A detailed study on the excited-state-excitation migration taking place within the tetranuclear complex [{(tbbpy)(2)Ru(tmbi)}(2){Pd(allyl)}(2)](PF(6))(2) (tbbpy = 4,4'-di-tert-butyl-2,2'-bipyridine and tmbi = 5,6,5',6'-tetramethyl-2,2'-bibenzimidazolate) is presented. The charge transfer is initiated by the photoexcitation into the lowest metal-to-ligand charge-transfer (MLCT) band of one of the peripheral ruthenium(II) chromophores and terminates on the central structurally complex Pd(2) (II)(allyl)(2) subunit. Thus, the system under investigation can be thought of as a functional model for the photosynthesis reaction center in plants. The kinetic steps involved in the overall process are inferred from femtosecond time-resolved transient-grating kinetics recorded at spectral positions within the regions of ground-state bleach and transient absorption. The kinetics features a complex non-exponential time behavior and can be fitted to a bi-exponential rise (tau(1)> or =200 fs, tau(2) approximately 1.5 ps) and a mono- or bi-exponential decay, depending on the experimental situation. The data leads to the formulation of a model for the intramolecular excitation-hopping ascribing intersystem crossing and subsequent cooling as the two fastest observed processes. Following these initial steps, charge transfer from the ruthenium to the central complex Pd(2)(allyl)(2) moiety is observed with a characteristic time constant of 50 ps. A 220-ps component that is observed in the ground-state recovery only is attributed to excitation equilibration between the two identical Pd(allyl) chromophores.

The reaction between [(η 6 -p-cymene)RuCl 2 ] 2 and tetra-p-tolyloxalic amidine (oxam1) results in a coupled cation/anion coordination forming the ion-paired complex [(η 6 -p-cymene)RuCl(oxam1)Cl] (1a). According to an X-ray single crystal diffraction analysis the Ru moiety is coordinated at the 1,2-diimine part yielding a five-membered chelate ring. Furthermore, the 1,2-diamine group on the opposite side binds to a chloride anion via two N−H groups. Exchange of the chloride anion by trifluoractetate yields [(η 6 -p-cymene)RuCl(oxam1)CF 3 CO 2 ] (1c) in which the C=O group is bonded to the diamine part. Similarly, bis(mesityl)bis(pyridylmethyl)oxalic amidine (oxam2) reacts with FeX 2 to yield the ion-paired complexes 3a (X: Cl), and 3b (X: Br). X-ray diffraction studies of both compounds reveal that the oxalic amidine ligand acts as a four-dentate chelating ligand. One halide is fixed in the same way as in 1a. The complex 1a

The reaction between [(tbbpy) 2 Ru(tmbiH 2 )](PF 6 ) 2 (tbbpy = 4,4Ј-di-tert-butyl-2,2Ј-bipyridine; tmbiH 2 = 5,5Ј,6,6Ј-tetramethyl-2,2Ј-dibenzimidazole) and LiMe/CuI affords the tetranuclear complex 1 containing the dication [{(tbbpy) 2

2,3-Bis(diphenylphosphino)-1,4-diazadienes RN=C(PPh2)-C(PPh2)=NR (1a, R = 4-tolyl; 1b, R = 4-tert-butylphenyl; 1c, R = mesityl) were used as novel ligands for transition metals. The metal complexes [(1c)Mo(CO)4] (2a), [(1c)[Mo(CO)4]2] (2b), [(1a)Cu(Cl)(PPh3)] (3), and [(1b)[(NiBr2(THF))]2] (4) were characterized by elemental analysis, MS, and 31P[1H], 1H, and 13C NMR spectra (except the paramagnetic complex 4). Additionally, the molecular structure of the complexes in the solid state was determined by single-crystal X-ray diffraction. In 2a and 2b the chelating ligand coordinates via the N,P donor set, whereas in 3 the chelating ligand coordinates via the two P atoms. 4 contains a square-planar (P,P)NiBr2 moiety on the one side of the bridging ligand 1b. On the opposite side the 1,2-dimine unit bonds to another Ni center having octahedral geometry. The bulkier ligand 1c reacts to form the mononuclear compound 5. X-ray diffraction analysis of single crystals shows that 5 contains a quinoxaline derivative with a cyclohexa-1,3-diene ring in the peripheral position. Furthermore, it contains a bis(diphenylphosphino)-ethylene unit coordinating the NiBr2. This arrangement is the result of an intramolecular [4 + 2] cycloaddition between the 1,2-diimine unit (as diheterodiene) and the benzene ring of the 4-tolyl-N substituent (as dieneophile). The same type of ring-closing reaction followed by a tautomerization reaction to form the mononuclear compound 6 occurred by dissolution of the binuclear complex 4 in methanol. This reaction can be used as a simple method for the synthesis of novel 1,2-bis(diarylphosphanyl)ethylenes containing a quinoxaline backbone.