Dicyclopentadienyl complexes structure

Two classes of material will be described here - the metal dithiolenes and rare earth metallocenes. In the metal dithiolenes a strong, low energy pi-pi transistion occurs in the near IR (9.10). This can be tuned from about 700 nm to 1400 nm by altering the metal ion, substituents or charge state of the dithiolene. The dithiolenes are particularly attractive because of their optical stability which has been exploited in their use as laser Q-switch materials. In the rare earth complexes the near IR band is provided by/-/transistions of the rare earth ion rather than the cyclopentadienyl ring structure various nonlinear optical phenomena have been observed in glasses incorporating similar ions. Previous studies have shown that dicyclopentadienyl complexes such as ferrocene have off-resonant nonlinearities similar to nitrobenzene or carbon disulphide (11-13)... 

For this purpose, the catalyst has to possess optimum thermodynamic parameters, for example, the redox potential corresponding to this process. As shown in practice, metal complexes with different structures are characterized by a very broad range of values. For example, for dicyclopentadienyl complexes of transition metals, depending on the nature of the central atom, the value ranges from -3 to +2 eV. The change in the donor-acceptor properties of substituents in the cyclopentadiene ring of ferrocene changes E by several electron volts. 

Figure 3.8 Zirconium and hafnium dicyclopentadienyl-1,3-dienyl complexes. See text for explanation of the structures.

Structural studies by Baker, Brown, and Raymond (42) have shown the dimeric nature of lanthanide dicyclopentadienyl halides. They reported that the molecular structure of [Y (C H CH ) Cl] consists of two ytterbium atoms, each with two n -bound methyl-cyclopentadienyl rings, which are nearly symmetrically bridged by the two chlorine atoms. The crystal structure of Yb(C(.H Me was reported by Halton et al. (43). The complex actually nas a dimeric structure, Cp2YbMe2YbCp2, remarkably similar to Me2ALMe2 AlMe2 The overall molecular geometry is identical with that or the chloride analogue Yb(C H CH )2CI. 

The dimeric dicyclopentadienyl methyl yttrium complex reacts readily with methyl aluminum dichloride with loss of the methyl group and formation of a stable di- u-chloro-bridged dicyclopentadienyl yttrium dimethyl aluminum complex (Holton et al., 1979c), and dicyclopentadienyl yttrium chloride reacts with aluminum hydride in ether with formation of a white crystalline 2 1 1 complex, of which the X-ray structure was determined (Lobkovskii et al., 1982) ... 

The structural problems were solved by Holton et al. (1976a, b) via the synthesis and the demonstration of the reactive behavior of some bimetallic complexes of the rare earths. The reaction of dicyclopentadienyl rare earth chlorides with lithium tetramethyl aluminate or lithium tetraethyl aluminate in toluene at 0°C gives in high yields the crystalline complexes shown in eq. (38) (Holton et al., 1979b, c) ... 

A new class of polymetallic organolanthanide polyhydride complexes was found by W.J. Evans et al. (1982b). Dicyclopentadienyl-tert-butyl erbium tetrahydrofur-anate decomposes in toluene in the presence of Uthium chloride within ten hours at room temperature with formation of 2-methylpropane, 2-methylpropene and a pink compound, which shows a broad absorption in the infrared spectrum between 1250 and 1200 cm for the j (ErH). A single crystal X-ray structural determination of a pink prismatic crystal shows cation-anion pairs with three dicyclopentadienyl... 

Dicyclopentadienyl rare earth chlorides react with a variety of compounds containing other anions than Cl. Maginn et al. (1963) prepared some methoxides and one phenoxide, Schumann et al. (1982) isolated the dicyclopentadienyl samarium tert-butoxide, and Watson (1982) found bis(pentamethylcyclopentadienyl) lutetium ethoxide as one of the reaction products of the ethanolysis of bis(pentamethylcyclo-pentadienyl) methyl lutetium. These compounds are much more stable against oxidation. No X-ray structural determination of these complexes has been done. 

ITie reaction of some dicyclopentadienyl lanthanide chlorides and some bis(meth-ylcyclopentadienyl) lanthanide chlorides with Na[WCp(CO)3] results in some complexes, stable up to 220°C, which are soluble in tetrahydrofuran and dimethylsulfo-xide. Other anionic metal carbonyl or metal nitrosyl compounds gave no satisfying results, mainly because of side reactions. Infrared spectra indicate polymeric structures containing isocarbonyl bridges (Crease and Legzdins, 1973b) ... 

For linear dicyclopentadienyls the results in Table XLII can be deduced from Eq. (2). It is interesting to compare the calculated /-values with the uicc and ycH of the ring ligands and with the deviation of the electronic structure of the metal from a filled inert gas shell. There is a clear relationship between electronic configuration and (symmetry) force constants. In addition, the values of ycu re lowest for complexes not having filled inert gas shells. 

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