Hypervalent Hydrosilicates Connected to Light Alkali Metal Amides: Synthesis, Structure, and Hydrosilylation Catalysis

Abstract

When light alkali metal amides [M(Me TACD)] (M=Li, Na, K; (Me TACD)H=1,4,7-trimethyl-1,4,7,10-tetraazacyclododecane) were treated with H SiPh in THF, [M{(H SiPh )Me TACD}(thf) ] containing a pendant hypervalent dihydridosilicate were formed and characterized by elemental analysis, NMR/IR spectroscopy, and single-crystal X-ray crystallography. The lithium complex catalyzed the hydrosilylation of styrene derivatives under mild conditions with anti-Markovnikov regioselectivity.

Calix[4]pyrrole Hydridosilicate: The Elusive Planar Tetracoordinate Silicon Imparts Striking Stability to Its Anionic Silicon Hydride

“…IR spectroscopy for salts [ 1 -H – ]­[M + ] showed distinct stretching modes of the Si–H bonds at 2176 cm –1 [K+] or 2243 cm –1 [PPh 4 + ]. Such values are much higher compared to other hydridosilicates (1550–1970 cm –1 ), ,, but rather match with those of Si–H bonds in neutral silanes or aminosilanes (2100–2200 cm –1 ). ,, The IR-spectra thus indicate a remarkably strong Si–H bond in [ 1 -H – ].…”

“…The archetypal SiH 5 – or SiH 6 2– anions have only been observed under gas phase or high-pressure conditions, respectively. − Recently, hydridosilicates were demonstrated to even react with C sp2 -F bonds in hydrodefluorination reactions . Already neutral silanes turn into effective reductants upon transient coordination of neutral or anionic donors. ,,− Besides being potent hydride donors, hydridosilicates are also involved in fundamentally different reactivity modes, like acting as strong bases, ,− electron or hydrogen atom donors, − making valuable dehydrogenative coupling processes feasible. − A reason for their high reactivity is the low hydride ion affinity of neutral silanes, which is indeed among the lowest known for neutral molecules, comparable with H 2 O or benzene. ,,, By consequence, the isolation of hydridosilicates needs special precautions, like the stabilization of the Si–H bonds by agostic interactions with transition metals. − However, also a small number of nontransition metal salts of [HSiR 4 ] − or [H 2 SiR 3 ] − (R = Ar, OR, F) have been observed spectroscopically. ,,,,− The first structural characterization of a hydridosilicate, H 2 SiPh 3 – , was achieved only in 2001, followed by some related derivatives. − A general requirement were strict anhydrous conditions to prevent immediate hydrolysis of the activated and unstable Si–H bonds.…”

Macrocyclic Ligands for Molecular Hydrides of s-Block Metals

“…6)) (Fig. 3) , 15 were formed when alkali metal amides [(Me 3 TACD)M] n (M = Li, Na, K) were treated with Ph 2 SiH 2 .…”

The Facile Synthesis of Lithium 2‐R‐Hydroquinolinide Complexes and Their High Activity toward ROP of ε‐Caprolactone

“…However, these simple lithium complexes could not control the polymerization well because of transesterification reaction. Subsequently, lithium complexes modified by ancillary ligands, such as iminophenoxide, Schiff base, β‐ketoiminate, bis‐iminopyrrolide, benzylphosphines, and dihydridosilicate, have been widely used as catalysts for the ring opening polymerization of cyclic esters. According to the literature, the steric and geometric properties of the ligands or the solvents used can influence catalytic effect of these lithium complexes in polymerization , …”