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Title: Intramolecular N-H⋯H-Ru proton-hydride interaction in ruthenium complexes with (2-(dimethylamino)ethyl)cyclopentadienyl and (3-(dimethylamino)propyl)cyclopentadienyl ligands. Hydrogenation of CO2 to formic acid via the N-H⋯H-Ru hydrogen-bonded complexes
Authors: Chu, HS
Lau, CP
Wong, KY 
Wong, WT 
Issue Date: 1998
Source: Organometallics, 1998, v. 17, no. 13, p. 2768-2777
Abstract: Addition of 1 equiv of HBF4 to (η5-C5H4(CH2) nNMez)RuH(dppm) (n = 2, 3) gave [(η5-C5H4(CH2) nNMe2H+)RuH(dppm)]BF4, in which the amine function was protonated. Relaxation time T1 measurements indicated the existence of an intramolecular N-H⋯H-Ru hydrogen-bonding interaction in these complexes. A spin saturation transfer study and H/D exchange experiment with [(η-C5H4(CH2)3NMe 2H+)RuH(dppm)]BF4 revealed fast exchange, probably via a dihydrogen complex intermediate, between the hydride ligand and N-H. An attempt to grow single crystals of [(η5-C5H4(CH2) 3NMe2H+)RuH(dppm)]BPh4 for X-ray study resulted in isolation of crystals of the complex, [(η5:η1-C5H4(CH 2)3NMe2)Ru(dppm)]-BPh4, with the chelating (3-(dimethylamino)propyl)cyclopentadienyl ligand. Exposure of [(η5:η1-C5H4(CH 2)3NMe2)Ru(dppm)]-BF4 to 60 atm of H2 at 60 °C gave [(η5-C5H4(CH2) 3-NMe2H+)RuH(dppm)]BF4 within 30 min. Reacting [(η5:η1-C5H4(CH 2)3NMe2)Ru(dppm)]BAr′4 (Ar′ = 3,5-(CF3)2C6H3) with Ph2SiH2 yielded [(η5-C5H4(CH2) 3NMe2H+)RuH(dppm)]BAr′4; it is proposed that hydrolysis of the η2-silane intermediate by adventitious moisture in the solvent affords an η2-dihydrogen species, and heterolytic cleavage of the dihydrogen ligand by the pendant amino group gives the final product. Heating solutions of [(η5:η1-C5H4(CH 2)n-NMe2)Ru(dppm)]BF4 under H2/CO2 (40 atm/40 atm) at 80 °C for 16 h gave formic acid in low yields (n = 2, TON = 6; n = 3, TON = 8). The formation of formic acid is best explained by a mechanism involving intramolecular heterolytic cleavage of the bound H2 to generate [(η5-C5H4(CH2) nNMe2H+)RuH(dppm)]BF4, followed by CO2 insertion into the Ru-H and then N-H protonation of the formato ligand. Carbon disulfide inserted into the Ru-H bond of [(η5-C5H4(CH2) 3NMe2H+)RuH(dppm)]BF4 to give [(η5-C5H4(CH2) 3NMe2H+)Ru(η 1-SCSH)-(dppm)]BF4.
Publisher: American Chemical Society
Journal: Organometallics 
ISSN: 0276-7333
EISSN: 1520-6041
DOI: 10.1021/om980071v
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