Bonding in Barium Boryloxides,Siloxides, Phenoxides and Silazides: A Comparison with the Lighter Alkaline Earths |
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| Authors: | Erwann Le Coz Joanna Hammoud Dr Thierry Roisnel Marie Cordier Dr Vincent Dorcet Dr Samia Kahlal Prof Dr Jean-François Carpentier Prof Dr Jean-Yves Saillard Dr Yann Sarazin |
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| Institution: | Univ Rennes, CNRS ISCR, Institut des Sciences Chimiques de Rennes)-UMR 6226, 35000 Rennes, France |
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| Abstract: | Barium complexes ligated by bulky boryloxides OBR2]− (where R=CH(SiMe3)2, 2,4,6-iPr3-C6H2 or 2,4,6-(CF3)3-C6H2), siloxide OSi(SiMe3)3]−, and/or phenoxide O-2,6-Ph2-C6H3]−, have been prepared. A diversity of coordination patterns is observed in the solid state for both homoleptic and heteroleptic complexes, with coordination numbers ranging between 2 and 4. The identity of the bridging ligand in heteroleptic dimers Ba(μ2-X1)(X2)]2 depends largely on the given pair of ligands X1 and X2. Experimentally, the propensity to fill the bridging position increases according to OB{CH(SiMe3)2}2)]−<N(SiMe3)2]−<OSi(SiMe3)3]−<O(2,6-Ph2-C6H3)]−<OB(2,4,6-iPr3-C6H2)2]−. This trend is the overall expression of 3 properties: steric constraints, electronic density and σ- and π-donating capability of the negatively charged atom, and ability to generate Ba ⋅ ⋅ ⋅ F, Ba ⋅ ⋅ ⋅ C(π) or Ba ⋅ ⋅ ⋅ H−C secondary interactions. The comparison of the structural motifs in the complexes Ae{μ2-N(SiMe3)2}(OB{CH(SiMe3)2}2)]2 (Ae = Mg, Ca, Sr and Ba) suggest that these observations may be extended to all alkaline earths. DFT calculations highlight the largely prevailing ionic character of ligand-Ae bonding in all compounds. The ionic character of the Ae-ligand bond encourages bridging coordination, whereas the number of bridging ligands is controlled by steric factors. DFT computations also indicate that in Ba(μ2-X1)(X2)]2 heteroleptic dimers, ligand predilection for bridging vs. terminal positions is dictated by the ability to establish secondary interactions between the metals and the ligands. |
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| Keywords: | alkaline-earth metals barium bonding analysis density functional calculations O-based ligands |
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