Reactions of Nickel(II) 2,21-Dimethyl-2-aza-21-carbaporphyrin with Phenyl Grignard Reagents, Phenyllithium, and n-Butyllithium

Abstract

Addition of a phenyl Grignard reagent to a toluene solution of the nickel(II) chloride complex of a dimethylated inverted porphyrin, (2-NCH3-21-CH3CTPP)NiIICl (1), at 203 K results in the formation of a rare paramagnetic (sigma-phenyl)nickel(II) species, (2-NCH3-21-CH3CTPP)NiIIPh (2). The coordination of the sigma-phenyl in 2 is determined by a unique pattern of three sigma-phenyl resonances (ortho 375.0 ppm; meta 108.94 ppm; para 35.68 ppm (at 283 K)) in the 1H NMR and 2H NMR spectra. The (sigma-phenyl)nickel(II) compound 2 is in the high-spin ground electronic state (dxy)2(dxz)2(dyz)2(dz2)1(dx2-y2)1, as confirmed by similarity of the NMR spectra of the equatorial ligand in 1 and 2. Titration of 1 with phenyllithium produces (2-NCH3-21-CH3CTPP)NiIIPh (2). One-electron reduction with excess PhLi yields [(2-NCH3-21-CH3CTPP)NiIIPh]- (3), which can be also generated by independent routes, e.g., by reduction of (2-NCH3-21-CH3CTPP)NiIIPh using lithium triethylborohydride or tetrabutylammonium borohydride. The spectroscopic data indicate that (2-NCH3-21-CH3CTPP)NiIIPh (2) undergoes one-electron reduction without a substantial disruption of the molecular geometry. The presence of two paramagnetic centers in 3, i.e., the high-spin nickel(II) and the carbaporphyrin anion radical, produces remarkable variations in a spectral patterns, such as the upfield and downfield positions of pyrrole resonances (103.78, 96.66, -25.35, -50.97, -92.15, -114.83 ppm (at 253 K)) and sign alternations of the meso-phenyl resonances (ortho -77.81, -79.34 ppm; meta 48.77, 48.04 ppm; para -85.65, -86.46 ppm (at 253 K)). A single species, 4, is detected in the 1H NMR titration of 1 with n-butyllithium. The formation of one- or two-electron-reduced species, [(2-NCH3-21-CH3CTPP)NiBu]- or [(2-NCH3-21-CH3CTPP)NiBu]2-, respectively, is considered to account for the spectroscopic properties of 4 (pyrrole 17.33, 15.45, -5.79, -7.74, -14.62, -58.14 ppm; 21-CH3 3 ppm (at 203 K)). The temperature dependence of the hyperfine shifts of 4 demonstrates pronounced anti-Curie behavior, interpreted in terms of a temperature-dependent spin equilibrium between diamagnetic and paramagnetic states with diamagnetic properties approached as the temperature is lowered. Warming of 2-4 results in complete decomposition via homolytic/heterolytic cleavage of an axial nickel-apical carbon bond. In the case of 2 or 3, the process yields a mixture of two compounds, 5 and 6, which are detected by EPR spectroscopy, demonstrating the anisotropy of the g tensor (5, g1 = 2.237, g2 = 2.092, g3 = 2.090; 6, g1 = 2.115, g2 = 2.030, g3 = 1.940 (in frozen toluene solution at 77 K)).

Blooming of confused porphyrinoids—fusion, expansion, contraction, and more confusion

“…15d), 90,91 and so on. [92][93][94][95][96][97][98][99] Additionally, oxidation of Ni II (NCTTP 2À ) in pyridine gives Ni III (21-oxo-NCTTP 3À )(py) (Fig. 15b).…”

Recent developments in heteroporphyrins and their analogues

“…N-confused porphyrins, a group of porphyrin isomers that have an inverted pyrrole sub-unit were independently isolated and characterized by Furuta et al in Japan [141] and Latos-Grażyński and co-workers in Poland [142] in 1994. Since Nconfused porphyrins have the presence of inner CH, external and internal nitrogen atoms, these porphyrins exhibited very interesting metal coordination properties, such as being organometallic in nature, exhibiting multivalency and formation of inner and outer coordination complexes and supramolecular structures [143][144][145][146][147][148][149][150][151][152][153]. Thus, the N-confused porphyrins have been explored to synthesize metal complexes in various oxidation states, such as Ni(II), Pd(II), Ag(III), Sb(V), Cu(II), Fe(II), Rh(I) and Zn(II) [154].…”

Enantiomer Resolution of Intrinsically Chiral C21‐Alkylated N‐Confused Porphyrin Complexes

“…Of several approaches targeting such systems, the alkylation of planar nickel(II) complexes of NCP seems to be the most efficient and facile. [31,32] A variety of mono-and dimeric systems have been obtained as racemic mixtures in the reaction of mesoaryl-2-aza-21-carbaporphyrinatonickel(II) 2 with mono-or dihaloalkanes (Scheme 1). [33][34][35][36][37] Here we report for the first time the separation of the stereoisomers of C21-alkylated complexes of NCP.…”