Synthesis, Structural Studies and Reactivity of Monomeric Organo Aluminum and Gallium Amides, Hydrogensulfides and Hydroxides Using N-Heterocyclic Carbene: Precursors for Heterobimetallic Systems

Abstract

The first part of this work was focused on reactions of elemental sulfur, selenium and tellurium with LAlH 2. Phosphine catalysis has significant influence on the reaction products and such reactions led to the isolation of LAl(µ-Se)2AlL (2), LAl(µ-Te)2AlL (3) and unique LAl(SH)2 (1). Reaction of 1 and LAlH2 produces LAl(µ-S)2AlL (4) as the only product.Furthermore, lithiation of 1 with LiN(SiMe3)2 in 1:1 and 1:2 molar ratios gave exclusive mono- and dilithium salts LAl(SH)(SLi) (6) and LAl(SLi)2 (5). Their reactions with Cp2MCl2 (M = Ti, Zr) resulted in the formation of the first mixed metal sulfides containing aluminum: LAl(µ-S)2MCp2 (7 M = Ti, 8 M = Zr).Deprotonation of the SH groups in 1 was achieved by use of N-heterocyclic carbenes as bases and generated the mono- and dicarbene salts CtH+[LAl(SH)(S)]- (9), CmH+2[LAl(S)2]2- (10) and CmH+[LAl(SH)(S)]- (11), respectively. These carbene salts showed to be excellent precursor for the formation of mixed sulfides based on aluminum and silicon, LAl(SSiMe3)2 (12), LAl(µ-S)2SiMe2 (13), and LAl(SSiMe2)2O (14). Thus, their synthesis was possible only through direct reaction of organoaluminum halides and lithium salts of silanethiols.In the second part, innovative synthetic routes using N-heterocyclic carbenes as proton scavengers were developed for the conversion of the metal halides to the corresponding hydroxides and amides. Reactions of LAlI2 with two equivalents of N,N'-bis-mesitylimidazolyl carbene and two equivalents of H2O and NH3, respectively, led in the first case to the previously described LAl(OH)2 (15) and LAl(NH2)2 (16) containing two terminal NH2 groups. The same methodology was used also for the preparation of hydroxides and amides: LAl(NH2)Cl (17), LAl(NH2)Me (18), LGa(NH2)2 (19) and LGa(OH)2 (20).The last part of this thesis was focused on reactivity studies of amides, hydrogensulfides, and heterobimetallic sulfides toward H2O and H2S and the mechanisms are discussed.Compounds 18 and 21 react with H2O under formation of LAl(OH)Me. Furthermore, addition of H2O to the THF/CH2Cl2 solution of LAl(µ-S)2MCp2 (7 M = Ti, 8 M = Zr) resulted in the formation of unprecedented heterobimetallic oxide-hydroxide-hydrogensulfides LAl(OH)(µ-O)M(SH)Cp2 (22, M = Ti; 23, M = Zr).