Chiral-at-Metal Ruthenium Complexes with Guanidinobenzimidazole and Pentaphenylcyclopentadienyl Ligands: Synthesis, Resolution, and Preliminary Screening as Enantioselective Second Coordination Sphere Hydrogen Bond Donor Catalysts

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Pentaphenylcyclopentadienyl ruthenium 2-guanidinobenzimidazole (GBI = H N ═C(NHH′)NHC(NHR)═ N R′) chelate complexes are accessed by treating (η 5 -C 5 Ph 5 )Ru(CO) 2 (Br) with Me 3 NO, GBI, and Ag + PF 6 – . Chromatographic workups give [(η 5 -C 5 Ph 5 )Ru(CO)(GBI)] + PF 6 – ( 2 + PF 6 –, 70%; silica gel) or 2 + BAr f – (69%; alumina, then Na + BAr f – (BAr f – = B(3,5-C 6 H 3 (CF 3 ) 2 ) 4 – )). Treatment of 2 + PF 6 – with K + t -BuO – deprotonates the GBI ligand to give the neutral species (η 5 -C 5 Ph 5 )Ru(CO)(GBI –H ) ( 3; 73%). Complexes 2 + PF 6 –, 2 + BAr f –, and 3 have been characterized by NMR, X-ray crystallography, and other methods. Protonation of 3 with enantiopure ( P )-1,1′-binaphthyl-2,2′-diyl hydrogen phosphate (( P )-H- 4 ) gives the diastereomeric salts ( R Ru / S Ru )- 2 + ( P )- 4 – (93%); ( S Ru )- 2 + ( P )- 4 – selectively precipitates from cold toluene/hexanes (35% or 70% of theory), and addition of Na + BAr f – gives ( S Ru )- 2 + BAr f – (71%). The absolute configuration is provisionally assigned by CD spectroscopy. ( S Ru )- 2 + BAr f – is an effective hydrogen bond donor catalyst for a variety of addition reactions by virtue of a synperiplanar NH triad involving the noncoordinating NH groups (some reactions with racemic 3 are also explored), but the enantioselectivities are uniformly low. Nonetheless, this provides insight regarding the mechanism of asymmetric induction for related catalysts with GBI-based carbon stereocenters.