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Manganese propane and manganese butane complexes derived from CpMn(CO)(3) were generated photochemically at 130-136 K with the alkane as solvent and characterized by FTIR spectroscopy and by (1)H NMR spectroscopy with in situ laser photolysis. Time-resolved IR spectroscopic measurements were performed at room temperature with the same laser wavelength. The ν(CO) bands in the IR spectra of the photoproducts in propane are shifted to low frequency with respect to CpMn(CO)(3), consistent with formation of CpMn(CO)(2)(propane). The (1)H NMR spectra conform to the criteria for alkane complexes: a high-field resonance for the η(2)-CH protons that shifts substantially on partial deuteration of the alkane and exhibits a coupling constant J(C-H) on (13)C-labeling of ca. 120 Hz. The NMR spectrum of each system exhibits two diagnostic product resonances in the high-field region for the η(2)-CH protons, corresponding to CpMn(CO)(2)(η(2)-C1-H-alkane) and CpMn(CO)(2)(η(2)-C2-H-alkane) isomers. Partial deuteration of the alkane at C1 results in characteristic strong isotopic perturbation of equilibrium of the η(2)-CH resonance of CpMn(CO)(2)(η(2)-C1-H-alkane). With propane-(13)C(1), the η(2)-CH resonance of CpMn(CO)(2)(η(2)-C1-H-alkane) isomer exhibits (13)C satellites with J(C-H) = 119 Hz. The corresponding resonance of CpMn(CO)(2)(η(2)-C2-H-alkane) is identified by use of propane-2,2-d(2). The lifetimes of the (η(2)-C1-H-alkane) isomers of the manganese complexes were determined by NMR spectroscopy as 22 ± 2 min at 134 K (propane) and 5.5 min at 136 K (butane). The corresponding spectra and lifetimes of the CpRe(CO)(2)(alkane) complexes were measured for reference (CpRe(CO)(2)(propane) lifetime ca. 60 min at 161 K; CpRe(CO)(2)(butane) 13 min at 171 K). The lifetimes determined by IR spectroscopy were similar to those determined by NMR spectroscopy, thereby supporting the assignments. These measurements extend the range of alkane complexes characterized by NMR spectroscopy from rhenium and rhodium derivatives to include less stable manganese derivatives.

Cationic Rh(I) and Ir(I) complexes of the form [M(PC)(COD)]BPh4 (M = Rh (4), Ir (5); PC = 3-[2-(diphenylphosphino)ethyl]-1-methylimidazol-2-ylidene) were synthesized by the addition of 3-[2-(diphenylphosphino)ethyl]-1-methylimidazolium (3) to [M(μ-OEt)(COD)]2 (M = Rh, Ir; COD = 1,5-cyclooctadiene) in the presence of base. COD was successfully displaced from [Rh(PC)(COD)]BPh4 (4) by addition of carbon monoxide to a methanol/hexane suspension to form [Rh(PC)(CO)2]BPh4 (6). The analogous addition of CO to the iridium compound 5 resulted in the formation of the five-coordinate Ir(I) complex [Ir(PC)(COD)(CO)]BPh4 (7). The single-crystal X-ray structures of 4, 5, and 7 were determined. The metal centers of 4 and 5 are square planar, and the metal center of 7 is a distorted trigonal bipyramid. Complexes 4−7 are effective as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to 2-methyl-1-pyrroline. Complete conversion (>97%) of 4-pentyn-1-amine was observed using complexes 4−7 as catalysts, in both chloroform-d and tetrahydrofuran-d 8. Reactions in chloroform-d in general exhibited higher turnover rates than reactions in tetrahydrofuran-d 8.

The synthesis of a series of iron and ruthenium complexes with the new ligand PP(i)(3) (1) P(CH(2)CH(2)P(i)Pr(2))(3) is described. The iron(0) and ruthenium(0) dinitrogen complexes Fe(N(2))(PP(i)(3)) (4) and Ru(N(2))(PP(i)(3)) (5) were synthesized by treatment of the iron(II) and ruthenium(II) cationic species [FeCl(PP(i)(3))](+) (2) and [RuCl(PP(i)(3))](+) (3) with potassium graphite under a nitrogen atmosphere. The cationic dinitrogen species [Fe(N(2))H(PP(i)(3))](+) (6) and [Ru(N(2))H(PP(i)(3))](+) (7) were prepared by treatment of 4 and 5, respectively, with 1 equiv of a weak organic acid. Complexes 2.[BPh(4)], 3.[BPh(4)], 4, 5, and 6.[BF(4)] were characterized by X-ray crystallography. The structural characterization of 5 is the first report for a ruthenium(0) dinitrogen complex.

