Classical Hydride Research Articles

A Novel Online Hydride Generation Technique for the Simultaneous Determination of Ultra Trace Amounts of Hydride Forming Elements in Water Samples by Inductively Coupled Plasma Optical Emission Spectrometry

A simple and rapid online hydride generation technique based on ultrasonic nebulizer was applied for the first time for the simultaneous determination of trace amounts of As, Bi, Sb, Se and Te by inductively coupled plasma optical emission spectrometry. In this method, we used an ultrasonic nebulizer as a hydride generator and sample introducer simultaneously. An ultrasonic nebulizer was applied for the online hydride generation technique without using any device, such as a gas phase separator, which is mandatory in the classic hydride generation method. This technique improved method detection limit comparing to the traditional hydride generation system which is a necessity in the ultra-trace determination of hydride forming elements. The developed technique shows an improvement factor ranging from 56 to 450 times in detection limits in comparison to a concentric nebulizer. The obtained detection limits were well below the maximum concentration limit. The practical applicability of the developed method was examined using natural water samples.

Electronic structure, optical and thermodynamic properties of ternary hydridesMBeH3(M= Li, Na, and K)

Electronic band structure, optical and thermodynamic properties of ternary hydrides MBeH3(M = Li, Na, and K) were studied using ab initio density functional theory (DFT). The effect of the adopted approximation to the exchange-correlation functional of the DFT is explicitly investigated by considering four different expressions of two different classes (local-density approximation and generalized-gradient approximation). The calculated magnitude of B classifies MBeH3(M = Li, Na, and K) as easily compressible materials. The bonding interaction in these compounds is quite complicated. The interaction between M and BeH6is ionic and that between Be and H comprises both ionic and covalent characters. The electronic structure of the complex hydride was investigated by calculating the partial and total densities of states, and electron charge density distribution. Large gaps in the density of states appear at the Fermi energy of LiBeH3, NaBeH3, and KBeH3indicating that these classes of hydrides are insulators. Optical properties, including the dielectric function, reflectivity, and absorption coefficient, each as a function of photon energy, are calculated and show an optical anisotropy for LiBeH3and KBeH3. Through the quasi-harmonic Debye model, in which the phononic effects are considered, temperature dependence of volume V(T), bulk modulus B(T), and thermal expansion coefficient α(T), constant-volume and constant-pressure specific heat (Cvand Cp) and Debye temperature ΘD, the entropy S, and the Grüneisen parameter γ were calculated at wide pressure and temperature ranges. The principal aspect of the obtained results is the close similarity of MBeH3(M = Li, Na, and K) compounds.

A van der Waals DFT study of PtH2 systems absorbed on pristine and defective graphene

We used a density functional that incorporates van der Waals interactions to study hydrogen adsorption onto Pt atoms attached to carbon-vacancies on graphene layers, considering molecular and dissociated hydrogen-platinum coordination structures. PtH2 complexes adsorbed on several sites of pristine graphene were also studied for comparison. Our results indicate that both a Kubas-type dihydrogen complex and a classic hydride without HH bond are the preferential PtH2 systems on the vacancy site of graphene. In contrast, the Kubas complex is unstable onto pristine graphene and the hydride is obtained at all adsorption sites. Our simulations suggest that the C-vacancy decreases the reactivity of the metal decoration, allowing a non-dissociative hydrogen adsorption. The H2 molecule is oriented almost perpendicular to the outermost CPt bond, interacting also with the graphene surface through σ-H and π-C states. This stabilization of the Kubas-type complex could play a very important role for hydrogen storage in Pt-decorated carbon adsorbents with vacancies.

Isolation of a bis(imino)pyridine molybdenum(i) iodide complex through controlled reduction and interconversion of its reaction products.

