Mo(PMe(3))(6) has been synthesized by the reduction of MoCl5 with Na(K) alloy using PMe(3) as a reactive solvent. In solution, Mo(PMe(3))(6) exists in equilibrium with Mo(PMe(3))(4)(eta(2)-CH(2)PMe(2))H and PMe(3). At 30 degrees C, the equilibrium constant is a factor of ca. 2 x 10(3) less than that for the analogous tungsten system. The reactions of Mo(PMe(3))(6) and Mo(PMe(3))(4)(eta(2)-CH(2)PMe(2))H With H2S, H2Se, Se, and Te/PMe(3) have provided convenient syntheses of Mo(PMe(3))(4)(E)(2) (E = S, Se, Te), the first series of terminal sulfide, selenido, and tellurido derivatives of molybdenum. Mo(PMe(3))(4)(S)(2) is monoclinic, P2/n (No. 13), a = 15.947(6) Angstrom, b = 9.704(2) Angstrom, c = 15.980(3) Angstrom, beta = 112.24(2)degrees, V = 2289(1) Angstrom(3), Z = 4. Mo(PMe(3))(4)(Se)(2) is monoclinic, P2/n (No. 13), a = 16.105(3) Angstrom, b = 9.777(3) A, c = 16.136(4) Angstrom, beta = 113.34(2)degrees, V = 2332(1) Angstrom(3), Z = 4. Mo(PMe(3))(4)(Te)(2) is tetragonal, I ($) over bar 42m (No. 121), a = b = 9.738(1) Angstrom, c = 12.373(2) Angstrom, V = 1171.2(6) Angstrom(3), Z = 2.