Javier Ángel Cabeza De Marco

Mechanochemical synthesis affords NDI-bridged Janus di-NHC Rh/Ir complexes, avoiding solution-phase degradation. The redox-active NDI enables strong metal–ligand coupling and reversible electronic switching for tunable catalysis and supramolecular assembly.

This work shows that the presence of germylene ligands of marked basicity in [FeFe]‐hydrogenase mimics of the type [Fe ₂ (µ‐S ₂ X)(E) _n (CO) _6–n ] (S ₂ X = (SCH ₂ ) ₂ N( p ‐MeOC ₆ H ₄ ) ( adt ), (SCH ₂ ) ₂ CH ₂ ( pdt ); E = amidinatogermylene; n = 1, 2; complexes 1 – 4 ), has a strong influence in the protonation and electrocatalytic behavior (proton reduction) of the mimics because these ancillary ligands appropriately increase the electron density of the [FeFe] core. Thus, electrochemical studies on 1 – 4 show cathodic shifts with respect to the all‐CO complexes [Fe ₂ (µ‐S ₂ X)(CO) ₆ ]. By protonation with trifluoracetic acid (TFA), complexes 1 – 4 form stable cationic hydride‐bridged complexes at room temperature, which, in the case of the adt ‐bridged complexes, arise from the transfer of the N H proton from a transient N ‐protonated adt fragment to the [FeFe] core. Such a proton transfer process has now been spectroscopically detected by low temperature ¹ H‐NMR. Electrocatalytic studies with TFA demonstrate hydrogen evolution reaction (HER) activity and high turnover frequencies, especially for the adt derivatives 1 and 2 .

The potential of 3,3,3-trifluoro-1-(2-pyridyl)prop-1-en-2-ol (tfppOH) as a precursor to synthesize air-stable heavier tetrylenes (HTs), either free or coordinated, was examined. Thus, the stability toward air and water of the homoleptic HTs E(tfppO)₂ (E = Ge (1_Ge), Sn (1_Sn)), which were previously reported by Mathur and coworkers and claimed to be highly air-stable, was evaluated together with that of the novel heteroleptic chloro-HTs E(tfppO)Cl (E = Ge (2_Ge), Sn (2_Sn)). These analyses have shown that all these compounds are susceptible to undergo hydrolysis at room temperature, albeit at very different rates for each HT. DFT calculations have been used to study the mechanism of these hydrolytic processes. Additionally, a preliminary study of the coordination chemistry of these HTs was conducted. The reactions of 0.5 equiv of [Ir₂Cl₂(μ-Cl)₂(η⁵-Cp*)₂] with 2_Ge cleanly afforded the Ge-Ir complex [IrCl₂(η⁵-Cp*){κ¹Ge-Ge(tfppO)Cl}] (3_Ge); however, the analogous stannylene 2_Sn led to a complex mixture, and the homoleptic derivatives 1_E resulted in ligand degradation (formation of the HT-free complex [IrCl(η⁵-Cp*){κ²N,O-(tfppO)}] (4)). The Ge-Au complexes [AuCl{κ¹Ge-Ge(tfppO)₂}] (5_Ge) and [AuCl{κ¹Ge-Ge(tfppO)₂}₂] (6_Ge) could be prepared by reacting 1_Ge with [AuCl(tht)] (tht = tetrahydrothiophene); however, only the precipitation of dark-purple solids was observed using 1_Sn. On the other hand, both 1_E were capable of rendering the diHT-Ag analogous compounds [Ag{κ¹E-E(tfppO)₂}₂]OTf (E = Ge (7_Ge), Sn (7_Sn)) in their reactions with AgOTf. The air-stability of all these complexes in solution was proven to be similar or lower (for 7_Sn) than that of the corresponding metal-free HTs.

A bare lead atom is a σ-donor ligand capable of linearly bonding and stabilizing two units of a classical polyhydride complex, with a high-valent metal center. As a proof of concept, we have prepared and characterized the μ₂-tetrylide complex (PⁱPr₃)₂H₄Os═Pb═OsH₄(PⁱPr₃)₂ in the reaction of OsH₆(PⁱPr₃)₂ with Pb{N(SiMe₃)₂}₂. Although the Pb-Os bonds exhibit electrostatic interaction, the main orbital interactions result from two dative σ bonds from the lead atom to the osmium centers. The latter also provide much weaker π-backdonations.

