Massimo Di Vaira

Crystal Structure of Nitromethane up to the Reaction Threshold Pressure

Angle dispersion X-ray diffraction (AXDX) experiments on nitromethane single crystals and powder were performed at room temperature as a function of pressure up to 19.0 and 27.3 GPa, respectively, in a membrane diamond anvil cell (MDAC). The atomic positions were refined at 1.1, 3.2, 7.6, 11.0, and 15.0 GPa using the single-crystal data, while the equation of state (EOS) was extended up to 27.3 GPa, which is close to the nitromethane decomposition threshold pressure at room temperature in static conditions. The crystal structure was found to be orthorhombic, space group P2(1)2(1)2(1), with four molecules per unit cell, up to the highest pressure. In contrast, the molecular geometry undergoes an important change consisting of a gradual blocking of the methyl group libration about the C-N bond axis, starting just above the melting pressure and completed only between 7.6 and 11.0 GPa. Above this pressure, the orientation of the methyl group is quasi-eclipsed with respect to the NO bonds. This conformation allows the buildup of networks of strong intermolecular O...H-C interactions mainly in the bc and ac planes, stabilizing the crystal structure. This structural evolution determines important modifications in the IR and Raman spectra, occurring around 10 GPa. Present measurements of the Raman and IR vibrational spectra as a function of pressure at different temperatures evidence the existence of a kinetic barrier for this internal rearrangement.

The P4Se3 cage molecule as a ligand. Crystal structure of [(N(CH2CH2PPh2)3) Ni(P4Se3]·2C6H6

Abstract The structure of the compound [(np 3 )Ni(P 4 Se 3 )]·2C 6 H 6 , obtained from reaction of the nickel(0) complex (np 3 )Ni (np 3  tris(2-diphenylphosphinoethyl)amine) with tetraphosphorus triselenide, P 4 Se 3 , has been determined by X-ray diffraction studies. Crystal data: cubic, space group P 2 1 3, a 17.413(7) A, Z  4; final R  0.050. The intact P 4 Se 3 entity is coordinated to the metal through the apical phosphorus atom. The small changes occurring in the geometry of the cage molecule upon coordination are analyzed by a comparison with the structure of uncoordinated P 4 Se 3 , which has been refined to R  0.045.

Stabilization of the tautomers HP(OH)2 and P(OH)3 of hypophosphorous and phosphorous acids as ligands

Treatment of [CpRu(PPh(3))(2)Cl] 1 with the stoichiometric amount of H(3)PO(2) or H(3)PO(3) in the presence of chloride scavengers (AgCF(3)SO(3) or TlPF(6)) yields compounds of formula [CpRu(PPh(3))(2)(HP(OH)(2))]Y (Y = CF(3)SO(3) 2a or PF(6) 2b) and [CpRu(PPh(3))(2)(P(OH)(3))]Y (Y = CF(3)SO(3) 3aor PF(6) 3b) which contain, respectively, the HP(OH)(2) and P(OH)(3) tautomers of hypophosphorous and phosphorous acids bound to ruthenium through the phosphorus atom. The triflate derivatives 2a and 3a react further with hypophosphorous or phosphorous acids to yield, respectively, the complexes [CpRu(PPh(3))(HP(OH)(2))(2)]CF(3)SO(3) 4 and [CpRu(PPh(3))(P(OH)(3))(2)]CF(3)SO(3) 5 which are formed by substitution of one molecule of the acid for a coordinated triphenylphosphine molecule. The compounds 2 and 3 are quite stable in the solid state and in solutions of common organic solvents, but the hexafluorophosphate derivatives undergo easy transformations in CH(2)Cl(2): the hypophosphorous acid complex 2b yields the compound [CpRu(PPh(3))(2)(HP(OH)(2))]PF(2)O(2) 6, whose difluorophosphate anion originates from hydrolysis of PF(6)(-); the phosphorous acid complex 3b yields the compound [CpRu(PPh(3))(2)(PF(OH)(2))]PF(2)O(2) 7, which is produced by hydrolysis of hexafluorophosphate and substitution of a fluorine for an OH group of the coordinated acid molecule. All the compounds have been characterized by elemental analyses and NMR measurements. The crystal structures of 2a, 3a and 7 have been determined by X-ray diffraction methods.

