Coordination Behavior of the (Diphenylphosphanyl)[α-(2-pyridyl)benzyl]amide Anion toward Lithium and Zinc Cations

• Published in: European Journal of Inorganic Chemistry 2010-04, Vol.2010 (12), p.1791-1797
• Main Authors: Olbert, Dirk, Görls, Helmar, Conrad, Delf, Westerhausen, Matthias
• Format: Article
• Language: English
• Subjects: C-C coupling reactions; Lithium; Metalation reactions; Pyridylmethylamines; Zinc
• ISSN: 1434-1948; 1099-0682
• DOI: 10.1002/ejic.201000039

A two‐step synthesis allows the preparation of [α‐(2‐pyridyl)benzyl]amine (1) in good yield. Phosphanylation in the presence of triethylamine gives (diphenylphosphanyl)[α‐(2‐pyridyl)benzyl]amine (2), which crystallizes as a racemate in the centrosymmetric triclinic space group P$\bar {1}$. The P–N bond lengths exhibit an average value of 168.3 pm. Lithiation of 2 with n‐butyllithium yields dimeric semi(tetrahydrofuran)lithium (diphenylphosphanyl)[α‐(2‐pyridyl)benzyl]amide (3) with the lithium atoms in different environments. One Li atom is in a distorted tetrahedral environment and the other in a trigonal‐planar coordination sphere with bridging amide moieties (av. Li–N 201.8, Li–O 192.4 pm). Zincation of 2 with dimethylzinc leads to the formation of dimeric methylzinc (diphenylphosphanyl)[α‐(2‐pyridyl)benzyl]amide (4) with a central six‐membered (ZnNP)2 ring in a boat conformation (av. Zn–N 201.8, Zn–P 245.9 pm). The endocyclic P–N bonds are rather short (av. value 162.7 pm). (2‐Pyridylmethyl)amide anions act as bidentate chelate ligands. N‐(Diphenylphosphanyl) substitution extends the coordination behavior. The hard lithium cation exclusively binds to the nitrogen donors, whereas methylzinc (diphenylphosphanyl)(2‐pyridylmethyl)amide dimerizes through bridging amide and phosphanyl moities (Zn red, P orange, N blue; C hollow spheres; H omitted).