Search

The metallocenes ferrocene (Cp2Fe, 1), nickelocene (Cp2Ni, 2), and cobaltocene (Cp2Co, 3) crystallize in the same space group (P21/a) and they have the same shape and similar size. Therefore, they form solid solutions with random distribution of the different molecules when crystallized from solution. Alternatively, the solid metallocenes can be ground together manually, and the solid solutions form at any molar ratio within minutes. The metallocenes 2 and 3 are paramagnetic. Solid solutions of 1/3 and 2/3 have been studied by paramagnetic solution and solid-state NMR spectroscopy. The effect of the paramagnetic species on the other components in the solid solutions has been investigated. The impact on the chemical shifts is limited. However, the halfwidths and the signal shapes, as defined by the rotational sideband intensities, change with increasing amounts of paramagnetic components. The 1H T1 relaxation times are shortened for diamagnetic protons in the presence of paramagnetic metallocenes in the solid solutions. It has been demonstrated that all metallocenes mix at the molecular level within the polycrystalline samples. The EPR spectra of the solid solutions are dominated by the most intensive signal of any paramagnetic metallocene in the solid samples. [ABSTRACT FROM AUTHOR]

Triphenylphosphine oxide (TPPO, 1) has been adsorbed on neutral alumina by dry grinding of the components in the absence of a solvent. The adsorption proves translational mobility of 1 on the surface of alumina. Different surface coverages from a densely packed monolayer (99% coverage) to a dilute sub-monolayer (25%) have been produced. The samples have been studied by diverse multinuclear 1H, 13C, and 31P variable temperature solid-state nuclear magnetic resonance (NMR) techniques. The interactions of 1 with the surface are determined by hydrogen bonding of the P=O group to OH groups on the surface. The 31P solid-state NMR spectra prove that even at low temperatures, the molecules of 1 are highly mobile on the surface. Using T1 and T2 relaxation time analyses of the 31P resonance in the solid state at variable temperatures allowed the identification and quantification of two different modes of mobility. Besides the translational mobility that consists of jumps from one hydrogen-bonding OH site on the surface to an adjacent one, a rotational movement around the axis defined by the P=O group of 1 occurs. [ABSTRACT FROM AUTHOR]

The phosphorus chemical shift anisotropies, 31PΔcs, and asymmetry parameters η were measured by the 31P{1H} NMR experiments in static and low‐frequency spinning samples of the zirconium phosphates and phosphonates and also in the mixed Zr (IV)/Sn (IV) phosphate/phosphonate material. The data obtained have shown a 111 connectivity in the HPO4 and PO3 groups, which does not change at modification and intercalation of the materials. The 31PΔcs values of the phosphonate groups (43–49 ppm) significantly surpass the values characterizing the HPO4 groups (23–37 ppm). The 31P Δcs values obtained for the metal (IV) phosphates were discussed in terms of P‐O distances. The 31P chemical shift anisotropy parameters can help at elucidation of local structures in phosphate and phosphonate materials. [ABSTRACT FROM AUTHOR]

The fluoride congener of Wilkinson's catalyst, [(Ph3P)3RhF] is synthesized and fully characterized. It is found that in sharp contrast with Wilkinson's catalyst, [(Ph3P)3RhF] easily cleaves the inert C-Cl bond of nonactivated chloroarenes under mild conditions to produce trans-[(Ph3P)2Rh(Ph2PF)(Cl)] as a result of C-Cl, Rh-F, and P-C bond cleavage and C-C, Rh-Cl, and P-F bond formation.

The direct and independent observation of the kinetics at the same temperature, is performed for the faster protonation of the hydride ligand site in complex Cp*FeH(dppe) and for the isomerization of the resulting Cp*Fe(H2)(dppe)(super +) intermediate to the thermodynamically preferred classical dihydride product. Strong evidence is obtained in favor of a direct isomerization process, not involving the reversible deprotonation of the hydride site and protonation of the metal site.

