Terminal Hydrogen Research Articles

Comparison of two-body and three-body decomposition of ethanedial, propanal, propenal, n-butane, 1-butene, and 1,3-butadiene

We investigated two-body (binary) and three-body (triple) dissociations of ethanedial, propanal, propenal, n-butane, 1-butene, and 1,3-butadiene on the ground potential-energy surfaces using quantum-chemical and Rice-Ramsperger-Kassel-Marcus calculations; most attention is paid on the triple dissociation mechanisms. The triple dissociation includes elimination of a hydrogen molecule from a combination of two separate terminal hydrogen atoms; meanwhile, the rest part simultaneously decomposes to two stable fragments, e.g., C(2)H(4), C(2)H(2), or CO. Transition structures corresponding to the concerted triple dissociation were identified using the B3LYP/6-311G(d,p) level of theory and total energies were computed using the method CCSD(T)/6-311+G(3df, 2p). The forward barrier height of triple dissociation has a trend of ethanedial < propanal < propenal < n-butane < 1-butene < 1,3-butadiene, pertaining to the reaction enthalpy. Ratios of translational energies of three separate fragments could be estimated from the transition structure of triple dissociation. The synchronous concerted dissociation of propanal, propenal, and 1-butene leading to three different types of molecular fragments by breaking nonequivalent chemical bonds is rare. The triple dissociation of propanal, n-butane, 1-butene, and 1,3-butadiene were investigated for the first time. To outline a whole picture of dissociation mechanisms, some significant two-body dissociation channels were investigated for the calculations of product branching ratios. The triple dissociation plays an important role in the three carbonyl compounds, but plays a minor or negligible role in the three hydrocarbons.

Synthesis, Structure, and Reactivity of RuII Complexes with Trimethylsilylethinylamidinate Ligands

AbstractThe mononuclear amidinate complexes [(η6‐cymene)‐RuCl(1a)] (2) and [(η6‐C6H6)RuCl(1b)] (3), with the trimethylsilyl‐ethinylamidinate ligands [Me3SiC≡CC(N‐c‐C6H11)2]– (1a–) and[Me3SiC≡CC(N‐i‐C3H7)2]– (1b–) were synthesized in high yields by salt metathesis. In addition, the related phosphane complexes[(η5‐C5H5)Ru(PPh3)(1b)] (4a) [(η5‐C5Me5)Ru(PPh3)(1b)] (4b), and [(η6‐C6H6)Ru(PPh3)(1b)](BF4) (5‐BF4) were prepared by ligand exchange reactions. Investigations on the removal of the trimethyl‐silyl group using [Bu4N]F resulted in the isolation of [(η6‐C6H6)Ru(PPh3){(N‐i‐C3H7)2CC≡CH}](BF4) (6‐BF4) bearing a terminal alkynyl hydrogen atom, while 2 and 3 revealed to yield intricate reaction mixtures. Compounds 1a/b to 6‐BF4 were characterized by multinuclear NMR (1H, 13C, 31P) and IR spectroscopy and elemental analyses, including X‐ray diffraction analysis of 1b, 2, and 3.

Electron and Hydrogen Transfer in Small Hydrogen Fluoride Anion Clusters

A new stable structure has been found for the anion clusters of hydrogen fluoride. The ab initio method was used to optimize the structures of the (HF)(3)(-), (HF)(4)(-), (HF)(5)(-), and (HF)(6)(-) anion clusters with an excess "solvated" electron. Instead of the well-known "zig-zag" (HF)(n)(-) structure, a new form, (HF)(n-1)F(-)···H, was found with lower energy. In this new form, the terminal hydrogen atom in the (HF)(n)(-) chain is separated from the other part of the cluster and the inner hydrogens transfer along the hydrogen bonds toward the outside fluoride. The negative charge also transfers from the terminal HF molecule of the chain to the center fluoride atoms. The (HF)(n)(-) clusters for n = 4, 5, and 6 have not yet been observed experimentally. These results should assist in the search for these systems and also provide a possible way to study the proton and electron transfer in some large hydrogen bonding systems.

