Michael D. Carducci

A Novel Electrophilic Diamination Reaction of Alkenes

A three-component electrophilic reaction transforms olefins into imidazoline and diamine derivatives. Rhodium(II) heptafluorobutyrate dimer (2 mol %) was utilized as the catalyst and N,N-dichloro-p-toluenesulfonamide (TsNCl2 ) and acetonitrile as the nitrogen sources. Modest to good yields (45-82 %) and high regio- and stereoselectivity were achieved.

Dendron-controlled nucleation and growth of gold nanoparticles

Passivation of the metal surface by dendrons bearing a focal 4-pyridone functionality (the second-generation dendron is shown; C: gray, N: blue, O: red) allows controlled nucleation and growth of gold nanoclusters. The particle size is a direct function of the generation number of the dendritic ligands, with higher generation dendron producing larger particles.

Stereoselective synthesis of conformationally constrained reverse turn dipeptide mimetics

Abstract Peptide side chains play critical roles in the event of molecular recognition. In order to study the bioactive conformation of parent peptides, a concise and straightforward five-step synthesis of [5.5]-bicyclic reverse turn dipeptide mimetic scaffolds with side chain functionality at the i +1 and i +2 positions has been developed. In the bicyclic structure, two dihedral angles ( ψ 2 and φ 3 ) are greatly restricted.

Six-coordinate molybdenum nitrosyls with a single ene-1,2-dithiolate ligand

The synthesis and molecular structures of the (Tp*)Mo(NO)(SS) family of compounds (where (Tp*) is hydrotris(3,5-dimethyl-1-pyrazolyl)borate; (SS) is an ene-1,2-dithiolate) are reported. The compounds; (Tp*)Mo(NO)(bdt) ( 1 ), (Tp*)Mo(NO)(tdt) ( 2 ), and (Tp*)Mo(NO)(bdtCl 2 ) ( 3 ) (bdt, 1,2-benzenedithiolate; tdt, 3,4-toluenedithiolate; bdtCl 2 , 3,6-dichlorobenzenedithiolate), are the first such structurally characterized {MoNO} 4 compounds that contain a [(Tp*)Mo(NO)] 2+ fragment ligated to an ene-1,2-dithiolate. The compounds crystallize in the space groups P 2 1 / c ( 1 ) ( a =11.115(2) A, b =13.667(3) A, c =16.410(3) A; β =98.36(3)°, Volume=2466.4(8) A 3 , Z =4); P 2 1 / n ( 2 ) ( a =15.579(3) A, b =9.942(2) A, c =16.527(3) A; β =95.79(3)°, Volume=2546.7(9) A 3 , Z =4); and Pnma ( 3 ) ( a =17.9879(9) A, b =13.2277(7) A, c =11.2505(6) A; Volume=2676.9(2) A 3 , Z =4). The molecular structures show that the inner coordination sphere remains invariant within this family. A remarkable feature is the fold angle ( θ ) between the MoS 2 plane and S 2 C 2 plane of the ene-1, 2-dithiolate chelate ring. The fold angles ( θ ) of 42.1° in 1 , 41.1° in 2 and 44.4° in 3 are substantially larger than in analogous compounds with a terminal oxo group. Additional insight into the chemistry and properties of complexes 1 – 3 has been obtained by cyclic voltammetry, IR, NMR, electronic absorption and He I photoelectron (PES) spectroscopies.

An inorganic-organic hybrid composite featuring metal-chalcogenide clusters

The cluster complex, “Re6(μ3-Se)8(PEt3)5(4-vinylpyridine)”(SbF6)2 (1), featuring the face-capped octahedral “Re6(μ3-Se)8”2+ cluster core and site-differentiating triethylphosphine and 4-vinylpyridine ligands has been synthesized and structurally characterized. The complex crystallized in monoclinic space group P21 with a=11.748(1)Å, b=15.1212(2)Å, c=19.941(2)Å, α=90°, β=94.411(3)°, γ=90°, V=3531.8(7)Å3, Z=2, R1=0.0531, wR2=0.0774. Copolymerization of styrene with 1 via the polymerizable 4-vinylpyridine ligand afforded a novel inorganic-organic hybrid composite of high molecular weight and a low polydispersity index. Structural integrity of the cluster building block is maintained upon hybrid formation.

Electronic Spectral Studies of Molybdenyl Complexes. 2. MCD Spectroscopy of [MoOS4]- Centers.

