Variable-temperature 1H NMR Research Articles

Unexpected Coordination Complexes of the Metal Tris-silylamides M{N(SiMe3)2}3 (M = Ti, V).

The synthesis, molecular structures, and spectroscopic details of a series of isocyanide and nitrile complexes of the early first-row transition-metal tris(silyl)amides M{N(SiMe3)2}3 (M = Ti, V) are reported. Previously, first-row transition-metal tris(silyl)amides were generally thought to be incapable of forming complexes with Lewis bases due to their excessive steric crowding. However, it is now shown that simple treatment of the base-free trisamides with 2 equiv of an isocyanide or nitrile base at room temperature results in the formation of the trigonal bipyramidal complexes Ti{N(SiMe3)2}3(1-AdNC)2 (1), Ti{N(SiMe3)2}3(CyNC)2 (2), Ti{N(SiMe3)2}3(ButNC)2 (3), Ti{N(SiMe3)2}3(PhCN)2 (4), V{N(SiMe3)2}3(1-AdNC)2 (5), V{N(SiMe3)2}3(CyNC)2 (6), V{N(SiMe3)2}3(ButNC)2 (7), and V{N(SiMe3)2}3(PhCN)2 (8), which incorporate two donor ligands (1-AdNC = 1-adamantyl isocyanide, CyNC = cyclohexyl isocyanide, ButNC = tert-butyl isocyanide, PhCN = benzonitrile). All complexes display a characteristic increase in the frequency of the multiple bonded C-N stretching mode which is observed to be in the range of 2170-2190 cm-1 for the isocyanide complexes 1-3 and 5-7 and at 2250 cm-1 for the nitrile complex 8. This effect was not observed for the titanium nitrile complex 4, suggesting weak binding of the donor to titanium. Paramagnetic 1H NMR studies showed these complexes to have detectable, though extremely broadened, signals attributable to the trimethylsilyl groups of the amide ligands (δ = ca. 2.8 ppm for titanium isocyanide complexes, ca. 4.5-4.7 ppm for vanadium isocyanide complexes). A variable-temperature 1H NMR study showed that in solution these complexes exist as mixtures of the five-coordinate species and a putative four-coordinate species coordinating a single Lewis basic ligand. Electronic spectroscopy indicated that the vanadium complexes 5-8 bind the Lewis bases more strongly than the corresponding titanium complexes, where the spectra of complexes 1-4 are essentially identical to the base-free Ti{N(SiMe3)2}3 at the temperatures and concentrations studied. In contrast to these results, no corresponding complexes were detected for the metal silylamides M{N(SiMe3)2}3 (M = Cr, Mn, Fe, or Co) when treated with the isocyanide or nitrile bases.

A Rotorlike Supramolecular Assembly, {[K(18-crown-6)]PbI3}∞, with a Reversible Breaking-Symmetry Phase Transition near Room Temperature.

A rotorlike supramolecular crystal, {[K(18-crown-6)]PbI3}∞, is composed of a linear [PbI3]∞ chain acting as a stator and [K(18-crown-6)]+ cations fastened to the [PbI3]∞ chain and K-I bond like rotators and axes, respectively. A reversible breaking-symmetry phase transition occurs at ∼305 K. Variable-temperature 1H NMR spectra and dielectrics were used for the dynamic analysis of [K(18-crown-6)]+ cations in the crystal.

NMR-based quantitative studies of the conformational equilibrium between their square and folded forms of ascidiacyclamide and its analogues.