Analysis of previously reported [((Ph2PPr)PDI)MoI][I] by cyclic voltammetry revealed a reversible wave at -1.20 V vs. Fc(+/0), corresponding to the Mo(ii)/Mo(i) redox couple. Reduction of [((Ph2PPr)PDI)MoI][I] using stoichiometric K/naphthalene resulted in ligand deprotonation rather than reduction to yield a Mo(ii) monoiodide complex featuring a Mo-C bond to the α-position of one imine substituent, (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoI. Successful isolation of the inner-sphere Mo(i) monoiodide complex, ((Ph2PPr)PDI)MoI, was achieved via reduction of [((Ph2PPr)PDI)MoI][I] with equimolar Na/naphthalene. This complex was found to have a near octahedral coordination geometry by single crystal X-ray diffraction and electron paramagnetic resonance (EPR) spectroscopy revealed an unpaired Mo-based electron which is highly delocalized onto the PDI chelate core. Attempts to prepare a Mo(i) monohydride complex upon adding NaEt3BH to ((Ph2PPr)PDI)MoI resulted in disproportionation to yield an equimolar quantity of (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoH and newly identified ((Ph2PPr)PDI)MoH2. Independent preparation of ((Ph2PPr)PDI)MoH2 was achieved by adding 2 equiv. NaEt3BH to [((Ph2PPr)PDI)MoI][I] and a minimum hydride resonance T1 of 176 ms suggests that the Mo-bound H atoms are best described as classical hydrides. Interestingly, ((Ph2PPr)PDI)MoH2 can be converted to (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoI upon iodomethane addition, while ((Ph2PPr)PDI)MoH2 is prepared from (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoI in the presence of excess NaEt3BH. Similarly, (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoI can be converted to (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoH with 1 equiv. of NaEt3BH, while the opposite transformation occurs following iodomethane addition to (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoH. Facile interconversion between [((Ph2PPr)PDI)MoI][I], (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoI, (κ(6)-P,N,N,N,C,P-(Ph2PPr)PDI)MoH, and ((Ph2PPr)PDI)MoH2 is expected to guide future reactivity studies on this unique set of compounds.

Simultaneous determination of traces of Pt, Pd, and Ir by SPE-ICP-OES. Test for chemical vapor generation

A method was developed for the simultaneous separation, preconcentration, and determination of platinum, palladium, and iridium by flow injection solid phase extraction coupled with online inductively coupled plasma optical emission spectrometry (SPE-ICP-OES). The system is based on the retention of the analytes onto a minicolumn filled with silica gel functionalized with 1,5-bis(di-2-pyridyl) methylene thiocarbonohydrazide (DPTH-gel) placed in the injection valve of a simple flow manifold. The determination of these elements through chemical vapor generation (CVG) was also tested and compared with the same method without CVG. So, the effects of chemicals and flow variables were investigated by both methodologies. The sensitivity of the method without CVG was better; this confirms the low yields of the reactions of these species compared with the yields of the classical hydrides and the necessity of more research work to improve these yields. With the SPE-ICP-OES method developed, the precision as relative standard deviation (n=10) was 2.8% for Pt, 2.7% for Pd, and 2.9% for Ir. The enrichment factors were 6.3, 6.7, and 6.3 for Pt, Pd, and Ir, respectively. Detection limits (3min sample loading time) were 1.4μgL−1 for Pt, 0.5μgL−1 for Pd and 0.6μgL−1 for Ir. The accuracy of the proposed method was checked with the certified reference material NIST-2557 autocatalyst. The results obtained using this method were in good agreement with the certified values. The recoveries for the method when applied to determine traces of analytes in spiked seawater were 94.5–105.8%.

Molecular structure of W(PMe3)3H6 in the solid state and in solution

The molecular structure of W(PMe3)3H6 has been identified by low temperature (−123°C) X-ray diffraction studies as a classical hydride compound, with a tricapped trigonal prismatic geometry in which two of the PMe3 ligands adopt eclipsed positions on opposite triangular faces of the prism and one PMe3 ligand caps a rectangular face. The solid state structure is reproduced well by density functional theory geometry optimization calculations on the molecule in the gas phase. NMR spectroscopic studies provide evidence that W(PMe3)3H6 also exists as a classical hydride compound in solution. For example, the T1(min) value for the hydride ligands of W(PMe3)3H6 is 380ms at 500MHz and 310ms at 400MHz, values that are more in accord with a classical hydride formulation than a nonclassical one. Likewise, the W(PMe3)3H6−xDx isotopologues (obtained by isotope exchange with either deuterobenzene or deuterotoluene) exhibit upfield (+13ppb) deuterium secondary isotope effects on the hydride chemical shift, which are also consistent with a classical description.

