On the analysis of the Cr-Cr multiple bond in several classes of dichromium compounds.
On the analysis of the Cr-Cr multiple bond in several classes of dichromium compounds.
复制标题
几类二铬化合物中 Cr-Cr 多重键的分析。
作者：
G. La Macchia;G. Li Manni;T. Todorova;M. Brynda;F. Aquilante;B. Roos;L. Gagliardi
自从 Power 及其同事于 2005 年在 Ar'CrCrAr' (CrCr = 1.835 A) 中发现正式的五重键以来，人们一直致力于分离具有五重键特征的二铬物质。在本研究中，我们研究了几种最近合成的二铬物质的电子构型，其配体使用氮来协调金属中心。将 Power 化合物和 Cr(2)-二氮杂二烯 (1) (CrCr = 1.803 A) 的双金属键距与 Cr(2)(mu-eta(2)-ArNC(R)NAr)(2) (2) (CrCr = 1.746 A; R = H, Ar = 2,6-Et(2)C(6)H(3)) 的双金属键距进行比较， Cr(2)(mu-eta(2)-Ar(Xyl)NC(H)NAr(Xyl))(3) (3) (CrCr = 1.740(还原型)/1.817(中性) A；Ar(Xyl)= 2,6-C(6)H(3)-(CH(3))(2)), Cr(2)(mu-eta(2)-TippPyNMes)(2) (4) (CrCr = 1.749 A；TippPyNMes = 6-(2,4,6-三异丙基苯基)吡啶-2-基(2,4,6-三甲基苯基)酰胺)，和 Cr(2)(mu-eta(2)-DippNC(NMe(2))N-Dipp)(2) (5) (CrCr = 1.729 A，Dipp = 2,6-i-Pr(2)C(6)H(3))。我们表明，CrCr 键长和有效键级 (EBO) 之间的相关性受到配体性质以及配体结构（例如配位氮的性质）造成的空间位阻的强烈影响。在同一组配体内建立了 EBO 和 CrCr 键距之间的线性相关性。因此，基于脒基、氨基吡啶基和胍基配体的 CrCr 物质具有与 Ar'CrCrAr' 化合物类似的键模式。与后一种物质不同，二铬二氮杂二烯络合物的特点是涉及 Cr-Npi 相互作用的不同键合模式，导致与短金属-金属键距相关的较低键序。在这种情况下，较短的 CrCr 距离很可能是二氮杂二烯配体施加的约束的结果，这意味着 Cr(2)N(4) 核具有更紧密的 CrCr 相互作用。
Since the discovery of a formal quintuple bond in Ar'CrCrAr' (CrCr = 1.835 A) by Power and co-workers in 2005, many efforts have been dedicated to isolating dichromium species featuring quintuple-bond character. In the present study we investigate the electronic configuration of several, recently synthesized dichromium species with ligands using nitrogen to coordinate the metal centers. The bimetallic bond distances of Power's compound and Cr(2)-diazadiene (1) (CrCr = 1.803 A) are compared to those found for Cr(2)(mu-eta(2)-ArNC(R)NAr)(2) (2) (CrCr = 1.746 A; R = H, Ar = 2,6-Et(2)C(6)H(3)), Cr(2)(mu-eta(2)-Ar(Xyl)NC(H)NAr(Xyl))(3) (3) (CrCr = 1.740(reduced)/1.817(neutral) A; Ar(Xyl)= 2,6-C(6)H(3)-(CH(3))(2)), Cr(2)(mu-eta(2)-TippPyNMes)(2) (4) (CrCr = 1.749 A; TippPyNMes = 6-(2,4,6-triisopropylphenyl)pyridin-2-yl (2,4,6-trimethylphenyl)amide), and Cr(2)(mu-eta(2)-DippNC(NMe(2))N-Dipp)(2) (5) (CrCr = 1.729 A, Dipp = 2,6-i-Pr(2)C(6)H(3)). We show that the correlation between the CrCr bond length and the effective bond order (EBO) is strongly affected by the nature of the ligand, as well as by the steric hindrance due to the ligand structure (e.g., the nature of the coordinating nitrogen). A linear correlation between the EBO and CrCr bond distance is established within the same group of ligands. As a result, the CrCr species based on the amidinate, aminopyridinate, and guanidinate ligands have bond patterns similar to the Ar'CrCrAr' compound. Unlike these latter species, the dichromium diazadiene complex is characterized by a different bonding pattern involving Cr-Npi interactions, resulting in a lower bond order associated with the short metal-metal bond distance. In this case the short CrCr distance is most probably the result of the constraints imposed by the diazadiene ligand, implying a Cr(2)N(4) core with a closer CrCr interaction.