Complexation of Diphenyl(phenylacetenyl)phosphine to Rhodium(III) Tetraphenyl Porphyrins: Synthesis and Structural, Spectroscopic, and Thermodynamic Studies

Stulz, Eugen, Scott, Sonya M., Bond, Andrew D., Otto, Sijbren and Sanders, Jeremy K.M. (2003) Complexation of Diphenyl(phenylacetenyl)phosphine to Rhodium(III) Tetraphenyl Porphyrins: Synthesis and Structural, Spectroscopic, and Thermodynamic Studies. Inorganic Chemistry, 42 (9), 3086-3096. (doi:10.1021/ic026257a).

Abstract

The coordination of diphenyl(phenylacetenyl)phosphine (DPAP, 1) to (X)RhIIITPP (X ) I (2) or Me (3); TPP ) tetraphenyl porphyrin) was studied in solution and in the solid state. The iodide is readily displaced by the phosphine, leading to the bis-phosphine complex [(DPAP)2Rh(TPP)](I) (4). The methylide on rhodium in 3 is not displaced, leading selectively to the mono-phosphine complex (DPAP)(Me)Rh(TPP) (5). The first and second association constants, as determined by isothermal titration calorimetry and UV-vis titrations, are in the range 104-107 M-1 (in CH2Cl2). Using LDI-TOF mass spectrometry, the mono-phosphine complexes can be detected but not the bisphosphine complexes. The electronic spectrum of 4 is similar to those previously reported with other tertiary phosphine ligands, whereas (DPAP)(I)Rh(TPP) (6) displays a low energy B-band absorption and a high energy Q-band absorption. In contrast to earlier reports, displacement of the methylide on rhodium in 5 could not be observed at any concentration, and the electronic spectra of 4 and 5 are almost identical. Isothermal titration calorimetry experiments showed that all binding events are exothermic, and all are enthalpy driven. The largest values of ¢G° are found for 6. The thermodynamic and UV-vis data reveal that the methylide and the phosphine ligand have an almost identical electronic trans-influence on the sixth ligand.

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Contributors

Author: Eugen Stulz

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