Metallization of magnesium polyhydrides under pressure

Evolutionary structure searches are used to predict stable phases with unique stoichiometries in the hydrogen-rich region of the magnesium/hydrogen phase diagram under pressure. MgH${}_{4}$, MgH${}_{12}$, and MgH${}_{16}$ are found to be thermodynamically stable with respect to decomposition into MgH${}_{2}$ and H${}_{2}$ near 100 GPa, and all lie on the convex hull by 200 GPa. MgH${}_{4}$ contains two H${}^{\ensuremath{-}}$ anions and one H${}_{2}$ molecule per Mg${}^{2+}$ cation, whereas the hydrogenic sublattices of MgH${}_{12}$ and MgH${}_{16}$ are composed solely of H${}_{2}^{\ensuremath{\delta}\ensuremath{-}}$ molecules. The high-hydrogen content stoichiometries have a large density of states at the Fermi level, and the ${T}_{c}$ of MgH${}_{12}$ at 140 GPa is calculated to be nearly three times greater than that of the classic hydride, MgH${}_{2}$, at 180 GPa.

Polyhydrides of the Alkaline Earth Metals: A Look at the Extremes under Pressure

Evolutionary structure searches are coupled with density functional theory calculations to predict the most stable stoichiometries and structures of beryllium and barium polyhydrides, MHn with n > 2 and M = Be/Ba, under pressure. Even though the BeHn stoichiometries we explored do not become thermodynamically stable with respect to decomposition into the classic hydride BeH2 and H2 up to 200 GPa, we find a new phase of BeH2 with R3̅m symmetry above 150 GPa. The barium polyhydrides become thermodynamically preferred by 20 GPa. They sport complex hydrogenic sublattices composed of H–, H3–, and H2 units. BaH6 is the first stoichiometry to emerge as stable and metallic (∼60 GPa using the Perdew–Burke–Ernzerhof functional), and the P4/mmm symmetry structure is estimated to become superconducting below 30–38 K at 100 GPa. Phases with an even greater hydrogen content lie on the convex hull at higher pressures, and an intriguing BaH10 stoichiometery becomes the global thermodynamic minimum around 150 GPa. BaH10 remains metallic over its predicted domain of existence, and its Ba–Ba distances resemble those found in the complex Ba–IVc structure at 19 GPa.

Group 14 Hydrides with Low Valent Elements for Activation of Small Molecules

Transition metal compounds are well known as activators of small molecules, and they serve as efficient catalysts for a variety of homogeneous and heterogeneous transformations. In contrast, there is a general feeling that main group compounds cannot act as efficient catalysts because of their inability to activate small molecules. Traditionally, the activation of small molecules is considered one of the key steps during a catalytic cycle with transition metals. As a consequence, researchers have long neglected the full range of possibilities in harnessing main group elements for the design of efficient catalysts. Recent developments, however, have made it possible to synthesize main group compounds with low-valent elements capable of activating small molecules. In particular, the judicious use of sterically appropriate ligands has been successful in preparing and stabilizing a variety of Group 14 hydrides with low-valent elements. In this Account, we discuss recent advances in the synthesis of Group 14 hydrides with low-valent elements and assess their potential as small-molecule activators. Group 14, which comprises the nonmetal C, the semimetals Si and Ge, and the metals Sn and Pb, was for years a source of hydrides with the Group 14 element almost exclusively in tetravalent form. Synthetic difficulties and the low stability of Group 14 hydrides in lower oxidation states were difficult to overcome. But in 2000, a divalent Sn(II) hydride was prepared as a stable compound through the incorporation of sterically encumbered aromatic ligands. More recently, the stabilization of GeH(2) and SnH(2) complexes using an N-heterocyclic carbene (NHC) as a donor and BH(3) or a metal carbonyl complex as an acceptor was reported. A similar strategy was also employed to synthesize the Si(II) hydride. This class of hydrides may be considered coordinatively saturated, with the lone pair of electrons on the Group 14 elements taking part in coordination. We discuss the large-scale synthesis of hydrides of the form LMH (where M is Ge or Sn, L is CH(N(Ar)(CMe))(2), and Ar is 2,6-iPr(2)C(6)H(3)), which has made it possible to test their reactivity in the activation of small molecules. Unlike the tetravalent Group 14 hydrides, the Ge(II) and Sn(II) hydrides were found to be able to activate a number of small molecules in the absence of any externally added catalyst. For example, the Ge(II) hydride and Sn(II) hydride can activate CO(2), and the reaction results in the formation of Ge(II) and Sn(II) esters of formic acid. This product represents a prototype of a new class of compounds of Group 14 elements. Moreover, we examined the activation of carbonyl compounds, alkynes, diazo and azo compounds, azides, and compounds containing the C═N bond. These Group 14 hydrides with low-valent elements are shown to be able to activate a number of important small molecules with C≡C, C═O, N═N, and C═N bonds. The activation of small molecules is an important step forward in the realization of main group catalyst development. Although it is not yet customary to assay the potential of newly synthesized main group compounds for small-molecule activation, our results offer good reason to do so.

