Vladimir I. Bakhmutov

NMR spectra and the products of interaction of iridium monohydrides IrHCl2L2 (LP(CH(CH3)2)3 and P(c-C6H11)3) with molecular hydrogen

Abstract Rapid and reversible η 2 -coordination of molecular hydrogen to the monohydrides IrHCl 2 L 2 , with LPPr i 3 ( I ) and P(c-C 6 H 11 ) 3 ( II ), has been established by 1 H and 2 H NMR. The complexes formed eliminate HCl to afford the dihydrides IrH 2 ClL 2 . The spectral data are reported and discussed in connection with the structure of the proposed intermediates.

Study of cryostructurization of polymer systems—X. 1H- and 2H-NMR studies of the formation of crosslinked polyacrylamide cryogels

Abstract Some features of the formation of polyacrylamide cryogels have been studied by means of 1H- and 2H-NMR. These gels were prepared by free radical copolymerization of acrylamide and N,N′-methylene-bis-acrylamide in a frozen aqueous medium. Using the spectral changes during polymerization, the cryotropic gelation may be conventionally subdivided into three stages during which the narrow NMR signals due to the low molecular weight components disappear, while the broad signals attributed to the formation of the polymeric compound develop. It was demonstrated that the dynamics of polymerization depend on the freezing procedure, i.e. on the thermal prehistory of a sample.

2H-T1 Relaxation and Deuterium Quadrupole Coupling Constants in Transition Metalη2-D2 Complexes

D2ligands differ significantly from classical deuteride ligands in their deuterium quadrupole coupling constants (DQCCs), which were derived from 2H-T1 min measurements on polydeuteride complexes such as [pp3MD2] and [pp3MD(D2)]+ (M = Ru, Os; pp3 = P(CH2CH2PPh2)3). The DQCC of the D2 ligand is much lower than that of the classical deuteride ligand (DQCC values given in kHz below structures in picture).

NMR evidence for formation of new alcohol rhenium complexes as intermediates in ionic hydrogenations of carbonyl groups with systems composed of ReH2(NO)(CO)(PR3)2 (R = Pri, CH3, OPri) and CF3COOH

Low-temperature hydrogenations of benzaldehyde and acetone by systems ReH2(CO)(NO)(PR3)2/CF3COOH in CD2Cl2 with R = Pri (1a), CHa (1b) and OPr1 (1c) result in formation of the new unstable alcohol complexes [ReH(CO)(NO)(PR3)2(R∗OH)] [CF3COO] (R∗C6H3CH2, (CH3)2CH) characterized by the low-temperature NMR spectra. Heating the reaction solutions above 210–240 K leads to alcohol elimination to form monohydrides ReH(CO)(NO)(PR3)2(CF3COO). Hydrogenation rates decrease in the order 1b > 1c > 1a and C6H5CHO > (CH3)2CO. Hydrogenation processes remain effective under H2 (or D2) atmosphere and in the presence of an excess of CF3COOH when the dihydrides exist as dihydrogen compounds [ReH(H2)(CO)(NO)(PR3)2]1 [CF4COO], Relative acidity of the dihydrogen complexes decreases in the order OPr1 > Pr1 > CH3. The hydrogenation with dihydrogen complexes is discussed in terms of an ionic mechanism.

Combined single crystal neutron diffraction and solution NMR relaxation studies of mono- and bis(silyl) substituted niobocene hydrides with nonclassical interligand interactions

A neutron diffraction study of the bis(silyl) complex Cp2NbH(SiMe2Cl)2 (3) provides unambiguous localization of the hydride ligand in a central position in the bisecting plane of the niobocene moiety, which is thus in accordance with the molecular symmetry group and the results of recent density functional theory (DFT) calculations. This result is compared with the quantitative localization of the hydride ligands in solutions of the isomeric mono(silyl) complexes Cp2NbH2(SiMe2Cl) (1 and 2) and the bis(silyl) complex 3 by means of T1min, T1, T1sel and T1bis NMR measurements. A good agreement between the solution and solid state structural data is observed. It is found that the presence of a neighbouring SiMe2Cl ligand increases the Nb–hydride bond length remarkably, probably through the mechanism of Si–H interligand hypervalent interaction (IHI). This effect is especially pronounced in the mono(hydride) complex 3 containing two Si groups, where the Nb–H distance is determined as 1.781(1) A (NMR relaxation, solution) and 1.816(8) A (neutron diffraction, solid state).

Deuterium NMR Relaxation as a Method for the Characterization and Study of Transition Metal Hydride Systems in Solution

Publisher Summary This chapter discusses the spectroscopy of multinuclear magnetic resonance in solution, which is one of the most important analytical methods in structural studies of transition-metal hydride complexes. Among different nuclei, the proton plays the main role because 1H NMR provides direct information about spectral properties of the hydride ligands. In addition, the proton, being a nonquadrupolar and long-relaxing nucleus, gives rise to well-resolved NMR spectra that are very conveniently analyzed. The NMR signals of quadrupole nuclei are usually broadened because of rapid relaxation and sometimes they even become unobservable. This situation relates to the well-known difficulties in the realization of the NMR experiments of such nuclei. The energy of interaction of the nuclear quadrupole moment, Q, with the molecular electric field gradient, EFG, can be experimentally measured as the nuclear-quadrupole coupling constant, NQCC. EFG and NQCC are very sensitive to changes in electronic distribution in the molecule, intermolecular association, and solid-state effects.