Olefin metathesis for metal incorporation and ligand exchange reactions for the preparation of new ruthenium compounds and materials
Two different strategies have been employed for the synthesis of ruthenium compounds and materials: Olefin Metathesis for Metal Incorporation (OMMI) and ligand exchange. OMMI was used to attach Ru to polyenes large and small, including PA, to give an orgamometallic polymer and compounds of the form L 2 Cl 2 Ru=CH(CH=CH) n CH=RuL 2 Cl 2 ( n = 0, 1).
Metal containing polymers have been prepared by treating polyacetylene (PA) with the olefin metathesis catalyst (H 2 IMes)RuCl 2 (=CHPh)(3-bromopyridine) 2 (G2B) to form "metal-incorporated polyacetylene" (MIPA). Many properties of the MIPAs mimicked those of the untreated polyacetylene, including iodine-doped conductivity. The resulting MIPA materials have been shown to be metathesis active. This process uses a new method for the preparation of the polymer through the polymerization of acetylene with G2B. The application of this method to graphite, rather than polyacetylene, has shown small amounts of incorporation of the ruthenium into the material. The ruthenium incorporated in the graphite no longer remains active towards methathesis.
The synthesis of complexes with n = 0 or 1 has been studied using the combination of two previously known strategies for metathesis reactions, namely OMMI and Relay Ring-Closing Metathesis (RRCM). Relay OMMI has been used in a proof-of-principle experiment to prepare a known conjugated diruthenium bisalkylidene complex, [(Cy 3 P) 2 Cl 2 Ru] 2 (μ-CHCH=CHCH). This method was applied towards the preparation of compounds previously inaccessible by direct OMMI on the CH 2 -terminated polyene. Spectroscopic evidence is suggestive that [(Cy 3 P) 2 Cl 2 Ru](μ-CH=CH) was formed in small quantities in the reaction. The steric strain in the molecule presumably makes it highly reactive.
The synthesis of several other ruthenium compounds using ligand exchange reactions began primarily with (PCy 3 ) 2 RuCl 2 (=CHPh) ( G1 ). One class of compounds used bridging bis(imidazolium) ligands. Benzobis(imidazolium) salts have been synthesized with many different substituents and numerous attempts have been made to attach these ligands to Ru to form metathesis active, diruthenium complexes. In all but one case, this has resulted in the recovery of starting materials. Reactions between tetrakis(tolyl) benzobis(imidazolium) chloride and G1 have resulted in the isolation of a new ruthenium compound. This new compound has been shown to be methathesis active.
Through the addition of measured amounts of carbon monoxide to (H 2 IMes)(PR 3 )RuCl 2 (=CHPh) (R = Me or Bu), saturated 18-electron complexes have been isolated. Excess CO resulted in the insertion of the benzylidene moiety into the N-heterocyclic carbene ligand, H 2 IMes.
Ligand exchange reactions have also been used for a class of compounds being developed that are aurophilic versions of Grubbs first-generation catalyst (G1) through the ligand substitution of G1 with bipyridine and a triazolium ligand. These compounds are intended to be used for single molecule conductivity studies. The progress towards aurophilic compounds is reported.