G. Ciani

Asymmetric hydrogenation catalyzed by aminophosphine-phosphiniterhodium complexes derived from natural aminoalcohols and x-ray crystal structure of (1,5-cyclooctadiene)-(S)-N-(diphenylphosphino)-2-diphenylphosphinoxymethylpyrrolidinerhodium(I) perchlorate

Abstract From the cheap and readily available amino alcohols (S)-pyrrolidinemethanol ((S)-prolinol), and (S)-α-N-ethyl-aminobutanol, we have obtained two new aminophosphine-phosphinite ligands: (S)-N-(diphenylphospino)-2-diphenylphos- phinooxymethylpyrrolidine ((S)-Prolophos) and (S)-1-diphenylphosphinoxy-2-N-ethyl-N-diphenylphosphinoaminobutane ((S)-Butaphos). The rhodium(I) complexes of these phosphines act as efficient homogeneous hydrogenation catalysts at ambient temperature and pressures for dehydro N-acetyl amino acids, dehydro N-benzoyl amino acids and itaconic acid. An X-ray diffraction study of the complex [Rh(COD)((S)-Prolophos)][ClO4]· THF has been shown that the crystals belong to the monoclinic space group P21 with a 10.680(2), b 10.448(2), c 18.207(3) A and β 104.97(1)ldg. Refinements based on 2105 significant counter reflections led to a final R value of 0.060. The cation is in a distorted square planar geometry, the rhodium atom being bound to the two phosphorus atoms and to the two double bonds of the diene molecule.

Synthesis of the carbonyl cluster dianion [RuRh4(CO)9(μ2-CO)6]2− and X-ray crystal structure of its bis(triphenylphosphine)iminium salt

The dianion [RuRh4(CO)15]2− has been obtained by reductive carbonylation of mixtures of Rh4(CO)12 and Ru3(CO)12, and the bis(triphenylphosphine)iminium salt has been characterized by single-crystal X-ray diffraction techniques. Triclinic crystals, space group P1 (No. 2), a 11.459(3), b 14.171(5), c 26.083(8) A, α 84.32(3), β 83.46(2), γ 82.81(2)°, Z = 2; the salt is isomorphous with (PPN)2[RuIr4(CO)15]. Least-squares refinement based on 2849 significant reflections gave a final R value of 0.059. The mixed metal cluster is an elongated trigonal bipyramid with the Ru atom located in apical position, as confirmed by variable temperature 13C NMR spectroscopy. The mean values of the Rheque5f8Rheq, Rheque5f8Rhap and Rheque5f8Ru bond lengths are 2.71, 3.03 and 2.99 A, respectively. The nine terminal and the six edge-bridging CO groups are disposed as in [RuIr4(CO)15]2−.

Reactions of the unsaturated anions [H3Re3(CO)10]2− and [H4Re3(CO)10]− with iodine in various solvents. X-ray characterization of the derivative H3Re3(CO)10(py)2

Abstract Treatment of [H 3 Re 3 (CO) 10 ](NEt 4 ) 2 (I) with acids gives [H 4 Re 3 (CO) 10 ](NEt 4 ) (II) which is unsaturated, like the parent compound I. Both I and II react with iodine in ethanol; I gives a mixture of two saturated species [H 3 Re 3 (CO) 10 I](NEt 4 ) (III) and [H 2 Re 3 (CO) 10 I](NEt 4 ) 2 (IV), while II gives only compound III. If the same reactions are carried out with iodine in pyridine, crystals of the saturated non-electrolyte compound H 3 Re 3 (CO) 10 (py) 2 (V) are obtained. The results of an X-ray analysis show that the latter species contains an equilateral metal atom triangle with long hydrogen-bridged Reue5f8Re bonds of mean length 3.292A.

