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The solution structures of the ytterbium heterobimetallic complexes Na(3)[Yb((S)-BINOL)(3)] (1), K(3)[Yb((S)-BINOL)(3)] (2), and Li(3)[Yb((S)-BINOL)(3)] (3), belonging to a family of well-known enantioselective catalysts, are studied by means of NMR and circular dichroism (CD) in the UV and near-IR regions. The experimental NMR paramagnetic shifts were employed to obtain a refined solution structure of 1. NMR analysis demonstrated that 1, 2, and 3 have the same solution geometry but different magnetic susceptibility anisotropy D factors. By comparing XRD and NMR structures of 1, we demonstrate that, upon dissolution, this complex experiences a rearrangement from the crystalline C(3) symmetry into the solution D(3) symmetry. Remarkably, Yb is not bound to water in solution, and Ln-BINOL bonds are labile as demonstrated through EXSY. NIR-CD is confirmed especially sensitive to changes in the ytterbium coordination sphere.

Diiron μ-aminocarbyne compounds, 1a-e, are prepared in two steps from Fe 2 Cp 2 (CO) 4 , negating the need for difficult purification procedures of intermediate species; they are efficiently isolated by alumina chromatography. Minor amounts of μ-aminocarbyne aryl isocyanide compounds, 2a-c, are obtained as side products. The structures of the cations in 1a,c,e are calculated using DFT; the carbyne carbon is generally predicted to be the thermodynamic site of hydride addition, in agreement with a previous experimental finding concerning 1a. Accordingly, the reaction of 1e with NaBH 4 affords a bridging aminocarbene complex, 4, in 85 % yield. Otherwise, the reaction of 1c with NaBH 4 yields the aminocarbyne-cyclopentadiene derivative 3 (70 %), presumably as a consequence of the [a] Scheme 1. Regioselective additions of nucleophiles to the diiron aminocarbyne complex 1a. Results and DiscussionThe commercial compound [Fe 2 Cp 2 (CO) 4 ] was reacted with the appropriate isocyanide, in a ca. 3:2 molar ratio, in acetonitrile solution. [16] The reactions with alkyl isocyanides were conducted under reflux conditions, whereas the reactions with aryl isocyanides proceeded at room temperature. The resulting mixtures were dried under vacuum and the residues were dissolved in dichloromethane and then treated with methyl triflate, thus affording the μ-aminocarbyne complexes 1a-e (Scheme 2). The difficult isolation of the monoisocyanide intermediates (see the Introduction) was unnecessary. The final products 1a-e were efficiently purified by alumina chromatography and were then isolated as microcrystalline, air-stable compounds in 65-92 % yields. The synthesis of 1c-e was accompanied by the side formation of minor products derived from di-isocyanide species, 2a-c. Compounds 2a-c were recovered by the chromatography in 3-12 % yields, although 2a was formerly reported as being Scheme 2. Synthesis of diiron μ-aminocarbyne complexes.Eur. J. Inorg. Chem. 2018, 960-971 www.eurjic.org

Although ferrocene derivatives have attracted considerable attention as possible anticancer agents, the medicinal potential of diiron complexes has remained largely unexplored. Herein, we describe the straightforward multigram‐scale synthesis and the antiproliferative activity of a series of diiron cyclopentadienyl complexes containing bridging vinyliminium ligands. IC50 values in the low‐to‐mid micromolar range were determined against cisplatin sensitive and resistant human ovarian carcinoma (A2780 and A2780cisR) cell lines. Notable selectivity towards the cancerous cells lines compared to the non‐tumoral human embryonic kidney (HEK‐293) cell line was observed for selected compounds. The activity seems to be multimodal, involving reactive oxygen species (ROS) generation and, in some cases, a fragmentation process to afford monoiron derivatives. The large structural variability, amphiphilic character and good stability in aqueous media of the diiron vinyliminium complexes provide favorable properties compared to other widely studied classes of iron‐based anticancer candidates.

