Nihal Deligonul

Phosphine- and Carbene-Ligated Silver Acetate: Easily-Accessed Synthons for Reactions with Silylated Nucleophiles

The useful synthon tricyclohexylphosphinesilver(I) acetate is easily prepared on gram scale by the reaction of silver(I) acetate and tricyclohexylphosphine in a 1:1 ratio in toluene. (PCy(3))Ag(OAc) (1) reacts with a wide range of silylated nucleophiles (Me(3)Si-X; product with X = N(3), 2; Cl, 3; SCN, 4; 1,2,4-triazol-1-yl, 5; trifluoromethanesulfonate (OTf), 6; SPh, 8; Br, 9) to effect room temperature Ag-X bond formation at the expense of the Ag-OAc bond. All new products were characterized by multinuclear NMR spectroscopies, IR spectroscopy, microanalysis, and X-ray crystallography. X-ray crystallography indicated a variety of coordination geometries at silver(I) are accessible, as di- and tetranuclear complexes were observed in all cases except 1, which forms a three-coordinate, mononuclear complex. In the case of 8, NMR and mass spectrometric data suggest fluxional species of variable nuclearity (but with empirical formula [(PCy(3))Au(SPh)](n)) exist in solution. To provide more definitive evidence of Ag-S bond formation, the ligand 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene (IPr) was used to synthesize a new starting material, (IPr)AgOAc (10), the Ag-OAc bond of which is amenable to silylation by Me(3)Si-X (complex with X = N(3), 11; Cl, 12; SPh, 14). Complex 14 was characterized crystallographically, and provided definitive evidence for Ag-S bond formation via silylation with PhS-SiMe(3). Me(3)SiBr and Me(3)SiI are also competent in the silylation of 10 to yield 13 and 15, but these compounds were more cleanly synthesized by the reaction of 12 and KBr/KI in a biphasic CH(2)Cl(2)/H(2)O mixture. In a preliminary exploration of reactivity, it was determined that azidosilver(I) complexes 2 and 11 react rapidly and quantitatively with (NO)(SbF(6)) (as was previously demonstrated in a related azidogold(I) system) to yield cationic silver(I) species (detected by mass spectrometry). In acetonitrile solution, ligand rearrangements of these cationic silver(I) species yield cationic bis(phosphine) or bis(carbene) complexes, the identities of which were authenticated by X-ray crystallography.

Branch-Selective Synthesis of Oxindole and Indene Scaffolds: Transition Metal-Controlled Intramolecular Aryl Amidation Leading to C3 Reverse-Prenylated Oxindoles

In an effort to access biologically important scaffolds, a concise branch-selective synthesis of C3 tertiary oxindoles by Cu(I)-catalyzed aryl amidation and 2,2-dimethyl indene by Pd(0)-catalyzed Heck cyclization has been accomplished from acyclic reverse-prenylated intermediates. Oxindole C3-enolate generation using NaH followed by alkylation in the presence of appropriate electrophiles provides a novel route to quaternary C3 reverse-prenylated oxindoles.

Room-temperature synthesis of cyclometalated iridium(III) complexes: kinetic isomers and reactive functionalities

Cyclometalated iridium(III) complexes have been prepared in high yields from base-assisted transmetalation reactions of cis-bis(aquo)iridium(III) complexes with boronated aromatic proligands. Reactions proceed at room temperature. Potassium hydroxide and potassium phosphate are effective supporting bases. Kinetic, meridional isomers are isolated because of the mildness of the new technique. Syntheses are faster with KOH, but the gentler base K3PO4 broadens the reactions scope. Complexes of chelated ketone, aldehyde, and alcohol complexes are reported that bind iridium through formally neutral oxygen and formally anionic carbon. The new complexes luminesce with microsecond-scale lifetimes at 77 K and nanosecond-scale lifetimes at room temperature; emission quenches in air. Two complexes, an aldehyde and its reduced (alcohol) derivative, are crystallographically characterized. Their bonding is examined with density-functional theory calculations. Time-dependent computations suggest that the Franck–Condon triplet states of these complexes have mixed orbital parentage, arising from one-particle transitions that mingle through configuration interaction.

Gold(I) Complexes of Brominated Azadipyrromethene Ligands

Azadipyrromethenes are luminescent, red-light absorbing dyes that readily bind BF(2)(+) and metals. Their framework allows for structural modification at the phenyl arms and the two pyrrolic carbon positions. Here we report five new gold(I) complexes with azadipyrromethene ligands brominated at the pyrrolic carbons and/or the four phenyl substituents. New complexes are characterized by multinuclear NMR spectroscopy, X-ray crystallography, optical absorption and emission spectroscopy, and elemental analysis. The new compounds have a perturbed two-coordinate geometry in the crystalline state, with gold(I) binding one dimethylphenylphosphine ancillary ligand and one pyrrole nitrogen of the azadipyrromethene. The second azadipyrromethene pyrrole nitrogen perturbs the linear coordination. These complexes maintain the absorption features of the free ligands. Excitation in the near-ultraviolet generates emission in the near-UV and visible regions. Density-functional theory calculations indicate that the photoproperties of the new compounds arise almost entirely from the conjugated ligands and not from the (phosphine)gold(I) fragments.

Naphthoxaphospholes as examples of fluorescent phospha-acenes

Seven new fluorescent 2-R-naphtho[2,3-d]oxaphospholes (R-NOPs) (4a–g; R = tBu (a), Ad (b), C(6)H(5) (c), 4-MeC(6)H(4) (d), 4-ClC(6)H(4) (e), 4-BrC(6)H(4) (f ), 4-MeOC(6)H(4) (g)), have been synthesized by cyclocondensation reactions of benzimidoyl chlorides with 3-phosphino-2-naphthol (3). The compounds were characterized by multinuclear NMR, UV-vis, and fluorescence spectroscopy. Compounds 4a–d and 4g were characterized by cyclic voltammetry experiments. The solid state structures of compounds 4b and 4d were also determined by single-crystal X-ray diffraction experiments.