Ascidiacyclamide [cyclo(-Ile1,5-oxazoline2,6-D-Val3,7-thiazole4,8-)] (1) is a cytotoxic cyclic peptide from the ascidian, or sea squirt. Through structural analyses using asymmetric analogues [Xxx1: Ala (2), Val (3), Leu (4), Phe (5), cyclohexylalanine (6) and phenylglycine (7)], we previously showed 1 to exist in a conformational equilibrium between square and folded forms. In the present study, five new asymmetric analogues [Xxx1: 2-aminobutyric acid (8), 2-aminopentyric acid (9), tert-butylalanine (10), cyclohexylglycine (11) and tert-leucine (12)] were synthesized, and their structures were analyzed with X-ray diffraction and CD spectral measurements. Variable temperature 1H NMR measurements were performed to determine their equilibrium constants and their thermodynamic parameters. The use of two reference peptides made these quantitative studies possible. T3ASC, which contains three thiazole rings as a result of replacing oxazoline2 with thiazole, and dASC, in which the two oxazoline rings were deleted, were respectively used as square and folded reference peptides. The estimated parameters enabled more detailed discussion of the relationship between the bulkiness of substituents and the conformational free energies (ΔG°) of the peptides as well as the relationship between structure and cytotoxicity. The ΔG° values for peptides 1, 2, 3, 8, 9 and 11 decreased with decreases in the bulkiness of their substituents. We suggest that spontaneous folding is promoted as the bulkiness of substituents decreases. Peptides 7 and 12, which have large positive ΔG° values independently of temperature, did not exhibit spontaneous folding at any temperature; that is, their conformations were very stable in the square form. Peptides 4, 5, 6 and 10 had negative ΔG° values, despite their bulky substituents. Peptides with a positive ΔG° value showed cytotoxicity, and peptides with a negative ΔG° value showed reduced or no cytotoxicity. However, peptides 5 and 6 showed cytotoxicity equal to or stronger than 1. Those ten peptides except for 5 and 6 showed a clear structure–cytotoxicity relationship based on ΔG° values.

Counterintuitive torsional barriers controlled by hydrogen bonding.

The torsional barriers along the Caryl-Caryl axis of a pair of isosteric disubstituted biphenyls were determined by variable temperature 1H NMR spectroscopy in three solvents with contrasted hydrogen bond accepting abilities (1,1,2,2-tetrachloroethane-d2, nitrobenzene-d5 and dimethyl sulfoxide-d6). One of the biphenyl scaffolds was substituted at its ortho and ortho' positions with N'-acylcarbohydrazide groups that could engage in a pair of intramolecular N-HO=C hydrogen bonding interactions at the ground state, but not at the transition state of the torsional isomerization pathway. The torsional barrier of this biphenyl was exceedingly low despite the presence of the hydrogen bonds (16.1, 15.6 and 13.4 kcal mol-1 in the three aforementioned solvents), compared to the barrier of the reference biphenyl (15.3 ± 0.1 kcal mol-1 on average). Density functional theory and the solvation model developed by Hunter were used to decipher the various forces at play. They highlighted the strong stabilization of hydrogen bond donating solutes not only by hydrogen bond accepting solvents, but also by weakly polar, yet polarizable solvents. As fast exchanges on the NMR time scale were observed above the melting point of dimethyl sulfoxide-d6, a simple but accurate model was also proposed to extrapolate low free activation energies in a pure solvent (dimethyl sulfoxide-d6) from higher ones determined in mixtures of solvents (dimethyl sulfoxide-d6 in nitrobenzene-d5).

Double donation in trigonal planar iron-carbodiphosphorane complexes - a concise study on their spectroscopic and electronic properties.

We present the syntheses of trigonal planar coordinated Fe(ii) carbodiphosphorane (CDPR) complexes, starting from iron(ii)-bis(trimethylsilylamide) [Fe{N(SiMe3)2}2] and hexaphenyl-(CDPPh) and sym-dimethyltetraphenyl-carbodiphosphoranes (CDPMe), respectively. Both complexes [CDPPh-Fe{N(SiMe3)2}2] (1) and [CDPMe-Fe{N(SiMe3)2}2] (2) were examined in solution and in the solid state. 1 shows a dissociation equilibrium in solution which we monitored by variable temperature 1H-NMR spectroscopy. Magnetic measurements of 1 and 2 yielded a high spin configuration (S = 2) for both complexes. Quantum chemical calculations were performed to analyze the bonding situation in compound 1.

Hydrogen bonding in dicyclohexylmethane – or diphenylmethane based urea compounds and their polymer counterparts investigated by NMR spectroscopy: Interplay of electronic and geometrical factors

We investigated the H-bonding behavior of urea compounds with different electronic nature of substituents and different spatial organization. Variable-temperature 1H NMR spectroscopy studies were performed in polar solvents which are capable (DMSO‑d6 and DMF-d7) or not (CDCl3) to form the intermolecular hydrogen bonds and non-polar solvent (toluene-d8) at the temperature range from 25 to 70 °C. Our results indicates that in the investigated systems the geometrical factors dominated over electronic effects of substituents at formation of intra- and intermolecular H-bonds. By the reaction between isocyanate and heavy water was synthesized the polymers with selectively deuterated urea groups and recorded their high-resolution solid-state 2H NMR spectra and measured their 2H quadrupole interaction parameters (i.e., the quadrupole coupling constant χ and asymmetry parameter η). Quite unexpectedly, the intermolecular hydrogen bonds are weaker in phenyl based urea polymers than in their cyclohexane based counterparts.

