Abstract
The compounds (R-Fe,R-C)-/(S-Fe,R-C)-[CpFe(Prophos)NCMe]X (X = I, PF6), configurationally labile at the metal center, were used in the MeCN/ligand exchange reactions with cyclohexyl isocyanide (CyNC) and tert-butyl isocyanide ((BuNC)-Bu-t). Kinetic measurements showed that the MeCN/CyNC exchange in diastereomerically pure (S-Fe,R-C)-[CpFe(Prophos)NCMe]X proceeded via the slow S(N)1-type ...
Abstract
The compounds (R-Fe,R-C)-/(S-Fe,R-C)-[CpFe(Prophos)NCMe]X (X = I, PF6), configurationally labile at the metal center, were used in the MeCN/ligand exchange reactions with cyclohexyl isocyanide (CyNC) and tert-butyl isocyanide ((BuNC)-Bu-t). Kinetic measurements showed that the MeCN/CyNC exchange in diastereomerically pure (S-Fe,R-C)-[CpFe(Prophos)NCMe]X proceeded via the slow S(N)1-type dissociation of the Fe-NCMe bond, already observed in the MeCN/phosphite exchange reactions. The product (R-Fe,R-C)-/(S-Fe,R-C)-[CpFe(Prophos)CNCy]X (X = I, PF6) was formed in diastereomer ratios between 40:60 and 60:40. However, specific for the MeCN/CyNC exchange in (S-Fe,R-C)-{CpFe(Prophos)NCMe]PF6, in some of the samples a fast initial reaction interfered, initiated by traces of oxygen, which oxidized the cation in (S-Fe,R-C)[CpFe(Prophos)NCMe]PF6 to (S-Fe,R-C)-[CpFe(Prophos)NCMe](2+). This dipositive cation started an electrocatalytic chain reaction, producing (R-Fe,R-C)-/(S-Fe,R-C)-[CpFe(Prophos)CNCy]PF6 with a high stereoselectivity of 2:98 in favor of (S-Fe,R-C)[CpFe(Prophos)CNCy]PF6. Deactivation processes terminated the chain reaction, depending on the varying amounts of (S-Fe,R-C)-[CpFe(Prophos)NCMe](2+) present in the system. Larger amounts of oxygen or oxidants, such as I-2 and AgPF6, caused immediate complete conversion to (R-Fe,R-C)/(S-Fe,R-C)-[CpFe(Prophos)CNR]PF6 in a diastereomer ratio of 2:98. In contrast to the hexafluorophosphate salt, addition of a crystal of iodine did not initiate the chain reaction in the iodide salt [CpFe(Prophos)NCMe]I, because I-2 added to I- to form I-3(-), which did not oxidize the cation of [CpFe(Prophos)NCMe]I. Instead, there was slow conversion according to the dissociative pathway. The correlation between the configuration of (R-Fe,R-C)and (S-Fe,R-C)-[CpFe(Prophos)CNCy]X and the conformation of the Fe-Prophos chelate ring on the one hand and the correlation with the P-P coupling constants of the Prophos ligand on the other hand was corroborated.
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