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.
Coordinatively saturated To(M)MgMe (1; To(M) = tris(4,4-dimethyl-2-oxazolinyl)phenylborate) is an active precatalyst for intramolecular hydroamination/cyclization at 50 °C. The empirical rate law of -d[substrate]/dt = k'(obs)[Mg](1)[substrate](1) and Michaelis-Menten-type kinetics are consistent with a mechanism involving reversible catalyst-substrate association prior to cyclization. The resting state of the catalyst, To(M)MgNHCH(2)CR(2)CH(2)CH═CH(2) [R = Ph, Me, -(CH(2))(5)-], is isolable, but isolated magnesium amidoalkene does not undergo unimolecular cyclization at 50 °C. However, addition of trace amounts of substrate allows cyclization to occur. Therefore, we propose a two-substrate, six-center transition state involving concerted C-N bond formation and N-H bond cleavage as the turnover-limiting step of the catalytic cycle.
The first example of a new class of oxazoline-based scorpionate ligand, tris(4,4-dimethyl-2-oxazolinyl)phenyl borate, [ToM]−, is prepared by reaction of 2-lithio-4,4-dimethyl-2-oxazolide and 0.3 equiv of dichlorophenylborane. The steric bulk of this ligand is greater than that of tris (3,
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