Three luminescent mixed ligand diorganotin(IV) complexes [Sn2Ph4(L)1–3(DPA)(MeOH)Cl] (where L1 = (Z)-N-((E)-3-ethoxy-2-hydroxybenzylidene)isonicotinohydrazonic acid, L2 = (Z)-N-((E)-5-bromo-2-hydroxybenzylidene)isonicotinohydrazonic acid, L3 = (Z)-N-((E)-2-hydroxy-3-methoxybenzylidene)isonicotinohydrazonic acid, and DPA = dipicolinic acid) (1–3) were synthesized and characterized physiochemically along with the single-crystal X-ray diffraction analysis of 1 and 3. Aqueous phase stabilities of the complexes were performed with UV–vis and 1H nuclear magnetic resonance, suggesting that they are stable in aqueous/biological media. The interaction of 1–3 with DNA was evaluated through analytical methods, which supported the intercalation mode of binding. Also, the interaction of complexes with bovine serum albumin was evaluated with fluorescence quenching experiments showing static quenching. In addition, the results of partition coefficients and cellular uptake suggest that the complexes are hydrophobic and can easily enter the cells. Cytotoxic potential of 1–3 was evaluated against HeLa, HT-29 (cancerous), and NIH-3T3 (normal) cell lines. Complex 2 is the most cytotoxic of the series having IC50 4.2 ± 0.7 μM against HeLa cells. Furthermore, all the complexes showed an apoptotic cell death confirmed by acridine orange/ethidium bromide, cell cycle analysis, and Annexin V-FITC/PI double staining assays. Finally, by using live cell confocal microscopy, it was found that the compounds target the mitochondria of cancer cells and raise the reactive oxygen species level.

This work is aimed at developing a density functional theory (DFT) approach that can be used to calculate 13C NMR shifts in any organometallic diamagnetic Pd complexes. Comparative analysis of calculated (GIAO method, DFT level) and experimental 13C NMR shifts for a wide range of diamagnetic palladium complexes (62 complexes in total) showed that the theory reproduces the experimental data well. A number of different basis sets, as well as quasi-relativistic and full-relativistic approximations, were tested. On the whole, the chemical shifts of carbon atoms directly bonded to Pd can be calculated within the framework of the Kohn–Sham theory level for most complexes with classical coordination bonds. The exceptions are complexes with carbons covalently bonded to metal and some NHC carbons due to relativistic effects. To summarize, in practice, the PBE0/{6-311G(2d,2p); Pd(SDD)}//PBE0/{6-31+G(d); Pd(SDD)} approximation can be recommended as a first step for most cases. Then, for complexes with the NHCs and covalently bonded ligands, 13C shifts should be calculated at a fully relativistic matrix Dirac–Kohn–Sham (mDKS) level, at least for atoms directly bonded to Pd (RMSE = 5.0 ppm). In all cases, a linear scaling procedure is necessary to minimize systematic errors.

The redox chemistry of [Cp‴Ni(η3-As3)] (A), an end-deck cyclo-As3 complex, is explored in terms of systematically accessing a series of Ni2As3 triple-decker compounds. While oxidation of A affords the cationic complex [{Cp‴Ni}2(μ,η3:3-As3)][FAl] (1, [FAl]− = [FAl{O(1-C6F5)C6F10}3]−), reduction of A yields the anionic [K@crypt][{Cp‴Ni}2(μ,η3:3-As3)] (2, crypt = [2.2.2]-cryptand). One-electron reduction of 1 and one-electron oxidation of 2 yield the neutral compound [{Cp‴Ni}2(μ,η3:3-As3)] (3), representing the missing link between 1 and 2, which is corroborated electrochemically. The cyclo-As3 ligand in 2 undergoes bond weakening and splitting of one As–As bond upon stepwise oxidation to 3 and 1, finally displaying an allylic As3 ligand. In-depth experimental studies shed light onto the reaction pathway of the oxidation of A, and additional DFT computations give insight into the electronic structure of the obtained complexes.