The diiron vinyliminium complexes [Fe2{μ-η1:η3-C(R‘)CHCN(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3] [R = Xyl, R‘ = Me, 1a; R = Xyl, R‘ = Tol, 1b; R = Xyl, R‘ = CO2Me, 1c; R = Xyl, R‘ = CH2OH, 1d; R = Xyl, R‘ = Bun, 1e; R = Me, R‘ = Me, 1f; R = Me, R‘ = Tol, 1g; R = Me, R‘ = CO2Me, 1h; R = Me, R‘ = Bun, 1i; R = Me, R‘ = CH2OH, 1l; R = p-C6H4-CN, R‘ = Tol, 1m; R = p-C6H4-OMe, R‘ = Me, 1n; Tol = 4-C6H4-Me; Xyl = 2,6-Me2C6H3] react with elemental sulfur or selenium, in the presence of NaH, to give the zwitterionic vinyliminium compounds [Fe2{μ-η1:η3-C(R‘)C(E)CN(Me)(R)}(μ-CO)(CO)(Cp)2] [R = Xyl, R‘ = Me, E = S, 2a; R = Xyl, R‘ = Tol, E = S, 2b; R = Xyl, R‘ = CO2Me, E = S, 2c; R = Xyl, R‘ = CH2OH, E = S, 2d; R = Xyl, R‘ = Bun, E = S, 2e; R = Xyl, R‘ = Me, E = Se, 3a; R = Xyl, R‘ = Tol, E = Se, 3b; R = Me, R‘ = Me, E = Se, 3c; R = Me, R‘ = Tol, E = Se, 3d; R = Me, R‘ = CO2Me, E = Se, 3e; R = Me, R‘ = Bun, E = Se, 3f; R = Me, R‘ = CH2OH, E = Se, 3g]. Similarly, the reaction of 1a with Me3NO/NaH results in the formation of [Fe2{μ-C(Me)C(O)CN(Me)(Xyl)}(μ-CO)(CO)(Cp)2] (4), in which the bridging ligand is better described as a bis-alkylidene. The reactions of 1a,c with S8/NaH afford also the five-membered metallacycles [Fe(Cp)(CO){Cα(NMe(Xyl))Cβ(H)Cγ(R‘)S}] [R‘ = Me, 6a; R‘ = CO2Me, 6b], as secondary products, in about 15% yield. Conversely, complexes [Fe2{μ-η1:η3-C(R‘)CHCN(Me)(R)}(μ-CO)(CO)(Cp)2][SO3CF3], 1f−h,m,n, react with S8/NaH, giving selectively the five-membered metallacycles [Fe(Cp)(CO){C(R‘)C(H)C{N(Me)(R)}S}] [R = Me, R‘ = Me, 7a; R = Me, R‘ = Tol, 7b; R = Me, R‘ = CO2Me, 7c; R = p−C6H4−CN, R‘ = Tol, 7d; R = p-C6H4-OMe, R‘ = Me, 7e]. The molecular structures of 2b·CH2Cl2, 3a, 4, 6a, and 7b have been determined by X-ray diffraction studies.

The complexes [Fe 2 {µ-CN(Me)(R)}(µ-CO)(CO)(NCMe)(Cp) 2 ][SO 3 CF 3 ] (R ) Xyl, 1a; R ) Me, 1b; R ) CH 2 Ph, 1c; Xyl ) 2,6-Me 2 C 6 H 3 ), containing a labile NCMe ligand, react under mild conditions with a variety of terminal alkynes HCtCR′ (R′) SiMe 3 , Me, Bu n , Tol, Ph, H; Tol ) 4-MeC 6 H 4 ) to give the bridging vinyliminium complexes [Fe 2 {µ-σ: 7). Insertion of the alkyne into the metal-carbyne carbon bond is regiospecific, resulting only in the product containing the R′ group on the carbon bound to Fe. Similarly, insertion of the disubstituted alkynes R′CtCR′ (R′ ) Me, Et) affords the analogous compounds [Fe 2 {µ-σ:). The molecular structure of complex 2a has been elucidated by an X-ray diffraction study.

The dibenzyl-substituted carbamic acid (PhCH 2 ) 2 NC(O)OH (1), its deprotonation product [(PhCH 2 ) 2 NH 2 ]-[(PhCH 2 ) 2 NCO 2 ] (2) and CoCl(NO) 2 [PhP(OCH 2 CH 2 ) 2 N-C(O)OH]•2MeCOMe(3•2MeCOMe) are reported, the diffractometric study showing the carbamic acids 1 and 3 to be paired through hydrogen bonds.

The molecular structure of 1,10-phenanthroline-5,6-dione has been determined by X-ray diffraction analysis. The compound reacts with the tetrachlorides of Group 4 metals affording adducts of general formula [MCl 4 (C 12 H 6 N 2 O 2 )] (M = Ti, Zr or Hf) and [(MCl 4 ) 2 (C 12 H 6 N 2 O 2 )] (M = Ti or Hf), N,NЈ-and N,NЈ,O,OЈ-co-ordinated respectively. The compound [HfCl 4 (C 12 H 6 N 2 O 2 )] is reactive towards TiCl 4 affording the bimetallic compound [Cl 4 Hf(C 12 H 6 N 2 O 2 )-TiCl 4 ]. The reaction of the dione with bis-cyclopentadienyl derivatives of titanium(), zirconium(), [MCp 2 (CO) 2 ], and vanadium(), VCp 2 , affords derivatives O,OЈ-co-ordinated to the MCp 2 moiety. By reaction of [TiCp 2 -(C 12 H 6 N 2 O 2 )] with [TiCp 2 (CO) 2 ] the bimetallic derivative [(TiCp 2 ) 2 (C 12 H 6 N 2 O 2 )] is obtained, which is suggested to contain two TiCp 2 fragments, O,OЈ-and N,NЈ-co-ordinated to 1,10-phenanthroline-5,6-dione. The [MCp 2 -(C 12 H 6 N 2 O 2 )] (M = Ti, Zr or V) derivatives react with MЈCl 4 (MЈ = Ti or Hf) to give [Cp 2 M(C 12 H 6 N 2 O 2 )MЈCl 4 ] bimetallics.