Synthesis and Characterization of Pyridine‐Ligated Bicyclic (Alkyl)(Amino)Carbene (BICAAC) Ruthenium Alkylidene Complexes

Grubbs‐type ruthenium–alkylidene catalysts are pivotal in olefin metathesis, with improved activity and initiation achieved through ligand design. While NHC‐ and CAAC‐based systems are well established, robust and strongly σ‐donating BICAACs remain underexplored, particularly in pyridine‐activated third‐generation catalysts important for Ring‐Opening Metathesis Polymerization (ROMP). Here we report the first synthesis and full characterization of pyridine‐ligated BICAAC–Ru alkylidene complexes. Using a modified Grubbs protocol that avoids bis‐carbene formation, pyridine complexes ( 1a – 3a , 3b ) were prepared from in situ generated BICAACs and bis‐pyridine phosphine intermediates. Spectroscopic, crystallographic, and DFT studies show that steric congestion at Ru disfavors bis‐pyridine coordination, with a second pyridine. These results establish pyridine‐coordinated BICAAC–Ru complexes as a well‐defined platform for next‐generation metathesis catalysts.