Side-On Bonded Complexes

When laser-ablated Ni atoms were reacted with CS2 during cocondensation in excess argon, the C-bonded Ni( /-CS2) and side-on bonded Ni(//2-CS)S complexes were formed on annealing, whereas the inserted SNiCS was formed on photolysis. All species were characterized by IR spectroscopy and DFT calculations.2466 The reaction of low-valent [Ni(CO)J (x=2, 3) with CS2 has been studied by FT-ICR spectroscopy.2467... 

The crystal structure of the dioxygen complex Tp V(0)(02)(L) has been determined, and revealed a side-on bonded O2 ligand. Based on the O - O distance of 1.379(6) A and vo-o of 960 cm it was formulated as a V(V) peroxo complex, even though these values are on the borderline between the peroxo and superoxo designations. The mechanism of this reaction is curious. Reaction with 02 showed incorporation of solely in the O2 ligand and not in the 0x0 groups. It appears that the O2 binding step must be preceded by a disproportionation (2 V(IV) V(III) + V(V)) followed by reaction of V(III) with O2. 

Finally, a well-characterized 02-insertion transforms Tp Cr(02)Ph into the paramagnetic 0x0 alkoxide Tp Cr(0)0Ph, see Scheme 12 [4]. This reaction proceeds below room temperature, and the starting material has only been characterized by in-situ IR spectroscopy. However, analogous O2 complexes were isolated and characterized by X-ray crystallography, so there can be little doubt about its assignment as a side-on bonded Cr(IH) superoxo complex. 

The transition state leading to the dissociative complex of surface methoxy and water is shown in Fig. 13, as are the final adsorbed products. The transition state is product-like, indicating that the reaction barrier appears to be dominated by the breaking of the methanol C-O bond. The overall thermodynamics of dehydration were predicted to be between 2 kJ/mol endothermic and 5 kJ/mol exothermic, depending on the precise method and cluster model used. With respect to the side-on physisorbed complex, the activation energy was calculated to be 185 kJ/mol. 

Unlike Au+(02), which was green,224 both Ag+(02) and Ag+(04) were colourless, although weak absorptions at 275 and 290 nm respectively were observed in their UV spectra. Ag+(02) was formulated as a side-on -bonded superoxo molecular species and this was supported by IR spectra. Ag+(C>4) was described as a tetraoxygen species rather than a bis(dioxygen) complex. Neither copper nor gold gave a secondary reaction to produce a related M+(04-) complex. 

Examples of side on bonding, i.e. involvement of the a-electrons, have not been established. This type of metal-ligand bonding is often encountered in metal complexes of the organic pseudohalides such as RNCS. 

For example, the C02 complex of iron(O), Fe(C02)(depe)2, which has a trigonal bipyramidal geometry with a side-on bonded C02, reacts with electrophiles such... 

Several dioxygen complexes of chromium featuring snperoxide (02 ) bound to Cr can be made by exposure of Cr precursors to 02. The first structurally characterized example of such an addnct that is, [TpiBu.Mecr(pz H)(02 )] -interestingly features the rare side-on bonding mode of the superoxide hgand. ... 

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