Gold(I) Styrylbenzene, Distyrylbenzene, and Distyrylnaphthalene Complexes: High Emission Quantum Yields at Room Temperature

One gold(I)-substituted styrylbenzene, six digold(I) distyrylbenzenes, one tetragold distyrylbenzene, and four digold distyrylnaphthalene complexes were synthesized using base-promoted auration, alkynylation, triazolate formation, and Horner-Wadsworth-Emmons reactions. The gold(I) fragments are either σ-bonded to the aromatic system, or they are attached through an alkynyl or triazolate spacer. Product formation was monitored using (31)P{(1)H} NMR spectroscopy. Systems in which gold(I) binds to the central benzene ring or the terminal phenyl rings were designed. All of these complexes have strong ultraviolet absorptions and emit blue light. The position of the gold(I) attachment influences the luminescence efficiency. Complexes with two gold(I) fragments attached to the ends of the conjugated system have fluorescence quantum yields up to 0.94, when using 7-diethylamino-4-methylcoumarin as the emission standard. Density-functional theory calculations on three high-yielding emitters suggest that luminescence originates from the distyrylbenzene or -naphthalene bridge.

Geminally Diaurated Aryls Bridged by Semirigid Phosphine Pillars: Syntheses and Electronic Structure

Geminally diaurated μ2 -aryl complexes have been prepared where gold(I) centers were bridged by the semirigid diphosphine ligands bis(2-diphenylphosphinophenyl)ether (DPEphos) and 4,6-bis(diphenylphosphanyl)dibenzo[b,d]furan (DBFphos). Diaurated complexes were synthesized in ligand redistribution reactions of the corresponding di-gold dichlorides with di-gold diaryls (six of them new) and silver(I) salts. Diaurated complexes were isolated as salts of the minimally coordinating anions SbF6 (-) and ReO4 (-). Efforts to prepare salts of the tetraarylborate [B(3,5-(CF3)2 C6 H3)4](-) led to transmetalation from boron, with crystallization of the fluorinated aryl complex. The new complexes were characterized by multinuclear NMR, absorption and emission spectroscopies, 77 K emission lifetimes, and by combustion analysis; three are crystallographically characterized. Structures of geminally diaurated aryl ligands are compared to those of mono-aurated analogues. Both crystal structures and density-functional theory calculations indicate slight but observable disruptions of aryl ligand aromaticity by geminal di-gold binding. An intermolecular aurophilic interaction in one structurally authenticated complex was examined computationally.

A hybrid lithium oxalate-phosphinate salt.

The novel organophosphorus-containing lithium salt Li(THF)[(C(2)O(4))B(O(2)PPh(2))(2)] (1; THF = tetrahydrofuran) was synthesized and characterized using a variety of spectroscopic techniques. An X-ray structural analysis on crystals of 1 grown from THF reveals a dimeric structure [Li(THF)(C(2)O(4))B(O(2)PPh(2))(2)](2)·THF, whereby the two units of 1 are bridged via P-O···Li interactions. Compound 1 displays high air and water stability and is also thermally robust, properties needed of electrolytes for their possible use as electrolytes and/or additives in lithium-ion battery applications.

Azadipyrromethene Complexes of d8 Metal Centers: Rhodium(I), Iridium(I), Palladium(II), and Platinum(II)

Azadipyrromethenes are blue pigments that chelate main-group and d-block Lewis acids. Reported here are azadipyrromethene complexes of d(8) metal centers. The new compounds are prepared in salt metathesis reactions with chlorinated organometallic precursors. Sixteen new complexes are reported. The principal absorption features are an intense peak near 600 nm and transitions in the ultraviolet; all are characteristic of the azadipyrromethene chromophore. All compounds are dark solids that yield blue or blue-violet solutions. Ten complexes are crystallographically characterized. The structures uniformly show backbone strain, with a meso-nitrogen atom that dilates from pure sp(2)-hybridization. Structural comparisons are made to related dipyrromethene and tetra-azaporphyrin complexes. The electron-donating capacity of azadipyrromethene ligands is evaluated from C≡O stretching frequencies of three rhodium(I) carbonyl complexes and from density-functional theory calculations. Frontier orbitals are confined to the azadipyrromethene ligand. HOMO-LUMO energy gaps are almost unperturbed from those of the free, anionic azadipyrromethene.

Azido, Triazolyl, and Alkynyl Complexes of Gold(I): Syntheses, Structures, and Ligand Effects

Gold(I) triazolyl complexes are prepared in [3 + 2] cycloaddition reactions of (tertiary phosphine)gold(I) azides with terminal alkynes. Seven such triazolyl complexes, not previously prepared, are described. Reducible functional groups are accommodated. In addition, two new (N-heterocyclic carbene)gold(I) azides and two new gold(I) alkynyls are described. Eight complexes are crystallographically authenticated; aurophilic interactions appear in one structure only. The packing diagrams of gold(I) triazolyls all show intermolecular hydrogen bonding between N-1 of one molecule and N-3 of a neighbor. This hydrogen bonding permeates the crystal lattice. Density-functional theory calculations of (triphenylphosphine)gold(I) triazolyls and the corresponding alkynyls indicate that the triazolyl is a stronger trans-influencer than is the alkynyl, but the alkynyl is more electron-releasing. These results suggest that trans-influences in two-coordinate gold(I) complexes can be more than a simple matter of ligand donicity.