The group's research work is structured around three fundamental lines. The following is a summary of the most recent work carried out during the execution of the current research project PID2021-122869nB-I00.

Line 1: Organofluorine late transition-metal chemistry.

Objective 1.1: Synthetic challenges in transition metal organometallic chemistry. Methodologies for the synthesis of new Au(III) and Ag(III) complexes.

The first line of this project focuses on the development of the chemistry of organofluorine compounds of late transition metals. This work focuses on trifluoromethylated derivatives of silver and gold, which the research group has been working on for some time, as well as on the preparation and study of new systems, either with other perfluorinated ligands (e.g. pentafluoroethyl) and/or with other metals (e.g. palladium and platinum).
Within this context, objective 1.1 is preparative in nature. Since the start of the project, we have made various contributions. For example, we have studied residual electrophilicity in complexes of formula [Ag(CF₃)₃L], which allow the formation of pentacoordinated Ag(III) species, which have few precedents in the scientific literature (cite). We have also prepared the first Ag(III) carbenoid complexes, obtained from the precursor [Ag(CF₃)₃F]^- by reaction with imidazolium salts (cite). This synthetic route represents an important methodological contribution and could be exportable to other transition metal systems. In addition, we have reviewed the acidic properties of the [Ag(CF₃)₃] fragment, having described the synthesis of new derivatives with the formulas [Ag(CF₃)₃L] and [Ag(CF₃)₃F]^- (cite).
In addition, we are expanding our field of work to include other perfluorinated ligands. In this regard, we have developed synthetic methodologies that have enabled us to synthesise the complexes [Au(C₂F₅) ₂]^- and [Ag(C₂F₅) ₂]^-. The former can be oxidised with XeF₂ or PhICl₂, giving rise to Au(III) derivatives [Au(C₂F₅) ₂X₂]- (X = F, Cl). We are currently exploring access to new Au(III) derivatives with the formula [Au(RF) ₂ (C₂F₅) ₂]^- (RF = CF₃, C₂F₅).
On the other hand, we have described a new synthetic route for the preparation of the palladium complex [Pd(CF₃)₄]^2-, obtained by using the complex [Ag(CF₃)₂]^- as a trifluoromethyl ligand transfer reagent (cite). This route suggests that the use of other perfluoroalkylated Ag(I) complexes, [Ag(RF) ₂]^-, could facilitate the preparation of new Pd(II) species with these ligands, [Pd(RF)₄]^2-.

Objective 1.2: Fundamental studies. Exploration of bond breaking and formation processes in new Au(III) and Ag(III) complexes.

This objective is focused on studying the fundamental reactivity of the perfluoroalkylated complexes synthesised.
Thus, we have prepared the derivatives [M(CF₃)₃(ONO₂)]^- and [(CF₃)₃(N₃)]^- (M = Ag, Au) and analysed their behaviour under MS-CID (mass spectrometry - collision-induced fragmentation) conditions. In particular, the Au complexes fragment, releasing NO₂ and N₂ respectively, and generate the species - formally Au(IV) - with the formula [Au(CF₃)₃E] ^- (E = O, n) (cite). Theoretical studies show that the spin density is located on the O and n atoms, so these species should really be described more accurately as Au(III) complexes.
Furthermore, in the study of the acidic properties of the [(CF₃)₃] fragment, we have described how, in the presence of an acid, this complex is capable of promoting the trimerisation of acetonitrile (cite). Theoretical calculations have allowed us to propose a detailed mechanism for this reaction, which requires the simultaneous and coordinated intervention of two acidic species, [(CF₃)₃] and H⁺.
On the other hand, and in the context of our studies with palladium, we have described the controlled transformation of Pd- CF₃ units in the [Pd(CF₃)₄]^2- complex into difluoro carbene, fluoro-amino carbene, isonitrile, and n-heterocyclic carbene ligands (Publication 1). Of particular note is the spectroscopic detection of the [Pd(CF₂)(CF₃)₃]^- complex, a highly reactive species with few precedents in late transition metal chemistry. We are currently exploring this type of reaction as a route to other stabilised F, O; F, S; O, O; O, S; O, N; S, S; and S, N carbene complexes.

Objective 1.3: Catalytic applications. Bond formation processes promoted by Au(III) and Ag(III) complexes.

This objective focuses on exploring the catalytic potential of available complexes in organic substrate coupling reactions. Within this objective, we have achieved the hydration of terminal and internal alkynes catalysed by Au(III) complexes. In particular, the [Au(CF₃)₃(NCCH₃)] complex proves to be a very active and robust catalyst for such reactions, yielding in most cases studied yields above 90% with catalyst loads around 0.25%. In addition, we have observed that the hydration of asymmetric internal alkynes proceeds regioselectively, with selectivities ranging from 65/35 to 90/10 (cite).
Other nucleophilic addition reactions of substrates such as amines, thiols or phosphines on alkynes will be explored in the near future.

Line 2. Synthesis and study of the reactivity of palladium and platinum organometallic complexes with basic properties toward electrophiles.

