Ring slippage

In a CO matrix, therefore, the primary product involves an expanded coordination nunber ("ring-slippage") and it is argued that such a species is consistent with the associative mechanism proposed for room temperature substitution reactions of (13 -05115)Co-... 

A ring slippage mechanism was first proposed tn 1966. Fora discussion of this week, see Basdo. F. Potyhcdnm 1990, 9. 505- 535. 

The chemical or electrochemical reduction of [(arene)Mn(CO)3]+ (23+) can lead to bimolecular coupling through the arene rings, CO loss followed by dimerization, or arene ring slippage.134 Which mode of decomposition is followed depends on many factors, especially the nature of the arene. In the presence of P(OBu)3, these decomposition pathways are short circuited in favor of ETC substitution to give [(arene)Mn(CO)2P(OBu)3]+. For example, Fig. 6 shows that application of a reducing current for a... 

Kinetic studies at different phosphine concentrations indicated that the substitution reactions occur totally by a dissociative mechanism, while the ring expansion reaction is by an associative mechanism. The associative reaction could proceed by an 18-electron transition state involving either a bent NO or an rj to rj ring slippage mechanism. The bent NO mechanism seems more likely, because the ring slippage mechanism is known to result in the formation of oxocyclobutenyl product with ring expansion and because the isoelec-tronic cobalt complex does not react by a parallel associative pathway. 

The mechanism of oxycyclobutenyl (CO)(NO)(PBu3)Fe(C3Ph3CO) formation by the associative substitution reaction is suggested to involve cyclopropenyl ring slippage... 

The hapticity of the Cp ring in CpCo(CO)2 has been the topic of much debate. If an associative mechanism for snbstitution is followed, a hapticity (see Hapticity) of f from ring slippage would result in a 19-electron intermediate and 17-electron product, while a hapticity of rf would result in a more unstable 21-electron intermediate. However, it has been shown that CO substitution follows a dissociative mechanism... 

CO addition probably involves a ring slippage toward -Cp, followed by intramolecular reductive elimination its reverse was established in low-temperature matrix... 

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