Synthesis, structure, and properties of magnesocene amine adducts. Structural distortions arising from N-H center dot center dot center dot C-5(5)H(-) hydrogen bonding and molecular orbital calculations thereof

摘要

Magnesocene amine adducts were prepared and characterized. Addition of primary (3-amino-2,4-dimethylpentane, isopropylamine, tert-butylamine, benzylamine, cyclohexylamine) and secondary (diethylamine, dibenzylamine, dicyclohexylamine, and N-isopropylbenzylamine) amines to magnesocene at ambient temperature in toluene afforded the stable amine adducts Cp2Mg(NH2CH(CH(CH3)(2))(2)) (91%), Cp2Mg(NH(2)iPr) (80%), Cp2Mg(NH(2)tBu) (67%), Cp2Mg(NH2CH2Ph) (80%), Cp2Mg(NH2(C6H11)) (93%), Cp2Mg(NHEt2) (84%), Co2Mg(NH(CH2Ph)(2)) (86%), Cp2Mg(NH(C6H11)(2)) (84%), and Cp2Mg(NH(iPr)(CH2Ph)) (91%). Most adducts can be sublimed at under 100 degreesC/0.05 Torr in good yields (72-95%) without decomposition (<1% residue). However, Cp2Mg(NH2CH2Ph) decomposes to Cp2Mg (70% of theory) and Cp2Mg(NH2CH2Ph)(2) (75% of theory) under reduced pressure, even at room temperature, and is thus unsuitable for sublimation. The solid-state structures of Cp2Mg(NH2(C6H11)), Cp2Mg(NH(iPr)(CH2Ph)), and Cp2Mg(NH2CH2Ph)(2) were determined by X-ray diffraction methods. In the solid-state structures, Cp2Mg(NH2(C6H11)) and Cp2Mg(NH2CH2Ph)(2) contain one eta(5)- and one eta(2)-coordinated cyclopentadienyl ring, while Cp2Mg(NH(iPr)(CH2Ph)) contains two eta(5)-cyclopentadienyl rings. Infrared spectroscopy suggests that the adducts are stabilized by N-H...C5H5- hydrogen bonding. Molecular orbital calculations on the model complex Cp2Mg(NH2CH3) support the idea of N-H...C5H5- hydrogen bonding and provide insight into the energetics and exchange processes associated with the hydrogen bond. The N-H...C5H5- hydrogen bond strength is estimated to be 4.2 +/- 1.4 kcal/mol, and molecular orbital calculations suggest that the amine hydrogen atoms undergo site exchange by a low-energy intramolecular rotational process that interconverts the eta(2)- and eta(5)-cyclopentadienyl ligands. [References: 74]