A Highly Asymmetric Gold(III) η3 -Allyl Complex.

A highly asymmetric AuIII η3‐allyl complex has been generated by treating Au(η1‐allyl)Br(tpy) (tpy=2‐(p‐tolyl)pyridine) with AgNTf2. The resulting η3‐allyl complex has been characterized by NMR spectroscopy and X‐ray crystallography. DFT calculations and variable temperature 1H NMR suggest that the allyl ligand is highly fluxional.

Chromium(III)-pyrazole complexes. X-Ray crystal structures, 1H NMR investigation of ligand fluxional behavior and EPR studies

Mononuclear chromium(III) complexes of formula mer-[CrIIICl3(pz*H)3] (pz*H = pyrazole (pzH), and substituted pyrazoles: 3-Me-pzH, 4-Me-pzH, 4-Cl-pzH, 4-Br-pzH, 4-I-pzH) and trans-[CrIIICl2(pzH)4]Cl were synthesized from reactions of CrCl3 hydrate and pyrazole ligands and crystallographically characterized. The fluxional behavior of the complexes, attributed to pyrazole tautomerization, was probed by variable temperature 1H NMR spectra in the −50 °C to +23 °C range and activation parameters were derived. Q-band EPR were recorded and analyzed for mer-[CrIIICl3(pz*H)3] (R = H, Me, Cl) showing satellite features corresponding to weak zero-field splitting (zfs).

Pyridine(diimine) Iron Diene Complexes Relevant to Catalytic [2+2]-Cycloaddition Reactions.

The synthesis, characterization, and catalytic activity of pyridine(diimine) iron piperylene and isoprene complexes are described. These diene complexes are competent precatalysts for (i) the selective cross-[2+2]-cycloaddition of butadiene or (E)-piperylene with ethylene and α-olefins and (ii) the 1,4-hydrovinylation of isoprene with ethylene. In the former case, kinetic analysis implicates the diamagnetic η4-piperylene complex as the resting state prior to rate-determining oxidative cyclization. Variable temperature 1H NMR and EXSY experiments established that diene exchange from the diamagnetic, 18e- complexes occurs rapidly in solution at ambient temperature through a dissociative mechanism. The solid-state structure of (Me(Et)PDI)Fe(η4-piperylene) (Me(Et)PDI = 2,6-(2,6-Me2-C6H3N═CEt)2C5H3N), was determined by single-crystal X-ray diffraction and confirmed the s-trans coordination of the monosubstituted 1,3-diene. Possible relationships between ligand-controlled diene coordination geometry, metallacycle denticity, and chemoselectivity of iron-mediated cycloaddition reactions are discussed.

Mechanistic Insight toward Understanding the Role of Charge in Thiourea Organocatalysis.

Pyranylation and glycosylation are pivotal for accessing a myriad of natural products, pharmaceuticals, and drug candidates. Catalytic approaches for enabling these transformations are of utmost importance and integral to advancing this area of synthesis. In exploring this chemical space, a combined experimental and computational mechanistic study of pyranylation and 2-deoxygalactosylation catalyzed by a cationic thiourea organocatalyst is reported. To this end, a thiourea-cyclopropenium organocatalyst was employed as a model system in combination with an arsenal of mechanistic techniques, including 13C kinetic isotope effect experiments, deuterated labeling studies, variable-temperature 1H NMR spectroscopy, and density functional theory calculations. From these studies, two distinct reaction pathways were identified for this transformation corresponding to either dual hydrogen bond (H-bond) activation or Brønsted acid catalysis. The former involving thiourea orchestrated bifurcated hydrogen bonding proceeded in an asynchronous concerted fashion. In contrast, the latter stepwise mechanism involving Brønsted acid catalysis hinged upon the formation of an oxocarbenium intermediate accompanied by subsequent alcohol addition.

Sequence-controlled proline-based polyacrylamides via RAFT polymerization: Influence of sequence structure on polymers performances

The synthesis of sequence-controlled polymers is an important emerging trend in recent polymer science. However, the relationship between the sequence structure and performance of the polymer was rarely studied. Here, we synthesized a series of sequence-controlled proline-based multi-block copolymers via one-pot iterative RAFT polymerization, it achieved high monomer conversions (>98%), precise control of molecular weight, and low polydispersity. The relationship studied between the sequence structure of multi-block copolymers and thermoresponsive performance revealed that the LCSTs of these copolymers are sequence dependent, and it can be altered by variation the sequence structure. In addition, temperature-variable 1H NMR analysis and dissipative particle dynamics (DPD) simulation technique were chosen to further study on the nature of phase transition and the relationship between sequence structure and thermoresponsiveness. Thus, we have demonstrated a concise method to construct sequence-controlled bio-based copolymers with precisely adjustable structures and functions which can be applied to the design of biological and medical materials.

