Scheme 670 Section 4.05.5) has been reported. Its reactivity toward cr-donors/7T-acceptor ligands demostrates that this complex does not behave like a low-valent titanium compound but rather bears a closer resemblance to Lewis-acidic Ti(iv) complexes. Based on theoretical calculations, this behavior can be attributed to a strong and appreciably covalent Ti-cycloheptatrienyl interaction which leads to highly stabilized frontier orbitals and consequently to a diminishing 7r-electron release ability.1706... 

Other structurally characterized metal carbonyl complexes with bi- and trifurcation at a carbonyl oxygen atom include, for example, the cycloheptatrienyl and cyclooctatetraene cobalt clusters Co4 CO)6ir -C ii9) r -C-J ii ), 92, Co4(CO)e-(t/ -CsHsXlti-CsHg), 93, and Co4(CO)8(Ai3-C8H8), 94 [153]. 

The structure of arene sandwich compounds (like that of cyclopentadienyl, cycloheptatrienyl, etc., derivatives) and the character of the M-arene bond may also be considered on the basis of ligand field theory assuming C ,v symmetry of the compound (cf. Chapter 9). The ligands connected to the metal via carbon atoms create a strong field. Therefore, the splitting parameters are large. The nephelauxetic coefficients P = BIBq, where B is the Racah parameter for the complex and Bq is the Racah parameter for the free metal ion (5o and B represent interelectron repulsion), generally assume values 0.5 0.1 for metallocenes and arene sandwich complexes. Low values of nephelauxetic coefficients indicate considerable covalent character of the metal-hydrocarbon bond. 

The synthesis, fluxional behaviour and X-ray structure of the cycloheptatrienyl bridged heterobimetallic complex [Fe(CX))3( i- n3,T 3.c. H7)PdCpl has been reported346. 

From 1971 to 1974 a group of Indian chemists published a series of papers in which the synthesis and the properties of more than 60 organo-Ce(IV) derivatives were described, including cyclopentadienyl, indenyl, fluorenyl, cycloheptatrienyl and cyclooctatetraenyl complexes (Table XLL). The structure of compounds was confirmed in the most cases by the data of elemental analysis (C, H, Ce), IR spectroscopy and chemical reactions. At the same time several attempts to repeat the described synthesis, which have been undertaken by other chemists, have failed, which gives the base for some doubts in reliability of the data of Kapur and coworkers. These reasons impelled us to collect all compounds of Ce(IV) described by the mentioned authors in a separate chapter. 

Ferrocenyl-containing Complexes. - A collection of compounds derived from ferrocenyl-substituted acetylide Ti-based tweezer molecules have been prepared and characterised." The crystal structure of the cyclohexadienyl-containing complex 168 has been reported." A series of multimetallic complexes have been prepared by addition of enolates of bis-(ferrocenyl)-1,3-diketones to a range of p -ethene-, riCcydohexatriene-, p -cycloheptatrienyl- and pCcyclo-heptatrienyl-containing complexes." The crystal structure of 169 has been described." Compounds 170 and 171 were obtained from the reaction between... 

The cycloheptatrienyl carbonyl anions [(C7H7)M(CO)3] involve // -coordination of the seven-membered rings at low temperatures (6) even though the // -bonded structure (7) is only slightly less stable.These complexes are fluxional, most probably as a result of a series of 1,2-shifts. Such a mechanism, however, does not require passage through the form (7). 

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