Synthesis, x-ray crystal structure and bonding in [(PPh3)2PtSe]2

Abstract The compound [(PPh 3 ) 2 PtSe] 2 has been obtained by reacting a selenide solution with (PPh 3 ) 2 PtCl 2 and its structure has been determined by X-ray diffraction analysis. The molecular geometry of the complex consists of a four membered Pt 2 Se 2 ring with two triphenylphosphine ligands coordinated to each platinum, giving a planar (P 2 Pt) 2 Se 2 arrangement. MO calculations have shown that the planar geometry is indeed slightly favoured for the neutral compound but anticipate a bent geometry for a hypothetical cationic species, in agreement with what has been found for related tellurium derivatives.

Controlling the Activation of White Phosphorus: Formation of Phosphorous Acid and Ruthenium‐Coordinated 1‐Hydroxytriphosphane by Hydrolysis of Doubly Metalated P4

The reactivity of white phosphorus with transition-metal compounds is a mature field of inorganic and organometallic chemistry that has been extensively investigated in the past few decades. Research in this field has led to the synthesis of an amazing variety of transition-metal complexes containing Pn units originating from either the coupling or the degradation of the cage molecule(s) as well as from the recombination of smaller fragments into polyatomic aggregates. These compounds often contain species with unique geometric and electronic properties which, apart from exhibiting a rich and intriguing chemistry, have found interest either as building blocks for the construction of networks of monoand polydimensional inorganic structures or as phosphorustransfer agents towards inorganic and organic molecules. The recent activation of white phosphorus with either heterocyclic carbenes or highly nucleophilic main group compounds has led to new opportunities in this area, especially by allowing the partial degradation of the molecule and its functionalization by insertion of organic fragments into the assembled polyphosphorus units without the involvement of a transition metal. Previous work from our group has highlighted the utility of {CpRuL2} moieties (Cp R =C5H5, C5Me5; L= phosphane) for coordinating the intact P4 molecule in reactions that yield stable monoor dinuclear cationic complexes [{CpRuL2}n(h -P4)] n+ (n= 1, 2). Furthermore, these monoor bimetallic compounds, which are easily obtained in gram amounts, have proved to be useful for investigating the reactivity of coordinated P4 under mild conditions. For example, we have found that the reactivity of the coordinated P4 molecule in the cyclopentadienyl derivatives is spectacularly modified with respect to that of the free molecule as it readily undergoes quantitative disproportionation with water at room temperature. Thus, addition of excess water (100 equivalents) to one equivalent of [CpRuL2(h -P4)](CF3SO3) (1) or [{CpRuL2}2(m,h -P4)](CF3SO3)2 (2) in THF hydrolyzes the coordinated P4 ligand in a few hours to yield a mixture of phosphine (PH3), diphosphane (P2H4), and the phosphorus oxyacids H3PO2 and H3PO3 in ratios that depend strongly on the hapticity of the P4 molecule (h 1 vs. m,h). The hydrogenated molecules are stabilized by coordination to {CpRu(PPh3)2} fragment(s), [8b,c,9] whereas the oxo derivatives are obtained as either free molecules or coordinate to ruthenium after tautomerization to the pyramidal species PH(OH)2 and P(OH)3, respectively. [10] The above products, which contain one or two phosphorus atoms from the parent P4 molecule, are clearly the thermodynamic sinks in the degradation of P4, which appears to follow aspecific pathways. Herein we report further breakthroughs in this reaction and show that the reactivity of coordinated P4 is a modular process which, surprisingly, is strongly dependent on the amount of water used for the hydrolysis reaction. In particular, we demonstrate that rapid quenching of the hydrolysis of the dinuclear derivative 2 with a large excess of water affords only phosphorous acid (H3PO3) and a new bimetallic compound containing the previously unknown 1hydroxytriphosphane molecule, which is stabilized as a bridging ligand between two {CpRu(PPh3)2} fragments (Scheme 1). The formation of this molecule, besides its intrinsic interest due to the fact that it has never been observed previously either in the free state or as a ligand, gives important hints regarding the initial step of the hydrolytic degradation of coordinated P4 and pinpoints the existence of a selective disproportionation of P4 that differs from its well-known alkaline hydrolysis, which gives only PH3 and hypophosphorous acid (H3PO2). The addition of 500 equivalents of water to one equivalent of 2 in THF is a simple process that leads to the formation of one equivalent of H3PO3 and one equivalent of the new complex [{CpRu(PPh3)2}2{m ,h-PH(OH)PHPH2}](CF3SO3)2 (3) within a few minutes ( P NMR monitoring). Work-up of this solution gave 3 in excellent yield, and recrystallization from CHCl3/n-hexane provided yellow crystals suitable for X-ray analysis. The diruthenium cation in 3 contains the previously unknown molecule PH(OH)PHPH2, which bridges two {CpRu(PPh3)2} moieties through the phosphorus atoms of the PH(OH) and PH2 end-groups. These two groups are affected by twofold positional disorder in the solid-state [*] Prof. Dr. M. Di Vaira, Dr. S. Seniori Costantini, Prof. Dr. P. Stoppioni Dipartimento di Chimica, Universit& di Firenze via della Lastruccia,3, 50019 Sesto Fiorentino, Firenze, (Italy) Fax: (+39)0554573385 E-mail: piero.stoppioni@unifi.it

