Complexation of the Triply-Bonded Dirhenium(II) Complex Re₂Cl₄(μ-dppm)₂ (dppm = Ph₂PCH₂PPh₂) by Up to Three Acetylene Molecules

The triply bonded dirhenium(II) synthons Re2X4(μ-dppm)2 (X = Cl, Br; dppm = Ph2PCH2PPh2) react with acetylene at room temperature in CH2Cl2 and acetone to afford the bis(acetylene) complexes Re2X4(μ-dppm)2(μ:η2,η2-HCCH)(η2-HCCH) (X = Cl (3), Br(4)). Compound 3 has been derivatized by reaction with RNC ligands in the presence of TlPF6 to give unsymmetrical complexes of the type [Re2Cl3(μ-dppm)2(μ:η2,η2-HCCH)(η2-HCCH)(CNR)]PF6 (R = Xyl (5), Mes (6), t-Bu (7)), in which the RCN ligand has displaced the chloride ligand cis to the η2-HCCH ligand. The reaction of 3 with an additional 1 equiv of acetylene in the presence of TlPF6 gives the symmetrical all-cis isomer of [Re2Cl3(μ-dppm)2(μ:η2,η2-HCCH)(η2-HCCH)2]PF6 (8). The two terminal η2-HCCH ligands in 8 are very labile and can be displaced by CO and XylNC to give the complexes [Re2Cl3(μ-dppm)2(μ:η2,η2-HCCH)(L)2]Y (L = CO when Y = PF6 (9); L = CO when Y = (PF6)0.5/(H2PO4)0.5 (10); L = XylNC when Y = PF6 (11)). These substitution reactions proceed with retention of the all-cis stereochemistry. Single-crystal X-ray structure determinations have been carried out on complexes 3, 5, 8, 10, and 11. In no instance have we found that the acetylene ligands undergo reductive coupling reactions.三键合二铼(II)合成子Re₂X₄(μ-dppm)₂（X=Cl、Br；dppm=双(二苯基膦)甲烷，Ph₂PCH₂PPh₂）在二氯甲烷与丙酮的混合溶剂中，于室温下与乙炔反应，生成双(乙炔)配合物Re₂X₄(μ-dppm)₂(μ:η²,η²-HCCH)(η²-HCCH)（X=Cl(3)、Br(4)）。 配合物3可在六氟磷酸亚铊（TlPF₆）存在下与异氰配体（RNC）发生衍生化反应，得到通式为[Re₂Cl₃(μ-dppm)₂(μ:η²,η²-HCCH)(η²-HCCH)(CNR)]PF₆的不对称配合物（R=二甲苯基(Xyl,5)、均三甲苯基(Mes,6)、叔丁基(t-Bu,7)），其中RCN配体取代了与η²-HCCH配体顺位的氯离子。 将配合物3与额外1当量的乙炔在六氟磷酸亚铊存在下反应，可得到全顺式对称异构体[Re₂Cl₃(μ-dppm)₂(μ:η²,η²-HCCH)(η²-HCCH)₂]PF₆(8)。 配合物8中的两个端基η²-HCCH配体具有较高反应活性，可被CO与二甲苯基异氰（XylNC）取代，生成通式为[Re₂Cl₃(μ-dppm)₂(μ:η²,η²-HCCH)(L)₂]Y的配合物：当L=CO时，Y=PF₆(9)；当L=CO时，Y=(PF₆)₀.₅/(H₂PO₄)₀.₅(10)；当L=XylNC时，Y=PF₆(11)。此类取代反应可在保持全顺式立体化学的前提下顺利进行。 目前已对配合物3、5、8、10及11完成单晶X射线结构测定。在所有测试案例中，均未观察到乙炔配体发生还原偶联反应。