Department of Chemistry, Tulane University, 6400 Freret Street, New Orleans, Louisiana 70118-5698, USA.
Inorg Chem. 2012 Jan 2;51(1):346-61. doi: 10.1021/ic201748v. Epub 2011 Dec 6.
The tetracarbonyl compounds [W(mdt)(CO)(4)] (1) and [W(Me(2)pipdt)(CO)(4)] (2) both have dithiolene-type ligands (mdt(2-) = 1,2-dimethyl-1,2-dithiolate; Me(2)pipdt = 1,4-dimethylpiperazine-2,3-dithione) but different geometries, trigonal prismatic (TP) and octahedral, respectively. Structural data suggest an ene-1,2-dithiolate ligand description, hence a divalent tungsten ion, for 1 and a dithioketone ligand, hence W(0) oxidation state, for 2. Density functional theory (DFT) calculations on 1 show the highest occupied molecular orbital (HOMO) to be a strong W-dithiolene π bonding interaction and the lowest unoccupied molecular orbital (LUMO) its antibonding counterpart. The TP geometry is preferred because symmetry allowed mixing of these orbitals via a configuration interaction (CI) stabilizes this geometry over an octahedron. The TP geometry for 2 is disfavored because W-dithiolene π overlap is attenuated because of a lowering of the sulfur content and a raising of the energy of this ligand π orbital by the conjugated piperazine nitrogen atoms in the Me(2)pipdt ligand. A survey of the Cambridge Structural Database identifies other W(CO)(4) compounds with pseudo C(4v) disposition of CO ligands and suggests a d(4) electron count to be a probable common denominator. Reduction of 1 induces a geometry change to octahedral because the singly occupied molecular orbital (SOMO) is at lower energy in this geometry. The cyclic voltammogram of 1 in CH(2)Cl(2) reveals a reduction wave at -1.14 V (vs Fc(+)/Fc) with an unusual offset between the cathodic and the anodic peaks (ΔE(p)) of 0.130 V, which is followed by a second, reversible reduction wave at -1.36 V with ΔE(p) = 0.091 V. The larger ΔE(p) observed for the first reduction is evidence of the trigonal prism-to-octahedron geometry change attending this process. Tungsten L(1)-edge X-ray absorption (XAS) data indicate a higher metal oxidation state in 1 than 2. Electron paramagnetic resonance data for 1 and 2 are both diagnostic of dithiolene ligand-based sulfur radical, indicating that one-electron reduction of 1 involves two-electron reduction of tungsten and one-electron oxidation of dithiolene ligand.
四羰基化合物[W(mdt)(CO)(4)]（1）和[W(Me(2)pipdt)(CO)(4)]（2）均具有二硫烯型配体（mdt(2-) = 1,2-二甲基-1,2-二硫代；Me(2)pipdt = 1,4-二甲基哌嗪-2,3-二硫酮），但具有不同的几何形状，分别为三角棱柱（TP）和八面体。结构数据表明 1 具有烯-1,2-二硫醇配体描述，因此为二价钨离子，而 2 具有二硫酮配体，因此为 W(0)氧化态。对 1 进行密度泛函理论（DFT）计算表明，最高占据分子轨道（HOMO）是强 W-二硫烯π键合相互作用，最低未占据分子轨道（LUMO）是其反键对应物。TP 几何结构是优选的，因为对称允许通过组态相互作用（CI）混合这些轨道，从而稳定了这种几何结构而不是八面体。2 的 TP 几何结构不受青睐，因为由于共轭哌嗪氮原子的存在，降低了硫含量并提高了 Me(2)pipdt 配体的π轨道能量，因此削弱了 W-二硫烯π重叠。对剑桥结构数据库的调查确定了其他具有 CO 配体伪 C(4v)排布的 W(CO)(4)化合物，并表明 d(4)电子计数可能是一个常见的因素。1 的还原导致几何结构变为八面体，因为单占据分子轨道（SOMO）在这种几何结构中处于较低的能量。1 在 CH(2)Cl(2)中的循环伏安图显示在-1.14 V（相对于 Fc(+)/Fc）处有一个还原波，其阴极和阳极峰之间的异常偏移（ΔE(p)）为 0.130 V，随后在-1.36 V 处有第二个可逆还原波，ΔE(p) = 0.091 V。第一个还原观察到的较大的ΔE(p)证明了该过程中伴随的三角棱柱到八面体的几何结构变化。钨 L(1)边 X 射线吸收（XAS）数据表明 1 中的金属氧化态高于 2。1和2的电子顺磁共振数据均诊断为二硫烯配体基硫自由基，表明 1 的单电子还原涉及两个电子还原钨和一个电子氧化二硫烯配体。
