Aminopyridinato-ligand-stabilized organoyttrium cations are accessible in very good yield through alkane elimination from trialkyl yttrium complexes with sterically demanding aminopyridines, followed by abstraction of one of the two alkyl functions using ammonium borates. At 80 degrees C and in the presence of small amounts of aluminum alkyl compounds, very high ethylene polymerization activities are observed if very bulky aminopyridinato ligands are used. During these polymerizations a reversible polyethylene chain transfer is observed between the organoyttrium cations and aluminum alkyls. The chain-transfer catalyst system described here is able to produce relatively long-chain (up to 4000 g mol-1) Al-terminated polyethylene with a molecular-weight distribution<1.1. In the synthesis of higher molecular PE a slight increase in polydispersity with increasing chain length (15,600 g mol-1, approximately 1.4) is observed owing to reduced reversibility caused by higher viscosity and precipitation of polymer chains (temperature of 80-100 degrees C).

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The low valent, coordinatively unsaturated, and formally quintuply bonded bimetallic aminopyridinato chromium complex 1 was investigated regarding its reactivity toward group 16 and 17 elements. Reaction of 1 with O(2) yielded a dimeric Cr oxo complex 2, a compound with a high formal oxidation state carrying both bridging and terminal oxo ligands. Reactions with the higher homologues of the group lead to the formation of dimeric Cr(II) complexes in which E(2)(2-) ligands were formed [E = S (3), Se (4), and Te (5)]. Here the quintuply bonded dichromium unit formally undergoes an addition reaction. Reaction of 1 with the homo diatomic molecules of the group 17 elements leads to products in which the Cr-Cr quintuple bond is inserted into the corresponding X(2) molecule [X = Cl (6), Br (7), and I (8)]. Complex 1 was also found to insert into the S-S and Se-Se bonds of 1,2-diphenyldisulfane or the corresponding selenium compound (complexes 9 and 10, respectively). All the compounds have been characterized by NMR and elemental analysis. Additionally, eight of the complexes have been characterized by X-ray analysis. The bimetallic Cr(II) complexes feature metal-metal distances between 1.8369(18) and 1.918(12) Å.

A series of mono(2-aminopyridinato)tris(dimethylamido) titanium complexes, ApTi(NMe 2 ) 3 (where Ap = 2-aminopyridinato), have been prepared via protonolysis, and their reactivity for the hydroamination of primary aminoalkenes has been explored. The Ti complex incorporating N,6-dimesityl-2-aminopyridinate as the supporting ancillary ligand has been shown to yield a catalyst suitable for roomtemperature intramolecular hydroamination reactions to give gem-disubstituted fiveand six-membered-ring products. The comparison of ApTi(NMe 2 ) 3 with other group 4 catalysts shows that controlling the steric environment at the metal center is the critical determining factor for hydroamination reactivity. The screening of known challenging primary aminoalkene substrates with the most reactive ApTi(NMe 2 ) 3 shows good breadth of reactivity for the reaction. This complex is not able to cyclize secondary aminoalkene substrates, suggesting this reaction proceeds via an intermediate imido [2+2] cycloaddition pathway. An Ap-supported Ti imido complex, which also exhibits hydroamination activity, has been prepared and fully characterized from ApTi(NMe 2 ) 3 and 2,6dimethylaniline.

A quintuply bonded dichromium complex stabilized by aminopyridinato ligands activates CO2 and SO2 by reducing the (formal) bond order of the metal-metal bonds. Oxygen abstraction is observed during CO2 activation. SO2 activation proceeds via formation of a unique dithionite complex/coordination. Furthermore, N2O activation was investigated and the formation of a tetrameric Cr-oxo complex was observed.