[2-C5H5)RU(DMPP)(2)L]PF6 COMPLEXES(2]PHOTOCYCLOADDITIONS OF [(ETA(5))

A series of [(eta(5)-C5H5)Ru(DMPP)(2)L]PF6 complexes, DMPP = 1-phenyl- 3,4-dimethylphosphole, L = CH3CN, Ph3P, PhS(O)(2)CH=CH2, (CH3)(2)NC(O) CH=CH2, PhN=C, CO and (CH3O)(3)P, was found to undergo sunlight initia ted [2 + 2] photodimerization of the coordinated phospholes only when L is a good pi-acceptor ligand. These [2 + 2] dimerizations are accomp anied by [4 + 2] dimerizations, The ratio of the [2 + 2] to [4 + 2] cy cloaddition 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 epsil on bands in the near UV region that are attributed to DMPP pi -->, pi transitions. The emission spectral lifetimes are a function of L and their magnitude at 77 K (about 0.2 to 2.0 mu s), together with large S tokes shifts, is indicative of phosphorescence from a triplet excited state. It is postulated that this triplet excited state undergoes cycl oaddition by way of a biradical intermediate. The complexes have been characterized by elemental analyses, infrared, electronic, and H-1, H- 1{P-31}, C-13{H-1} and P-31{H-1} NMR spectroscopy and cyclic voltammet ry, The structure of {(eta(5)-C5H5)Ru(DMPP)(2)[2 + 2](CO)}PF6 was conf irmed by X-ray crystallography. The complex cation possesses a non-cry stallographic mirror plane, the two Ru-P distances (2.282(1) and 2.281 (2)Angstrom) are equivalent and the cyclobutane ring has a long(1.607( 8)Angstrom) and a short (1.550(8)Angstrom) C-C bond.