1-Arsanaphthalene. The Structure of Tricarbonyl(2-trimethylsilyl-1-arsanaphthalene)molybdenum

1-Arsanaphthalene (3) and 2-trimethylsilyl-1-arsanaphthalene (4) have been prepared from the corresponding 1,4-dihydro-1,1-dimethyl-1-stannanaphthalenes 7 and 17, respectively, via an exchange reaction with AsCl3 followed by dehydrohalogenation by DBU. Both 3 and 4 are in mobile equilibrium with their 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 shows that the Mo(CO)3 group is η6-bound to the C5As ring of the arsanaphthalene.