Control over the Redox Cooperative Mechanism of Radical Carbene Transfer Reactions for the Efficient Active‐Metal‐Template Synthesis of [2]Rotaxanes

Abstract

A 5,15‐bis(1,1′‐biphenyl)porphyrin‐based molecular clip covalently connected to a ditopic aliphatic ester loop moiety yields a semi‐rigid macrocycle with a well‐defined cavity. The resulting macrocycle fits the structural requirements for the preparation of porphyrinates capable of promoting formation of C−C bonds. To demonstrate the usefulness of porphyrin‐based macrocycles, an active‐metal‐template synthesis of rotaxanes through a redox non‐innocent carbene transfer reaction is described. Coordination of CoII ions into the porphyrin subunit followed by addition of appropriate monodentate nitrogen‐based additives to function as axial ligands enables the radical carbene transfer reactions to styrene derivatives to occur exclusively through the cavity of the macrocycle to afford cyclopropane‐linked rotaxanes in excellent 95 % yield. Investigation of the product distribution afforded from the rotaxane assembly reaction reveals how the redox cooperative action between the carbene species and the CoII ions can be manipulated to gain control over the radical‐type mechanism to favor the productive rotaxane forming process.

Ru(II)Porphyrinate-Based Molecular Nanoreactor with Unusual Coordinative Properties and Extraordinary Chemical Selectivity in N–H Bond Carbene Insertion Reactions

“…The crystal structure (CDCC ID 1883084) of 7 ( Figure 2) reveals a virtually flat porphyrin core which together with the aromatic backbone creates a central cavity with dimensions of 8.49 and 7.91 Å (centroid-to-centroid of the phenyl spacers and porphyrin centroid-to-midpoint of C26-C26 i bond on the phenanthrene moiety, respectively, with symmetry code: i = 1/2-x, y, z; see Supplementary Figure S1 for complete atom numbering). Such cavity dimensions in 7 are rather smaller than those observed for a similar but semi-rigid porphyrin-based macrocycle reported in our previous work 24,25 (cavity dimensions 10.30 and 8.40 Å). The angle between the porphyrin and the molecular aromatic loop mean planes is 62.12 o , which is smaller than the expected 90 o .…”

“…35 Congruently, 13 C NMR and FTIR analyses (Supplementary Figures S4 and S5, respectively) show one single resonance at  = 180.1 ppm and one stretching band (COstretch = 1926 cm -1 ) for the carbonyl axial ligand in the isolated product, thus confirming formation of one single complex. Such coordinative properties are not ubiquitous as performing the metalation reaction under the same conditions used for 7 but with our previously reported 24,25 semi-rigid and larger macrocycle as ligand yields the two expected isomers as revealed by 1 H NMR spectroscopy (for spectrum and chemical structures see Supplementary Figure S6). Therefore, the structural features of 7, which yield a hollow receptor with a relatively small central cavity, is most likely the reason for such selectivity in the metalation reaction.…”

“…The rich coordination chemistry of porphyrinates [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] is useful in the design of macrocyclic receptors, in which the porphyrinate subunits are positioned on the top of molecular capsules to create hollow structures with well-defined cavities. [19][20][21][22][23][24][25][26][27][28] In such molecular architectures, one of the axial positions of the metallic center is shielded from the environment, while the other has unencumbered reactivity. This asymmetry between the two axial coordination sites of the porphyrinate subunit can be explored to introduce a steric bias in the binding modes of the receptor.…”

“…With such configuration of the ligands around the metal center, the internal coordination site of the porphyrinate-based receptor can bind nonbulky substrates to efficiently and selectively promote their reactions inside the central cavity. [23][24][25][26][27][28][29][30][31][32] Such versatile strategy has been explored in the active-metal template synthesis of interlocked molecules, [24][25][26][27] asymmetric catalysis 28,29 and biomimetics. [30][31][32] However, in those applications, the porphyrinate-based macrocycles has virtually the same reactivity as their acyclic analogues.…”

Ru(II)Porphyrinate-based molecular nanoreactor for carbene insertion reactions and quantitative formation of rotaxanes by active-metal-template syntheses

“…he rich coordination chemistry of porphyrinates [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] is useful in the design of macrocyclic receptors, in which the porphyrinate subunits are positioned on the top of molecular capsules to create hollow structures with well-defined cavities [19][20][21][22][23][24][25][26][27][28] . In such molecular architectures, one of the axial positions of the metallic center is shielded from the environment, while the other has unencumbered reactivity.…”