Synthesis and structural characterization of tris(pyrazolyl)hydroaluminate and tris(pyrazolyl)hydrogallate lithium compounds

Abstract

The tris(pyrazolyl)hydroaluminate derivatives, [HAlTp Bu t ,Me ]Li and {[HAlTp Me 2 ]Li} 2 , have been synthesized via the reactions of LiAlH 4 with 3-tert-butyl-5methylpyrazole and 3,5-dimethylpyrazole, respectively, while the tris(pyrazolyl)hydrogallate counterparts, [HGaTp Bu t ,Me ]Li and {[HGaTp Me 2 ]Li} 2 , are obtained from the corresponding reactions with LiGaH 4. X-ray diffraction studies demonstrate that the 3-tert-butyl-5-methylpyrazolyl derivatives, [HAlTp Bu t ,Me ]Li and [HGaTp Bu t ,Me ]Li, are monomeric with lithium in a trigonal coordination environment, whereas the less sterically demanding 3,5-dimethylpyrazolyl derivatives, {[HAlTp Me 2 ]Li} 2 and {[HGaTp Me 2 ]Li} 2 , are dimeric. In addition to the tris(pyrazolyl)hydroaluminate derivative, [HAlTp Bu t ,Me ]Li, the tetrakis derivative, [(pz Bu t ,Me)AlTp Bu t ,Me ]Li, has also been isolated. X-ray diffraction studies demonstrate that [(pz Bu t ,Me)AlTp Bu t ,Me ]Li, as obtained from solutions in benzene, exists as a monomer in the solid state with tridentate coordination, whereas crystals obtained from THF exhibit a bidentate coordination mode, which is supplemented by coordination of THF, i.e. [(pz Bu t ,Me) 2 AlBp Bu t ,Me ]Li(THF). NMR spectroscopic studies, however, indicate that [(pz Bu t ,Me)AlTp Bu t ,Me ]Li is fluxional in both benzene and THF solutions.

Molecular Main Group Metal Hydrides

“…As with carbon-supported aluminum hydride systems, a common reactivity pathway is the hydroalumination of organic π-bonds. Given the plethora of new N -donor aluminum hydride systems reported in the past two decades, ,− this section will aim to focus on the new bonding motifs and reactivity pathways uncovered in this area.…”

Bis- and Tris(2-oxobenzimidazolyl)hydroborato Complexes of Sodium and Thallium: New Classes of Bidentate and Tridentate Oxygen Donor Ligands

“…Following Trofimenko’s 1996 report, the reactivity of alkali metal borohydrides, MBH 4 (M = Li, Na, K), towards pyrazoles, Hpz R,R′ , has been employed extensively as a general method to afford a wide variety of [Bp R,R′ ] and [Tp R,R′ ] ligands. ,, This approach was adapted by Reglinsiki and Spicer in 1996 for the synthesis of the [ S 3 ] donor tris­(mercaptoimidazolyl)­hydroborato ligand, [Tm Me ] (Figure ), via the reaction of NaBH 4 with 2-mercapto-1-methylimidazole (methimazole) . A variety of other [Tm R ] ligands that feature other substituents, e.g., Me, Et, Bu t , 1-Ad, Bz, Cy, Ph, p -Tol, o -Tol, p -C 6 H 4 Pr i , 2,6-C 6 H 3 Me 2 , 2,6-C 6 H 3 Pr i 2 , Mes, and 2-biphenyl, have been subsequently reported, , as have derivatives which feature benzannulated rings, [Tm RBenz ] .…”

Cyclooctadiene Rh(I) Bis- and Tris(pyrazolyl)aluminate Complexes and Their Catalytic Activity on the Polymerization of Phenylacetylene

“…In stark contrast to the ubiquitous poly(pyrazolyl)borates [1][2][3][4] very few reports of the heavier aluminum analogs are known [5][6] . In addition to easy tuning of steric and electronic properties promoted by the rich pyrazole chemistry, the change from boron to aluminum would be highly valuable due to the availability of ligands with wider bites and redox activity.…”

“…In stark contrast to the ubiquitous poly­(pyrazolyl)­borates, − very few reports of the heavier aluminum analogues are known. , In addition to easy tuning of steric and electronic properties promoted by the rich pyrazole chemistry, the change from boron to aluminum would be highly valuable due to the availability of ligands with wider bites and redox activity. Although the first report on such a ligand system dates to the 1970s, it was not until a few years ago that one of us reported the first authenticated sodium poly­(pyrazolyl)­aluminate exhibiting Al–CH 3 bonds .…”

“…Although the first report on such a ligand system dates to the 1970s, it was not until a few years ago that one of us reported the first authenticated sodium poly­(pyrazolyl)­aluminate exhibiting Al–CH 3 bonds . A remarkable series of poly­(pyrazolyl)­aluminates with Al–H bonds were also reported, , with the aim of transferring the aluminate to different metal halides. Significantly, the successful transfer of the hydrotris­(pyrazolyl)­aluminate [HAl­(Ph 2 pz) 3 ] − to a Zn center was accompanied by the undesired hydride transfer from aluminum to zinc giving [{HAl­(Ph 2 pz) 3 }­ZnH].…”