Evaluation of pyridoindoles, pyridylindoles and pyridylpyridoindoles as matrices for ultraviolet matrix-assisted laser desorption/ionization time-of-flight mass spectrometry.

In an effort to gain an understanding of the processes governing ultraviolet matrix-assisted laser desorption/ionization (UV-MALDI), direct comparison was made of the mass spectra of proteins, carbohydrates and synthetic polymers (polyethylene glycol, polyester and polyamide) by using pyridylindoles, pyridoindoles and pyridylpyridoindoles as UV (337 nm)-MALDI-TOFMS matrices in positive and negative ion mode. In order to study the combined effect of the indole N-H and the pyridine nitrogen of the MALDI matrix on the desorption/ionization process in MALDI, compounds were selected that include either or both of these functions in their structure. Within the compounds studied only those that possess simultaneously both functions in a 1,4-relation behave as very good matrices for proteins. These compounds also work as matrices for some carbohydrates and synthetic polymers used as analytes in the present study. Some of the compounds were also found to be useful for the post-source decay (PSD) analysis of cyclodextrins in positive and negative ion mode. In several cases we also examined the matrix behavior of the corresponding N-methylindole derivatives.

Cyclometalated complexes of Ru(II) with 2-aryl derivatives of quinoline and 1,10-phenanthroline.

Difficulty in cyclometalating 1-(2'-quinolinyl)pyrene and 1,3-di-(2'-quinolinyl)pyrene with Ru(II) led to a more detailed study of the cyclometalation process. A series of 2-aryl-1,10-phenanthrolines, where aryl = phenyl, 2-naphthyl, 1-anthracenyl, and 1-pyrenyl, were treated with [Ru(tpy)Cl(3)] to provide either the N5Cl complex [Ru(tpy)(L)Cl](+) or this same material as a mixture with the N5C cyclometalated species [Ru(tpy)L](+). Steric effects appear to govern the ability of the ligand to attain the near planar conformation required for cyclometalation. The bridged ligand 3,1'-dimethylene-2-(2'-pyrenyl)-1,10-phenanthroline was prepared along with a quinoline analogue. The former species was found to cyclometalate at the C1 of pyrene and afford the N5Cl complex. Both the N5C (P2(1)/n (monoclinic), a = 28.1102(11), b = 8.4638(3), c = 31.2908(12) A, Z = 8) and N5Cl (P-1 (triclinic), a = 11.7235 (10), b = 14.5306(12), c = 14.5725(12) A, Z = 2) complexes were analyzed by X-ray crystallography, and the N5Cl species evidenced a congested environment for pyrene, which is apparently stabilized by pi stacking with tpy. Similar reactions with a series of three 3,2'-bridged derivatives of 2-phenyl-1,10-phenanthroline provide both N5Cl and cyclometalated products in proportions which support the importance of pi stacking. The electronic absorption spectra and redox potentials for these complexes evidence strong sigma donation by the cyclometalated ligand and an apparent insensitivity to the orthogonal 2-aryl group.

Friedländer synthesis of chiral alkyl-substituted 1,10-phenanthrolines.

The synthetic scope of the Friedländer condensation in the preparation of chiral alkyl-substituted 1,10-phenanthrolines has been investigated. A range of chiral [x,y-b]-cycloalkeno-condensed phenanthrolines has been prepared in one step from steroidal or other cyclic ketones from the chiral pool and 8-amino-7-quinolinecarbaldehyde (1) via base-catalyzed condensation. Phenanthroline derivatives are formed in good yields with unhindered ketones, but the reaction proceeds even with sterically congested substrates such as camphor, albeit in low yield. The utility of the Friedländer condensation has been extended to the synthesis of chiral 3-alkyl-substituted phenanthrolines from monoalkyl-substituted acetaldehydes.

Crowded Cu(I) complexes involving benzo[h]quinoline: pi-stacking effects and long-lives excited states.

