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An Acidity Scale of Tetrafluoroborate Salts of Phosphonium and Iron Hydride Compounds in [D 2 ]Dichloromethane
Author(s) -
Li Tianshu,
Lough Alan J.,
Morris Robert H.
Publication year - 2007
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200601484
Subject(s) - chemistry , phosphonium , hydride , dichloromethane , tetrafluoroborate , medicinal chemistry , inorganic chemistry , diethyl ether , triphenylphosphine , ether , catalysis , ionic liquid , organic chemistry , hydrogen , solvent
Equilibrium constants ( K ) for reactions between acids and the conjugate base forms of a number of phosphonium salts, [HPR 3 ][BF 4 ], and iron hydrides, [Fe(CO) 3 H(PR 3 ) 2 ][BF 4 ], in CD 2 Cl 2 have been determined by means of 31 P and 1 H NMR spectroscopy at 20 °C. The anchor compound chosen for p K CD 2 Cl 2determinations was [HPCy 3 ][BF 4 ] with a p K CD 2 Cl 2value of 9.7, as assigned by literature convention (Cy: cyclohexyl). A continuous scale of p K CD 2 Cl 2values covering the range from 9.7 to −3 was created and correlated with the Δ H values reported by Angelici and co‐workers and literature p K a values. The p K CD 2 Cl 2values 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) 3 H(PCy 2 Ph) 2 ][BF 4 ] 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.