Mechanistic studies on the alcoholysis and aminolysis of [(MeZn)2{μ-N(H)tBu}{μ-N(CH2Py)2}]

The reaction of bis(2-pyridylmethyl)amine (II) with t-butylamine and dimethylzinc gives the heteroleptic [(MeZn)2{μ-N(H)tBu}{μ-N(CH2Py)2}] (1). Stoichiometric alcoholysis of 1 with methanol leads to the exchange of the μ-N(H)tBu moiety. Almost quantitatively the corresponding methoxide [(MeZn)2(μ-OMe){μ-N(CH2Py)2}] (2) is formed. Alternatively bis(alkylzinc)methoxide-bis(2-pyridylmethyl)amides (Alkyl = methyl (2), bis(trimethylsilyl)methyl) (3)) are also accessible by direct zincation of bis(2-pyridylmethyl)amine (II) and methanol with dialkylzinc regardless of the bulkiness of the alkyl groups. Extensive DFT calculations on the alcoholysis mechanism reveal the preferential insertion of methanol into a zinc amide bond rather than the cleavage of zinc carbon bonds. An intermediate with a Zn[μ-(MeO⋯H⋯NHR)]Zn functionality is predicted. Aminolyis of 1 with t-butylamine leads to intermediates with Zn[μ-(RNH ⋯ H ⋯ NHR)]Zn functionalities, respectively. We were able to detect the latter by 1H NMR spectroscopy. The aminolysis of 1 with an excess of phenylamine results in a partial decomposition of the complex leading to the hexanuclear amide [{Zn(μ-N(H)Ph)}{MeZn(μ-N(H)Ph)}2{μ-N(CH2Py)2}]2 (4). Compound 2 is able to cleave silicon grease when dissolved in t-butylamine yielding [(MeZn)2{μ-N(CH2Py)2}2Zn{μ-(OMe2Si)2O}] (5). The X-ray structures of complexes 1–5 are discussed.

Treatment of [(MeZn)2{μ-N(H)tBu}{μ-N(CH2Py)2}] with methanol or t-butylamine leads to the exchange of the μ-N(H)tBu moiety. Extensive DFT calculations on the mechanism predict intermediates with Zn[μ-(X⋯H⋯Y)]Zn (X = O, N; Y = N) functionalities which could be detected by 1H NMR spectroscopy.Figure optionsDownload as PowerPoint slide