Synthesis, Structure, and Activity of Enhanced Initiators for Olefin Metathesis

A series of ruthenium olefin metathesis catalysts of the general structure (H2IMes)(PR3)(Cl)2RuCHPh (H2IMes = 1,3-dimesityl-4,5-dihydroimidazol-2-ylidene) have been prepared; these complexes
are readily accessible in two steps from commercially available (H2IMes)(PCy3)(Cl)2RuCHPh. Their
phosphine dissociation rate constants (k1), relative rates of phosphine reassociation, and relative reaction
rates in ring-opening metathesis polymerization (ROMP) and ring-closing metathesis (RCM) have been
investigated. The rates of phosphine dissociation (initiation) from these complexes increase with decreasing
phosphine donor strength. Complexes containing a triarylphosphine exhibit dramatically improved initiation
relative to (H2IMes)(PCy3)(Cl)2RuCHPh. Conversely, phosphine reassociation shows no direct correlation
with phosphine electronics. In general, increased phosphine dissociation leads to faster olefin metathesis
reaction rates, which is of direct significance to both organic and polymer metathesis processes.

我们制备了一系列通式为(H2IMes)(PR3)(Cl)₂Ru=CHPh的钌烯烃复分解催化剂，其中H2IMes为1,3-二均三甲苯基-4,5-二氢咪唑-2-亚基；该类配合物可通过市售原料(H2IMes)(PCy3)(Cl)₂Ru=CHPh经两步反应便捷合成。我们对这类配合物的膦解离速率常数（k1）、膦重新缔合相对速率，以及开环复分解聚合（ROMP，Ring-Opening Metathesis Polymerization）和关环复分解（RCM，Ring-Closing Metathesis）中的相对反应速率展开了系统研究。研究发现，这类配合物的膦解离（引发）速率随膦给电子能力的减弱而提升。含三芳基膦配体的配合物，其引发活性相较(H2IMes)(PCy3)(Cl)₂Ru=CHPh有显著提升。与之相反，膦重新缔合过程与膦配体的电子效应并无直接关联。总体而言，膦解离程度的提升会加快烯烃复分解反应速率，这一结论对有机复分解过程与聚合物复分解过程均具有直接的应用价值。