Syntheses, spectra and crystal structures of ruthenium(II) complexes with polypyridyl: [Ru(bipy)2(phen)](ClO4)2 · H2O and [Ru(bipy)2(Me-phen)](ClO4)2

Two ruthenium(II) complexes with polypyridyl, Ru(bipy)₂(phen)](ClO₄)₂·H₂O (1) and [Ru(bipy)₂(Me-phen)](ClO₄)₂ (2), (phen = 1,10-phenanthroline, bipy = 2,2′-bipyridine, Me-phen = 5-methyl-1,10-phenanthroline), were synthesized and characterized by IR, MS and NMR spectra. Their structures were determined by single crystal X-ray diffraction techniques. The strong steric interaction between the polypyridyl ligands was relieved neither by the elongation of the Ru---N bonds nor increase of the N---Ru---N bite angles. The coordination sphere was distorted to relieve the ligand interaction by forming specific angles (δ) between the polypyridyl ligand planes and coordination planes (N---Ru---N), and forming larger twisted angles between the two pyridine rings for each bipy. The bond distances of Ru---N(bipy) and Ru---N(phen) were virtually identical with experimental error, as expected of π back-bonding interactions which statistically involve each of the ligands present in the coordination sphere.     

The synthesis and characterization of a cationic technetium(V) phenylimido complex. The X-ray crystal structure of [TcCl2(NPh)(PMe2Ph)3](BPh4)

The reaction of the neutral Tc(V) phenylimido complex [TcCl₃(NPh)(PPh₃)₂] with excess PMe₂Ph in refluxing MeOH gives the cationic, tris-dimethylphenylphosphine complex [TcCl₂(NPh)(PMe₂Ph)₃]⁺, which is isolated as the tetraphenylborate salt. The IR spectrum of the crystalline product shows a medium intensity band at 1102 cm⁻¹ which is assigned to ν(TcN) from the phenylimido core. The ¹H NMR spectrum of the diamagnetic complex shows a series of multiplets in the aryl region and three distinct signals near 2 ppm from the phosphine methyl groups. The X-ray crystal structure, which is the first for a cationic technetium organoimido complex, shows a meridional arrangement of phosphine ligands with a chloride ligand coordinated trans to the phenylimido unit. The TcN bond length of 1.711(2) Å is consistent with the dianionic nature of the organonitrogen core. The Tc---N---C bond angle of 178.8(2)° reflects the sp hybridization of the phenylimido nitrogen atom. The coordination geometry is best described as a distorted octahedron. Crystal data for C₅₄H₅₈BCl₂NP₃Tc: triclinic space group

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. Structure solution based on 9986 observed reflections converged at R = 3.65%, R_w = 5.43%, GOF = 1.82.     

Kinetic studies on the first dihydrogen aquacomplex, [Ru(H2)(H2O)5]: Formation under H2 pressure and catalytic H/D isotope exchange in water

The ruthenium(II) hexaaqua complex [Ru(H₂O)₆]²⁺ reacts with dihydrogen under pressure to give the η²-dihydrogen ruthenium(II) pentaaqua complex [Ru(H₂)(H₂O)₅]²⁺.The complex was characterized by ¹H, ²H and ¹⁷O NMR: δ_H = −7.65 ppm, J_HD = 31.2 Hz, δ_O = −80.4 ppm (trans to H₂) and δ_O = −177.4 ppm (cis to H₂).The H-H distance in coordinated dihydrogen was estimated to 0.889 Å from J_HD, which is close to the value obtained from DFT calculations (0.940 Å).Kinetic studies were performed by ¹H and ²H NMR as well as by UV-Vis spectroscopy, yielding the complex formation rate and equilibrium constants: k_f = (1.7 ± 0.2) × 10⁻³ kg mol⁻¹ s⁻¹ and K_eq = 4.0 ± 0.5 mol kg⁻¹.The complex formation rate with dihydrogen is close to values reported for other ligands and thus it is assumed that the reaction with dihydrogen follows the same mechanisn (I_d).In deuterated water, one can observe that [Ru(H₂)(H₂O)₅]²⁺ catalyses the hydrogen exchange between the solvent and the dissolved dihydrogen.A hydride is proposed as the intermediate for this exchange.Using isotope labeling, the rate constant for the hydrogen exchange on the η²-dihydrogen ligand was determined as k₁ = (0.24 ± 0.04) × 10⁻³ s⁻¹.The upper and lower limits of the pK_a of the coordinated dihydrogen ligand have been estimated:3 < pK_a < 14.     

