Core electrons planar complexes

Recently we have seen identical chemistry in the carbahemiporphyrazines. As can be seen in Figure 4, we have observed this chemistry with the metals manganese, iron, cobalt, copper and silver with the dicarbahemiporphyrazine macrocycle (30, 33). With the exception of copper, which will be described below, both internal C-H bonds are retained upon metalation. The lack of C-H activation in these complexes distorts the macrocycle in these compounds from planarity. Since there are two intact C-H bonds at the core, the planar distortion is much greater than that seen in A -confiised porphyrin. The C-M distances are longer than those seen in iV-confused porphyrins (> 2.4 A), and, based on our H NMR measurement of the Ag(I) complex, the electronic structure of the C-H bond is not greatly perturbed when compared to the free base macrocycle (6.77 ppm in the silver adduct versus 6.91 ppm). 

Electronic stmcture calculations reveal that the actual EEG in linear Au(l) and square-planar Au(lll) complexes is not merely a matter of 5d occupation. Instead, the EEG is markedly determined by AO populations, including Au core 5p as well as valence 6p orbitals and further by the charge in the overlap area (AOAuAOug) and on the ligands (Table 7.14). 

The central Ir-P4 core assumes a coordination intermediate between planar and tetrahedral. The cation undergoes two subsequent, chemically reversible, one-electron reductions (E+j0 = -1.56 V = -1.76V (vs. Ag/Ag+)). The corresponding lr(0) and Ir(-I) complexes... 

The unique TEE framework facilitates -conjugation with pendant aromatic substituents by allowing coplanar orientation throughout the molecular core, as was first witnessed in the X-ray crystal structure of tetrakis(phenylethynyl)ethene 1 determined by Hopf and co-workers [9]. In contrast, coplanarity is prevented by steric interactions in molecules such as cis-stilbenes or tetraphenylethene 2 [10] (Figure 2). The planarity makes it possible for 1 to form highly ordered 1 2 stoichiometric donor-acceptor -complexes in the solid state with electron-deficient molecules such as 2,4,7-trinitrofluoren-9-one and (2,4,7-trinitrofluoren-9-ylidene)malonitrile [11]. In solution, relatively weak 1 1 complexes with each of these two acceptors are formed, with association constants of 7.9 m 1 and 31.5 m 1, respectively, at 300 K in CDCl3. 

There are a number of Ni111 complexes with macrocyclic nitrogen ligands. They are usually made by one-electron oxidation of the Ni11 species the ring size and size of cavity in the macrocycles has an influence on the Nin/Niin redox potential. Some Ni111 macrocycles can also be oxidized to NiIv. A structurally characterized example of a Nim macrocycle is the deep purple complex (17-G-XV) which contains a square-planar NiN4 core.12... 

---