Resonance raman excitation profile of a ruthenium(II) complex of dipyrido[2,3-a:3',2'-c]phenazine.

The lowest energy transition of [Ru(CN)(4)(ppb)](2-) (ppb = dipyrido[2,3-a:3',2'-c]phenazine), a metal-to-ligand charge transfer, has been probed using resonance Raman spectroscopy with excitation wavelengths (488, 514, 530, and 568 nm) spanning the lowest energy absorption band centered at 522 nm. Wave packet modeling was used to simultaneously model this lowest energy absorption band and the cross sections of the resonance Raman bands at the series of excitation wavelengths across this absorption band. A fit to within +/-20% was obtained for the Raman cross sections, close to the experimental uncertainty which is typically 10-20%. Delta values of 0.1-0.4 were obtained for modes which were either localized on the ppb ligand (345-1599 cm(-1)) or the CN modes (2063 and 2097 cm(-1)). DFT calculations reveal that the resonance Raman bands observed are due to modes delocalized over the entire ppb ligand.

Probing ruthenium-acetylide bonding interactions: synthesis, electrochemistry, and spectroscopic studies of acetylide-ruthenium complexes supported by tetradentate macrocyclic amine and diphosphine ligands.

The synthesis and spectroscopic properties of trans-[RuL4(C[triple bond]CAr)2] (L4 = two 1,2-bis(dimethylphosphino)ethane, (dmpe)2; 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, 16-TMC; 1,12-dimethyl-3,4:9,10-dibenzo-1,12-diaza-5,8-dioxacyclopentadecane, N2O2) are described. Investigations into the effects of varying the [RuL4] core, acetylide ligands, and acetylide chain length for the [(-)C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph] and [(-)C[triple bond]C(C6H4)(n-1)Ph] (n = 1-3) series upon the electronic and electrochemical characteristics of trans-[RuL4(C[triple bond]CAr)2](0/+) are presented. DFT and TD-DFT calculations have been performed on trans-[Ru(L')4(C[triple bond]CAr)2](0/+) (L' = PH3 and NH3) to examine the metal-acetylide pi-interaction and the nature of the associated electronic transition(s). It was observed that (1) the relationship between the transition energy and 1/n for trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)(n-1)Ph}2] (n = 1-3) is linear, and (2) the sum of the d(pi)(Ru(II)) --> pi*(C[triple bond]CAr) MLCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2] and the pi(C[triple bond]CAr) --> d(pi)(Ru(III)) LMCT energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]+ corresponds to the intraligand pi pi* absorption energy for trans-[Ru(16-TMC or N2O2)(C[triple bond]CAr)2]. The crystal structure of trans-[Ru(dmpe)2{C[triple bond]C(C6H4C[triple bond]C)2Ph}2] shows that the two edges of the molecule are separated by 41.7 A. The electrochemical and spectroscopic properties of these complexes can be systematically tuned by modifying L4 and Ar to give E(1/2) values for oxidation of trans-[RuL4(C[triple bond]CAr)2] that span over 870 mV and lambda(max) values of trans-[RuL4(C[triple bond]CAr)2] that range from 19,230 to 31,750 cm(-1). The overall experimental findings suggest that the pi-back-bonding interaction in trans-[RuL4(C[triple bond]CAr)2] is weak and the [RuL4] moiety in these molecules may be considered to be playing a "dopant" role in a linear rigid pi-conjugated rod.

Probing the ruthenium-cumulene bonding interaction: synthesis and spectroscopic studies of vinylidene- and allenylidene-ruthenium complexes supported by tetradentate macrocyclic tertiary amine and comparisons with diphosphine analogues of ruthenium and osmium.

