Uranocene substituted compounds

In this section we summarize the e gperimental results for a number of substituted uranocenes. The compounds studied are listed in Table III and Fig. 3. 

Many substituted uranocenes have been made and there is a substantial body of organometallic chemistry of uranocene derivatives now known 16, 17). Some of this chemistry will be mentioned in passing but wiU not be covered in a systematic way since other reviews of the organic chemistry are available 18). The only other actinide cyclooctatetraene complex structurally characterized to date is bis[(l,3,5,7-tetramethylcyclooctatetraenyl]uranium(IV) 19), which was of interest because the presence of methyl groups allowed the planarity and relative orientation of the dianion rings to be determined. Crystal and molecular parameters for these three actinide compounds are summarized in Table 1. 

Intermolecular electron-transfer rates have been studied for uranocene and substituted derivatives of uranium, neptunium, and plutonium by examining the variable-temperature NMR spectra of mixtures of (CgH8)2An and [(C8Hg)2An]. In all cases, electron-transfer rates are rapid. Specific rates could not be derived for uranium and plutonium derivatives owing to the small chemical shift differences between analogous An(fV) and An(III) compounds, but in the case of (f-BuC8H7)2Np, the rate has been estimated to be of the same order of magnitude as comparable lanthanide cyclooctatetraene compounds ( 10 s ). ... 

Numerous substituted uranocenes are now known and could, in principle, provide useful tests. Other factors now, however, become involved and need to be evaluated. The lower symmetry of these compounds means that X and Y are no longer constrained to be equal and the eq. 3 needs to be considered in its entirety. Moreover, the substituent could have an effect on magnetic anisotropy. Finally, some substituents have more than one possible conformation which would need to be considered. 

C. Monosubstituted UrariOCeheg. Some monosubstituted uranocenes are known, compounds with one COT and one substituted COT ligands. The mono-t-butoxycarbonyluranocene, 42, was prepared by reaction of one mole of the corresponding COT dianion with one mole of COT dianion itself and UC14(4 ). It could be separated from the disubstituted compound, 41, also formed, by its greater stability towards hydrolysis. Mono-t-butyluranocene, 32, was obtained and measured as a 1.8 1 mixture with the disubstituted compound, 33. A separate preparation of pure 33 allowed complete analysis of the mixture. Mono-(di-t-butylphosphino)uranocene has also been reported by Fischer, et al(45). 

Few reactions have been noted for the 8]annulene compounds of actinides and lanthanides except for uranocene itself. The reactions of uranocene with nitro-compounds o and of some substituted uranocenes with or-... 

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