Tetravalent chemistry salts

Abstract The Shilov system, a mixture of di- and tetravalent chloroplatinate salts in aqueous solution, provided the first indication of the potential of organotransition metal complexes for activating and functionalizing alkanes under mild conditions the participation of higher-valent species plays a crucial role. In this chapter, we discuss the experimental and computational studies that have led to detailed mechanistic understanding of C-H activation and functionalization by both the original Shilov system and the many subsequent modifications that have been developed, and assess the prospects for practical, selective catalytic oxidation of alkanes using this chemistry. 

The study of coordination compounds of the lanthanides dates in any practical sense from around 1950, the period when ion-exchange methods were successfully applied to the problem of the separation of the individual lanthanides,131-133 a problem which had existed since 1794 when J. Gadolin prepared mixed rare earths from gadolinite, a lanthanide iron beryllium silicate. Until 1950, separation of the pure lanthanides had depended on tedious and inefficient multiple crystallizations or precipitations, which effectively prevented research on the chemical properties of the individual elements through lack of availability. However, well before 1950, many principal features of lanthanide chemistry were clearly recognized, such as the predominant trivalent state with some examples of divalency and tetravalency, ready formation of hydrated ions and their oxy salts, formation of complex halides,134 and the line-like nature of lanthanide spectra.135... 

The tetravalent K2K dendron 35 was synthesized from 34 on a PAM resin using Boc chemistry. The synthesis of the first level of carrier core to form Boc-Lys(Boc)-Ala-OCH2-PAM-resin was achieved using a fourfold excess of Boc-Lys(Boc)-OH-DCHA salt via BOP in CH2C12. The second level of lysine was generated by the same protocol. After Boc deprotection, tetravalent chloroacetyl moieties were introduced to the K2K dendron core by using a tenfold excess of QCH2C02H via DIC/HOBt activation. The tetravalent chloroacetyl K2K core 20c (Xaa = Ala) was cleaved from the resin by HF/anisole (9 1) and finally purified by RP-HPLC. MALDI-MS m/z [M + H]+ calcd 780.5 found 780.5 [M+Na - H]+ calcd 802.5 found 802.3. 

This chapter gives an overview on the chemistry of tetravalent lanthanide compounds, especially those of tetravalent cerium. Following a brief introduction, it covers the tetrahalides, dioxides, and other lanthanides(IV) salts. Coordination compounds of cerium in the oxidation state +4 include halogeno complexes and complexes of oxo acids, /3-diketonates and related Schiff-base complexes, as well as porphyrinates and related complexes. 

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