Photocatalytic Reduction of CO to CO in Aqueous Solution under Red-Light Irradiation by a Zn-Porphyrin-Sensitized Mn(I) Catalyst.

This work demonstrates photocatalytic CO reduction by a noble-metal-free photosensitizer-catalyst system in aqueous solution under red-light irradiation. A water-soluble Mn(I) tricarbonyl diimine complex, [MnBr(4,4'-{EtOPCH}-2,2'-bipyridyl)(CO)] (), has been fully characterized, including single-crystal X-ray crystallography, and shown to reduce CO to CO following photosensitization by tetra(-methyl-4-pyridyl)porphyrin Zn(II) tetrachloride [Zn(TMPyP)]Cl () under 625 nm irradiation. This is the first example of employed as a photosensitizer for CO reduction.

Synthesis and characterization of the mixed-ligand coordination polymer CuCl(NC-NO).

Reduction of copper(ii) chloride using sodium ascorbate in the presence of pure sodium 5-nitro-tetrazolate (NaNT) forms copper(i) 5-nitrotetrazolate - a known initiatory explosive (DBX-1) - and the novel mixed-ligand copper(i) chloride 5-nitrotetrazolate coordination polymer Cu3Cl(N4C-NO2)2, as well as mixtures of both. The reaction is controlled by the presence of seed crystals and transition metal compounds other than CuCl2. Cu3Cl(N4C-NO2)2 is obtained as a wine-red, air stable, water-insoluble, crystalline and highly sensitive explosive material with a greater crystal density, lower thermal stability and a higher sensitivity toward hydrolysis and shock than DBX-1.

Syntheses, Structures, and Infrared Spectra of the Hexa(cyanido) Complexes of Silicon, Germanium, and Tin.

The rare octahedral EC coordination skeleton type is unknown for complexes with coordination centers consisting of group 14 elements. Here, the first examples of such EC species, the hexacoordinate homoleptic cyanido complexes E(CN), E = Si, Ge, Sn, have been synthesized from element halides SiCl, GeCl and SnF and isolated as salts with PPN counterions (PPN = (PhP)N) on a scale of 0.2-1 g.

Labile Low-Valent Tin Azides: Syntheses, Structural Characterization, and Thermal Properties.

The first two examples of the class of tetracoordinate low-valent, mixed-ligand tin azido complexes, Sn(N)(L), are shown to form upon reaction of SnCl with NaN and SnF with MeSiN in either pyridine or 4-picoline (2, L = py; 3, L = pic). These adducts of Sn(N) are shock- and friction-insensitive and stable at r.t.

Synthesis of six-coordinate mono-, bis-, and tris(tetrazolato) complexes via [3 + 2] cycloadditions of nitriles to silicon-bound azido ligands.

A convenient synthetic route to poly(tetrazolato) silicon complexes is described based on the four reactive centres of the N-rich, highly endothermic tetraazides of the type Si(N)(L). Hypercoordinate azido(tetrazolato) silicon complexes Si(N)(NC-R)(L), R = CH, CH, 4-CHCH (4a, 5, 6, 7) and Si(N)(NC-L) (9, L = 2-CHN), L = 2,2'-bipyridine, 1,10-phenanthroline, with SiN skeletons were synthesised via multiple [3 + 2] dipolar cycloaddition reactions starting from Si(N)(L) and a nitrile. The isolated new complexes were characterised by standard analytical methods, single crystal X-ray diffraction and differential scanning calorimetry (4a,b).

Homoleptic Poly(nitrato) Complexes of Group 14 Stable at Ambient Conditions.

Using a novel approach in homoleptic nitrate chemistry, Sn(NO3)6(2-) (3c) as well as the previously unknown hexanitrato complexes Si(NO3)6(2-) (1c), Ge(NO3)6(2-) (2c) were synthesized from the element tetranitrates as salt-like compounds which were isolated and characterized using (1)H, (14)N, and (29)Si NMR and IR spectroscopies, elemental and thermal analyses, and single-crystal XRD. All hexanitrates are moderately air-sensitive at 298 K and possess greater thermal stability toward NO2 elimination than their charge-neutral tetranitrato congeners as solids and in solution. The complexes possess distorted octahedral coordination skeletons and adopt geometries that are highly symmetric (3c) or deformed (1c, 2c) depending on the degree of steric congestion of the ligand sphere.

Taming Tin(IV) Polyazides.

