Design of Catalytic Systems based on Halogen Bonding Interactions: Synthesis and Application in Catalytic Reactions

Abstract

[eng] The use of supramolecular interactions in catalysis has been widely studied and exploited for the straightforward preparation of the backbones of an array of structurally diverse stereoselective catalysts. In addition to the broad application of halogen bond donors as organocatalysts, the use of this non covalent interaction has been also employed for the preparation of catalytically active complexes. Our group pioneered the use of halogen bonding interactions for the construction of bidentate phosphorus ligands by assembly of suitably designed phosphorus(III)-based complementary ligands (XBphos Rh C1). The present doctoral thesis encompasses the synthesis and study of halogen bond-assembled complexes based on rhodium(I) and iridium(I) metal centers as well as their application in catalysis. We initially directed our research efforts to the effects that modifications on the halogen bond acceptor and donor ligands cause on the structure of the final rhodium(I) complexes. Structurally diverse halogen bond acceptor and donor ligands have been designed, synthesized, and subsequently tested in the preparation of halogen bond-assembled rhodium(I) complexes. The final complexes have been fully characterized by spectroscopic techniques in solution and in the solid state. It has been demonstrated that halogen bond acceptors containing a phosphaamidine moiety efficiently lead to halogen bond assembled complexes in combination with (2-iodo-3,4,5,6-tetrafluorobenzene)phosphane-based halogen bond donor ligand L2. On the other hand, substitution of the iodo group in L2 by a bromo or fluoro group led to changes in the Rh−P complexation behavior. Afterwards, a series of XBphos-Rh C1 analogues incorporating diverse counterions were successfully synthesized and fully characterized. These halogen bonded complexes have been successfully applied in the hydroboration reaction of terminal alkynes with the aim of maximizing the regioselectivity of the hydroboration of alkynes towards the branched alkenyl boronates by variation of the counterion. We demonstrated that the stronger the coordination ability of the counterion, the higher the activity and selectivity towards hydroboration products were. Our study concluded that linear and inactivated alkyl-substituted alkynes led to the highest levels of chemo- and regio-selectivity in the hydroboration reaction. Moreover, the practicality of our synthetic method was demonstrated by developing a one-pot hydroboration/Csp2−Csp2 coupling process. Then, we expanded the use of our halogen bond-assembled rhodium complexes as a suitable catalyst in other chemical transformations of interest. Efficient intramolecular [4+2] cycloadditions of dien-γ-ynes mediated by the halogen-bonded rhodium(I) complex XBphos-Rh-BArF in combination with a silver(I) salt have been developed. The cooperative action of the Rh/Ag derivatives efficiently leads to the corresponding [4+2] cycloadducts (yields ranging from 66% to 99%) with high selectivity. The synthetic protocol features simple operation and good functional group tolerance and represents a good example of bimetallic cooperation. Studies aimed at determining the role of rhodium(I) and Ag(I) derivatives were performed and revealed that both metallic derivatives are required for the reaction to take place. Finally, research efforts were directed to the expansion of the structural diversity of the XBphos-metal complexes to iridium(I) halogen-bonded complexes. Two closely related halogen bonded iridium complexes [Ir(CO)2(κ3I,P,P L1·L2)]BArF C9 and [Ir(CO)(κ3I,P,P L1·L2)]BArF C10 have been successfully prepared and characterized in solution and in the solid state. NMR spectroscopic analysis revealed an equilibrium between both iridium complexes, involving exchange of one CO molecule taking place in solution. Crystals suitable for X-Ray analysis allowed us to unequivocally elucidate the structure of both iridium(I) complexes: trigonal bipyramidal geometry in case of C9 and a square planar geometry in the monocarbonyl derivative C10. Our halogen bond assembled complex C9 has been efficiently applied in the consecutive double intra- and intermolecular hydroalkoxylation of alkynyl alcohols for the synthesis of O,O ketal products. The best results have been achieved when using linear alkynyl alcohols and more preorganized substrates that led to the formation of O-containing spiro-type compounds.

[cat] Les interaccions de pont d'halogen han captat l'atenció de molts investigadors durant els últims anys i s'han aplicat principalment en organocatàlisi. El nostre grup va ser pioner en l'ús d'aquestes interaccions per a la preparació de lligands bidentats constituïts a través de ponts d'halogen. Aquesta tesi doctoral comprèn la síntesi i l'estudi dels complexos de rodi(I) i iridi(I) constituïts a través d'interaccions del tipus pont d'halogen, així com l'aplicació d'aquests complexos metàl·lics en catàlisis. Inicialment, s'ha abordat l'estudi de l'efecte que causen les modificacions electròniques i estructurals dels lligands donadors i acceptors de pont d'halogen en els processos de complexació Rh−P. Els complexos de rodi obtinguts C1-C6 han estat estudiats mitjançant tècniques espectroscòpiques estàndard en dissolució i en estat sòlid. Seguidament, aquests sistemes catalítics s'han aplicat de manera lògica en diverses transformacions químiques d'interès. D'una banda, els complexos basats en rodi s'han utilitzat de manera eficaç en reaccions d’hidroboració d’alquins terminals, obtenint resultats altament interessants en termes de regioselectivitat (11 exemples, fins a un 78% de l'isòmer ramificat (br)-P). D'altra banda, el complex XBphos-Rh C1 s'ha utilitzat en reaccions de cicloaddició [4+2] de substrats tipus dien-γ-í. S'ha demostrat l'eficàcia del sistema catalític format per l'acció cooperativa del complex XBphos-Rh C1 i AgOTf en la formació d'estructures bicícliques més complexes (5 exemples, fins a 99% de rendiment). Finalment, s'ha expandit la família XBphos amb l'ús d'iridi com a metall. Els complexos constituïts mitjançant ponts d'halògens basats en iridi [Ir(CO)2(κ3I,P,P L1·L2)]BArF C9 i [Ir(CO)(κ3I,P,P L1·L2)]BArF C10 han estat completament caracteritzats. El complex C9 ha estat avaluat com a catalitzador en la doble hidroalcoxilació intra- i intermolecular de substrats tipus alquinol de manera eficaç (7 exemples, fins a un 96% de rendiment). A més, s'ha dut a terme un estudi més exhaustiu del mecanisme de la reacció.