The Influence of Peripheral Substituent Modification on P^V, Mn^III, and Mn^V(O) Corrolazines: X-ray Crystallography, Electrochemical and Spectroscopic Properties, and HAT and OAT Reactivities

Abstract

The influence of remote peripheral substitution on the physicochemical properties and reactivity of phosphorus and manganese corrolazine (Cz) complexes was examined. The substitution of p-MeO for p-t-Bu groups on the eight phenyl substituents of the β-carbon atoms of the Cz ring led to changes in UV–vis transitions and redox potentials for each of the complexes. The oxygen atom transfer (OAT) and hydrogen atom transfer (HAT) reactivity of the MnV(O) complexes was also influenced by p-MeO substitution. The OAT reactivity of MnV(O)(MeOP8Cz) (MeOP8Cz = octakis-(p-methoxyphenyl)corrolazinato3−) with triarylphosphine (PAr3) substrates led to second-order rate constants from 10.2(5) to 3.1(2) × 104 M−1 s−1. These rates of OAT are slower than those seen for MnV(O)(TBP8Cz) (TBP8Cz = octakis(p-tert-butylphenyl) corrolazinato3−). A Hammett study involving para-substituted PAr3 substrates reveals a Hammett ρ-value for MnV(O)(MeOP8Cz) that is more negative than that observed for MnV(O)(TBP8Cz), consistent with a less electrophilic Mn center. The HAT reactivity of MnV(O)(MeOP8Cz) with C–H substrates was examined and revealed second-order rate constants from 6.8(5) × 10−5 to 1.70(2) × 10−1 M−1 s−1. The rate constants varied with the C–H bond strength of the substrate. Slightly faster HAT rates with C–H substrates were observed with MnV(O)(MeOP8Cz) compared to MnV(O)(TBP8Cz), indicating that the basicity of the putative [MnIV(O)]− intermediate likely compensates for the more negative redox potential in the driving force for HAT. In addition, the complete, large-scale synthesis of the para-phenyl-substituted porphyrazines RP8PzH2 (R = p-tert-butylphenyl (TB), p-methoxyphenyl (MeO), and p-isopropylphenyl) and corrolazines RP8CzH3 (TBP8CzH3 and MeOP8CzH3) is presented. The crystal structures of the monoprotonated, metal-free corrolazine [(TBP8CzH3)(H)]+[BArF]−, PV(OMe)2-(MeOP8Cz), and MnIII(MeOP8Cz)(MeOH) are presented. This work provides the first insights into the influence of electronic substituent effects on the corrolazine periphery.

Factors Affecting Hydrogen Atom Transfer Reactivity of Metal–Oxo Porphyrinoid Complexes

“…This new ligand was used to generate Mn V (O)-(MeOP 8 Cz). 7 The redox potential of the Mn V /Mn IV couple (−0.57 V vs Fc + /Fc) was shifted in the negative direction by 40 mV, and that of the Cz ring oxidation (+0.45 V vs Fc + /Fc) was shifted by 60 mV in the same direction. The reactivity of Mn V (O)(MeOP 8 Cz) was examined with C–H substrates, and rate constants ranging from 6.8(5) × 10 −5 to 1.70(2) × 10 −1 M −1 s −1 were obtained, similar to what was seen for the p-tBu derivative.…”

Redox Reactions of Water Soluble N-Methylated PV Octa(2-pyridyl)corrolazine with Sodium Dithionite and Cobalamins

“…In the case of octaaryl substituted P V corrolazines the reduction occurs only by Na/NH 3 and leads to irreversible dephosphorylation. [9] In contrast to the initial corrolazine complex [(Me + Py) 8 CAP(OH) 2 ] the reduced "yellow" and "brown" forms are not fluorescent. Both of them are stable and their Redox Reactions of Water Soluble N-Methylated P V Octa(2-pyridyl)corrolazine spectra remain invariable in anaerobic conditions and room temperature at рН 7.0-9.2 for at least 12 hours.…”

“…[5] The contraction of the porphyrazine macrocycle requires the reductive conditions, and complexes of tetrabenzo fused corrolazines (TBCA) with Si IV , Ge IV , Al III and Ga III can be prepared from the corresponding metal phthalocyanines in the presence of reductants (NaBH 4 , Mg/Alk 3 SiCl). [6][7][8][9] Non-metalated TBCA and its complexes with other metals are not-known, but P V complexes of octaaryl substituted corrolazines can be reductively dephosphorylated (Na/NH 3 in THF) [5,9] and converted to the transition metal complexes -an effective catalysts in oxidation reactions. [10] The reduction processes involving corrolazines as reactants or products were studied only in non-aqueous solvents.…”

meso-N-Methylation of a porphyrinoid complex: activating the H-atom transfer capability of an inert ReV(O) corrolazine

“…3c The synthesis of ring-contracted porphyrins, and in particular, ring-contracted tetraazaporphyrins, or corrolazines (Cz), 1a,b, 4 has been a focus of our research group. The corrolazine ligands are able to support a range of metal ions in various oxidation states, including high-valent metal-oxo and metal-imido species.…”

“…5 However, synthetic modification of the corrolazine ring has thus far been limited to the peripheral substituents on the β-carbon positions. 4 …”