School of Chemistry, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
Chemistry. 2012 Oct 8;18(41):13180-7. doi: 10.1002/chem.201201542. Epub 2012 Sep 11.
Hollow graphitized carbon nanofibres (GNF) are employed as nanoscale reaction vessels for the hydrosilylation of alkynes. The effects of confinement in GNF on the regioselectivity of addition to triple carbon-carbon bonds are explored. A systematic comparison of the catalytic activities of Rh and RhPt nanoparticles embedded in a nanoreactor with free-standing and surface-adsorbed nanoparticles reveals key mechanisms governing the regioselectivity. Directions of reactions inside GNF are largely controlled by the non-covalent interactions between reactant molecules and the nanofibre channel. The specific π-π interactions increase the local concentration of the aromatic reactant and thus promote the formation of the E isomer of the β-addition product. In contrast, the presence of aromatic groups on both reactants (silane and alkyne) reverses the effect of confinement and favours the formation of the Z isomer due to enhanced interactions between aromatic groups in the cis-orientation with the internal graphitic step-edges of GNF. The importance of π-π interactions is confirmed by studying transformations of aliphatic reactants that show no measurable changes in regioselectivity upon confinement in carbon nanoreactors.
中空石墨化碳纳米纤维 (GNF) 可用作炔烃氢硅烷化的纳米尺度反应容器。研究了在 GNF 中的受限效应对三碳-碳键加成区域选择性的影响。将嵌入纳米反应器中的 Rh 和 RhPt 纳米颗粒与自由和表面吸附纳米颗粒的催化活性进行系统比较，揭示了控制区域选择性的关键机制。GNF 内部反应的方向主要受反应物分子与纳米纤维通道之间的非共价相互作用控制。特定的π-π相互作用增加了芳香族反应物的局部浓度，从而促进了β加成产物 E 异构体的形成。相比之下，由于反应物（硅烷和炔烃）上都存在芳族基团，增强了顺式构象中芳族基团与 GNF 内部石墨阶梯之间的相互作用，从而导致受限效应反转，并有利于 Z 异构体的形成。通过研究没有在碳纳米反应器中受到限制时在区域选择性上没有可测量变化的脂肪族反应物的转化，证实了π-π相互作用的重要性。
