The reactions of metallaaziridinium ion pairs [Cp2M(h2- CH2NMePh)][B(C6F5)4] [M = Zr (1), Hf (2)] with 1-hexene and 2- methyl-1-heptene were investigated by means of NMR spec- troscopy and DFT calculations. We found that a single insertion of the olefin into the M–C bond led to the formation of stable five-membered heterocycles (3–6). The reactions were 1,2-re- gioselective and afforded two diastereoisomers whose ratio was mainly controlled by the nature of the olefin, whilst thenature of the metal only played a marginal role. In particular, the reaction with 1-hexene was found to be not only more fa- vored than that with 2-methyl-1-heptene from a thermodynam- ic point of view but it was also more diastereoselective. In all cases, the observed diastereoisomeric ratio was dictated by thermodynamics because the products interconverted into each other, as indicated by EXSY NMR spectroscopy and by DFT calculations.
An Integrated NMR and DFT Study on the Single Insertion of alpha-Olefins into the M-C
ROCCHIGIANI, LUCA;CIANCALEONI, Gianluca;ZUCCACCIA, Cristiano;MACCHIONI, Alceo
2013
Abstract
The reactions of metallaaziridinium ion pairs [Cp2M(h2- CH2NMePh)][B(C6F5)4] [M = Zr (1), Hf (2)] with 1-hexene and 2- methyl-1-heptene were investigated by means of NMR spec- troscopy and DFT calculations. We found that a single insertion of the olefin into the M–C bond led to the formation of stable five-membered heterocycles (3–6). The reactions were 1,2-re- gioselective and afforded two diastereoisomers whose ratio was mainly controlled by the nature of the olefin, whilst thenature of the metal only played a marginal role. In particular, the reaction with 1-hexene was found to be not only more fa- vored than that with 2-methyl-1-heptene from a thermodynam- ic point of view but it was also more diastereoselective. In all cases, the observed diastereoisomeric ratio was dictated by thermodynamics because the products interconverted into each other, as indicated by EXSY NMR spectroscopy and by DFT calculations.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
