d10s2 Post-Transition Metal Anions: Identifying and Analyzing Their Dual-Mode Lewis Basicity

Liquid-phase d10s2 post-transition metal anions, such as [SnCl3]-, appear in a range of applications with a focus on catalysis and material preparation. However, little is known about their electronic structure and how it relates to reactivity. Using X-ray photoelectron spectroscopy and ab initio calculations, we demonstrate that liquid-phase d10s2 post-transition metal anions can act as dual-mode Lewis bases, interacting through the metal center and/or the ligands, with the interaction mode depending on the identity of the Lewis acid/electron acceptor. The Lewis basicity of the metal donor atom is controlled mainly by the metal identity; the ligand can be used for fine-tuning. Changing the metal center has a strong effect on the ligand basicity. These findings provide insight into d10s2 post-transition metal anion electronic structure, which will enable better molecular-level design of catalytic systems.

Cooperative Atomically Dispersed Fe-N4 and Sn-Nx Moieties for Durable and More Active Oxygen Electroreduction in Fuel Cells

One grand challenge for deploying porous carbons with embedded metal-nitrogen-carbon (M-N-C) moieties as platinum group metal (PGM)-free electrocatalysts in proton-exchange membrane fuel cells is their fast degradation and inferior activity. Here, we report the modulation of the local environment at Fe-N4 sites via the application of atomic Sn-Nx sites for simultaneously improved durability and activity. We discovered that Sn-Nx sites not only promote the formation of the more stable D2 FeN4C10 sites but also invoke a unique D3 SnNx-FeIIN4 site that is characterized by having atomically dispersed bridged Sn-Nx and Fe-N4. This new D3 site exhibits significantly improved stability against demetalation and several times higher turnover frequency for the oxygen reduction reaction (ORR) due to the shift of the reaction pathway from a single-site associative mechanism to a dual-site dissociative mechanism with the adjacent Sn site facilitating a lower overpotential cleavage of the O-O bond. This mechanism bypasses the formation of the otherwise inevitable intermediate that is responsible for demetalation, where two hydroxyl intermediates bind to one Fe site. As a result, a mesoporous Fe/Sn-PNC catalyst exhibits a positively shifted ORR half-wave potential and more than 50% lower peroxide formation. This, in combination with the stable D3 site and enriched D2 Fe sites, significantly enhanced the catalyst's durability as demonstrated in membrane electrode assemblies using complementary accelerated durability testing protocols.

Accessing Homo- and Heterobimetallic Complexes with a Dianionic Pentadentate Ligand

The tetrapyrazolylpyridyl diborate (B2Pz4Py) ligand provides a suitable platform for the isolation of heterobimetallic main-group element compounds as well as homotetrametallic copper complexes. The heterobimetallic tin(II)-lithium(I) (1) and tin(II)-thallium(I) (2) complexes have been synthesized, isolated, and fully characterized including single-crystal X-ray diffraction analysis. When reacted with copper(I) sources, complex 2 grants access to a homotetrametallic copper(I) complex (4). Upon subsequent oxidation, 4 gives rise to the bimetallic copper(II) complex 5, in which the two copper(II) centers are connected via a bridging bromido ligand (CuII-μ-Br-CuII).

Luminescent Tetranuclear Copper(I) and Gold(I) Heterobimetallic Complexes: A Phosphine Acetylide Amidinate Orthogonal Ligand Framework for Selective Complexation

The synthesis of phosphine acetylide amidinate stabilized copper(I) and gold(I) heterobimetallic complexes was achieved by reacting ligand [{Ph2PC≡CC(NDipp)2}Li(thf)3] (Dipp=2,6-N,N'-diisopropylphenyl) with CuCl and Au(tht))Cl, yielding the eight membered ring [{Ph2PC≡CC(NDipp)2}2Cu2] and the twelve membered ring [{Ph2PC≡CC(NDipp)2}2Au2]. {Ph2PC≡CC(NDipp)2}2Cu2] features a Cu2 unit, which is bridged by two amidinate ligands, served as a metalloligand to synthesize the heterobimetallic CuI/AuI complexes [{(AuX)Ph2PC≡CC(NDipp)2}2Cu2] (X=Cl, C6F5). In these reactions, the central ring structure is retained. In contrast, when the twelve membered ring [{Ph2PC≡CC(NDipp)2}2Au2] was reacted with CuX (X=Cl, Br, I and Mes), the reaction led to the rearrangement of the central ring structure to give [{(AuX)Ph2PC≡CC(NDipp)2}2Cu2] (X=Cl, Br, I and Mes), which feature the same the eight membered Cu2 ring as above. These compounds were also synthesized by a one-pot reaction. The luminescent heterobimetallic complexes were further investigated for their photophysical properties.

