作者:Wan-Yi Chu、Casseday P. Richers、Elizabeth R. Kahle、Thomas B. Rauchfuss、Federica Arrigoni、Giuseppe Zampella
DOI:10.1021/acs.organomet.6b00318
日期:2016.9.12
Fundamental reactions of imino-phosphine ligands were elucidated through studies on Ph2PC6H4CH=NC6H4-4-Cl (PCHNArCl) complexes of iron(0), iron(I), and iron(II). The reaction of PCHNArCl with Fe(bda)(CO)(3) gives Fe(PCHNArCl)(CO)(3) (1), featuring an eta(2)-imine. DNMR studies, its optical properties, and DFT calculations suggest that 1 racemizes on the NMR time scale via an achiral N-bonded imine intermediate. The N-imine isomer is more stable in Fe(PCHNArOMe)(CO)(3) (1(OMe)), which crystallized despite being the minor isomer in solution. Protonation of 1 by HBF4Et2O gave the iminium complex [1H]BF4. The related diphosphine complex Fe(PCHNArCl)(PMe3)(CO)(2) (2), which features an eta(2)-imine, was shown to also undergo N protonation. Oxidation of 1 and 2 with FcBF(4) gave the Fe(I) compounds [1]BF4 and [2]BF4. The oxidation-induced change in hapticity of the imine from eta(2) in [1](0) to kappa(1) in [1](+) was verified crystallographically. Substitution of a CO ligand in 1 with PCHNArCl gave Fe[P-2(NArCl)(2)](CO)(2) (3), which contains the tetradentate diamidodiphosphine ligand. This C-C coupling is reversed by chemical oxidation of 3 with FcOTf. The oxidized product of [Fe(PCHNArCl)(2)(CO)(2)](2+) ([4](2+)) was prepared independently by the reaction of [1](+), PCHNArCl, and Fc(+). The C-C scission is proposed to proceed concomitantly with the reduction of Fe(II) via an intermediate related to [2](+).