Synthesis and optical properties of C3-ethynylated chlorin and π-extended chlorophyll dyads

A C3-ethynylated chlorophyll derivative was prepared from methyl pyropheophorbide- d possessing a 3-formyl group by treatment of Bestmann–Ohira reagent. The mono-substituted acetylene was subjected to coupling reactions at the terminal acetylenic carbon atom to form a series of π-extended chlorophyll derivatives. Replacement of the terminal hydrogen to phenyl, phenylethynyl and C3-chlorin-ethynyl caused red-shifts of their Q y (0,0) maxima from 675 to 679, 686, and 696 nm, respectively. Optical properties of C3 2-substituted 3-ethynyl-chlorophyll derivatives including chlorophyll dyads were investigated in comparison with those of their related compounds. Partial quenching of the fluorescence emission ( Φ flu=0.14) was observed for ortho-substituted dyad, compared to meta- ( Φ=0.27) and para-dyads ( Φ=0.29), suggesting a through-space interaction between the two chlorin macrocycles in a molecule.

Ketonethiosemicarbazones: Structure–activity relationships for their melanogenesis inhibition

A series of 2-(1-phenylalkylidene)hydrazinecarbothioamides 2, 2-(1-phenylalkyl)hydrazinecarbothioamides 3, 2-(3,4-dihydronaphthalen-1(2H)-ylidene)hydrazinecarbothioamide (4), and 2-(1-(thiophen-2-yl)ethylidene)hydrazinecarbothioamide (5) were synthesized for their melanogenesis inhibition in melanoma B16 cells. The SAR of these ketonethiosemicarbazones revealed that the benzylidene hydrogen in aldehydethiosemicarbazones 1 can be replaced by hydrophobic moiety and substitutions with alkyl group for the terminal amino hydrogen of ketonethiosemicarbazones improved the activity appreciably. In addition, the double bond in thiosemicarbazones is an important factor for the increment of hydrophobicity. Thus hydrophobic ketonethiosemicarbazones are excellent inhibitors of melanogenesis like aldehydethiosemicarbazones.

Syntheses and Surprising Regioselectivity of 5- and 6-Substituted Decaboranyl Ethers via the Nucleophilic Attack of Alcohols on 6- and 5-Halodecaboranes

The selective syntheses of new classes of decaboranyl ethers containing a range of functional groups substituted at the B5 or B6 positions were achieved through the reaction of alcohols with halodecaboranes. The surprising regioselectivity of the reaction, where the reaction of the 6-halodecaboranes (6-X-B(10)H(13)) with alcohols yielded the 5-substituted decaboranyl ethers (5-RO-B(10)H(13)) and the reaction with 5-halodecaboranes (5-X-B(10)H(13)) gave the 6-substituted decaboranyl ethers (6-RO-B(10)H(13)), was confirmed by NMR and X-ray crystallographic analyses. The crystallographic determinations also showed that the decaboranyl ethers had shortened B-O bonds and apparent sp(2) hybridization at oxygen indicating significant π-backbonding from oxygen to the cage boron. A possible substitution mechanism was computationally identified involving: (1) initial nucleophilic attack by the alcohol-oxygen at a site adjacent to the 5- or 6-halo-substituted boron, (2) movement of the terminal hydrogen at the point of attack to a bridging position, (3) formation of a 5-membered (B-O-H-Cl-B) cyclic transition state allowing the acidic methanolic-hydrogen to bond to the halogen, (4) release of HX, and finally (5) movement of a bridging hydrogen into the vacated terminal position. Deuterium labeling studies confirmed the movement of hydrogen from a bridging position of the halodecaborane into the halogen-vacated terminal position on the decaboranyl ether product. The relative reaction rates of the 6-X-B(10)H(13) compounds (X = F, Cl, Br, I) with alcohols were likewise found to be consistent with this mechanism.

