Reactions of Nickel(II) 2,21-Dimethyl-2-aza-21-carbaporphyrin with Phenyl Grignard Reagents, Phenyllithium, and n-Butyllithium Piotr J. Chmielewski* and Lechoslaw Latos-Graz 3 yn ´ ski* Department of Chemistry, University of Wroclaw, 14 F. Joliot-Curie Street, 50-383 Wroclaw, Poland ReceiVed January 11, 2000 Addition of a phenyl Grignard reagent to a toluene solution of the nickel(II) chloride complex of a dimethylated inverted porphyrin, (2-NCH 3 -21-CH 3 CTPP)Ni II Cl (1), at 203 K results in the formation of a rare paramagnetic (σ-phenyl)nickel(II) species, (2-NCH 3 -21-CH 3 CTPP)Ni II Ph (2). The coordination of the σ-phenyl in 2 is determined by a unique pattern of three σ-phenyl resonances (ortho 375.0 ppm; meta 108.94 ppm; para 35.68 ppm (at 283 K)) in the 1 H NMR and 2 H NMR spectra. The (σ-phenyl)nickel(II) compound 2 is in the high-spin ground electronic state (d xy ) 2 (d xz ) 2 (d yz ) 2 (d z 2) 1 (d x 2 -y 2) 1 , as confirmed by similarity of the NMR spectra of the equatorial ligand in 1 and 2. Titration of 1 with phenyllithium produces (2-NCH 3 -21-CH 3 CTPP)Ni II Ph (2). One-electron reduction with excess PhLi yields [(2-NCH 3 -21-CH 3 CTPP)Ni II Ph] - (3), which can be also generated by independent routes, e.g., by reduction of (2-NCH 3 -21-CH 3 CTPP)Ni II Ph using lithium triethylborohydride or tetrabutylammonium boro- hydride. The spectroscopic data indicate that (2-NCH 3 -21-CH 3 CTPP)Ni II Ph (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 1 H NMR titration of 1 with n-butyllithium. The formation of one- or two-electron-reduced species, [(2-NCH 3 -21-CH 3 CTPP)NiBu] - or [(2-NCH 3 -21-CH 3 CTPP)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-CH 3 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, 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)). Introduction Interchange of a nitrogen and a -methine group in a pyrrole of 5,10,15,20-tetraphenylporphyrin (TPPH 2 ) results in the creation of the porphyrin-like skeleton 5,10,15,20-tetraphenyl- 2-aza-21-carbaporphyrin (21-CTPPH 2 , inverted tetraphenylpor- phyrin) although with fundamentally changed electronic and coordination properties. 1,2 A peralkylated, meso-unsubstituted inverted porphyrin has been synthesized as well. 3,4 The inverted porphyrin belongs to a larger group of recently emerged porphyrin isomers 5-9 although this particular molecule repre- sents the only case where the pattern of the porphyrin framework is preserved. A complementary and relevant area of porphyrin modification involves the replacement of one pyrrole ring by benzene, 10 semiquinone, 11,12 cycloheptatriene, 13,14 indene, 13,15 azulene, 16 cyclopentadiene, 17 an aliphatic bicyclic alkene, 18 and 2,4-linked thiophene 19 moieties. 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