Synthesis of heteroleptic iron(II) 2-pyridylmethylamides and 2-pyridylmethylideneamines via the reaction of [(thf)Fe{N(SiMe3)2}2Cl] with (2-pyridylmethyl)(trialkylsilyl)amines.

Research paper by Astrid A Malassa, Nicole N Herzer, Helmar H Görls, Matthias M Westerhausen

Indexed on: 07 May '10Published on: 07 May '10Published in: Dalton Transactions


The deprotonation of (2-pyridylmethyl)(triorganylsilyl)amines of the type Py-CH(2)-N(H)-SiR(3) with SiR(3) = SiMe(2)tBu (1a), SiMe(2)(CMe(2)iPr) (1b), SiiPr(3) (1c) and SiPh(3) (1d) with (thf)Fe[N(SiMe(3))(2)](2)Cl in THF is accompanied by redox reactions and leads to the formation of iron(II) compounds. The products with lower solubility precipitated first and are the pale yellow and paramagnetic complexes chloro-(2-pyridylmethyl)(triorganylsilyl)amido iron(ii) [SiR(3) = SiMe(2)tBu (2a), SiMe(2)(CMe(2)iPr) (2b), SiiPr(3) (2c), and SiPh(3) (2d)]. These complexes crystallized dimeric with Fe(2)N(2) rings with different Fe-N bond lengths (average values of 211.1 and 203.2 pm). The Fe-Cl distances vary around an average value of 225.6 pm. Another isolated product consists of orange to blue crystals of dichloro-(2-pyridylmethylidene)(triorganylsilyl)amino iron(II) [SiR(3) = SiMe(2)tBu (3a), SiMe(2)(CMe(2)iPr) (3b), SiiPr(3) (3c), and SiPh(3) (3d)] which are obtained from very concentrated reaction solutions. These (2-pyridylmethylidene)(triorganylsilyl)amino ligands (imines) act as bidentate bases at FeCl(2) with average Fe-N and Fe-Cl bond lengths of 211.8 and 223.5 pm, respectively. The metallation of the (2-pyridylmethyl)(triorganylsilyl)amines with dimeric Fe[N(SiMe(3))(2)](2) yields homoleptic iron(II) bis[(2-pyridylmethyl)(triorganylsilyl)amides] (4) with distorted tetrahedrally coordinated iron centers. Metathesis reactions of FeCl(3) with lithium (2-pyridylmethyl)(triorganylsilyl)amide as well as employing a mixture of Fe[N(SiMe(3))(2)](2) and FeCl(3) with (2-pyridylmethyl)(triorganylsilyl)amine give similar results and the formation of chloro-(2-pyridylmethyl)(triorganylsilyl)amido iron(II) (2) and dichloro-(2-pyridylmethylidene)(triorganylsilyl)amino iron(II) (3) are observed.