Department of Chemistry, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA.
Inorg Chem. 2010 Sep 6;49(17):7904-16. doi: 10.1021/ic100856n.
A potentially useful trianionic ligand for the reduction of dinitrogen catalytically by molybdenum complexes is one in which one of the arms in a (RNCH(2)CH(2))(3)N ligand is replaced by a 2-mesitylpyrrolyl-alpha-methyl arm, that is, (RNCH(2)CH(2))(2)NCH(2)(2-MesitylPyrrolyl) (R = C(6)F(5), 3,5-Me(2)C(6)H(3), or 3,5-t-Bu(2)C(6)H(3)). Compounds have been prepared that contain the ligand in which R = C(6)F(5) (C(6)F(5)N)(2)Pyr); they include [(C(6)F(5)N)(2)Pyr]Mo(NMe(2)), [(C(6)F(5)N)(2)Pyr]MoCl, [(C(6)F(5)N)(2)Pyr]MoOTf, and [(C(6)F(5)N)(2)Pyr]MoN. Compounds that contain the ligand in which R = 3,5-t-Bu(2)C(6)H(3) (Ar(t-Bu)N)(2)Pyr) include {[(Ar(t-Bu)N)(2)Pyr]Mo(N(2))}Na(15-crown-5), {[(Ar(t-Bu)N)(2)Pyr]Mo(N(2))}[NBu(4)], [(Ar(t-Bu)N)(2)Pyr]Mo(N(2)) (nu(NN) = 2012 cm(-1) in C(6)D(6)), {[(Ar(t-Bu)N)(2)Pyr]Mo(NH(3))}BPh(4), and [(Ar(t-Bu)N)(2)Pyr]Mo(CO). X-ray studies are reported for [(C(6)F(5)N)(2)Pyr]Mo(NMe(2)), [(C(6)F(5)N)(2)Pyr]MoCl, and [(Ar(t-Bu)N)(2)Pyr]MoN. The [(Ar(t-Bu)N)(2)Pyr]Mo(N(2))(0/-) reversible couple is found at -1.96 V (in PhF versus Cp(2)Fe(+/0)), but the [(Ar(t-Bu)N)(2)Pyr]Mo(N(2))(+/0) couple is irreversible. Reduction of {[(Ar(t-Bu)N)(2)Pyr]Mo(NH(3))}BPh(4) under Ar at approximately -1.68 V at a scan rate of 900 mV/s is not reversible. Ammonia in [(Ar(t-Bu)N)(2)Pyr]Mo(NH(3)) can be substituted for dinitrogen in about 2 h if 10 equiv of BPh(3) are present to trap the ammonia that is released. [(Ar(t-Bu)N)(2)Pyr]Mo-N=NH is a key intermediate in the proposed catalytic reduction of dinitrogen that could not be prepared. Dinitrogen exchange studies in [(Ar(t-Bu)N)(2)Pyr]Mo(N(2)) suggest that steric hindrance by the ligand may be insufficient to protect decomposition of [(Ar(t-Bu)N)(2)Pyr]Mo-N=NH through a variety of pathways. Three attempts to reduce dinitrogen catalytically with [(Ar(t-Bu)N)(2)Pyr]Mo(N) as a "catalyst" yielded an average of 1.02 +/- 0.12 equiv of NH(3).
一种可能对钼配合物催化还原氮气有用的三阴离子配体是其中一个臂在(RNCH(2)CH(2))(3)N配体中被 2- 甲巯基吡咯基-α-甲基臂取代，即(RNCH(2)CH(2))(2)NCH(2)(2- 甲巯基吡咯基)（R = C(6)F(5)、3、5-Me(2)C(6)H(3)或 3、5-t-Bu(2)C(6)H(3)）。已经制备了含有配体的化合物，其中 R = C(6)F(5)C(6)F(5)N)(2)Pyr；它们包括[(C(6)F(5)N)(2)Pyr]Mo(NMe(2))、[(C(6)F(5)N)(2)Pyr]MoCl、[(C(6)F(5)N)(2)Pyr]MoOTf 和[(C(6)F(5)N)(2)Pyr]MoN。含有配体的化合物，其中 R = 3、5-t-Bu(2)C(6)H(3)Ar(t-Bu)N)(2)Pyr，包括{[(Ar(t-Bu)N)(2)Pyr]Mo(N(2))}Na(15-crown-5)、{[(Ar(t-Bu)N)(2)Pyr]Mo(N(2))}[NBu(4)]、[(Ar(t-Bu)N)(2)Pyr]Mo(N(2))（nu(NN) = 2012 cm(-1) 在 C(6)D(6)中）、{[(Ar(t-Bu)N)(2)Pyr]Mo(NH(3))}BPh(4)和[(Ar(t-Bu)N)(2)Pyr]Mo(CO)。报道了[(C(6)F(5)N)(2)Pyr]Mo(NMe(2))、[(C(6)F(5)N)(2)Pyr]MoCl 和[(Ar(t-Bu)N)(2)Pyr]MoN 的 X 射线研究。[(Ar(t-Bu)N)(2)Pyr]Mo(N(2))(0/-)可逆偶对在-1.96 V（相对于 Cp(2)Fe(+/0)，在 PhF 中）处找到，但[(Ar(t-Bu)N)(2)Pyr]Mo(N(2))(+/0)偶对是不可逆的。在大约-1.68 V 的扫描速率为 900 mV/s 的 Ar 下，[(Ar(t-Bu)N)(2)Pyr]Mo(NH(3))BPh(4)的还原不是可逆的。如果存在 10 当量的 BPh(3)来捕获释放的氨，则[(Ar(t-Bu)N)(2)Pyr]Mo(NH(3))中的氨可以在大约 2 小时内替代氮气。[(Ar(t-Bu)N)(2)Pyr]Mo-N=NH 是拟议的催化还原氮气的关键中间体，但不能制备。[(Ar(t-Bu)N)(2)Pyr]Mo(N(2))中的氮气交换研究表明，配体的空间位阻可能不足以通过各种途径保护[(Ar(t-Bu)N)(2)Pyr]Mo-N=NH 的分解。用[(Ar(t-Bu)N)(2)Pyr]Mo(N)作为“催化剂”催化还原氮气的三次尝试平均得到 1.02 +/- 0.12 当量的 NH(3)。