The first charge-neutral Lewis base adducts of tin(IV) tetraazide, [Sn(N3)4(bpy)], [Sn(N3)4(phen)] and [Sn(N3)4(py)2], and the salt bis{bis(triphenylphosphine)iminium} hexa(azido)stannate [(PPN)2Sn(N3)6] (bpy = 2,2'-bipyridine; phen = 1,10-phenanthroline; py = pyridine; PPN = N(PPh3)2) have been prepared using covalent or ionic azide-transfer reagents and ligand-exchange reactions. The azides were isolated on the 0.3 to 1 g scale and characterized by IR and NMR spectroscopies, microanalytical and thermal methods and their molecular structures determined by single-crystal XRD.

Homoleptic low-valent polyazides of group 14 elements.

First examples of coordinatively unsaturated, homoleptic azido complexes of low-valent group 14 elements are reported. A simple strategy uses low-valent precursors, ionic azide transfer reagents and bulky cations to obtain salt-like compounds containing E(N3)3(-) of Ge(II)/Sn(II) which are fully characterised, including XRD. Remarkably, these compounds are kinetically stable at r.

Picosecond time-resolved infrared spectroscopy of rhodium and iridium azides.

Picosecond time-resolved infrared spectroscopy was used to elucidate early photochemical processes in the diazido complexes M(Cp*)(N3)2(PPh3), M = Rh (), Ir (), using 266 nm and 400 nm excitation in THF, CH2Cl2, MeCN and toluene solutions. The time-resolved data have been interpreted with the aid of DFT calculations on vibrational spectra of the singlet ground states and triplet excited states and their rotamers. While the yields of phototransformations via N2 loss are low in both complexes, cleaves a N3 ligand under 266 nm excitation.

Dinitrogen release from arylpentazole: a picosecond time-resolved infrared, spectroelectrochemical, and DFT computational study.

p-(Dimethylamino)phenyl pentazole, DMAP-N5 (DMAP = Me2N-C6H4), was characterized by picosecond transient infrared spectroscopy and infrared spectroelectrochemistry. Femtosecond laser excitation at 310 or 330 nm produces the DMAP-N5 (S1) excited state, part of which returns to the ground state (τ = 82 ± 4 ps), while DMAP-N and DMAP-N3 (S0) are generated as double and single N2-loss photoproducts with η ≈ 0.14.

Simulating the pyrolysis of polyazides: a mechanistic case study of the [[P(N3)6]- anion.

Pyrolysis of the homoleptic azido complex [P(N(3))(6)](-) was simulated using density functional theory based molecular dynamics and analyzed further using electronic-structure calculations in atom-centered basis sets to calculate the geometries and electronic structures. Simulations at 600 and 1200 K predict a thermally induced and, on the simulation time scale, irreversible dissociation of an azido anion. The ligand loss is accompanied by a barrierless (free-energy) transition of the geometry of the complex coordination sphere from octahedral to trigonal bipyramidal.

Combined experimental and theoretical investigation into C-H activation of cyclic alkanes by Cp'Rh(CO)2 (Cp' = η5-C5H5 or η5-C5Me5).

Fast time-resolved infrared spectroscopic measurements have allowed precise determination of the rate of C-H activation of alkanes by Cp'Rh(CO) {Cp' = η(5)-C(5)H(5) or η(5)-C(5)Me(5); alkane = cyclopentane, cyclohexane and neopentane (Cp only)} in solution at room temperature and allowed the determination of how the change in rate of oxidative cleavage varies between complexes and alkanes. Density functional theory calculations on these complexes, transition states, and intermediates provide insight into the mechanism and barriers observed in the experimental results. Unlike our previous study of the linear alkanes, where activation occurred at the primary C-H bonds with a rate governed by a balance between these activations and hopping along the chain, the rate of C-H activation in cyclic alkanes is controlled mainly by the strength of the alkane binding.

Understanding the factors affecting the activation of alkane by Cp'Rh(CO)2 (Cp' = Cp or Cp*).

Fast time-resolved infrared spectroscopic measurements have allowed precise determination of the rates of activation of alkanes by Cp'Rh(CO) (Cp(') = η(5)-C(5)H(5) or η(5)-C(5)Me(5)). We have monitored the kinetics of C─H activation in solution at room temperature and determined how the change in rate of oxidative cleavage varies from methane to decane. The lifetime of CpRh(CO)(alkane) shows a nearly linear behavior with respect to the length of the alkane chain, whereas the related Cp*Rh(CO)(alkane) has clear oscillatory behavior upon changing the alkane.

A new hexakis(isocyanato)silicate(IV) and the first neutral Lewis-base adducts of silicon tetraisocyanate.

The new silicates K2Si(NCE)6, E = O, S (1a,b) were synthesised directly by reaction of silicon tetrachloride with potassium cyanate or thiocyanate. 1a,b can be converted to the salts (PPN)2[Si(NCE)6] (2a,b) with bulky cations (PPN+ = N(PPh3)2+), which contain isolated silicate dianions. Reaction of 1a with diimines affords the hexacoordinate complexes Si(NCO)4L, L = bpy (3), phen (4), which are the first isolated neutral adducts to Si(NCO)4.