We have analyzed the rate of C(sp2)–C(sp2) reductive elimination from nickel(II) bis(2,4,6-trifluorophenyl) complexes (P–P)Ni(2,4,6-C6H2F3)2 containing either MeOBiPhep (3a) or a macrocyclic bisphosphine ligand (3b–3e) as a function of force applied to the biaryl backbone of these ligands through intramolecular tension generated by a molecular force probe. Nickel complexes 3 were isolated in 22–60% yield from the reaction of bisphosphine with the bis(tetrahydrofuranyl) complex (THF)2Ni(2,4,6-C6H2F3)2 followed by chromatography. Thermolysis of complexes 3 in C6D6 at 68 °C leads to first-order decay through >3 half-lives to the form 2,2′,4,4′,6,6′-hexafluorobiphenyl as the exclusive fluorine-containing product in ≥93% yield. Whereas compressive forces up to −65 pN have no significant effect on the rate of reductive elimination, extension forces increase the rate of reductive elimination by a factor of 3 over an ∼230 pN range of restoring forces relative to the strain-free MeOBiphep complex. The rate response of reductive elimination from nickel(II) bis(trifluorophenyl) complexes as a function of extension force is similar to the previously reported 2.8-fold increase in the rate of reductive elimination from platinum diaryl complexes (P–P)Pt(4-C6H4NMe2)2 over the same range of forces.

There is a common assumption that replacement of the classical catalyst based on rare and expensive noble metals by the catalysts based on earth-abundant metals will dramatically reduce the costs of organic synthesis. Herein we demonstrate that it may not be true, mainly because sophisticated organic substrates and modern reagents are often as expensive as catalytic amounts of noble metals. The particular cost analysis of the syntheses of 3,4-diphenyl-isoquinolone by various C–H activation methods revealed that the main costs fall on the stoichiometric reagents rather than the catalysts. As a result, the metal-free synthesis appears to be even more expensive than the procedures involving ruthenium and rhodium catalysts. Overall, metal prices should not be considered the sole reason for conducting academic research without any preliminary analysis.

There is significant interest in developing chemo- and regioselective intermolecular multicomponent syntheses of N-heterocycles, which are common motifs in pharmaceuticals and natural products. Herein we examine the potential of allenes to serve as selective coupling partners in a Ti-catalyzed [2 + 2 + 1] pyrrole synthesis reaction, which typically involves a [2 + 2] cycloaddition with an unsaturated substrate followed by a 1,2-insertion with a second unsaturated substrate. 1,2-Cyclononadiene acts as a regioselective insertion coupling partner to afford 2,3-annulated pyrroles through reaction with alkynes and azobenzene. Additionally, propadiene was found to undergo both [2 + 2] cycloaddition and insertion in a highly regioselective manner, yielding exclusively N-phenyl-2,5-dimethylpyrrole. In contrast, the [2 + 2 + 1] reaction of propyne, a propadiene isomer, results in an unselective regioisomeric mixture. This difference highlights how allenes can provide complementary (or better) selectivity compared to alkynes in multicomponent synthesis.

Complexes of the type (diphosphine)Ni(μ-SR)2Fe(CO)3 are investigated with azadithiolate (adt, HN(CH2S–)2) as the dithiolate. The resulting complexes are hybrid models for the active sites of the [NiFe]- and [FeFe]-hydrogenases. The key complex (dppv)Ni(μ-adt)Fe(CO)3 (3) was prepared from the complex Ni[(SCH2)2NCbz](dppv), which contains a Cbz-protected adt ligand (Cbz = C(O)OCH2Ph, dppv = cis-1,2-(Ph2P)2C2H2). This complex combines with Fe2(CO)9 to give (dppv)Ni[(μ-SCH2)2NCbz]Fe(CO)3, which is readily deprotected to give 3. Complex 3 undergoes protonation at both Fe and N to give successively [(dppv)Ni(μ-adt)FeH(CO)3]+ ([H3]+) and [(dppv)Ni(μ-adtH)FeH(CO)3]2+ ([H3H]2+). The redox properties and dynamics of these complexes resemble previously reported analogues with propanedithiolate. Solutions of [H3]+ readily degrade to [(dppv)Ni[(μ-SCH2)2NCH2]Fe(CO)3]+ ([4]+), which features a methylene group linking N and Fe. Complex [4]+ can be made in high yield by reaction of [H3]+ with CH2O, and this conversion was also demonstrated with 13CH2O. Complex [4]+ undergoes hydrogenolysis by photochemical reaction with H2 to give [(dppv)Ni[(μ-SCH2)2NMe]FeH(CO)3]+, the N-methylated analogue of [H3]+. Upon treatment ith Me3O+, [4]+ undergoes quaternization, giving [(dppv)Ni[(μ-SCH2)2N(Me)CH2]Fe(CO)3]2+. In contrast with the lability of [H3]+, the phosphine-substituted derivative [(dppv)Ni(μ-adt)FeH(CO)2(PPh3)]+ did not degrade. Most complexes were characterized by X-ray crystallography.

