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Axial-ligand substitution reactions of dirhodium(II) tetraacetate with phosphines and phosphites in acetonitrile

Journal Article · · Inorg. Chem.; (United States)
DOI:https://doi.org/10.1021/ic00263a028· OSTI ID:5522769
;

The kinetic and thermodynamic parameters for the axial-ligand substitution reactions of the bis(acetonitrile) adduct of dirhodium(II) tetraacetate with a variety of phosphines and phosphites in acetonitrile have been measured. The rate-determining formation of the Rh/sub 2/(O/sub 2/CCH/sub 3/)/sub 4/(CH/sub 2/CN)PR/sub 3/ adduct occurs with a rate constant that is independent of the nature of the ligand: k/sub 1/(25.0/sup 0/C) = (1.05 +/- 0.05) x 10/sup 5/ M/sup -1/ s/sup -1/, ..delta..H/sub 1//sup ++/ = 10.9 +/- 0.6 kcal mol/sup -1/, and ..delta..S/sub 1//sup ++/ = 1 +/- 2 cal K/sup -1/ mol/sup -1/. Slightly higher rate constants (1.6 x 10/sup 5/ M/sup -1/ s/sup -1/ at 25.0/sup 0/C) were found for several diphosphines (PPh/sub 2/(CH/sub 2/)/sub n/PPh/sub 2/, n = 2-4) and are attributed to the presence of two ligand coordination sites. A dissociative mechanism is proposed for substitution of the axially coordinated acetonitrile, and the rate parameters are compared with values reported for substitutions of oxygen-donor solvent molecules on the dirhodium(II) complex. The stability constants for the mono- and bisadducts have been measured at 25/sup 0/C with K/sub 1//K/sub 2/ approx. 20. The dependence of K/sub 1/ and K/sub 2/ on the nature of the phosphine or phosphite correlates well with the sigma-donor strength of the ligand, with ..pi..-acceptor strengths and steric effects being relatively insignificant.

Research Organization:
Queen's Univ. Kingston, Ontario
OSTI ID:
5522769
Journal Information:
Inorg. Chem.; (United States), Journal Name: Inorg. Chem.; (United States) Vol. 26:16; ISSN INOCA
Country of Publication:
United States
Language:
English

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
400201* -- Chemical & Physicochemical Properties
ACETATES
ACETONITRILE
CARBOXYLIC ACID SALTS
CHEMICAL REACTION KINETICS
CHEMICAL REACTIONS
COMPLEXES
DATA
EXPERIMENTAL DATA
HYDROGEN COMPOUNDS
INFORMATION
INORGANIC ACIDS
KINETICS
LIGANDS
NITRILES
NUMERICAL DATA
ORGANIC COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PHOSPHINES
PHOSPHORIC ACID
PHOSPHORUS COMPOUNDS
PHYSICAL PROPERTIES
REACTION KINETICS
RHODIUM COMPLEXES
THERMODYNAMIC PROPERTIES
TRANSITION ELEMENT COMPLEXES