Geometric and electronic effects on hydrogenation of cinnamaldehyde over unsupported Pt-based nanocrystals

It is reported that catalytic hydrogenation of cinnamaldehyde to cinnamyl alcohol is a structural sensitive reaction dependent on size and type of metal doper of unsupported platinum nanocrystals used. Smaller sizes of platinum nanocrystals are found to give lower selectivity to cinnamyl alcohol, which suggests the high index Pt sites are undesirable for the terminal aldehyde hydrogenation. A plot of reaction selectivity across the first row of transition metals as dopers gives a typical volcano shape curve, the apex of which depicts that a small level of cobalt on platinum nanocrystals can greatly promote the reaction selectivity. The selectivity towards cinnamyl alcohol over the cobalt doped Pt nanocrystals can reach over 99.7%, following the optimization in reaction conditions such as temperature, pressure and substrate concentration. Detailed studies of XRD, CO chemisorption (for FTIR), TEM, SEM, AES and XPS of the nanostructure catalyst clearly reveal that the decorated cobalt atoms not only block the high index sites of Pt nanocrystals (sites for Co deposition) but also exert a strong electronic influence on reaction pathways. The d-band centre theory is invoked to explain the volcano plot of selectivity versus metal doper.

A homobimetallic complex of chromium(0) with a σ-borane component

The synthesis, characterization, and reactivity of a chromium(0) complex bearing an amine-borane moiety (η(6)-C(6)H(5)CH(2)NMe(2)·BH(3))Cr(CO)(3) (2) is reported. Photolysis of complex 2 results in the elimination of a CO ligand followed by the formation of an intramolecular σ-borane complex (η(1)-(η(6)-C(6)H(5)CH(2)NMe(2)·BH(2)-H))Cr(CO)(2) (3). This species was characterized in solution by NMR spectroscopy. Reaction of complex 2 with photochemically generated (OC)(5)Cr(THF) affords a novel homobimetallic σ-borane complex (OC)(3)Cr(η(6)-C(6)H(5)CH(2)NMe(2)·BH(2)-H-Cr(CO)(5)) (4), wherein one of the BH moieties is bound to the chromium center in an η(1)-fashion. The σ-borane complex 4 was isolated in moderate to good yield (72%). The BH(3) fragment in the complexes 3 and 4 are highly dynamic involving exchange of the BH hydrogen bound to the metal with the terminal BH hydrogen atoms. The dynamics has been studied using variable-temperature NMR spectroscopy. Complexes 2 and 4 have been characterized by X-ray crystallography.

Halogenation of Carbon Substrates for Increased Reactivity with Alkenes

Carbon substrates are readily functionalized with alkene-containing molecules via an ultraviolet-light-catalyzed reaction, resulting in the formation of a carbon-carbon bond with the surface. This reaction is typically performed on hydrogen-terminated carbon substrates, limiting its utility as alkene molecules with low electron affinities do not readily attach to this surface. Recently, a wet-chemical method for preparing bromine- and chlorine-terminated carbon substrates has been developed. Replacing the terminal hydrogen atoms with a halogen analog increases the surface's reactivity with alkene-containing molecules, affording a means of modifying the carbon substrate with the alkene molecules that do not readily attach to the hydrogen-terminated surface and with a greatly reduced reaction time.

Visible light flavin photo-oxidation of methylbenzenes, styrenes and phenylacetic acids

We report the photocatalytic oxidation of benzylic carbon atoms under mild conditions using riboflavin tetraacetate as photocatalyst and blue-emitting LEDs (440 nm) as light source. Oxygen is the terminal oxidant and hydrogen peroxide appears as the only byproduct in most cases. The process oxidizes toluene derivatives, stilbenes, styrenes and phenylacetic acids to their corresponding benzaldehydes. A benzyl methyl ether and acylated benzyl amines are oxidized directly to the corresponding methyl ester or benzylimides. The mechanism of the reactions has been investigated and the results indicate that oxygen addition to benzyl radicals is a key step of the oxidation process in the case of phenylacetic acids.

Rigidity Percolation in Plasma Enhanced Chemical Vapor Deposited a-SiC:H Thin Films

Plasma Enhanced Chemically Vapor Deposited SiC:H thin films are compelling materials for both semiconductor nano-electronic and MEMS/NEMS technologies due to the extreme chemical inertness of this material and the ability to tune a variety of material properties across an extreme range of values. As one example of the latter, we demonstrate that using PECVD the dielectric constant and Young's modulus of SiC:H thin films can be varied from < 3 to > 7 and < 10 GPa to > 200 GPa respectively. Utilizing Fourier Infrared-Transform Spectroscopy, we show that this remarkable range in materials properties is achieved primarily via the incorporation of terminal hydrogen groups which lowers the overall connectivity of the Si-C network bonding. We find that once the average network coordination number for Si and C falls below 2.6, the SiC network becomes under constrained and there is a loss of rigidity percolating through the system thus limiting the range of materials properties that can be achieved in this system.

