Cr-bond complexes

Figure 4.17 A qualitative molecular orbital scheme for a cr-bonded complex ion [AuL2]+. (Reprinted with permission from Inorg. Chem., 1982, 21, 2946. Copyright (1982) American...

Simple alkyl and aryl cr-bonded complexes are conveniently prepared by reaction of an alkylating reagent with a halocobalt(II) precursor. All-alkyl systems are rare, but the penta-methylcobaltate(II) anion is known.197 More typically, the coordination sphere of the metal contains additional co-ligands, particularly with P, S, or N donors. Some examples that reflect the style of reactions extant appear below. 

Reforming reactions comprise dehydro-/hydrogenations and olefins might also be intermediates of other reactions—such as the above-mentioned exchange reactions. The two forms of associatively adsorbed olefins have been already mentioned n complexes and afl two-cr-bonded complexes. The questions posed are as follows (a) Do dissociative forms of olefins also exist (b) are any of these forms reactive enough to be an intermediate of hydrogenation/dehydrogenation reactions ... 

The 1,3-butadiene ligand rivals 1,5-COD and arenes in its utility in metal atom syntheses. Within the main group elements, hydrolysis of metal vapour-butadiene condensates indicate that cr-bonded complexes are generally produced (110, 116) ... 

Fig. 18. Interaction of ethene with a zeolite proton, (a) shows the j7-bonded complex, (b) the transition state, and (c) the cr-bonded complex (260).

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... 

G. J. Kubas, Metal Dihydrogen and cr-bond Complexes , Kluwer Academic/Plenum Publishers, New York, 2001. 

Another catalytic cycle can be drawn. The first step, oxidative addition of Pd(0) to Bn-OR, is the same as before. The Bn-Pd(II)-OR complex might then form a cr-bond complex with H2, with the H-H cr bond acting as a two-electron donor. The H atoms are made electrophilic upon coordination. Intramolecular deprotonation of the cr complex by OR would then give ROH and Bn-Pd(II)-H, and the latter would undergo reductive elimination to complete the catalytic cycle. 

Under typical millimolar concentrations, only a few percent of the [Cr(CO)3Cp]2 complex dissociates to radicals at room temperature according to Equation 10.25. For [Cr(CO)3Cp ]2underthe sameconditions, only afewpercentremains as Cr-Crdimer— the complex is almost totally dissociated to radicals. For thepentaphenyl system, even in the solid state there is no Cr-Cr bond complex, only Cr(CO)3C5Ph5 exists. 

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