Cationic metal carbonyls halogen-containing

Recently we have been interested in phosphine-containing carbonyl cations of the noble metals (55) such as [M(CO)3(PR3)2X]+ (M = Fe, Ru, Os X = halogen) and [M(CO)2(PR3)2]+ (M = Rh, Ir) which we prepared from the corresponding metal carbonyl halides under atmospheric CO pressure. 

Using a somewhat different approach, Fischer and Fichtel (85) have obtained a variety of ethylene-containing cationic complexes by reaction of TT-cyclopentadienyl carbonyl halides of Mo, W, and Fe with ethylene under pressure in the presence of aluminum chloride. The cations were isolated in the form of their salts with heavy anions such as PFe , B(C6H5)4, etc. Presumably the aluminum chloride serves as a halogen acceptor and activates a coordination site on the metal, facilitating coordination of ethylene. 

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