Tris(oxazolinyl)boratomagnesium-Catalyzed Cross-Dehydrocoupling of Organosilanes with Amines, Hydrazine, and Ammonia

Abstract

We report magnesium-catalyzed cross-dehydrocoupling of Si-H and N-H bonds to give Si-N bonds and H2. A number of silazanes are accessible using this method, as well as silylamines from NH3 and silylhydrazines from N2H4. Kinetic studies of the overall catalytic cycle and a stoichiometric Si-N bond-forming reaction suggest nucleophilic attack by a magnesium amide as the turnover-limiting step. KeywordsBond-forming reactions, Catalytic cycles, kinetic study, nucleophilic attack, organosilanes, si-N bonds, silazanes, magnesium, silicon, ammonia, hydrogen, magnesium derivative, nitrogen, tris(oxazolinyl)boratomagnesium, chemical binding, cross coupling reaction, nucleophilicity, stoichiometry ABSTRACT: We report magnesium-catalyzed cross-dehydrocoupling of SiÀH and NÀH bonds to give SiÀN bonds and H 2 . A number of silazanes are accessible using this method, as well as silylamines from NH 3 and silylhydrazines from N 2 H 4 . Kinetic studies of the overall catalytic cycle and a stoichiometric SiÀN bond-forming reaction suggest nucleophilic attack by a magnesium amide as the turnoverlimiting step.

Alkaline‐Earth‐Catalyzed Dehydrocoupling of Amines and Boranes

“…We suggest that subsequent and facile B-N coupling occurs through nucleophilic attack of the magnesium-bound anilide on the Lewis acidic 9-BBN substrate and rapid b-hydride transfer to the magnesium center via the borate intermediate E in as equence reminiscent of that deduced by both Sadow and co-workers and Sarazin and co-workers for ac losely related silane-amine dehydrocoupling and our previous observations of group 2-centered amine-borane dehydrocoupling catalysis. [17,13] Forthe reaction derived from HBpin, we suggest that the formation of an off-cycle borohydride similar to A is disfavored by the significantly reduced Lewis acidity of the borate ester substrate.A lthough facile aniline protonolysis will ensue under this regime,direct nucleophilic attack by the anilide on HBpin is also likely to be disfavored by the attenuated Lewis acidity of the borane.Wesuggest, therefore, that the second-order dependence on [I]implicates the action of afurther borohydrido magnesium species akin to A,and is necessary to deliver the HBpin substrate to the magnesium anilide.I nt his case,i ti sf easible that the formation of the [H 2 Bpin] À anion will facilitate the assembly of ab imetallic intermediate through the augmentation of the Lewis basicity of the pinacolate oxygen centers and ac onsequently enhanced facility for intermolecular Mg-O coordination.…”

Dehydrocoupling routes to element–element bonds catalysed by main group compounds

“…Silylation reactions of primary anilines including electron deficient anilines was also very effective at 60-70 1C to give the products in 88-97% yield. 48 The 4-coordinate magnesium pre-catalyst TO M MgMe [TO M = tris(4,4-dimethyl-2oxazolinyl)phenylborate] (Scheme 23) was found to be active in the cross-dehydrocoupling of N-H and Si-H bonds to give Si-N bonded products with the release of hydrogen. Whilst pyrroles were unreactive, diamines and indoles were active in the intermolecular heterodehydrocoupling with silanes.…”

Alkaline‐Earth‐Catalyzed Dehydrocoupling of Amines and Boranes

“…We suggest that subsequent and facile B–N coupling occurs through nucleophilic attack of the magnesium-bound anilide on the Lewis acidic 9-BBN substrate and rapid β-hydride transfer to the magnesium center via the borate intermediate E in a sequence reminiscent of that deduced by both Sadow and co-workers and Sarazin and co-workers for a closely related silane–amine dehydrocoupling and our previous observations of group 2-centered amine–borane dehydrocoupling catalysis. [17, 13]…”