Metal-Templated Hydrogen Bond Donors as “Organocatalysts” for Carbon–Carbon Bond Forming Reactions: Syntheses, Structures, and Reactivities of 2‑Guanidinobenzimidazole Cyclopentadienyl Ruthenium Complexes

The reaction of 2-guanidinobenzimidazole (GBI) and (η5-C5H5)­Ru­(PPh3)2(Cl) in refluxing toluene gives the chelate [(η5-C5H5)­Ru­(PPh3)­(GBI)]+Cl– (1+Cl–; 96%). Subsequent anion metatheses yield the BF4–, PF6–, and BArf– (B­(3,5-C6H3(CF3)2)4–) salts (77–85%). Reactions with CO give the carbonyl complexes [(η5-C5H5)­Ru­(CO)­(GBI)]+X– (2+X–; X– = Cl–, BF4–, PF6–, BArf–; 87–92%). The last three salts can also be obtained by anion metatheses of 2+Cl– (77–87%), as can one with the chiral enantiopure anion P­(o-C6Cl4O2)3– ((Δ)-TRISPHAT–; 81%). The reaction of [(η5-C5H5)­Ru­(CO)­(NCCH3)2]+PF6– and GBI also gives 2+PF6– (81%). The pentamethylcyclopentadienyl analogues [(η5-C5Me5)­Ru­(CO)­(GBI)]+X– (3+X–; X– = Cl–, BF4–, PF6–, BArf–; 61–84%) are prepared from (η5-C5Me5)­Ru­(PPh3)2(Cl), GBI, and CO followed (for the last three) by anion metatheses. An indenyl complex [(η5-C9H7)­Ru­(PPh3)­(GBI)]+Cl– (96%) is prepared from (η5-C9H7)­Ru­(PPh3)2(Cl) and GBI. All complexes are characterized by NMR (1H, 13C, 31P, 19F, 11B), with 2D spectra aiding assignments. Crystal structures of 1+PF6–·CH2Cl2 and 1+BArf–·CH2Cl2 are determined; the anion is hydrogen bonded to the cation in the former. Complexes 1–3+X– are evaluated as catalysts (10 mol %, RT) for condensations of indoles and trans-β-nitrostyrene. The chloride salts are ineffective (0–5% yields, 48–60 h), but the BArf– salts exhibit excellent reactivities (97–46% yields, 1–48 h), with the BF4– and PF6– salts intermediate. Evidence for hydrogen bonding of the nitro group to the GBI ligand is presented. GBI shows no catalytic activity; a BArf– salt of methylated GBI is active, but much less so than 2–3+BArf–.