Department of Chemistry, University of Wisconsin-La Crosse, 1725 State Street, La Crosse, WI 54601, USA.
Dalton Trans. 2011 Oct 7;40(37):9439-46. doi: 10.1039/c1dt10994d. Epub 2011 Aug 16.
The para-aminobiphenyl compound [(η(6)-C(6)H(5))(C(6)H(4)-4-NH(2))]Cr(CO)(3) (1) has an arene-phenyl dihedral angle of 38.01(6)°, as determined by single-crystal X-ray crystallography, and 34.7(11)°, as determined by DFT calculations. It undergoes haptotropic rearrangement at 140 °C in solution to form [(η(6)-C(6)H(4)-4-NH(2))(C(6)H(5))]Cr(CO)(3) (2), even though previous reports have suggested that such rearrangements should not be observed in compounds with arene-phenyl dihedral angles greater than 22°. NMR analysis gave a rate constant of k = 5.0 × 10(-5) s(-1) for the rearrangement of 1 to 2. The ortho-substituted analog [(η(6)-C(6)H(5))(C(6)H(4)-2-NH(2))]Cr(CO)(3) (3) has an arene-phenyl dihedral angle of 67.70(7)°, as determined by single-crystal X-ray crystallography, and 51.9(10)°, as determined by DFT calculations. Surprisingly, even though it displays a more extreme canting of arene rings, 3 rearranges to [(η(6)-C(6)H(4)-2-NH(2))(C(6)H(5))]Cr(CO)(3) (4) at 140 °C in solution with a rate constant of k = 2.6 × 10(-4) s(-1). This approximately five-fold rate enhancement likely results from the ortho-amino group providing intramolecular stabilization for intermediates formed during the rearrangement.
对氨基联苯化合物 [(η(6)-C(6)H(5))(C(6)H(4)-4-NH(2))]Cr(CO)(3) (1) 通过单晶 X 射线晶体学确定的芳基-苯基二面角为 38.01(6)°，通过 DFT 计算确定的为 34.7(11)°。它在溶液中于 140°C 下经历变构重排，形成 [(η(6)-C(6)H(4)-4-NH(2))(C(6)H(5))]Cr(CO)(3) (2)，尽管之前的报道表明，在芳基-苯基二面角大于 22°的化合物中不应观察到这种重排。NMR 分析给出了 1 到 2 的重排的速率常数 k = 5.0 × 10(-5) s(-1)。邻位取代的类似物 [(η(6)-C(6)H(5))(C(6)H(4)-2-NH(2))]Cr(CO)(3) (3) 通过单晶 X 射线晶体学确定的芳基-苯基二面角为 67.70(7)°，通过 DFT 计算确定的为 51.9(10)°。令人惊讶的是，尽管它显示出芳环的更极端倾斜，但 3 在溶液中于 140°C 下以速率常数 k = 2.6 × 10(-4) s(-1)重排为 [(η(6)-C(6)H(4)-2-NH(2))(C(6)H(5))]Cr(CO)(3) (4)。这种大约五倍的速率增强可能是由于邻位氨基提供了重排过程中形成的中间体的分子内稳定化。
