Insertion of CO2 and related heteroallenes into the Si–N-bond of methyl(N-morpholino)silanes

Abstract

Abstract Trimethyl(N-morpholino)silane (Me3SiMorph) and dimethyl-di(N-morpholino)silane (Me2SiMorph2) were synthesised. The insertion reactions of both silanes with CO2, n-butylisocyanate (nBuNCO), phenylisocyanate (PhNCO), methylisothiocyanate (MeNCS), n-butylisothiocyanate (nBuNCS) and phenylisothiocyanate (PhNCS) into the Si–N-bond were investigated. One CO2 molecule inserts into each Si–N-bond forming carbamoylic moieties. The insertion reaction of isocyanates depends on the organic substituents bound to the heteroallene unit. PhNCO inserts twofold forming a biuret moiety, while nBuNCO yields urea units by insertion of just one molecule per Si–N-bond. The isothiocyanates are less reactive forming thiourea moieties. Aliphatic isothiocyanates furnish equilibria between the reactants and the insertion product at room temperature. All products have been characterized by spectroscopic methods. Single crystal X-ray diffraction analyses of five insertion products have been performed. The observed reactivity is discussed on the basis of NBO charges and calculated Gibbs free energies of the insertion reactions.