Inorganic Chemistry, Vol.56, No.24, 14979-14990, 2017
Silyl-Hydrosilane Exchange at a Magnesium Triphenylsilyl Complex Supported by a Cyclen-Derived NNNN-Type Macrocyclic Ligand
The magnesium triphenylsilyl complex [(Me(3)TACD)Mg(SiPh3)] (2) was synthesized from magnesium bis(triphenylsilyl) [Mg(SiPh3)(2)(THF)(2)]center dot THF (1; THF = tetrahydrofuran) and the NNNN-type macrocyclic amidotriamine proligand (Me(3)TACD)H ((Me(3)TACD)H = Me-3-aneN(4) = 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 [(Me(3)TACD center dot 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 [(Me(3)TACD center dot AlEt3)MgEt] with H3SiPh gave [(Me(3)TACD-AlEt3)MgH] (4), albeit not in a reproducible manner. The silyl-hydrosilane exchange allows access to other magnesium silyls of the type [(Me(3)TACD)Mg(SiR'(3))] (5a: SiR'(3) = SiH2Ph; 5b: SiR'(3) = SiHPh2) and [(Me(3)TACD center dot 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 (K-eq approximate to 1). Protonolysis of 2 with Bronsted acids (HX) 2,5-di-tert-butylphenol, phenylacetylene, acetophenone, aniline, and triethylammonium chloride each gave a compound [(Me(3)TACD)-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.