Aryl-oxazoline chelates of first-row transition metals: Structures of {Κ-C,N-(o-C_6H_4)CMe_2(COCH _2CMe_2N)}FeCl(py) and [(Κ-C,N-(o-C_6H _4)CMe_2(COCH_2CMe_2N)}Cr(μ-Cl)] _2

摘要

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-Me_2-2-(o-C _6H_4)oxazoline)2 (Zn(PhOx)_2), aryl-coupling reactions were noted with 4,4-dimethyl-2-(2-lithiophenyl)oxazoline (LiPhOx) and MX_2; [Κ-N,N-{4,4-Me_2-(2-o-C _6H_4)-2-oxazoline}_2]CoCl_2 (1-Co) was structurally characterized. Metalations with 4,4-dimethyl-2-benzyloxazoline (PhCH_2Ox) were prone to deprotonation, as exemplified by (Me _2N)_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 (BrPhCMe _2Ox) to Ni(COD)_2 provided [{Κ-C,N-(o-C _6H_4)CMe_2(COCH_2CMe _2N)}Ni]_2(μ-Br)_2 (4_2). With 4,4-dimethyl-2-(2-lithiophenylpropan-2-yl)oxazoline (LiPhCMe_2Ox), salt (FeBr_2) metathesis proved uncompetitive with oxazoline ring-opening, as exhibited by [{Κ-N,O-C_6H_4CMe _2C=NCMe_2CH_2(μ-O)-}BrFe{Κ-N,O-C _6H_4CMe_2C=NCMe_2CH_2(μ-O) -}FeBr]Li {Κ-N,O-C_6H_4CMe_2-C=NCMe _2CH_2(μ-O)-}(DME) (5-Fe_2Li). Metatheses utilizing (PhCMe_2Ox)_2Zn, prepared from LiPhCMe _2Ox and ZnCl_2, gave structurally characterized dichromium, i.e., [{Κ-C,N-(o-C_6H_4)CMe_2 (COCH _2CMe_2N)}Cr]_2(μ-Cl)_2 (6 _2), and iron, i.e., {Κ-C,N-{(o-C_6H _4)CMe_2(COCH_2CMe_2N)}Fe(py)Cl (7) products. Bis-aryloxazoline metal complexes proved difficult to prepare, with {Κ-C,N-(o-C_6H_4)CMe_2(COCH _2CMe_2N)}_2M (M = Ni, 9) the only clear example, although NMR evidence exists for M = Fe (8).