Phenyl-bis(imino)pyridine (PhI2P) complexes, (PhI2P)ZnCl2 (1), (PhI2P−)ZnCl (2) and (PhI2P−)Zn(py)Cl (3) were obtained with the I2P ligand in both the neutral and the one-electron reduced state. In all examples, the metal ion is Zn(II). Metrical parameters obtained from solid state structures of 2 and 3 indicate that the PhI2P− ligand exists as a radical which is supported at the carbon atom of the imino donor, and this electronic state is also apparent in the analogous one-electron reduced ligand Al(III) complex, (PhI2P−)AlCl2 (4), that we prepared for comparison. We were unable to obtain PhI2P Mg complexes, and so the more electron rich methyl-substituted bis(imino)pyridine ligand, MeI2P, was investigated. Reaction of two-electron reduced MeI2P with MgCl2 and Mg(OTf)2 did afford the two-electron reduced ligand complexes [(MeI2P2−)Mg(THF)]2(μ-MgCl2) (5) and (MeI2P2−)Mg(THF)2 (6), respectively (MeI2P = 2,6-bis(1-methylethyl)-N-(2-pyridinylmethylene)phenylamine). Complex 5 crystallizes as a trinuclear Mg complex consisting of two (MeI2P2−)Mg moieties bridged by MgCl2 and the (MeI2P2−) ligand is symmetric across the pyridine ring, but is not planar. In contrast, the (MeI2P2−) ligand in 6 is asymmetric across the pyridine ring and all atoms in the ligand are coplanar. Cyclic voltammetry measurements reveal that in complexes, 1, 4, 5, 6, the I2P0, I2P−, and I2P2− ligand charge states are accessible electrochemically.

Phenyl-bis(imino)pyridine (PhI2P) complexes, (PhI2P)ZnCl2 (1), (PhI2P−)ZnCl (2) and (PhI2P−)Zn(py)Cl (3) were obtained with the I2P ligand in both the neutral and the one-electron reduced state. In all examples, the metal ion is Zn(II). Metrical parameters obtained from solid state structures of 2 and 3 indicate that the PhI2P− ligand exists as a radical which is supported at the carbon atom of the imino donor, and this electronic state is also apparent in the analogous one-electron reduced ligand Al(III) complex, (PhI2P−)AlCl2 (4), that we prepared for comparison. We were unable to obtain PhI2P Mg complexes, and so the more electron rich methyl-substituted bis(imino)pyridine ligand, MeI2P, was investigated. Reaction of two-electron reduced MeI2P with MgCl2 and Mg(OTf)2 did afford the two-electron reduced ligand complexes [(MeI2P2−)Mg(THF)]2(μ-MgCl2) (5) and (MeI2P2−)Mg(THF)2 (6), respectively (MeI2P = 2,6-bis(1-methylethyl)-N-(2-pyridinylmethylene)phenylamine). Complex 5 crystallizes as a trinuclear Mg complex consisting of two (MeI2P2−)Mg moieties bridged by MgCl2 and the (MeI2P2−) ligand is symmetric across the pyridine ring, but is not planar. In contrast, the (MeI2P2−) ligand in 6 is asymmetric across the pyridine ring and all atoms in the ligand are coplanar. Cyclic voltammetry measurements reveal that in complexes, 1, 4, 5, 6, the I2P0, I2P−, and I2P2− ligand charge states are accessible electrochemically.

The synthesis and characterization of one novel proligand and six novel vanadium(III) trichloride complexes is described. The controlled radical polymerization activity towards vinyl acetate of these, and eight other bis(imino)pyridine vanadium trichloride complexes previously reported, is investigated. Those complexes possessing variation at the N-aryl para-position with no steric protection offered by ortho-substituents (4 examples) result in poor control over poly(vinyl acetate) polymerization. Control is improved with increasing steric bulk at the ortho-position of the N-aryl substituent (4 examples) although attempts to increase steric bulk past isopropyl were unsuccessful. Synthesizing bis(imino)pyridine vanadium trichloride complexes with substituted imine backbones restores polymerization control when aliphatic substituents are used (4 examples) but ceases to make any drastic improvements on catalyst lifetime. Modification of the polymerization conditions is also investigated, in an attempt to improve the catalyst lifetime. Expansion of the monomer scope to include other vinyl esters, particularly those derived from renewable resources, shows promising results.

The synthesis and characterization of one novel proligand and six novel vanadium(III) trichloride complexes is described. The controlled radical polymerization activity towards vinyl acetate of these, and eight other bis(imino)pyridine vanadium trichloride complexes previously reported, is investigated. Those complexes possessing variation at the N-aryl para-position with no steric protection offered by ortho-substituents (4 examples) result in poor control over poly(vinyl acetate) polymerization. Control is improved with increasing steric bulk at the ortho-position of the N-aryl substituent (4 examples) although attempts to increase steric bulk past isopropyl were unsuccessful. Synthesizing bis(imino)pyridine vanadium trichloride complexes with substituted imine backbones restores polymerization control when aliphatic substituents are used (4 examples) but ceases to make any drastic improvements on catalyst lifetime. Modification of the polymerization conditions is also investigated, in an attempt to improve the catalyst lifetime. Expansion of the monomer scope to include other vinyl esters, particularly those derived from renewable resources, shows promising results.

