Synthesis and Activity of Ruthenium Alkylidene Complexes Coordinated with Phosphine and N-Heterocyclic Carbene Ligands

This paper reports the synthesis and characterization of a variety of ruthenium complexes
coordinated with phosphine and N-heterocyclic carbene (NHC) ligands. These complexes include several
alkylidene derivatives of the general formula (NHC)(PR3)(Cl)2RuCHR‘, which are highly active olefin
metathesis catalysts. Although these catalysts can be prepared adequately by the reaction of bis(phosphine)
ruthenium alkylidene precursors with free NHCs, we have developed an alternative route that employs
NHC-alcohol or -chloroform adducts as “protected” forms of the NHC ligands. This route is advantageous
because NHC adducts are easier to handle than their free carbene counterparts. We also demonstrate
that sterically bulky bis(NHC) complexes can be made by reaction of the pyridine-coordinated precursor
(NHC)(py)2(Cl)2RuCHPh with free NHCs or NHC adducts. Two crystal structures are presented, one of
the mixed bis(NHC) derivative (H2IMes)(IMes)(Cl)2RuCHPh, and the other of (PCy3)(Cl)(CO)Ru[η2-(CH2-C6H2Me2)(N2C3H4)(C6H2Me3)], the product of ortho methyl C−H bond activation. Other side reactions
encountered during the synthesis of new ruthenium alkylidene complexes include the formation of hydrido-carbonyl-chloride derivatives in the presence of primary alcohols and the deprotonation of ruthenium
vinylcarbene ligands by KOBut. We also evaluate the olefin metathesis activity of NHC-coordinated
complexes in representative RCM and ROMP reactions.

本论文报道了一系列由膦配体与氮杂环卡宾（N-heterocyclic carbene, NHC）配位的钌配合物的合成与表征。这类配合物包含多款通式为(NHC)(PR3)(Cl)2Ru=CHR'的亚烷基衍生物，均为高活性烯烃复分解催化剂。尽管通过双膦亚烷基钌前驱体与游离氮杂环卡宾的反应即可充分制备这类催化剂，但我们开发了一种替代合成路线：以氮杂环卡宾-醇或氮杂环卡宾-三氯甲烷加合物作为氮杂环卡宾配体的"保护态"形式。该路线的优势在于，氮杂环卡宾加合物相较于其游离卡宾形式更易于处理。我们还证实，通过吡啶（pyridine）配位前驱体(NHC)(py)2(Cl)2Ru=CHPh与游离氮杂环卡宾或氮杂环卡宾加合物的反应，可制备空间位阻较大的双(NHC)钌配合物。本文呈现两种晶体结构：其一为混合型双(NHC)衍生物(H2IMes)(IMes)(Cl)2Ru=CHPh；其二为(三环己基膦(tricyclohexylphosphine, PCy3))(Cl)(CO)Ru[η²-(CH2-C6H2Me2)(N2C3H4)(C6H2Me3)]，即邻位甲基碳氢键活化产物。在新型亚烷基钌配合物的合成过程中，还遇到了其他副反应：包括在伯醇存在下生成氢基-羰基-氯配合物，以及叔丁醇钾（potassium tert-butoxide, KOBut）对钌乙烯基卡宾配体的去质子化反应。我们还评估了氮杂环卡宾配位的配合物在典型环烯烃复分解环化（ring-closing metathesis, RCM）与开环易位聚合（ring-opening metathesis polymerization, ROMP）反应中的烯烃复分解催化活性。