Matrix photolysis of 2-pyrazinyl azides/tetrazolo[1,5-a]pyrazines generates nitrile ylides 15 via pyrazinylnitrenes 13 and triazacycloheptatetraenes 14. The nitrile ylides 15 are characterized by IR spectroscopy in conjunction with harmonic and anharmonic vibrational frequency calculations. The nitrile ylides exist in the matrices in the Z,Z-conformations in which they are born. Substitution on the nitrile carbon of nitrile ylides has a profound effect on their structure. Even different conformers of the same molecule can have differences up to 200 cm(-1) in the IR absorptions of the ylide moieties. Nitrile ylides 15a and 15b (R = H or Cl, R' = H) have allenic structures (15 Allenic). Nitrile ylide 15c (R = R' = CH3) has a distinctly propargylic structure (15 Propargylic) in the experimentally observed Z,Z-conformation.

Matrix photolysis of 4‐quinolyl azide 22 affords 4‐quinolylnitrene 21, identified by electron spin resonance (ESR) and infrared (IR) spectroscopy. Minor absorptions assigned to azirene 23 (1741 cm−1) were also observed. Further photolysis affords strong absorptions at 1902 and 1909 cm−1 ascribed to the cyclic ketenimine 19 as well as weaker absorptions at 2044 cm−1 ascribed to the open‐chain ketenimine 26 and at 1982 cm−1 assigned to the open‐chain nitrile ylide 25. Both 2‐(5‐tetrazolyl)quinoxaline 14 and triazolo[1,5‐a]quinoxaline 16 give rise to an absorption at 2084 cm−1 because of formation of the diazo compound 15 on mild flash vacuum thermolysis (FVT) with Ar matrix isolation of the product. Matrix photolysis of 16 affords diazo compound 15, cyclic ketenimine 19 and open‐chain ketenimine 26. 2‐Quinoxalinylcarbene 17 was also formed in the matrix photolysis and identified by its ESR spectrum. FVT of either 22 or 15/16 afforded 4‐quinolylnitrene, identified by its Ar‐matrix ESR spectrum. A second nitrene ESR signal obtained in several FVT and photolysis experiments from both 22 and 16 is ascribed to the phenylnitrene derivative 24 formed by ring opening of 2‐quinoxalinylcarbene 17. FVT of 14, 16, and 22 affords 3‐cyanoindole 27 as the major product. Minor amounts of 2‐cyanoindole 28, 4‐aminoquinoline 29 and 4,4′‐azoquinoline 30 are also formed. Preparative photolysis of 22 in solution in the presence of dialkylamines leads to trapping of the azirene 23 to afford 5‐dialkylaminobenzo[e]‐1,4‐diazepines 35. Copyright © 2011 John Wiley & Sons, Ltd.

Photolysis of 3-azidoquinoline 6 in an Ar matrix generates 3-quinolylnitrene 7, which is characterized by its electron spin resonance (ESR), UV, and IR spectra in Ar matrices. Nitrene 7 undergoes ring opening to a nitrile ylide 19, also characterized by its UV and IR spectra. A subsequent 1,7-hydrogen shift in the ylide 19 affords 3-(2-isocyanophenyl)ketenimine 20. Matrix photolysis of 1,2,3-triazolo[1,5-c]quinoxaline 26 generates 4-diazomethylquinazoline 27, followed by 4-quinazolylcarbene 28, which is characterized by ESR and IR spectroscopy. Further photolysis of carbene 28 slowly generates ketenimine 20, thus suggesting that ylide 19 is formed initially. Flash vacuum thermolysis (FVT) of both 6 and 26 affords 3-cyanoindole 22 in high yield, thereby indicating that carbene 28 and nitrene 7 enter the same energy surface. Matrix photolysis of 3-quinolyldiazomethane 30 generates 3-quinolylcarbene 31, which on photolysis at > 500 nm reacts with N-2 to regenerate diazo compound 30. Photolysis of 30 in the presence of CO generates a ketene (34). 3-Quinolylcarbene 31 cyclizes on photolysis at > 500 nm to 5-aza-2,3-benzobicyclo[4.1.0]hepta-2,4,7-triene 32. Both 31 and 32 are characterized by their IR and UV spectra. FVT of 30 yields a mixture of 2- and 3-cyanoindenes via a carbene-carbene-nitrene rearrangement 31 -> 2-quinolylcarbene 39 -> 1-naphthylnitrene 43. The reaction mechanisms are supported by density functional theory calculations of the energies and spectra of all relevant ground and transition state structures at the B3LYP/6-31G* level.

