Apical substituents ligands

Katsuki et al. have reported that the CoIII(salen) ((98) X = I, Y = t-Bu) bearing an apical halide ligand shows high trara-selectivity in the cyclopropanation of styrene and its derivatives, albeit with moderate enantioselectivity (Scheme 71).267 The enantioselectivity is influenced, however, by the natures of the apical ligand and the 5,5 -substituents, and high enantio- and traMs-selectivity has been realized by their appropriate tuning ((98) X = Br, Y = OMe).268 It is noteworthy that the CoIII(salen) complex bearing substituents at C3 and C3 shows no catalytic activity. 

Semiclathrochelate N3S3- and Nc-complexes with one of the tetrapodal units as apical substituent were prepared by the interaction of cobalt(III) ion with potentially octadentate tetrapodal N4S4- and Ns-ligands (Scheme 62). Cyclization of these complexes... 

The E values depend on the electron density on the encapsulated metal ion and on donor atoms, and as a result, correlate a sum of the inductive constants of apical substituents. The slope of three linear correlation regressions for Ns-sarcophaginates (including a sepulchrate) and for sarta.cn and capten (higher potentials) and absar (lower potentials) ligand complexes is the same hence, in each group the E values are governed by an inductive effect. 

Treatment of the all lidenes M(=CHBu )(OBu )2(NAr) (M = Mo, W Ar = C6H3Pr 2 2,6) with the peifluroalkyl aldehyde C5F5CHO results in the 2>oxametallacyclobutane complexes Mo(CHBu CH(C sX) (OBu )2(NAr). These exist as two isomers, the major molybdenum isomer is square pyramidal with an apical imido ligand. The stability these species is a function of the ring substituents. 2... 

In addition to the foregoing explanation of retention of configuration, two possibilities may be taken into account. The first is that apical entry is followed by basal departure, and vice versa. Second, the sulfurane intermediate formed may have the structure of a square basal pyramid. In both cases nucleophilic substitution reactions may occur with retention of configuration without ligand reorganization. It appears that the apicophilicity of substituents in sulfurane species... 

The coordination geometry of the complexes with the ligands with an NP2 donor set (ligands XXXI, XXXII) is strictly dependent on the nature of the substituents on the nitrogen donor. The (NiX2(R-bda)] complexes are low-spin five-coordinate when R = H or Me and square planar when R = Cy. All of the complexes become square planar, [NiX(R-bda)]+, in solution.1365 The structure of the complex [NiBr2(H-bda)] (165) is typical of low-spin square pyramidal nickel(II) complexes, with the apical Ni—Br distance longer than the basal one and the nickel atom substantially in the basal plane.1299... 

The deformations induced by steric interactions of the ethylene bridge substituents with apical ligands can produce distortions from a square pyramidal geometry towards a trigonal bipyramid. 

---