Bridged Chromium Complexes

Binuclear difluoro-bridged chromium complexes are rare and the only well-characterized previous example is the multidentate Cr(in) derivative [A, A"-(2-0-3, 5- Bu2-C6H2-CH2)2-1,2-NHCH2CH2NH]Cr(p,-F) 2 [25]. The terphenyl stabilized chromium fluoride 4-CF3-Ar Cr(p,-F) 2 (11) was obtained by decomposition during the reduction of 4-CF3-Ar Cr(p,-Cl) 2 with KCg in THF. Unlike the generally blue color observed for the chlorides, 11 has a pale purple color. 

Bridged Chromium Complexes.—The mixed Cr -Co -dimer ion [(en)aCr(OH)a-Co(en)j] + behaves like a bridged dichromium(iii) complex and is totally unlike the analogous dicobalt(iii) species. The first bridge hydrolysis was examined (Scheme 9). 

Chromium, (ri6-benzene)tricarbonyl-stereochemistry nomenclature, 1,131 Chromium complexes, 3,699-948 acetylacetone complex formation, 2,386 exchange reactions, 2,380 amidines, 2,276 bridging ligands, 2,198 chelating ligands, 2,203 anionic oxo halides, 3,944 applications, 6,1014 azo dyes, 6,41 biological effects, 3,947 carbamic acid, 2,450 paddlewheel structure, 2, 451 carboxylic acids, 2,438 trinuclear, 2, 441 carcinogenicity, 3, 947 corroles, 2, 874 crystal structures, 3, 702 cyanides, 3, 703 1,4-diaza-1,3-butadiene, 2,209 1,3-diketones... 

The vanadium(iii) ion [V(H20)6] (9.9) exhibits this behaviour, with a log AT of 4 associated with the formation of the hydroxy-bridged dinuclear complex 9.10. This is a general phenomenon. For example, chromium(iii) and iron(iii) form strictly... 

Table 8.5 Stability of g-Hydroxo Bridged Chromium(lII) Complexes...

The use of /r-hydroxo or ju-alkoxo bridged polynuclear complexes of chromium, molybdenum, tungsten, or rhenium in this route leads to the formation of monomeric bis(NHC) complexes, to the elimination of hydrogen, and to the partial oxidation of the metal [Eq.(ll)]. Chelating and nonchelating imidazolium salts as well as benzimidazolium and tetrazolium salts can be used. 

Pair-of-dimer effects, chromium, 43 287-289 Palladium alkoxides, 26 316 7t-allylic complexes of, 4 114-118 [9JaneS, complexes, 35 27-30 112-16]aneS4 complexes, 35 53-54 [l5]aneS, complexes, 35 59 (l8)aneS4 complexes, 35 66-68 associative ligand substitutions, 34 248 bimetallic tetrazadiene complexes, 30 57 binary carbide not reported, 11 209 bridging triazenide complex, structure, 30 10 carbonyl clusters, 30 133 carboxylates... 

IX. Equilibria between Mono- and Dihydroxo-Bridged Dinuclear Complexes of Chromium(III), Rhodium(III), and Iridium(III)... 

In this section the methods which have been used to gain structural information are briefly summarized. The term structure is used in this context in its broadest sense, including more qualitative observations concerning the skeleton of the bridging atoms. As a general rule, the hydroxo-bridged polynuclear complexes of chromium(III) and cobalt(III) can be isolated as well-defined crystalline salts and it is therefore quite natural that single-crystal X-ray structure analysis has... 

Only a few trihydroxo-bridged chromium(III) complexes have been studied. The cation (metacn)Cr(OH)3Cr(metacn)3+ has J = 128 cm-1 (137, 138), and the corresponding tacd complex has J = 96 cm-1 (98). 

A very large number of dihydroxo-bridged chromium(III) and cobalt(III) complexes have been synthesized from the parent mononuclear species by aqueous hydrolysis, as shown in Eq. (1) for a cationic species, but also neutral and... 

Acid Strength of Bridging Hydroxide in Singly Bridged Chromium(III) Complexes at 20°C... 

Hydrolysis of polynuclear hydroxo-bridged chromium (III) complexes in concentrated solutions of strong acid yields the corresponding mononuclear species. Such cleavage reactions are fast in comparison with the hydrolysis in dilute acid and proceed with retention of configuration of the mononuclear entities. A few representative examples are shown in Eqs. (46)-(49) (40, 42,161, 252). 

Chromium complexes acetylacetone complex formation, 386 exchange reactions, 380 amidines, 276 bridging ligands, 198 chelating ligands, 203 carbamic add, 450 paddlewheel structure, 451 carboxylic adds, 438 trinuclear, 441 oorroles, 874... 

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... 

Chromium complexes (continued) organohalide activation, 5, 381 with phosphine-based supporting ligands, 5, 365 porphyrin-ligated derivatives, 5, 364 pyridinebis(imine) ligand derivatives, 5, 361 salen-ligated complexes, 5, 379 surface chemistry on oxides, 12, 525 tetradentate [04] compounds, 5, 352 tetradentate thioether derivatives, 5, 365 thiolate-bridged, Fe- and Rh complexes, 5, 308 with Ti(IV), 4, 627... 

Heterometal alkoxide precursors, for ceramics, 12, 60-61 Heterometal chalcogenides, synthesis, 12, 62 Heterometal cubanes, as metal-organic precursor, 12, 39 Heterometallic alkenes, with platinum, 8, 639 Heterometallic alkynes, with platinum, models, 8, 650 Heterometallic clusters as heterogeneous catalyst precursors, 12, 767 in homogeneous catalysis, 12, 761 with Ni—M and Ni-C cr-bonded complexes, 8, 115 Heterometallic complexes with arene chromium carbonyls, 5, 259 bridged chromium isonitriles, 5, 274 with cyclopentadienyl hydride niobium moieties, 5, 72 with ruthenium—osmium, overview, 6, 1045—1116 with tungsten carbonyls, 5, 702 Heterometallic dimers, palladium complexes, 8, 210 Heterometallic iron-containing compounds cluster compounds, 6, 331 dinuclear compounds, 6, 319 overview, 6, 319-352... 

The preformation of the bridging-hydrazine complex is a strategy which has been extended to the analogous chromium (295, 296) and tungsten (297) complexes, although the latter is best prepared by the oxidation of fW(CO)5(N2H4)]. 

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