Evaluation of the individual hydrogen bonding energies in N-methylacetamide chains

The individual hydrogen bonding energies in N-methylacetamide chains were evaluated at the MP2/6-31+G** level including BSSE correction and at the B3LYP/6-311++G(3df,2pd) level including BSSE and van der Waals correction. The calculation results indicate that compared with MP2 results, B3LYP calculations without van der Waals correction underestimate the individual hydrogen bonding energies about 5.4 kJ mol−1 for both the terminal and central hydrogen bonds, whereas B3LYP calculations with van der Waals correction produce almost the same individual hydrogen bonding energies as MP2 does for those terminal hydrogen bonds, but still underestimate the individual hydrogen bonding energies about 2.5 kJ mol−1 for the hydrogen bonds near the center. Our calculation results show that the individual hydrogen bonding energy becomes more negative (more attractive) as the chain becomes longer and that the hydrogen bonds close to the interior of the chain are stronger than those near the ends. The weakest individual hydrogen bonding energy is about −29.0 kJ mol−1 found in the dimer, whereas with the growth of the N-methylacetamide chain the individual hydrogen bonding energy was estimated to be as large as −62.5 kJ mol−1 found in the N-methylacetamide decamer, showing that there is a significant hydrogen bond cooperative effect in N-methylacetamide chains. The natural bond orbital analysis indicates that a stronger hydrogen bond corresponds to a larger positive charge for the H atom and a larger negative charge for the O atom in the N-H⋯O=C bond, corresponds to a stronger second-order stabilization energy between the oxygen lone pair and the N-H antibonding orbital, and corresponds to more charge transfer between the hydrogen bonded donor and acceptor molecules.

Theoretical Study on Hetero‐Diels–Alder Reaction of Butadiene with Benzaldehyde Catalyzed by Chiral InIII Complexes

AbstractThe mechanism of the hetero‐Diels–Alder reaction of butadiene with benzaldehyde catalyzed by chiral N,N′‐dioxide/In(OTf)3 complexes was studied theoretically by using density functional theory (DFT) and model system. The computational results indicate that the catalyzed reaction proceeded through a concerted mechanism via a highly zwitterionic transition state. The lowest energy barrier was 11.8 kJ mol–1, which is 63.0 kJ mol–1 lower than that of the uncatalyzed reaction. The results indicate that the endo approach is advantageous over the exo approach, because exo transitions states suffer from more steric hindrance than the endo transitions states as a result of interactions among the substrates, the trifluoromethanesulfonic group and the R4 groups of the ligand. The (S) configuration was observed predominantly over the (R) form, because there is no distinguishable repulsion between butadiene and the exo amino side or the endo amino side of the ligand. Besides, the interactions between the terminal hydrogen atoms of butadiene and the oxygen atoms of the trifluoromethanesulfonic group make the structure more stable. Thus, the experimental results were explained well by calculation of the chiral N,N′‐dioxide/In(OTf)3 complex catalyzed hetero‐Diels–Alder reaction at the molecular level.

Electrochemical Hydrogen Oxidation on Pt(110): A Combined Direct Molecular Dynamics/Density Functional Theory Study

A first-principles direct molecular dynamics and density functional theory study of the electrooxidation of molecular hydrogen at the Pt(110)/water interface was conducted to gain an atomic-level understanding of the electrocatalytic processes and of adsorbed reaction intermediates. The H2 electrooxidation follows the Tafel−Volmer mechanism—a homolytic H−H bond cleavage and formation of adsorbed terminal hydrogen atoms atop the topmost platinum, followed by oxidation of the adsorbed reaction intermediates. Potential-dependent activation energies computed for the hydrogen redox reactions were employed to predict the Tafel plot for hydrogen electrooxidation. The theoretically predicted Tafel plot is in very good agreement with experiment in support of the Tafel−Volmer mechanism for the Pt(110) surface.

