Bi- and Polydentates

Bi- and poly-thioethers with aliphatic backbones are produced by attack of RS on the appropriate haloalkane. This is the method of choice for RS(CH2)raSR (R = Me or Ph),26 MeC(CH2SR)3,27,28 MeS(CH2)raS(CH2)raSMe (n = 2 or 3) and MeS(CH2)raS(CH2) S(CH2) SMe.28,29 [Caution Some of these syntheses involve sulfur mustard derivatives as intermediates - these are very powerful vesicants and should be handled only with extreme care.] The other tridentates RS(CH2)3S(CH2)3SR (R = Et, Pr or Ph) may be obtained from nucleophilic attack by RS on the ditosylate TsO(CH2)3S(CH2)3OTs.30 Tetra-dentate thioethers involving o-phenylene interdonor linkages are also known.31 More recently the preparation and coordination chemistry of the silicon-apex derivative MeSi(CH2SMe)3 has been described.32 

The diselenoethers RSe(CH2) SeR (n = 1-3, 6, 12, etc) are obtained in good yield by reaction of RSeLi with the appropriate dihaloalkane in thf solution,37 

The tripodal MeC(CH2SeR)3 (R = Me or Ph) are obtained readily from RSeLi with MeC(CH2Br)3 in thf.37 The other tri- and tetra-dentates MeSe(CH2)2Se(CH2)2SeMe,44 MeSe(CH2)3Se(CH2)3SeMe37 and MeSe(CH2)2. Se(CH2)3Se(CH2)2SeMe45 require the Se to be introduced stepwise. 

In general the alkyl-substituted ditelluroethers are yellow, extremely malodorous, air-sensitive oils, whereas those with phenyl substituents are low-melting solids or oils and are rather less susceptible to oxidation. 

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There has been intense study of the complexes of bi- and polydentate ammines since the mid-1970s, driven by interest in the catalytic photodecomposition of water using the excited states of Ru(bipy)g+ (n = 2,3) and related systems (Figure 1.18) [5, 7, 8, 71]. 

Bi- and polydentate ligands also form Ti complexes with a variety of stoichiometries. For example, [Ti(L)3] + complexes are produced by the ligands en and pn, " whereas bpy and phen give [TiCl2(L)2][TiCLi(L)], " [Til2(phen)2]I," and [Til2(bpy)2][Til4(bpy)]." ... 

Bi- and polydentate ligands containing arsenic in combination with other Group 15 or 16 donors have also been known for many years.6,7 Some new examples are shown in Figure 1. 

Substitution of various chelating bi- and polydentate amines, for example, en, 1,3-diaminopropane, dien, trien, and so on, in nonaqueous media yields an extensive series of octahedral amine complexes, which range in color from blue to purple. Their effective magnetic moments (4.7-4.9/xb) and electronic spectra are best explained assuming tetragonally distorted octahedral geometries. 

A more negative AG° will result in a larger value of K. Therefore, the second equation will have a larger AT because it has a larger AS°, and hence a more negative AG°. This exercise shows the effect of bi- and polydentate ligands on the position of equilibrium. 

Most of the bi- and polydentate phosphines resolved to date by means of... 

Table 2.4 Bi- and polydentate phosphines resolved by means of chiral palladacycles.

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