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

Abstract

The deprotonation of (2-pyridylmethyl)(triorganylsilyl)amines of the type Py-CH₂-N(H)-SiR₃ with SiR₃ = SiMe₂tBu (1a), SiMe₂(CMe₂iPr) (1b), SiiPr₃ (1c) and SiPh₃ (1d) with (thf)Fe[N(SiMe₃)₂]₂Cl 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) [SiR₃ = SiMe₂tBu (2a), SiMe₂(CMe₂iPr) (2b), SiiPr₃ (2c), and SiPh₃ (2d)]. These complexes crystallized dimeric with Fe₂N₂ 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) [SiR₃ = SiMe₂tBu (3a), SiMe₂(CMe₂iPr) (3b), SiiPr₃ (3c), and SiPh₃ (3d)] which are obtained from very concentrated reaction solutions. These (2-pyridylmethylidene)(triorganylsilyl)amino ligands (imines) act as bidentate bases at FeCl₂ 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(SiMe₃)₂]₂ yields homoleptic iron(II) bis[(2-pyridylmethyl)(triorganylsilyl)amides] (4) with distorted tetrahedrally coordinated iron centers. Metathesis reactions of FeCl₃ with lithium (2-pyridylmethyl)(triorganylsilyl)amide as well as employing a mixture of Fe[N(SiMe₃)₂]₂ and FeCl₃ 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.