The terminal chalcogenido complexes trans-W(PMe(3))(4)(E)(2) (E = S, Se, Te) have been synthesized by the reactions of W(PMe(3))(4)(eta(2)-CH(2)PMe(2))H With H(2)E (E = S, Se) and elemental Te. W(PMe(3))(4)(Te)(2) is the first example of a transition-metal complex containing a terminal tellurido ligand. Each of the chalcogenido complexes W(PMe(3))4(E)2 reacts reversibly with RCHO to yield the eta(2)-aldehyde derivatives W(PMe(3))(2)(E)(2)(eta(2)-OCHR), although the equilibrium constants vary strongly as a function of the chalcogen, with Ks much greater than Ks, > KTe The Phle3 ligands of W(PMe3)4(S)2 and W(PMe(3))(4)(Te)(2) are readily displaced by Bu(t)NC to give W(PMe(3))(2)(CNBUt)(2)(E)(2). In marked contrast, however, the corresponding reaction of the tellurido derivative W(PMe(3))(4)(Te)(2) with Bu(t)NC results in the unprecedented coupling of the two terminal tellurido ligands, leading to the formation of the eta(2)-ditellurido derivative W(PMe(3))(CNBu(t))(4)(eta(2)-Te-2). Structural and bonding aspects of the terminal chalcogenido complexes have been probed by X-ray diffraction, while Se-77 and Te-125 NMR spectroscopies have identified a linear correlation between Se-77 and Te-125 NMR chemical shifts for structurally analogous selenido and tellurido complexes. W(PMe(3))(4)(S)(2) is monoclinic, P2/n (No. 13), a = 15.914(2) Angstrom, b = 9.682(2) Angstrom, c = 15.926(3) Angstrom, beta = 111.92(2)degrees, Z = 4. W(PMe(3))(4)(Se)(2) is monoclinic, P2/n (No. 13), a = 16.040(5) Angstrom, b = 9.738(2) Angstrom, c = 16.096(3) Angstrom, beta = 113.27(2)degrees, Z = 4, W(PMe(3))(4)(Te)(2) is tetragonal, I<(4)over bar2m> (No. 121), a = b = 9.717(1) Angstrom, c = 12.360(2) Angstrom, Z = 2.