Substitution Five-coordinated complexes

The five-coordinate complexes Ir(CO)(PPh3)2L, where HL = /3-diketone, A-benzoyl-A-phenyl-hydroxylamine, salicylaldehyde, 8-hydroxyquinoline, 2-hydroxybenzophenone, 2-hydroxy-8-methoxybenzophenone, were prepared from [Ir(CO)(PPh3)2Cl].632 The resulting compounds all underwent oxidative addition reactions with Br2. Reaction of [(cod)2IrCl]2 with N-substituted 3-hydroxy-2-methyl-4-pyridine gives the bichelated complex (389). 33... 

Chromium(II) forms the trigonal bipyramidal complex [CrBr(Me6tren)]Br with the tripod ligand tris(2-dimethylaminoethyl)amine (Me6tren) (Section 35.3.4.3), and pyrazolyl-substituted ligands also form five-coordinate complex cations (Section 35.3.3.4.v see also Table 42). 

Closely related to this tetrahedral nickel molecule is the five-coordinate complex shown in Fig. 15. Bis(7V-/3-diethylamine-ethyl-5-chlorosalisyl-aldiminato)nickel(II) differs from the previous system in three main features AMsopropyl groups are replaced by tertiary amines, the phenyl rings are substituted with chlorine atoms para to the oxygen donor atoms, and the coordination is approximately square pyramidal rather than distorted tetrahedral. Crystal... 

Kinetically inert square-planar complexes are found by d8 low-spin ions, particularly Pt2+. Ligand substitution is associative and correlated with the ease of forming a five coordinate transition state (or intermediate). Substitution is much faster with Ni2+ where five-coordinate complexes such as [Ni(CN)5]3- are more stable than for Pt. For a given metal, the rate of substitution is controlled by ... 

When the addition of the base is controlled, that is, when only one equivalent of base is added to one eqnivalent of PFe, typically only the four- and six-coordinate, and essentially none of the five-coordinate, species are detected the five-coordinate complex usually disproportionates into the fonr-and six-coordinate iron(II) porphyrins. Only when L is a hindered ligand, such as a 2-substituted imidazole or pyridine, is Ki sufficiently greater than K2 that the five-coordinate complex is observed in solution. This has relevance for the stabilization of five-coordinate Fe porphyrins in solntion, discussed in Sections 4.2 and 4.3. 

Mononuclear octahedral complexes have been obtained for carbonyl-bound acetic acid, and five-coordinate complexes of sterically hindered phenoxides of the type [V(py)3(C6H3Ph2-2,6)2]. A more hindered phenol gave a four-coordinate complex, [V (C6H3Pr2-2,6)4 Li(thf) 2] in which two pairs of cfr-phenolates were linked by a single Li(thf)+ unit. A binuclear complex of a substituted acetylacetone has the stmcture shown in(l). 

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