Ligand and metal-centred reactivity in 2,6-bis(imino)-1,4-dihydropyridinate Zn(II) alkyls: the dual behaviour of an intriguing type of complex.

Dihydropyridines, either free or metal-coordinated, are organic hydride transfer reductants that perform on the same premises as the natural redox cofactor NAD(P)+/NAD(P)H. 1-Bn and 1-Me are alkylzinc complexes containing dihydropyridinate-based pincer ligands that have been synthesized through different routes involving the addition of ZnR2 (R = Bn, Me) to the 2,6-bis(imino)-pyridine and 2,6-bis(imino)-4-Bn-dihydropyridine (iPrBIP and 4-BniPrBIPH2) ligands, respectively. The alkyls complexes 1-R react with fluorinated alcohols RFOH (RF = C6F5 or t-C4F9) yielding isolable fluoroalkoxides 2-F5 and 2-F9, in which the reactive 1,4-dihydropyridinate ligand remains unchanged. The crystal structure of 2-F5 shows the shortest Zn⋯F-C interaction reported so far, involving one of the o-F atoms of the C6F5 group. However, the mechanism of the alcoholysis reactions is not straightforward, as NMR monitoring revealed that acidic RFOH first protonates the dihydropyridine nitrogen, releasing the dihydropyridine base 4-BniPrBIPH2 and a highly reactive Zn(R)(ORF) species that re-captures the dihydropyridine in a subsequent step, eliminating the corresponding alkane (R-H). Depending on the mixing conditions, the pincer dihydropyridinate ligand may undergo aromatization to produce the new Zn(II) dialkoxides 3-F5 and 3-F9 stabilised by a neutral iPrBIP ligand [(4R-iPrBIP)Zn(ORF)2]. These protonation and hydride transfer reactions illustrate the dual reactivity of the pincer 1,4-dihydropyridinate zinc entity.

Zwitterionic amidinates as effective ligands for platinum nanoparticle hydrogenation catalysts.

Ligand control of metal nanoparticles (MNPs) is rapidly gaining importance as ligands can stabilize the MNPs and regulate their catalytic properties. Herein we report the first example of Pt NPs ligated by imidazolium-amidinate ligands that bind strongly through the amidinate anion to the platinum surface atoms. The binding was established by 15N NMR spectroscopy, a precedent for nitrogen ligands on MNPs, and XPS. Both monodentate and bidentate coordination modes were found. DFT showed a high bonding energy of up to -48 kcal mol-1 for bidentate bonding to two adjacent metal atoms, which decreased to -28 ± 4 kcal mol-1 for monodentate bonding in the absence of impediments by other ligands. While the surface is densely covered with ligands, both IR and 13C MAS NMR spectra proved the adsorption of CO on the surface and thus the availability of sites for catalysis. A particle size dependent Knight shift was observed in the 13C MAS NMR spectra for the atoms that coordinate to the surface, but for small particles, ∼1.2 nm, it almost vanished, as theory for MNPs predicts; this had not been experimentally verified before. The Pt NPs were found to be catalysts for the hydrogenation of ketones and a notable ligand effect was observed in the hydrogenation of electron-poor carbonyl groups. The catalytic activity is influenced by remote electron donor/acceptor groups introduced in the aryl-N-substituents of the amidinates; p-anisyl groups on the ligand gave catalysts several times faster the ligand containing p-chlorophenyl groups.

A betaine adduct of N-heterocyclic carbene and carbodiimide, an efficient ligand to produce ultra-small ruthenium nanoparticles.

The betaine adduct of N-heterocyclic carbene and carbodiimide (ICy·((p-tol))NCN) was found to be a very efficient ligand to prepare very small (1-1.3 nm) ruthenium nanoparticles (RuNPs). The coordination of the ligand on the metal surface takes place through the carbodiimide moiety. The resulting RuNPs led to decarbonylation of THF and showed size selectivity for styrene hydrogenation.

Synthesis and insertion reactions of the cyclometalated palladium-alkyl complexes Pd(CH(2)CMe(2)-o-C(6)H(4))L(2). Observation of a pentacoordinated intermediate in the insertion of SO(2).

Palladacycles of the type 2, have been synthesized by treatment of the corresponding chloroalkylcomplexes Pd(CH(2)CMe(2)C(6)H(5))ClL(2) (L(2) = (PMe(3))(2), 2a, or 1,5-cyclooctadiene (cod), 2b) with suitable bases, or by simple ligand exchange reactions from the cyclooctadiene derivative 2b. The metallacycles 2 react with activated alkynes and with sulfur dioxide, giving rise to different insertion products.

P-glycoprotein, metallothionein and NM23 protein expressions in breast carcinoma.

Cellular drug resistance and increased metastatic potential are the major obstacles in the successful treatment of cancer with chemotherapy. The aim of this study was to investigate whether the immunohistochemical expression of two proteins implicated in drug resistance (P-glycoprotein and metallothionein) and the product of the suppressor gene nm23 could be related to prognosis in breast cancer. Seventy-two patients with palpable or occult breast carcinoma, not treated with chemotherapy or endocrine therapy, were examined. Immunohistochemical methods were used to determine the expression of P-glycoprotein (PG), metallothionein (MT), nm23, as well as the estrogen receptor (ER), the p53 status, and the Ki67 index. The results were correlated with clinical and morphological features. Cytoplasmic and membrane-specific immunostainings of PG were seen exclusively in tumor cells and identified in 14 of 72 cases (19.4%). Only a statistically significant association with metastases, (p = 0.06) and recurrences (p = 0.1) was observed. MT-positive reaction was identified in the cytoplasm of the tumor cells in 47 (65.3%) cases. Statistical significance was associated with metastases (p = 0.07), but not with death or recurrences. Specific immunostaining of nm23 protein was seen only in the cytoplasm of tumor cells. A positive reaction was observed in 55 of 72 (89.3%) cases. Although a significant association between nm23 protein expression and other morphologic and immunohistochemical variables did not exist, we observed a higher morbidity in patients with the MT-positive/nm23-negative tumor phenotype. Univariate analysis for survival selected the following variables: histologic grade (p = 0.001), ER (p = 0.002), mitotic index (p = 0.005), Ki 67 index (p = 0.068), MT (p = 0.046) and PG (p = 0.085). The Cox model provided the following independent variables: histologic grade (p = 0.021) and metallothionein (p = 0.03). These data confirm the prognosis observed in patients with PG or metallothionein expression as well as the independence of these two variables. It also suggests that nm23 is not necessarily involved in the development of an invasive phenotype.