Chelate complexes with larger-ring

Rhodium Complexes with Larger-ring Chelates of Chiral Biphosphines... 

Formation of metal-organic chelate complexes results in stronger complexation (i.e., larger values) compared to interaction with monodentate ligands (Chapter 3). The common types of bidentate ligands are presented in Table 4.9 the chemistry of these complexes has been extensively discussed in the literature [14,47], Chapter 3 presents the most important factors in the formation of such complexes (1) the type of binding atom (2) the chelate ring size (or bite ) ... 

In Table 42, in complexes with SBs (97)-(99), the / values of compounds with n = 2 (n in R = (CH2) ) are larger than with n = 3. This suggests that the antiferromagnetic exchange interaction is stronger with n = 2, and this has been attributed to the difference in the chelate ring (five- or six-membered).775 For n-2, the J values also depend appreciably on the nature and position of the Hsal substituent for n - 3, they are relatively insensitive to ring substituents.358... 

Werner based some of his conclusions on the supposition that a chelate ring could span only the cis positions in a complex. While this is valid for the small rings with which he was familiar, it does not necessarily hold for larger rings. Several investigators have prepared compounds in which a single bidentate ligand occupies trans positions in a planar complex. 

The two most important structines for [M(bidentate)s] are shown in Figure 16, drawn as idealized bicapped square antiprisms. Isomer I is possible at all values of the normalized bite whereas isomer II is expected only for larger chelate rings. A number of lanthanoid and actinoid complexes with four-membered nitrate or carbonate rings, [M (N03)5] and [M (C03)5] , have structure I. The only monomeric molecule in which structure II is observed is [Ba(MeCONHCOMe)5](C104)2 with six-membered chelate rings. 

Transition metal complexes of the larger polyaza macrocyclic ligands have been less extensively studied than for the smaller ring systems. For the pentaaza macrocycles, [ISJaneNs with ethylene bridges appears to form the most stable complexes with most metal ions. Structural data for a variety of pentaaza macrocyclic complexes have been reviewed. The N-H bonds as well as the different sized chelate rings must be considered in calculating the... 

Bromination of Pt(II) complexes with phosphorus or arsenic ligands containing a coordinated or pendant double bond results in metallation by addition of Br2 across the Pt—C=C unit . In the bromination of a series of 2-alkenylpyridine complexes metallation takes place when a small chelate ring may be formed where larger rings would be involved, however, addition of Bt2 across the double bond occurs ... 

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