John W. Kenney

[2 + 2] Photocycloadditions of [(η5-C5H5) Ru(DMPP)2L]PF6 complexes

A series of [(η5-C5H5)Ru(DMPP)2L]PF6 complexes, DMPP = 1-phenyl-3,4-dimethylphosphole, L = CH3CN, Ph3P, PhS(O)2CHCH2, (CH3)2NC(O)CHCH2, PhNC, CO and (CH3O)3P, was found to undergo sunlight initiated [2 + 2] photodimerization of the coordinated phospholes only when L is a good π-acceptor ligand. These [2 + 2] dimerizations are accompanied by [4 + 2] dimerizations. The ratio of the [2 + 2] to [4 + 2] cycloaddition products is a function of the steric bulk of L. The nature of the photoexcited state has been probed by electron absorption and emission spectroscopy. The electron absorption spectra show high ɛ bands in the near UV region that are attributed to DMPP π → π* transitions. The emission spectral lifetimes are a function of L and their magnitude at 77 K (about 0.2 to 2.0 μs), together with large Stokes shifts, is indicative of phosphorescence from a triplet excited state. It is postulated that this triplet excited state undergoes cycloaddition by way of a biradical intermediate. The complexes have been characterized by elemental analyses, infrared, electronic, and 1H, 1H31P, 13C1H and 31P1H NMR spectroscopy and cyclic voltammetry. The structure of (η5-C5H5)Ru(DMPP)2[2 + 2](CO)PF6 was confirmed by X-ray crystallography. The complex cation possesses a non-crystallographic mirror plane, the two RuP distances (2.282(1) and 2.281(2) A) are equivalent and the cyclobutane ring has a long (1.607(8) A) and a short (1.550(8) A) CC bond.

Reactions of co-ordinated ligands: amide formation from reactions of isocyanates with β-ketoimine complexes

Several organic isocyanates, R–NCO, have been found to undergo simple, quantitative, stepwise addition at the methine positions of CuII and NiIIβ-ketoimine complexes, to produce amides.

Pressure Effects on Emissive Materials

The investigation of the properties of substances under high pressures has emerged as a major multidisciplinary research endeavor embracing a diverse arsenal of spectroscopic, physical, and chemical probes. High pressure NMR, ESR, IR, Raman, Brillouin, electronic absorption, electronic emission, X-ray, and Mossbauer spectroscopic experiments are now commonplace.1 The vigorous state of high pressure research is attested to by a number of excellent books2–5 and review articles,1,6–8 to which the reader is referred to gain insight into the historical origins and current breadth of high pressure studies. Holzapfel’s review provides a thorough, up-to-date compendium of high pressure references.8 The exhaustive compilation of earlier high pressure literature (1900–1968) by Merrill also should be noted.9 Many have contributed to the development of high pressure science. However, particular mention should be made of the pioneering high pressure work of Bridgman,10,11 rightly called the father of high pressure science, and the thorough and richly diverse high pressure spectroscopic studies of Drickamer.12–15