Syntheses ofN-(Diphenylphosphanyl)-2-pyridylmethylamine and Its Use as a Ligand in Magnesium and Zinc Complexes

Lithium, Magnesium, and Zinc Centers N,N'-Chelated by an Amine-Amide Hybrid Ligand

The synthesis and structure of lithium, magnesium, and zinc complexes N,N'-chelated by a hybrid amine-amido ligand ([2-(Me₂NCH₂)C₆H₄NR]^-, abbreviated as L^NR, where R = H, SiMe₃, or Bn) are reported. The reaction of the least sterically demanding L^NH with various magnesium sources gives the hexameric imide [L^NMg]₆ (4) by the elimination of n-butane from L^NHMgⁿBu (2) or by the reaction of L^NHLi (1) with MeMgBr. [L^NH]₂Mg (3) is obtained through the addition of 0.5 equiv of ⁿBu₂Mg or Mg[N(SiMe₃)₂]₂ to L^NH₂ and with 1 equiv of ⁿBu₂Mg reacting to 2. Both L^NHMgN(SiMe₃)₂ (6) and isostructural L^NHZnN(SiMe₃)₂ (16) have been prepared using two different approaches: monodeprotonation of L^NH₂ by Zn/Mg[N(SiMe₃)₂]₂ in a 1:1 ratio or ligand substitution of 2 or L^NHZnEt (12) by 0.5 equiv of Sn[N(SiMe₃)₂]₂. The reactions of 2 or 3 with 1 provide the heterotrimetallic complex [L^NH]₄Li₂Mg (5). Benzyl- or trimethylsilyl-substituted anilines [L^N(SiMe₃)H (7) and L^N(Bn)H (8)] with 0.5 equiv of ⁿBu₂Mg allow the formation of homoleptic bis(amides) of the [L^N(R)]₂Mg type (10 and 11). Nevertheless, only the silylated secondary amine 7 is able to provide the heteroleptic n-butylmagnesium amide L^N(SiMe₃)MgⁿBu (9) upon reaction with an equimolar amount of ⁿBu₂Mg. Similarly, 12, [L^NH]₂Zn (13), L^N(R)ZnEt (17 and 18), and [L^N(R)]₂Zn [R = SiMe₃ (19) and Bn (20)] were prepared by the monodeprotonation of L^NH₂ or L^N(R)H using Et₂Zn in the corresponding stoichiometric ratio. L^NHZnI was prepared by the nucleophilic substitution of an ethyl chain in 12 by molecular iodine. A heterometallic complex, [L^NH]₄Li₂Zn (14), analogous to 5 was prepared from 12 or 13 with 1 or 2 equiv of 1, respectively.

High-spin, tetrahedral cobalt(ii) and nickel(ii) complexes supported by monoprotic aminophosphine ligands, and attempted extension to copper(ii) complexes: synthesis, characterization, and unexpected reactivity

We report the synthesis and characterization of two bidentate ligands containing an aliphatic monoprotic aminophosphine moiety, as well as novel complexes with Co(ii), Ni(ii), and Cu(ii).

Electrochemical, mechanistic, and DFT studies of amine derived diphosphines containing Ru(II)-cymene complexes with potent in vitro cytotoxic activity against HeLa and triple-negative breast cancer cells MDA-MB-231

Complexes with general formula [RuCl(η6-p-cymene)(P-NR-P)]X (R = CH2Py (Py = pyridine) - [1a]+, CH2Ph (Ph = phenyl) - [1b]+, Ph - [1c] and p-tol (p-tol = p-tolyl) - [1d]+; X = PF6- or BF4-) were evaluated as cytotoxic agents against two cancer cell lines (HeLa and MDA-MB-231). All metal complexes are active in the range of concentrations tested (up to 100 μmol L-1). The IC50 (μmol L-1) values for the metal complexes are lower than that found for cisplatin. The activities are up to 6- and 15-fold higher than cisplatin for HeLa and MDA-MB-231 cancer cell lines, respectively. Studies of DNA binding and DNA cleavage were performed. DNA binding studies revealed a modest hypochromic shift in the metal complexes electronic spectra, indicating a weak interaction with Kb values in the range of 1.7 × 103-1.6 × 104. Although the cleavage tests revealed that in the dark DNA is not a biological target for these metal complexes, upon blue light irradiation they are activated causing DNA cleavage. Electrochemical studies showed the presence of two independent redox processes, one attributed to the oxidation process of Ru2+ → Ru3+ (EC process) and the other one to the reduction of Ru2+ → Ru1+, which is further reduced to Ru0 (ECE mechanism). In both processes, coupled chemical reactions were observed. DFT calculations were performed to support the electrochemical/chemical behavior of the complexes. The reactivity of complex [1b]BF4 with CH3CN was evaluated and two complexes were isolated [2b]BF4 and [3b]BF4. The complex mer-[RuCl(CH3CN)3(P-NCH2Ph-P)]BF4 ([2b]BF4) was isolated after refluxing the precursor [1b]BF4 in CH3CN. Isomerization of [2b]BF4 in CH3CN resulted in the formation of fac-[RuCl(CH3CN)3(P-NCH2Ph-P)]BF4. An attempt to isolate the fac-isomer by adding diethyl ether was unsuccessful, and the complex [3b]BF4 was observed as the major component. The complex [Ru2(μ-Cl3)(CH3CN)2(P-NCH2Ph-P)2]BF4 ([3b]BF4) proved to be very stable and can be obtained from both the mer- and the fac-isomers. The molecular structures of [1b]BF4 and [3b]BF4 were solved by single-crystal X-ray diffraction.

