Reactions of the electron-rich solvates (h5-C5MenH5-n)(CO)2Mn(THF) (n = 5, 1) and (CO)5M(THF) (M = Cr, W) or of the complex (h6-C6Me6)(CO)2CrP(OMe)3 with the strong acceptor ligands tetracyanoethene (TCNE) and tetracyano-p-quinodimethane (TCNQ) yield mononuclear complexes. An electron transfer autocatalytic mechanism is invoked to rationalize the extremely rapid exchange of THF or phosphite by TCNE or TCNQ as compared with conventional substitution reactions of these carbonylmetal species. Varying degrees of electron transfer from the metal fragments to the acceptor ligands are evident from electrochem. studies and from C$\equiv$N, C:C and C:O stretching frequencies as obtained by IR vibrational spectroscopy. IR data also show that the neutral diamagnetic M(CO)5 complexes are p coordinated whereas the mixed carbonyl/carbocycle contg. metal fragments are bonded in s fashion via nitrile N centers. A p $\rightarrow$ s coordination change has been established ESR-spectroscopically for the one-electron redn. of (TCNE)W(CO)5. on SciFinder(R)
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