Improved Solvent Formulations for Efficient CO2 Absorption and Low‐Temperature Desorption

This experimental study describes efficient CO₂ capture by 2-amino-2-methyl-1-propanol (AMP)/piperazine (PZ) in ethylene glycol monoethyl ether (EGMEE, 2-ethoxyethanol) containing approximately 15 wt % of water. In these experiments, the solvent is continuously circulated between the absorber (packed-bed reactor at 30, 40, or 45 °C) and the desorber (at 80, 85, or 90 °C). The CO₂ -solvent reaction equilibria have been investigated by using ¹³C NMR spectroscopy, which provides confirmatory evidence that the formation of mono- and biscarbamate derivatives of PZ accounts for most of the CO₂ absorbed by the AMP/PZ/EGMEE/H₂O blend. The solid-state structures of AMP carbamate and of the carbonate salt of protonated AMP have been determined by using XRD. Both AMPCO₂(-) and CO(3)(2-) species completely convert to the monoalkyl carbonates on dissolving the respective salts in methanol, ethanol, or ethylene glycol.

Addition of copper(I) and silver(I) to a P–P bond in [(triphos)MP3] [triphos=1,1,1-tris(diphenylphosphinomethyl)ethane; M=Co, Rh]: X-ray crystal structure of [{(triphos)CoP3}2Cu]PF6

Abstract Treatment of the [(triphos)MP3] compounds [triphos=1,1,1-tris(diphenylphosphinomethyl)ethane; M=Co, Rh], which have a pseudotetrahedral core formed by three unsubstituted phosphorus atoms and a cobalt group metal fragment, with copper(I) and silver(I) derivatives affords the compounds [{(triphos)MP3}2M′]Y (M=Co, M′=Cu, Y=BF4, PF6; M′=Ag, Y=ClO4, PF6. M=Rh, M′=Ag, Y=CF3SO3, PF6). X-ray crystallographic analysis of the [{(triphos)CoP3}2Cu]PF6 derivative shows that the copper atom is bound to two pairs of unsubstituted phosphorus atoms belonging to the P3 units of two [(triphos)CoP3] fragments; the copper atom has a co-ordination geometry intermediate between elongated tetrahedral and square planar. The same structure is assigned to all the complexes on the basis of 31P{1H} NMR data which are indicative of dynamic behaviour of the compounds in solution. The unexpected elimination of phosphane ligands from copper(I) and silver(I) parent salts and the lengthening of the P–P bonds to which addition of the M′ metal occurs is indicative of significant interaction between the metal and the MP3 clusters.

