Single-Boron Complexes of N-Confused and N-Fused Porphyrins

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.