Synthesis and Structure of Alkaline Earth Bis{hydrido-tris(3,5-diisopropyl-pyrazol-1-yl)borate} Complexes: Ae(TpiPr2)2 (Ae = Mg, Ca, Sr, Ba)
- 21 January 2021
- journal article
- research article
- Published by American Chemical Society (ACS) in Inorganic Chemistry
- Vol. 60 (3), 1877-1884
- https://doi.org/10.1021/acs.inorgchem.0c03294
Abstract
The synthesis and structural characterization of Ae(TpiPr2)2 (Ae = Mg, Ca, Sr, Ba; TpiPr2 = hydrido-tris(3,5-diisopropyl-pyrazol-1-yl)borate) are reported. In the crystalline state, the alkaline earth metal centers are six-coordinate, even the small Mg2+ ion, with two κ3-N,N′,N′′-TpiPr2 ligands, disposed in a bent arrangement (B···Ae···B < 180°). However, contrary to the analogous Ln(TpiPr2)2 (Ln = Sm, Eu, Tm, Yb) compounds, which all exhibit a bent-metallocene structure close to Cs symmetry, the Ae(TpiPr2)2 compounds exhibit a greater structural variation. The smallest Mg(TpiPr2)2 has crystallographically imposed C2 symmetry, requiring both bending and twisting of the two TpiPr2 ligands, while with the similarly sized Ca2+ and Sr2+, the structures are back toward the bent-metallocene Cs symmetry. Despite the structural variations, the B···M···B bending angle follows a linear size-dependence for all divalent metal ions going from Mg2+ to Sm2+, decreasing with increasing metal ion size. The complex of the largest metal ion, Ba2+, forms an almost linear structure, B···Ba···B 167.5°. However, the “linearity” is not due to the compound approaching the linear metallocene-like geometry, but is the result of the pyrazolyl groups significantly tipping toward the metal center, approaching “side-on” coordination. An attempt to rationalize the observed structural variations is made.Funding Information
- University of Alberta
- Otto-von-Guericke-Universit??t Magdeburg (N/A)
- NSERC Canada
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