Stereoselective Synthesis of <i>ortho</i>-Carbaborane-Containing<i> P</i>-Chiral Phosphanylferrocenes^†

Diastereomerically pure 1-[1-(1,2-dicarba-closo-dodecaboran(12)yl)chlorophosphanyl]-2-N,N-dimethylaminomethylferrocene ((RP,SFc/SP,RFc)-3) and enantiomerically pure (S)-N,N-dimethyl-1-{(R)-2-[(S)-{1-(1,2-dicarba-closo-dodecaboran(12)yl)}chlorophosphanyl]ferrocenyl}ethylamine ((SC,SP,RFc)-4) were prepared by reaction of monolithiated 1,2-dicarba-closo-dodecaborane(12) and the corresponding racemic or enantiomerically pure aminoalkylferrocenyldichlorophosphanes (1 or (S,R)-2). Two equivalents of 1 also reacted with dilithiated 1,2-dicarba-closo-dodecaborane(12) to yield stereoselectively the RP,RP‘,SFc,SFc‘/SP,SP‘,RFc,RFc‘ diastereomer of 1,2-bis[chloro(2-N,N-dimethylaminomethylferrocenyl)phosphanyl]-1,2-dicarba-closo-dodecaborane(12) ((RP,RP‘,SFc,SFc‘/SP,SP‘,RFc,RFc‘)-5). Chlorophosphane (RP,SFc/SP,RFc)-3 was treated with LiAlH4 to afford diastereoselectively the secondary phosphane 1-[1-(1,2-dicarba-closo-dodecaboran(12)yl)phosphanyl]-2-N,N-dimethylaminomethylferrocene ((RP,RFc/SP,SFc)-6) with inverted stereochemistry at the phosphorus center, which in this case was found to slowly undergo epimerization in solution. The chloro groups of (RP,SFc/SP,RFc)-3 and (SC,SP,RFc)-4 were also substituted by various alkoxides to give a series of diastereomerically and enantiomerically pure carbaboranylferrocenyl phosphinites ((RP,RFc/SP,SFc)-7, (RP,RFc/SP,SFc)-8, (RP,RFc/SP,SFc)-9, (SC,RP,RFc)-10, and (SC,RP,RFc)-11). The substitutions occurred with 100% stereoselective inversion of the configurations of the phosphorus centers. The phosphinites display high stability toward oxidation and epimerization. All new compounds were structurally characterized to verify the configurations of the stereogenic centers. The monophosphanyl-substituted carbaboranes exhibit intramolecular hydrogen-bonding interactions between the dimethylamino group and the proton of the second cluster carbon atom.非对映纯的1-[1-(1,2-碳代闭式十二硼烷(12)（1,2-dicarba-closo-dodecaborane(12)）基)氯膦基]-2-二甲氨基甲基二茂铁（ferrocene）((RP,SFc/SP,RFc)-3)与对映纯的(S)-N,N-二甲基-1-{(R)-2-[(S)-{1-(1,2-碳代闭式十二硼烷(12)基)}氯膦基]二茂铁基}乙胺((SC,SP,RFc)-4)，通过单锂化1,2-碳代闭式十二硼烷(12)与相应的外消旋或对映纯的氨基烷基二茂铁二氯膦（1或(S,R)-2）反应制得。两当量的1亦可与双锂化1,2-碳代闭式十二硼烷(12)反应，立体选择性地得到1,2-双[氯(2-二甲氨基甲基二茂铁基)膦基]-1,2-碳代闭式十二硼烷(12)的RP,RP',SFc,SFc'/SP,SP',RFc,RFc'非对映异构体((RP,RP',SFc,SFc'/SP,SP',RFc,RFc')-5)。将氯膦(RP,SFc/SP,RFc)-3用氢化铝锂（LiAlH4）处理，非对映选择性地得到磷中心构型反转的仲膦1-[1-(1,2-碳代闭式十二硼烷(12)基)膦基]-2-二甲氨基甲基二茂铁((RP,RFc/SP,SFc)-6)，该产物在溶液中会缓慢发生差向异构化。(RP,SFc/SP,RFc)-3与(SC,SP,RFc)-4中的氯基团亦可被多种醇盐取代，得到一系列非对映纯及对映纯的碳硼烷基二茂铁基次膦酸酯((RP,RFc/SP,SFc)-7、(RP,RFc/SP,SFc)-8、(RP,RFc/SP,SFc)-9、(SC,RP,RFc)-10与(SC,RP,RFc)-11)。该取代反应以100%的立体选择性实现了磷中心构型的反转。该类次膦酸酯对氧化与差向异构化表现出较高的稳定性。所有新合成的化合物均经过结构表征，以确认各立体中心的构型。单膦基取代的碳硼烷展现出二甲氨基与第二簇碳原子上质子之间的分子内氢键相互作用。