Single boron complexes of N-confused and N-fused porphyrins

Latos-Grażyński, L.; Młodzianowska, A.; Szterenberg, L.; Stępień, M.
Inorg. Chem. 2007, 46, 6950–6957 | view at publisher's site

Boron(III) has been inserted into N-confused porphyrin, (NCPH)H2 (1), and N-fused porphyrin, (NFP)H (2). The reaction of dichlorophenylborane and 1 yields σ-phenylboron N-confused porphyrin (4). The boron atom is bound by two pyrrolic nitrogen atoms and the σ-phenyl ligand. The N-confused pyrrole ring is not involved in the direct coordination because the C(21)−H fragment remains intact. A reaction between PhBCl2 and N-fused porphyrin produces σ-phenylboron N-fused porphyrin (3+). 4 converts quantitatively into 3+ under protonation. In σ-phenylboron N-fused porphyrin [(NFP)BPh]Cl, the coordinating environment of boron(III) resembles a distorted trigonal pyramid, with the nitrogen atoms occupying equatorial positions and with the phenyl ligand lying at the unique apex. Boron(III) is displaced by 0.547(4) Å from the N3 plane. The B−N distances are as follows: B−N(22), 1.559(4) Å; B−N(23), 1.552(4) Å; B−N(24), 1.568(4) Å; B−CipsoPh, 1.621(4) Å. 3+ can be classified as a boronium cation considering a filled octet and a complete coordination sphere. 3+ is susceptible to alkoxylation at the inner C(9) carbon atom, yielding 5-OR. The addition of acid results in protonation of the alkoxy group and elimination of alcohol, restoring the original 3+. Density functional theory has been applied to model the molecular and electronic structure of 4, 3+, and syn and anti isomers of methoxy adducts 5-OMe.