| The photo-initiated coupling of ({dollar}pi{dollar}-allyl)nickel halide complexes with iodo imidazoles proceeds efficiently in toluene solution without the use of coordinating solvent or added ligand, leading to allylated imidazoles (11 examples, 38-91% yield). Nickel-promoted allylation, and symmetrical coupling, of non-imidazole aryl halides and triflates in toluene solution is enhanced by using N-methylimidazole as an additive. {dollar}sp1{dollar}H NMR analysis of a solution of N-methylimidazole and {dollar}etasp3{dollar}-prenylnickel bromide dimer in C{dollar}sb6{dollar}D{dollar}sb6{dollar} shows coordination of the imidazole N-3 to nickel.; Steady-state fluorescence and transient absorbance measurements have been used to determine electron transfer (ET) rates of four model compounds in which zinc tetratolylporphyrin (P) and naphthoquinone (Q) are held at fixed distances by homologous, fully {dollar}sigma{dollar}-bonded, oligospirocyclic spacers. The synthesis and characterization of the PQ models are described. Structural studies of several spirocyclic systems show that the operative P{dollar}...{dollar}Q separations are {dollar}approx{dollar}5.9, 8.1, 10.2, and 12.1 A, respectively, for the {dollar}sigma{dollar}-pathways containing 6, 8, 10, and 12 bonds. Spectroscopic identification of the P{dollar}sp+{dollar}Q{dollar}sp-{dollar} transient species shows that diminished {dollar}sp1{dollar}P* lifetimes and fluorescence yields result from ET. The ET rates are attenuated per bond according to the relationship k{dollar}sb{lcub}rm ET{rcub}{dollar} = 10{dollar}sp{lcub}12{rcub}{dollar}Aexp(-{dollar}beta{dollar}N{dollar}sbsigma{dollar}), where the values of {dollar}beta{dollar} are 1.03, 1.06, and 1.15 per bond for n-butanol, pyridine, and acetonitrile, respectively. |