The direct reactions of PI3 with –H or –C6H5 substituted diiminopyridine ligands yield the N,N′,N′′-chelated P(I) cations. The analogous chemistry with the ubiquitous –CH3 substituted derivative produces a complex mixture of products underscoring the importance of the substitution on the α-carbon atom. The I3− counteranion of the compounds could be easily exchanged with the more robust B12Cl122− dianion. Reactions of PCl3 and PBr3 with –CH3 and –C6H5 substituted ligands led to indiscernible mixtures or no reaction. However, heating PBr3 with the –H derivative in the presence of a halide trap produced the corresponding phosphorus(I) cation as the bromide salt. These species represent the first phosphorus diiminopyridine complexes reported.

The direct reactions of PI3 with –H or –C6H5 substituted diiminopyridine ligands yield the N,N′,N′′-chelated P(I) cations. The analogous chemistry with the ubiquitous –CH3 substituted derivative produces a complex mixture of products underscoring the importance of the substitution on the α-carbon atom. The I3− counteranion of the compounds could be easily exchanged with the more robust B12Cl122− dianion. Reactions of PCl3 and PBr3 with –CH3 and –C6H5 substituted ligands led to indiscernible mixtures or no reaction. However, heating PBr3 with the –H derivative in the presence of a halide trap produced the corresponding phosphorus(I) cation as the bromide salt. These species represent the first phosphorus diiminopyridine complexes reported.

Attempted coordination of “GaII” with two new sterically bulky, aryl substituted bis(imino)pyridine ligands lead to GaIII species [2,6-{ArNCPh}2(NC5H3)]GaI2+GaI4− (Ar = 2,5-tBu2C6H3, 2,6-iPr2C6H3 = Dipp) arising from thermodynamically favorable disproportionation reactions. Examination of these reactions lead to isolation of a neutral radical species [2,6-{DippNCPh}2(NC5H3)]GaI2. Both EPR spectroscopy and DFT calculations on this compound indicate that the unpaired electron is localized in a di(imino)pyridine π* orbital of an anionic ligand with nearly zero contribution from the Ga or I centers. Reaction of {2,5-tBu2C6H3NCPh}2(NC5H3) with AlCl3 yielded an analogous Al(III) product, [{2,5-tBu2C6H3NCPh}2(NC5H3)]AlCl2+AlCl4−.

Attempted coordination of “GaII” with two new sterically bulky, aryl substituted bis(imino)pyridine ligands lead to GaIII species [2,6-{ArNCPh}2(NC5H3)]GaI2+GaI4− (Ar = 2,5-tBu2C6H3, 2,6-iPr2C6H3 = Dipp) arising from thermodynamically favorable disproportionation reactions. Examination of these reactions lead to isolation of a neutral radical species [2,6-{DippNCPh}2(NC5H3)]GaI2. Both EPR spectroscopy and DFT calculations on this compound indicate that the unpaired electron is localized in a di(imino)pyridine π* orbital of an anionic ligand with nearly zero contribution from the Ga or I centers. Reaction of {2,5-tBu2C6H3NCPh}2(NC5H3) with AlCl3 yielded an analogous Al(III) product, [{2,5-tBu2C6H3NCPh}2(NC5H3)]AlCl2+AlCl4−.

The bis(imino)pyridine scaffold provides for the synthesis and characterization of the unique Ag(I) pincer complexes [{ArNCPh}2(NPh)]Ag+(OTf)− (Ar = 2,5-tBu2C6H3; 2,6-iPr2C6H3). The similar covalent radii of Ag(I) and In(I), prompted a bonding comparison of these species with their In(I) analogues. Coordination of toluene to the Ag center revealed the stronger Lewis acidity of the metal site in these compounds relative to In(I) analogues.

The bis(imino)pyridine scaffold provides for the synthesis and characterization of the unique Ag(I) pincer complexes [{ArNCPh}2(NPh)]Ag+(OTf)− (Ar = 2,5-tBu2C6H3; 2,6-iPr2C6H3). The similar covalent radii of Ag(I) and In(I), prompted a bonding comparison of these species with their In(I) analogues. Coordination of toluene to the Ag center revealed the stronger Lewis acidity of the metal site in these compounds relative to In(I) analogues.

The bis(imino)pyridine scaffold provides support for the synthesis and characterization of unique Ag(I) pincer complexes [{ArNCPh}2(NPh)]Ag+(OTf)− (Ar = 2,5-tBu2C6H33; 2,6-iPr2C6H34). The bonding interactions between the cation–anion and between the bis(imino)pyridine ligand and the Ag centre are presented. Coordination of pyridine, toluene, 2-butyne and cyclooctene to the Ag centre led to the isolation and crystallographic characterization of labile transient adduct species. Bonding analysis of the adducts revealed conventional ligand–Ag coordination and important unconventional electron donation from the ligand to a π*-orbital of the bis(imino)pyridine group.

The bis(imino)pyridine scaffold provides support for the synthesis and characterization of unique Ag(I) pincer complexes [{ArNCPh}2(NPh)]Ag+(OTf)− (Ar = 2,5-tBu2C6H33; 2,6-iPr2C6H34). The bonding interactions between the cation–anion and between the bis(imino)pyridine ligand and the Ag centre are presented. Coordination of pyridine, toluene, 2-butyne and cyclooctene to the Ag centre led to the isolation and crystallographic characterization of labile transient adduct species. Bonding analysis of the adducts revealed conventional ligand–Ag coordination and important unconventional electron donation from the ligand to a π*-orbital of the bis(imino)pyridine group.