Synthesis and properties of the dichloro [tetramethyl (trifluoromethyl)cyclopentadienyl]ruthenium dimer: X-ray structure of [M2(η-C5Me4CF3)2Cl2(μ-Cl)2] (M=Ru, Rh)

The reaction of RuCl₃(H₂O), with C₅Me₄CF₃J in refluxing EtOH gives [Ru₂(η⁵-C₅Me₁CF₂)₂ (μ-Cl₂] (20 in 44% yield. Dimer 2 antiferromagnetic (−2J=200 cm¹). The crystal structures of 2 (rhombohedral system, R3 space group, Z=9, R=0.0589) and [Rh₂(η⁵-C₅Me₄CF₃(₂Cl₂(μ-Cl)₂] (3) (rhombohedral system. space group, Z = 9, R = 0.0641) were solved; both complexes have dimeric structures with a trans arrangement of the η⁵-C₅Me₄CF₄ rings. Comparison of the geometry of 2 and 3 with those of the corresponding η⁵-C₅Me₅ complexes shows that lowering the ring symmetry causes significant distortion of the M₂(μ-Cl)₂ moiety. The analysis of the MCl₃ fragment conformations in 2 and 3 and in the η⁵-C₅ME₅ analogues shows that they are correlated with the M---M distances. The Cl atoms are displaced by Br on reaction of 2 with KBr in MeOH to give the diamagnetic dimer [Ru₂(η⁵-C₅Me₄CF₃)₂Br₂ (μ-Br₂] (4). Complex 2 reacts with O₂ in CH₂Cl₂ solution at ambient temperature to form a mixture of isomeric η⁶-fulvene dimers [Ru₂(η⁶-C₅Me₃CF₃ = CH₂)₂Cl₂(μ-Cl)₂] (5). Reactions of 5 with CO and allyl chloride give Ru(η⁵-C₅Me₃CF₃CH₂Cl)(CO)₂Cl (6) and Ru(η⁵-C₅Me₃CF₃CF₃CH₂Cl)(η³-C₃H₅)Cl₂ (7) respectively.     

Unusual ruthenium hydride complexes supported by the [N(2-PPh2-4-Me-C6H3)2] pincer ligand

Complexes of Ru(II) containing the pincer ligand [⁻N(2-PPh₂-4-Me-C₆H₃)₂] (PNP^Ph) were prepared. The complex (PNP^PhH)RuCl₂ (1) was treated with 2 equiv AgOTf to produce the triflate complex (PNP^PhH)Ru(OTf)₂ (2). Complex 1 was also treated with an excess of NaBH₄ to give a bimetallic complex [(PNP^Ph)RuH₃]₂ (3). A number of methods, including X-ray crystallography, NMR spectroscopy, and computational studies, were used to probe the structure of 3. Addition of Lewis bases to 3 resulted in octahedral complexes containing a hydride ligand trans to a dihydrogen ligand.     

Synthesis, crystal structure and magnetic properties of the first structurally characterized 1,2-dithiocroconato-containing Cu(II) complex, [Cu(bpca)(H2O)]2[Cu(1,2-dtcr)2]·2H2O

The first crystal and molecular structure of a transition metal complex containing 1,2-dithiocroconate (1,2-dtcr, dianion of 1,2-dimercaptocylopent-1-ene-3,4,5-trione), [Cu(bpca)(H₂O)]₂[Cu(1,2-dtcr)₂]·2H₂O (where bpca is the bis(2-pyrdidylcarbonyl)amide anion), has been determined by single crystal X-ray diffraction methods. The compound crystallizesin the monoclinic syste, space group P2₁/c, with a = 11.661(3), b = 20.255(6), c = 8.265(3) Å, ß = 107.26(2)° and Z = 2. The structure is formally built of [Cu(1,2-dtcr)₂]²⁻ and [Cu(bpca)(H₂O)]⁺ ions and water of hydration. The copper atom of the anion is situated at a crystallographic inversion centre, bonded to four sulfur atoms in a planar, approximately square arrangement. In the cation the copper equatorial plane is formed by the three nitrogen atoms of the bpca ligand and a water oxygen atom. In addition there is a very weak axial bond to one of the sulfur atoms of a 1,2-dtcr ligand in the anion. Through these latter weak bonds each anion is connected to, and sandwiched between, two cations, resulting in neutral, trinuclear, centrosymmetric formula units. The triple-decker molecules are arranged in stacks along the crystallographic a-axis creating close contacts between the terminal copper atoms and bpca groups of the neighbouring molecules. This intermolecular interaction is, however, too weak to define the structure as a chain compound. The distance between adjacent copper atoms within the trinuclear unit is 4.189(1) Å, while the shortest intra-stack metal-metal separation between terminal copper atoms is 5.281(1) Å. Variable-temperature magnetic susceptibility measurements in the temperature r.2–140 K reveal that a Curie law is followed; with three non-interacting copper(II) ions in the formula unit.     

