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

Boron(III) has been inserted into N-confused porphyrin, (NCPM)H-2 (1), and N-fused porphyrin, (NFP)H (2). The reaction of dichlorophenylborane and 1 yields sigma-phenylboron N-confused porphyrin (4). The boron atom is bound by two pyrrolic nitrogen atoms and the sigma-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 sigma-phenylboron N-fused porphyrin (3(+)). 4 converts quantitatively into 3+ under protonation. In sigma-phenylboron Mused 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)angstrom from the N-3 plane. The B-N distances are as follows: B-N(22), 1.559(4)angstrom; B-N(23), 1.552(4) angstrom; B-N(24), 1.568(4) angstrom; B-C-ipsoPh, 1.621(4) angstrom. 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.