8-Cyanotetrazolo[1,5-a]pyridine 6T undergoes photochemical ring expansion to afford 1,3diazepine 7 with diisopropylamine, but with stronger nucleophiles such as dimethylamine a rapid, quantitative ring opening reaction affords dienyltetrazoles 8 and 9 in the dark (an Addition of Nucleophile -Ring Opening reaction).

The coordination-driven self-assembly of four different trigonal prisms from 3 equiv of one of four different tetrapyridyl star connectors and 6 equiv of a platinum linker dication in nitromethane is presented. This face-directed approach affords high yields without template assistance. The prisms have been characterized by multinuclear and DOSY NMR and dual ESI-FT-ICR mass spectrometry. The use of a conformationally chiral star connector leads to a conformationally chiral prism when connector arm ends attached to a vertex have a strongly correlated twist sense and chirality is communicated across polyhedral faces, edges, and vertices. Molecular mechanics results suggest that in the smallest prism 3d collective effects dominate and the all-P and all-M conformers are strongly favored. NMR data prove that the two edges of the pyridine rings in the triflate salts of 3a-3d are distinct. An Eyring plot of rates obtained from line-shape analysis and 1-D EXCHSY NMR yields an activation enthalpy DeltaH(double dagger) of approximately 12 kcal/mol and activation entropy DeltaS(double dagger) of approximately -15 cal/mol x K for the edge interconversion process, compatible with pyridine rotation around the Pt-N bond. For 3c, this behavior is observed only up to approximately 318 K. At higher temperatures, the Eyring plot is again linear but follows a very different straight line, with a DeltaH(double dagger) of approximately 35 kcal/mol and DeltaS(double dagger) of approximately 60 cal/mol x K. This highly unusual result is further investigated and discussed in the following companion paper.

Cyano-substituted tetrazolo[1,5-a]pyridines/2-azidopyridines 8T and 15T undergo thermal ring opening to the azides 8A and 15A. Solution photolysis causes nitrogen elimination and ring expansion to 1,3-diazacyclohepta-1,2,4,6-tetraenes 10 and 17, which react with alcohols to afford 2-alkoxy-1H-1,3-diazepines, with secondary amines to 2-dialkylamino-5H-1,3-diazepines, and with water to 1,3-diazepin-2-ones (12–14, 19, 21). Argon matrix photolysis of the azides affords the diazacycloheptatetraenes 10 and 17 as principal products together with ring-opened dicyanovinylketenimines 11 and 18. The matrix-isolated species were identified on the basis of comparison of the infrared spectra with those calculated at the B3LYP/6–31+G* level.

Flexible, ambidentate pyridyl-carboxylate based donor ligands such as sodium 3-(3-pyridyl)benzoate, sodium 4-(3-pyridyl)benzoate, and potassium 4-(3-pyridyl)ethynylbenzoate self-assemble into discrete [2 + 2] macrocyclic species instead of infinite networks when combined with a 90 degrees platinum-containing acceptor. In each case, only one isomeric ensemble is selectively formed in high yield. All products are characterized by electrospray ionization mass spectrometry (ESI-MS) and 31P{1H} and 1H NMR spectroscopy. They are the first examples of discrete supramolecules incorporating flexible, ambidentate donor ligands. Despite their potential versatility, these pyridyl-carboxylate donors adjust their bonding directionality to accommodate a rigid platinum acceptor in the formation of one discrete ensemble.

The synthesis of a bis(pyridyl)-substituted perylene diimide ligand and its incorporation into a supramolecular rhomboid and rectangle via platinum-mediated self-assembly is reported. Both ensembles are characterized by multinuclear NMR and electrospray ionization mass spectrometry. In addition, the UV/vis spectra of the ensembles exhibit displaced and enhanced absorptions relative to the starting ligand. Size estimations using MM2 simulations show the assemblies are almost 46 A in length.

