Chloride-supported tungsten alkyne complexes. Synthesis, electronic and molecular structures of [W2Cl4(µ-Cl)2(µ-C2R2)(thf)2](R = H or Me) and [WCl4(η-C2Me2)(thf)](thf = tetrahydrofuran)
The complex Na[W2Cl7(thf)5](thf = tetrahydrofuran) reacts with alkynes to afford the dimetallatetrahedrane complexes [W2Cl4(µ-Cl)2(µ-RC2R′)(thf)2](1, R = R′= Me; 4, R = R′= H; 5, R = R′= Et; 6, R = H, R′= Ph) for which the X-ray crystal structures of 1 and 4 have been determined. In contrast, treatment of the related [W2Cl7(thf)2]– ion with C2Me2 yields the η-bound alkyne complex [NBun4][W2Cl4(µ-Cl)3(η-C2Me2)2]7. The µ-alkyne complex 1 reacts with further C2Me2 to give low yields of the mononuclear η-alkyne derivative [WCl4(η-C2Me2)(thf)]2 which has been structurally characterised. Treatment of 2 with pyridine(py) affords the corresponding adduct [WCl4(η-C2Me2)(py)]3. Treatment of 1 with one or two equivalents of [N(PPh3)2]Cl gives the mono- or dianonic derivatives [N(PPh3)2][W2Cl5(µ-Cl)2(µ-C2Me2)(thf)]8 or [N(PPh3)2]2[W2Cl6(µ-Cl)2(µ-C2Me2)]9 respectively. Extended Hückel molecular orbital calculations suggest that tight metal–µ-alkyne binding in the ditungsten complexes [W2Cl4(µ-Cl)2(µ-RC2R′)(thf)2] Suppresses a potential second-order Jahn–Teller distortion in these systems.