Open metallocenes

In addition to the mixed Cp/carborane complexes, there has been one report on the lanthanacarboranes with the open pentadienyl ligand, R7C5 (R = H or an alkyl derivative). This is an alternate 6-7T electron donor that has led to the syntheses of number of so-called open metallocenes where the pentadienyl group replaces one or more Cp ligands. This lanthanacarborane report covered the syntheses and structural determinations of two open... 

Fig. 20. Comparison of the average metal-carbon bond distances for the open metallocenes of vanadium, chromium, and iron with those of some of the metallocenes themselves. Error bars are drawn at the 3 cr confidence limits...

Fig. 22. Possible approximate relative d orbital splitting patterns for the metallocenes (left) and open metallocenes (right)...

Table 4. Barriers (AG, kcal/mol) to pentadienyl ligand oscillation in various open metallocenes ...

Complexes containing an open chain are also metallocenes analogs. For instance, pentadienyl anions see Pentadienyl Ligand) form open metallocenes with transition metals as efficiently as do cyclopentadienyls. Half-open metallocenes can be obtained in a similar way starting from CpZrCl2Br (Scheme 17). ... 

For the closely related pentadienyl compounds, or open metallocenes, I and II, PE spectroscopy has shown interesting differences in electronic structure from the closed analogs. 

Figure 14 (a) Relation between the 7r-orbitals of C5H5 and C5H7. Breaking of the C-C bond stabilizes those orbitals that are antibonding across this interaction and destabilizes the orbitals that are bonding across this interaction, (b) Representations of the dbg and Qbu orbitals of the open metallocenes. ... 

Casey, A.T. and Vecchio, A.M. (1990) The electrochemical synthesis of metallocenes, polymethylmetallocenes, open metallocenes and metal phenylacetylides ,y4/>p/. Organometal. Chem., 4, 513-522. 

Nickel - The disilyl-bridged cyclopentadienyl nickelocene derivative 91 has been prepared in the reaction of NiBr2(THF)i.3 with the cyclopentadienyl anion and deprotonated tetrahydro-4,4,8,8-tetramethyl-4,8-disila-s-indacene. " The triple decker cation [CpNi( -Cp)NiCp] BF4 reacts with the half open metallocene 92 to give the unusual complex 93. ... 

C. Open Metallocene Complexes with Halide and Related Ligands. 149... 

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