The synthesis and spectroscopic properties of trans-[Cl(16-TMC)Ru[double bond]C[double bond]CHR]PF(6) (16-TMC = 1,5,9,13-tetramethyl-1,5,9,13-tetraazacyclohexadecane, R = C(6)H(4)X-4, X = H (1), Cl (2), Me (3), OMe (4); R = CHPh(2) (5)), trans-[Cl(16-TMC)Ru[double bond]C[double bond]C[double bond]C(C(6)H(4)X-4)(2)]PF(6) (X = H (6), Cl (7), Me (8), OMe (9)), and trans-[Cl(dppm)(2)M[double bond]C[double bond]C[double bond]C(C(6)H(4)X-4)(2)]PF(6) (M = Ru, X = H (10), Cl (11), Me (12); M = Os, X = H (13), Cl (14), Me (15)) are described. The crystal structures of 1, 5, 6, and 8 show that the Ru-C(alpha) and C(alpha)-C(beta) distances of the allenylidene complexes fall between those of the vinylidene and acetylide relatives. Two reversible redox couples are observed by cyclic voltammetry for 6-9, with E(1/2) values ranging from -1.19 to -1.42 and 0.49 to 0.70 V vs Cp(2)Fe(+/0), and they are both 0.2-0.3 and 0.1-0.2 V more reducing than those for 10-12 and 13-15, respectively. The UV-vis spectra of the vinylidene complexes 1-4 are dominated by intense high-energy bands at lambda(max) < or = 310 nm (epsilon(max) > or = 10(4) dm(3) mol(-1) cm(-1)), while weak absorptions at lambda(max) > or = 400 nm (epsilon(max) < or = 10(2) dm(3) mol(-1) cm(-1)) are tentatively assigned to d-d transitions. The resonance Raman spectrum of 5 contains a nominal nu(C[double bond]C) stretch mode of the vinylidene ligand at 1629 cm(-1). The electronic absorption spectra of the allenylidene complexes 6-9 exhibit an intense absorption at lambda(max) = 479-513 nm (epsilon(max) = (2-3) x 10(4) dm(3) mol(-1) cm(-1)). Similar electronic absorption bands have been found for 10-12, but the lowest energy dipole-allowed transition is blue-shifted by 1530-1830 cm(-1) for the Os analogues 13-15. Ab initio calculations have been performed on the ground state of trans-[Cl(NH(3))(4)Ru[double bond]C[double bond]C[double bond]CPh(2)](+) at the MP2 level, and imply that the HOMO is not localized purely on the metal center or allenylidene ligand. The absorption band of 6 at lambda(max) = 479 nm has been probed by resonance Raman spectroscopy. Simulations of the absorption band and the resonance Raman intensities show that the nominal nu(C[double bond]C[double bond]C) stretch mode accounts for ca. 50% of the total vibrational reorganization energy, indicating that this absorption band is strongly coupled to the allenylidene moiety. The excited-state reorganization of the allenylidene ligand is accompanied by rearrangement of the Ru[double bond]C and Ru[bond]N (of 16-TMC) fragments, which supports the existence of bonding interaction between the metal and C[double bond]C[double bond]C unit in the electronic excited state.

Photoreactions of 3-diazo-3H-benzofuran-2-one; dimerization and hydrolysis of its primary photoproduct, a quinonoid cumulenone: a study by time-resolved optical and infrared spectroscopy.

Light-induced deazotization of 3-diazo-3H-benzofuran-2-one (1) in solution is accompanied by facile (CO)-O bond cleavage yielding 6-(oxoethenylidene)-2,4-cyclohexadien-1-one (3), which appears with a rise time of 28 ps. The expected Wolff-rearrangement product, 7-oxabicyclo[4.2.0]octa-1,3,5-trien-8-ylidenemethanone (4), is not formed. The efficient light-induced formation of the quinonoid cumulenone 3 opens the way to determine the reactivity of a cumulenone in solution. The reaction kinetics of 3 were monitored by nanosecond flash photolysis with optical (lambda(max) approximately 460 nm) as well as Raman (1526 cm(-1)) and IR detection (2050 cm(-)(1)). Remarkably, the reactivity of 3 is that expected from its valence isomer, the cyclic carbene 3H-benzofuran-2-one-3-ylidene, 2. In aqueous solution, acid-catalyzed addition of water forms the lactone 3-hydroxy-3H-benzofuran-2-one (5). The reaction is initiated by protonation of the cumulenone on its beta-carbon atom. In hexane, cumulenone 3 dimerizes to isoxindigo ((E)-[3,3']bibenzofuranylidene-2,2'-dione, 7), coumestan (6H-benzofuro[3,2-c][1]benzopyran-6-one, 8), and a small amount of dibenzonaphthyrone ([1]benzopyrano[4,3-][1]benzopyran-5,11-dione, 9) at a nearly diffusion-controlled rate. Ab initio calculations (G3) are consistent with the observed data. Carbene 2 is predicted to have a singlet ground state, which undergoes very facile, strongly exothermic (irreversible) ring opening to the cumulenone 3. The calculated barrier to formation of 4 (Wolff-rearrangement) is prohibitive. DFT calculations indicate that protonation of 3 on the beta-carbon is accompanied by cyclization to the protonated carbene 2H(+), and that dimerization of 3 to 7 and 9 takes place in a single step with negligible activation energy.

Metal-metal interactions in heterobimetallic d8-d10 complexes. Structures and spectroscopic investigation of [M'M' '(mu-dcpm)2(CN)2]+ (M' = Pt, Pd; M' ' = Cu, Ag, Au) and related complexes by UV-vis absorption and resonance Raman spectroscopy and ab initio calculations.

