Intramolecular N-H⋯H-Ru proton-hydride interaction in ruthenium complexes with (2-(dimethylamino)ethyl)cyclopentadienyl and (3-(dimethylamino)propyl)cyclopentadienyl ligands. Hydrogenation of CO2to formic acid via the N-H⋯H-Ru hydrogen-bonded complexes

Hei Shing Chu, Chak Po Lau, Kwok Yin Wong, Wing Tak Wong

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Abstract

Addition of 1 equiv of HBF4to (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 T1measurements 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)3NMe2H+)RuH(dppm)]BF4revealed 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)]BPh4for X-ray study resulted in isolation of crystals of the complex, [(η5:η1-C5H4(CH2)3NMe2)Ru(dppm)]-BPh4, with the chelating (3-(dimethylamino)propyl)cyclopentadienyl ligand. Exposure of [(η5:η1-C5H4(CH2)3NMe2)Ru(dppm)]-BF4 to 60 atm of H2at 60 °C gave [(η5-C5H4(CH2)3-NMe2H+)RuH(dppm)]BF4within 30 min. Reacting [(η5:η1-C5H4(CH2)3NMe2)Ru(dppm)]BAr′4(Ar′ = 3,5-(CF3)2C6H3) with Ph2SiH2yielded [(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(CH2)n-NMe2)Ru(dppm)]BF4under 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 H2to generate [(η5-C5H4(CH2)nNMe2H+)RuH(dppm)]BF4, followed by CO2insertion 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)]BF4to give [(η5-C5H4(CH2)3NMe2H+)Ru(η1-SCSH)-(dppm)]BF4.
Original languageEnglish
Pages (from-to)2768-2777
Number of pages10
JournalOrganometallics
Volume17
Issue number13
Publication statusPublished - 22 Jun 1998

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Organic Chemistry
  • Inorganic Chemistry

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