Institute of Chemical Physics, Beijing Institute of Technology, Beijing 100081, PR China.
Inorg Chem. 2010 Feb 15;49(4):1961-75. doi: 10.1021/ic902395v.
The structures for the binuclear Cp(2)Ti(2)(CO)(n) derivatives (Cp = eta(5)-C(5)H(5); n = 8, 7, 6, 5, 4, 3, 2) have been optimized using density functional theory. Furthermore, the thermodynamics of CO dissociation, disproportionation into Cp(2)Ti(2)(CO)(n+1) + Cp(2)Ti(2)(CO)(n-1), and dissociation into mononuclear fragments of these Cp(2)Ti(2)(CO)(n) derivatives have been studied. An unbridged Cp(2)Ti(2)(CO)(8) structure with a long approximately 3.9 A Ti-Ti bond is found. As expected from the long Ti-Ti bond, the predicted dissociation energy of this dimer into CpTi(CO)(4) fragments is relatively low at 7 +/- 3 kcal/mol. The lowest energy Cp(2)Ti(2)(CO)(6) structure has two CpTi(CO)(3) units linked by a formal approximately 2.8 A Ti identical withTi triple bond and thus is the next member of the M identical withM triply bonded series Cp(2)V(2)(CO)(5), Cp(2)Cr(2)(CO)(4), Cp(2)Mn(2)(CO)(3), all three of which are stable compounds. The lowest energy structures of Cp(2)Ti(2)(CO)(7), Cp(2)Ti(2)(CO)(5), and Cp(2)Ti(2)(CO)(4) all contain one or two four-electron donor bridging eta(2)-mu-CO groups. However, they are not likely to be stable molecules since their disproportionation energies into Cp(2)Ti(2)(CO)(n+1) + Cp(2)Ti(2)(CO)(n-1) are either nearly thermoneutral (n = 5) or exothermic (n = 7 and 4). The lowest energy structure of Cp(2)Ti(2)(CO)(3), in which all three carbonyl groups are four-electron donor eta(2)-mu-CO groups bridging a approximately 3.05 A formal Ti-Ti single bond, is a promising synthetic target since it is thermodynamically stable with respect to both CO dissociation and disproportionation into Cp(2)Ti(2)(CO)(4) + Cp(2)Ti(2)(CO)(2). In the lowest energy Cp(2)Ti(2)(CO)(2) structure both carbonyl groups are four-electron donor eta(2)-mu-CO groups bridging a formal 2.74 A Ti[triple bond]Ti triple bond. These low energy Cp(2)Ti(2)(CO)(n) (n = 3, 2) structures have only a 16-electron titanium configuration rather than the usually favorable 18-electron configuration for metal carbonyl complexes.
双核 Cp(2)Ti(2)(CO)(n) 衍生物（Cp = eta(5)-C(5)H(5); n = 8, 7, 6, 5, 4, 3, 2）的结构已使用密度泛函理论进行了优化。此外，还研究了 CO 解离、歧化为 Cp(2)Ti(2)(CO)(n+1) + Cp(2)Ti(2)(CO)(n-1) 以及这些 Cp(2)Ti(2)(CO)(n) 衍生物的单体碎片解离的热力学。发现了具有大约 3.9 A Ti-Ti 键的无桥接 Cp(2)Ti(2)(CO)(8)结构。由于 Ti-Ti 键较长，预计该二聚体解离成 CpTi(CO)(4)片段的解离能相对较低，为 7 +/- 3 kcal/mol。最低能量的 Cp(2)Ti(2)(CO)(6)结构具有两个 CpTi(CO)(3)单元，通过一个形式上大约 2.8 A 的 Ti-Ti 三重键连接，因此是 M 等于 M 三重键系列 Cp(2)V(2)(CO)(5)、Cp(2)Cr(2)(CO)(4)、Cp(2)Mn(2)(CO)(3)的下一个成员，所有这三个都是稳定的化合物。Cp(2)Ti(2)(CO)(7)、Cp(2)Ti(2)(CO)(5)和 Cp(2)Ti(2)(CO)(4)的最低能量结构都包含一个或两个四电子供体桥接 eta(2)-mu-CO 基团。然而，它们不太可能是稳定的分子，因为它们歧化为 Cp(2)Ti(2)(CO)(n+1) + Cp(2)Ti(2)(CO)(n-1) 的能量要么几乎是热中性的（n = 5），要么是放热的（n = 7 和 4）。Cp(2)Ti(2)(CO)(3)的最低能量结构，其中所有三个羰基都是四电子供体 eta(2)-mu-CO 基团，桥接一个大约 3.05 A 的形式 Ti-Ti 单键，是一个有前途的合成目标，因为它在 CO 解离和歧化为 Cp(2)Ti(2)(CO)(4) + Cp(2)Ti(2)(CO)(2)方面都是热力学稳定的。在最低能量的 Cp(2)Ti(2)(CO)(2)结构中，两个羰基都是四电子供体 eta(2)-mu-CO 基团，桥接一个形式上的 2.74 A Ti[三重键]Ti 三重键。这些低能 Cp(2)Ti(2)(CO)(n)（n = 3,2）结构只有 16 个电子的钛配置，而不是通常有利的 18 个电子的金属羰基配合物配置。