Objective 2.1: Study of the basicity of the Pt(II) centre in square-planar complexes in the presence of electrophiles such as H⁺ or CH₃⁺.

The basicity of the metal centre in Pt(II) and Pd(II) square-planar complexes is well known and has enabled the preparation of complexes with Pt→M bonds, where M⁺ is an acidic metal (typically Ag and, to a lesser extent, Au, among others). One of the objectives of this project is to extend the study of these basic properties to other electrophiles (E) such as CH₃⁺ or H⁺.
The planar compounds [Pt(CNC)L] (CNC = 2,6-di(phen-2-yl)-pyridine) have been used as starting substrates, and MeI and fostane ligands containing an OH fragment with an acidic hydrogen in their skeleton have been used as sources of CH₃⁺ or H⁺, respectively. In both cases, the products obtained evolve from the formation of the Pt→E intermediate to the methylation or protonation of one of the phenylene rings of the CnC ligand. This results in the breaking of Pt-C bonds and the formation of C-H or C-C bonds. The end result is the formation of new square-planar complexes [PtI(CN-C-Me)(PPh₃)] or [Pt(CN-C-H)(P^O)]. In the first case, the Cn-C-Me ligand can be cyclometallated again to give [Pt(CnCMe)(PPh₃)], a complex that undergoes a second methylation by the addition of another equivalent of MeI, giving [PtI(CN-C-Me₂)(PPh₃)].

Objective 2.2: Study of the basicity of the Pt(II) centre in square-planar complexes towards acidic M(I) metals (M = Ag, Au).

The above products [Pt(CNCMe)(PPh₃)] and [Pt(Cn-C-H)(PnO)] are square-planar complexes in which the metal continues to have basic characteristics. Therefore, the reactions of these substrates with acidic M(I) metals (M = Ag, Au) were tested. In the case of the starting product with the methylated ligand, several di- and trinuclear complexes with the formula [(CNCMe)(PPh₃)PtM(PPh₃)]⁺ and [{Pt(CNCMe)(PPh₃)}₂M]⁺ have been successfully prepared. These complexes exhibit Pt→M donor-acceptor bonds and M-C interactions with the C_ipso of the methylated phenylene ring of the CNC ligand. The nature and strength of these interactions still need to be studied using theoretical calculations. In the case where the basic metal substrate is [Pt(CN-C-H)(P^O)], the oxygen atom present, which has free electron pairs and therefore also basic properties, successfully competes with the platinum centre, and what is observed is the presence of an O-M bond but not a Pt-M bond.

Line 3. Phosphorescent platinum complexes: photoactive materials for optoelectronic and chemical applications.

Objective 3.1: Synthesis of new phosphorescent materials with application in electroluminescent devices.

Research in this field has focused on the search for platinum phosphides in the most complex regions: the blue region of the visible spectrum and the near-infrared region above 1000 nm (nIR-II). Among the complexes prepared, the dinuclear derivative with a “butterfly” structure with a cyclometallated n-heterocyclic carbene [{Pt(CO₂Et-C^C^*)(µ-3,5-dppz)} ₂], and the cluster [{Pt(CO₂Et-C^C^*)(μ-3,5-dppz)}₂AgPPh₃]PF₆ cluster have been studied as active materials in PhOLEDs or LEECs with encouraging results. (cite, cite).

Objective 3.2: Synthesis of new phosphorescent materials for use as oxygen sensors and biosensors.

In this part of our research, we have prepared new phosphorescent acac derivatives [Pt(Naph^C^*Me/iPr)(acac)] and [Pt(Naph^Npz/dmpz) (acac)] with π-extended systems to lengthen the deactivation time of the excited state and promote interaction with oxygen. These complexes were highly sensitive to oxygen, and the derivative [Pt(Naph^C^*Me)(acac)] was used for indirect glucose detection, with a detection limit of 5x10^-4 M, suitable for blood glucose detection. The sensitivity and stability of this material represent a significant advance in the application of cyclometallated N-heterocyclic carbenes in biosensors. The results have led to a publication (cite).

Objective 3.3: Light-promoted activation of Pt-C bonds.

On the one hand, we studied the mechanisms of oxidative addition of MeI and BnBr to the dinuclear complex [{Pt(C^C^*)(μ-pz)}₂] [Pt₂]. This detailed study led us to the preparation of dinuclear platinum complexes in different oxidation states: Pt₂(III,III), Pt₂(III,III)↔Pt₂(II,IV), Pt₂(IV,IV), which have been characterised by single crystal X-ray diffraction and one- and two-dimensional ¹H and ¹⁹⁵Pt{¹H} NMR spectra. This allowed us to compare structural and spectroscopic data from platinum complexes with the same core [{Pt(C^C*)(µ-pz)}₂], but different oxidation states. (cite)
We also studied the mechanisms of light-promoted Pt-C bond activation in dinuclear compounds of the Pt₂(III,III)XR type (X= Br, I). These Pt(III) derivatives with metal-metal bonds react when irradiated with UV light, yielding different organic products (R-R, ROH, RCOH) depending on the reaction conditions (Ar or O₂ atmosphere).