SnCl2-catalyzed multicomponent coupling: synthesis of 1,3-oxazolidine derivatives using paraformaldehyde as a C1 feedstock

SnCl2 catalyzed the three-component coupling of aniline, epoxide, and paraformaldehyde, resulting in the synthesis of 1,3-oxazolidine derivatives. The reaction is simple and does not require any additives, bases, or oxidants, and proceeds at moderate temperature with good functional group tolerance. The scope of the utilization of paraformaldehyde as the methylene source was further extended to the synthesis of benzothiazole and 4,4'-methylenebis(N,N-dimethylaniline) using the same catalyst. A catalytic pathway was proposed based on the control experiments.

Aminocarbonylation Reaction Using a Pd-Sn Heterobimetallic Catalyst: Three-Component Coupling for Direct Access of the Amide Functionality

A heterobimetallic "Pd-Sn" catalyst, namely, PdCl(PPh3)2SnCl3, efficiently catalyzes the aminocarbonylation reaction of aryl iodides with amines under the atmospheric pressure of CO in the absence of a base and additive. Primary, secondary, and alkyl amines all afforded the corresponding amides in good to excellent yields with high selectivity. A broad range of functional groups were tolerated. The method was further extended to the synthesis of biologically active isoindoline-1,3-diones in the presence of triethylamine. A mechanism is proposed for the reaction.

Heterobimetallic Complexes Bridged by an Unsymmetrical Bis(NHC) Ligand: Study of Enhanced Catalytic Activity in Tandem Transformations and Understanding of Cooperativity between the Metal Centers

The bis(azolium) salt [L1-H2 ]Br2 was found to serve as a suitable platform for accessing the heterobimetallic IrIII -M (M=PdII /AuI ) and PdII -IrIII complexes. Initially, selective mono-metalation of [L1-H2 ]Br2 yielded an orthometalated IrIII - or non-orthometalated PdII -complex. Sequential metalation of the mono-IrIII complex resulted in the formation of heterobimetallic IrIII -PdII /AuI complexes. Similarly, a distinct heterobimetallic PdII -IrIII complex was synthesized starting from the mono-PdII complex. Further, the corresponding homobimetallic IrIII -IrIII and PdII -PdII complexes were directly obtained from [L1-H2 ]Br2 . Additionally, monometallic PdII and IrIII analogues were synthesized from [L2-H]Br and [L3-H]Br, respectively. The heterobimetallic IrIII -PdII and PdII -IrIII complexes were then evaluated as catalysts in various one-pot tandem catalytic reactions in which they demonstrated superior activity than the mixtures of both their corresponding homobimetallic IrIII -IrIII /PdII -PdII and monometallic IrIII /PdII counterparts, under the constant concentrations of metal centers. Moreover, while comparing complexes IrIII -PdII and PdII -IrIII , the former exhibits higher activity in all the studied reactions. All these findings suggest the presence of some form of cooperativity between the two metal centers (Ir and Pd) connected by a single ligand framework in IrIII -PdII and PdII -IrIII complex, with IrIII -PdII displaying better cooperativity that has been validated by electrochemical, NMR, and DFT studies.

Role of Au-Sn bonding for stabilizing a gold nanocatalyst: a reinvestigation of purple of Cassius

Purple of Cassius is a pigment based on a gold colloid that has been known for hundreds of years. It has had a profound influence on modern nanoscience. But the origin of the small size of the Au nanoparticles (NPs) and their superior stability remains ambiguous. The experiments and characterization studies discussed here confirmed that SnCl₂ functioned not only as a reducing agent but also as an effective surface capping agent through bimetallic Au-Sn bonding. This finding expands the types of Au NP stabilizer from traditional organic examples (e.g., thiolate or phosphine) to metallic examples. The formation of a Au-Sn interface also endows Au NPs with excellent activity and separability for the hydration of alkynes to ketones.

H2 , B-H, and Si-H Bond Activation and Facile Protonolysis Driven by Pt-Base Metal Cooperation

We report a series of heterobimetallic Pt/Zn and Pt/Ca complexes to study the effect of proximity of a dicationic base metal on the organometallic Pt species. Varying degrees of Pt⋅⋅⋅Zn and Zn interaction with the bridging Me group are achieved, showcasing snapshots of a hypothetical process of retrotransmetalation from Pt to Zn. In contrast, only weak interactions were observed for Ca with a Pt-bound Me group. Activation of H₂ , B-H and Si-H bonds leads to the formation of hydride-bridged Pt-H-Zn complexes, which is not observed in the absence of Zn, pointing out the importance of metal-metal cooperation. Reactivity of PtMe₂ /M²⁺ with terminal acetylene, water and methanol is also studied, leading to facile protonation of one of the Me groups at the Pt center only when Zn is present. This study sheds light on various ways in which the presence of a 2+ metal cation significantly affects the reactivity of a common organoplatinum complex.

