Side-on bonding

The adoption of a planar structure in these adducts, rather than the sterically more favourable tetrahedral one, is in keeping with a platinum(II) oxidation state. The side-on bonding of the 02 molecule is believed to involve two components, as in Zeise s salt (Figure 3.18). 

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 fifth product was detected at high lithium concentrations. Its IR spectrum presented a N=N stretching mode at 1795 cm , characteristic of the Li+ N2 ion pair with side-on bonding of the lithium atom and equivalent nitrogen atoms. However, this species was not observed in solid argon without ethylene having been added to the sample . 

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. 

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... 

The side-on bonding of H2 to the metal involves the transfer of a bonding electrons of H2 to a vacant metal d orbital (or hybrid orbital), together with the transfer of electrons from a tilled metal d orbital into the empty a orbital of H2, as shown in Fig. 11.5.2. This synergistic (mutually assisting) bonding mode is similar to that of CO and ethylene with metal atoms. The n back donation from... 

Figure 15.1.5(f) shows a planar, side-on bonded N2 ligand between two Zr atoms in the compound [Cp"2Zr]2(N2) [Cp" = l,3-(SiMe2)2C5H3], The N-N bond length is 147 pm. Side-on coordination of the dinitrogen ligand appears to be important for its reduction. 

Figure 29. Two-dimensional potential energy diagram for the convesion of /-N2 (vertically adsorbed) to a-N2 (side-on bonded) [246-248] on the Fe(l 11) surface [249],...

Unlike unit II, in the solid state I does not coordinate Li+ ions side-on. The side-on bond lengths for the atoms Li2 and Li3 were determined to be 192 and 188 pm, respectively. The angles at N5 and N6, which bind Li3 side-on, are nearly identical the angles at N1 and N2, which coordinate Li2, deviate by 7°. Thus, Li3 is positioned centrosymmetrically above the N—N bond. 

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