A combined theoretical and experimental study on the role of spin states in the chemistry of Fe(CO)5 photoproducts.

A combined experimental and theoretical study is presented of several ligand addition reactions of the triplet fragments (3)Fe(CO)(4) and (3)Fe(CO)(3) formed upon photolysis of Fe(CO)(5). Experimental data are provided for reactions in liquid n-heptane and in supercritical Xe (scXe) and Ar (scAr). Measurement of the temperature dependence of the rate of decay of (3)Fe(CO)(4) to produce (1)Fe(CO)(4)L (L = heptane or Xe) shows that these reactions have significant activation energies of 5.

Cell design for picosecond time-resolved infrared spectroscopy in high-pressure liquids and supercritical fluids.

The design of a new high-pressure infrared (IR) cell for carrying out picosecond time-resolved infrared (ps-TRIR) spectroscopy in supercritical fluids is described. We have employed thin (2 mm) MgF(2) windows in order to overcome possible undesirable nonlinear optical effects caused by the extremely high peak powers of ultrashort ultraviolet (UV)/visible pulses. The design of our cell allows for the study of systems at pressures of up to 5500 psi at temperatures of up to approximately 50 degrees C.

A delicate balance of complexation vs. activation of alkanes interacting with [Re(Cp)(CO)(PF3)] studied with NMR and time-resolved IR spectroscopy.

The organometallic alkane complexes Re(Cp)(CO)(PF(3))(alkane) and Re(Cp)(CO)(2)(alkane) have been detected after the photolysis of Re(Cp)(CO)(2)(PF(3)) in alkane solvent. NMR and time-resolved IR experiments reveal that the species produced by the interaction of n-pentane with [Re(Cp)(CO)(PF(3))] are an equilibrium mixture of Re(Cp)(CO)(PF(3))(pentane) and Re(Cp)(CO)(PF(3))(pentyl)H. The interaction of cyclopentane with [Re(Cp)(CO)(PF(3))] most likely results in a similar equilibrium between cyclopentyl hydride and cyclopentane complexes.

Time-resolved infrared (TRIR) study on the formation and reactivity of organometallic methane and ethane complexes in room temperature solution.

We have used fast time-resolved infrared spectroscopy to characterize a series of organometallic methane and ethane complexes in solution at room temperature: W(CO)5(CH4) and M(eta5-C5R5)(CO)2(L) [where M = Mn or Re, R = H or CH3 (Re only); and L = CH4 or C2H6]. In all cases, the methane complexes are found to be short-lived and significantly more reactive than the analogous n-heptane complexes. Re(Cp)(CO)2(CH4) and Re(Cp*)(CO)2(L) [Cp* = eta5-C5(CH3)(5) and L = CH4, C2H6] were found to be in rapid equilibrium with the alkyl hydride complexes.

Characterization of an organometallic xenon complex using NMR and IR spectroscopy.

Photolysis of Re(iPrCp)(CO)2(PF3) in liquid or supercritical Xe yields two new compounds [Re(iPrCp)(CO)2Xe and Re(iPrCp)(CO)(PF3)Xe]. Re(iPrCp)(CO)(PF3)Xe has been characterized by NMR and IR spectroscopies. The compound is an organometallic Xe complex that has been characterized by using NMR spectroscopy and is shown to be longer-lived than other organometallic Xe complexes by IR spectroscopy.

Unraveling the photochemistry of Fe(CO)5 in solution: observation of Fe(CO)3 and the conversion between 3Fe(CO)4 and 1Fe(CO)4(Solvent).

The photochemistry of Fe(CO)5 (5) has been studied in heptane, supercritical (sc) Ar, scXe, and scCH4 using time-resolved infrared spectroscopy (TRIR). 3Fe(CO)4 ((3)4) and Fe(CO)3(solvent) (3) are formed as primary photoproducts within the first few picoseconds. Complex 3 is formed via a single-photon process.

The hexaazidosilicate(IV) ion: synthesis, properties, and molecular structure.

The reaction of SiCl4 with an excess of (PPN)N3 (PPN+ = [(Ph3P)2N]+) affords selectively (PPN)2[Si(N3)6] (1). Simultaneous thermal analysis (TG-DTA) shows that the hexaazidosilicate salt is remarkably stable, melting at Tonex = 214 degrees C. Melting of 1 is followed by two distinct exothermic decomposition processes at Ton = 256 and 321 degrees C, the first one involving elimination of N2 and the second one degradation of the PPN cations and evolution of Si(N3)4, N2, and some HN3.