The Friedländer condensation was employed to synthesize two series of 3,3'-polymethylene bridged ligands, L, based on 2-(2'-pyridyl)-benzo[h]quinoline and 2,2'-bibenzo[h]quinoline (BHQ) along with the fully aromatic naphtho[1,2-b]-1,10-phenanthroline. Complexes [Cu(L)(2)](+) were prepared as their perchlorate or hexafluorophosphate salts. The solution state structures were analyzed by NMR and shielding effects reflected significant interligand pi-stacking interaction in the complexes. Solid-state structures of the complexes where L = 3,3'-tetramethylene-2,2'-bibenzo[h]quinoline or naphtho[1,2-b]-1,10-phenanthroline were determined by X-ray analysis. The tetramethylene bridged complex showed a highly distorted coordination geometry with the BHQ rings of opposing ligands pi-stacked at a interplanar distance of about 3.37 A. Complexes of the BHQ series showed a pronounced MLCT absorption maximum which shifted bathochromically from 496 to 610 nm as the 3,3'-bridge decreased from 4 to 2 carbons. The BHQ complexes luminesced strongly in CH(2)Cl(2) solution and the tetramethylene-bridged system showed the longest yet recorded excited-state lifetime for a copper MLCT excited state, tau = 5.3 micros and Phi = 0.10.

Evaluation of diimine ligand exchange on Cu(I).

Four ligands have been prepared, 8,8-dimethyl-6,7,9-trihydropyrido[1,2-b]acridine and three 4,4',6,6'-tetrasubstituted derivatives of 2,2'-bipyrimidine where the substituents are methyl, phenyl, and p-tolyl. The corresponding [CuL(2)](+) salts of these ligands evidence nonequivalent NMR signals that allow an estimation of the ligand exchange barrier in both acetonitrile and chloroform solution. Lower barriers are found in the former solvent and attributed to solvent participation in the exchange process. Corresponding differences in the oxidation potentials of the complexes are explained in a similar manner. The electronic absorption properties of the complexes are also consistent with the steric and electronic properties of the ligands. [Cu(2c)(2)](PF(6)), where 2c = 4,4',6,6'-tetraphenyl-2,2'-bipyrimidine, was analyzed by X-ray diffraction and found to crystallize in the space group Pccn with a = 14.761(2) A, b = 15.007(2) A, c = 24.407(4) A, and Z = 4. The internal and external phenyl rings are disposed quite differently, with the internal rings interacting strongly with the orthogonal ligand.

Mono- and dinuclear ruthenium(II) and osmium(II) polypyridine complexes built around spiro-bridged bis(phenanthroline) ligands: synthesis, electrochemistry, and photophysics.

Two new dyads have been synthesized in which terminal Ru(II) and Os(II) polypyridine complexes are separated by sterically constrained spiro bridges. The photophysical properties of the corresponding mononuclear complexes indicate the importance of the decay of the lowest-energy triplet states localized on the metallo fragments through the higher-energy metal-centered excited states. This effect is minimized at 77 K, where triplet lifetimes are relatively long, and for the Os(II)-based systems relative to their Ru(II)-based counterparts. Intramolecular triplet energy transfer takes place from the Ru(II)-based fragment to the appended Os(II)-based unit, the rate constant being dependent on the molecular structure and on temperature. In all cases, the experimental rate constant matches surprisingly well with the rate constant calculated for Förster-type dipole-dipole energy transfer. As such, the disparate rates shown by the two compounds can be attributed to stereochemical factors. It is further concluded that the spiro bridging unit does not favor through-bond electron exchange interactions, a situation confirmed by cyclic voltammetry.

Bidentate ligands that contain pyrrole in place of pyridine.

A series of ligands are prepared that are analogues of benzo-fused derivatives of 2,2'-bipyridine (bpy), in which pyrrole has been substituted for a pyridine ring. These ligands include 2-(2'-pyridyl)-indole, 2-(2'-pyrrolyl)-quinoline, and pyrrolo[3,2-h]quinoline. A novel reductive cyclization approach to the latter species is presented. All these ligands react with [Ru(bpy-d8)2Cl2], undergoing cyclometalation with concurrent deprotonation, to form complexes of the type [Ru(L)(bpy-d8)2]+ where L binds as a monoanionic ligand. The complexes are readily characterized by their 1H NMR spectra. Changes in the redox potentials and the electronic absorption spectra of both the ligands and the complexes are interpreted in terms of charge delocalization on the ligand.