Tellurium does not insert directly into the MnC bond of RMn(CO)5 (R = Me or PhCH2). However, reactions between RMn(CO)5 (R = Me, PhCH2) and TePR′3 (R′ = Me, Et) result in Te insertion accompanied by CO substitution to produce RTeMn(CO)3(PR′3)2 complexes. These complexes are formed by initial substitution to give RMn(CO)3(PR′3)2 followed by Te insertion. The crystal structure of the complex with R = PhCH2 and R′ = Et has been determined from X-ray diffraction data. Crystal data: C22H37O3P2MnTe; M = 594.0; P1, a = 9.263(2), b = 14.650(5), c = 20.265(7)Å, α = 91.27(3), β = 90.67(2), γ = 103.96(2)°, U = 2667.7(14) Å3; Dcalc = 1.479 (Z = 4), Dmeas = 1.480(5) mg m-3, μ = 1.687 mm-1 for Mo-Kα radiation (λ = 0.7107 Å), final R = 3.11, Rw = 5.46, from 7788 observed reflections (12974 collected). The geometry about manganese is slightly distorted octahedral with a trans-arrangement of the phosphine groups and a meridional placement of the carbonyls. Pyrolysis of PhCH2TeMn(CO)3(PEt3)2 at 300°C in a hydrogen stream gives a film of MnTe. Treatment of Mn(CO)5Br with LiTeR yields the dimeric products [Mn(CO)4(μ-TeR)]2 (R = Me, Et, Pri, CH2SiMe3, Si(SiMe3)3, and Ph). For most of these complexes, two conformations have been detected by multinuclear NMR spectroscopy. Variable temperature 1H NMR spectroscopy shows that the conformers interconvert for R = Me and CH2SiMe3. The mass spectra of [Mn(CO)4(μ-TeR)]2 (R = Me, Et, Pri) show gas phase fragmentation to MnxTey species. Pyrolysis of two of these complexes (R = Me, Et) in a hydrogen atmosphere produced a film containing MnTe. Addition of PEt3 to a solution of [Mn(CO)4(μ-TeME)]2 results in bridge cleavage to yield MeTeMn(CO)3(PEt3)2, but the reaction is slow and other unidentified products are formed. A similar reaction occurs when R = CH2SiMe3. The formation of MeTeMn(CO)3 (PEt3)2 was also achieved from the reaction between BrMn(CO)3(PEt3)2 and LiTeMe. The HgMn complex MeHgMn(CO)5 was obtained by treatment of [Mn(CO)5]- with MeHgCl. This complex readily disproportionates to Me2Hg and Hg[Mn(CO)5]2. Pyrolysis of MeHgMn(CO)5 at 300°C gives a film of manganese with no retention of mercury.