Procedures for the preparation of transition metal complexes having intact bicyclic cepham or penam systems as ligands have been developed. Starting from readily available 4-azido-2-azetidinones, a synthetic approach has been tuned using a copper-catalyzed azide-alkyne cycloaddition between 3-azido-2-azetinones and alkynes, followed by methylation and transmetalation to Au(I) and Ir(III) complexes from the mesoionic carbene Ag(I) complexes. This methodology was applied to 6-azido penam and 7-azido cepham derivatives to build 6-(1,2,3-triazolyl)penam and 7-(1,2,3-triazolyl)cepham proligands, which upon methylation and metalation with Au(I) and Ir(III) complexes yielded products derived from the coordination of the metal to the penam C⁶ and cepham C⁷ positions, preserving intact the bicyclic structure of the penicillin and cephalosporin scaffolds. The crystal structure of complex 28b, which has an Ir atom directly bonded to the intact penicillin bicycle, was determined by X-ray diffraction. This is the first structural report of a penicillin-transition-metal complex having the bicyclic system of these antibiotics intact. The selectivity of the coordination processes was interpreted using DFT calculations.

This review article focuses on amidinatotetrylenes that potentially can (or have already shown to) behave as bi‐ or tridentate ligands because they contain at least one amidinatotetrylene moiety (silylene, germylene or stannylene) and one (or more) additional coordinable fragment(s). Currently, they are being widely used as ligands in coordination chemistry, small molecule activation and catalysis. This review classifies those that have been isolated as transition metal‐free compounds into five families that differ in the position(s) of the donor group(s) (D) on the amidinatotetrylene moiety, namely: ED{R¹NC(R²)NR¹}, EX{DNC(R²)NR¹}, EX{R¹NC(D)NR¹}, EX{DNC(R²)ND} and E{R¹NC(R²)ND}₂ (E=Si, Ge or Sn). Those that do not exist as transition metal‐free compounds but have been observed as ligands in transition metal complexes are cyclometallated and ring‐opened amidinatotetrylene ligands. This article presents schematic descriptions of their structures, the approaches used for their syntheses and a quick overview of their involvement (as ligands) in transition metal‐catalysed reactions. The literature is covered up to the end of 2023.

E(hmds)(bqfam) (E = Ge (1a), Sn (1b); hmds = N(SiMe3)(2), bqfam = N,N '-bis(quinol-8-yl)formamidinate), which are amidinatotetrylenes equipped with quinol-8-yl fragments on the amidinate N atoms, have been synthesized from the formamidine Hbqfam and Ge(hmds)(2) or SnCl(hmds). Both 1a and 1b are fluxional in solution at room temperature, as the E atom oscillates from being attached to the two amidinate N atoms to being chelated by an amidinate N atom and its closest quinolyl N atom (both situations are similarly stable according to density functional theory calculations). The hmds group of 1a and 1b is still reactive and the deprotonation of another equivalent of Hbqfam can be achieved, allowing the formation of the homoleptic derivatives E(bqfam)(2) (E = Ge, Sn). The reactions of 1a and 1b with [AuCl(tht)] (tht = tetrahydrothiophene), [PdCl2(MeCN)(2)], [PtCl2(cod)] (cod = cycloocta-1,5-diene), [Ru-3(CO)(12)] and [Co-2(CO)(8)] have been investigated. The gold(I) complexes [AuCl{kappa E-E(hmds)(bqfam)}] (E = Ge, Sn) have a monodentate kappa E-tetrylene ligand and display fluxional behavior in solution the same as that of 1a and 1b. However, the palladium(II) and platinum(II) complexes [MCl{kappa E-3,N,N '-ECl(hmds)(bqfam)}] (M = Pd, Pt; E = Ge, Sn) contain a kappa E-3,N,N '-chloridotetryl ligand that arises from the insertion of the tetrylene E atom into an M-Cl bond and the coordination of an amidinate N atom and its closest quinolyl N atom to the metal center. Finally, the binuclear ruthenium(0) and cobalt(0) complexes [Ru-2{mu(E)-kappa E-3,N,N '-E(hmds)(bqfam)}(CO)(6)] and [Co-2{mu(E)-kappa E-3,N,N '-E(hmds)(bqfam)}(mu-CO)(CO)(4)] (E = Ge, Sn) have a related kappa E-3,N,N '-tetrylene ligand that bridges two metal atoms through the E atom. For the kappa E-3,N,N '-metal complexes, the quinolyl fragment not attached to the metal is pendant in all the germanium compounds but, for the tin derivatives, is attached to (in the Pd and Pt complexes) or may interact with (in the Ru-2 and Co-2 complexes) the tin atom.

Diverse [FeFe]-H₂ase mimics are available by cross-metathesis of [FeFe]-H₂ase mimics bearing a double bond in the ADT-bridge nitrogen moiety and vinylmetallocenes, vinyl half-sandwich, or octahedral Ir-complexes.