Olefin Cyclopropanation by Radical Carbene Transfer Reactions Promoted by Cobalt(II)/Porphyrinates: Active‐Metal‐Template Synthesis of [2]Rotaxanes

Abstract

A Co /porphyrinate-based macrocycle in the presence of a 3,5-diphenylpyridine axial ligand functions as an endotopic ligand to direct the assembly of [2]rotaxanes from diazo and styrene half-threads, by radical-carbene-transfer reactions, in excellent 95 % yield. The method reported herein applies the active-metal-template strategy to include radical-type activation of ligands by the metal-template ion during the organometallic process which ultimately yields the mechanical bond. A careful quantitative analysis of the product distribution afforded from the rotaxane self-assembly reaction shows that the Co /porphyrinate subunit is still active after formation of the mechanical bond and, upon coordination of an additional diazo half-thread derivative, promotes a novel intercomponent C-H insertion reaction to yield a new rotaxane-like species. This unexpected intercomponent C-H insertion illustrates the distinct reactivity brought to the Co /porphyrinate catalyst by the mechanical bond.

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 .…”

“…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.…”

Olefin Cyclopropanation by Radical Carbene Transfer Reactions Promoted by Cobalt(II)/Porphyrinates: Active‐Metal‐Template Synthesis of [2]Rotaxanes

“…Proposed mechanism for the active-metal-template synthesis of rotaxanes using the radical-carbene transfer reaction to olefins promoted by Co II /porphyrinates. [11] Table 1: Experiments to determine the optimal reaction conditionsf or formation of 9 using the radical-carbene-transfer cyclopropanation reaction as ametal-active-template methodology. Crystal structure of the macrocycle 1/DMSO.…”

“…Ellipsoids are drawn at 50 %p robability levels. [11] Table 1: Experiments to determine the optimal reaction conditionsf or formation of 9 using the radical-carbene-transfer cyclopropanation reaction as ametal-active-template methodology. [a] Entry…”