Sn,P-coordinated Ru cation: a robust catalyst for aerobic oxidations of benzylamine and benzyl alcohol

A stable ionic κ²Sn,P-coordinated Ru complex shows excellent catalytic activity in aerobic oxidations of benzylamine and benzyl alcohol. This complex is stabilized by a stannylene-phosphine peri-substituted naphthalene ligand, which can act as either a reducing agent for a Ru(III) complex or as a κ²Sn,P-chelating ligand for Ru(II) compounds.

Cation-π interactions enabling hard/soft Ti/Ag heterobimetallic cooperativity in lactide ring-opening polymerisation

The combination of a Ti-salen complex with AgBArF reveals unique hard/soft heterobimetallic cooperativity in lactide ring-opening polymerisation (ROP), enabling significant activity at room temperature. Reactivity, mechanistic and computational studies highlight the role of cation-π interactions in the formation of heterobimetallic species and provide key insights into the role of both metals in ROP.

Bismuth species in the coordination sphere of transition metals: synthesis, bonding, coordination chemistry, and reactivity of molecular complexes

This contribution is focused on bismuth species in the coordination sphere of transition metals. In molecular transition metal complexes, three types of Bi-M bonding are considered, namely dative Bi→M interactions (with Bi acting as a donor), dative Bi←M interactions (with Bi acting as an acceptor) and covalent Bi-M interactions (M = transition metal). Synthetic routes to all three classes of compounds are outlined, the Bi-M bonding situation is discussed, trends in the geometric parameters and in the coordination chemistry of the compounds are addressed, and common spectroscopic properties are summarized. As an important part of this contribution, the reactivity of bismuth species in the coordination sphere of transition metal complexes in stoichiometric and catalytic reactions is highlighted.

H2 and carbon-heteroatom bond activation mediated by polarized heterobimetallic complexes

The field of heterobimetallic chemistry has rapidly expanded over the last decade. In addition to their interesting structural features, heterobimetallic structures have been found to facilitate a range of stoichiometric bond activations and catalytic processes. The accompanying review summarizes advances in this area since January of 2010. The review encompasses well-characterized heterobimetallic complexes, with a particular focus on mechanistic details surrounding their reactivity applications.

Synthesis, structure, and catalytic activity of dinuclear aluminium bis(amidinate) and bis(guanidinate) complexes

The ring-opening polymerization grand prix: Bis(amidinate)s outpaced their bis(guanidinate) competitors and won the race, while the drivers’ engines using acidic co-initiators collapsed before take-off.

Molecular Complexes Featuring Unsupported Dispersion-Enhanced Aluminum-Copper and Gallium-Copper Bonds

The reaction of the copper(I) β-diketiminate copper complex {(Cu(BDI^Mes))₂(μ-C₆H₆)} (BDI^Mes = N,N'-bis(2,4,6-trimethylphenyl)pentane-2,4-diiminate) with the low-valent group 13 metal β-diketiminates M(BDI^Dip) (M = Al or Ga; BDI^Dip = N,N'-bis(2,6-diisopropylphenyl)pentane-2,4-diiminate) in toluene afforded the complexes {(BDI^Mes)CuAl(BDI^Dip)} and {(BDI^Mes)CuGa(BDI^Dip)}. These feature unsupported copper-aluminum or copper-gallium bonds with short metal-metal distances, Cu-Al = 2.3010(6) Å and Cu-Ga = 2.2916(5) Å. Density functional theory (DFT) calculations showed that approximately half of the calculated association enthalpies can be attributed to London dispersion forces.

Orbital energy mismatch engenders high-spin ground states in heterobimetallic complexes

The spin state in heterobimetallic complexes heavily influences both reactivity and magnetism. Exerting control over spin states in main group-based heterobimetallics requires a different approach as the orbital interactions can differ substantially from that of classic coordination complexes. By deliberately engendering an energetic mismatch within the two metals in a bimetallic complex we can mimic the electronic structure of lanthanides. Towards this end, we report a new family of complexes, [^Ph,MeTpMSnPh₃] where M = Mn (3), Fe (4), Co (5), Ni (6), Zn (7), featuring unsupported bonding between a transition metal and Sn which represent an unusual high spin electronic structure. Analysis of the frontier orbitals reveal the desired orbital mismatch with Sn 5s/5p primarily interacting with 4s/4p M orbitals yielding localized, non-bonding d orbitals. This approach offers a mechanism to design and control spin states in bimetallic complexes.

We report a series of high spin bimetallic transition metal–tin complexes. The unusual high spin configuration in a bimetallic complex is enabled by an energetic mismatch in the orbital energies, leading to lanthanide-like nonbonding interactions.

Bimetallic iron–tin catalyst for N2 to NH3 and a silyldiazenido model intermediate

A new tin-supported iron complex catalyzes N₂ fixation. The role of this heavy main group element in the catalysis is evaluated.