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)(3)(Pic)Bpy-PdTPP][PF(6)]) have been investigated. The single crystal X-ray structure for the thiocyanate analogue, [Re(CO)(3)(NCS)Bpy-PdTPP], exhibits torsion angles of 69.1(9)°, 178.1(7)°, and 156.8(9)° between porphyrin plane, porphyrin-linked C(6)H(4) group, amide moiety, and Bpy, respectively. Steady-state photoexcitation (λ(ex) = 520 nm) of [Re(CO)(3)(Pic)Bpy-PdTPP][PF(6)] in dimethylformamide (DMF) results in substitution of Pic by bromide at the Re(I)Bpy core. When [Re(CO)(3)(Pic)Bpy-PdTPP][PF(6)] is employed as a photocatalyst for the reduction of CO(2) to CO in DMF/NEt(3) solution with λ(ex) > 420 nm, 2 turnovers (TNs) CO are formed after 4 h. If instead, a two-component mixture of PdTPP sensitizer and mononuclear [Re(CO)(3)(Pic)Bpy][PF(6)] 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)(3)(Pic)Bpy][PF(6)], 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(ox)* = -0.08 eV. Electron transfer from Pd(II) porphyrin to Re(I) tricarbonyl bipyridine in [Re(CO)(3)(Pic)Bpy-PdTPP][PF(6)] 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(2)Cl(2) with and without NEt(3). Picosecond TRIR spectroscopy shows rapid growth of bands assigned to the π-π* excited state (2029 cm(-1)) and to the charge-separated state (2008, 1908 cm(-1)); 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).

The photochemistry of (η6-C6H6)M(CO)3 (M = Cr or Mo) is described. Photolysis with λexc. > 300 nm of (η6-C6H6)Cr(CO)3 in low-temperature matrixes containing CO produced the CO-loss product, while lower energy photolysis (λexc. > 400 nm) produced Cr(CO)6. Pulsed photolysis (λexc. = 400 nm) of (η6-C6H6)Cr(CO)3 in n-heptane solution at room temperature produced an excited-state species (1966 and 1888 cm−1) that decays over 150 ps to (η6-C6H6)Cr(CO)2(n-heptane) (70%) and (η6-C6H6)Cr(CO)3 (30%). Pulsed photolysis (λexc. = 266 nm) of (η6-C6H6)Cr(CO)3 in n-heptane produced bands assigned to (η6-C6H6)Cr(CO)2(n-heptane) (1930 and 1870 cm−1) within 1 ps. These bands increase with a rate identical to the rate of decay of the excited-state species and the rate of recovery of (η6-C6H6)Cr(CO)3. Photolysis of (η6-C6H6)Mo(CO)3 at 400 nm produced an excited-state species (1996 and 1898 cm−1) and traces of (η6-C6H6)Mo(CO)2(n-heptane) within 1 ps. For the chromium system CO-loss can occur following excitation at both 400 and 266 nm via an avoided crossing of a MACT (metal-to-arene charge transfer) and MCCT/LF (metal-to-carbonyl charge transfer/ligand field) states. This leads to an unusually slow CO-loss following excitation with 400 nm light. Rapid CO-loss is observed following 266 nm excitation because of direct population of the MCCT/LF state. The quantum yield for CO-loss in the chromium system decreases with increasing excitation energy because of the competing population of a high-energy unreactive MACT state. For the molydenum system CO-loss is a minor process for 400 nm excitation, and an unreactive MACT state is evident from the TRIR spectra. A higher quantum yield for CO-loss is observed following 266 nm excitation through both direct population of the MCCT/LF state and production of a vibrationally excited reactive MACT state. This results in the quantum yield for CO-loss increasing with increasing excitation energy.

