Phosphine Substitution in Indenyl- and Cyclopentadienylruthenium Complexes. Effect of the η5 Ligand in a Dissociative Pathway

Phosphine substitution and linkage isomerization in cyclopentadienylruthenium bis(triphenylphosphine)thiocyanide and selenocyanide, CpRu(PPh3)2NCS and CpRu(PPh3)2SeCN

The reaction between CpRu(PPh3)2NCS (1a) and PMePh2 yields CpRu(PPh3)(PMePh2)NCS (2a) while CpRu(PPh3)(PMePh2)Cl reacts with SCN- to form the S-bonded isomer, CpRu(PPh3)(PMePh2)SCN (2b). Compound 1a and the linkage isomers of 2 were characterized by X-ray crystallography. The kinetics of the reaction between 1a and PMePh2 under pseudo-first order conditions in THF and in fluorobenzene to form 2a are consistent with a dissociative interchange mechanism. Activation parameters for the reaction are: ΔH† = 15.7 ± 0.6 kcal mol-1 and ΔS† = -35 ± 2 cal mol-1 K-1 in THF vs. ΔH† = 24.8 ± 1.2 kcal mol-1 and ΔS† = -6 ± 4 cal mol-1 K-1 in C6H5F. In the presence of added SCN-, the rate of phosphine substitution is unchanged but a mixture of 2a and 2b is observed. The selenocyanate derivative, CpRu(PPh3)2SeCN (3b), crystallizes as the Se-bonded linkage isomer. Compound 3b reacts with PMePh2 under pseudo-first order conditions in fluorobenzene to form CpRu(PPh3)(PMePh2)SeCN (4b) at a much faster rate than 1a with activation parameters: ΔH† = 30.9 ± 4.8 kcal mol-1 and ΔS† = 22.4 ± 15.9 cal mol-1 K-1 with no evidence for linkage isomerization to the N-bonded products.

Explaining the High Catalytic Activity in Bis(indenyl)methyl Zirconium Cation Using Combined EDA-NOCV/QTAIM Approach

The main purpose of this study is to elucidate some discrepancies already observed in the catalytic activity values of some zirconocene methyl cations. The EDA-NOCV scheme was employed for a theoretical description of the interactions between an ethylene molecule and five catalysts of zirconocene methyl cation. The nature of the chemical interactions has been elucidated through the QTAIM topological analysis. The steric hindrance due to the ligands was evaluated qualitatively by means of an IRI-based analysis and quantitively through Fisher information. The findings prove that the indenyl ligand seems to favor the orbital interaction between the ethylene molecule and the metal centre of zirconocene methyl cation. Both electrostatic and orbital contributions play a crucial role in stabilising the studied complexes. Based on the NOCV deformation density contributions, the strongest orbital interaction is reached with the bis(indenyl)methyl zirconium cation, which is the only one exhibiting covalent interactions. Especially, the strong contribution of π-back donation (occurring from the occupied orbitals of the zirconium atom to the π* anti-bonding orbital of ethylene) may be a key to understand why this catalyst has a higher polymerisation yield than the other studied catalysts. This work suggests a perspective for predicting values of catalytic activity when theoretically designing novel catalysts of zirconocene type.

Transition metals induce control of enhanced NLO properties of functionalized organometallic complexes under laser modulations

The molecular engineering of organometallic complexes has recently attracted renewed interest on account of their potential technological applications for optoelectronics in general and optical data storage. The transition metal which induces control of enhanced nonlinear optical properties of functionalized organometallic complexes versus not only the intensity but also the polarization of the incident laser beam is original and important for all optical switching. This makes organometallic complexes valuable and suitable candidates for nonlinear optical applications. In the present work, we report the synthesis and full characterization of four organometallic complexes consisting of N, N-dibutylamine and azobenzene fragments but differ by auxiliary alkynyl ligands or metal cations. Thus, a ferrocenyl derivative 1 and three ruthenium complexes 2-4 have been prepared. The nonlinear optical properties of the four new azo-based ruthenium and iron organometallic complexes in the solid state, using polymethylmethacrylate as matrix, have been thoroughly studied. This concept is extended to computing the HOMO and LUMO energy levels of the considered complexes, dipole moment, first and second order hyperpolarizabilities using the 6-31 + G(d,p) + LANL2DZ mixed basis set. The second and third nonlinear optical properties of the resulting polymer composites were obtained by measuring SHG and THG response by means of the Maker fringe technique using a laser generating at 1,064 nm with a 30 ps pulse duration. The values of the second and third order NLO susceptibilities of the four organometallic complexes were found to be higher than the common references used. Theoretical calculation shows that the large first and second order hyperpolarizablities are caused by strong intramolecular charge transfer between the transition metal parts and the ligands though a conjugated transmitter. These results indicate that the present organometallic complexes are valuable candidates for optoelectronic and photonic applications.