Time-resolved IR Studies on the Mechanism for the Functionalization of Primary C−H Bonds by Photoactivated Cp*W(CO)3(Bpin)

Recently, transition-metal-boryl compounds have been reported that selectively functionalize primary C-H bonds in alkanes in high yield. We have investigated this process with one of the well-defined systems that reacts under photochemical conditions using both density functional theory calculations and pico- through microsecond time-resolved IR spectroscopy. UV irradiation of Cp*W(CO)(3)(Bpin) (Cp* = C(5)(CH(3))(5); pin = 1,2-O(2)C(2)-(CH(3))(4)) in neat pentane solution primarily results in dissociation of a single CO ligand and solvation of the metal by a pentane molecule from the bath within 2 ps. The spectroscopic data imply that the resulting complex, cis-Cp*W(CO)(2)(Bpin)(pentane), undergoes C-H bond activation by a sigma-bond metathesis mechanism--in 16 micros, a terminal hydrogen on pentane appears to migrate to the Bpin ligand to form a sigma-borane complex, Cp*W(CO)(2)(H-Bpin)(C(5)H(11)). Our data imply that the borane ligand rotates until the boron is directly adjacent to the C(5)H(11) ligand. In this configuration, the B-H sigma-bond is broken in favor of a B-C sigma-bond, forming Cp*W(CO)(2)(H)(C(5)H(11)-Bpin), a tungsten-hydride complex containing a weakly bound alkylboronate ester. The ester is then eliminated to form Cp*W(CO)(2)(H) in approximately 170 micros. We also identify two side reactions that limit the total yield of bond activation products and explain the 72% yield previously reported for this complex.

1H NMR and Molecular Dynamics Evidence for an Unexpected Interaction on the Origin of Salting-In/Salting-Out Phenomena

By employing (1)H NMR spectroscopy and molecular simulations, we provide an explanation for recent observations that the aqueous solubilities of ionic liquids exhibit salting-out to salting-in regimes upon addition of distinct inorganic salt ions. Using a typical ionic liquid [1-butyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide], we observed the existence of preferential specific interactions between the low electrical charge density ("apolar moiety") parts of the ionic liquid cation and the inorganic salts. These a priori unexpected interactions become increasingly favorable as one moves from salting-out to salting-in effects. More specifically, this interpretation is validated by distinct aqueous solution (1)H NMR data shifts in the ionic liquid cation upon inorganic salt addition. These shifts, which are well noted in the terminal and preterminal hydrogens of the alkyl chain appended to the imidazolium ring, correlate quantitatively with solubility data, both for cases where the nature of inorganic salt is changed, at constant concentration, and for those where the concentration of a given inorganic salt is varied. Molecular simulations have also been performed permitting us to garner a broader picture of the underlying mechanism and structure of this complex solvation phenomenon. These findings can now be profitably used to anticipate solution behavior upon inorganic salt addition well beyond the specificity of the ionic liquid solutions, i.e., for a diversity of distinct solutes differing in chemical nature.

Unsymmetrically Bridged Methyl Groups as Intermediates in the Transformation of Bridging Methylene to Bridging Acetyl Groups: Ligand Migrations and Migratory Insertions in Mixed Iridium/Ruthenium Complexes