Structure of salts of lithium chloride and lithium hexafluorophosphate as solvates with pyridine and vinylpyridine and structural comparisons: (C5H5N)LiPF6, [p-(CH2=CH)C5H4N]LiPF6, [(C5H5N)LiCl]n, and [p-(CH2=CH)C5H4N]2Li(μ-Cl)2Li[p-(CH2=CH)C5H4N]2

Due to the flammability of liquid electrolytes used in lithium ion batteries, solid lithium ion conductors are of interest to reduce danger and increase safety. The two dominating general classes of electrolytes under exploration as alternatives are ceramic and polymer electrolytes. Our group has been exploring the preparation of molecular solvates of lithium salts as alternatives. Dissolution of LiCl or LiPF₆ in pyridine (py) or vinylpyridine (VnPy) and slow vapor diffusion with diethyl ether gives solvates of the lithium salts coordinated by pyridine ligands. For LiPF₆, the solvates formed in pyridine and vinylpyridine, namely tetrakis(pyridine-κN)lithium(I) hexafluorophosphate, [Li(C₅H₅N)₄]PF₆, and tetrakis(4-ethenylpyridine-κN)lithium(I) hexafluorophosphate, [Li(C₇H₇N)₄]PF₆, exhibit analogous structures involving tetracoordinated lithium ions with neighboring PF₆^- anions in the I-4 and Aea2 space groups, respectively. For LiCl solvates, two very different structures form. catena-Poly[[(pyridine-κN)lithium]-μ₃-chlorido], [LiCl(C₅H₅N)]_n, crystalizes in the P2₁2₁2₁ space group and contains channels of edge-fused LiCl rhombs templated by rows of π-stacked pyridine ligands, while the structure of the LiCl-VnPy solvate, namely di-μ-chlorido-bis[bis(4-ethenylpyridine-κN)lithium], [Li₂Cl₂(C₇H₇N)₄], is described in the P2₁/n space group as dinuclear (VnPy)₂Li(μ-Cl)₂Li(VnPy)₂ units packed with neighbors via a dense array of π-π interactions.

Chiral amino-phosphine and amido-phosphine complexes of Ir and Mg. Catalytic applications in olefin hydroamination

The reactions of rac- and (S,S)-trans-9,10-dihydro-9,10-ethanoanthracene-11,12-diamine (ANDEN) with PClPh2 in the presence of NEt3 yield the chiral amino-phosphine ligands rac-6 and (S,S)-6, respectively, on multi-gram scales. Both forms of 6 react quantitatively with MgPh2 to afford the C2-symmetric, N-bound Mg amidophosphine complexes rac-7 and (S,S)-7. The former crystallizes as a racemic conglomerate, which is a rare occurrence. Mixing (S,S)- or rac-6 with [IrCl(COE)2]2 leads in both cases to the homochiral dinuclear chloro-bridged P-ligated aminophosphine iridium complexes (S,S,S,S)-9 and rac-9 in excellent yields. X-ray quality single crystals only grow as the racemic compound (or 'true racemate') rac-9 thanks to its lowered solubility. In the coordinating solvent CH3CN, rac-9 transforms in high yield into mononuclear Ir-complex rac-10. The crystal structures of compounds rac-6, (S,S)-7, rac-9, and rac-10 reveal the ambidentate nature of the P-N function: amide-coordination in the Mg-complex (S,S)-7 and P-chelation of the softer Ir(i) centres in complexes rac-9 and rac-10. Furthermore, the crystal structures show flexible, symmetry lowering seven-membered P-chelate rings in the Ir complexes and a surprising amount of deformation within the ANDEN backbone. The simulation of this deformation by DFT and SCF calculations indicates low energy barriers. (S,S)-7 and (S,S,S,S)-9 catalyze the intra- and intermolecular hydroamination of alkenes, respectively: 5 mol% of (S,S)-7 affords 2-methyl-4,4'-diphenylcyclopentyl amine quantitatively (7% ee), and 2.5 mol% of (S,S,S,S)-9 in the presence of 5.0 mol% co-catalyst (LDA, PhLi, or MgPh2) gives exo-(2-arylamino)bornanes in up to 68% yield and up to 16% ee.

Imido-pyridine Ti(IV) compounds: synthesis of unusual imido-amido heterobimetallic derivatives

The reaction of lithiated picolines and [TiCl3(η(5)-C5Me5)] leads to several bridging or terminal imido compounds, each of which can be selectively formed by controlling the stoichiometry and temperature. Specifically, the dinuclear imido-bridged [TiCl(η(5)-C5Me5)(μ-NR)]2 (1a, NR = 2-imido-3-picoline; 1b, NR = 2-imido-5-picoline) species and the unusual Ti-Li imido-amido heterobimetallic complex [{Li(THF)}{Ti(η(5)-C5Me5)(NR)(NHR)2}] (2a, NR = 2-imido-3-picoline; 2b, NR = 2-imido-5-picoline) were isolated. Compounds 2 are in effect the first structurally characterized examples of titanium(IV) coordinated to terminal imido-pyridines. DFT-D calculations for 2a denote a multiple bond character between titanium and the imido ligand and a strong polarization of the electron density by the alkali cation in spite of the lack of intermetallic bonding.