The iodine(III) bistriflamide complex (C6F5)IIII(NTf2)2 in HNTf2 (bistriflimide acid; (CF3SO2)2NH) selectively aminates methane and ethane. At a 100 °C reaction with methane after 3 h, it resulted in the exclusive formation of MeNTf2 with a yield of approximately 40%. For ethane, at 100 °C in 2 h, a > 80% yield was found for a combination of monofunctionalized and difunctionalized amination products. In contrast to alkanes giving functionalized products, the reaction of (C6F5)IIII(NTf2)2 with benzene resulted in being stalled at (C6F5)IIII(Ph)(NTf2) with a <5% conversion to PhNTf2 even at 120 °C. PWPB95-D3(BJ) density functional theory calculations indicate that C–H activation is the lowest energy pathway to break the hydrocarbon bonds and is lower in energy than radical, electron-transfer, proton-coupled electron-transfer, or hydride substitution pathways. For methane, from the (C6F5)IIII(CH3)(NTf2) intermediate, there is a one-step amine functionalization mechanism that avoids a carbocation intermediate. For ethane, from the (C6F5)IIII(Et)(NTf2) intermediate, dynamics simulations suggest the possibility of a competitive two-step functionalization pathway that involves a short-lived carbocation intermediate. A reaction coordinate strain analysis provides a straightforward model for understanding the relative reactivity rates for alkyl versus aryl functionalization.

Controlling N2 binding at transition-metal centers is essential in facilitating its rapid functionalization. Herein, we report the synthesis of high-spin four-coordinate Co–N2 complexes bound by our recently developed class of N,N,C heteroscorpionate ligands. End-on bridging and terminal binding modes for Co-bound N2 are both readily accessed by adjusting the steric profile of the supporting ligand. In the reported complexes, N2 is only weakly bound and is reversibly lost upon application of vacuum or an Ar atmosphere, with concomitant formation of an unusual Co–C–Si 3-center–2e– interaction. This work further demonstrates the power of steric control in modulating small-molecule binding at low valent centers.

We communicate a general method for the syntheses of acenaphthene-fused imidazolinium salts that are direct precursors to augmented N-heterocyclic carbenes with a fixed cis geometry. Reduction of bis(imino)acenaphthene ligands with a LiAlH4/AlCl3 reagent mix initially produced the corresponding 1,2-diamines which, upon ring-closing reaction with triethyl orthoformate in acidic solution, gave the requisite ionic intermediates. Formation of the carbenes was then shown by preparation of selected [Cu(NHC)] complexes that were obtained via treatment of the respective imidazolinium salt with base in the presence of a Cu(I) source.

Catalytic asymmetric dehydrocoupling of secondary phosphines is a potentially valuable route to enantiomerically enriched P-stereogenic diphosphines for use as ligands or building blocks for chiral bis(phosphines). Rh(diphos*) catalyst precursors converted a rac/meso mixture of PhHP(CH2)3PHPh (1) to the C2-symmetric P-stereogenic anti-diphospholane PhP(CH2)3PPh (2) in up to a 58:42 enantiomeric ratio (er) with complete diastereoselectivity via catalyst-mediated isomerization of the intermediate syn-diphospholane 3 to 2 (mistake correction by conversion of the diastereomer meso-3 to chiral C2-2). NMR studies of catalytic reactions identified the resting state Rh((R,R)-i-Pr-DuPhos)(PhHP(CH2)3PPh) (4) and suggested a proposed mechanism for stereocontrolled P–P bond formation via oxidative addition and reductive elimination steps.

Density functional theory applied in a mechanistic study of the oxidation of pincer complex PdII(mer-NCN)(K1–O2CPh) (NCN = 2,6-(dimethylaminomethyl)phenyl-N,C,N) by diphenyliodine(III) triflate, in the presence of the widely used bicarbonate base as an additive/reagent in organic synthesis, indicates that concerted oxidative addition by Ph2I(OCO2H) is preferred over a Ph+ transfer mechanism to initially form octahedral PhPdIV(mer-NCN)(K1–O2CPh){I(Ph)(···OCO2H)–I}. Interaction of bicarbonate with the iodine center has little effect on the dz2 orbital interaction with the σ* I–Ph orbital required for the concerted transition state but does destabilize the Ph+ transfer mechanism, which requires a later transition state with a much weaker interaction with bicarbonate.

