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

Abstract

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 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 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) A from the N3 plane. The B-N distances are as follows: B-N(22), 1.559(4) A; B-N(23), 1.552(4) A; B-N(24), 1.568(4) A; B-C(ipsoPh), 1.621(4) A. 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.

Carbatriphyrin(3.1.1)–A Distinct Coordination Approach of BIII to Generate Organoborane and Weak C−H⋅⋅⋅B Interactions

“…As reflected from the spectral analysis, the B III in 8 is coordinated with the dipyrromethene unit and the remaining two positions are occupied by the σ‐phenyl and the chloride ion. The B−N bond lengths (B−N1 and B−N2) are 1.604(8) and 1.571(8) Å, which are longer than the B−N bond lengths reported earlier . The geometry around the boron center is tetrahedral (Supporting Information Figure S28c) and the boron(III) ion is 1.45(6) Å above the mean macrocyclic plane.…”

“…The disappearance of inner NH (H 20) signal confirms the formation of 8 (Figure b and Supporting Information Figures S20–S22). The spectral analysis reveals that the inner CH (H 19) is shifted 2.20 ppm upfield and resonates at 5.31 ppm, suggesting a weak nonbonding interaction with the boron ion –. The σ‐phenyl protons are merged with biphenyl as well as meso ‐phenyl units, however, one of the σ‐phenyl protons distinctly resonates at 7.90 ppm.…”

Reversible Reduction of Oxatriphyrin(3.1.1)—Adjusting the Coordination Abilities to the Central Ion

“…Noticeably the formed bridges ((N) 2 BB(N) 2 , (N) 2 BOB(N) 2 or (N) 2 B(O) 2 B(N) 2 ) stabilize the final structures 3. A single boron complex has been reported for N‐fused porphyrins, in which the size of the coordination cavity is noticeably reduced 4. In fact the flexibility of N‐confused porphyrin,5 also observed for 21‐telluraporphyrin6 or even pentaphyrin(1.1.1.1.1),7 allows a remarkable adjustment of the macrocycle to the phosphorus cation via a fusion step as seen for 1 , 2 , and 3 , respectively (Scheme ).…”

Figure Eights, Möbius Bands, and More: Conformation and Aromaticity of Porphyrinoids

“…[161] Subsequent research showed that coordination of metallic and nonmetallic elements with small ionic radii is also capable of inducing ring fusion (these complexes can also be made starting directly from the fused ligand). Examples reported to date include 8b-Re(CO) 3 [167] (oxidizable to 8b-ReO 3 [168] , Figure 6), 8f-BPh + Cl À , [169] and 9f-P=O. [142] The phenylboron species, is cationic and easily undergoes nucleophilic addition at position 3, while retaining uninterrupted macrocyclic conjugation.…”