Photodissociation of the phosphine-substituted transition metal carbonyl complexes Cr(CO)5L and Fe(CO)4L:: A theoretical study
Photodissociation of the phosphine-substituted transition metal carbonyl complexes Cr(CO)5L and Fe(CO)4L:: A theoretical study
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DOI：
10.1021/ja029135q
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发表时间：
2003-03-26
影响因子：
15
通讯作者：
Lammertsma, K
中科院分区：
文献类型：
--
作者：
Goumans, TPM;Ehlers, AW;Lammertsma, K
采用瞬态DFT理论研究了膦取代过渡金属羰基配合物Cr(CO)(5)PH3和ax-Fe(CO)(4)PH3的光化学，以探索激发分子驱逐其配体的倾向。将 PH3 配体对这些配合物性质的影响与二元羰基配合物 Cr(CO)(6) 和 Fe(CO)(5) 的光解离行为进行了比较。 Cr(CO)(5)PH3 的最低激发态是金属到配体电荷转移 (MLCT) 态，其中前三个态对 PH3 是排斥的，但对轴向和赤道 CO 配体有适度的键合。排斥性质是由于初始 MLCT 状态与配体场 (LF) 状态的混合所致。如果避免这些状态之间的交叉发生在平衡距离之外，则沿着解离坐标会遇到势垒。这是 CO 排出的情况，但 PH3 基团则不然，因为避免的态跨越发生在平衡 Cr-P 距离内。 ax-Fe(CO)(4)PH3 的最低激发态是 LF 态，对 PH3 和轴向 CO 均具有排斥作用。该态的激发态量子动力学计算表明，轴向膦配体相对于轴向 CO 配体的排斥的支化比为 99 比 1。这些 Cr 和 Fe 配合物中磷配体的性质并不重要。含有三元磷杂环或不饱和磷杂环的配合物的最低激发态解离曲线与具有 PH3 配体的配合物相似。对它们的基态 Cr-P 键性质结合前沿轨道参数的分析表明，这些小杂环基团与 PH3 基团的不同之处主要在于它们增强的 a 供体能力。所有计算表明，激发的 Cr(CO)(5)L 和 Fe(CO)(4)L 分子（L = PH3、PC2H5 和 PC2H3）更倾向于磷取代基的解离而不是 CO 配体的解离。这表明光化学方法可能是对目前用于脱金属过渡金属络合有机磷化合物的配体交换和氧化还原方法的可行补充。
The photochemistry of the phosphine-substituted transition metal carbonyl complexes Cr(CO)(5)PH3 and ax-Fe(CO)(4)PH3 is studied with time-dependent DFT theory to explore the propensity of the excited molecules to expel their ligands. The influence of the PH3 ligand on the properties of these complexes is compared with the photodissociation behavior of the binary carbonyl complexes Cr(CO)(6) and Fe(CO)(5). The lowest excited states of Cr(CO)(5)PH3 are metal-to-ligand charge transfer (MLCT) states, of which the first three are repulsive for PH3 but modestly bonding for the axial and equatorial CO ligands. The repulsive nature is due to mixing of the initial MLCT state with a ligand field (LF) state. A barrier is encountered along the dissociation coordinate if the avoided crossing between these states occurs beyond the equilibrium distance. This is the case for expulsion of CO but not for the PH3 group as the avoided state crossing occurs within the equilibrium Cr-P distance. The lowest excited state of ax-Fe(CO)(4)PH3 is a LF state that is repulsive for both PH3 and the axial CO. Excited-state quantum dynamics calculations for this state show a branching ratio of 99 to 1 for expulsion of the axial phosphine ligand over an axial CO ligand. The nature of the phosphorus ligand in these Cr and Fe complexes is only of modest importance. Complexes containing the three-membered phosphirane or unsaturated phosphirene rings have dissociation curves for their lowest excited states that are similar to those having a PH3 ligand. Analysis of their ground-state Cr-P bond properties in conjunction with frontier orbital arguments indicate these small heterocyclic groups to differ from the PH3 group mainly by their enhanced a-donating ability. All calculations indicate that the excited Cr(CO)(5)L and Fe(CO)(4)L molecules (L = PH3, PC2H5, and PC2H3) prefer dissociation of their phosphorus substituent over that of an CO ligand. This suggests that the photochemical approach may be a viable complement to the ligand exchange and redox methods that are currently employed to demetalate transition metal complexed organophosphorus compounds.