The sandwich complexes bis(q6-naphthalene)molybdenum(O) (l), bis(q6-1-methylnaphtha1ene)molybdenum(0) (Z), and bis(q6-1,4-dirnethylnaphthalene)molybdenum(O) (3) are synthesized by cocondensation of Mo-atoms with the naphthalene ligands. Complexes 1-3 are also obtained by reduction of MoCI, or MoCl4.2THF with highly activated Mg in the presence of the naphthalene ligands. Mg was activated by sublimation of the metal in a simple rotating solution reactor. Complex 2 exists as a mixture of regio-and stercoisomers. Three regioisomers, 3a*, are formed in reactions of Mo-atoms with 1,4-dimethylnaphthalene, whereas 3a, the isomer with the Mo-atom coordinated to the unsubstituted rings, is formed selectively via the reductive method. The ligands in 1-3 are highly labile. CO displaces both naphthalene rings in 2 and 3 to give [Mo(CO),], while PF,, P(OMe),, and PMe, displace only one coordinated naphthalene in 1 to yield the [Mo(q6-naphthalene)L3] complexes 46. In toluene, arene exchange is a competitive process in reactions of 1 with PF,. Complexes 5 (L = P(OMe)3) and 6 (L = PMe,) react with HBF, to give the cationic metal hydride complexes 8 and 9. The X-ray crystal structures of [Mo(q6-na~hthaIene){P(OMe)~)J (5) and [M~(H)(q~-naphthaIene){P(OMe),}~][BF~] (8) are reported.