Chromium imido complexes

Figure 17-C-4 Syntheses and reactions of chromium imido complexes (from refs. 33 and 34).

Chromium corroles have been isolated as 6-coordinate Cr(III) and 5-coordinate Cr(IV/V/VI) oxo, nitrido, and imido complexes. The synthesis of Cr(tpfc)(py)2 (py = pyridine), which is oxidized to (oxo)Cr(tpfc) on standing in aerated solution, was reported in 2001 [78]. Cr(tfpc)(0) could be reduced by cobaltocene to give... 

Edwards NY, Eikey RA, Loring MI, Abu-Omar MM (2005) High-valent imido complexes of manganese and chromium corroles. Inorg Chem 44 3700-3708... 

Two additional chromium-based cationic complexes were reported by Gibson et al that also exhibit high activity as homogeneous ethylene polymerization catalysts [36]. These cationic complexes were prepared from the Bis(imido) Chromium (VI) complex (R-N=),Cr(CH,CHJ, where R is t-butyl. The structure of this precursor complex is illustrated in Figure 3.29. 

Bishomoallyl alcohols, via allyindium reagents, 9, 703 Bis(hydrostannation), in tin-carbon bond formation, 3, 814 Bis(imidazolyl) ligands, chromium complexes, 5, 359 Bis(imido) systems, with chromium(VI), as models, 5, 377 Bis(imido)tungsten complexes, synthesis, 5, 749 Bis(imido)uranium(VI) complexes, synthesis, 4, 216-217 Bis(imino)carbenes, with Zr(IV), 4, 798 Bis(iminooxazolidine) complexes, biaryl-bridged, with Zr(IV) and Hf(IV), 4, 811-812... 

Imido and 0x0 compounds are intermediates in many of the transfers of oxygen atoms and nitrene units to olefins to form epoxides and aziridines, and they are intermediates in many of the insertions of oxygen atoms and nitrene units into the C-H bonds of hydrocarbons to form alcohols and amine derivatives. The enantioselective epoxidation of allylic alcohols (Scheme 13.22) " is the most widely used epoxida-tion process, and the discovery and development of this process was one of the sets of chemistry that led K. Barry Sharpless to receive the Nobel Prize in Chemistry in 2001. The mechanism of this process is not well established, despite the long time since its discovery and development. Nevertheless, most people accept that transfer of the oxygen atom occurs from a titanium-peroxo complex - rather than from an 0x0 complex. Jacobsen s and Katsuki s - manganese-salen catalysts for the enantioselective epoxidations of unfunctionalized olefins, which were based on Kochi s achiral chromium- and manganese-salen complexes, are a second set of... 

As stated by Gibson, the most striking feature in the structure of the Bis(imido) chromium(VI) precursor is the manner in which the two benzyl ligands are bonded to the chromium atom through and r coordination modes. Figure 3.30 shows the two cationic complexes prepared from the precursor complex to form ethylene polymerization catalysts. 

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