H/D exchange via reversible pyridine ortho-metallation, and competition between CH oxidative addition and CO coordination in hydrido-carboxyl triangular rhenium clusters: a 1H-NMR investigation. X-ray crystal structure of the anion [Re3( μ-H)2(CO)11(Py)]−

The triangular cluster anion [Re3(μ-H)3(μ-NC5H4)(CO)10]− (2), containing an ortho-metallated pyridine bridging a cluster edge, undergoes in acetone solution a selective H/D exchange between the basal hydridic site and the α-position of the ortho-metallated pyridine, with k = 1.9(1) × 10−6 s−1, at room temperature. The process was studied by NMR on the partially deuterated derivative [Re3(μ-H)2(μ-D)(μ-NC5D4)(CO)10]− and an equilibrium isotope effect was observed, the equilibrium concentration of the isotopomer containing C-bound deuterium being about double that of the isotopomer containing Re-bound deuterium. In pyridine-d5 solutions, in contrast, the preferential deuteration of the hydrides bridging the lateral edges of [Re3(μ-H)3(μ-NC5H4)(CO)10]− was observed, with a rate about half that of the deuteration of the ortho-metallated pyridine (k = 2.9(1) × 10−5 s−1 at 302 K for the latter process). The H/D exchange processes in both solvents have been rationalized as arising from the reversible reductive elimination of the ortho-metallated pyridine. The different behavior in the two solvents is discussed. In the presence of CO, the anion 2 gave [Re3(μ-H)2(CO)12]− (4, t12 ≈ 48 h) in acetone solution, while in pyridine it gave the novel anion [Re3(μ-H)2(CO)11(Py)]− (3). In py-d5, under CO, the resonances of the ortho-metallated pyridine of 2 decreased at the same rate as in the absence of CO. The competition ratio r between CO coordination and pyridine ortho-metallation on the intermediate generated by Cue5f8H reductive elimination has been estimated as 0.45(15). The reaction of [Re3(μ-H)4(CO)10]− (1) with CO in pyridine follows two parallel paths, affording both compounds 3 and 2, the latter, in turn, converting into 3 at a slower rate. The rate of disappearance of 1 was the same as that measured in the absence of CO (k = 2.1(2) × 10−4 s−1 at 302 K) and the value of the competition ratio r between the two pathways leading to 3 and 2, respectively, was found to be 0.5(1). Under high H2 pressure, 2 slowly transforms back into the unsaturated parent anion 1, showing the complete reversibility of the ortho-metallation reaction. The structure of the anion [Re3(μ-H)2(CO)11(Py)]− (3), as [NEt4]+ salt, has been investigated by X-ray analysis. The crystals are monoclinic, space group P21/c, with a = 14.327(3), b = 12.310(2), c = 17.437(3) A, β = 91.67(2)° and Z = 4. The refinements, performed by full-matrix least-squares on the basis of 2064 significant [I > 2σ(I)] reflections, gave final agreement indices R and wR2 of 0.0397 and 0.0835, respectively. The anion contains an isosceles triangle of rhenium atoms, with one shorter edge [3.025(1) A], and two longer hydrogen-bridged edges [3.202(1) and 3.209(1) A]; it bears eleven terminal CO groups and an N-bonded pyridine molecule [Reue5f8N 2.21(2) A].

The crystal and molecular structure of hepta-μ-carbonyltetracarbonyl-tetrahedron-tetrarhodate(2—) in its bis(triphenylphosphine)iminium salt

Abstract The solid state structure of the cluster complex undecacarbonyltetrarhodate(2—) has been determined in the salt (PPh3NPPh3)2[Rh4(CO)11], which crystallizes in the space group P 1 with cell constants a 22.394(3), b 14.351(2), c 11.937(2) A, α 93.05(2)°, β 96.25(2)°, υ 88.38(2)°, Z = 2. The structure was refined by least-squares to a conventional discrepancy factor R of 0.060, based on 3884 reflection intensities collected by counter methods. The metal atom cluster is a distorted tetrahedron to which the ligands are bound four terminally and seven edge bridging; the idealized symmetry of the anion is C2[itv. The Rhue5f8Rh distances range from 2.662(2) to 2.986(2) A, and are discussed in terms of ligand topology and the localized character of the anionic charge.

High nuclearity PtRh carbonyl clusters. Synthesis and X-ray characterization of the [Pt2Rh9(CO)22]3− trianion

Abstract The new mixed Ptue5f8Rh cluster trianion [Pt 2 Rh 9 (CO) 22 ] 3− has been isolated as a minor product of the pyrolysis of [PtRh 5 (CO) 15 ] − , and has been characterized by X-ray diffraction. The metal skeleton, which has ideal D 3 h symmetry, consists of three face-to-face condensed octahedra, as previously found in the isoelectronic species [Rh 11 CO) 23 ] 3− , with the Pt atoms on the three-fold axis, in the positions of maximum Mue5f8M connectivity.

