Metal-Templated Hydrogen Bond Donors as 鈥淥rganocatalysts鈥?for Carbon鈥揅arbon Bond Forming Reactions: Syntheses, Structures, and Reactivities of 2-Guanidinobenzimidazole Cyclopentadienyl Ruthenium Compl
文摘
The reaction of 2-guanidinobenzimidazole (GBI) and (畏5-C5H5)Ru(PPh3)2(Cl) in refluxing toluene gives the chelate [(畏5-C5H5)Ru(PPh3)(GBI)]+Cl鈥?/sup> (1+Cl鈥?/sup>; 96%). Subsequent anion metatheses yield the BF4鈥?/sup>, PF6鈥?/sup>, and BArf鈥?/sup> (B(3,5-C6H3(CF3)2)4鈥?/sup>) salts (77鈥?5%). Reactions with CO give the carbonyl complexes [(畏5-C5H5)Ru(CO)(GBI)]+X鈥?/sup> (2+X鈥?/sup>; X鈥?/sup> = Cl鈥?/sup>, BF4鈥?/sup>, PF6鈥?/sup>, BArf鈥?/sup>; 87鈥?2%). The last three salts can also be obtained by anion metatheses of 2+Cl鈥?/sup> (77鈥?7%), as can one with the chiral enantiopure anion P(o-C6Cl4O2)3鈥?/sup> ((螖)-TRISPHAT鈥?/sup>; 81%). The reaction of [(畏5-C5H5)Ru(CO)(NCCH3)2]+PF6鈥?/sup> and GBI also gives 2+PF6鈥?/sup> (81%). The pentamethylcyclopentadienyl analogues [(畏5-C5Me5)Ru(CO)(GBI)]+X鈥?/sup> (3+X鈥?/sup>; X鈥?/sup> = Cl鈥?/sup>, BF4鈥?/sup>, PF6鈥?/sup>, BArf鈥?/sup>; 61鈥?4%) are prepared from (畏5-C5Me5)Ru(PPh3)2(Cl), GBI, and CO followed (for the last three) by anion metatheses. An indenyl complex [(畏5-C9H7)Ru(PPh3)(GBI)]+Cl鈥?/sup> (96%) is prepared from (畏5-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鈥?/sup>路CH2Cl2 and 1+BArf鈥?/sup>路CH2Cl2 are determined; the anion is hydrogen bonded to the cation in the former. Complexes 1鈥?b>3+X鈥?/sup> are evaluated as catalysts (10 mol %, RT) for condensations of indoles and trans-尾-nitrostyrene. The chloride salts are ineffective (0鈥?% yields, 48鈥?0 h), but the BArf鈥?/sup> salts exhibit excellent reactivities (97鈥?6% yields, 1鈥?8 h), with the BF4鈥?/sup> and PF6鈥?/sup> salts intermediate. Evidence for hydrogen bonding of the nitro group to the GBI ligand is presented. GBI shows no catalytic activity; a BArf鈥?/sup> salt of methylated GBI is active, but much less so than 2鈥?b>3+BArf鈥?/sup>.