Reactivity of alkynes toward M-η2-CS2 metal complexes. 3. The coupling products obtainable with bis(cyclopentadienyl)molybdenum fragments and their relative stability

[Cp₂Mo-η²-CS₂] (1) is shown to react with one, two, and three molecules of activated alkynes. The nature of the different coupling products and the reaction conditions are described. In particular, while CF₃O≡CCF₃ reacts with 1 to give the metallacycle derivative [Cp₂MoC(S)SC(R)=C(R) ] (2, R = CF₃), the reaction of 1 with CO₂MeC≡CCO₂Me affords two isomers: 3, the analogue of 2 with R = CO₂Me, and [Cp₂ MoSC(S)C(R)=CR] (4, R = CO₂Me). The complexes obtained from the reaction of HC≡CCN with 2 and 3, [CpMo{C₅H₄C(SCH=CHCN)SC(R)=CR}] (5, R = CF₃; 6, R = CO₂Me), correspond to a new type of combination of CS₂ with two alkynes. Direct reaction of 1 with HC≡CCN does not yield an analogue of complexes 5 and 6 but gives depending on the experimental conditions either compound 7 [Cp₂Mo-(C₁₀H₃N₃S₂)], the first example of a complex in which CS₂ is combined with three molecules of alkyne, or [Cp₂Mo(η²-CS₃)] (8) and [S((Z)-CH=CHCN)₂] (9). The crystal and molecular structures of complexes 2, 4, 6, and 7 have been determined by single-crystal X-ray diffraction studies. 2 crystallizes in the monoclinic space group P2₁/c with a = 13.032 (2) Å, b = 8.066 (2) Å, c _= 18.155 (2) Å, β = 124.70 (1)°, U = 1569 (1) ų, and Z = 4. 4 crystallizes in the triclinic space group P1 with a = 7.662 (4) Å, b = 14.661 (5) Å, c = 15.414 (4) Å, α = 96.00 (3)°, β = 96.19 (3)°, γ = 90.79 (4)°, U = 1711.3 (5) ų, and Z = 4. 6 crystallizes in the monoclinic space group P2₁/c with a = 10.246 (4) Å, b = 15.245 (9) Å, c = 15.140 (8) Å, β = 103.89 (5)°, U = 2296 (2) ų, and Z = 4. 7 crystallizes in the orthorhombic space group Pbca with a = 22.089 (5) Å, b = 10.699 (2) Å, c = 15.660 (3) Å, U = 3701 (2) ų, and Z = 8. Extended Hückel calculations and qualitative MO theory are used to analyze the electronic features of the most simple models obtainable from the coupling of CS₂ with an alkyne molecule, namely, Cp₂MoC(S)SC(R)=C(R) (complexes 2 and 3) and Cp₂MoSC(S)C(R)=C(R) (complex 4). The study illustrates the major orbital effects and points out that in the course of the coupling reaction to form the latter complex, the metal may undergo an oxidation state change.