Mixed anion lanthanide(III) crown ether complexes: crystal structures of [LaCl2(NO3)(12-crown-4)]2, [La(NO3)(OH2)4-(12-crown-4)]Cl2·CH3CN and [LaCl2(NO3)(18-crown-6)]

Reaction of LaCl₃·7H₂O containing small amounts of La(NO₃)₃·7H₂O as an impurity with 12-crown-4 or 18-crown-6 in 3:1 CH₃CN:CH₃OH resulted in the isolation of the mixed anion complexes [LaCl₂(NO₃)(12-crown-4)]₂, [La(NO₃)(OH₂)₄(12-crown-4)]Cl₂·CH₃CN and [LaCl₂(NO₃)(18-crown-6)]. The nine-coordinate dimer, [LaCl₂(NO₃)(12-crown-4)]₂, has all of the anions in the inner coordination sphere and La³⁺ has a capped square antiprismatic geometry. It crystallizes in the orthorhombic space group Pbca with (at −150 °C) a = 12.938(6), B = 15.704(3), C = 13.962(2) Å, and D_calc = 2.08 g cm⁻³ for Z = 4. The second complex isolated from the same reaction, [La(NO₃)(OH₂)₄(12-crown-4)]Cl₂·CH₃CN, has the bidentate nitrate anion in the inner coordination sphere but the two chloride anions are in a hydrogen bonded outer sphere. This complex is ten-coordinate 4A,6B-expanded dodecahedral and crystallizes in the monoclinic space group P2₁ with (at 20 °C) A = 7.651(2), B = 11.704(7), C = 11.608(4) Å, β = 95.11(2)°, and D_calc = 1.80 g cm⁻³ for Z = 2. The 18-crown-6 complex, [LaCl₂(NO₃)(18-crown-6)], has all inner sphere anions and has ten-coordinate 4A,6B-expanded dodecahedral La³⁺ centers. It crystallizes in the orthorhombic space group Pbca with (at 20 °C) a = 14.122(7), B = 13.563(5), C = 19.311(9) Å, and D_calc = 1.89 g cm⁻³ for Z = 8.     

Photoirradiation reactions and crystal structures of two geometrical isomers of [Ru(OAc)(2cqn)2NO] (H2cqn=2-chloro-8-quinolinol)

The photoirradiation reactions of two geometrical isomers (cis-1 and cis-2) of [Ru(OAc)(2cqn)₂NO] (H2cqn=2-chloro-8-quinolinol) were studied. Cis-2 [Ru(OAc)(2cqn)₂NO] (2) photochemically isomerized to cis-1 [Ru(OAc)(2cqn)₂NO] (1) in CH₂Cl₂ or DMSO using an Xe lamp as a light source and the reaction was irreversible. The 2 to 1 isomerization coexisting with ¹⁵NO gas and its evolution of the ¹H NMR spectra showed that the dissociation and recombination of both the NO and the acetate ion involve in the isomerization. On the other hand, 1 did not isomerize but the NO ligand exchanged with ¹⁵NO. The crystal structures of 1 and 2 were determined by X-ray diffraction.     

A novel ferromagnetic coupling one-dimensional complex {Cu(II)(NIT3Py)2[N(CN)2]2(H2O)2}

The novel ferromagnetic coupling one-dimensional complex {Cu(NIT3Py)₂[N(CN)₂]₂(H₂O)₂} (NIT3Py=2-(3^′-pyridyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide) was synthesized and characterized structurally and magnetically. It crystallizes in the monoclinic space group C2/c. The Cu(II) ion is in a distorted octahedral environment. The units of {Cu(NIT3Py)₂[N(CN)₂]₂(H₂O)₂} were connected as one-dimensional structure by the intermolecular hydrogen bonds. Magnetic measurements show that there are intramolecular ferromagnetic interactions and intermolecular antiferromagnetic interactions within the chain.     