A Single Thermoresponsive Diblock Copolymer Can Form Spheres, Worms or Vesicles in Aqueous Solution

AbstractIt is well‐known that the self‐assembly of AB diblock copolymers in solution can produce various morphologies depending on the relative volume fraction of each block. Recently, polymerization‐induced self‐assembly (PISA) has become widely recognized as a powerful platform technology for the rational design and efficient synthesis of a wide range of block copolymer nano‐objects. In this study, PISA is used to prepare a new thermoresponsive poly(N‐(2‐hydroxypropyl) methacrylamide)‐poly(2‐hydroxypropyl methacrylate) [PHPMAC‐PHPMA] diblock copolymer. Remarkably, TEM, rheology and SAXS studies indicate that a single copolymer composition can form well‐defined spheres (4 °C), worms (22 °C) or vesicles (50 °C) in aqueous solution. Given that the two monomer repeat units have almost identical chemical structures, this system is particularly well‐suited to theoretical analysis. Self‐consistent mean field theory suggests this rich self‐assembly behavior is the result of the greater degree of hydration of the PHPMA block at lower temperature, which is in agreement with variable temperature 1H NMR studies.

A Single Thermoresponsive Diblock Copolymer Can Form Spheres, Worms or Vesicles in Aqueous Solution.

It is well‐known that the self‐assembly of AB diblock copolymers in solution can produce various morphologies depending on the relative volume fraction of each block. Recently, polymerization‐induced self‐assembly (PISA) has become widely recognized as a powerful platform technology for the rational design and efficient synthesis of a wide range of block copolymer nano‐objects. In this study, PISA is used to prepare a new thermoresponsive poly(N‐(2‐hydroxypropyl) methacrylamide)‐poly(2‐hydroxypropyl methacrylate) [PHPMAC‐PHPMA] diblock copolymer. Remarkably, TEM, rheology and SAXS studies indicate that a single copolymer composition can form well‐defined spheres (4 °C), worms (22 °C) or vesicles (50 °C) in aqueous solution. Given that the two monomer repeat units have almost identical chemical structures, this system is particularly well‐suited to theoretical analysis. Self‐consistent mean field theory suggests this rich self‐assembly behavior is the result of the greater degree of hydration of the PHPMA block at lower temperature, which is in agreement with variable temperature 1H NMR studies.

Hot-spot guided design of macrocyclic inhibitors of the LSD1-CoREST1 interaction

New modalities such as cyclic peptides are attractive structures to inhibit challenging targets. The interaction between LSD1 and CoREST1 is required for histone demethylation and represents an attractive therapeutic target. The large interaction surface between these two proteins was analyzed by virtual alanine scanning using DrugScore PPI and a cluster of hot-spot residues was identified on CoREST1. The cluster was converted into a series of cyclic peptides and the inhibitory potency was optimized by stereochemical inversion at one of the amino acids alpha carbons combined with modification of amino acid side chains. Active peptides were further studied by variable temperature 1H NMR and docking to evaluate the effect of conformation on binding. Potent inhibitors of the challenging PPI were obtained and will allow future optimization into more druglike structures.

Prototropic behavior of cyclohexane substituted urethane and urea compounds. Observation of H-bond mediated 4HJH1H3 coupling constants across urea fragments

Two 1-aryl-3-cyclohexylurea and two 1-aryl-3-cyclohexylurethane with and without alkyl tail in aryl fragments were synthesized and their variable-temperature 1H NMR spectra in chloroform, DMSO and DMF were recorded. The temperature dependences of chemical shift of NH protons for all compounds have been observed. The type of dependence has been explained by the aggregation of molecules and formation of ionic structures. The formation of intermolecular complexes leads to possible formation of symmetrical N1 … … H ……N3 intramolecular hydrogen bond in urea fragment. As a result,4hJH1H3 trans-hydrogen bond scalar coupling constants have been observed for the first time in low molecular weight compounds using a simple one-dimensional 1H NMR experiment. The formation of strong intramolecular H-bond leads to π-conjugation not only with spacer but with phenyl ring too. It support the Gilli conception that RAHB formation is a result of π-electron delocalization. The presence in urea fragment of such kind interaction leads to formation of ionic structure, which has been detected by NMR and UV spectroscopies. The formation of ionic structure can explain the catalytic activity of such compounds and the mechanism of transformation in organic and bioorganic reactions in which involved the urea compounds.

