Pyrylium cations/ions/salts formation

The formation of 17-electron radicals as the result of thermal electron transfer from a carbonyl metallate to a cationic pyrylium acceptor (P+) is also observed with the charge-transfer salts of [TpM(CO)3 ] (Tp = hydrido-fn s-(3,5-dimethylpyrazolyl)-borate M = Mo, W, Cr) [127]. Owing to the stability of the TpM(CO)3 radical [182], electron-transfer equilibria (Eet) are established by UV-Vis and IR spectroscopy which generally favor the intimate ion-pair state (see Structure D in Figure 5) in accord with the electron-transfer energetics [127] (Eq. 57). 

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