Formation and reactivity of paramagnetic organometallic nickel complexes of 21-oxa- and 21-selenaporphyrins 1H NMR and EPR investigations

Addition of aryl Grignard reagents to a toluene solution of nickel(II) monohalide complexes of 5,20-bis(p-tolyl)-10,15-diphenyl-21-oxaporphyrin (ODTDPPH) and 5,20-diphenyl-10,15-bis(p-tolyl)-21-selenaporphyrin (SeDPDTPH) at 203 K resulted in formation of paramagnetic sigma-aryl nickel(II) derivatives which were identified and characterized by means of H-1 NMR. The coordination of the aryl ligand has been unambiguously proven by the unique downfield pattern of the corresponding resonances. The (sigma-aryl) nickel(II) derivatives are in the high-spin electronic state: (d(xy))(2)(d(xz))(2)(d(y)z)(2)(d(z2))(1)(d(x2-y2))(1). A homolytic cleavage of the Ni-II-C bond has been determined for (ODTDPP)Ni-II(Ar) and (SeDPDTP)Ni-II(Ar) in toluene with formation of low-valent nickel species: (ODTDPP)Ni and (SeDPDTP)Ni. One-electron reduction of (SeDPDTP)(NiCl)-Cl-II to generate (SeDPDTP)Ni has been investigated by means of EPR, involving Ni-61 isotope enrichment and spectral simulations. A considerable increase in metal d-orbital contribution to the singly occupied molecular orbital has been observed upon coordination of 1-methylimidazole to (SeDPDTP)Ni. (C) 1998 Elsevier Science S.A. All rights reserved.