Electrochemical and spectroscopic studies of (P)Rh(R)(L) and [(P)Rh(L)2]+ where P is the dianion of octaethyl- or tetraphenylporphyrin, R is a .sigma.-bonded alkyl group, and L is triphenylphosphine or dimethylphenylphosphine

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The electrochemistry and spectroelectrochemistry of (P)Rh(R), (P)Rh(R)(L), and ((P)Rh(L)/sub 2/)/sup +/ where P is the dianion of octaethylporphyrin (OEP) or tetraphenylporphyrin (TPP), R is CH/sub 3/, C/sub 2/H/sub 5/, or C/sub 4/H/sub 9/, and L is triphenylphosphine or dimethylphenylphosphine are reported. At polarographic concentrations of (P)Rh(R) (approx.10/sup -3/ M), the binding of one triphenylphosphine ligand and the formation of (P)Rh(R)(PPh/sub 3/) are observed. This contrasts to lower porphyrin concentrations where the bis(triphenylphosphine) adduct ((P)Rh(PPh/sub 3/)/sub 2/)/sup +/ is formed in solution. Formation constants for the conversion of (P)Rh(R) to (P)Rh(R)(PPh/sub 3/) were calculated by using electrochemical and spectroscopic methodologies and varied between 1.0 and 4.0 x 10/sup 3/ depending upon the porphyrin macrocycle (OEP or TPP), the specific R group, and the solvent (methylene chloride or benzonitrile). The electroreduction of (P)Rh(R)(PPh/sub 3/) initially leads to a porphyrin ..pi.. radical and the transient formation of ((P)Rh(R)(PPh/sub 3/))/sup -/ was spectrally characterized on the thin-layer electrochemical time scale. The formation of a porphyrin ..pi.. radical is also observed after reduction of ((TPP)Rh(PPhMe/sub 2/)/sub 2/)/sup +/. This reaction was characterized by thin-layer spectroelectrochemistry and provides the first example for reduction of a non-sigma-bonded Rh(III) porphyrin at the porphyrin ..pi..-ring and provides the firstmore » example for reduction of a non-sigma-bonded Rh(III) porphyrin at the porphyrin ..pi..-ring system.« less