Shakeri Ehsan, Hoefler John C, Blümel Janet
Department of Chemistry, Texas A&M University, College Station, TX 77843-3012, USA.
Molecules. 2025 Jun 25;30(13):2737. doi: 10.3390/molecules30132737.
Bis- and trisphosphines incorporating methylene and aryl spacers readily adsorb on the surface of porous activated carbon (AC). The adsorption can be performed in the absence of solvents, even when the phosphines have high melting points, or from solutions. The diverse phosphines PhPCHPPh (), PhP(CH)PPh (), PhP(CH)PPh (), PhP(-CH)PPh (), and (PhPCH)CCH () were adsorbed in submonolayers on AC. The adsorbed phosphines were studied by P MAS (magic angle spinning) NMR spectroscopy, and their mobilities on the surface were confirmed by determining the P T relaxation times. All phosphine groups of each bis- and trisphosphine molecule are in contact with the surface, and the molecules exhibit translational mobility as one unit. All phosphines used here are air-stable. Once a submonolayer is created on the AC surface, oxygen from the air is co-adsorbed and transforms all phosphines quantitatively into phosphine oxides at room temperature. The oxidation proceeds in a consecutive manner with the oxidation of one phosphine group after another until the fully oxidized species are formed. Studies of the kinetics are based on integrating the signals in the solution P NMR spectra. High temperatures and low surface coverages increase the speed of the oxidation, while light and acid have no impact. The oxidation is fast and complete within one hour for 10% surface coverage at room temperature. In order to study the mechanism and slow down the oxidation, a higher surface coverage of 40% was applied. No unwanted P(V) side products or water adducts were observed. The clean phosphine oxides could be recovered in high yields by washing them off of the AC surface. The oxidation is based on radical activation of O on the AC surface due to delocalized electrons on the AC surface. This is corroborated by the result that AIBN-derived radicals enable the air oxidation of PPh in solution at 65 °C. When the air-stable complex (CO)Ni(PPh) is applied to the AC surface and exposed to the air, OPPh forms quantitatively. The new surface-assisted air oxidation of phosphines adsorbed on AC renders expensive and hazardous oxidizers obsolete and opens a synthetic pathway to the selective mono-oxidation of bis- and trisphosphines.
含有亚甲基和芳基间隔基的双膦和三膦很容易吸附在多孔活性炭（AC）表面。即使膦具有高熔点，吸附也可以在无溶剂的情况下进行，也可以从溶液中进行。多种膦，如PhPCHPPh（）、PhP(CH)PPh（）、PhP(CH)PPh（）、PhP(-CH)PPh（）和(PhPCH)CCH（），以亚单层形式吸附在AC上。通过磷的魔角旋转（MAS）核磁共振光谱对吸附的膦进行了研究，并通过测定磷的横向弛豫时间证实了它们在表面上的迁移率。每个双膦和三膦分子的所有膦基团都与表面接触，并且分子作为一个整体表现出平移迁移率。这里使用的所有膦在空气中都是稳定的。一旦在AC表面形成亚单层，空气中的氧气就会共吸附，并在室温下将所有膦定量转化为膦氧化物。氧化以连续的方式进行，一个膦基团接着一个膦基团被氧化，直到形成完全氧化的物种。动力学研究基于对溶液中磷核磁共振光谱信号的积分。高温和低表面覆盖率会提高氧化速度，而光和酸没有影响。在室温下，对于10%的表面覆盖率，氧化在一小时内快速且完全。为了研究氧化机理并减缓氧化，采用了40%的更高表面覆盖率。未观察到不需要的五价磷副产物或水加合物。通过将清洁的膦氧化物从AC表面冲洗下来，可以高收率回收。氧化是基于AC表面上离域电子对氧气的自由基活化。这一点得到了如下结果的证实：源自偶氮二异丁腈的自由基能够在65℃下使溶液中的三苯基膦发生空气氧化。当将空气稳定的配合物(CO)Ni(PPh)应用于AC表面并暴露于空气中时，定量形成氧化三苯基膦。吸附在AC上的膦的这种新的表面辅助空气氧化使昂贵且危险的氧化剂过时，并为双膦和三膦的选择性单氧化开辟了一条合成途径。
