C5 H2 Research Articles

On the Reactivity of Mes*P(PMe3 ) towards Aluminum(I) Compounds - Evidence for the Intermediate Formation of Phosphaalumenes.

Phosphaalumenes are the heavier isoelectronic analogs of alkynes and have eluded facile synthesis until recently. We have reported that the combination of a phosphinidene transfer agent, Ar TerP(PMe3 ) (Ar Ter=2,6-Ar2 -C6 H3 ), with (Cp*Al)4 (Cp*=C5 (CH3 )5 ) afforded the phosphaalumenes Ar TerPAlCp* as isolable, violet, thermally stable compounds. In here we describe attempts to utilize Mes*P(PMe3 ) (Mes*=2,4,6-tBu3 -C6 H2 ) as a phosphinidene source in combination with different Al(I) precursors, namely Dip NacnacAl (Dip Nacnac=HC[C(Me)NDip]2 , Dip=2,6-iPr2 -C6 H3 ), (Cp*Al)4 and Cp3t Al (Cp3t =1,2,4-tBu3 -C5 H2 ). In all cases the formation of phosphaalumenes was not observed, however, their intermediate formation is indicated by formation of the dimer [Cp*Al(μ-PMes*)]2 (2) and C-H-bond activation products along the putative P=Al bond, giving unusual 1,2-P,Al-tetrahydronaphtalene derivatives 1 and 4, clearly underlining the role the sterically demanding group on phosphorus plays in these transformations. The reactivity studies are supported by theoretical studies, demonstrating a thermodynamic preference for the C-H activation products. Additionally, we show that there are potential pitfalls in the synthesis of Cp*2 AlH, the precursor to make (Cp*Al)4 and give recommendations how to circumvent these.

Photoluminescence and mechanoluminescence of solid-state zirconocene dichlorides.

Spectral-luminescence properties of 23 samples of zirconium complexes were studied. Mechanoluminescence spectra of 10 complexes were obtained. The solid-state component of the mechanoluminescence spectrum, that is the luminescence of the crystal itself, coincided with the photoluminescence spectra of these complexes, which indicated identical emission from the same excited states in mechanoluminescence and photoluminescence, despite the different ways of excitation. The luminescence maximum was red shifted as substituents appeared in the ligand, in particular in the presence of a bridging group connecting π-ligands (ansa-complexes) and also for a substituted bis-indenyl complex rac-Me2 Si(2-Me-4-Ph-5-OMe-6-But -Ind)2 ZrCl2 ). It was found that mechanical destruction of the rac-isomer of complex Mе2 С(2-Me-4-But -C5 H2 )2 ZrCl2 , unlike that of the meso-isomer, was accompanied by a more than a 10-fold increase in intensity and by a shift in the mechanoluminescence spectrum to longer wavelengths.

Molecular Thorium Trihydrido Clusters Stabilized by Cyclopentadienyl Ligands.

Hydrogenolysis of alkyl-substituted cyclopentadienyl (CpR ) ligated thorium tribenzyl complexes [(CpR )Th(p-CH2 -C6 H4 -Me)3 ] (1-6) afforded the first examples of molecular thorium trihydrido complexes [(CpR )Th(μ-H)3 ]n (CpR =C5 H2 (t Bu)3 or C5 H2 (SiMe3 )3 , n=5; C5 Me4 SiMe3 , n=6; C5 Me5 , n=7; C5 Me4 H, n=8; 7-10 and 12) and [(Cp# )12 Th13 H40 ] (Cp# =C5 H4 SiMe3 ; 13). The nuclearity of the metal hydride clusters depends on the steric profile of the cyclopentadienyl ligands. The hydrogenolysis intermediate, tetra-nuclear octahydrido thorium dibenzylidene complex [(Cpttt )Th(μ-H)2 ]4 (μ-p-CH-C6 H4 -Me)2 (Cpttt =C5 H2 (t Bu)3 ) (11) was also isolated. All of the complexes were characterized by NMR spectroscopy and single-crystal X-ray analysis. Hydride positions in [(CpMe4 )Th(μ-H)3 ]8 (CpMe4 =C5 Me4 H) were further precisely confirmed by single-crystal neutron diffraction. DFT calculations strengthen the experimental assignment of the hydride positions in the complexes 7 to 12.

Ring Contraction by NHC-Induced Pnictogen Abstraction.

