Reactions of hexacarbonylmolybdenum, hexacarbonyltungsten and arene complexes of tricarbonylmolybdenum and tricarbonyltungsten with trimethyl-and triethyl-aluminium have been studied. It has been found, based on IR and NMR spectra, that trialkylaluminium does not form complexes with hexacarbonyls of molybdenum and tungsten. Arene (mesitylene, toluene and benzene) complexes of tricarbonylmolybdenum form 1 : 1 complexes with triethylaluminium, and arene complexes of tricarbonyltungsten form complexes with trimethyland triethyl-aluminium. Regardless of the molar ratios of reactants (arene)M(CO),/AIEt,, only one of the three CO groups bonded to molybdenum or tungsten forms a complex with AIEt,.Fast exchange between free and complexed trialkylaluminium and an exchange of trialkylaluminium between all three carbonyl groups have been observed in benzene, toluene and decalin solutions. In the 'H NMR spectra of the products of the reactions of (mesitylene)Mo(CO), with AIEt, and AIMe,, signals at -9 to -14 ppm (characteristic for molybdenum hydrides) were present. It confirmed an alkylation of molybdenum followed by 0-or a-hydrogen elimination with the formation of the corresponding molybdenum hydrides, the actual catalyst of aromatic hydrocarbon hydrogenation.

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