Electron-Triggered Imine Coupling: Synthesis and Characterization of Three Redox States (0,-1,-2) of a Ni(N2 S2 ) Complex.

Metal imine-thiolate complexes, M(NS)2 are known to undergo imine C-C bond formation to give M(N2 S2 ) complexes (M=Co, Ni) containing a redox-active ligand. Although these transfor-mations are not typically quantitative, we demonstrate here that the one-electron reduction of a related Ni bis(imine-thiolate) complex affords the corresponding paramagnetic [Ni(N2 S2 )]- anion (2⋅- ) exclusively; subsequent oxidation with [Cp2 Fe]BF4 then affords a high yield of neutral 2 (Cp=η5 -cyclopentadienyl). Moreover, electrochemical studies indicate that a second one-electron reduction affords the diamagnetic dianion. Both anionic products were isolated and characterized by SC-XRD and their electronic structures were investigated by UV-vis spectro-electrochemistry, EPR and NMR spectroscopy, and DFT studies. These studies show that reduction proceeds primarily on the ligand, with (N2 S2 )4- containing both thiolate and ring-delocalized anions.

Cytotoxicity, anti-tumor effects and structure-activity relationships of nickel and palladium S,C,S pincer complexes against double and triple-positive and triple-negative breast cancer (TNBC) cells.

Triple-Negative Breast Cancer (TNBC) is a highly aggressive form of breast cancer. The high rate of metastasis associated with TNBC is attributed to its multidrug resistance, making the treatment of this metastatic condition difficult. The development of metal-based antitumor agents was launched with the discovery of cisplatin, followed by the development of related antitumor drugs such as carboplatin and oxaliplatin. Yet, the severe side effects of this approach represent a limitation for its clinical use. The current search for new metal-based antitumor agents possessing less severe side effects than these platinum-based complexes has focused on various complexes of nickel and palladium, the group 10 congeners of platinum. In this work, we have prepared a series of SCS-type pincer complexes of nickel and palladium featuring a stable meta-phenylene central moiety and two chelating but labile thioamide donor moieties at the peripheries of the ligand. We have demonstrated that the complexes in question, namely L1NiCl, L1NiBr, L1PdCl, L2PdCl, and L3PdCl, are active on the proliferation of estrogen-dependent breast tumor cells (MCF-7 and MC4L2) and triple-negative breast cancer (4 T1). Among the complexes studied, the palladium derivatives were found to be much safer anticancer agents than nickel counterparts; these were thus selected for further investigations for their effects on tumor cell adhesion and migration as well. The results of our studies show that palladium complexes are effective for inhibiting TNBC 4 T1 cells adhesion and migration. Finally, the HOMO and LUMO analysis was used to determine the reactivity and charge transfer within the compounds.

Reactivities of cyclonickellated complexes with hydroxylamines: formation of κO-hydroxylamine and κN-imine adducts and a κO, κN-aminoxide derivative.

This report discusses the reactivities of hydroxylamines with a family of nickellacyclic complexes prepared by C-H nickellation of aryl phosphinites. Treating the dimeric complexes κC,κP-{2-OPR2,4-R'-C6H4}2Ni2(µ-Br)2 (R = i-Pr; R' = H, Cl, OMe, NMe2) or their monomeric acetonitrile adducts κC,κP-{2-OPR2,4-R'-C6H4}Ni(Br)(NCMe) with hydroxylamines showed three types of reactivities depending on the Ni complex, the reaction solvent, and the substrate used: (1) the benzyl-protected substrate PhCH2ONH2 gave simple N-bound adducts with all Ni complexes; (2) the parent Ni dimer (R' = H) reacted with Et2NOH and (PhCH2)2NOH in CH2Cl2 to give, respectively, the zwitterionic amine oxide κC,κP-{2-OPR2-C6H5}Ni(κO-ONHEt2)Br and the bidentate aminoxide (i-R2POPh)Ni{κO,κN-ON(CH2Ph)2}Br; (3) the analogous reaction of substituted Ni complexes (R' = Cl, OMe, NMe2) with hydroxylamines in acetonitrile gave adducts of imines derived from dehydration of Et2NOH and (PhCH2)2NOH. The latter reactivity proceeds optimally in acetonitrile, but it also occurs to a lesser extent in C6D6 if the reaction is allowed to go for more than 24 h. Different mechanistic scenarios have been considered to rationalize the observed hydroxylamine → imine transformation.