The reaction of [Cp'''Co(η4 -P4 )] (1) (Cp'''=1,2,4-tBu3 C5 H2 ) with Me NHC (Me NHC=1,3,4,5-tetramethylimidazol-2-ylidene) leads through NHC-induced phosphorus cation abstraction to the ring contraction product [(Me NHC)2 P][Cp'''Co(η3 -P3 )] (2), which represents the first example of an anionic CoP3 complex. Such NHC-induced ring contraction reactions are also applicable for triple-decker sandwich complexes. The complexes [(Cp*Mo)2 (μ,η6:6 -E6 )] (3 a, 3 b) (Cp*=C5 Me5 ; E=P, As) can be transformed to the complexes [(Me NHC)2 E][(Cp*M)2 (μ,η3:3 -E3 )(μ,η2:2 -E2 )] (4 a, 4 b), with 4 b representing the first structurally characterized example of an NHC-substituted AsI cation. Further, the reaction of the vanadium complex [(Cp*V)2 (μ,η6:6 -P6 )] (5) with Me NHC results in the formation of the unprecedented complexes [(Me NHC)2 P][(Cp*V)2 (μ,η6:6 -P6 )] (6), [(Me NHC)2 P][(Cp*V)2 (μ,η5:5 -P5 )] (7) and [(Cp*V)2 (μ,η3:3 -P3 )(μ,η1:1 -P{Me NHC})] (8).

Light Lanthanide Metallocenium Cations Exhibiting Weak Equatorial Anion Interactions.

As the dysprosocenium complex [Dy(Cpttt)2][B(C6F5)4] (Cpttt=C5H2 tBu3‐1,2,4, 1‐Dy) exhibits magnetic hysteresis at 60 K, similar lanthanide (Ln) complexes have been targeted to provide insights into this remarkable property. We recently reported homologous [Ln(Cpttt)2][B(C6F5)4] (1‐Ln) for all the heavier Ln from Gd–Lu; herein, we extend this motif to the early Ln. We find, for the largest LnIII cations, that contact ion pairs [Ln(Cpttt)2{(C6F5‐κ1‐F)B(C6F5)3}] (1‐Ln; La–Nd) are isolated from reactions of parent [Ln(Cpttt)2(Cl)] (2‐Ln) with [H(SiEt3)2][B(C6F5)4], where the anion binds weakly to the equatorial sites of [Ln(Cpttt)2]+ through a single fluorine atom in the solid state. For smaller SmIII, [Sm(Cpttt)2][B(C6F5)4] (1‐Sm) is isolated, which like heavier 1‐Ln does not exhibit equatorial anion interactions, but the EuIII analogue 1‐Eu could not be synthesised due to the facile reduction of EuIII precursors to EuII products. Thus with the exception of Eu and radioactive Pm this work constitutes a structurally similar family of Ln metallocenium complexes, over 50 years after the [M(Cp)2]+ series was isolated for the 3d metals.

Ring Expansions of Nonpolar Polyphosphorus Rings.

The reaction of the phosphinidene complex [Cp*P{W(CO)5 }2 ] (1 a) (Cp*=C5 Me5 ) with the anionic cyclo-Pn ligand complex [(η3 -P3 )Nb(ODipp)3 ]- (2, Dipp=2,6-diisopropylphenyl) resulted in the formation of [{W(CO)5 }2 {μ3 ,η3:1:1 -P4 Cp*}Nb(ODipp)3 ]- (3), which represents an unprecedented example of a ring expansion of a polyphosphorus-ligand complex initiated by a phosphinidene complex. Furthermore, the reaction of the pnictinidene complexes [Cp*E{W(CO)5 }2 ] (E=P: 1 a, As: 1 b) with the neutral complex [Cp'''Co(η4 -P4 )] (Cp'''=1,2,4-tBu3 C5 H2 ) led to a cyclo-P4 E ring (E=P, As) through the insertion of the pentel atom into the cyclo-P4 ligand. Starting from 1 a, the two isomers [Cp'''Co(μ3 ,η4:1:1 -P5 Cp*){W(CO)5 }2 ] (5 a,b), and from 1 b, the three isomers [Cp'''Co(μ3 ,η4:1:1 -AsP4 Cp*){W(CO)5 }2 ] (6 a-c) with unprecedented cyclo-P4 E ligands (E=P, As) were isolated. The complexes 6 a-c represent unique examples of ring expansions which lead to new mixed five-membered cyclo-P4 As ligands. The possible reaction pathways for the formation of 5 a,b and 6 a-c were investigated by a combination of temperature-dependent 31 P{1 H} NMR studies and DFT calculations.