Reactions of the carbido cluster anion [Re7C(CO)21]3− with group IB metals: X-ray crystal structure of the novel heterometallic carbide [{Re7AgC(CO)21}2Br]5−

The carbido cluster anion [Re7C(CO)21]3− reacts with compounds containing metals, M, of Group IB, namely AuClPPh3, (AgClPPh3)4, AgBF4 and [Cu(NCMe)4]PF6, to give adducts exhibiting a Re7M skeleton, of trans-bicapped octahedral geometry, as demonstrated by the X-ray investigation of the [{Re7AgC(CO)21}2Br]5− anion.

Reactions of the unsaturated anion [Re3(μ-H)4(CO)10]− with phosphines. Synthesis of the anions [Re3(μ-H)2(CO)10(PR3)2]−, and crystal structure of [NEt4][Re3(μ-H)2(CO)10(PPh3)2]

Abstract The reaction of the unsaturated cluster anion [Re 3 (μ-H) 4 (CO) 10 ] − with tertiary phosphines at room temperature results in the substitution of two hydride ligands (eliminated as H 2 ) by two PR 3 ligands, leading to saturated [Re 3 (μ-H) 2 (CO) 10 -(PR 3 ) 2 ] − compounds. A single crystal X-ray diffraction study of the PPh 3 derivative revealed that the two phosphines occupy non-equivalent equatorial coordination sites on the triangular cluster. The rate of the reaction greatly increases with increase of the basicity of the phosphine.

A benzamido bridged rhenium carbonyl cluster produced by attack of oh OH− on coordinated PhCn. X-ray characterization of the anion [Re3(μ-H)3(CO)10(μ-η2-OC(Ph)NH)]−

Abstract The novel anion [Re3(μ-H)3(CO)10(μ-η2-OC(Ph)NH)]−, obtained by reaction of Re3(μ-H)3(CO)10(NCPh)2 with (NBu4OH, has been characterized by X-ray analysis. It contains a triangle of rhenium atoms, with the three Reue5f8Re edges bridged by the hydrides, bearing a benzamido ligand diaxially bridging the shortest Reue5f8Re bond. 1H NMR spectroscopy has revealed dynamic behaviour of the ligand. Treatment of the anion with H+ in PhCN solution results in regeneration of the parent compound and liberation of one molecule of benzamide.

Structural characterization in solid state and solution of the hydridocarbonyl cluster anion [Re4(ν-H)4(CO)13]12−

Abstract The salt [AsPh 4 ] 2 [Re 4 (ν-H) 4 (CO) 13 ], obtained by pyrolysis of [AsPh 4 ][ReH 2 (CO) 4 ] in ethanol, has been investigated by X-ray analysis. The crystals are monoclinic, space group P 2 1 / n , with a = 12.630(3), b = 38.062(6), c = 12.916(3) A, β = 105.94(2)° and Z = 4. The refinements, performed by full-matrix least-squares on the basis of 3389 significant reflections, gave final agreement indices R and R w of 0.035 and 0.040, respectively. The anion contains a tetrahedron of rhenium atoms [Re-Re in the range 3.048(1)-3.126(1) A], bearing thirteen terminal carbonyl groups and four edge-bridging hydride ligands. The variable temperature 1 H NMR investigation showed three hydridic resonances (ratio 1:2:1) at 153 K, in agreement with the C s symmetry of the solid state structure. At higher temperatures, two different degenerate exchange processes concerning the hydride ligands are operative. The first, frozen only below 153 K, equalizes the three hydrides bridging the edges of the basal triangle. The second, frozen below 188 K, exchanges all the hydrides, leading to a single hydride resonance at room temperature. Band shape analysis provided an estimate of the rate constants and of the activation parameters of the two processes: intrabasal exchange, E a = 30.4 ± 1.3 kJ/mol, Δ H ‡ = 29.0 ± 1.3 kJ/mol, Δ S ‡ = −8.1±7.5 J/K mol; overall scrambling, E a , = 42.7±0.6 kJ/mol, Δ H ‡ = 40.7±0.6 kJ/mol, Δ S ‡ = −16.6 ± 2.6 J/K mol.