Monomeric Organo Aluminum and Gallium Monohydroxides as Precursor for Homo and Hetero Bimetallic Oxides: Synthetic, Reactivity and Structural Investigations Including Gold(I) N heterocyclic Carbene Complexes

Abstract

The first part of my thesis deals with the syntheses of β-diketiminate Group 13 methyl chlorides of the general formula LM(Me)Cl (M = Al, Ga, In) [L = HC{(CMe)N(2,6-iPr2C6H3)}2]. These compounds represent examples of complexes where the metal atom is asymmetrically substituted to carry two different functional groups.Under given reaction conditions one of these two groups can be selectively substituted or replaced by another similar or different functional group. Utilizing this approach, a program of assembling stable lipophilic terminal hydroxides of Group 13 elements was embarked. Interestingly in the synthesis of hydroxo complex the procedure adapted was the use of N-heterocyclic carbenes as base which affords smooth transformation of M-Cl to M-OH in the presence of water. Thus, the tailor made organometallic hydroxides of the type LM(Me)OH (M = Al, Ga) have been isolated and structurally.The successful syntheses of hydroxo complexes led to explore their reaction chemistry. Consequently the organo-aluminum (gallium) hydroxides have been used as precursor for the synthesis of homo- and heterobimetallic oxides. The reaction of aluminum hydroxide with AlH3·NMe3 and GaH3·NMe3 have been carried out which afforded the first tetranuclear alumoxane hydride [LAl(Me)OAlH2]2 containing an {Al4O2} core and the gallium congener [LAl(Me)OGaH2]2 with an {Al2Ga2O2} core respectively.Further reaction of aluminum hydroxide with various metal amides like Sb(NMe2)3 and Sn[N(SiMe3)2]2 allowed to assemble heterodinuclear compounds [{LAl(Me)(μ-O)}2SbNMe2], [LAl(Me)(μ-O)]SnN(SiMe3)2, and [LAl(Me)(μ-O)]2Sn with Al-O-Sb and Al-O-Sn moieties respectively, which mimic in part the naturally occurring mixed oxides of aluminum (or tin). Reaction of LAl(Me)OH with strong base like LiN(SiMe3)2 leads to the deprotonation reaction to afford the corresponding lithium salt [LAl(Me)OLi]3·C6H14. Similarly, [LGa(Me)OLi]3·C6H14 was obtained when LGa(Me)OH was treated with LiN(SiMe3)2.In order to explore other heterobimetallic systems the reaction of LGa(Me)OH was carried out with Cp2ZrMe2 which affords a heterodimetallic derivative LGa(Me)(μ-O)Zr(Me)Cp2 containing Ga-O-Zr core.When LGa(Me)OH was treated with LnCp3 (Ln = Sm, Dy, Yb) the compounds LGa(Me) (μ-O)LnCp2 were expected as products under the elimination of CpH however, 1:1 adducts of composition LGa(Me)(μ OH)LnCp3 were formed and no elimination of CpH was observed. This is probably due to very mild acidity of the hydroxide hydrogen in LGa(Me)OH.The last part of my thesis describes a single-step synthesis of N-heterocyclic carbene complexes of gold (I) chlorides. Accordingly, the reaction of Au(CO)Cl with N,N -bis-tert-butylimidazol-2-ylidene (CtBu) or N,N -bis-mesitylimidazol-2-ylidene (CMes) substitutes the CO ligand and generates the corresponding carbene gold chloride adducts, CtBuAuCl and CMesAuCl. These complexes have been used further to assemble terminal acetylides of gold(I). Therefore the reaction of CtBuAuCl and CMesAuCl with ethynylmagnesium chloride leads to the formation of CtBuAuC≡CH·C7H8 and CMesAuC≡CH. The latter compounds represent the first example of N-heterocyclic carbene gold(I) ethynyl complexes that contains a terminal -C≡CH group.