Photochemistry and photophysics of a Pd(II) metalloporphyrin: Re(I) tricarbonyl bipyridine molecular dyad and its activity toward the photoreduction of CO to CO

TY - JOUR

T1 - Photochemistry and photophysics of a Pd(II) metalloporphyrin

T2 - Re(I) tricarbonyl bipyridine molecular dyad and its activity toward the photoreduction of CO to CO

AU - Schneider, J.

AU - Whitwood, A.C.

AU - Perutz, R.N.

AU - Vuong, K.Q.

AU - Calladine, J.A.

AU - Sun, X.-Z.

AU - George, M.W.

PY - 2011/12/5

Y1 - 2011/12/5

N2 - The photochemistry and photophysics of the cationic molecular dyad, 5-{4-[rhenium(I)tricarbonylpicoline-4-methyl-2,2′-bipyridine-4′- carboxyamidyl]phenyl}-10,15,20-triphenylporphyrinatopalladium(II) ([Re(CO) (Pic)Bpy-PdTPP][PF ]) have been investigated. The single crystal X-ray structure for the thiocyanate analogue, [Re(CO) (NCS)Bpy-PdTPP], exhibits torsion angles of 69.1(9)°, 178.1(7)°, and 156.8(9)° between porphyrin plane, porphyrin-linked C H group, amide moiety, and Bpy, respectively. Steady-state photoexcitation (λ = 520 nm) of [Re(CO) (Pic)Bpy-PdTPP][PF ] in dimethylformamide (DMF) results in substitution of Pic by bromide at the Re(I)Bpy core. When [Re(CO) (Pic)Bpy-PdTPP][PF ] is employed as a photocatalyst for the reduction of CO to CO in DMF/NEt solution with λ > 420 nm, 2 turnovers (TNs) CO are formed after 4 h. If instead, a two-component mixture of PdTPP sensitizer and mononuclear [Re(CO) (Pic)Bpy][PF ] catalyst is used, 3 TNs CO are formed. In each experiment however, CO only forms after a slight induction period and during the concurrent photoreduction of the sensitizer to a Pd(II) chlorin species. Palladium(II) meso-tetraphenylchlorin, the hydrogenated porphyrin analogue of PdTPP, has been synthesized independently and can be substituted for PdTPP in the two-component system with [Re(CO) (Pic)Bpy][PF ], forming 9 TNs CO. An intramolecular electron transfer process for the dyad is supported by cyclic voltammetry and steady-state emission studies, from which the free energy change was calculated to be ΔG * = -0.08 eV. Electron transfer from Pd(II) porphyrin to Re(I) tricarbonyl bipyridine in [Re(CO) (Pic)Bpy-PdTPP] [PF ] was monitored using time-resolved infrared (TRIR) spectroscopy in the ν(CO) region on several time scales with excitation at 532 nm. Spectra were recorded in CH Cl with and without NEt . Picosecond TRIR spectroscopy shows rapid growth of bands assigned to the π-π* excited state (2029 cm ) and to the charge-separated state (2008, 1908 cm ); these bands decay and the parent recovers with lifetimes of 20-50 ps. Spectra recorded on longer time scales (ns, μs, and seconds) show the growth and decay of further species with ν(CO) bands indicative of electron transfer to Re(Bpy).

AB - The photochemistry and photophysics of the cationic molecular dyad, 5-{4-[rhenium(I)tricarbonylpicoline-4-methyl-2,2′-bipyridine-4′- carboxyamidyl]phenyl}-10,15,20-triphenylporphyrinatopalladium(II) ([Re(CO) (Pic)Bpy-PdTPP][PF ]) have been investigated. The single crystal X-ray structure for the thiocyanate analogue, [Re(CO) (NCS)Bpy-PdTPP], exhibits torsion angles of 69.1(9)°, 178.1(7)°, and 156.8(9)° between porphyrin plane, porphyrin-linked C H group, amide moiety, and Bpy, respectively. Steady-state photoexcitation (λ = 520 nm) of [Re(CO) (Pic)Bpy-PdTPP][PF ] in dimethylformamide (DMF) results in substitution of Pic by bromide at the Re(I)Bpy core. When [Re(CO) (Pic)Bpy-PdTPP][PF ] is employed as a photocatalyst for the reduction of CO to CO in DMF/NEt solution with λ > 420 nm, 2 turnovers (TNs) CO are formed after 4 h. If instead, a two-component mixture of PdTPP sensitizer and mononuclear [Re(CO) (Pic)Bpy][PF ] catalyst is used, 3 TNs CO are formed. In each experiment however, CO only forms after a slight induction period and during the concurrent photoreduction of the sensitizer to a Pd(II) chlorin species. Palladium(II) meso-tetraphenylchlorin, the hydrogenated porphyrin analogue of PdTPP, has been synthesized independently and can be substituted for PdTPP in the two-component system with [Re(CO) (Pic)Bpy][PF ], forming 9 TNs CO. An intramolecular electron transfer process for the dyad is supported by cyclic voltammetry and steady-state emission studies, from which the free energy change was calculated to be ΔG * = -0.08 eV. Electron transfer from Pd(II) porphyrin to Re(I) tricarbonyl bipyridine in [Re(CO) (Pic)Bpy-PdTPP] [PF ] was monitored using time-resolved infrared (TRIR) spectroscopy in the ν(CO) region on several time scales with excitation at 532 nm. Spectra were recorded in CH Cl with and without NEt . Picosecond TRIR spectroscopy shows rapid growth of bands assigned to the π-π* excited state (2029 cm ) and to the charge-separated state (2008, 1908 cm ); these bands decay and the parent recovers with lifetimes of 20-50 ps. Spectra recorded on longer time scales (ns, μs, and seconds) show the growth and decay of further species with ν(CO) bands indicative of electron transfer to Re(Bpy).

UR - http://www.scopus.com/inward/record.url?scp=82355187838&partnerID=8YFLogxK

U2 - 10.1021/ic200243y

DO - 10.1021/ic200243y

M3 - Article

AN - SCOPUS:82355187838

SN - 0020-1669

VL - 50

SP - 11877

EP - 11889

JO - Inorganic Chemistry

JF - Inorganic Chemistry

IS - 23

ER -