Bite angle of chelate ligands

Bite angle of chelate ligand. cExocyclic SnCjpS00(Me). 

X-ray crystal structure determinations of compounds 194, 195 and 196 (Figure 95) revealed that these compounds exist in the solid state as discrete monomers. In 194, the zinc atom is trigonal planar coordinated as a result of the Af,Af-chelate-bonding [Zn—N 2.007(1) and 1.995(1) A]. The N—Zn—N bond angle is rather acute [73.83(6)°], but that is a logical consequence of the small bite angle of the ligand. 

As shown in structure 231, bite angle is defined as the preferred chelation angle determined only by ligand backbone constraints. In other words, bite angle is assumed to be solely based on steric factors, and any electronic preference imposed by the metal center is ignored. The natural bite angles of the ligands dppe and BISBI are about 85° and 113°, respectively. 

Various mixed tridentate ligands with P,N,0/S/N donor sets have been explored in Ni11 chemistry. For example, condensation of 2-(diphenylphosphino)aniline with substituted (5-chloro-, 5-nitro, 5-bromo-, 5-methoxy-, and 3-methoxy-) salicylaldehydes yields (253).697 The deprotonated ligand coordinates through its P,N,0 donor set in a square planar geometry with some distortion, which is probably due to the bulk of the phosphine group and to the bite angle of the P,N chelate. 

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