318501-60-9Relevant academic research and scientific papers
Synthesis and reactivity of porphyrinatorhodium(II)-triethylphosphine adducts: The role of PEt3 in stabilizing a formal Rh(II) state
Collman,Boulatov
, p. 11812 - 11821 (2000)
Rh(por)H, where por is an octaethyl- or meso-tetraphenylporphyrin dianion, reacts with triethylphosphine to form stable mononuclear paramagnetic formally-Rh(II) complexes, Rh(OEP)(PEt3) and Rh(TPP)-(PEt3)2. The former adduct is also obtained as the sole product of the reaction between Rh2(OEP)2 and PEt3. The EPR spectroscopy at 77 K shows both complexes to have mainly porphyrin-based HOMOs. The composition and the reactivity of Rh(TPP)(PEt3)2 support its formulation as Rh(III)(TPP)(PEt3)2. In contrast, Rh(OEP)-(PEt3) demonstrates the reactivity of both a Rh(II) d7 center and a porphyrin π-anion radical. The adduct reacts with O2 as a Rh(II)(por) species, originally forming a Rh(III)-superoxido derivative. In contrast, with water Rh-(OEP)(PEt3) reacts as a porphyrin π-anion radical, yielding a Rh(III)-octaethylphlorin complex. The latter is the first characterized phlorin complex of a heavy transition metal. The dual reactivity of Rh(OEP)(PEt3) is proposed to arise from thermal excitation of the unpaired electron from the porphyrin-based HOMO onto the metal-based LUMO (dσ*(Rh-P)). Unlike the other reported 1:1 adducts of Rh(II)(por) species with σ-basic ligands, Rh(OEP)(PEt3) is remarkably stable toward disproportionation to Rh(I) and Rh(III). To understand the origin of this stability, the affinity of Rh(III)(OEP)+ toward PEt3 and pyridine was measured spectrophotometrically. The high binding affinity of PEt3 to Rh(OEP) is proposed as the underlying cause of the increased stability of Rh(OEP)(PEt3) toward disproportionation.