Kinetics of phosphine substitution in CpRu(PPh3)2X (X = Cl, Br, I, N3, and NCO)

The kinetics of phosphine substitution in CpRu(PPh₃)₂X (X = Cl, Br, I, N₃, and NCO) is consistent with a dissociative mechanism. The complexes react with chloroform to yield CpRu(PPh₃)₂Cl by a mechanism that involves phosphine loss.

Phosphine substitution reactions of (η5-cyclopentadienyl)ruthenium bis(triarylphosphine) chloride, CpRu(PAr3)2Cl {PAr3 = PPh3, P(p-CH3C6H4)3, P(p-FC6H4)3, P(p-CH3OC6H4)3, and PPh2(p-CH3C6H4)}: a tale of two mechanisms

The kinetics of phosphine substitution in CpRu(PAr3)2Cl by PMePh2 under pseudo-first order conditions in CDCl3 have been measured for PAr3 = PPh3, 1a, PPh2(p-tol), 1b, P(p-tol)3, 1c, P(p-CH3OC6H4)3, 1d, and P(p-FC6H4)3), 1e. Activation parameters characteristic of a dissociative pathway (ΔH(†) = 110-124 ± 2 kJ mol(-1), ΔS(†) = 16-44 ± 5-12 J mol(-1) K(-1)) are observed for all five compounds. The rate of substitution in CpRu(PAr3)2Cl (1a) and CpRu[P(p-FC6H4)3]2Cl (1e) is independent of added chloride ion and decreases in the presence of excess PAr3, however, the rate of substitution in CpRu[P(p-CH3OC6H4)3]2Cl (1d) is first order in added chloride ion and is less dependent on added PAr3. A mechanism involving [CpRu(PAr3)2(PMePh2)](+)[Cl](-) intermediates contributes to the substitution in 1b-d.

Spontaneous formation in the dark, and visible light-induced cleavage, of a Ru-S bond in water: a thermodynamic and kinetic study

In this work the thermal and photochemical reactivity of a series of ruthenium complexes [Ru(terpy)(N-N)(L)](X)2 (terpy = 2,2';6',2″-terpyridine, L = 2-(methylthio)ethanol (Hmte) or water, and X is Cl(-) or PF6(-)) with four different bidentate chelates N-N = bpy (2,2'-bipyridine), biq (2,2'-biquinoline), dcbpy (6,6'-dichloro-2,2'-bipyridine), or dmbpy (6,6'-dimethyl-2,2'-bipyridine), is described. For each chelate N-N the thermodynamic constant of the dark equilibrium between the aqua- and Hmte- complexes, the Hmte photosubstitution quantum yield, and the rate constants of the thermal interconversion between the aqua and Hmte complexes were measured at room temperature. By changing the steric hindrance and electronic properties of the spectator N-N ligand along the series bpy, biq, dcbpy, dmbpy the dark reactivity clearly shifts from a nonlabile equilibrium with N-N = bpy to a very labile thermal equilibrium with N-N = dmbpy. According to variable-temperature rate constant measurements in the dark near pH = 7 the activation enthalpies for the thermal substitution of H2O by Hmte are comparable for all ruthenium complexes, whereas the activation entropies are negative for bpy and biq, and positive for dcbpy and dmbpy complexes. These data are indicative of a change in the substitution mechanism, being interchange associative with nonhindered or poorly hindered chelates (bpy, biq), and interchange dissociative for more bulky ligands (dcbpy, dmbpy). For the most labile dmbpy system, the thermal equilibrium is too fast to allow significant modification of the composition of the mixture using light, and for the nonhindered bpy complex the photosubstitution of Hmte by H2O is possible but thermal binding of Hmte to the aqua complex does not occur at room temperature. By contrast, with N-N = biq or dcbpy the thermodynamic and kinetic parameters describing the formation and breakage of the Ru-S bond lie in a range where the bond forms spontaneously in the dark, but is efficiently cleaved under light irradiation. Thus, the ratio between the aqua and Hmte complex in solution can be efficiently controlled at room temperature using visible light irradiation.

Dicarba-closo-dodecarborane-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium: biological relevance and synthetic strategies

This review describes how the incorporation of dicarba-closo-dodecarboranes into half-sandwich complexes of ruthenium, osmium, rhodium and iridium might lead to the development of a new class of compounds with applications in medicine. Such a combination not only has unexplored potential in traditional areas such as Boron Neutron Capture Therapy agents, but also as pharmacophores for the targeting of biologically important proteins and the development of targeted drugs. The synthetic pathways used for the syntheses of dicarba-closo-dodecarboranes-containing half-sandwich complexes of ruthenium, osmium, rhodium and iridium are also reviewed. Complexes with a wide variety of geometries and characteristics can be prepared. Examples of addition reactions on the metal centre, B-H activation, transmetalation reactions and/or direct formation of metal-metal bonds are discussed (103 references).