In developing the approach to understanding dynamics of intercalates in layered materials, crystalline‐layered zirconium phosphate Zr (HPO4)2·0.35D2O has been prepared and characterized by the 1H, 31P, and 2H solid‐state MAS NMR spectra, including 31P and 2H T1 measurements. At temperatures >253 K, the intercalated water shows two spectrally‐distinguished deuterons unprecedentedly with different DQCC's and 2H T1 times, one of which is hydrogen bonded. The collected data allowed to identify an unexpected bonding/dynamic mode of water molecules, which experience fast rotation around the hydrogen bond, formed with a zirconium‐coordinated oxygen. The low‐temperature 2H MAS NMR experiments have demonstrated the presence of additional hydrogen bond P(H)O˙˙˙ DO, population of which grows on cooling to 195 K corresponding to the doubly hydrogen‐bonded immobile water molecule. [ABSTRACT FROM AUTHOR]

Results show that borane adducts reveal 'frozen' envelope conformations in solution with BR(sub)3 groups occupying equatorial positions. The H(sup)delta- ....(sup)delta+H contacts in solution are similar to those found in solid state as indicated by the relaxation studies.

The (carbonyl)dihydride complex [(triphos)Ru(CO)[H.sub.2]] (2) has been synthesized by reaction of the ruthenate [(triphos)Ru[H.sub.3]]K (triphos = MeC[(C[H.sub.2]P[Ph.sub.2]).sub.3]) with ethanol saturated with CO. A single crystal X-ray analysis and IR and NMR experiments have shown that 2 adopts in both the solid state and solution an octahedral coordination geometry with a facial triphos ligand, two cis terminal hydrides, and a terminal carbonyl. The reaction of hexafluoro-2-propanol (HFIP) with 2 has been studied in C[H.sub.2] [Cl.sub.2] solution by IR and NMR spectroscopy. The proton donor interacts with a terminal hydride of 2 forming a rather strong hydrogen bond. The resulting H-bonded adduct [{(triphos)Ru(CO)(H)H}***{HOCH [(C[F.sub.3]).sub.2]}] (2a) has fully been characterized by in situ NMR and IR techniques. Compound 2a is in equilibrium with the nonclassical [[eta].sup.2]-[H.sub.2] complex [[(triphos)Ru(CO)H([H.sub.2])].sup.+] (2b), which can independently be prepared by protonation of 2 with a strong protic acid at low temperature. Unequivocal characterization of the dihydrogen complex (2b) has been achieved by a multifaceted spectroscopic investigation ([T.sup.obs.sub.1min] = 0.005 s (200 MHz), [J.sub.H,D] [approximately equal to] 30 Hz, DQCC = 78.3 kHz). A combined IR and NMR study of the proton transfer reaction involving 2 and HFIP in C[H.sub.2][Cl.sub.2] to give, first, the H-bonded adduct (2a) and, then, the dihydrogen complex (2b) has demonstrated that all these species are in equilibrium in the temperature range from 190 to 260 K. The thermodynamic parameters for the formation of 2a have independently been determined by NMR and IR methods, while those for the formation of 2b have been obtained by IR spectroscopy. An energetic profile for the reaction sequence 2 [right arrow] 2a [right arrow] 2b is proposed and discussed. Key words: hydrides, hydrogen bonding, ruthenium, IR spectroscopy, NMR spectroscopy.

Novel mixed tantalum-gold and tantalum-copper trihydrides of the formula (Cp'2TaH3MPPH3)(PF6) where M = Au, Cu and Cp' = C5H4C(CH3)3 with two bridging hydride ligands. Their structures were studied through relaxation measurements and analysis of proton-proton and phosphorus-proton couplings. The hydride-hydride and metal-hydride distances are similar in structure with the related niobium trihydride ((Nb(C5H3RR')2H3)2Au)(PF6) with R = R' = Si(CH3)3. The Ta-H dipole-dipole interactions were found to be valuable in hydride relaxation.

