Chromium complexes fluoro

Fluoro- and chloroarenes activated by complexation with chromium tricarbonyl react readily with primary and secondary alcohols under basic conditions in the presence of a quaternary ammonium catalyst [46, 47]. Reaction of the chromium complexes with acetone oxime produces O-aryloximes in good yields (55-80%) [48]. 

Luminescence spectrocopy is potentially a powerful technique for studying chromium(III) complexes and a series of fluoro and aqua complexes have been studied.1066 The luminescence correlates well with ligand field strength and, at. liquid air temperatures, the lifetime of the doublet state from which phosphorescence originates is 2 x 1CT7 s 1. 

Fluorine atoms in electron-deficient benzene derivatives, such as l-fluoro-2-nitroben-zene,149-150 l-fluoro-4-nitrobenzene.151 153 2-fluorobenzaldchyde,154"156 2-fluoroaceto-phenone,155156 4-fluoroacetophenonc,157 2-fluorobenzophenone.156 2- and 4-fluorobenzoni-trile,158 and 4-fluorophenyl trifluoromethyl sulfone,152,159 are easily substituted by N-nucleophiles. Even fluorine in electron-deficient sandwich complexes, such as tricarbonyl(t/6-fluoro-benzene)chromium (3), is substituted by amines.160161... 

While the first transition metal carbene complex was reported in 1964134, the first cyclopropylcarbene complex salt [(CO)5Cr=C(chromium hexacarbonyl, followed by tetramethylammonium bromide135. Subsequent reaction with trimethyloxonium fluoro-borate gave methoxycarbene complex (CO)5Cr=C(OMe)(c-Pr) (equation 62)136. 

Activation of aromatic compounds by transition-metal complexes was initially studied with Cr(CO)3 complexes. Nucleophilic addition of 2-lithio-l,3-dithianes to arene-chromium(O) complexes 185 followed usually by iodine-promoted decomplexation affords the corresponding 2-arylated 1,3-dithianes 186. The reaction of //-(toluene)- and (anisole)tricarbonylchromium (185) with compound 161 gave mixtures (52 46 and 10 90, respectively) of ortho and meta substituted derivatives (186) (Scheme 54)244. The meta directing effect was also observed (mainly better than 95%) with amino and fluoro substituted complexes245. 

Fluoro- and chloro-substituted tricarbonyl chromium arene complexes can be reductively coupled with ketones, in the presence of samarium iodide, to give tertiary alcohols (Scheme 109). A related reaction of a tethered alkoxyimine furnished a tricyclic compound (Scheme 110). Samarium also promotes the formation of a benzyhc ketyl... 

We have also expanded our studies to include chromium(III) systems. However, for the chromium centers we have chosen the more volatile tri-fluoro (tfa") and hexafluoro (hfa ) derivatives of 2,4-pentanedione. Since the fluorinated derivatives are deactivated relative to the electrophilic attack used in these polymerizations, the Cr(acac)2(tfa) mixed ligand complex has been used initially to obtain polymeric products with sulfur halides. Whereas the intrinsic viscosity of one of the polymers so obtained was 0.17 dL/g, the GPC results suggest only oligomeric products. 

Mechanistic studies of chromium chemistry tend to concentrate on complexes of the inert + 3 oxidation state which are, therefore, dealt with first. A few references to work involving other oxidation states are included at the end. There have been no major reviews of mechanistic chromium chemistry during this period, although a useful article deals with the preparations and reactivities of fluoro-containing complexes of chromium(III). Further reviews deal with the determination of volumes of activation, and their use for elucidating inorganic reaction mechanisms, and these are particularly useful for an understanding of chromium(III) substitutions. 

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