Low-Valent Nickel Thiaporphyrins. Nuclear Magnetic Resonance and Electron Paramagnetic Resonance Studies

Chmielewski, Piotr J.; Latos‐Grażyński, Lechosław; Pacholska, Ewa

doi:10.1021/ic00087a040

Cited by 42 publications

(61 citation statements)

References 2 publications

(3 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…The heteroatom substituted porphyrins were first synthesized in 1969 [12][13][14][15] and for the last 35 years some elegant methodologies have been developed which resulted in much research activity on these porphyrin systems. However, until the late 1990s, most of the work on heteroporphyrins was limited to the preparation of different metal derivatives and the exploration of their structural, spectroscopic and electrochemical properties [3,4,6,[9][10][11]16,[18][19][20][21][22][23][24]. Latos-Grażyński, who is one of the pioneers in developing the heteroporphyrin chemistry has reviewed recently all the work that appeared on heteroporphyrins until 1998 in "The Porphyrin Handbook" [2].…”

Section: Introductionmentioning

confidence: 99%

Recent developments in heteroporphyrins and their analogues

Gupta

Ravikanth

2006

Coordination Chemistry Reviews

158

View full text Add to dashboard Cite

Section: Introductionmentioning

confidence: 99%

Recent developments in heteroporphyrins and their analogues

Gupta

Ravikanth

2006

Coordination Chemistry Reviews

158

View full text Add to dashboard Cite

“…24,[31][32][33][34][35][36][37][38][39] The shift pattern of the carbaporphyrin equatorial ligand resembles that found for the [(2-NCH 3 -21-CH 3 CTPP)Ni II (py)] + species, generated by titration of (2-NCH 3 -21-CH 3 CTPP)Ni II Cl with pyridine, as shown in Figure 2 (toluene-d 8 , 223 K):…”

Section: Resultsmentioning

confidence: 73%

“…On the other hand, the g i components approach g e as the extent of localization of the electron density on the macrocycle increases. 36 (P •-)Ni I (ad z 2 + bd x 2 -y 2 )(S ) 0) a (P •-)Ni I (ad z 2 + bd x 2 -y 2 )(S ) 1)…”

Section: Resultsmentioning

confidence: 99%

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

Chmielewski

Latos‐Grażyński

2000

Inorg. Chem.

Self Cite

View full text Add to dashboard Cite

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)).

show abstract

“…If the spin density is delocalized from the metal ion onto the ligand mainly through the σ framework (as it is for the metal (d

_{italicx^{2} − italicy^{2}}

) 1 ground state), only downfield isotropic shift is anticipated for pyrrole protons 19. 20 The alternation of chemical shift may suggest contribution of a radical electronic structure similar to that observed previously for oxidized copper(II) complexes of porphyrins or biliverdin analogues 21. Such a metal radical species may be formed here by an intramolecular redox process involving tricoordinate copper and the heptaphyrin ring.…”

Section: Methodsmentioning

confidence: 99%