Mock Michael T, Pierpont Aaron W, Egbert Jonathan D, O'Hagan Molly, Chen Shentan, Bullock R Morris, Dougherty William G, Kassel W Scott, Rousseau Roger
‡Center for Molecular Electrocatalysis, Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99352, United States.
†Department of Chemistry, Villanova University, Villanova, Pennsylvania 19085, United States.
Inorg Chem. 2015 May 18;54(10):4827-39. doi: 10.1021/acs.inorgchem.5b00351. Epub 2015 May 1.
The reduction of fac-[CrCl3(P(Ph)3N(Bn)3)], (1(Cl3)), (P(Ph)3N(Bn)3 = 1,5,9-tribenzyl-3,7,11-triphenyl-1,5,9-triaza-3,7,11-triphosphacyclododecane) with Mg in the presence of dmpe (dmpe = 1,2-bis(dimethylphosphino)ethane) affords the first example of a monodinitrogen Cr(0) complex, Cr(N2)(dmpe)(P(Ph)3N(Bn)3), (2(N2)), containing a pentaphosphine coordination environment. 2(N2) is supported by a unique facially coordinating 12-membered phosphorus macrocycle containing pendant amine groups in the second coordination sphere. Treatment of 2(N2) at -78 °C with 1 equiv of [H(OEt2)2][B(C6F5)4] results in protonation of the metal center, generating the seven-coordinate Cr(II)-N2 hydride complex, [Cr(H)(N2)(dmpe)(P(Ph)3N(Bn)3)][B(C6F5)4], 2(H)(N2). Treatment of 2((15)N2) with excess triflic acid at -50 °C afforded a trace amount of (15)NH4(+) from the reduction of the coordinated (15)N2 ligand (electrons originate from Cr). Electronic structure calculations were employed to evaluate the pKa values of three protonated sites of 2(N2) (metal center, pendant amine, and N2 ligand) and were used to predict the thermodynamically preferred Cr-NxHy intermediates in the N2 reduction pathway for 2(N2) and the recently published complex trans-[Cr(N2)2(P(Ph)4N(Bn)4)] upon the addition of protons and electrons.
在1,2-双（二甲基膦基）乙烷（dmpe）存在下，用镁还原面式-[三氯化铬（三苯基膦基三苄基胺）]，（1(Cl3)），（三苯基膦基三苄基胺 = 1,5,9-三苄基-3,7,11-三苯基-1,5,9-三氮杂-3,7,11-三磷杂环十二烷）得到了首例单二氮铬(0)配合物，Cr(N₂)(dmpe)(三苯基膦基三苄基胺)，（2(N₂)），其具有五膦配位环境。2(N₂)由一个独特的面式配位12元磷大环支撑，该大环在第二配位层含有侧链胺基。在-78°C下用1当量的[H(OEt₂)₂][B(C₆F₅)₄]处理2(N₂)，导致金属中心质子化，生成七配位的Cr(II)-N₂氢化物配合物，[Cr(H)(N₂)(dmpe)(三苯基膦基三苄基胺)][B(C₆F₅)₄]，[2(H)(N₂)]⁺。在-50°C下用过量的三氟甲磺酸处理2((¹⁵)N₂)，从配位的(¹⁵)N₂配体的还原中得到了痕量的(¹⁵)NH₄⁺（电子源自Cr）。采用电子结构计算来评估2(N₂)的三个质子化位点（金属中心、侧链胺和N₂配体）的pKa值，并用于预测在加入质子和电子时2(N₂)以及最近发表的配合物反式-[Cr(N₂)₂(四苯基膦基四苄基胺)]在N₂还原途径中热力学上优选的Cr-NxHy中间体。