Protonation of the methylene-bridged, tetracarbonyl species [IrRu(CO)4(μ-CH2)(dppm)2][X] (X = CF3SO3, BF4) (1) at −90 °C yields the methyl-bridged product [IrRu(CO)4(μ-CH3)(dppm)2][X]2 (X = CF3SO3, BF4) (3), in which the methyl group is carbon-bound to Ir while engaged in an agostic interaction with Ru. Compound 3 is unusual in that exchange of the terminal and agostic protons of the methyl group is slow on the NMR time scale at −90 °C, allowing for the direct observation of both sets of protons and measurement of their respective C−H coupling constants at this temperature. Protonation of [IrRu(PMe3)(CO)3(μ-CH2)(dppm)2][CF3SO3] also yields an unsymmetrically bridged methyl complex, [IrRu(PMe3)(CO)3(μ-CH3)(dppm)2][CF3SO3]2 (7), analogous to 3, and again 1H NMR spectroscopy at temperatures below −60 °C shows separate resonances for the agostic and the terminal hydrogens of the methyl group. Both compounds display very low 1JCH values (65 Hz (3); 72 Hz (7)) for the agostic interactions, consistent with substantial weakening of the C−H bond. Warming a solution of 3 to −80 °C affords a new species, [IrRu(CH3)(CO)4(dppm)2][X]2 (4), in which the methyl group has migrated from the bridging site to a terminal position on Ir. Further warming of the triflate salt of 4 to ambient temperature results in disproportionation to give an unstable tricarbonyl, [IrRu(CH3)(CF3SO3)(CO)3(dppm)2][CF3SO3] (6), that subsequently decomposes, and the pentacarbonyl species [IrRu(CH3)(CO)5(dppm)2][CF3SO3]2 (5). Compound 5 can be obtained as the sole product upon warming a solution of 4 under an atmosphere of CO. Stirring a solution of 5 for two days gives the migratory-insertion product, [IrRu(CO)4(μ-C(CH3)O)(dppm)2][X]2 (8), in which the acetyl group is carbon-bound to Ir and oxygen-bound to Ru. One carbonyl ligand can be removed from 8 by reflux in CH2Cl2 to give [IrRu(CO)3(μ-C(CH3)O)(dppm)2][BF4]2 (9), in the case of 8-BF4, or [IrRu(CF3SO3)(CO)3(μ-C(CH3)O)(dppm)2][CF3SO3] (10), in the case of 8-CF3SO3, with retention of the bridging acetyl group. Refluxing 8-CF3SO3 in THF removes two carbonyl ligands to give the dicarbonyl species [IrRu(CF3SO3)(CO)2(μ-C(CH3)O)(dppm)2][CF3SO3] (11). Reaction of 9 or 10 with H2 yields the monohydride species [IrRuH(CO)3(μ-C(CH3)O)(dppm)2][X]2 (12; X = BF4, CF3SO3) via heterolytic cleavage of dihydrogen, while reaction of 11 with H2 at −90 °C yields the dihydrogen adduct [IrRu(H2)(CO)2(μ-C(CH3)O)(dppm)2][CF3SO3] (13), which upon warming above −60 °C yields the dihydride [IrRu(H)2(CF3SO3)(CO)2(μ-C(CH3)O)(dppm)2][CF3SO3] (14). Although compound 12 yields acetaldehyde upon reaction with CO, compound 14 gives rise to triflate ion displacement by CO, but no acetaldehyde is formed.

Crystal chemistry of synthetic Co- and Ni-analogues of natrochalcite the shortest known hydrogen bonds among mineral-type compounds. Part II: Spectroscopic studies

Four new representatives of the natrochalcite structure type s.s. – A + Me 2+ 2 ( X 6+ O 4 ) 2 [(H 2 O)(OH)], monoclinic, space group C 2/ m , Z = 2 – with A + = Na or K, Me 2+ = Co or Ni, and X 6 + = S or Se, were structurally characterised in Part I of this study. These compounds feature an extraordinary hydrogen bonding system, based on formal H 3 O − 2 units with extremely strong intramolecular hydrogen bonds. In particular, the Na-sulphates of Co and Ni exhibit the shortest known oxygen donor–acceptor distances hitherto reported for minerals or mineral-type phases at ambient conditions (and with fully occupied donor/acceptor positions), i.e. 2.429 and 2.420 A , respectively. In the present part, the nature of these formal H 3 O 2 − units is investigated by powder- and polarised single-crystal FTIR spectroscopy. The single-crystal spectra are characterised by a strictly polarised, extremely broad and asymmetric absorption band, caused by the O–H stretching vibration of the strong intramolecular hydrogen bond. In the sulphates the maximum of this band is located around 1000 cm −1 , shifted to slightly higher wavenumbers in the selenates, while the stretching modes of the longer terminal hydrogen bonds are found around 3400 cm −1 . The additional occurrence of various bending modes, e.g. at ~1640 cm −1 , strongly indicates the assignment of relevant absorption bands to distinct H 2 O and OH − groups. This also confirms the non-centrosymmetric configuration of the formal H 3 O 2 − unit and the presence of a split hydrogen position along the strong hydrogen bond, even at O···O distances as short as 2.42 A . In addition, polarised optical absorption spectra of the two sodium cobalt compounds are presented. The spectra are interpreted in terms of a pseudotetragonal crystal field, compressed along the short octahedral H (2) O–Co–OH (2) axis. The extracted crystal field and interelectronic repulsion parameters indicate the presence of comparatively strong crystal fields and a rather high ionic character of the Co–O bonds in these natrochalcite-type compounds. Due to the strong contribution of the close H 2 O/OH − ligands along the pseudotetragonally compressed axis, the spectroscopic tetragonal field compression exceeds the respective geometric compression of the CoO 6 polyhedra, in agreement with the high position of water molecules in the spectrochemical series of ligands.

