Search

High level electronic structure theory is used to calculate the heats of formation of [N.sub.2]H, diazene (cis- and trans-[N.sub.2][H.sub.2]), [N.sub.2][H.sub.3], and hydrazine ([N.sub.2][H.sub.]), as well as their protonated species (diazenium, [N.sub.2][H.sub.3.sup.+], and hydrazinium, [N.sub.2][H.sub.5.sup.+]). The results for the hydrogenation reaction RNNR + [H.sub.2]-> RHNNHR have shown that substitution of an organic substituent for H improved the energetics, indicating that these types of compounds might be possible to use in a chemical hydrogen storage system.

High levels of ab initio electronic structure theory were used for calculating the heats of formation of saturated and unsaturated diaminocarbenes. 56.4 kcal/mol was the value of heat of formation for the unsaturated triplet carbene.

The air-stable crystalline carbene 1,3-dimesityl-4,5-dichloroimidazol-2-ylidene (2) was formed through the chlorination of 1,3-dimesitylimidazol-2-ylidene (1) by carbon tetrachloride. The physical and spectroscopic characteristics were investigated. Further reaction of 2 with carbon tetrachloride was found to cause the reduction of CCl4 to dichlorocarbene. The tellurones derived from 1 and 2 were synthesized and compared.

The carbene-pnictinidene adducts of phenylphosphinidene, phenyllarsinidene, (trifluoromethyl)phosphinidene and (pentafluorophenyl)arsinidene with 1,3-dimesityllimidazol-2-ylidene are described. The formation of these adducts is via the direct reaction of a stable nucleophilic carbene with the corresponding pnictinidene cyclic oligomers. The adducts have strongly polarized pnictinidene-carbene bonds and are best described as coordination complexes between the singlet pnictinidenes and the nucleophilic carbene.

Deuterated starting materials enable the synthesis of stable carbene perdeuterio-1,3,4, 5-tetramethylimidazol-2-ylidene. X-ray diffraction and neutral diffraction at 80 and 173 K enable the determination of electron distribution in these molecules. Experimental determination and density functional calculations show the molecule as a true carbene having negligible ylidic character.

Density functional theory calculations and first-order time-dependent perturbation theory simulate the experimental photoelectron spectra of a carbene, a silylene and a germylene. Analysis of the bands in the spectra shows that carbene has a lone pair of electrons in HOMO at HOMOs derived from the pi-3 orbital. X-ray analysis facilitates the structural characterization of 1, 3-ditert-butylimidazol-2-ylidene.

Solid-state NMR methods characterize the electronic and structural features associated with 1,3,4, 5-tetramethylimidazol-2-ylidene. The carbene site in this compound exhibits large chemical shielding anisotropy characteristic of singlet carbenes. The results agree with ab initio studies of the singlet carbene imidazol-2-ylidene, :CH2 and :CF2.

10-P-3 squared 3, 7-di(tert-butyl)-5-aza-2,8-dioxa-1-phosphabicyclo(3.3.0)octa-2,4,6-triene (ADPO) is the first synthetic tricoordinated hypervalent phosphorus compound. A condensation reaction between a diketo amine ligand and PCl3 produces the stable ADPO ring system. Different valence band structures explain the low-coordinate hypervalent phosphorus and x-ray studies help examine the structures of di-tert-butyl-ADPO and dicumyl-ADPO. These compounds exhibit edge inversion and undergo oxidative addition reactions with different Hx (x = Cl or O) compounds. 31P NMR helps determine the geometries of various ADPO products. Lone pairs or electrons in 10-P-3 ADPO systems help the formation of various transition metal complexes.

A study of the low-coordinate carbene complexes of Ni(0) and Pt(0) revealed a linear 2-coordinate geometry, with the imidazole rings of Ni and Pt twisting at 53 degrees and 51 degrees respectively, relative to one another. These carbenes, which contained zerovalent transition-metal centers, were involved in different organometallic transformations.

A novel bimetallic carbene complex structured design that includes a cyclopentadienyl-annulated imidazol-2-ylidene moiety is described. Moreover, this first bimetallic ruthenium palladium complex that is developed displays its ability to perform as a catalyst in the Suzuki reaction in the water soluble media.

A combined X-ray crystallographic and quantum chemical evaluation of the first stable rhodium carbenoid intermediate is described to substantiate the independent existence of rhodium carbenoids and to more fully characterize the Rh-Rh bonding. The compound shows an increase in the Rh-Rh distance expected for carbene complexation, along with a somewhat long and weak Rh-C bond.

The synthesis and structure of the first carbene complex of a phosphorus(V) center, perphosphoranide (2), is presented. Perphosphoranide is produced in quantitative yield by the direct reaction of the stable imidazol-2-ylidene with phenyltetrafluorophosphorane in tetrahydrofuran solution. The structure of compound 2 indicates the expected octahedral geometry at the phosphorus center. The structural and NMR data indicate that the imidazole moiety in 2 has more imidazolium-like characteristics while the imidazole ring in the phenylphosphinidene*carbene adduct retains some of its carbene characteristics.

The nuclear magnetic resonance and x-ray diffraction characterization of a stable carbene, 1,3-dimesitylimidazolin-2-ylidene, is discussed. Specifically, 1,3-dimesitylimidazolinium chloride was reacted with potassium hydride to form a 72%-pure, stable carbene as a colorless, crystalline solid. Its stability shows that a stable diaminocarbene may be obtained even without a C4-C5 double bond in the imidazole ring.

The synthesis of bis(carbene)-proton complexes involves the reaction of a carbene with 1, 3-dimesitylimidazolium salt. High melting points of these colorless complexes agree with their ionic structures. A C-H-C hydrogen bond connects the imidazole units of the cations. NMR experiments indicate that the bis(carbene)-proton system is more dynamic than the related iodine structure. X-ray studies reveal the involvement of the anions in the secondary hydrogen bonding of the extended solid state structure and the position of the anions favor the formation of a near linear C-H-X arrangement.

The reaction of a carbene and bis(pentamethylcyclopentadienyl)samarium-thf toluene solvate yields a green, carbon-samarium(II) complex. The reaction of this complex with another carbene yields a bis adduct. NMR studies reveal unusual shifts for methyl groups of carbenes due to samarium's anisotropic effects. A carbene-yttrium complex reveals typical chemical shifts for the C-CH3 and N-CH3 centers. X-ray analysis reveals the longer carbene-metal bond distances in these compounds compared to s-, p- and d-block metals.

Bis(carbene)-iodine(1+) complex is formed when carbene reacts with 2-iodo-1,3-di-mesitylimidazolium salt. X-ray crystal studies show near-linear geometries at the central atom. Homoleptic bis(carbene) adducts of transmission metals, which are similar to iodine complex structures, are also synthesized.

Alane adduct, a stable carbene, is a white solid represented as 1,3-bis(2,4, 6-trimethylphenyl)imidazol-2-ylidene-AlH3 obtained by synthesis. The various resonance results indicate an electronic complex between an imidazolium ion and a free carbene. Alane adducts have complicated carbene structures.