Electrochemically promoted nucleophilic aromatic substitution in room temperature ionic liquids—an environmentally benign way to functionalize nitroaromatic compounds

The current manuscript shows the electrochemical studies performed to rationalize the mechanism and develop new green synthetic routes for the synthesis of substituted nitroaromatics based on the advantages of the electrochemical approach to the nucleophilic aromatic substitution reaction (such as (a) low cost and ready availability of reagents, (b) atom economy, (c) high yields, approaching 100%) and the use of Room Temperature Ionic Liquids (RTILs) as green alternative solvents to organic aprotic solvents. Four of the most popular RTILs (1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4), 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]PF6), 1-butyl-3-methyl-imidazolium bis(trifluoromethylsulfonyl)-imide ([BMIM]TFSI) and 1-butyl-3-methylimidazolium acetate ([BMIM]AcO) have been chosen since they have different properties in terms of solvation effects that can increase the regioselectivity of the reaction. The nucleophiles used to study the feasibility and viability of the reaction were the classical hydride, methoxide, ketones, cyanides and amines, whereas the nitroarenes selected were 4-nitrotoluene, 1,3-dinitrobenzene, 2,4-dinitroaniline, 1,3,5-trinitrobenzene, 1,3-dinitronaphthalene, 1-chloro-2,4,6-trinitrobenzene and 2,4,6-trinitroanisole. The electrocatalysis and regioselectivity effects of using RTILs are also investigated. The article concludes by analyzing the economic cost of performing this electrosynthesis in RTILs and organic solvent electrolyte systems, which contain 0.1 M of supporting electrolyte.

Ab Initio Studies on the Electronic Structure and Properties of Aluminum Hydrides that Are Analogues of Boron Hydrides

Although the boron hydrides are well-known in the literature, the aluminum hydride chemistry is limited to very few systems such as AlH(3), its dimer, and its polymeric form. In view of the recent experimental studies on the possible existence of the aluminum hydrides, herein, we have undertaken a systematic study on the electronic structure and properties of these aluminum hydrides. Under this, we have studied different classes of hydrides, viz., closo (Al(n)H(n+2)), nido (Al(n)H(n+4)), and arachno (Al(n)H(n+6)), similar to the boranes. All the aluminum hydrides are found to have exceptionally large highest-occupied molecular orbital-lowest-unoccupied molecular orbital gaps, low electron affinities, large ionization potentials and also large enthalpy and free energy of atomization. In addition, most of the structures are also found to have high symmetries. These exceptional properties can be indicative of the pronounced stability, and hence, it is expected that other aluminum hydride complexes can indeed be observed experimentally.

Analytical Evaluation of an Integrated Ultrasonic Nebulizer-hydride Generator System for Simultaneous Determination of Hydride and Non-hydride Forming Elements by Microwave Induced Plasma Spectrometry

