Reactions of nickel(II) 2,21-dimethyl-2-aza-21-carbaporphyrin with phenyl Grignard reagents, phenyllithium, and n-butyllithium

Addition of a phenyl Grignard reagent to a toluene solution of the nicker(II) chloride complex of a dimethylated inverted porphyrin, (2-NCH3-21-CH3CTPP)(NiCl)-Cl-II (1), at 203 K results in the formation of a rare paramagnetic (sigma -phenyl)nickel(II) species, (2-NCH3-21-CH3CTPP)(NiPh)-Ph-II (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 H-1 NMR and H-2 NMR spectra. The (sigma -phenyl)nickel(II) compound 2 is in the high-spin ground electronic state (d(xy))(2)(d(xz))(2)(d(yz))(2)(d(z2))(1)(d(x2-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)(NiPh)-Ph-II (2). One-electron reduction with excess PhLi yields [(2-NCH3-21-CH3CTPP)(NiPh)-Ph-II](-) (3), which can be also generated by independent routes, e.g., by reduction of (2-NCH3-21-CH3CTPP)(NiPh)-Ph-II using lithium triethylborohydride or tetrabutylammonium borohydride. The spectroscopic data indicate that (2-NCH3-21-CH3CTPP)(NiPh)-Ph-II (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 fat 253 K)). A single species, 4, is detected in the H-1 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 fat 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, g(1) = 2.237, g(2) = 2.092, g(3) = 2.090; 6, g(1) = 2.115, g(2) = 2.030, g(3) = 1.940 (in frozen toluene solution at 77 K)).