The spectral and thermodynamic properties of a type of hydrogen bond where the hydride atom of a transition metal plays the role of proton acceptor were examined using nuclear magnetic resonance, x-ray and infrared spectroscopy. Results of the stretching vibrations of the proton donors reflect the coordination of the proton donors with hydride atoms as proton acceptor site. The structure and energy of the hydrogen bonds indicate the importance of the electrostatic interactions of hydride atoms of the boron hydrides and the hydrogen atoms of proton-donating XH groups.

Research was conducted to study the metal-hydride and hydride-hydride distances from measurements of selective and nonselective 1H T1 relaxation of hydride ligands. The detailed 1H NMR relaxation study was focused on Cp2NbH3 since this classical trihydride and its derivatives usually demonstrate proton-proton exchange couplings. Results demonstrate that Nb-H dipole-dipole interactions are very critical for the hydride relaxation in Cp2NbHx(sub 2)(H(super A)) due to the shortened hydride T1 times of the hydride ligands.

Chemical research using a room-temperature high-yield reaction between Cp2TaH3 and M(CO)5 has resulted in the synthesis of the new bimetallic trihydrides Cp2TaH2(mu-H)M(CO)5(M=Cr, Mo, W). Nuclear magnetic resonance and infra red spectroscopy analysis of the structure and hydride ligand complexes is given. The hydride/hydride exchange energy barrier reduction occurs during bimetallic systems Cp2TaH2(Mu-H)Cr(CO)5 and Cp2TaH2(Mu-H)W(CO)5 synthesis.

The heterobimetallic (PPh3)HRu(mu-H)(mu-PME2Cp*)2(mu-Cl)ZrCl Ru/Zr complex was synthesized by the reaction of RuH2(H2)(PPh3)3 with (PMe2Cp*)2ZrCl2. The novel isomeric ruthenium/zirconium dihydride is composed of ZrCl units that are bridged by a monoatomic Cl and H ligands together with two bifunctional phosphinocyclopentadienyl ligands. The ruthenium atom of the complex heterobimetallic dihydrides exhibits a distorted octahedral geometry composed of five-coordinated zirconium atoms and six-coordinated ruthenium atoms.

Tungstenocene dichloride reacts with (PPh2M(CO)5)Li salts, M = Cr or W, to form the binuclear compounds (eta(super 5)-C5H5)(eta(super 5)-C5H4PPh2M(CO)5)W(H)Cl. Reduction of these compounds yields the respective dihydrides which undergo photochemical irradiation to produce the heterobimetallic compounds containing intramolecular bridging hydrido ligands. The two metallic centers are considerable separated and the proton-proton distance between the two H ligands is 2.0 angstroms. The bimetallic compounds exhibit structural rigidity.

Deuterium quadrupole coupling constants (DQCC) and ionic contribution to the M-D bond are computed using D ligands of certain transition metal hydride complexes, for which H T NMR relaxation times are estimated in solution. DQCC values ranged from 55 to 158 KHz for classical terminal W, Mn, Re, Os and Rh deuterides. Rh deuterides with very short M-H bond length have the largest constants.

An economical source of hydrogen forms a metal hydride under wild conditions when the hydrogen is split heterolytically. The splitting is categorized by the presence of molecular H2 to be Bronsted-acidic. Coordinated H2 is known to quickly dissociate, disallowing the intracellular molecular rearrangement in d octahedra. Hydrogen binds with five-coordinate substructures, varying in equilibrium constants. The varying lengths of the bonding H2 are caused by a reduction in the strength of the sigma bond. The reducing power of the bonding fragments also vary.

New hydride complexes of manganese, such as (MnH(NO2)(PEt3)2, MnH(CO)3(PEt3)2) and rhenium (ReH(CO)n(PMe3)5-n; ReH2(CO)(NO)(PR3)2) are synthesized and their H1 nonselective and selective relaxation times as a function of temperature are determined for each compound. The model of an isotropic motion is used in the calculation of the M-H bond lengths, and in the function of the M-H dipole-dipole interaction to the relaxation times of H ligands.