Increase of Direct C–C Coupling Reaction Yield by Identifying Structural and Electronic Properties of High-Spin Iron Tetra-azamacrocyclic Complexes

Abstract

Macrocyclic ligands have been explored extensively as scaffolds for transition metal catalysts for oxygen and hydrogen atom transfer reactions. C-C reactions facilitated using earth abundant metals bound to macrocyclic ligands have not been well-understood but could be a green alternative to replacing the current expensive and toxic precious metal systems most commonly used for these processes. Therefore, the yields from direct Suzuki-Miyaura C-C coupling of phenylboronic acid and pyrrole to produce 2-phenylpyrrole facilitated by eight high-spin iron complexes ([FeL1(Cl)], [FeL4(Cl)], [FeL5(Cl)], [FeL6(Cl)], [FeL7(Cl)], [FeL8(Cl)], [FeL9(Cl)], and [FeL10(Cl)]) were compared to identify the effect of structural and electronic properties on catalytic efficiency. Specifically, catalyst complexes were compared to evaluate the effect of five properties on catalyst reaction yields: (1) the coordination requirements of the catalyst, (2) redox half-potential of each complex, (3) topological constraint/rigidity, (4) N atom modification(s) increasing oxidative stability of the complex, and (5) geometric parameters. The need for two labile cis-coordination sites was confirmed based on a 42% decrease in catalytic reaction yield observed when complexes containing pentadentate ligands were used in place of complexes with tetradentate ligands. A strong correlation between iron(III/II) redox potential and catalytic reaction yields was also observed, with [FeL6(Cl)] providing the highest yield (81%, -405 mV). A Lorentzian fitting of redox potential versus yields predicts that these catalysts can undergo more fine-tuning to further increase yields. Interestingly, the remaining properties explored did not show a direct, strong relationship to catalytic reaction yields. Altogether, these results show that modifications to the ligand scaffold using fundamental concepts of inorganic coordination chemistry can be used to control the catalytic activity of macrocyclic iron complexes by controlling redox chemistry of the iron center. Furthermore, the data provide direction for the design of improved catalysts for this reaction and strategies to understand the impact of a ligand scaffold on catalytic activity of other reactions.

Functionalized pyridine in pyclen-based iron(iii) complexes: evaluation of fundamental properties

“…[11][12][13][14][15][16] As a result of these modications, pyridinophanes have been successfully used as mimics of biological systems, 17 scaffolds for magnetic resonance imaging, 18 and ligands for catalysis. 12,[19][20][21] The impact of the functionalization of the pyridine moiety, which has not been evaluated in pyridinophanes to date, adds a new method of tuning the reactivity of the ligand and the redox activity of a metal chelated to the pyridinophane. Such modications are anticipated to control the characteristics and reactivity of daughter metal complexes.…”

Stabilisation of Exotic Tribromide (Br3−) Anions via Supramolecular Interaction with a Tosylated Macrocyclic Pyridinophane. A Serendipitous Case

“…Pyridinophane 3,6,9,15-tetraazabicyclo[9.3.1]pentadeca-1(15),11,13-triene (L, Figure 1 ) is a member of this family that was first synthesised in 1981 [ 5 ]. It was later in the spotlight for its ability to form metal complexes [ 6 , 7 , 8 ], but its wider success was achieved thanks to its utilisation as a scaffold for the preparation of new materials that have proven effective in a variety of applications. Indeed, L derivatives decorated with different hanging functionalities have been studied for several biomedical (MRI contrast agents [ 9 , 10 , 11 , 12 ], antiproliferative treatments [ 13 , 14 , 15 , 16 ], radiotherapy [ 17 , 18 ], enzyme mimicking [ 19 , 20 ] and antioxidant activity [ 21 , 22 , 23 ]), chemosensing [ 24 , 25 , 26 , 27 ] and catalytic [ 28 , 29 , 30 , 31 , 32 , 33 ] applications.…”

Sensing Zn2+ in Aqueous Solution with a Fluorescent Scorpiand Macrocyclic Ligand Decorated with an Anthracene Bearing Tail

“…Scorpiand type aza-macrocyclic ligands, that is aza-macrocyclic ligands with coordinating tails [1], and their metal complexes have attracted considerable interest thanks to the numerous uses they have been tested for, including but not limited to various biomedical applications [2,3] (MRI contrast agents [4,5], radioisotopes complexation and radiolabelling [6][7][8][9], radiotherapy [10][11][12][13][14], chelation therapy [15][16][17], antiproliferative treatments [18][19][20][21], enzyme mimicking [22][23][24][25][26][27][28][29]), catalysis [30][31][32][33][34][35][36] and chemosensing [37][38][39][40][41][42][43].…”