X-ray structural and spectroscopic properties of a series of heterodinuclear d(8)-d(10) metal complexes [M'M' '(mu-dcpm)(2)(CN)(2)](+) containing d(8) Pt(II), Pd(II), or Ni(II) and d(10) Au(I), Ag(I), or Cu(I) ions with a dcpm bridging ligand have been studied (dcpm = bis(dicyclohexylphosphino)methane; M' = Pt, M' ' = Au 4, Ag 5, Cu, 6; M' ' = Au, M' = Pd 7, Ni 8). X-ray crystal analyses showed that the metal...metal distances in these heteronuclear metal complexes are shorter than the sum of van der Waals radii of the M' and M' ' atoms. The UV-vis absorption spectra of 4-6 display red-shifted intense absorption bands from the absorption spectra of the mononuclear trans-[Pt(phosphine)(2)(CN)(2)] and [M' '(phosphine)(2)](+) counterparts, attributable to metal-metal interactions. The resonance Raman spectra confirmed assignments of (1)[nd(sigma)-->(n + 1)p(sigma)] electronic transitions to the absorption bands at 317 and 331 nm in 4 and 6, respectively. The results of theoretical calculations at the MP2 level reveal an attractive interaction energy curve for the skewed [trans-Pt(PH(3))(2)(CN)(2)-Au(PH(3))(2)(+)] dimer. The interaction energy of Pt(II)-Au(I) was calculated to be ca. 0.45 ev.

Transient resonance Raman and density functional theory investigation of the 4-acetamidophenylnitrenium ion.

This paper reports a transient resonance Raman and density functional theory study of the 4-acetamidophenylnitrenium ion in a mostly aqueous solvent. The transient Raman bands combined with results from density functional theory calculations indicate that the spectrum should be assigned to the singlet state of the 4-acetamidophenylnitrenium ion. The 4-acetamidophenylnitrenium ion was found to have a substantial iminocyclohexadienyl character comparable to previously studied para-phenyl-substituted phenylnitrenium ions and noticeable charge on both the acetamido and nitrenium moieties. The structure and properties of the 4-acetamidophenylnitrenium ion are compared to those of other arylnitrenium ions. We briefly discuss the chemical reactivity and selectivity of the para-acetamido-substituted phenylnitrenium ions compared to para-phenyl- or para-alkoxy-substituted phenylnitrenium ions.

Time-resolved resonance Raman and density functional study of an azirine intermediate in the 2-fluorenylnitrene ring-expansion reaction to form a dehydroazepine product.

We report time-resolved resonance Raman spectra for the azirine intermediate produced in the 2-fluorenylnitrene ring-expansion reaction to form a dehydroazepine product. The Raman bands obtained with a 252.7 nm probe wavelength and 500 ns delay time exhibit reasonable agreement with predicted vibrational frequencies from density functional calculations for two isomers of azirine intermediates that may be formed from a 2-fluorenylnitrene precursor. The Raman bands observed for delay times of 15 ns and 10 micros were consistent with predicted vibrational frequencies from density functional calculations for the 2-fluorenylnitrene and dehydroazepine product species as well as previously reported 416 nm time-resolved Raman spectra obtained on the ns and micros time scales. Our results demonstrate that the 2-fluorenylnitrene ring-expansion reaction to produce dehydroazepine products proceeds via relatively long-lived 2-fluorenylnitrene and azirine intermediates. Substitution of a phenyl ring para to the nitrene group of phenylnitrene appears to lead to significant changes in the ring-expansion reaction so that longer lived arylnitrene and azirine intermediates can be observed. This should enable the chemical reactivity of azirine intermediates formed from arylnitrenes to be examined more readily.

Metal-metal interactions in dinuclear d(8) metal cyanide complexes supported by phosphine ligands. Spectroscopic properties and ab initio calculations of [M(2)(mu-diphosphine)(2)(CN)(4)] and trans-[M(phosphine)(2)(CN)(2)] (M = Pt, Ni).

Structural, spectroscopic properties on the dinuclear [M(2)(dcpm)(2)(CN)(4)] (M = Pt, 1a; Ni, 2a, dcpm = bis(dicyclohexylphosphino)methane) and [M(2)(dmpm)(2)(CN)(4)] (M = Pt, 1b; Ni, 2b, dmpm = bis(dimethylphosphino)methane) and the mononuclear trans-[M(PCy(3))(2)(CN)(2)] (M = Pt, 3; Ni, 4, PCy(3) = tricyclohexylphosphine) and theoretical investigations on the corresponding model compounds are described. X-ray structural analyses reveal Pt.Pt and Ni.Ni distances of 3.0565(4)/3.189(1) A and 2.957(1)/3.209(8) A for 1a/1b and 2a/2b, respectively. The UV-vis absorption bands at 337 nm (epsilon 2.41 x 10(4) dm(3) mol(-)(1) cm(-)(1)) for 1a and 328 nm (epsilon 2.43 x 10(4) dm(3) mol(-)(1) cm(-)(1)) for 1b in CH(2)Cl(2) are assigned to (1)(5d(sigma) --> 6p(sigma)) electronic transitions originating from Pt(II)-Pt(II) interactions. Resonance Raman spectroscopy of 1a, in which all the Raman intensity appears in the Pt-Pt stretch fundamental (93 cm(-)(1)) and overtone bands, verifies this metal-metal interaction. Complexes 1a and 1b exhibit photoluminescence in the solid state and solution. For the dinuclear nickel(II) complexes 2a and 2b, neither spectroscopic data nor theoretical calculation suggests the presence of Ni(II)-Ni(II) interactions. The intense absorption bands at lambda > 320 nm in the UV-vis spectra of 2a and 2b are tentatively assigned to d --> d transitions.

