RESUMEN
A magnesium hydride cation [(L)MgH]+ supported by a macrocyclic ligand (L = Me4TACD; 1,4,7,10-tetramethyl-1,4,7,10-tetraazacyclododecane) has been prepared by partial protonolysis of a mixed amide hydride [(L)MgH2Mg{N(SiMe3)2}2] and shown to undergo a variety of reactions with unsaturated substrates, including pyridine.
RESUMEN
A series of heteroleptic monoamido-monohydrido-dialkylaluminate complexes of general formula [iBu2 AlTMPHLiâ donor] were synthesized and characterised in solution and in the solid state. Applying these complexes in catalytic hydroboration reactions with representative aldehydes and ketones reveals that all are competent, however a definite donor substituent effect is discernible. The bifunctional nature of the complexes is also probed by assessing their performance in metallation of a triazole and phenylacetylene and addition across pyrazine. These results lead to an example of phenylacetylene hydroboration, which likely proceeds via deprotonation, rather than insertion as observed with the aldehydes and ketones. Collectively, the results emphasise that reactivity is strongly influenced by both the mixed-metal constitution and mixed-ligand constitution of the new aluminates.
RESUMEN
The magnesium triphenylsilyl complex [(Me3TACD)Mg(SiPh3)] (2) was synthesized from magnesium bis(triphenylsilyl) [Mg(SiPh3)2(THF)2]·THF (1; THF = tetrahydrofuran) and the NNNN-type macrocyclic amidotriamine proligand (Me3TACD)H ((Me3TACD)H = Me3[12]aneN4 = 1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane). Treating 2 with AlR3 (R = Me, Et) gave the magnesium triphenylsilyl complexes with "blocked" amido function [(Me3TACD·AlR3)Mg(SiPh3)] (3a: R = Me; 3b: R = Et). Instead of forming a Mg-H bond upon reaction with dihydrogen or hydrosilanes, 2 and 3a,b underwent rapid silyl-silane exchange with hydrosilanes. Treating the ethyl complex [(Me3TACD·AlEt3)MgEt] with H3SiPh gave [(Me3TACD·AlEt3)MgH] (4), albeit not in a reproducible manner. The silyl-hydrosilane exchange allows access to other magnesium silyls of the type [(Me3TACD)Mg(SiR'3)] (5a: SiR'3 = SiH2Ph; 5b: SiR'3 = SiHPh2) and [(Me3TACD·AlR3)Mg(SiR'3)] (6a: SiR'3 = SiH2Ph, R = Me; 6b: SiR'3 = SiH2Ph, R = Et; 7a: SiR'3 = SiHPh2, R = Me; 7b: SiR'3 = SiHPh2, R = Et). The reaction of 2 with H2SiMePh in THF at room temperature resulted in an equilibrium (Keq ≈ 1). Protonolysis of 2 with Brønsted acids (HX) 2,5-di-tert-butylphenol, phenylacetylene, acetophenone, aniline, and triethylammonium chloride each gave a compound [(Me3TACD)Mg(X)] with the conjugated base coordinated at the magnesium along with HSiPh3. The magnesium silyls 1, 2, and 7b as well as the magnesium hydride 4 contain a distorted square-pyramidal magnesium center according to single-crystal X-ray diffraction.