Synthesis, Solid State, Solution and ESI‐MS Studies of Zinc(II) Cluster Complexes with a Branched Mixed Donor Thiolate Ligand

Synthesis of the unusual spirobicyclic pentanuclear complex [Zn((ZnL)2(µ‐OH))2](ClO4)4·CH3CN·7H2O (1) (LH = N‐(2‐pyridylmethyl)‐N‐(2‐(methylthio)ethyl)‐N‐(2‐thioethyl)‐amine is described. Compound 1 was thoroughly characterized by a combination of X‐ray crystallography, XPRD, IR, variable temperature 1H NMR and ESI‐MS. The peripheral zinc ions of 1 have distorted trigonal bipyramidal coordination geometry provided by the NN′SS′ donor set of one L and a µ2‐hydroxido bridge to another peripheral zinc ion. The central zinc atom has a distorted tetrahedral Zn(SR)4 coordination environment provided by four µ2‐thiolate bridges from L. In crystalline form, the complex ions of 1 are largely insulated from contact by an elaborate hydrogen bond network involving µ2‐hydroxido bridges, perchlorate ions and all the solvent molecules. Dissociation of 1 in CD3CN solution and recombination to form other multinuclear complexes was investigated by variable temperature 1H NMR.

Copper-catalyzed synthesis of oxime ethers from iminoxy radical (C[dbnd]N–O[rad]) and maleimides via radical addition

An efficient Cu(II)-catalyzed radical addition of maleimides has been achieved. The identified copper catalyst enables the formation of oxime radicals (N–O) by cleaving the O–H bond in ketoximes, followed by the radical addition to N-substituted maleimides. The oxime radicals (N–O) were detected and confirmed by EPR spectroscopy and variable-temperature 1H NMR. The simple one-pot reaction realizes the facile preparation of a variety of oxime ether adduct products in moderate to good yields.

Dinuclear Copper Complexes Triply Bridged by a Tetraphosphane, rac‐Ph2PCH2P(Ph)CH2P(Ph)CH2PPh2

Reaction of [Cu(MeCN)4]BF4 with rac‐Ph2PCH2P(Ph)CH2P(Ph)CH2PPh2 (rac‐dpmppm) gave [Cu2(µ‐rac‐dpmppm)(MeCN)4](BF4)2 (1), and that of CuCl with rac‐dpmppm in the presence of 2,6‐xylyl isocyanide (XylNC) and NH4PF6 afforded [Cu2(µ‐rac‐dpmppm)(XylNC)4](PF6)2 (2). Complex 1 was converted by treatment with diimino ligands (N^N) to a series of CuI2 complexes, [Cu2(µ‐rac‐dpmppm)(N^N)2]2+ (N^N = phen (3), 4‐Mephen (4), 4,7‐Me2phen (5), 5,6‐Me2phen (6), 2,9‐Me2phen (7), 3,4,7,8‐Me4phen (8), 4,7‐Ph2phen (9), bpy (10), 4,4′‐Me2bpy (11), and 1,8‐naphtyridine (nap) (12)), where phen = 1,10‐phenanthroline and bpy = 2,2′‐bipyridyl. The isolated complexes were characterized by spectroscopic and X‐ray crystallographic analyses to reveal that two CuI ions are triply bridged by a rac‐dpmppm ligand in κ2,κ2 fashion resulting in robust Z‐form dicopper structures, where the Cu···Cu distances vary from 4.2 to 5.6 Å depending on the ancillary ligands through altering conformation of the fused six‐membered chelate rings. The bulky ligands of XylNC and 2,9‐Me2phen deform the conformation to boat (2) and twist boat (7) forms, leading to elongation of Cu···Cu separation (Cu···Cu = 5.3488(5) Å (2), 5.5681(6) Å (7)), and other non‐bulky ligands render them deformed chair forms with Cu···Cu = 4.2051(5) Å (8) to 4.7341(5) Å (10). The solution behaviors of 5 and 11 were examined by variable temperature 1H NMR measurements to show fluxional exchange of the two nitrogen atoms attaching to the tetrahedral Cu centers with ΔG‡ of 14 kcal/mol at room temperature. Photophysical properties of 3–12 were also investigated to show rapid fluorescence at 394–467 nm in CH2Cl2 solutions and phosphorescence at 582–608 nm in the solid states. Reaction of [Cu(MeCN)4]BF4 with rac‐dpmppm and NaBH4 in MeOH/CHCl3 afforded [Cu4(µ4‐H)(µ‐Cl)2(µ‐rac‐dpmppm)2]BF4 (13), in which two rac‐dpmppm ligands exhibited a new coordination mode of κ2,κ1,κ1 M3‐bridge to hold two {Cu2(µ‐Cl)(µ‐rac‐dpmppm)}+ units connected by a central µ4‐hydride.

