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

Abstract

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 σ-aryl nickel(II) derivatives which were identified and characterized by means of 1H NMR. The coordination of the aryl ligand has been unambiguously proven by the unique downfield pattern of the corresponding resonances. The ( σ-aryl)nickel(II) derivatives are in the high-spin electronic state: (d xv ) 2(d vz ) 2(d vz ) 2(d z 2 ) 2(d z 2 ) 1(d x 2 y 2 ) 1. A homolytic cleavage of the Ni 11-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)Ni IICl to generate (SeDPDTP)Ni has been investigated by means of EPR, involving 61Ni 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.