1-arsanaphthalene. The structure of tricarbonyl(2-trimethylsilyl-1-arsanaphthalene)molybdenum

1-Arsanaphthalene (3) and 2-trirnethylsilyl-1-arsanaphthalene (4) have been prepared from the corresponding 1,4-dihydro-1,1-dimethyl-1-stannanaphthale nes 7 and 17, respectively, via an exchange reaction with AsCl3 followed by dehydrohalogenation by DBU. Both 3 and 4 are in mobile equilibrium with th eir head-to-head Diels-Alder dimers. The reaction of 4 with Mo(CO)(3)(Py)(3 ) and BF3. OEt2 affords Mo(CO)(3) complex 5. The crystal structure of 5 sho ws that the Mo(CO)(3) group is eta (6)-bound to the C5As ring of the arsana phthalene.