Synthesis and crystal structure of tetranuclear copper(I) and silver(I) complexes bridged by 2-amino-1,3,4-thiadiazole (atdz): [Cu4(atdz)6](ClO4)4·2CH3OH and [Ag4(atdz)6](ClO4)4

Two novel tetracopper(I) and tetrasilver(I) complexes [Cu₄(atdz)₆](ClO₄)₄·2CH₃OH (1) and [Ag₄(atdz)₆](ClO₄)₄ (2), have been prepared using 2-amino-1,3,4-thiadiazole (atdz), and their crystal structures and properties have been determined. On each tetranuclear complex, two Cu or Ag atoms (M) are bridged by two atdz ligands to form a six-membered N₂M₂N₂ framework. The two N₂M₂N₂ frameworks are in parallel linked by another atdz ligand to provide the tetranuclear structure with a rectangular M₄ core. The four Cu or Ag atoms possess a trigonal-square geometry. The two adjacent MM separations are (3.096(1) and 3.412(1) Å) and (3.316(2) and 3.658(2) Å) for 1 and 2, respectively. On both tetranuclear complexes there are two species of hydrogen bonds between the ClO₄ ⁻ anions and the NH₂ group of atdz ligands. It is proposed that the hydrogen bonds are related to the stabilization of the tetranuclear structure during the crystallization process.     

Convenient preparation of [CuX(PCy3)2](X = Br, I, SCN, N3) complexes. X-ray crystal structure of [Cu(N3)(PCy3)2] (Cy = cyclo-C6H11)

The labile cations [Cu(F-BF₃)(PCy₃)₂] and [Cu(OTf)(PCy₃)₂] are versatile precursors for the formation of [Cu(X)(PCy₃)₂] (X = Br, I, SCN, N₃) complexes by metathesis with NaX. The azide [Cu(N₃)(PCy₃)₂] is triclinic, space group , a = 9.755(4), B = 22.78(1), C = 9.284(6) Å, = 96.76(3), β = 115.36(3), γ = 94.20(5)°, Z = 2.     

Alkene rotation in [Ru(η-C5H5) (L2) (η-alkene][CF3SO3] with L2 = iPr- or pTol-diazabutadiene. X-ray crystal structure of [Ru(η-C5H5(pTol-DAB) (η-ethene][CF3SO3]

Reaction of RuCl(η⁵-C₅H₅(pTol-DAB) with AgOTf (OTf = CF₃SO₃) in CH₂Cl₂ or THF and subsequent addition of L′ (L′ = ethene (a), dimethyl fumarate (b), fumaronitrile (c) or CO (d) led to the ionic complexes [Ru(η⁵-C₅H₅)(pTol-DAB)(L′)][OTf] 2a, 2b and 2d and [Ru(η⁵-C₅H₅)(pTol-DAB)(fumarontrile-N)][OTf] 5c. With the use of resonance Raman spectroscopy, the intense absorption bands of the complexes have been assigned to MLCT transitions to the iPr-DAB ligand. The X-ray structure determination of [Ru(η⁵-C₅H₅)(pTol-DAB)(η²-ethene)][CF₃SO₃] (2a) has been carried out. Crystal data for 2a: monoclinic, space group P2₁/n with A = 10.840(1), b = 16.639(1), C = 14.463(2) Å, β = 109.6(1)°, V = 2465.6(5) ų, Z = 4. Complex 2a has a piano stool structure, with the Cp ring η⁵-bonded, the pTol-DAB ligand σN, σN′ bonded (Ru-N distances 2.052(4) and 2.055(4) Å), and the ethene η²-bonded to the ruthenium center (Ru-C distances 2.217(9) and 2.206(8) Å). The C = C bond of the ethene is almost coplanar with the plane of the Cp ring, and the angle between the plane of the Cp ring and the double of the ethene is 1.8(0.2)°. The reaction of [RuCl(η⁵-C₅H₅)(PPh)₃ with AgOTf and ligands L′ = a and d led to [Ru(η⁵-C₅H₅)(PPh₃)₂(L′)]OTf] (3a) and (3d), respectively. By variable temperature NMR spectroscopy the rottional barrier of ethene (a), dimethyl fumarate (b and fumaronitrile (c) in complexes [Ru(η⁵-C₅H₅)(L₂)(η²-alkene][OTf] with L₂ = iPr-DAB (a, 1b, 1c), pTol-DAB (2a, 2b) and L = PPh₃ (3a) was determined. For 1a, 1b and 2b the barrier is 41.5±0.5, 62±1 and 59±1 kJ mol⁻¹, respectively. The intermediate exchange could not be reached for 1c, and the ΔG^# was estimated to be at least 61 kJ mol⁻. For 2a and 3a the slow exchange could not be reached. The rotational barrier for 2a was estimated to be 40 kJ mol⁻. The rotational barier for methyl propiolate (HC≡CC(O)OCH₃) (k) in complex [Ru(η⁵-C₅H₅)(iPr-DAB) η²-HC≡CC(O)OCH₃)][OTf] (1k) is 45.3±0.2 kJ mol⁻¹. The collected data show that the barrier of rotational of the alkene in complexes 1a, 2a, 1b, 2b and 1c does not correlate with the strength of the metal-alkene interaction in the ground state.     

