Functionalization of Metal-Protected Chiral Phosphines via Simple Organic Transformations

With metal as protection, the introduction of functionalities on coordinated chiral phosphines using
organic transformations was demonstrated. Bis(diphenylphosphino)-substituted oxa- and azanorbornene
metal complexes were subjected to a series of organic transformations including hydrogenation,
hydroboration, electrophilic addition, and dihydroxylation reactions. Hydrogenation of the oxanorbornene
double bond stabilizes the free diphosphino-substituted oxanorbornene ligand, which is otherwise prone
to the retro-cycloaddition reaction. Hydroboration of the oxanorbornenic double bond using borane,
followed by oxidation with alkaline hydrogen peroxide, generated two regioisomeric products with the
introduction of a hydroxy group at the exo position. However, regioselective hydroboration could be
achieved with the use of 9-BBN as the hydroborating agent. Stereoselective electrophilic addition of the
oxanorbornenic double bond with phenylselenenyl chloride resulted in the formation of a sole anti-addition product. Subsequent oxidative syn-elimination of the resultant selenide product was also shown
to proceed regioselectively to give the vinyl chloride complex. Dihydroxylation of the oxa- and
azanorbornenic double bond with osmium tetraoxide proceeded stereoselectively with the introduction
of two hydroxy group at the exo positions. Liberation of the functionalized chiral phosphine ligands
from the metal complexes was also illustrated.

以金属作为保护基，本研究展示了通过有机转化在配位手性膦（chiral phosphine）配体上引入官能团的方法。双(二苯基膦基)取代的氧杂降冰片烯与氮杂降冰片烯金属配合物，先后经历了氢化、硼氢化、亲电加成以及双羟基化等一系列有机转化反应。氧杂降冰片烯双键的氢化反应可稳定游离的双膦取代氧杂降冰片烯配体——该配体在无保护条件下极易发生逆环加成（retro-cycloaddition）反应。使用硼烷对氧杂降冰片烯双键进行硼氢化，再经碱性过氧化氢氧化后，可得到两种区域异构体产物，二者均在外型（exo）位点引入了羟基。但当使用9-硼双环(3,3,1)壬烷（9-BBN）作为硼氢化试剂时，可实现区域选择性硼氢化。氧杂降冰片烯双键与氯化苯硒基发生立体选择性亲电加成反应，仅得到反式加成（anti-addition）产物。随后对所得硒醚产物进行氧化顺式消除（syn-elimination），同样可区域选择性地得到氯乙烯金属配合物。使用四氧化锇（osmium tetraoxide）对氧杂降冰片烯与氮杂降冰片烯的双键进行双羟基化反应时，反应具有立体选择性，可在两个外型位点引入羟基。本研究同时展示了从金属配合物中释放官能化手性膦配体的方法。