Low-Coordinate Chromium Siloxides: The “Box” [Cr(μ-Cl)(μ-OSi<sup>t</sup>Bu<sub>3</sub>)]<sub>4</sub>, Distorted Trigonal [(<sup>t</sup>Bu<sub>3</sub>SiO)<sub>3</sub>Cr][Na(benzene)] and [(<sup>t</sup>Bu<sub>3</sub>SiO)<sub>3</sub>Cr][Na(dibenzo-18-c-6)], and Trigonal (<sup>t</sup>Bu<sub>3</sub>SiO)<sub>3</sub>Cr
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Treatment of CrCl2(THF)2 with NaOSitBu3 afforded the tetrameric “box” [Cr(μ-Cl)(μ-OSitBu3)]4 (1, X-ray). THF cleaved 1 to provide trans-(silox)ClCr(THF)2 (2), whereas degradation of 1 with 4-picoline caused disproportionation and the generation of trans-Cl2Cr(4-pic)2 and trans-(silox)2Cr(4-pic)x (n = 2, 3; 3, 3-4-pic). Chromous centers in 1 were antiferromagnetically coupled, and density functional calculations on the high-spin (multiplicity = 17) model [Cr(μ-Cl)(μ-OH)]4 (1‘) revealed that its singly occupied 3d orbitals spanned an energy range of ∼2 eV. The addition of 8 equiv of Na(silox) to 1 yielded [(tBu3SiO)Cr(μ-OSitBu3)2]Na·C6H6 (4, Y shaped, ∠OCrO(Na) = 91.28(7)°), and treatment of 4 with dibenzo-18-crown-6 produced [(silox)3Cr][Na(dibenzo-18-crown-6)] (5, ∠OCrO = ∼120°, (120 + α)°, (120 − α)°). Calculations of [(tBu3SiO)Cr(μ-OSitBu3)2]Na (4‘) and Cr(silox)3- (5‘) provided reasonable matches with the experimental geometries (X-ray). The trigonal chromic derivative (silox)3Cr (6) was synthesized from CrCl3(THF)3 for structural and calculational comparisons to the chromous derivatives.
