Ferrocene, bonding studies

An X-ray structural study of the ferrocenylphosphonium salt (147) shows a significant shortening of the phosphorus-ferrocene bond, lending support to an earlier suggestion by McEwen that there may be overlap of the filled hog MO of the ferrocenyl group with an empty 3d orbital of phosphorus. The possible existence of an equilibrium between the substituted methylphosphonium salts (148) and the cationic phosphorane system (149) has been ruled out following spectroscopic and structural studies of a series of such salts. ... 

The effects of the nature of the nitrogen donor atom vs. sp ) upon the properties and chemistry of palladated complexes with cr(Pd-G(i/) )), ferrocene) bonds were studied by Lopez et Mossbauer spectra show that... 

As a consequence of the molecular orbital interactions, ferrocene adopts an axially symmetrical sandwich structure with two parallel Cp ligands with a distance of 3.32 A (eclipsed conformation) and ten identical Fe-C distances of 2.06 A as well as ten identical C-C distances of 1.43 A [12]. Deviation of the parallel Cp arrangement results in a loss of binding energy owing to a less efficient orbital overlap [8]. All ten C-H bonds are slightly tilted toward the Fe center, as judged from neutron-diffraction studies [13]. 

Again a distorted tetrahedral coordination of Hg is achieved in the l,l-bis(diphenylphos-phino)ferrocene (dppf) complex with Hgl2. Both Hg—P in the dppf chelate ring and terminal Hg—I bonds (averages 256.5 pm and 277.6 pm, respectively) are clearly longer than in the previous examples all angles around Hg are close to the value for a tetrahedron. Nonlinear optical properties of the material have been studied.241... 

However, more quantitative molecular orbital treatments still leave scope for improvement, and in particular a systematic treatment of the whole metallocene series, rather than of isolated members such as ferrocene, is much to be desired. Moreover, theoretical studies have generally neglected the bis-arene and mixed sandwich series, and in both cases such treatments would be of value in indicating the extent to which the mainly metal n level is or is not less anti-bonding than in the metallocenes. In this connection it is interesting to note that in the (Ch) Cr(Cp)- anion the mainly metal n dxz, dyz ) level may still lie relatively high since esr measurements 1 78) indicate the odd electron to... 

The electrochemical properties of ferrocene have been utilized by many workers in the field of electrochemical molecular recognition. Saji (1986) showed that the previously synthesized (Biernat and Wilczewski, 1980) ferrocene crown ether molecule (Fig. 3 [1]), whose binding properties had previously been studied only by nmr and UV/Vis techniques (Akabori et al., 1983), could be used as an electrochemical sensor for alkali metal cations involving a combination of through-space and through-bond interactions. 

Ruthenocene is an example of a stable x-bonded organometallic compound which undergoes substitution reactions similar to those displayed by ferrocene. Because ruthenocene has heretofore been relatively unavailable, its chemistry has not been extensively studied. 

A single-crystal X-ray diffraction study revealed that the two ferrocene units are in anti conformation. Cyclic voltammetric results are in accord with a strong interaction between the iron centres. Electronic interactions through bonds are mediated by the bridging dimethylsilyl groups and this is discussed in more detail in Section n.E.3. 

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