Syntheses and characterizations of α-iminopyridine compounds (alkylNCHpy)2Fe(L/Xn), and an assessment of redox non-innocence

Treatment of cis-(Me3P)4FeMe2 with two equiv neoPeNCH(2-py) afforded {κ-N,N′-neoPeNCH(2-pyridyl)}2FeMe2 (2-P). Reductions of FeCl2 with Na/Hg in the presence of neoPeNCH(2-pyridyl) or neoHexNCH(2-pyridyl) and L (H2CCHCO2Me, PhCCPh, PMe3) gave tentative evidence of {κ-N,N′-neoPeNCH(2-pyridyl)}2Fe(H2CCHCO2Me) (2-P), but {κ-N,N′-neoPeNCH(2-pyridyl)}2Fe(PhCCPh) (5-P), {κ-N,N′-neoHexNCH(2-pyridyl)}2Fe(PhCCPh) (5-H), and {κ-N,N′-neoHexNCH(2-pyridyl)}2Fe(PMe3) (6-H) were all isolated in good yield. Phosphine complex 6-H could be alkylated with CH3I or CH3OTf to afford [{κ-N,N′-neoHexNCH(2-pyridyl)}2Fe(PMe3)Me]+I− (7-H-I) or [{κ-N,N′-neoHexNCH(2-pyridyl)}2Fe(PMe3)Me]+ OTf− (7-H-OTf). [{κ-N,N′-RNCH(2-pyridyl)}3Fe][OTf]2 (R = neoPe, 8-P-OTf; neoHex, 8-H-OTf) complexes were also prepared from Fe(OTf)2 in order to identify potential byproducts in certain reactions. Compounds 2-P and 7-H-OTf were tested for ethylene oligomerization activity, to no avail. Complexes 2-P, 5-H, 6-H, and 7-H-OTf were structurally characterized and evaluated by Mössbauer spectroscopy, and 5-H was shown to possess a redox non-innocent alkyne ligand, while the α-alkyliminopyridine ligands of 6-H were classified as radical anions, rendering all compounds describable as Fe(II).

Formally Fe(0) α-alkyliminopyridine compounds, such as the (tBuCH2CH2NCHpy)2FeL (L = PMe3, PhCCPh) species shown, are best construed as Fe(II) derivatives with redox non-innocent ligands according to X-ray structural and Mössbauer spectroscopic studies.Figure optionsDownload as PowerPoint slide