Synthesis, Structure, and Reactivity of Ruthenium Carboxylato and 2-Oxocarboxylato Complexes Bearing the Bis(3,5-dimethylpyrazol-1-yl)acetato Ligand

Phosphine-functionalised tris(pyrazolyl)methane ligands and their mono- and heterobimetallic complexes

The synthesis, characterisation and reactivity of new phosphine-functionalised tris(pyrazolyl)methane ligands (TpmPR₂, 2a-c, with R = Ph, nBu, iPr) are presented. The reaction of 2a-c with [Rh(CO)₂Cl]₂ furnished N,P-heterochelate carbonyl complexes (3a-c), which were used to quantify the donor abilities of the ligands via IR spectroscopy. The coordination flexibility was demonstrated by treating representative members of this new ligand class with [CpRu(acn)₃][PF₆] (acn = acetonitrile), [(tht)AuCl] (tht = tetrahydrothiophene) and [Pd(allyl)Cl]₂ providing either a N,N,P-heteroscorpionate complex (4) or the P-coordinated complexes (5,6) without any involvement of the pyrazolyl entities. With 2a and [Pd(cod)Cl₂], another P,N-heterochelate complex (7) was obtained, which served as a precursor for a heterobimetallic complex containing palladium and copper (8). Detailed NMR spectroscopic and X-ray crystallographic investigations have been performed on all new complexes.

Computation provides chemical insight into the diverse hydride NMR chemical shifts of [Ru(NHC)4(L)H]0/+ species (NHC = N-heterocyclic carbene; L = vacant, H2, N2, CO, MeCN, O2, P4, SO2, H-, F- and Cl-) and their [Ru(R2PCH2CH2PR2)2(L)H]+ congeners

Relativistic density functional theory calculations, both with and without the effects of spin-orbit coupling, have been employed to model hydride NMR chemical shifts for a series of [Ru(NHC)₄(L)H]^0/+ species (NHC = N-heterocyclic carbene; L = vacant, H₂, N₂, CO, MeCN, O₂, P₄, SO₂, H^-, F^- and Cl^-), as well as selected phosphine analogues [Ru(R₂PCH₂CH₂PR₂)₂(L)H]⁺ (R = ⁱPr, Cy; L = vacant, O₂). Inclusion of spin-orbit coupling provides good agreement with the experimental data. For the NHC systems large variations in hydride chemical shift are shown to arise from the paramagnetic term, with high net shielding (L = vacant, Cl^-, F^-) being reinforced by the contribution from spin-orbit coupling. Natural chemical shift analysis highlights the major orbital contributions to the paramagnetic term and rationalizes trends via changes in the energies of the occupied Ru d_π orbitals and the unoccupied σ*_Ru-H orbital. In [Ru(NHC)₄(η²-O₂)H]⁺ a δ-interaction with the O₂ ligand results in a low-lying LUMO of d_π character. As a result this orbital can no longer contribute to the paramagnetic shielding, but instead provides additional deshielding via overlap with the remaining (occupied) d_π orbital under the L_z angular momentum operator. These two effects account for the unusual hydride chemical shift of +4.8 ppm observed experimentally for this species. Calculations reproduce hydride chemical shift data observed for [Ru(ⁱPr₂PCH₂CH₂PⁱPr₂)₂(η²-O₂)H]⁺ (δ = -6.2 ppm) and [Ru(R₂PCH₂CH₂PR₂)₂H]⁺ (ca. -32 ppm, R = ⁱPr, Cy). For the latter, the presence of a weak agostic interaction trans to the hydride ligand is significant, as in its absence (R = Me) calculations predict a chemical shift of -41 ppm, similar to the [Ru(NHC)₄H]⁺ analogues. Depending on the strength of the agostic interaction a variation of up to 18 ppm in hydride chemical shift is possible and this factor (that is not necessarily readily detected experimentally) can aid in the interpretation of hydride chemical shift data for nominally unsaturated hydride-containing species. The synthesis and crystallographic characterization of the BAr^F₄^- salts of [Ru(IMe₄)₄(L)H]⁺ (IMe₄ = 1,3,4,5-tetramethylimidazol-2-ylidene; L = P₄, SO₂; Ar^F = 3,5-(CF₃)₂C₆H₃) and [Ru(IMe₄)₄(Cl)H] are also reported.

Development of ruthenium-based complexes as anticancer agents: toward a rational design of alternative receptor targets

In the search for novel anticancer agents, the development of metal-based complexes that could serve as alternatives to cisplatin and its derivatives has received considerable attention in recent years. This becomes necessary because, at present, cisplatin and its derivatives are the only coordination complexes being used as anticancer agents in spite of inherent serious side effects and their limitation against metastasized platinum-resistant cancer cells. Although many metal ions have been considered as possible alternatives to cisplatin, the most promising are ruthenium (Ru) complexes and two Ru compounds, KP1019 and NAMI-A, which are currently in phase II clinical trials. The major obstacle against the rational design of these compounds is the fact that their mode of action in relation to their therapeutic activities and selectivity is not fully understood. There is an urgent need to develop novel metal-based anticancer agents, especially Ru-based compounds, with known mechanism of actions, probable targets, and pharmacodynamic activity. In this paper, we review the current efforts in developing metal-based anticancer agents based on promising Ru complexes and the development of compounds targeting receptors and then examine the future prospects.

Experimental and theoretical investigation of the spectroscopic and electronic properties of pyrazolyl ligands

The electronic and spectroscopic properties of seven pyrazole derivatives are presented in order to give a clear understanding of their distinguishing features. Four out of the seven ligands are synthesised and are also characterised experimentally. A very high correlation was observed between the experimental and the theoretical IR, (1)H NMR and (13)C NMR, which help in the characterisation of the ligands. The excitation properties computed using the TDDFT shows that most of experimentally observed absorptions of the ligands are predominantly form either the HOMO or HOMO-1 to LUMO or LUMO+1. The characteristic features of the (*)N atoms (i.e. metal available coordinating centre) shows that the carboxylic unit may possibly decrease the metal affinity of the pyrazole unit while the pyridine unit will increase the affinity. The conductivity properties of the seven ligands are found to be in the order of bdmpzpy>bpzpy>bphpza>bdcpzpy>phpz>dcpz. The J-coupling of (*)NN can give an insight into the variation in their bond distance, bond stretch and bond strength in the ligands. Also the atomic properties of the (*)N atoms and their (*)NN bonds can help in the molecular characterisation, differentiation and in prediction of the non-linear optical properties of the ligands as conductive materials.

Transition metal complexes bearing a 2,2-bis(3,5-dimethylpyrazol-1-yl)propionate ligand: one methyl more matters

The new N,N,O ligand 2,2-bis(3,5-dimethylpyrazol-1-yl)propionic acid (2,2-Hbdmpzp) (2) and its transition metal complexes [Mn(2,2-bdmpzp)(CO)(3)] (3), [Re(2,2-bdmpzp)(CO)(3)] (4), [Cu(2,2-bdmpzp)(2)] (5), and [Ru(2,2-bdmpzp)Cl(L)(PPh(3))] [L = PPh(3) (6), N(2) (7), CO (8a/b), SO(2) (9a/b)] have been synthesized, characterized and compared to analogous complexes bearing a bis(3,5-dimethylpyrazol-1-yl)acetic acid. It was found that the additional methyl group has a remarkable influence on the stability and reactivity of transition metal complexes.