Yousif Maryam, Cabelof Alyssa C, Martin Philip D, Lord Richard L, Groysman Stanislav
Department of Chemistry, Wayne State University, 5101 Cass Ave, Detroit, MI 48202, USA.
Department of Chemistry, Grand Valley State University, Allendale, MI 49401, USA.
Dalton Trans. 2016 Jun 14;45(24):9794-804. doi: 10.1039/c6dt00279j.
In this paper, we report the synthesis and reactivity of a rare mononuclear chromium(ii) bis(alkoxide) complex, Cr(OR')2(THF)2, that is supported by a new bulky alkoxide ligand (OR' = di-t-butyl-(3,5-diphenylphenyl)methoxide). The complex is prepared by protonolysis of square-planar Cr(N(SiMe3)2)2(THF)2 with HOR'. X-ray structure determination disclosed that Cr(OR')2(THF)2 features a distorted seesaw geometry, in contrast to nearly all other tetra-coordinate Cr(ii) complexes, which are square-planar. The reactivity of Cr(OR')2(THF)2 with aldehydes, ketones, and carbon dioxide was investigated. Treatment of Cr(OR')2(THF)2 with two equivalents of aromatic aldehydes ArCHO (ArCHO = benzaldehyde, 4-anisaldehyde, 4-trifluorbenzaldehyde, and 2,4,6-trimethylbenzaldehyde) leads cleanly to the formation of Cr(iv) diolate complexes Cr(OR')2(O2C2H2Ar2) that were characterized by UV-vis and IR spectroscopies and elemental analysis; the representative complex Cr(OR')2(O2C2H2Ph2) was characterized by X-ray crystallography. In contrast, no reductive coupling was observed for ketones: treatment of Cr(OR')2(THF)2 with one or two equivalents of benzophenone forms invariably a single ketone adduct Cr(OR')2(OCPh2) which does not react further. QM/MM calculations suggest the steric demands prevent ketone coupling, and demonstrate that a mononuclear Cr(iii) bis-aldehyde complex with partially reduced aldehydes is sufficient for C-C bond formation. The reaction of Cr(OR')2(THF)2 with CO2 leads to the insertion of CO2 into a Cr-OR' bond, followed by complex rearrangement to form a diamagnetic dinuclear paddlewheel complex Cr2(O2COR')4(THF)2, that was characterized by NMR, UV-vis, and IR spectroscopy, and X-ray crystallography.
在本文中，我们报道了一种罕见的单核铬（II）双（醇盐）配合物Cr(OR')2(THF)2的合成及反应活性，该配合物由一种新型大位阻醇盐配体（OR' = 二叔丁基 -（3,5 - 二苯基苯基）甲醇盐）支撑。该配合物通过用HOR'对平面正方形Cr(N(SiMe3)2)2(THF)2进行质子解反应制备。X射线结构测定表明，与几乎所有其他平面正方形的四配位Cr（II）配合物不同，Cr(OR')2(THF)2具有扭曲的跷跷板几何构型。研究了Cr(OR')2(THF)2与醛、酮和二氧化碳的反应活性。用两当量的芳香醛ArCHO（ArCHO = 苯甲醛、4 - 茴香醛、4 - 三氟苯甲醛和2,4,6 - 三甲基苯甲醛）处理Cr(OR')2(THF)2可顺利形成Cr（IV）二醇盐配合物Cr(OR')2(O2C2H2Ar2)，通过紫外可见光谱、红外光谱和元素分析对其进行了表征；代表性配合物Cr(OR')2(O2C2H2Ph2)通过X射线晶体学进行了表征。相比之下，未观察到酮的还原偶联反应：用一当量或两当量的二苯甲酮处理Cr(OR')2(THF)2总是形成单一的酮加合物Cr(OR')2(OCPh2)，且该加合物不再进一步反应。量子力学/分子力学计算表明，空间位阻需求阻止了酮的偶联反应，并证明具有部分还原醛的单核Cr（III）双醛配合物足以形成C - C键。Cr(OR')2(THF)2与CO2的反应导致CO2插入Cr - OR'键中，随后配合物重排形成抗磁性的双核桨轮配合物Cr2(O2COR')4(THF)2，通过核磁共振、紫外可见光谱、红外光谱和X射线晶体学对其进行了表征。
