Macrocycles planes

The fe-Ir1 complex (344) of the selena sapphyrin ligand has been synthesized and characterized by X-ray diffraction studies.551 The pairs of bound N atoms in (344) are bent towards the Ir1 centers, and the respective pyrrole rings are twisted from the macrocyclic plane. The coordination geometry around the Ir is close to square-planar, and the Ir Ir distance is 4.233 A. The Se center is not involved in bonding to the Ir centers. 

The crystal structure for 179b was determined which showed a planar geometry for the silver center and the carbaporphyrin ligand. A small tilt angle of 5.09° for the indene unit relative to the mean macrocyclic plane was determined, and the Ag-C bond length was 2.015(4) A. Extension of the work to the benzocarba-, benzi-, oxybenzi-,... 

The above results were later complemented by the observation that the monopro-tonated form of sapphyrin is also capable of chelating chloride anion in the solid state.Here, in analogy to what was seen in the case of the bishydrochloride salt, the single chloride counteranion was found to lie ca. 1.72 A above the macrocycle plane, being held there by four hydrogen bonds (Figure 3). 

A most interesting example of the corrinoid structure is corrole, a macrocycle where an 18 electron aromatic it system analogous to that of a porphyrin is maintained. Corrole has been shown to be a versatile ligand capable of coordinating transition and main group metals without significant distortion of the macrocycle plane. 

The distortion is the result of the strain imposed on the whole molecule by the geometric requirements of the corrole structure. It is not, however, very significant the rhodium atom is displaced by only 0.26 A from the plane of the four coordinating nitrogen atoms, a value much smaller than that observed in the structure of the P-unsubstituted complex Co(Corrole)PPh3 shown in Fig. 12 where the cobalt atom is displaced by 0.38 A from the macrocycle plane [32]. In both compounds the four coordinating nitrogen atoms are strictly coplanar. 

Fig. 16. The tin atom is pulled out of the macrocycle plane such geometry introduces a distortion in the macrocycle that can now be planar or ruffled and the disruption of the classical N-S symmetry of corrole is also reflected by the NMR spectrum of the complex (see Sect. 4.5).

The prime indicates the meso-phenyl protons located on the same side of the axial ligand with respect to the macrocycle plane. d Deuteriated benzene solutions. 

Fig. 4. Structure and reference frame for the dimethoxy tetraethyl dimethyl trivalent lanthanide texaphyrin. The a angle measures the out-ofplane location of / (Ill) with respect to the mean macrocyclic plane (adapted from Lisowski et al. (1995a)).

Single crystal X-ray diffraction studies of each of the above iron(III) and iron(IV) corrole complexes (2.175-2.178) showed that in each case the corrole macrocycles are nearly planar. In the case of both the iron(III) corrole 2.178 (Figure 2.1.11) and the a-phenyl iron(IV) corrole 2.177, the iron atom was found to lie 0.27 A above the mean plane of the macrocycle. The structures of the iron(IV) corrole species 2,175 (Figure 2.1.12) and 2.176, on the other hand, revealed the iron atom as being c. 0.40 A above the mean macrocycle plane. 

Under more forcing conditions, the, iV -dialkyl corroles 2.243 and 2.244 were prepared in high yield from the starting corrole 2.39. The N-substituents were concluded to be in a trans disposition with respect to one another (i.e., one is found above the mean macrocyclic plane and the other below), thereby making the molecule achiral. This was determined by partial resolving of the o-camphorsulphonate derivative of corrole 2.244. ... 

A single crystal X-ray diffraction analysis has been carried out on the bromo-substituted isocorrole derivative 2.269. This analysis revealed a somewhat non-planar macrocyclic structure (Figure 2.2.2). The non-planarity in 2.269 was presumed to arise primarily as the result of NH steric interactions present within the core of the macrocycle. As a consequence of these interactions, the two pyrroles of the dipyrrylmethene-like end of the macrocycle each twist by 23° in opposite directions out of the mean macrocyclic plane. This out-of-plane rotation of two pyrrole rings is in contrast to that observed in a typical corrole structure. In this latter case, three of the pyrrole rings are nearly coplanar, and one of the pyrroles is rotated out of plane but only by 8-10°... 

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