A series of C^N-cyclometalated platinum(II) complexes [Pt(ppy)X(L)] (ppy = 2-phenylpyridinate, X = Cl and I) with 10-(aryl)phenoxarsines, namely 10-(p-tolyl)phenoxarsine (L1), 10-(p-fluorophenyl)phenoxarsine (L2), 10-(m-fluorophenyl)phenoxarsine (L3), and 10-(phenyl)phenoxarsine (L4), was synthesized. The structure of the complexes was determined by in-dept NMR spectroscopy, mass spectrometry, and X-ray analysis. The UV/vis absorption and emission properties were studied and rationalized by DFT and time-dependent DFT calculations. In the solid state, under UV irradiation, platinum complexes with chloro ligands exhibit an intense green emission, which was attributed to a 3IL/3(X,M)LCT triplet state.

Metal-mediated aryl fluoride activation not only presents challenges because of the thermodynamically robust C–F bond but also provides opportunities to develop C–C coupling reactions with this unconventional electrophile. Here, we report that the metallanucleophile, K[CpFe(CO)2] (KFp), is readily arylated by aryl fluorides to provide CpFe(CO)2Ar (FpAr) complexes under ambient conditions in the absence of any catalyst, contrary to previous literature reports. This C–F activation likely proceeds by a SNAr mechanism rather than the more common oxidative addition pathway for metal-mediated C–F cleavage. Facile access to FpAr derivatives has enabled further development of Fe-promoted coupling reactions of aryl fluorides with alkenes and alkynes. Under stoichiometric Fe conditions, Heck-type coupling reactions with aryl fluoride electrophiles are reported herein. Various aryl fluorides were found to couple with olefins to provide E-alkene products; aliphatic derivatives unexpectedly underwent reduction to 1,2-disubstituted ethane products to varying extents. Aryl fluorides were also found to couple with 5-decyne to yield indene derivatives in a one-pot manner; indenone and indanone products were also observed in selected cases. A mechanistic investigation to identify the apparently potent hydride donor generated under these conditions was conducted, leading to a mechanistic hypothesis involving the intermediacy of metal carbonyl-capped, triple-decker ferrocene compounds as reductants. Despite the involvement of these di-iron intermediates limiting stoichiometric product yields, the observed C–C coupling reactions expand the limits of organofluorine chemistry.

As an earth-abundant transition metal, manganese is now recognized as a good candidate for the development of catalysts for reduction-type reactions. It is often associated with a noninnocent tridentate ligand, featuring an acidic NH moiety. We report here that a simple bidentate and phosphine-free bis-N-heterocyclic ligand associated with manganese in the complex [Mn(bis-NHCMes)(CO)3Br] could catalyze the hydrogenation of carboxylic esters in the presence of KBHEt3 as an activator at 100–120 °C under 50 bar of H2 at 1 mol % catalyst loading in 2-Me-THF.

With the exception of iron, metals suitable for hydrosilylation catalysis are typically cross-applicable to dehydrogenative hydrosilane homocoupling reactions that afford useful σ-conjugated oligosilanes and polysilanes. Herein, we report the synthesis of iron pivalate complexes supported by a PNN pincer ligand and their application in the dehydrogenative coupling of hydrosilanes, showing that tertiary silanes are not consumed even under thermal conditions, whereas primary and secondary silanes are converted into poly- and disilanes, respectively. Disproportionation reactions are found to compete with coupling reactions, similar to previous studies using noble-metal catalysts. The addition of B2pin2 as a hydrogen acceptor is shown to increase the overall fraction and yield of coupling products, whereas the addition of alkenes is revealed to afford hydrosilylation products. Finally, a mechanism for the initial activation of iron pivalate complexes by hydrosilanes and a catalytic mechanism involving the silyl migration of a silyl–silylene iron complex are proposed based on the results of reaction mixture monitoring by nuclear magnetic resonance spectroscopy and the observed (by)products.

Enyne metathesis reactions involving metallacyclobutene intermediates have been comprehensively studied and utilized in numerous synthetic processes and catalytic transformations. We describe here our initial results toward the utilization of metalla-aromatic in classical [2 + 2] cycloaddition that η3-allyl structures are formed stoichiometrically through hydrogen-bonding-induced [2 + 2] cycloaddition between several propynol and a ruthenabenzene complex. The effect of the intramolecular hydrogen bonding interaction was analyzed by experimental and computational studies.

