The coordination and organometallic chemistry of ruthenium porphyrin species
Creators: name: Alexander, Christopher Scott
Publisher: name: University of British Columbia
Year: 2009

description: Treatment of RuII(porp)L₂ complexes with HX acids in C₆H₆ yields the corresponding paramagnetic RuIV(porp)X₂complexes, where porp = the 2, 3, 7, 8, 12, 13, 17, 18- octaethylporphyrin dianion(OEP), L= pyridine(py), X= Cl; and porp = the 5, 10, 15, 20- tetramesitylporphynn dianion(TMP), L =CH₃CN, X= Cl or Br. The 3 day reactions ( at room temperature) proceed via the paramagnetic Ru III(porp)X(L) intermediates, as demonstrated by isolation of Ru III(OEP)Cl(py) and Ru III(TMP)Br(CH₃CN). The Ru(OEP)Cl(py) complex was also produced in situ by the reaction of Ru(OEP)Cl₂ with Ru(OEP)py₂.Reduction of the dihalo species with anhydrous ammonia yields the paramagnetic Ru III(porp)X(NH₃)species. Cyclic voltammograms of the Ru(porp)X₂ complexes (where porp = OEP, X = Cl; porp = TPP (TPP 5, 10, 15, 20-tetraphenylporphyrin dianion), X = Cl; porp = TMP, X Br and Cl) show reversible Ru IV(porp⁺) /Ru IV(porp) couples in the range of 1.22 to 1.35 V, reversible Ru(IV)fRu(III) couples from 0.41 to 0.64 V, and a third irreversible response (tentatively assigned to the Ru III(porp)/Ru III(porp) couples) in the range of -0.82 to -0.56 V vs. Ag/AgCI. The reversible Ru IV(porp⁺)/Ru IV(porp) couples of Ru(OEP)Cl(NH₃)and Ru(TMP)Cl(NH₃)were measured at 1.31 and 1.45 V vs. AgIAgC1, respectively, while the reversible Ru(IV)/Ru(III) couples were found at 0.74 and 0.85 V. Reversible signals (tentatively assigned as the Ru(III)/Ru(ll) couples) were also observed at -0.51 and -0.42 V vs. AgIAgC1 for the OEP and TIVIP complexes, respectively. The diamagnetic Ru(TMP)R₂ complexes (R = Me, Ph) were isolated from the reaction of Ru(TMP)X₂ (X = Br, Cl) with an excess (≈6 equivalents) of the corresponding RLi reagents. On the other hand, the products of the reactions of Ru(OEP)Cl₂ with the alkylating agents RnM [where n 1, R = neopentyl (Np), M = Li; n = 1, R = benzyl (Bz), M = K; n = 2, R = 2-methyl-2-phenylpropyl (neophyl), M = Mg] and reactions of Ru(TMP)X₂ (X = Cl, Br) with NpLi were dependent on the ratios of the starting material. In situ experiments reveal the importance of the reducing power of these alkylating agents, as complexes of oxidation states ll-IV were observed, with the yield of the Ru(ll) products increasing as the ratio of NpLi/Ru(OEP)Cl₂ increased. The paramagnetic Ru(OEP)Np and Ru(OEP)(neophyl), and the diamagnetic, lithium-bridged dimer [Ru(OEP)Np]₂(μ-Li)₂,were isolated from these reactions and unambiguously characterized by microanalysis, UV/visible and ¹H NMR spectroscopies, and X-ray crystal diffraction. The Ru(OEP)Np species is also produced along with Ru(OEP)(NH₃)₂ from the reaction of Ru(OEP)Cl(NH₃)with 1 equivalent of NpLi. The paramagnetic nature of the new Ru(TMP)Cl₂,Ru(OEP)Cl(py), Ru(TMP)Cl(NH₃), Ru(TMP)Br(NH 3)and Ru(OEP)Np and Ru(OEP)(neophyl) species is evidenced by their broad, temperature-dependent ¹H NMR spectra and the solution magnetic susceptibilities of Ru(TIVIP)Cl₂ (2.5 B.M.), Ru(TMP)Cl(NH₃) (1.61 B.M.), Ru(OEP)Np (2.4 B.M.) and Ru(OEP)(neophyl) (2.2 B.M.). The lithium-bridged species is of a unique type among metalloporphyrin complexes, and the structure is maintained in solution; however, oxidation by air or byH₂O gave [Ru(OEP)OH]₂(μ-O)and Ru(OEP)Np, respectively. The Ru(TMP)R₂ species (R = Me, Ph) react with CO at 1 atm under laboratory light to yield Ru(TMP)(CO)₂ via the corresponding Ru(TMP)(COR)R intermediate. The conversion of Ru(TMP)(COPh)Ph is light-dependent and thus this benzyol species was produced in almost quantitative yield by performing the reaction in the dark, and was identified by microanalysis, IR and ¹H NMR spectroscopy. The Ru(TMP)Me₂ species also undergoes a photo-reaction with dioxygen to produce Ru(TMP)CO(L), where L is tentatively assigned as MeOH. The Ru(TMP)R₂ complexes (R = Ph, Me) undergo thermal decomposition under anaerobic conditions to yield the corresponding five-coordinate, paramagnetic Ru(TMP)R species, as does Ru(OEP)(COPh)Ph to give Ru(TMP)Ph. The in situ Ru(OEP)Np₂ complex thermally decomposes to give a 50:50 mixture of Ru(OEP)Np and Ru(OEP)=CHC(CH₃)₃.All these reactions proceed by the rate-determining homolysis of the axial metal-carbon bond, and Eyring plots of the first-order rate constants (k₁) obtained at various temperatures yield activation parameters for cleavage of the various Ru-R bonds [Ru(TMP)Ph₂,ΔS₁↕, 33 kcal mol⁻¹ , ΔS₁↕= 6.9 e.u. ; Ru(TMP)(COPh)Ph, ΔH₁↕ = 22, ΔS₁↕ = -11; Ru(TMP)Me₂, ΔH₁↕ = 22, ΔS₁↕= -17; Ru(OEP)Np₂, ΔH₁↕ = 16, ΔS₁↕ = -27]. The bond dissociation energies (BDE) of these bonds are then estimated by an established method (i.e. BDE = ΔH₁↕-2 kcal mol⁻¹), and the accuracy of these estimates is discussed in light of the kinetic results.