Coordination modes

S. Kawaguchi, Uariety in Coordination Modes of Eigands in Metal Complexes, Spriager-Vedag, Berlin, 1988. 

The solvated sulfenamides [Li2( BuNSC6H4Me-4)2(THF)n] (n = 2,4) have dimeric structures with a central Li2N2 ring. The coordination mode is determined by the extent of solvation of the Li" ions monosolvation allows for rj -N,S coordination whereas disolvation restricts the coordination mode to // -M Variable temperature NMR studies indicated that a dynamic exchange between these two structural types occurs in THF solution (Scheme 10.10). The dihapto coordination mode is observed exclusively in transition-metal complexes and the... 

Scheme 10.10 and if Coordination modes for the [RSNR ] anion in solvated lithium complexes... 

The combination of hard (A) and soft (5) coordination in the 1,5-P2N4S2 ring system leads to a diversity of coordination modes in complexes with transition metals (Lig. 13.1). In some cases these complexes may be prepared by the reaction of the dianion [Ph4P2N4S2] with a metal halide complex, but these reactions frequently result in redox to regenerate 13.3 (L = S, R = Ph). A more versatile approach is the oxidative addition of the neutral ligand 13.3 (L = S) to the metal centre. 

Fig. 13.1 Coordination modes in metal complexes of [Pli4P2N4S2]. The uncoordinated sulfur atom in (c) and (d) acts as a bridge to give dimeric stmetures...

Figure 6.14 Examples of the various coordination modes of BH4 (continued on facing page).

Many complexes have more than one coordination mode of BH4 featured in their structure, e.g. [U ()9 -BH4)()9 -BH4)2(dmpe)2]. Likewise, whereas [M(BH4)4] are monomeric 12-coordinate complexes for M = Zr, Hf, Np, Pu, they are polymeric for M = Th, Pa, U the coordination number rises to 14 and each metal centre is coordinated by two r) -BH4 and four bridging r) -BH4 groups. It is clear that among the factors which determine the mode adopted are the size of the metal atom and the steric requirements of the co-ligands. Many of the complexes... 

While it remains true that tetrahedral and octahedral coordination modes are the predominant stereochemistries adopted by the group 13 metals, nevertheless increasing diversity is being achieved by carefully selecting appropriate electronic and geometric features to enhance the stabilization of unusual stereochemistries. Some representative examples follow. 

Fig. 8.22) features a unique tris(bidentate) sex-tuply bridging carbonato ligand as well as three bidentate piT-carbonato ligands. Other chelating and bridging coordination modes are also known.< 2 >... 

Stable thiocarbonyl complexes containing the elusive CS ligand are also now well established and known coordination modes, which include terminal, bridging and polyhaplo, are as shown at the top of the next column/ ... 

The molecule has an almost linear N3 group and an angle C-N-N of 112.4° (Fig. II.4a).( ) The (linear) azide ion, N3", is isoelectronic with N2O, CO2, OCN", etc. and forms numerous coordination complexes by standard ligand replacement reactions. Various coordination modes have been established, including end-on bridging... 

In this new type of coordination mode d(O-O) is long (147 pm) and the weakness of the 0-0 linkage is also shown by the very low value of 851 cm for v(O-O), both values being more characteristic of peroxo than of superoxo complexes/ ... 

Figure 17.21 Coordination modes of CIO4 as determined by X-ray crystallography.

Figure 19.33 Some further coordinating modes of CgHs-...

Cp(CO)2Re(THF) forms the complex 105 upon reaction with thiophene (89JA8753, 910M2436). Similar species are known for 2- and 3-methyl-, 2,5-dimethyl, and tetramethylthiophene (91IC1417). Thiophene in 105 is S-coordi-nated, and the sulfur atom is pyramidal. Treatment of 105 with Fc2(CO)9 produces 106, where the thiophene ligand is bridge-coordinated via the sulfur atom to rhenium and four carbon atoms of the dienic system with iron (the coordination mode). The pyramidal nature of the sulfur atom is preserved. The -coordination of thiophene separates the dienic and sulfur counterparts of the ligand and decreases the TT-electron delocalization, which leads to the enhanced basicity of the sulfur atom. 

R" = R = Me) (890M2739), in the solid state slowly rearranges into a species with amixed coordination mode, 205 (92JA1732). Solutions of 205 on interacting with air give the S-oxide, [Cp Rh(Ti -C4Mc4SO)] (90JA2432). 

The switch in coordination mode was observed on thermolysis of the S-coordi-nated species 235 to give 236 (940M721). 

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