Effect of Core Cross-linking on the Physical Properties of Poly(dimethylsiloxane)-Based Diblock Copolymer Worms Prepared in Silicone Oil

A trithiocarbonate-capped poly(dimethylsiloxane) (PDMS) precursor is chain-extended via reversible addition–fragmentation chain transfer dispersion polymerization of 2-(dimethylamino)ethyl methacrylate (DMA) in decamethylcyclopentasiloxane (D5) silicone oil at 90 °C. For a fixed mean degree of polymerization (DP) of 66 for the PDMS steric stabilizer block, targeting core-forming PDMA block DPs of between 105 and 190 enables the preparation of either well-defined worms or vesicles at a copolymer concentration of 25% w/w. The as-synthesized linear PDMS66–PDMA100 worms exhibit thermoresponsive behavior in D5, undergoing a worm-to-sphere transition on heating to 100 °C. Variable temperature 1H NMR spectroscopy indicates that this thermal transition is driven by reversible solvent plasticization of the PDMA cores. This change in copolymer morphology is characterized by transmission electron microscopy (TEM) studies, variable temperature dynamic light scattering and small-angle X-ray scattering experiments. Oscillatory rheology studies indicate that degelation occurs at 32 °C, but shear-induced polarized light imaging measurements suggest that full conversion of worms into spheres requires significantly higher temperatures (∼110 °C). 1,2-Bis(2-iodoethoxy)ethane (BIEE) is evaluated as a cross-linker for PDMS66–PDMAx diblock copolymer nano-objects in D5. This bifunctional reagent quaternizes the tertiary amine groups on the DMA residues within the worm cores, introducing cross-links via the Menshutkin reaction. TEM studies confirm that such covalently-stabilized worms no longer undergo a worm-to-sphere transition when heated to 100 °C. Kinetic studies performed on PDMS66–PDMA176 vesicles suggest that cross-linking requires approximately 13 h at 20 °C to ensure that these nano-objects remain intact when dispersed in chloroform, which is a good solvent for both blocks. Oscillatory rheology studies of a PDMS66–PDMA100 worm gel indicated that covalent stabilization using a BIEE/DMA molar ratio of 0.15 increased its dynamic elastic modulus (G′) by almost two orders of magnitude. Furthermore, such cross-linked worms exhibit a much lower critical gelation concentration (∼2% w/w) compared to that of the linear precursor worms (∼12% w/w).

Fluxionality, substitution, and hydrogen exchange at eight-coordinate rhenium(V) polyhydride centers

Towards a better understanding of the dynamic processes within eight-coordinate rhenium pentahydride complexes, a set of eight-coordinate rhenium(V) pentahydride complexes supported by two triphenylphosphine ligands and either a bidentate amine with a pendant functional group (1,2-diaminoethane, 1,3-diaminopropane, 2-aminoethanol) or by an unsymmetrically-substituted aromatic amine ligand (3-aminopyridine or 3-picoline) was prepared from thermolysis reactions of ReH7(PPh3)2. Variable temperature 1H NMR spectroscopy and simulation of those results indicate a previously uncharacterized exchange of hydrogen between the unique hydride ligand residing in a dodecahedral B site and hydrogen atoms from adventitious water. The same data also indicate two processes for hydride ligand fluxionality and a process for isomer interconversions of the complexes supported by an unsymmetrically substituted aromatic amine ligand. The hydride exchange process that exchanges A site hydride ligands also exchanges B site ligands. The likely mechanism for the A and B site atom exchanges involves concerted, successive, inversions of the A site ligands into B sites and concomitant inversions of B site ligands into A sites of the D2d dodecahedron. Values of ΔG‡, ΔH‡, and ΔS‡ for all of the dynamic processes were determined.