Matsubara Toshiaki, Ito Tomoyoshi
Department of Chemistry, Faculty of Science, Kanagawa University , 2946, Tsuchiya, Hiratsuka, Kanagawa 259-1293, Japan.
J Phys Chem A. 2017 Mar 2;121(8):1768-1778. doi: 10.1021/acs.jpca.6b12478. Epub 2017 Feb 20.
The mechanism of the σ bond cleavage of HO, NH, MeC═O, H, CH, BH, and SiH on the Ge═O bond of germanone is examined by means of both quantum mechanical (QM) and molecular dynamics (MD) methods. The QM calculations show that the σ bonds of all the substrates are heterolytically broken on the very largely polarized Ge═O bond. Before the σ bond cleavage, the substrate at first approach the Ge═O germanium in the cases of HO, MeC═O, and NH, and in contrast, the Ge═O oxygen in the cases of H, CH, BH, and SiH. For the cases of HO, NH, and MeC═O, a cluster in which the substrate coordinates to the Ge exists before the σ bond cleavage, and this coordination of the substrate plays an important role on the heterolytic σ bond cleavage. The QM-MD simulations are also conducted for the case of HO, and they show that the kinetic energy of the HO-coordinated cluster especially concentrates on the coordinated HO oxygen to strongly oscillate the coordinate bond between the HO oxygen and the Ge. This oscillation further enlarges just before the O-H σ bond cleavage, and the kinetic energy of this oscillation would be transmitted to the normal mode of the O-H bond breaking. Thus, the coordination and the vibration of the HO oxygen was thought to be an important driving force of the heterolytic cleavage of the O-H σ bond in both electronic and dynamical aspects.
采用量子力学（QM）和分子动力学（MD）方法研究了氢氧根（HO）、氨基（NH）、乙酰基（MeC═O）、氢原子（H）、甲基（CH）、硼氢基（BH）和硅氢基（SiH）在锗酮的锗氧（Ge═O）键上的σ键断裂机理。量子力学计算表明，所有底物的σ键在高度极化的Ge═O键上均发生异裂。在σ键断裂之前，对于HO、MeC═O和NH的情况，底物首先靠近Ge═O键的锗原子，而对于H、CH、BH和SiH的情况，底物则首先靠近Ge═O键的氧原子。对于HO、NH和MeC═O的情况，在σ键断裂之前存在底物与Ge配位的簇，这种底物的配位对异裂σ键断裂起着重要作用。还对HO的情况进行了QM-MD模拟，结果表明，HO配位簇的动能特别集中在配位的HO氧原子上，从而强烈振荡HO氧原子与Ge之间的配位键。这种振荡在O-H σ键断裂之前进一步增大，并将这种振荡的动能传递到O-H键断裂的正常模式。因此，HO氧原子的配位和振动在电子和动力学方面都被认为是O-H σ键异裂的重要驱动力。