Coinage metal amido and thiolate SNS complexes: consequences of catalyst speciation in Cu(I)-catalysed carbonyl hydroboration.

Three new IPr-Ag- and -Au-SNS amido and thiolate complexes were synthesized and compared to their previously reported Cu analogues as carbonyl hydroboration catalysts (IPr = bis(2,6-diisopropylphenyl)imidazol-2-ylidene). Although these complexes showed no catalytic activity, treatment of the IPr-Ag-SNS amido complex with pinacolborane released the N-borylated ligand, SMeNBpinSMe, (L1-Bpin). This finding led us to reinvestigate the IPr-Cu-SNS amido precatalyst, revealing that immediate loss of L1-Bpin converts our catalyst system to [CuH(IPr)]2.

Correction: C-H nickellation of phenol-derived phosphinites: regioselectivity and structures of cyclonickellated complexes.

Correction for 'C-H nickellation of phenol-derived phosphinites: regioselectivity and structures of cyclonickellated complexes' by Loïc P. Mangin et al., Dalton Trans., 2017, 46, 16159-16170, DOI: 10.1039/C7DT03403B.

C-H nickellation of phenol-derived phosphinites: regioselectivity and structures of cyclonickellated complexes.

This report describes the results of a study on the ortho-C-H nickellation of the aryl phosphinites i-Pr2P(OAr) derived from the following four groups of substituted phenols: 3-R-C6H4OH (R = F (b), Me (c), MeO (d), Cl (e)); 3,5-R2-C6H3OH (R = F (f), Me (g), Cl (h), OMe (i)); 2-R-C6H4OH (R = Me (j), Ph(k)); and 2,6-R2-C6H3OH (R = Me (l), Ph (m)). No nickellation was observed with the phosphinites derived from the 3,5-disubstituted phenols g and h, and the 2,6-disubstituted phenols l and m; in all other cases nickellation occurred at an ortho-C-H to generate either the Br-bridged dimers [{κP,κC-(i-Pr)2POAr}Ni(µ-Br)]2 (1b-1f, 1j, and 1k) or the monomeric acetonitrile adduct {κP,κC-ArOP(i-Pr)2}Ni(Br)(NCMe) (1i-NCMe). Analysis of C-H nickellation regioselectivity with 3-R-C6H4OH pointed to the importance of substituent sterics, not electronics: nickellation occurred at the least hindered position either exclusively (for R = Me (c), MeO(d), and Cl (e)) or predominantly (for R = F (b); 6 : 1). This conclusion is also consistent with the observation that C-H nickellation is possible with the 3,5-disubstituted aryl phosphinites bearing F and OMe, but not with the more bulky substituents Me or Cl. For the 2-substituted aryl phosphinites, C-H nickellation occurs at the unsubstituted ortho-C-H and not on the R substituent, regardless of whether the alternative C-H moiety of the substituent is sp3 (R = Me (j)) or sp2 (R = Ph (k)). The system thus reveals a strong preference for formation of 5-membered metallacycles. Consistent with this reactivity, no nickellation occurs with (2,6-R2-C6H3O)P(i-Pr)2. Tests with the parent dimer derived from i-Pr2P(OPh) showed that conversion to the monomeric acetonitrile adduct is highly favored, going to completion with only a small excess of MeCN. All new cyclonickellated complexes reported in this study were fully characterized, including by single crystal X-ray diffraction studies. The solid state structures of the dimers 1b and 1d showed an unexpected feature: two halves of the dimers displayed non-coplanar conformations that place the two Ni(ii) centers at shortened distances from each other (2.94-3.16 Å). Geometry optimization studies using DFT have shown that such non-coplanar conformations stabilize the complex, implying that the "bending" observed in these complexes is not caused by packing forces. Indeed, it appears that the occurrence of coplanar conformations in the solid state structures of these dimers is a simple consequence of packing forces rather than an intrinsic property of the compound.

Manganese-mediated synthesis of an NHC core non-symmetric pincer ligand and evaluation of its coordination properties.

The alkylation of N-(2-pyridyl)imidazole by the MnI methylene-phosphonium complex [Cp(CO)2Mn(η2-P,C-Ph2P[double bond, length as m-dash]C(H)Ph)]BF4 offers a straightforward route to a tridentate pro-ligand featuring an NHC core and phosphine/pyridine arms. The ability of this PCN ligand to coordinate in a pincer mode was recognized in RhI, RhIII, and NiII complexes.