Magnetic circular dichroism (MCD) and absorption spectroscopies have been used to probe the electronic structure of [PPh4][MoO(p-SC6H4X)4] (X = H, Cl, OMe) and [PPh4][MoO(edt)2] complexes (edt = ethane-1,2-dithiolate). The results of density functional calculations (DFT) on [MoO(SMe)4]- and [MoO(edt)2]- model complexes were used to provide a framework for the interpretation of the spectra. Our analysis shows that the lowest energy transitions in [MoVOS4] chromophores (S4 = sulfur donor ligand) result from S-->Mo charge transfer transitions from S valence orbitals that lie close to the ligand field manifold. The energies of these transitions are strongly dependent on the orientation of the S lone-pair orbitals with respect to the Mo atom that is determined by the geometry of the ligand backbone. Thus, the lowest energy transition in the MCD spectrum of [PPh4][MoO(p-SC6H4X)4] (X = H) occurs at 14,800 cm-1, while that in [PPh4][MoO(edt)2] occurs at 11,900 cm-1. The identification of three bands in the absorption spectrum of [PPh4][MoO(edt)2] arising from LMCT from S pseudo-sigma combinations to the singly occupied Mo 4d orbital in the xy plane suggests that there is considerable covalency in the ground-state electronic structures of [MoOS4] complexes. DFT calculations on [MoO(SMe)4]- reveal that the singly occupied HOMO is 53% Mo 4dxy and 35% S p for the equilibrium C4 geometry. For [MoO(edt)2]- the steric constraints imposed by the edt ligands result in the S pi orbitals being of similar energy to the Mo 4d manifold. Significant S pseudo-sigma and pi donation may also weaken the Mo identical to O bond in [MoOS4] centers, a requirement for facile active site regeneration in the catalytic cycle of the DMSO reductases. The strong dependence of the energies of the bands in the absorption and MCD spectra of [PPh4][MoO(p-SC6H4X)4] (X = H, Cl, OMe) and [PPh4][MoO(edt)2] on the ligand geometry suggests that the structural features of the active sites of the DMSO reductases may result in an electronic structure that is optimized for facile oxygen atom transfer.

Organic crystal engineering with piperazine-2,5-diones. 2. Crystal packing of weakly dipolar piperazinediones derived from 2-amino-4-bromo-7-methoxyindan-2-carboxylic acid

Abstract Piperazine-2,5-diones with the potential to manifest three chemically distinct and linearly independent intermolecular interactions were synthesized from the enantiomers of 2-amino-4-bromo-7-methoxyindan-2-carboxylic acid. Samples of enantiomerically pure, racemic, and meso piperazinediones were characterized in the solid state by X-ray crystallography. “Ladder-like” intermolecular amide-to-amide hydrogen bonding interactions were observed in each case, establishing tape structures parallel to one crystallographic axis. The observed tape morphologies and crystal packing closely resemble that previously observed for a topographically similar tetramethoxy-piperazinedione. The results obtained demonstrate that the weak dipoles associated with the p-bromoanisole moiety play no role in determining order in the crystalline state.

Organic crystal engineering with piperazine-2,5-diones. 1. Crystal packing of piperazinediones derived from substituted 2-aminoindan-2-carboxylic acids

Abstract We have postulated that molecules engineered to participate in three chemically distinct and linearly independent intermolecular interactions will self-assemble in a predictable fashion. Six prototypes for molecules capable of manifesting such interactions were synthesized from 2-aminoindan-2-carboxylic acid, 2-amino-5,6-dimethylindan-2-carboxylic acid, and 2-amino-4,7-dimethoxyindan-2-carboxylic acid. These piperazinediones were characterized in solution by NMR spectroscopy and in the solid state by X-ray crystallography. “Ladder-like” intermolecular amide-to-amide hydrogen bonding interactions were observed in each case, establishing tape structures parallel to one crystallographic axis. Tape morphology varied depending on the arene substitution pattern and was governed by the development of arene and/or van der Waals contact interactions.

A new bis(ethylenedithio)tetrathiafulvalene chloride: (BEDT-TTF)2Cl·3H2O

A new BEDT-TTF chloride (BEDT-TTF)2Cl·3H2O was obtained by electrochemical oxidation of the donor in dichloroethane solution containing K2[Cu(OX2−)2]·2H2O (OX2−: oxalate ion). The compound crystallized in the space group Pcca with a = 32.621(1), b = 6.720(3) and c = 14.894(6) A. The unit cell contained four units of the compound formula. Close side-by-side contacts of adjacent donor molecules formed a one-dimensional array that was parallel to the b-axis. In this array, the shortest SS distance of 3.47 A was less than the van der Waals contact of 3.70 A. The donor molecules were also stacked face-to-face along the c-axis. The shortest SS distance in the stack, however, was 3.76 A; there was no SS pair closer than the van der Waals contact. The electrical conductivity along the b-axis was c. 90 S cm− at 300 K, and exhibited metallic temperature dependence down to c. 120 K; around this temperature, a metal-insulator transition occurred. One-dimensional charge transport is attributed to the isolated array of BEDT-TTF molecules. When K2(OX2−)·H2O was used as an electrolyte instead of the bis(oxalato)cuprate(II), the known chloride, (BEDT-TTF)3Cl2·2H2O, was obtained.

Crystallography of molecular excited states. Transition-metal nitrosyl complexes and the study of transient species

The study of photoinduced processes in crystals is a frontier area of crystallographic research, which requires development of novel experimental and computational methods. In a series of studies, long-lived metastable states, generated upon photoirradiation of transition-metal nitrosyl complexes, have been identified as ç nitrosyl and isonitrosyl linkage isomers, and their detailed geometry has been determined. Calculations using density functional theory indicate that the species correspond to minima on the ground-state potential energy surface. The time-structure of synchrotron sources opens the possibility of time-resolved studies of transient species in crystals at the atomic level. Possible strategies for such experiments are described.