Tris(pyrazolyl)borate Complexes of the Alkaline-Earth Metals: Alkylaluminate Precursors and Schlenk-Type Rearrangements
dataset
posted on 2016-02-21, 13:55 authored by Olaf Michel, H. Martin Dietrich, Rannveig Litlabø, Karl W. Törnroos, Cäcilia Maichle-Mössmer, Reiner AnwanderA series of 3,5-substituted tris(pyrazolyl)borate (TpR,Me; R = Me, Ph, tBu) complexes of the alkaline-earth
metals (Mg, Ca, Ba) was synthesized by salt metathesis reactions.
The influence of different organometallic precursors on Schlenk-type
rearrangement reactions was studied, putting emphasis on the metal
size and the steric encumbrance of the Tp ligands. Magnesium alkyls
MgR2 (R = AlMe4, CH3) react with
KTpR,Me to form the heteroleptic complexes (TpMe,Me)Mg(CH3), (TptBu,Me)Mg(CH3), and (TpMe,Me)Mg(AlMe4). The latter
tetramethylaluminate complex can also be obtained by treatment of
TpMe,MeMg(CH3) with an excess of trimethylaluminum.
The formally six-coordinate cyclopentadienyl derivative (C5Me5)Mg(Me)(thf)2 is synthesized from MeMgBr
and 1 equiv of K(C5Me5). Equimolar reactions
of the tetraethylaluminates [M(AlEt4)2]n of the heavier alkaline-earth metals calcium
and barium with KTpR,Me give the homoleptic complexes of
Ca(TpR,Ph)2 and Ba(TpR,Me)2. Heterotrimetallic [BaK(AlEt4)3]n is identified as a ligand rearrangement product
and can be independently obtained by adding [K(AlEt4)]n to [Ba(AlEt4)2]n. Treatment of Ba[N(SiMe3)2]2(thf)2 with KTpMe,Me generates
the heteroleptic complex (TpMe,Me)Ba[N(SiMe3)2](thf)2. All complexes are fully characterized
including X-ray structure analyses.
