Aminopyridinato ligands

The dimethylzinc route has also been extended to aminopyridinato ligands (cf. Section Scheme 160 depicts the reaction of a dimeric zinc guanidinate... 

Aminopyridinato ligands form a special class of anionic ligands in which an aromatic ring is part of an amidinate system. These ligands have frequently been employed in early transition metal and lanthanide coordination chemistry. Their diverse and interesting chemistry has been described in detail by Kempe et al. ° and will thus be covered here only briefly. Typical reaction pathways leading to titanium aminopyridinato complexes are outlined in Scheme 169. Metathetical as well as salt-free routes have been developed. 

A promising recent extension of the aminopyridinato ligand concept involves the use of potentially tridentate amidinato-cyclopentadienyl ligands. Typical complexes with M = Ti, Zr are depicted in Scheme 171. Other heterocycles can be incorporated in the ligand system instead of the pyridine ring. ... 

The tris(aminopyridinato) ligand complex TiCl((NC5H3MeNSiMe2)3CH) (37) was prepared by reaction of the neutral ligand with TiCl(NMe2)3. Crystallographic data confirmed a seven-coordinate metal center.309... 

Aminopyridinato ligands are an important group of asymmetric A,A-bidentate ligands and derived from deprotonation of 2-aminopyridines. The flexibility of binding modes of aminopyridinato ligands can be explained by two resonance forms the amidopyridine and the aminopyridinato. The anionic function is localized at either... 

HL3 and HL4 were also reacted with [Ln N(SiHMe2)2 3(THF)2] via amine elimination to form the corresponding mono(aminopyridinato) complexes (Ln = Y (14 and 15), La (16 and 17)). Complexes 14-17 are not active for the polymerization of ethylene in the presence of alkylaluminium compounds. The reactions of the mono(aminopyridinato) complexes with aluminum compounds AlEts or AIH/BU2 showed a fast aminopyridinato ligand transfer to the aluminum atom. The products of the transfer reaction are aminopyridinato-stabilized dialkylaluminium compounds. The catalytic activity was believed to be prohibited by the ligand transfer reaction (Scheme 5) [41]. 

Kretschmer, W.P., Hessen, B., Noor, A. et al. (2007) Highly active/selective and adjustable zirconium polymerization catalysts stabilized by aminopyridinato ligands. Journal of Organometallic Chemistry, 692,4569 579. 

Treatment of NbCl3(PhC=CSiMe3) with Li3L (LH3 is a tris(amino-pyridine) ligand) in hex produced LNb(PhC=CSiMe3) (244), with two of the aminopyridinato arms coordinated at the amido and pyridine N atoms, but the third coordinated at the amido N atom only.579... 

A few other complexes with N-N coordinating atoms have been tested as olefin polymerization catalysts. The aminopyridinato complex 181 is only able to oligomerize propylene and 1-butene (Mn < 3500) with low activity.1222 The /3-diketiminato Zr complex 182 exhibits moderate ethylene polymerization activity ( 50gPE(mmol M)-1 h-1 bar-1), but molecular masses were disappointingly low (Mn up to 30000).1117 Finally, at 100°C, the MAO-activated Ti complex 183, with a tridentate triazacyclononane ligand, yields PE with very high activity (104gPE(mmol M)-1 h-1 bar-1) but rather low molecular masses and broad polydispersity (Mn = 39500 Mw/Mn = 7.0).1223... 

In 1998, Kempe and coworkers [34] reported the first aminopyridinato rare-earth metal complexes. 4-Methyl-2-[(trimethylsilyl)amino]pyridine(HLl) was utilized in this complex. The reaction of lithiated LI and YCI3 in ether and pyridine led to the ate complex [Y(Ll)4(LiPy)] (Py = pyridine) (1). The complex 1 catalytically mediated a ligand transfer reaction to form [Pd(Ll)2] and [Y(Ll)3(py)] (2) from [Pd(cod)Cl2] (cod = cyclooctadiene). The LI ligand transfer from yttrium to palladium and the regeneration of 1 are significant in the efficient synthesis of the very strained amido palladium complexes (Scheme 2). Lithiated LI underwent a salt metathesis reaction with ScCb, at low temperature in THF, to yield the homoleptic complex [Sc(L1)3] (3) (Scheme 2). 3 is the first reported scandium aminopyridinato complex [35]. 

KL3 and KL5 underwent clean salt metathesis with NdCls in THF to form a dinuclear mono(aminopyridinato) complex, [Nd(L3)Cl2(THF)2]2 (23) (Scheme 7) and a mononuclear bis-aminopyridinato complex, [Nd(L5)2Cl(THF)] (19) (Scheme 6), respectively. The steric effect of bulky ligand L3 favors the... 

---