The reductive amination reaction of imines catalyzed by Knölker-type iron complexes under hydrogen at high pressure is very interesting in synthetic terms. This type of reaction is an important catalytic challenge, since harsh conditions are necessary and do not occur easily. In a previous work ( Organometallics 2022, 41, 1204−1215), we carried out a computational study of the reaction mechanism showing that electron-withdrawing groups (EWGs) attached to the cyclopentadienone of the Knölker-type iron complexes favor the reductive amination of imines. The synthesis of Knölker-type iron complexes with cyclopentadienones having EWGs is not straightforward, since the direct bonding of EWGs on the cyclopentadienone would lead not to the reductive amination but to undesired dimerization. A possible solution consists in the addition of phenyl substituents in the cyclopentadienones of these catalysts and then introduction of EWGs in the phenyl rings. We have performed computational studies using density functional theory (DFT) for the reductive amination of imines to analyze the efficiency of such an approach. We have found that some EWGs in the phenyl groups facilitate the reductive amination of imines. This computational result has been later confirmed experimentally, and therefore, we have computationally designed new catalysts that improve the performances of the previously known Knölker-type iron complexes.

Two compounds containing a Sn(II) atom supported by a bidentate biscarborane ligand have been synthesized via salt metathesis. The synthetic procedures for (bc)Sn·THF (bc = 1,1′ (ortho-carborane) (1) and K2[(bc)Sn]2 (2) involved the reaction of K2[bc] with SnCl2 in either a THF solution (1) or in a benzene/dichloromethane solvent mixture (2). Using the same solvent conditions as those used for 2 but using a shorter reaction time gave a dibiscarboranyl ethene (3). The products were characterized by 1H, 13C, 11B, 119Sn NMR, UV–vis, and IR spectroscopy, and by X-ray crystallography. The diffraction data for 1 and 2 show that the Sn atom has a trigonal pyramid environment and is constrained by the bc ligand in a planar five-membered C4Sn heterocycle. The 119Sn NMR spectrum of 1 displays a triplet of triplets pattern signal, which is unexpected given the absence of a Sn–H signal in the 1H NMR, IR spectrum, and X-ray crystallographic data. However, a comparison with other organotin compounds featuring a Sn atom bonded to carboranes reveal similar multiplets in their 119Sn NMR spectra, likely arising from long-range nuclear spin–spin coupling between the carboranyl 11B and 119Sn nuclei. Compound 3 displays structural and spectroscopic characteristics typical of conjugated alkenes.

An orthometallated 1-naphthylketone has been generated on osmium by coupling of γ-hydroxyalkynyl and diphenylallenylidene ligands. Treatment of Os{C≡C–C(OH)Ph2}2(═C═C═CPh2){κ3-P,O,P-[xant(PiPr2)2]}(1) with HBF4 leads to [Os{κ2-O,C-[O═C(CHPh2)-naphthyl-Ph]}(≡C–CH═CPh2){κ3-P,O,P-[xant(PiPr2)2]}](BF4)2 (2), which gives [Os{κ2-O,C-[O═C(CHPh2)-naphthyl-Ph]}(═C═C═CPh2){κ3-P,O,P-[xant(PiPr2)2]}]BF4 (3) by deprotonation with (piperidinomethyl)polystyrene. The formation of the ketone of 2 and 3 is an HF-catalyzed process. The H+ and F– fragments of HF are introduced sequentially with two different HBF4 molecules. The first molecule delivers H+, while the second provides F–. The proton from the first molecule adds to the Cβ atom of the diphenylallenylidene ligand of 1 to form [Os{C≡C–C(OH)Ph2}2(≡C–CH═CPh2){κ3-P,O,P-[xant(PiPr2)2]}]BF4 (4). The hydroxide group from a γ-hydroxyalkynyl of 4 is removed with the proton of the second HBF4 molecule, whereas the osmium center abstracts a fluoride of [BF4]−, to give [OsF{═C[−C≡C–C(OH)Ph2]–CH═CPh2}(═C═C═CPh2){κ3-P,O,P-[xant(PiPr2)2]}]BF4 (5). Once both fragments of HF are strategically located, the alkenyl-(γ-hydroxyalkynyl)alkylidene ligand experiences a Rupe-type rearrangement intercepted by a Diels–Alder cycloaddition, in two steps. A dehydration intercepted by Diels–Alder cycloaddition initially occurs, which affords the fluoroalkenylnaphthyl derivative [Os{κ2-F,C-[FC(═CPh2)-naphthyl-Ph]}(═C═C═CPh2){κ3-P,O,P-[xant(PiPr2)2]}]BF4 (7). The subsequent reaction of the latter with water yields the orthometallated 1-naphthylketone of 3, releasing HF. The protonation of 3 with HBF4 leads to 2.