ABSTRACT The commercial ultrasonic nebulizer NOVA-DUO (ultrasonic nebulizer dual capillary system USN/DCS) has been evaluated for the simultaneous determination of classical hydride forming (As, Bi, Ge, Sb, Se, Sn) and conventional non-hydride forming (Ba, Ca, Fe, Li, Mg, Sr) elements by microwave induced plasma-optical emission spectrometry (MIP-OES). Simultaneous mixing and nebulization of the two solutions (acidified sample and reductant) on the piezoelectric transducer, with the possibility of flow rate adjustment, permits a wide variation of sensitivity. The hydrides and aerosols were rapidly transported via a stream of Ar carrier to a MIP for simultaneous multi-element determination by OES. A univariate approach and simplex optimization procedure was used to achieve optimized conditions and derive analytical figures of merit. Analytical performance of the ultrasonic nebulization system was characterized by determination of the limits of detection (LODs) and precision (RSDs) with the USN/DCS observed at 11 µL min−1 flow rate. The experimental concentration detection limits for simultaneous determination, calculated as the concentration giving a signal equal to three times of standard deviation of the blank (LOD, 3σblank criterion, peak height) were 1.3, 5.9, 6.6, 1.8, 3.6, 2.6, 41, 8.1, 11, 7.5, 9.2, and 12 ng mL−1 for As, Bi, Ge, Sb, Se Sn, Ba, Ca, Fe, Li, Mg, and Sr, respectively. The method offers relatively good precision (RSD ranged from 9 to 13%) for liquid analysis and microsampling capability. Interference effects by transition metals have been shown to be corrected by the addition of thiourea, as a pre-reducing agent and masking agent. The accuracy of the method was verified by the use of certified reference materials (NRCC DOLT-2, NRC GBW 07302, NIST SRM 2710, NIST SRM 1643e) and by aqueous standard calibration technique. All results obtained for reference materials were in agreement with certified values at 95% confidence level by Student t-test.

Theoretical study of tetrahydroborates and alanates L(MH4)4, HL(MH4)3, H2L(MH4)2, and H3L(MH4) (L = Al, Sc, Ti, V, Cr; M = B, Al)

The structural and energetic characteristics of the lowest-lying structures for isolated molecules and ions of light-metal boro- and aluminohydrides L(MH4)4, HL(MH4)3, H2L(MH4)2, and H3L(MH4) (L = Al, Sc, Ti, V, Cr; M = B, Al) with different coordination modes of BH 4 − - and AlH 4 − groups were calculated by the perturbation theory (MP2), coupled cluster (CCSD(T)), and density functional theory (B3LYP) methods using the 6-31G*, 6-311+G**, and 6-311++G** basis sets. The results are compared with the computational data obtained at the same level of theory for related complexes L(MH4)3, HL(MH4)2, H2L(MH4), L(MH4)2, and HL(MH4). The preferable coordination modes of the ligands in these complexes are analyzed, and the energies of dissociation with elimination of BH3 (AlH3) molecules and BH 4 − (AlH 4 − ) anions in various series of related hydroborates and hydroaluminates are estimated. The structure and relative stability of classical hydride and (μ-H2)-hydrogen complexes in the H2L (MH4)2 and H3L(MH4) systems are discussed.

Sulfonamido−Phosphoramidite Ligands in Cooperative Dinuclear Hydrogenation Catalysis

Sulfonamido-phosphoramidite ligands lead to the formation of Rh-Rh dinuclear complexes through the anionic P-N(-) bridging character. The resulting "boat-shaped" dinuclear catalysts activate molecular H(2) through a cooperative dinuclear endocyclic mechanism, resulting in one bridging and one classical hydride on the dinuclear complex. These new complexes are very active hydrogenation catalysts that operate via a new cooperative hydrogenation activation mechanism, as calculated with density functional theory, and they display unequaled high selectivities in the hydrogenation of hindered cyclic acetamidoalkenes.

Determination of the Heat of Hydride Formation/Decomposition by High-Pressure Differential Scanning Calorimetry (HP-DSC)

Among the thermodynamic properties of novel materials for solid-state hydrogen storage, the heat of formation/decomposition of hydrides is the most important parameter to evaluate the stability of the compound and its temperature and pressure of operation. In this work, the desorption and absorption behaviors of three different classes of hydrides are investigated under different hydrogen pressures using high-pressure differential scanning calorimetry (HP-DSC). The HP-DSC technique is used to estimate the equilibrium pressures as a function of temperature, from which the heat of formation is derived. The relevance of this procedure is demonstrated for (i) magnesium-based compounds (Ni-doped MgH2), (ii) Mg-Co-based ternary hydrides (Mg-CoHx) and (iii) Alanate complex hydrides (Ti-doped NaAlH4). From these results, it can be concluded that HP-DSC is a powerful tool to obtain a good approximation of the thermodynamic properties of hydride compounds by a simple and fast study of desorption and absorption properties under different pressures.

