Synthesis And Property Study Of Functional Ru-Based Olefin Metathesis Complexes

Olefin metathesis is a unique carbon skeleton redistribution in which unsaturated carbon-carbon bonds are rearranged in the presence of metal carbene complexes. Recently, Ru-based olefin metathesis catalysts are widely used in organic synthesis. However, similar as many other homogenous catalysts, these ruthenium carbene complexes face some problems needed to be solved, such as recycle, reuse and removal of Ru from the products. In order to resolve these problems, a series of functional Ru carbene olefin metathesis catalysts were designed and synthesized, which were highly recyclable and reusable. Also the Ru residues in the products were significantly decreased.In this paper, the following aspects were included.1. A series of Ru carbene catalysts containing a closo-1, 2-carborane, or an anionic [nido-7, 8-C2B9H11] tag were developed, and their catalytic activities were carefully investigated for the ring-closing metathesis reactions. It is interestingly found that the anionic [nido-7, 8-C2B9H11] appended Ru catalyst exhibits highly robust and recyclable, up to 10 cycles could be achieved in ionic liquid (IL) with only 2.5 mol% Ru loading.2. A pyrene-tagged Ru carbene catalyst was synthesized and immobilized on single-walled carbon nanotubes (SWNTs) viaπ-πstacking interactions. Theseπ-πinteractions were greatly affected by the reaction temperature and the polarity of the solvents, and thus, offering a new reversible immobilization model of these catalysts through polarity control of solvents. Importantly, the SWNTs could also be easily recycled and reused after complete loss of activity of the supported Ru catalysts.3. A ferrocene-tagged Ru carbene complex was prepared, and its polarity could be varied via controlled redox reaction of the ferrocene tag. This Ru catalyst could be immobilized in ionic liquids when the ferrocene was converted to a ferrocene cation by adding a specific oxidant. After the catalytic reaction finished, the Ru catalyst could be separated from the ionic liquids by reduction of ferrocene cation to neutral ferrocene via a suitable reducing agent, and thus offering a new strategy to recycle both the catalysts and the IL. 4. A new recyclable model for homogenous catalyst was proposed, in which the spiropyran (SP) isomer was used as light response "phase transfer shuttle". Inspired by the model, a SP tagged Ru carbene catalyst was designed and synthesized. This Ru catalyst could change from a weak polar state to a strong polar state when SP tag undergoes photoisomerization to turn to merocyanine (MC) under visible light irradiation. The ionic (MC) tag could turn back to neutral SP tag, a weak polarity state, in dark, and these changes are reversible. By this way, the catalyst could be recycled and reused under light-controlled conditions, offering a new model for recycle and reuse of the homogeneous catalysts.