Time-resolved resonance Raman spectroscopy and density functional study of 2-fluorenylnitrene and its dehydroazepine products.

We report time-resolved resonance Raman spectra for 2-fluorenylnitrene and its dehydroazepine products acquired after photolysis of 2-fluorenylnitrene in acetonitrile. The experimental Raman band frequencies exhibit good agreement with the calculated vibrational frequencies from UBPW91/cc-PVDZ density functional calculations for the singlet and triplet states of the 2-fluorenylnitrene as well as BPW91/cc-PVDZ calculations for the two dehydroazepine ring-expansion product species. The decay of the 2-fluorenylnitrene Raman signal and the appearance of the dehydroazepine products suggest the presence of an intermediate species (probably an azirine) that does not absorb very much at the 416 nm probe wavelength used in the time-resolved resonance Raman experiments. Comparison of the singlet 2-fluorenylnitrene species with the singlet 2-fluorenylnitrenium ion species indicates that protonation of the nitrene to give the nitrenium ion leads to a significant enhancement of the cyclohexadienyl character of the phenyl rings without much change of the C-N bond length.

Electronic excited states of [Au(2)(dmpm)(3)](ClO(4))(2) (dmpm= bis(dimethylphosphine)methane).

We present studies of the resonance Raman and electronic luminescence spectra of the [Au(2)(dmpm)(3)](ClO(4))(2) (dmpm = bis(dimethylphosphine)methane) complex, including excitation into an intense band at 256 nm and into a weaker absorption system centered about approximately 300 nm. The resonance Raman spectra confirm the assignment of the 256 nm absorption band to a (1)(dsigma --> psigma) transition, a metal-metal-localized transition, in that nu(Au-Au) and overtones of it are strongly enhanced. A resonance Raman intensity analysis of the spectra associated with the 256 nm absorption band gives the ground-state and excited-state nu(Au-Au) stretching frequencies to be 79 and 165 cm(-1), respectively, and the excited-state Au-Au distance is calculated to decrease by about 0.1 A from the ground-state value of 3.05 A. The approximately 300 nm absorption displays a different enhancement pattern, in that resonance-enhanced Raman bands are observed at 103 and 183 cm(-1) in addition to nu(Au-Au) at 79 cm(-1) The compound exhibits intense, long-lived luminescence (in room-temperature CH(3)CN, for example, tau = 0.70 micros, phi(emission) = 0.037) with a maximum at 550-600 nm that is not very medium-sensitive. We conclude, in agreement with an earlier proposal of Mason (Inorg. Chem. 1989, 28, 4366-4369), that the lowest-energy, luminescent excited state is not (3)(dsigma --> psigma) but instead derives from (3)(d(x2-y2,xy --> psigma) excitations. We compare the Au(I)-Au(I) interaction shown in the various transitions of the [Au(2)(dmpm)(3)](ClO(4))(2) tribridged compound with previous results for solvent or counterion exciplexes of [Au(2)(dcpm)(2)](2+) salts (J. Am. Chem. Soc. 1999, 121, 4799-4803; Angew. Chem. 1999, 38, 2783-2785; Chem. Eur. J. 2001, 7, 4656-4664) and for planar, mononuclear Au(I) triphosphine complexes. It is proposed that the luminescent state in all of these cases is very similar in electronic nature.

Transient resonance Raman and density functional theory investigation of the chlorine atom/carbon disulfide molecular complex involved in selective alkane photochlorination reactions.

The structure and bonding of the chlorine atom/carbon disulfide (CS(2)/Cl) complex involved in selective photochlorination reactions with alkanes was directly probed using transient resonance Raman spectroscopy. The experimental Raman vibrational frequencies were compared to those computed from density functional theory calculations for probable structures of the CS(2)/Cl complex. Our results indicate that the S [double bond] C [double bond] S...Cl complex species is responsible for the approximately 370 nm transient absorption band observed after ultraviolet photolysis of CCl(4) in the presence of CS(2). We discuss the structure and properties of the S [double bond] C [double bond] S...Cl complex and compare them with those for the related benzene/Cl and pyridine/Cl complexes.