Reactivity of The P4 Molecule with Cobalt(I) and Rhodium(I) Polyphosphane Fragments

The reaction of white phosphorus with the electronically and coordinatively unsaturated systems [(PP3)M]+ [PP3 = tris(2-diphenylphosphanylethyl)phosphane; M = Co, Rh] and [(NP3)Rh]+ [NP3 = tris(2-diphenylphosphanylethyl)amine] in tetrahydrofuran affords new tetraphosphorus complexes. The PP3 metal fragments yield the trigonal bipyramidal [(PP3)M(η1-P4)]+ complex cations [M = CoI(1), RhI(2)] containing the intact P4 molecule bonded end-on to the metal. In contrast, the [(NP3)Rh]+ system yields an octahedral rhodium(III) complex of formula [(NP3)Rh(η2-P4)]BPh4(3) which contains a bicyclotetraphosphane ligand (P42−) coordinated to the metal through the wing-tip P atoms. Compound 3 forms through the oxidative addition of the P4 molecule to the metal fragment. These new tetraphosphorus derivatives, which are very reactive, have been characterized in solution at low temperature by 31P NMR spectroscopy.

Synthesis and coordinating properties of the functionalized macrocyclic ligand 1,4-bis(1-methylimidazol-2-ylmethyl)-7-carboxymethyl-1,4,7-triazacyclononane. Crystal structures of cobalt(III), nickel(II) and zinc(II) complexes

Abstract The synthesis of the new unsymmetrically derivatized macrocycle 1,4-bis(1-methylimidazol-2-ylmethyl)-7-carboxymethyl-1,4,7-triazacyclononane (LH) is reported. The potentially hexadentate ligand yields cobalt(III), nickel(II) and zinc(II) complexes of formulae COL (PF6)2 (1), NiLPF6 · CH3OH (2) and ZnLClO4 · H2O (3), which have been isolated in the solid state and characterized. The nickel complex is remarkably stable towards ligand dissociation in water solution even in the presence of a large excess of CN−. The structures of the complexes have been determined by single-crystal X-ray analyses. Compound 1 crystallizes in the triclinic space group P1, a = 7.397(2), b = 10.960(4), c = 17.420(5) A, α=101.51(3), β = 91.85(4), γ = 98.24(3)°, Z = 2. Compound 2 is monoclinic P21/a, a = 14.094(15), b = 11.045(4), c = 16.905(5) A, β = 105.54(7)°, Z = 4; 3 is triclinic P1, a = 7.903(4), b = 9.218(5), c = 16.996(10) A, α = 98.51(6), β = 96.76(8), γ = 101.98(7)°, Z = 2. In each complex cation the metal atom is six-coordinated, being surrounded by the three macrocycle nitrogens, the two imidazole nitrogens and one carboxylate oxygen atom, with a coordination geometry which is approximately trigonal antiprismatic in 1 and 2 and trigonal prismatic in 3.

Crystallographic evidence for decomposition of dimethylformamide in the presence of ruthenium(III) chloride

A crystalline product is obtained in high yield when ruthenium(III) chloride is dissolved in dimethylformamide, in the presence of small amounts of hydrochloric acid. The structure of this product has been determined by X-ray diffraction studies. We have found that the obtained product is ionic and may be formulated as (Me 2 NH 2 ) 4 Cl(RuCl 6 ), the structure being formed by dimethylammonium cations, chloride anions and hexachlororuthenate(III) anions. The presence of the dimethylammonium cation in this structure suggests that substantial cleavage of DMF has occurred under the relatively mild experimental conditions used in this study. The implications of these findings are briefly discussed.