Hydrothermal synthesis and structural investigation of silver magnesium complex of benzenehexacarboxylic acid (mellitic acid), Ag2Mg2[C6(COO)6] · 8H2O with two-dimensional layered structure

Crystal and molecular structure of silver magnesium mellitate, Ag₂Mg₂[C₆(COO)₆] · 8H₂O, was synthesized hydrothermally and characterized by X-ray structure analysis. The complex crystallizes in the monoclinic system, space group P2/n, with unit cell dimensions of a=7.4347(2), b=9.9858(2), c=14.4248(3) Å, β=99.2429(5)°, V=1055.01(4) ų, and Z=2. The structure was solved and refined to R=0.036 (R_w=0.045) for 1707 independent reflections [I_o>2σ(I_o)]. The Ag cations are coordinated by six carboxylic oxygen atoms of mellitate anions with composition of [C₆(COO)₆]⁶⁻ on the (1 0 1) plane; each mellitate anion linking three neighboring Ag distorted trigonal prisms produces a two-dimensional layered structure parallel to (1 0 1). The Mg cations, which are coordinated by four water molecules and two carboxylic oxygen atoms, are intercalated between the two-dimensional layer stacks. The carboxylate group coordinated to Mg and Ag cations serve as a tridentate ligand in that structure. The number of water molecules incorporated into the mellitate compound is controlled mainly by ionic radii of metal cation in the structure. Furthermore, the ionic radii of metal cations in the mellitate compound play an essential role in arrangement of mellitate anions in the structure, whether as a one-dimensional infinite chain, a two-dimensional layered structure, or a three-dimensional framework structure.     

Ruthenium(II) thiacrown complexes: Synthetic, spectroscopic, electrochemical, DFT, and single crystal X-ray structural studies of [Ru([15]aneS5)Cl](PF6)

We wish to report the synthesis of the Ru(II) crown thioether complex, (1,4,7,10,13-pentathiacyclopentadecane)chlororuthenium(II) hexafluorophosphate, [Ru([15]aneS₅)Cl](PF₆), and a study of its properties utilizing single crystal X-ray diffraction, electronic spectroscopy, NMR spectroscopy, density functional theory calculations and cyclic voltammetry. The crystal structure shows a single [15]aneS₅ macrocycle and a chloro ligand coordinated in a distorted octahedral fashion around the ruthenium(II) center. A significant shortening (0.15 Å) of the trans Ru-S bond length occurs in this complex compared to the related PPh₃ complex (2.4458(10) to 2.283(1) Å) due to the differences in the trans influence of the two ligands. ¹³C NMR spectroscopy demonstrates that the structure of [Ru([15]aneS₅)Cl]⁺ is retained in solution. As expected for a Ru(II) complex, the electronic absorption spectrum shows two d-d transitions at 402 and 331 nm. These are red-shifted compared to hexakis(thioether)ruthenium(II) complexes and consistent with the weaker ligand field effect of the chloro ligand. The electrochemical behavior of the complex in acetonitrile shows a single one-electron reversible oxidation-reduction at +0.722 V versus Fc/Fc⁺ which is assigned as the Ru(II)/Ru(III) couple. DFT calculations for [Ru([15]aneS₅)Cl]⁺ show a HOMO with orbital contributions from a t_2g type orbital of the Ru ion, a π component from a p orbital of the axial S atom of [15]aneS₅, and a p orbital of the chloro ligand while the LUMO consists of orbital contributions of d_x²-y² orbital of the Ru center and p orbitals of the four equatorial S donors.     

