Liebing P, Harmgarth N, Yang Y, McDonald R, Engelhardt F, Kühling M, Edelmann FT, Takats J. Synthesis and Structure of Alkaline Earth Bis{hydrido-tris(3,5-diisopropyl-pyrazol-1-yl)borate} Complexes: Ae(Tp
iPr2)
2 (Ae = Mg, Ca, Sr, Ba).
Inorg Chem 2021;
60:1877-1884. [PMID:
33476516 DOI:
10.1021/acs.inorgchem.0c03294]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
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.
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