Preparation and characterization of chloro- and polyhydride complexes of rhenium: Variable-temperature NMR spectroscopy and protonation studies

The rhenium complex fac-[ReOCl 3L] [ 1; L = 1,3-bis(diphenylphosphanyloxy)propane] was prepared by reacting L with [ReOCl 3(AsPh 3) 2]. Refluxing complex 1 in ethanol gave [ReOCl 2(OEt)L] ( 2), which X-ray crystallography showed to have an octahedral rhenium environment and an Re–O–Et fragment of unusual linearity. The paramagnetic chlorocomplexes mer-[ReCl 3LL′] [ 3; L′ = P(OEt) 3 in 3a, PPh(OEt) 2 in 3b, PPh 2(OEt) in 3c] were obtained by treating compound 1 with L′. Reaction of complexes 1 and 3a– c with excess NaBH 4 gave the polyhydrides [ReH 7L] ( 4) and [ReH 5LL′] ( 5a– c), respectively, all of which were characterized by variable-temperature (VT) NMR spectroscopy as highly fluxional classical hydrides. Complete protonation of these polyhydrides with HBF 4 · OMe 2 required 3 equiv. of acid, and the cationic polyhydride complexes so obtained were characterized as non-classical species by VT NMR spectroscopy and T 1 measurements.

Mono‐ and Dinuclear Rhenium Polyhydride Complexes Bearing the Chelating Ligand 1,2‐Bis(dicyclohexylphosphanyloxy)ethane

AbstractVariable‐temperature NMR spectroscopic studies of new rhenium polyhydride compounds of the type [ReH7(dcype)] (1), [Re2H8(dcype)2] (3) and [ReH5(dcype)L] (5a−f) [dcype = Cy2PO(CH2)2OPCy2; L = PPhn(OR)3−n, n = 0−2, R = Me, Et] show them to be highly fluxional classical hydride complexes. In the case of the ethoxy compounds 5b, 5d and 5f, three hydride interchange processes were observed in the temperature range 283−173 K and their activation parameters were determined by NMR line‐shape analysis. A mechanism is proposed for each. Protonation of 1 and 5 with HBF4·OMe2 gave the nonclassical hydrides [ReH8(dcype)]BF4 (2) and [ReH6(dcype)L]BF4 (6) which are relatively stable. Compound 2 decomposes at 273 K in solution releasing H2,whereas compound 6 can be stored at room temperature for more than 24 h without decomposition. Protonation of 3 with HBF4·OMe2 gave the classical dinuclear hydride [Re2H9(dcype)2]BF4. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)

Structural and Chemical Properties of Zwitterionic Iridium Complexes Featuring the Tripodal Phosphine Ligand [PhB(CH2PPh2)3]-