Metal-Assisted Opening of Intact P4 Tetrahedra.

The reactivity of ruthenium and manganese complexes bearing intact white phosphorus in the coordination sphere was investigated towards the low-valent transition-metal species [Cp'''Co] (Cp'''=η5 -C5 H2 -1,2,4-tBu3 ) and [L0 M] (L0 =CH[CHN(2,6-Me2 C6 H3 )]2 ; M=Fe, Co). Remarkably, and irrespective of the metal species, the reaction proceeds by the selective cleavage of two P-P edges and the formation of a square-planar cyclo-P4 ligand. The reaction products [{CpRu(PPh3 )2 }{CoCp'''}(μ,η1:4 -P4 )][CF3 SO3 ] (5), [{CpBIG Mn(CO)2 }2 {CoCp'''}(μ,η1:1:4 -P4 )] (6) and [{CpBIG Mn(CO)2 }2 {ML0 }(μ,η1:1:4 -P4 )] (CpBIG =C5 (C6 H4 nBu)5 ; L0 =CH[CHN(2,6-Me2 C6 H3 )]2 ; M=Fe (7 a), Co (7 b)), respectively, were fully characterized by single-crystal X-ray diffraction and spectroscopic methods. The electronic structure of the cyclo-P4 ligand in the complexes 5-7 is best described as a π-delocalized P4 2- system, which is further stabilized by two and three metal moieties, respectively. DFT calculations envisaged a potential intermediate in the reaction to form 5, in which a quasi-butterfly-shaped P4 moiety bridges the two metals and behaves as an η3 -coordinated ligand towards the cobalt center.

Iron Precatalysts with Bulky Tri(tert-butyl)cyclopentadienyl Ligands for the Dehydrocoupling of Dimethylamine-Borane.

In an attempt to prepare new Fe catalysts for the dehydrocoupling of amine-boranes and to provide mechanistic insight, the paramagnetic FeII dimeric complex [Cp'FeI]2 (1) (Cp'=η5 -((1,2,4-tBu)3 C5 H2 )) was used as a precursor to a series of cyclopentadienyl FeII and FeIII mononuclear species. The complexes prepared were [Cp'Fe(η6 -Tol)][Cp'FeI2 ] (2) (Tol=C6 H5 Me), [Cp'Fe(η6 -Tol)][BArF4 ] (3) (BArF4 =[B(C6 H3 (m-CF3 )2 )4 ]- ), [N(nBu)4 ][Cp'FeI2 ] (4), Cp'FeI2 (5), and [Cp'Fe(MeCN)3 ][BArF4 ] (6). The electronic structure of the [Cp'FeI2 ]- anion in 2 and 4 was investigated by SQUID magnetometry, EPR spectroscopy and ab initio Complete Active Space Self Consistent Field-Spin Orbit (CASSCF-SO) calculations, and the studies revealed a strongly anisotropic S=2 ground state. Complexes 1-6 were investigated as catalysts for the dehydrocoupling of Me2 NH⋅BH3 (I) in THF at 20 °C to yield the cyclodiborazane product [Me2 N-BH2 ]2 (IV). Complexes 1-4 and 6 were active dehydrocoupling catalysts towards I (5 mol % loading), however 5 was inactive, and ultra-violet (UV) irradiation was required for the reaction mediated by 3. Complex 6 was found to be the most active precatalyst, reaching 80 % conversion to IV after 19 h at 22 °C. Dehydrocoupling of I by 1-4 proceeded via formation of the aminoborane Me2 N=BH2 (II) as the major intermediate, whereas for 6 the linear diborazane Me2 NH-BH2 -NMe2 -BH3 (III) could be detected, together with trace amounts of II. Reactions of 1 and 6 with Me3 N⋅BH3 were investigated in an attempt to identify Fe-based intermediates in the catalytic reactions. The σ-complex [Cp'Fe(MeCN)(κ2 -H2 BH⋅NMe2 H][BArF4 ] was proposed to initially form in dehydrocoupling reactions involving 6 based on ESI-MS (ESI=Electrospray Ionisation Mass Spectroscopy) and NMR spectroscopic evidence. The latter also suggests that these complexes function as precursors to iron hydrides which may be the true catalytic species.

