The reaction of trans-[M(C2H4)2(PMe3)4] with the tripodal phosphine 1,1,1-tris[(dimethylphosphino)methyl]ethane (CP3) affords complexes trans-[M(C2H4)2(η2-CP3)(PMe3)2] (M = Mo 1a or W 1b). A detailed NMR study, including hetero- and homo-nuclear two-dimensional correlations, has been carried out for 1b which allows a complete assignment of signals and a structural spectroscopic determination. In solution, no ethylene rotation is observed at room temperature and the preferential conformer of the six-membered ring W[η2-CH3C(CH2PMe2)3] fragment is, on the basis of steric arguments, the skew-boat conformation. Interaction of compounds 1 with CO affords trans-[M(C2H4)2(η2-CP3)(CO)(PMe3)] (M = Mo 2a or W 2b), while reaction of 1a with CNBut furnishes the compound trans-[Mo(C2H4)2(η2-CP3)(CNBut)(PMe3)] 3. The bidentate co-ordination of CP3 induces chirality at the metal center and compounds 2 and 3 are obtained as a ca. 1∶1 mixture of diastereoisomers, identified by the presence of two different patterns of resonances in their 31P-1H} NMR spectra at low temperature. At the fast regimen exchange, the isomers are interconverted through bis(ethylene) rotation. A variable-temperature 31P-1H} NMR study carried out for 2a gives an approximate value of ΔG‡ for this process of 55 kJ mol–1 at 298 K.
反式-[M(
C2H4)2(PMe3)4]与三元膦 1,1,1-三[(二
甲基膦)甲基]
乙烷(CP3)反应生成了反式-[M( )2(η2-CP3)(PMe3)2]复合物(M = Mo 1a 或 W 1b)。我们对 1b 进行了详细的核磁共振研究,包括异核和同核二维相关性研究,从而对信号进行了完整的分配,并确定了结构光谱。在溶液中,室温下没有观察到
乙烯旋转,根据立体论证,六元环 W[η2-CH3C(
CH2PMe2)3] 片段的优先构象为斜舟构象。化合物 1 与 CO 反应生成反式-[M( )2(η2-CP3)(CO)(PMe3)](M = Mo 2a 或 W 2b),而 1a 与 CNBut 反应生成化合物反式-[Mo( )2(η2-CP3)(CNBut)(PMe3)] 3。CP3 的双齿配位引起
金属中心的手性,化合物 2 和 3 以约 1∶1 的非对映异构体混合物的形式出现。在低温下的核磁共振光谱中存在两种不同的共振模式。在快速制度交换时,异构体通过双(
乙烯)旋转而相互转化。对 2a 进行了变温 31P-1H} NMR 研究。对 2a 进行的变温 31P-1H} NMR 研究得出,在 298 K 时,这一过程的 ΔG‡ 近似值为 55 kJ mol-1。