Several new iridium compounds bearing the PhB(CH_2PPh_2)_3^- (herein abbreviated as [PhBP_3]) ligand have been prepared and characterized, and a comparison of steric, electronic, and chemical properties is made with those of related pentamethylcyclopentadienyl (Cp^*) and hydridotris(3,5-dimethylpyrazolyl)borate (Tp^(Me)_2) complexes. The complexes [PhBP_3]Ir(H)(η_3-C_8H_(13)) (2) and [PhBP_3]Ir(H)(η^3-C_3H_5) (3) were synthesized from the reaction of [Li(TMED)][PhBP_3] (1) with the corresponding [(alkene)_2IrCl]_2 complex. These allyl complexes serve as precursors to the dihalides [PhBP_3]IrX_2 (10, X = I; 12, X = Cl). In addition to these dihalides, the five-coordinate species [PhBP_3]IrMe_2 (16) and [ClB(CH_2PPh_2)_3]IrCl_2 (13) have been isolated. Addition of CO to 2 or 3 gave [PhBP_3]Ir(CO)_2 (7), while reaction of H_2 with 2 yielded {[PhBP_3]IrH_2}_2 (8) in benzene and [PhBP_3]Ir(COE)H_2 (9) in THF (where COE = cyclooctene). Complex 2 reacted with PMePh_2 to give [PhBP_3]Ir(PMePh_2)H_2 (5) and 1,3-cyclooctadiene. The protonation of 5 with [H(OEt_2)]{B[3,5-C_6H_3(CF_3)_2]_4} gave the classical hydride complex {[PhBP_3]Ir(PMePh_2)H_3}{B[3,5-C_6H_3(CF_3)_2]_4} (6). In addition to the formation of allyl complexes 2 and 3, several C−H activation reactions have been observed; addition of P^(Me)_3 to 2 provided the cyclometalated product {PhB[(CH_2PPh_2)_2(CH_2PPhC_6H_4)]}Ir(H)(PMe_3)(4) and COE. Photolysis of 5 gave PhB[(CH_2PPh_2)_2(CH_2PPhC_6H_4)]}Ir(H)(PMePh_2) (A) and [PhBP_3]Ir(H)(PMePhC_6H_4) (B). Complex 9 catalyzes H/D exchange between COE and benzene-d_6. Metathesis reactions of diiodide 10 with LiBHEt_3 gave [Li(THF)_n]{[PhBP_3]Ir(H)_2I} (14a) and [Li(THF)_n]{[PhBP_3]Ir(H)_3} (15). Comparison of the spectroscopic properties of related [PhBP_3]Ir, Cp^*Ir, and Tp^(Me)_2Ir complexes suggests that relative donating abilities follow the trend [PhBP_3] ≥ Cp^* > Tp^(Me)_2, and structural comparisons indicate that [PhBP_3] is the most sterically demanding ligand.

Synthesis and characterization of ReCl(H(2))(AsMePh(2))(4), a classical hydride complex; reexamination of ReCl(H(2))(PMePh(2))(4) and theoretical calculations on model compounds.

The synthesis of ReCl(H(2))(AsMePh(2))(4) is reported and verified on the basis of (1)H NMR and FAB-MS. The minimum T(1) time for the metal-bonded hydrogen atoms was determined to be 44 ms (-78 degrees C) and 89 (-48 degrees C) ms at 200 and 400 MHz, respectively. From this minimum T(1) time, and, allowing for contributions from other nuclei to the relaxation, a metal-bonded H to H atom distance of 1.57 A can be assessed. The complex is reversibly oxidized at a potential E(1/2)(ox) = +0.07 V. The J(HD) coupling in the related ReCl(HD)(AsMePh(2))(4) compound was at 3.3 Hz. These data for ReCl(H(2))(AsMePh(2))(4) suggest that this molecule contains classical hydrides, and interpretations on T(1) and X-ray data published previously for ReCl(H(2))(PMePh(2))(4) suggest that this molecule contains a very long metal-bonded H-H interaction of 1.39 A. Theoretical calculations on model compounds ReCl(H(2))(XR(3))(4) (X = P, As; R = H, Me) give virtually identical average d(H-H) values of 1.5 (XH(3)) and 1.63 (XMe(3)) A.

The synthesis, structure, and reactivity of the osmium(IV) trihydrido silyl complex, OsH 3(SiMe 3)(CO)(PPh 3) 2

Reaction between the five coordinate complex, Os(Ph)Cl(CO)(PPh 3) 2, and HSiMe 3 produces the osmium(IV) trihydrido silyl complex, OsH 3(SiMe 3)(CO)(PPh 3) 2 ( 1). The structure of 1 has been determined by single crystal X-ray crystallography and by multi-nuclear NMR spectroscopy. The structure has an approximately tetrahedral disposition of silyl, carbonyl and the two PPh 3 ligands about osmium with the three classical hydride ligands located, one trans to CO, and the other two each approximately trans to a PPh 3. Treatment of complex 1 with HSiR 3 (R=Et, Ph), HSn( p-tolyl) 3, or HC 2Ph gives OsH 3(SiR 3)(CO)(PPh 3) 2 (R=Et ( 2), Ph ( 3)), OsH 2[Sn( p-tolyl) 3] 2(CO)(PPh 3) 2 ( 4) or OsH(C 2Ph)(CO)(PPh 3) 3 ( 5), respectively. A likely intermediate in these reactions is the coordinatively unsaturated complex, OsH 2(CO)(PPh 3) 2.