Synthesis and Characterization of an Eclipsed Digermylene as a Building Block to Construct a Cyclic Octagermylene.

The preparation of an unprecedented GeI -GeI bonded digermylene [K2 {Ge2 (μ-κ2 :η2 :η4 -2,6-(2,6-i Pr2 C6 H3 -N)2 -4-CH3 C5 H2 N)2 }] in an eclipsed conformation stabilized by two bridging diamidopyridyl ligands is presented. Although it exhibits an eclipsed conformation, the Ge-Ge bond length is 2.5168(6) Å, which is shorter than those in the trans-bent and gauche digermylenes. In combination with two pendant amido groups, the GeI2 motif is employed as a building block to assemble the first example of octagermylene [Ge4 (μ-κ2 :κ1 -2,6-(2,6-i Pr2 C6 H3 -N)2 -4-CH3 C5 H2 N)2 ]2 showing a cyclic configuration and containing three distinct types of GeI -GeI bonds.

Unexpected Reactivity of [(η(5) -1,2,4-tBu3 C5 H2 )Ni(η(3) -P3 )] towards Main Group Nucleophiles and by Reduction.

The reduction of [Cp'''Ni(η(3) -P3 )] (1; Cp'''=η(5) -1,2,4-tBu3 C5 H2 ) with potassium produces the complex anion [(Cp'''Ni)2 (μ,η(2:2) -P8 )](2-) (2), which contains a realgar-like P8 unit. The anionic triple-decker sandwich complex [(Cp'''Ni)2 (μ,η(3:3) -P3 )](-) (3) with a cyclo-P3 middle deck is obtained when 1 is treated with NaNH2 as a nucleophile. Na[3] can subsequently be oxidized with AgOTf to the neutral triple-decker complex [(Cp'''Ni)2 (μ,η(3:3) -P3 )] (4). In contrast, 1 reacts with LiPPh2 to give the anionic compound [(Cp'''Ni)2 (μ,η(2:2) -P6 PPh2 )](-) (5), a complex containing a bicyclic P7 fragment capped by two Cp'''Ni units. Protonation of Li[5] with HBF4 leads to the neutral complex [(Cp'''Ni)2 (μ,η(2:2) -(HP6 PPh2 )] (6). Adding LiNMe2 to 1 results in [Cp'''Ni(η(2) -P3 NMe2 )](-) (7) becoming accessible, a complex which forms as a result of nucleophilic attack at the cyclo-P3 ring of 1. The complexes K2 [2], Na[3], 4, 6, and Li[7] were fully characterized and their structures determined by single-crystal X-ray diffraction.

Insights into the Cascade Reaction of CO and Heteroallenes Mediated by Dinitrogen Hafnocene Complexes: The Indirect Effect of Nitride's Nucleophilicity

A DFT mechanistic exploration of the reactivity of the dinitrogen hafnocene complex, [{(η(5)-C5 H2 -1,2,4-Me3)2 Hf}2 (μ2-N2)], towards mixtures of CO/CO2 and CO/OCNtBu is reported. The crucial role of the nitride intermediate is highlighted, as well as the importance of the bridging mode of the cyanate ligand between the two Hf metal atoms throughout the process. Interestingly, the CO2 addition to the nitride intermediate occurs through an outer-sphere transition state, whereas the addition of the heteroallene is governed by the steric congestion imposed by cyclopentadienyl ligands.

Thermal simulation of basic volcanic fluid influence on different source rocks

Based on thermal simulation experiment, interactions between volcanic fluids and source rocks were studied. Gas generations in the dry system and fluid system under different temperatures were analyzed. The results showed that the various types of source rocks are similar in composition, containing gaseous C1–C5 hydrocarbons, H2 and CO2 whose gas yields increase with increasing temperature. The gas yield of source rocks of type I is the highest, followed by type II, and that of source rocks of type III is the lowest, indicating that the yield of hydrocarbon gases is related to their hydrocarbon generating potential. Although the generating potential of type III is the lowest, it can still be regarded as a useful gas source when it is buried deeply enough. The basic volcanic fluid restrains the generation of gaseous hydrocarbons in different types of source rocks, but promotes the generation of inorganic gases.

