American Chemical Society
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Aryl−Oxazoline Chelates of First-Row Transition Metals: Structures of {κ-C,N-(o-C6H4)CMe2(COCH2CMe2N)}FeCl(py) and [(κ-C,N-(o-C6H4)CMe2(COCH2CMe2N)}Cr(μ-Cl)]2

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journal contribution
posted on 2010-12-27, 00:00 authored by Emily C. Volpe, David R. Manke, Erika R. Bartholomew, Peter T. Wolczanski, Emil B. Lobkovsky
Aryl−oxazoline synthons have been explored for the preparation of strong-field first-row transition metal chelate species. With 4,4-dimethyl-2-phenyloxazoline (HPhOx), no CH bond activations afforded complexation, and aside from Zn(κ-C,N-4,4-Me2-2-(o-C6H4)oxazoline)2 (Zn(PhOx)2), aryl-coupling reactions were noted with 4,4-dimethyl-2-(2-lithiophenyl)oxazoline (LiPhOx) and MX2; [κ-N,N-{4,4-Me2-(2-o-C6H4)-2-oxazoline}2]CoCl2 (1-Co) was structurally characterized. Metalations with 4,4-dimethyl-2-benzyloxazoline (PhCH2Ox) were prone to deprotonation, as exemplified by (Me2N)3Ti(η-N-(4,4-dimethyl-(2-CHPh)oxazoline)) (2) and bis-N,N′-(4,4-dimethyl-(2-pyridylmethylyl)oxazoline)Fe (3). Oxidative addition of 4,4-dimethyl-2-(2-bromophenylpropan-2-yl)oxazoline (BrPhCMe2Ox) to Ni(COD)2 provided [{κ-C,N-(o-C6H4)CMe2(COCH2CMe2N)}Ni]2(μ-Br)2 (42). With 4,4-dimethyl-2-(2-lithiophenylpropan-2-yl)oxazoline (LiPhCMe2Ox), salt (FeBr2) metathesis proved uncompetitive with oxazoline ring-opening, as exhibited by [{κ-N,O-C6H4CMe2CNCMe2CH2(μ-O)-}BrFe{κ-N,O-C6H4CMe2CNCMe2CH2(μ-O)-}FeBr]Li {κ-N,O-C6H4CMe2-CNCMe2CH2(μ-O)-}(DME) (5-Fe2Li). Metatheses utilizing (PhCMe2Ox)2Zn, prepared from LiPhCMe2Ox and ZnCl2, gave structurally characterized dichromium, i.e., [{κ-C,N-(o-C6H4)CMe2 (COCH2CMe2N)}Cr]2(μ-Cl)2 (62), and iron, i.e., {κ-C,N-{(o-C6H4)CMe2(COCH2CMe2N)}Fe(py)Cl (7) products. Bis-aryloxazoline metal complexes proved difficult to prepare, with {κ-C,N-(o-C6H4)CMe2(COCH2CMe2N)}2M (M = Ni, 9) the only clear example, although NMR evidence exists for M = Fe (8).