Preparation, Facile Deprotonation, and Rapid H/D Exchange of the μ-Hydride Diiron Model Complexes of the [FeFe]-Hydrogenase Containing a Pendant Amine in a Chelating Diphosphine Ligand

The CO-displacement of [(μ-pdt)Fe2(CO)6] with (Ph2PCH2)2N(n-Pr) in refluxing toluene gave an unsymmetrical chelating complex [(μ-pdt){Fe(CO)3}{Fe(CO)(κ2-Ph2PCH2N(n-Pr)CH2PPh2}] (1) as a major product, together with a small amount of the symmetrical intramolecular bridging complex [(μ-pdt){μ-Ph2PCH2N(n-Pr)CH2PPh2}{Fe(CO)2}2] (2) and the intermolecular bridging complex [{μ,κ1,κ1-Ph2PCH2N(n-Pr)CH2PPh2}{(μ-pdt)Fe2(CO)5}2] (3). In contrast, the reaction of [(μ-pdt)Fe2(CO)6] with (Ph2PCH2)2NR (R = n-Pr, Ph) afforded the intermolecular bridging isomers 3 and 4 in the presence of a CO-removing reagent Me3NO·2H2O in CH3CN at room temperature. The molecular structures of 1, 3, and 4, as well as the doubly protonated complex [1(HNHμ)](OTf)2] were determined by X-ray analyses. The protonation processes of 1 with HBF4·Et2O and HOTf were studied in different solvents. The presence of the Hμ···HN interaction in [1(HNHμ)]2+ was studied by relaxation time T1 and spin saturation transfer measurements. The μ-hydride of [1(Hμ)]+ and [1(HNHμ)]2+ undergo facile deprotonation with aniline and rapid H/D exchange with deuterons in solution. In contrast, neither deprotonation nor H/D exchange was detected for [(μ-H)(μ-pdt){Fe(CO)3}{Fe(CO)(κ2-dppp)}]+ ([5(Hμ)]+, dppp = Ph2PCH2CH2CH2PPh2) without internal base.

在回流甲苯中，以N-正丙基双(二苯基膦甲基)胺与μ-丙二硫醇桥联二铁六羰基配合物([(μ-pdt)Fe₂(CO)₆])发生CO置换反应，主要产物为非对称螯合配合物[(μ-pdt){Fe(CO)₃}{Fe(CO)(κ²-Ph₂PCH₂N(n-Pr)CH₂PPh₂})]（记为化合物1），同时伴随少量对称分子内桥联配合物[(μ-pdt){μ-Ph₂PCH₂N(n-Pr)CH₂PPh₂}{Fe(CO)₂}₂]（化合物2）与分子间桥联配合物[{μ,κ¹,κ¹-Ph₂PCH₂N(n-Pr)CH₂PPh₂}{(μ-pdt)Fe₂(CO)₅}₂]（化合物3）生成。与之不同，当以三甲基氮氧化物二水合物（Me₃NO·2H₂O）作为脱CO试剂，在乙腈（CH₃CN）中室温条件下，μ-丙二硫醇桥联二铁六羰基配合物与(Ph₂PCH₂)₂NR（R = 正丙基、苯基）反应，得到分子间桥联异构体3和4。通过X射线单晶衍射分析，确定了化合物1、3、4以及双质子化配合物[1(HNHμ)](OTf)₂（其中OTf为三氟甲磺酸根）的分子结构。研究了化合物1分别与乙醚合四氟硼酸（HBF₄·Et₂O）和三氟甲磺酸（HOTf）在不同溶剂中的质子化过程。通过弛豫时间T₁与自旋饱和转移实验，探究了[1(HNHμ)]²+中存在的Hμ···HN氢键相互作用。溶液中，[1(Hμ)]+与[1(HNHμ)]²+的μ-桥氢可与苯胺发生快速脱质子反应，并与氘代试剂发生快速氢氘交换。与之相反，对于不含内部碱的[(μ-H)(μ-pdt){Fe(CO)₃}{Fe(CO)(κ²-dppp)}]+（记为[5(Hμ)]+，其中dppp为1,3-双(二苯基膦基)丙烷，即Ph₂PCH₂CH₂CH₂PPh₂），未检测到脱质子反应与氢氘交换过程。