A flexible, pyridine-functionalized diaza-crown ether was self-assembled into discrete supramolecules of differing stoichiometries upon combination with various organoplatinum molecules. They are characterized by electrospray ionization mass spectrometry and (31)P[(1)H] and (1)H NMR. In one case, (1)H-(1)H NOE enhancements of a [1 + 1] assembled structure demonstrate the puckered shape of the macrocyclic ring. Despite its inherent flexibility, the dipyridyl-substituted 18-membered diaza-crown ligand prefers to self-assemble into closed systems when reacted with platinum-containing acceptors.

Discrete, nanoscopic 3-D cages are prepared in high yield via coordination-driven self-assembly from a variety of building blocks, including bidentate 3-substituted pyridines, chiral, and silicon-based tripods. All are characterized by NMR ((31)P, (1)H) and electrospray ionization mass spectrometry.

Self-recognition in the transition-metal-mediated self-assembly of some 2-D polygons is presented, Prolonged heating of two or three organoplatinum reagents with 4,4'-dipyridyl in aqueous acetone results in the predominant formation of a rectangle, triangle, and/or square. All mixtures are characterized with NMR and electrospray ionization mass spectrometry (ESIMS). Despite the potential for ill-defined oligomeric products, these mixed ligand systems prefer to self-assemble into discrete species.

The coordination-driven self-assembly of discrete 2D macrocyclic species from ambidentate pyridyl-carboxylate-based donor ligands and platinum-containing acceptors is presented. All these species are characterized by electrospray ionization mass spectrometry (ESIMS), multinuclear NMR, and in one example, X-ray crystallography. In each case only one isomeric assembly is selectively formed in high yield, despite the potential for more than one product as a consequence of differences in connectivity.

Flexible, pyridine-functionalized ligands were self-assembled into discrete supramolecules of differing stoichiometries upon combination with various organoplatinum molecules. They are characterized by electrospray ionization mass spectrometry, /sup 31/{/sup 1/H} and /sup 1/H NMR. Despite its inherent flexibility, 3-substituted pyridines 1 and di-pyridyl substituted 18-membered diaza-crown ligand 8 prefer to self-assemble into closed systems when reacted with platinum-containing acceptors.

Argon matrix photolysis of tetrazolo[1,5-a]quinoline 8 and tetrazolo[5,1-a]isoquinoline 7 causes nitrogen elimination and ring expansion to 1,3-diazabenzo[d]cyclohepta-1,2,4,6-tetraene 13. The photolysis of tetrazolo[5,1-a]isoquinoline 7 also causes ring opening to o-cyanophenylketenimine 22. Mechanisms of ring opening of heteroarylnitrenes are discussed.

Flexible donor ligands like 1,2-bis(3-pyridyl)ethyne or 1,4-bis(3-pyridyl)-1,3-butadiyne self-assemble into discrete supramolecules instead of infinite networks upon combination with organoplatinum 90, 120, and 180 degree acceptor units. These systems are unique examples of versatile pyridine donors adjusting their bonding directionality to accommodate rigid platinum acceptors in the formation of closed macrocycles.

Tetrazolo[1,5-a]pyrazine/2-azidopyrazine 9T/9A undergo photolysis in Ar matrix at cryogenic temperatures to yield 1,3,5-triazacyclohepta-1,2,4,6-tetraene 21 as the first observable intermediate, and 1-cyanoimidazole 11 and (2-isocyanovinyl)carbodiimide 22 as the final products. The latter tautomerizes to 2-(isocyanovinyl)cyanamide 23 on warming to 40 K. The same intermediate 21 and the same final products are obtained on matrix photolysis of the isomeric tetrazolo[1,5-c]pyrimidine/4-azidopyrimidine 24T/24A. These photolysis results as well as those of the previously reported thermal ring contraction of N-15-labeled 2-pyrazinyl- and 4-pyrimidylnitrenes to 1-cyanoimidazoles can all be rationalized in terms of selective ring opening of 21 or nitrine 10 to a nitrile ylide zwitterion 28 prior to formation of the final products, 11 and 22. The results are supported by high-level ab initio and DFT calculations (CASPT2-CASSCF(6,6), G3(MP2), and B3LYP/6-31+G*) of the energies and IR spectra of the intermediates and products.