Metal carbonyls reaction with phospholes

Both arsoles and stiboles can act as ligands in reactions with metal carbonyls. The arsoles have been studied in depth and are reviewed by Abel (79MI11801). They are particularly versatile, forming a wide range of derivatives. In this respect their chemistry closely parallels that of the phospholes. This is illustrated by Scheme 13. Reaction of either l-chIoro-2,3,4,5-pentaphenylarsole or the corresponding alkali metal compound with a transition metal... 

The earliest studies of the coordination chemistry of phospholes involved reactions with metal carbonyls. Braye et al. found that 1,2,3,4,5-pentaphenylphosphole (PPP) reacts with Fe3(CO)i2 to form a mixture of complexes among which there is one with a PPP ring > -bonded to Fe(CO)3. These types of complexes must be very unstable and very difficult to prepare due to the high reactivity of the lone pair of die phosphorus atom. In order to obtain them it is necessary to deactivate the phosphorus atom by electron withdrawing substituents and to prevent complexation through the lone pair by steric hindrance. These facts explain why only two i -phosphole complexes have been found, both of them with 2,5-diphenyl substituted phospholes (PPP and TPP ), and why no unambiguous characterization of the bonding mode has been established. 

An interesting new development in aromatic phosphole chemistry has been the preparation and subsequent study of the electrophilic substitution reactions of transition-metal complexes of phospholyl anions, e.g. the phosphaferrocenes (165), which are obtained by the reaction of the appropriate P-phenylphosphole with transition-metal cyclopentadienyls or carbonyls, - and which undergo acetylation at... 

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