Extremely Bulky Amido and Amidinato Complexes of Boron and Aluminium Halides: Synthesis and Reduction Studies

An extremely bulky secondary amine, HN(Ar-dagger)(SiPr3i) HL dagger (Ar-dagger = C6H2{C(H)Ph-2}(2)Pr-i-2,6,4) has been synthesised and deprotonated with KH in toluene, to afford the potassium amide [KL dagger(eta(6)-toluene)], which was structurally authenticated. Reaction of this with BBr3 and AlBr3, reproducibly gave the crystallographically characterised amido bromo-borane, [(LB)-B-dagger(H)Br], and aluminacycle, [AlBr2{kappa(2)-C,N-N(H)(SiPr3i){C6H2[CPh2][C(H)Ph-2]Pr-i-2,6,4}}], respectively, via ligand C-H activation processes. The known secondary amines, HN(Dip)(Mes) (HLMes) and HN(Dip)(Trip) (HLTrip) (Dip = 2,6-diisopropylphenyl, Mes = mesityl, Trip = 2,4,6-triisopropylphenyl), have been structurally characterised, and deprotonated to give the in situ generated lithium amides, [Li(L-Mes)] and [Li(L-Trip)]. Reaction of these with BBr3 and AlBr3 has given the amido group 13 element halide complexes, [(LBBr2)-B-Mes] and [LAlBr2(THF)] (L = L-Mes or L-Trip), the crystal structures of all of which have been determined. Synthetic routes to two new bulky amidine pro-ligands, ArN = C(Bu-t)N(H)Ar, Ar = C6H2C(H)Ph-2}(2)Me-2,6,4 (Piso*H) or C6H2Pr2i(CPh3)-2,6,4 (Piso '' H), have been developed, and the compounds crystallographically characterised. Deprotonation of Piso '' H gave the potassium amidinate, [K(Piso '')], which was reacted with BBr3 to give [(Piso '')BBr2]. Reaction of Piso '' H with AlMe3 afforded [(Piso '')AlMe2], which, when treated with I-2 yielded [(Piso '')AlI2], the crystal structure of which was determined. Reductions of all of the prepared amido and amidinato group 13 element(III) halide complexes were attempted using a variety of reducing reagents, with a view to prepare boron(I) or aluminium(I) complexes. While these were not successful, this study does offer synthetic inorganic chemists a variety of new very bulky anionic N-donor ligands, and boron/aluminium halide complexes thereof, for use in their own research.