Synthesis and Reactivity of Porphyrinatorhodium(II)−Triethylphosphine Adducts: The Role of PEt3 in Stabilizing a Formal Rh(II) State
摘要:
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 Rh-2(OEP)(2) and FEt3. 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)(2) demonstrates the reactivity of both a Rh-II d(7) center and a porphyrin pi -anion radical. The adduct reacts with O-2 as a Rh-II(por) species, originally forming a Rh-III-superoxido derivative. In contrast, with water Rh(OEP)(PEt3) reacts as a porphyrin sz-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 (d sigma*(Rh-P)) Unlike the other reported 1:1 adducts of Rh-II(por) species with sigma -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.
Synthesis and Reactivity of Porphyrinatorhodium(II)−Triethylphosphine Adducts: The Role of PEt3 in Stabilizing a Formal Rh(II) State
摘要:
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 Rh-2(OEP)(2) and FEt3. 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)(2) demonstrates the reactivity of both a Rh-II d(7) center and a porphyrin pi -anion radical. The adduct reacts with O-2 as a Rh-II(por) species, originally forming a Rh-III-superoxido derivative. In contrast, with water Rh(OEP)(PEt3) reacts as a porphyrin sz-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 (d sigma*(Rh-P)) Unlike the other reported 1:1 adducts of Rh-II(por) species with sigma -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.