Bonding in Barium Boryloxides, Siloxides, Phenoxides and Silazides: A Comparison with the Lighter Alkaline Earths

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 numbers ranging between 2 4. The identity bridging ligand dimers [Ba(μ2-X1)(X2)]2 depends largely on given pair ligands X1 X2. Experimentally, propensity to fill position increases according [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 overall expression 3 properties: steric constraints, electronic density σ- π-donating capability negatively charged atom, ability generate Ba ⋅ F, C(π) H−C secondary interactions. comparison structural motifs [Ae{μ2-N(SiMe3)2}(OB{CH(SiMe3)2}2)]2 (Ae = Mg, Ca, Sr Ba) suggest that these observations may be extended all alkaline earths. DFT calculations highlight prevailing ionic character ligand-Ae bonding compounds. Ae-ligand bond encourages coordination, whereas number controlled factors. computations also indicate dimers, predilection vs. terminal positions dictated establish interactions metals ligands.