The photophysics and photochemistry of transition-metal compounds are of great interest, particularly since such materials have been exploited for a wide range of applications including photocatalysis, photosynthesis and photosynthetic model compounds, artificial light-harvesting antenna systems for solar energy conversion, sensing and imaging, supramolecular photochemically driven machines, multiphotonabsorption materials, probes for monitoring biological processes, and the fabrication of high-performance organic lightemitting diodes (OLEDs).[1] A full understanding of the excited-state behavior of organometallic compounds is crucial for the design of new materials for all of these applications. An attractive feature of this class of compounds is that subtle changes in the ligand environment or metal can be used to tune the properties, thereby allowing the control required for a particular application. [1, 3] and both the diimine and C^N cyclometalated complexes can exhibit highly emissive triplet excited states.Mononuclear metal complexes usually show very rapid conversion from singlet into triplet excited states, which is attributed to the "heavy-atom effect". The heavy-atom effect is the promotion of intersystem crossing (ISC) processes by the spin-orbit coupling (SOC) of the metal atom. These effects can begin to be observed with elements as light as sulphur (z = 16).[4] For example, the formation of the 3 MLCT (MLCT = metal-to-ligand charge transfer) excited state of [Ru(bpy) occurs in less than 20 fs, whereas the second-row complexes [Re(X)(CO) 3 (bpy)] + (X = Cl, Br, I) show a much slower interconversion (ca. 100 fs).[6] Furthermore, the order was found to be Cl (85 fs) < Br (128 fs) < I (152 fs), which is contrary to that predicted by the simplistic consideration of the effect of the heavy atom. Tetrahedral [Pt(binap) 2 ] (binap = 2,2'-bis(diphenylphosphino)-1,1'-binaphthyl) and [Cu{bis(diimine)}]+ complexes have been shown to have unusually long-lived 1 MLCT states of t = 3 ps and t = 15 ps, respectively, attributed to a distortion towards a squareplanar geometry which reduces the mixing of the 1,3 MLCT states. [7] Our long-standing interest in rhodium-acetylide compounds [8] and luminescent bis(arylethynyl)arenes [9] led us to the development of a high-yielding, one-pot synthesis of a 2,5-bis(phenylethynyl)rhodacyclopentadiene, which we reported to be luminescent.[10] Our subsequent investigations, reported herein, indicate that this new class of luminescent rhodium complexes shows unprecedented excited-state behavior. Our luminescence spectroscopic studies are supported by picosecond time-resolved IR (TRIR) vibrational spectra of the ground and excited states as a means by which to obtain accurate kinetic data on the processes involved. Herein we demonstrate that despite the presence of the second-row transition metal the compounds show remarkable photophysical properties: specifically, long-lived, highly emissive singlet excited states. This new class of material challenges our understandin...

A series of N,N-donor ligands (bis(pyrazol-1-yl)methane (bpm), bis(N-methylimidazol-2-yl)methane (bim), 1-(phenylmethyl)-4-(1H-pyrazol-1-yl methyl)-1H-1,2,3-triazole (PyT)), and one N,P-donor ligand precursor (1-(3,5-dimethylpyrazol-1-yl)(2-bromoethane) (dmPyBr)) were synthesized and functionalized with aniline. Diazotization of the aniline into an aryl diazonium, using nitrous acid in aqueous conditions, was performed in situ such that the ligands could be reductively adsorbed onto glassy carbon electrode surfaces. The N,N-donor ligands (bpm, bim, PyT) were immobilized in a single step, while several steps were required to immobilize the N,P-donor ligand (dmPyP) to prevent oxidation of the phosphine group. The complexation of the anchored ligands with the metal complex precursor ([Rh(CO)2(μ-Cl)]2) led to the formation of anchored Rh(I) complexes with each of the ligands (bpm, bim, PyT, dmPyP). X-ray photoelectron spectroscopy (XPS) confirmed the formation of the anchored ligands as well as the anchored complexes. The surface coverage of functionalized electrodes was estimated by means of cyclic voltammetry, and the nature of the coverage was close to being a monolayer for each immobilized complex. The anchored Rh(I) complexes were active as catalysts for the intramolecular hydroamination of 4-pentyn-1-amine to form 2-methyl-1-pyrroline.