Copper(II) complexes with (2-hydroxybenzyl-2-pyridylmethyl)amine–Hbpa: syntheses, characterization and crystal structures of the ligand and [Cu(II)(Hbpa)2](ClO4)2·2H2O

Copper(II) complexes were synthesized and characterized by means of elemental analysis, IR and visible spectroscopies, EPR and electrochemistry, as well as X-ray structure crystallography. The group consists of discrete mononuclear units with the general formula [Cu(II)(Hbpa)₂](A)₂·nH₂O, where Hbpa=(2-hydroxybenzyl-2-pyridylmethyl)amine and A=ClO₄ ⁻, n=2 (1), CH₃COO⁻, n=3 (2), NO₃ ⁻, n=2 (3) and SO₄ ²⁻, n=3 (4). The structures of the ligand Hbpa and complex 1 have been determined by X-ray crystallography. Complexes 1–4 have had their UV–Vis spectra measured in both MeCN and DMF. It was observed that the compounds interact with basic solvents, such that molecules coordinate to the metal in axial positions in which phenol oxygen atoms are coordinated in the protonated forms. The values were all less than 1000 M⁻¹ cm⁻¹. EPR measurements on powdered samples of 1–3 gave g/A values between 105 and 135 cm⁻¹, typical for square planar coordination environments. Complex 4·3H₂O exhibits a behaviour typical for tetrahedral coordination. The electrochemical behaviour for complexes 1 and 2 was studied showing irreversible redox waves for both compounds.     

New palladacyclic complexes with pyridylphosphine ligands: crystal structures of [Pd(Azb)(Ph2POCH2Py-P,N)][PF6] and [Pd(Phpy)(Ph2PNHPy-P,N)][PF6]

The synthesis of palladacyclic derivatives with the hybrid pyridylphosphine ligands Py(CH₂)OPPh₂ (a) and PyNHPPh₂ (b) in a neutral P,N-chelating coordination mode has been achieved. Treatment of selected chloride-bridged cyclometallated precursors [Pd(C^∧N)(μ-Cl)]₂ [C^∧N = 2-pyridinin-phenyl Phpy, I-compounds; 7,8-benzoquinolyl Bzq, II-compounds; phenylazophenyl Azb, III-compounds or 2-(2-oxazolinyl)phenyl Phox, IV-compounds] with a or b in the presence of stoichiometric KPF₆ gave the mononuclear derivatives Ia-IVa and Ib-IVb. The crystal structures of compounds [Pd(Azb)(Ph₂POCH₂Py-P,N)][PF₆] (IIIa) and [Pd(Phpy)(Ph₂PNHPy-P,N)][PF₆] (Ib) have been determined. The new palladacyclopentadiene precursor [Pd{C₄COOMe₄}(CH₃CN)₂] (V) has been prepared starting from the polymeric complex [Pd{C₄COOMe₄}]_n. Its usefulness in the preparation of new derivatives has been tested by means of the straightforward reaction with ligands (a) or (b) to give mononuclear compounds [Pd{C₄(COOMe)₄}(Ph₂POCH₂Py-P,N)] (Va) and [Pd{C₄(COOMe)₄}(Ph₂PNHPy-P,N)] (Vb). The reactions of hydroxo-bridged precursors [Pd(C^∧N)(μ-OH)]₂ or [Pd₂{C₄(COOMe)₄}₂ (μ-OH)₂][NBu₄]₂ with PyNHPPh₂ afforded mononuclear complexes Ic-Vc in which a less common anionic P,N-binding mode is forced as a result of ligand deprotonation. The new complexes were characterised by partial elemental analyses and spectroscopic methods (IR, FAB, ¹H and ³¹P{¹H} NMR).     

Probing the nature of H2 activation in catalytic asymmetric hydrogenation

Despite many years of intensive study, the natures of turnover-limiting and enantio-determining steps in catalytic asymmetric hydrogenation of prochiral enamides are poorly understood. An intriguing set of studies involving isotopic labeling distributions in catalytic enamide hydrogenation reactions were reported by Brown and Parker (Organometallics, 1 (1982) 950–956) more than a decade ago. In this paper we report the results of studies re-examining the application of isotopic probes to the catalytic hydrogenation enamides. These results provide some insights into the nature of the H₂ activation step in enamide hydrogenation.     

