Protonation of Ferrous Dinitrogen Complexes Containing a Diphosphine Ligand with a Pendent Amine
Protonation of Ferrous Dinitrogen Complexes Containing a Diphosphine Ligand with a Pendent Amine
复制标题
DOI：
10.1021/ic4000704
复制
发表时间：
2013-04-01
影响因子：
4.6
通讯作者：
Bullock, R. Morris
中科院分区：
文献类型：
--
作者：
Heiden, Zachariah M.;Chen, Shentan;Bullock, R. Morris
向亚铁二氮络合物[FeX（N-2）（（PNPEt）-N-Et-P-Me）（dmpm）]（+）（X = H、Cl或Br;（PNPEt）-N-Et-P-Me = Et 2 PCH 2N（Me）CH 2 PEt 2;且dmpm = Me 2 PCH 2PMe 2）中添加酸在二膦配体的侧基胺而不是在二氮配体处产生质子化。这种质子化使络合物的nu（N2）带增加了25 cm（-1），并使Fe（II/I）对向更正的电势移动了0.33 V。对于相关的羰基络合物[FeH（CO）（（PNPEt）-N-Et-P-Me）（dmpm）]（+），观察到类似的IR位移和Fe（II/I）对的稍小的位移（0.23 V）。发现[FeH（（PNPEt）-N-Et-P-Me）（dmpm）]（+）与N-2的结合比NH3强约三倍。计算分析表明，配位的N-2的Fe（II）中心增加碱性的N-2（相对于自由N-2）的13和20 pK（a）单位的反式卤化物和反式卤化物，分别。虽然铁中心增加了结合的N2配体的碱性，但配位的N-2的碱性不足以被质子化。在含有侧基甲胺的亚铁二氮络合物的情况下，与N-2配体相比，胺位点被确定为30 pK（a）单位的最碱性位点。进行这些亚铁二氮络合物的化学还原以试图增加N-2配体的碱度，足以促进质子从侧基胺转移到N-2配体。代替分离还原的Fe（0）-N-2络合物，还原导致HFe（Et 2 PC（H）N（Me）CH 2 PEt 2）（（PNPEt）-N-Et-P-Me）的分离和表征，其为（PNPEt）-N-Et-P-Me配体的亚甲基C-H键与Fe的氧化加成的产物。
The addition of acids to ferrous dinitrogen complexes [FeX(N-2)((PNPEt)-N-Et-P-Me)(dmpm)](+) (X = H, Cl, or Br; (PNPEt)-N-Et-P-Me = Et2PCH2N(Me)CH2PEt2; and dmpm = Me2PCH2PMe2) gives protonation at the pendent amine of the diphosphine ligand rather than at the dinitrogen ligand. This protonation increased the nu(N2) band of the complex by 25 cm(-1) and shifted the Fe(II/I) couple by 0.33 V to a more positive potential. A similar IR shift and a slightly smaller shift of the Fe(II/I) couple (0.23 V) was observed for the related carbonyl complex [FeH(CO)((PNPEt)-N-Et-P-Me)(dmpm)](+). [FeH((PNPEt)-N-Et-P-Me)(dmpm)](+) was found to bind N-2 about three times more strongly than NH3. Computational analysis showed that coordination of N-2 to Fe(II) centers increases the basicity of N-2 (vs free N-2) by 13 and 20 pK(a) units for the trans halides and hydrides, respectively. Although the iron center increases the basicity of the bound N2 ligand, the coordinated N-2 is not sufficiently basic to be protonated. In the case of ferrous dinitrogen complexes containing a pendent methylamine, the amine site was determined to be the most basic site by 30 pK(a) units compared to the N-2 ligand. The chemical reduction of these ferrous dinitrogen complexes was performed in an attempt to increase the basicity of the N-2 ligand enough to promote proton transfer from the pendent amine to the N-2 ligand. Instead of isolating a reduced Fe(0)-N-2 complex, the reduction resulted in isolation and characterization of HFe(Et2PC(H)N(Me)CH2PEt2)((PNPEt)-N-Et-P-Me), the product of oxidative addition of the methylene C-H bond of the (PNPEt)-N-Et-P-Me ligand to Fe.