Organometallic reactivity patterns of the rhodium tetraphenylporphyrin derivatives Rh(TPP)(H), Rh(TPP)-, and (Rh(TPP)), are found to closely parallel those of the corresponding rhodium octaethylporphyrin species. Preparation and physical properties of the formyl, hydroxymethyl, and alkyl complexes of Rh(TPP) are described along with the photoinduced insertion of carbon monoxide into the Rh-CH, bond. Thermodynamic values for the reaction Rh(TPP)(H) + CO F? Rh(TPP)(CHO) in C6D6 are AHo = -42 kJ/mol and ASo = -89 f 15 J/(K mol).Organometallic reactions of rhodium octaethylporphyrin species have been used to imply that unusually strong Rh-C bonds (>50 kcal) are a dominant factor in this chemistry.'" A primary purpose of this study was to determine whether changes in the electronic structure of t h e porphyrin macrocycle could be used in tuning the Rh-C bond energy over a sufficient range to alter t h e general reactivity patterns of the rhodium porphyrin species. Tetraphenylporphyrin, (TPP), and the p-methyl derivative, tetratolylporphyrin, (TTP), were chosen for comparison with octaethylporphyrin (OEP) complexes because these ligands represent extremes in the electronic properties of the porphyrins. T h e OEP and TPP dianions are respectively among the strongest and weakest porphyrin u donors and metallwTPP complexes are also more easily reduced than the corresponding OEP derivatives.' This paper reports on a comparison of the general organometallic reactivity patterns of Rh'(TPP)-, (Rh"(TPP)),, and Rh"'(TP-P ) ( H ) species with the corresponding R h ( 0 E P ) derivatives. Thermodynamic values for the reaction of Rh(TPP)(H) with CO t o produce the metalloformyl complex, R h ( T P P ) ( C H O ) are reported and compared with the corresponding values for the Rh-(OEP) system.
Experimental SectionProton N M R spectra were obtained with a Bruker Instruments WM250 NMR spectrophotometer with an Aspect 2000 computer. The variable-temperature and proton-decoupled spectra were obtained over a temperature range of 20-100 OC with an IBM Instruments SY200 N M R spectrophotometer interfaced to an Aspect 2000 computer with a Bruker Instruments BVTlOOO variable-temperature controller. The temperature in the probe was calibrated with a sample of ethylene glycol.Electronic and IR spectra were obtained on a Cary recording spectrophotometer, Model 14. All solvents and gases were used without further purification except where noted. Benzene was dried over sodium metal and benzophenone. Deuterated benzene, C6D6, was degassed and then dried by refluxing over CaH, for several days. Chloroform was purified by washing with water and then drying by passing through a column of grade I alumina. The H2 and CO gases used were grade 5.5 and 4.5, respectively. Proton NMR samples were prepared on a vacuum line, by using dried and degassed C6D6, and then sealed. (TPP)(R~I(CO)~),. The synthesis of (TPP)(Rh(CO),), follows literature procedures.* IH NMR (6 in C6D6): 8.81 (d, 4 H, pyrrole), 8.70 (1) Van Voorhees, S. L.; Wayland, B. B.