Thermodynamic and reactivity studies of a tin corrole-cobalt porphyrin heterobimetallic complex

A heterobimetallic complex, (TPFC)Sn-Co(TAP) (TPFC = 5,10,15-tris(pentafluorophenyl)corrole, TAP = 5,10,15,20-tetrakis(p-methoxyphenyl)porphyrin), was synthesized. The complex featured a Sn-Co bond with a bond dissociation enthalpy (BDE) of 30.2 ± 0.9 kcal mol^-1 and a bond dissociation Gibbs free energy (BDFE) of 21.0 ± 0.2 kcal mol^-1, which underwent homolysis to produce the (TPFC)Sn radical and (TAP)Co^II under either heat or visible light irradiation. The novel tin radical (TPFC)Sn, being the first four-coordinate tin radical observed at room temperature, was studied spectroscopically and computationally. (TPFC)Sn-Co(TAP) promoted the oligomerization of aryl alkynes to give the insertion products (TPFC)Sn-(CH 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 1111111111111111111111111111111111 1111111111111111111111111111111111 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 0000000000000000000000000000000000 C(Ar)) _n -Co(TAP) (n = 1, 2, or 3) as well as 1,3,5-triarylbenzenes. Mechanistic studies revealed a radical chain mechanism involving the (TPFC)Sn radical as the key intermediate.

Theoretical insights into the nature of PtSn bond: Reevaluating the bonding/back-bonding properties of trichlorostannate with comparison to the cyano ligand

The coordinating properties of the trichlorostannate ligand in hydrido platinum trichlorostannato and platinum bis-trichlorostannato complexes, containing various phosphine ligands, have been elucidated by means of charge decomposition analysis, the Ziegler-Rauk Energy Decomposition with the Natural Orbitals for Chemical Valence, Domain-Averaged Fermi Hole, and natural bond orbital methods. Trichlorostannate has been found to be a strong σ-donor and a weak π-acceptor ligand with coordination properties not far from those of the cyano ligand. For back-bonding, the tin-chlorine σ∗ orbitals are mostly responsible. In contrast to previous assumptions, the 5d orbitals of tin play no role at all in the interaction with the platinum center. QTAIM calculations suggest, that the platinum-tin interaction should be interpreted as donor-acceptor, rather than covalent type. Trichlorostannate has been found to have weaker trans influence in comparison to the cyano ligand. © 2017 Wiley Periodicals, Inc.

Cu/Pd cooperatively catalyzed tandem C–N and C–P bond formation: access to phosphorated 2H-indazoles

An unprecedented Cu/Pd cooperatively catalyzed tandem C–N/C–P bond formation reaction for the synthesis of phosphorated 2H-indazoles has been developed.

Novel organotin(iv) complexes derived from 4-fluorophenyl-selenoacetic acid: synthesis, characterization and in vitro cytostatic activity evaluation

A cluster of novel organotin(iv) complexes were designed, synthesized, and characterized by elemental analysis, FT-IR, and NMR (¹H, ¹³C, and ¹¹⁹Sn) spectroscopy as well as single-crystal X-ray diffraction.

Glaser–Hay hetero-coupling in a bimetallic regime: a Ni(ii)/Ag(i) assisted base, ligand and additive free route to selective unsymmetrical 1,3-diynes

A Ni(OAc)₂/Ag(OTf) catalysed coupling of aryl alkynes and propargylic alcohol/ether/ester gave the corresponding unsymmetrical 1,3-diynes in good to excellent yields.

Synthesis and reactivity of fluorenyl-tethered N-heterocyclic stannylenes

A fluorenyl (Fl) tethered diamine was synthesised by nucleophilic substitution of (bromoethyl)fluorene with a diisopropylphenyl (Dipp) substituted diamine to give FlC2H4N(H)C2H4N(H)Dipp (1a) in good yield (85%). Lithiation of 1a with n-BuLi proceeded with coordination of the Li cation to the aromatic fluorenide ring (2), and with subsequent equivalents of n-BuLi, the secondary amines were then sequentially deprotonated. A fluorenyl-tethered N-heterocyclic stannylene (NHSn) was synthesised from the reaction of 1a with SnN''2 {N'' = N(SiMe3)2} as a neutral dimeric species (5), and this was deprotonated with LiN'' to give the corresponding dianionic fluorenide-tethered NHSn (6). Reactions of [{Rh(cod)(μ-Cl)}2] with the mono-deprotonated ligand 2 led to the formation of a mixed-donor amide-amine Rh(i) compound (7), whereas reactions with the anionic NHSn 6 led to a Rh-fluorenyl complex of low stability with an uncoordinated pendent NHSn arm, which X-ray crystallography showed to be dimeric in the solid state.