The heritability of metabolic profiles in newborn twins

Identifying genetic and metabolic biomarkers in neonates has the potential to improve diagnosis and treatment of common complex neonatal diseases, and potentially lead to risk assessment and preventative measures for common adulthood illnesses such as diabetes and cardiovascular disease. There is a wealth of information on using fatty acid, amino acid and organic acid metabolite profiles to identify rare inherited congenital diseases through newborn screening, but little is known about these metabolic profiles in the context of the 'healthy' newborn. Recent studies have implicated many of the amino acid and fatty acid metabolites utilized in newborn screening in common complex adult diseases such as cardiovascular disease, insulin resistance and obesity. To determine the heritability of metabolic profiles in newborns, we examined 381 twin pairs obtained from the Iowa Neonatal Metabolic Screening Program. Heritability was estimated using multilevel mixed-effects linear regression adjusting for gestational age, gender, weight and age at time of sample collection. The highest heritability was for short-chain acylcarnitines, specifically C4 (h²=0.66, P=2 × 10⁻¹⁶), C4-DC (h²=0.83, P<10⁻¹⁶) and C5 (h²=0.61, P=1 × 10⁻⁹). Thyroid stimulating hormone (h²=0.58, P=2 × 10⁻⁵) and immunoreactive trypsinogen (h²=0.52, P=3 × 10⁻⁹) also have a strong genetic component. This is direct evidence for a strong genetic contribution to the metabolic profile at birth and that newborn screening data can be utilized for studying the genetic regulation of many clinically relevant metabolites.

Synthesis, Structure, and Reactivity of a Diphosphadiferratetrahedrane with a Fe-Fe Double Bond.

The short thermolysis of the butterfly molecule [{Cp'''(OC)2 Fe}2 P4 ] affords, besides [Cp'''FeP5 ] and [{Cp'''Fe}2 P4 ], the diphosphadiferratetrahedrane [{Cp'''Fe}2 (μ-CO)(μ-η2 :η2 -P2 )] with a Fe-Fe double bond in 18 % yield. The P2 building block was split photochemically into two μ-P ligands with elimination of CO. In the resulting dinuclear complex 1, the 31 P NMR signal is shifted to extremely low field (δ=1406.9), and the rhombic Fe2 P2 four-membered ring is almost orthogonal to the eclipsed Cp''' five-membered rings; Cp'''=tBu3 C5 H2 .

Biodegradation of 2,4‐dichlorophenoxy acetic acid (2,4‐d) by pseudomonas cepacia: Stoichiometric study

AbstractPseudomonas cepacia biodegraded 2,4‐dichlorophenoxyacetic acid (2,4‐D) according to the following stoichiometric equation:C8 H6 Cl2 O3 + c1 O2 + c2 NH3 → c3 CHx Nz Oy + c4 CO2 + c5 H2 O + c6 Cl− + c7 REIMwhere CHx Nz Oy represents the bacterial cells and REIM is the residual extracellular intermediate metabolites. The stoichiometric coefficients c1 to c7 were determined from C, N, O, H and Cl balances together with the experimental data on the biodegradation of 14 C‐carboxy‐labeled‐2,4‐D and 14 C‐ring‐uniformly‐labeled‐2,4‐D. The stoichiometric equation obtained predicted satisfactorily the total oxygen consumption for and the total heat production from the biodegradation of 2,4‐D for a wide range of initial concentrations from 80 to 500 mg/L.

Pyrolysis of cyclopentane behind reflected shock waves

Gas samples containing either 0.20% or 1.0% cyclopentane plus 0.25% tert-butyl alcohol in argon have been heated to 1185–1257 K in a single pulse shock tube. The previously studied dehydration of the alcohol was used as an internal standard reaction for temperature measurement. Pyrolysis of the cyclopentane yielded a broad spectrum of C1–C5 hydrocarbon products; however, the products and their concentration ratios were in good agreement with those recently reported by Tsang, in a comparative rate study of cyclopentane pyrolysis vs. cyclo-hexene decyclization. Thus strong support is offered for Tsang's proposed complex mechanism involving (a) molecular isomerization to 1-pentene and subsequent degradation of that product, (b) molecular decomposition to cyclopropane and ethene, followed by isomerization of cyclopropane to propene, and (c) induced decomposition to a variety of C1–C5 hydrocarbons plus H2 via hydrogen atom abstraction from cyclopentane by various radicals generated from 1-pentene. The only significant disagreement with Tsang's study is a ∼40° temperature discrepancy; possible sources of this are discussed.