Silyl reagents (Me3Si-X) efficiently transfer X to Ir(H)2F(PBuP2Ph)2

Me₃Si-X reagents react to completion at 25°C in a short time to convert Ir(H)₂FL₂ (L=P^tBu₂Ph) to Ir(H)₂XL₂. This involves formation of Ir-O, Ir-N, Ir-I, Ir-S and Ir-C(sp) bonds. Products include some η²-X ligands such as carboxylate and acetamide, NHC(O)CH₃. The acetamide is shown to be η² in the solid state and in solution, but readily rearranges, by a transition state with Ir-O bond cleavage, to effect site exchange of the two inequivalent hydrides. The same synthetic approach succeeds for the more crowded metallated species and these reactions arc shown to fail when F is replaced by Cl in the iridium reagent. Unsaturation at Ir is suggested to be central to the mechanism of these F/X transposition reactions.     

Synthesis, magnetic properties and crystal structures of two compounds: [Cu(en)(H2O)]2[Fe(CN)6]·4H2O and [Cu(en)2][KFe(CN)6] (en=ethylenediamine)

Two new heterometallic complexes, [Cu(en)(H₂O)]₂[Fe(CN)₆]·4H₂O (1) and [Cu(en)₂][KFe(CN)₆] (2), have been isolated from the reactions of CuCl₂ and en with K₃[Fe(CN)₆] in different molar ratios. Both complexes have been characterized by X-ray analyses, IR spectra and elemental analyses. Complex 1 is a cyanide bridged bimetallic assembly, its crystal structure consists of a two-dimensional polymeric sheet with two different rings, one a four-membered square ring and another a 12-membered hexagonal ring. The Fe(II) ion of 1 has two terminal, two linear bridging and two 1,1 en-on bridging cyanide groups. In the crystal structure of 2, the neighboring [Fe(CN)₆]³⁻ units are bridged by the K⁺ and the [K[Fe(CN)₆]]²⁻ units forming a three-dimensional network structure. The [Cu(en)₂]²⁺ units fill in the holes of the network acting as counter cations and charge compensations. Variable temperature magnetic susceptibility studies of 1 indicate that the complex exhibits ferromagnetic interaction between the Cu(II) ions.     

The coordination chemistry of cationic main group clusters: syntheses and structures of [Fe3(Se2)2(CO)10] and [Fe4(Se2)3(CO)12]

The reactions of the polysulfur and selenium cationic clusters S₈²⁺ and Se₈²⁺ with various iron carbonyls were investigated. Several new chalcogen containing iron carbonyl cluster cations were isolated, depending on the nature of the counteranion. In the presence of SbF₆⁻ as a counterion, the cluster [Fe₃(E₂)₂(CO)₁₀] [SbF₆]₂·SO₂ (E = S, Se) could be isolated from the reaction of E₈²⁺ and excess iron carbonyl. The cluster is a picnic-basket shaped molecule of two iron centers linked by two Se₂ groups, with the whole fragment capped by an Fe(CO)₄ group. Crystallographic data for C₁₀O₁₂Fe₃Se₄Sb₂F₁₂S (I): space group monoclinic P2₁/c, A = 11.810(9), b = 24.023(6), c = 10.853(7) Å, β = 107.15(5)°, V = 2942(3) ų, Z = 4, R = 0.0426, R_w = 0.0503. When Sb₂F₁₁⁻ is present as the counterion, or Se₄[Sb₂F₁₁]₂ is used as the cluster cation source, a different cluster can be isolated, which has the formula [Fe₄(Se₂)₃(CO)₁₂] [SbF₆]₂·3SO₂. The dication contains two Fe₂Se₂ fragments bridged by an Se₂ group. Crystallographic data for C₁₂O₁₈Fe₄Se₆Sb₂F₁₂S₃ (III): space group triclinic , b = 18.400(9), C = 10.253(4) Å, = 93.10(4), β = 103.74(3), γ = 93.98(3)°, V = 1995(1) ų, Z = 2, R = 0.0328, R_w = 0.0325. The CO stretches in the IR spectrum all show a large shift to higher wavenumbers, suggesting almost no τ backbonding from the metals. This also correlates with the observed bond distances. All the compounds are extremely sensitive to air and water, and readily lose SO₂ when removed from the solvent. Thus all the crystals were handled at −100°C. The clusters seem to be either insoluble or unstable in all solvents investigated.