Cyclic Ruthenium(II)-Halocarbon Complexes Derived from Ru(II)-Induced Cyclization of Homopropargylic Halopyridines: Mechanism, Bonding and Reactivity

Abstract

The activation of various homopropargylic pyridines by cis-[Ru^II/Os^II(dppm)₂Cl₂] (dppm=1,1-bis(diphenylphosphino)methane) has previously been shown to generate a diverse array of metallacycles and metalated heterocyclic complexes. However, a minor structural modification of introducing a halide onto the pyridyl group of the alkyne substrate resulted in the formation of unprecedented Ru(II)/Os(II)-haloquinolizine complexes. These complexes display (1) κ²(X,C)-haloquinolizine chelates arising from the cycloisomerization of HC≡CC(OH)(CH₂(6-X-2-py))(Ph) on [Ru^II/Os^II(dppm)₂]²⁺ moieties via a vinylidene pathway, (2) five-membered Ru/Os-X-C-N-C rings (X=F, Cl, Br) ortho- and peri-fused to quinolizinium skeletons, and (3) uncommon M-X-R bonding interactions that are atypical in coordination complexes. Despite being divalent and integrated into a five-membered Ru-X-C-N-C ring system, the X atoms in the Ru(II) complexes are susceptible to substitution by O in the presence of ^-OH, resulting in the formation of quinolizinium-fused ruthenaoxazole complexes. Overall, this work highlights the importance of considering metal-halocarbon bonding interactions in catalytic or coordination designs.

Keywords: @WongLabCHEMCit1; Alkynes; Chelates; Cyclization; Halocarbon; Ruthenium.