title: An acidity scale of tetrafluoroborate salts of phosphonium and iron hydride compounds in [D2]dichloromethane.
abstract: Equilibrium constants (K) for reactions between acids and the conjugate base forms of a number of phosphonium salts, [HPR3][BF4], and iron hydrides, [Fe(CO)3H(PR3)2][BF4], in CD(2)Cl(2) have been determined by means of 31P and 1H NMR spectroscopy at 20 degrees C. The anchor compound chosen for pK(CD(2)Cl(2)) determinations was [HPCy3][BF4] with a pK(CD(2)Cl(2)) value of 9.7, as assigned by literature convention (Cy: cyclohexyl). A continuous scale of pK(CD(2)Cl(2)) values covering the range from 9.7 to -3 was created and correlated with the DeltaH values reported by Angelici and co-workers and literature pK(a) values. The pK(CD(2)Cl(2)) values for 15 other hydride or dihydrogen complexes of the iron group elements and of diethyl ether were also placed on this scale. The crystal structures of [Fe(CO)3H(PCy(2)Ph)2][BF4] and [Fe(CO)3(PCy(2)Ph)2] revealed that the trans-oriented, bulky, unsymmetrical phosphane ligands distort the equatorial plane of the complexes. The acidity of iron carbonyl hydrides is an important feature of the reactions of iron hydrogenase enzymes.
authors.affiliation: Department of Chemistry, University of Toronto, 80 St. George Street, Toronto, ON M5S 3H6, Canada.
authors.forename: Tianshu
authors.initials: T
authors.lastname: Li
authors.forename: Alan J
authors.initials: AJ
authors.lastname: Lough
authors.forename: Robert H
authors.initials: RH
authors.lastname: Morris
mesh_terms: D000143:Acids / Q000737:chemistry; D001881:Borates / Q000737:chemistry*; D001888:Boric Acids / Q000737:chemistry*; D003903:Deuterium; D005290:Ferric Compounds / Q000737:chemistry*; D005296:Ferrous Compounds / Q000737:chemistry*; D006859:Hydrogen / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D009682:Magnetic Resonance Spectroscopy; D008752:Methylene Chloride / Q000737:chemistry*; D009943:Organophosphorus Compounds / Q000737:chemistry*; D012492:Salts / Q000737:chemistry; D012997:Solvents / Q000737:chemistry
chemical_list: D000143:Acids; D001881:Borates; D001888:Boric Acids; D005290:Ferric Compounds; D005296:Ferrous Compounds; D009943:Organophosphorus Compounds; D012492:Salts; D012997:Solvents; D008752:Methylene Chloride; D006859:Hydrogen; D003903:Deuterium; C098759:fluoroboric acid