Mononuclear and binuclear manganese carbonyl hydrides: the preference for bridging hydrogens over bridging carbonyls

The structures of the mononuclear derivatives HMn(CO)n (n=4 and 3) are shown by density functional theory (B3LYP and PB86) to derive from octahedral HMn(CO)5 by losses of various combinations of carbonyl groups with relatively little change in the C-Mn-C angles involving the remaining carbonyl groups. The binuclear H2Mn2(CO)n structures are predicted to have bridging hydrogen atoms in preference to bridging carbonyl groups. Thus, two structures are found for the binuclear H2Mn2(CO)9, isoelectronic with Fe2(CO)9, in which all nine of the carbonyl groups are terminal carbonyl groups. The lowest lying H2Mn2(CO)9 structure is the dihydrogen complex (OC)5Mn-Mn(CO)4(eta2-H2), in which one of the equatorial CO groups of Mn2(CO)10 is replaced by a dihydrogen ligand. A slightly higher energy H2Mn2(CO)9 structure by approximately 6 kcal mol(-1) has an Mn-Mn bond bridged by a single hydrogen and all terminal carbonyl groups as well as a single terminal hydrogen. The H2Mn2(CO)8 molecule is predicted to have a structure with a central Mn(micro-H)2Mn core related to diborane. In this structure the manganese-manganese bond of length 2.703 A (BP86) can be considered the diprotonated formal double bond required to give both manganese atoms the favoured 18-electron configuration. The more highly unsaturated H2Mn2(CO)n (n=7, 6) derivatives have similar structures derived from the H2Mn2(CO)8 structure by loss of one or two carbonyl groups. In many cases the Mn[triple bond, length as m-dash]Mn distance in the central Mn(micro-H)2Mn unit shortens to approximately 2.4 A suggesting a diprotonated triple bond.

Reactions of Hydrazines with AlH3·NMe2Et – Formation of Aluminum‐Nitrogen Heterocycles

AbstractTreatment of the alane–amine adduct AlH3·NMe2Et with 1,2‐diphenylhydrazine, H5C6–N(H)–N(H)–C6H5, afforded a five‐membered Al2N3 heterocycle (1) by the elimination of hydrogen and partial cleavage of N–N bonds. The structure of 1 comprises two aluminum atoms bridged by a dianionic diphenylhydrazinediido (–H5C6–N–N–C6H5–) and an imido ligand (H5C6–N2–). Each aluminum atom is further attached to a terminal hydrogen atom and a (ethyl)dimethylamino group. 1‐Aminopyrrole, H2N–NC4H4 gave a singular tricyclic cage compound (2) under similar conditions. The amino groups were completely deprotonated. N–N bond cleavage was not observed. Compound 2 possesses a central Al2N2 ring. Its nitrogen atoms are bridged by an Al2N group, whereas an N2Al group bridges both aluminum atoms. All nitrogen atoms are part of N–N bonds, and all metal atoms are further bonded to terminal hydrogen atoms. (© Wiley‐VCH Verlag GmbH &amp; Co. KGaA, 69451 Weinheim, Germany, 2009)