Polipirazolilborato complejos de cobre (I) como catalizadores en reacciones de transformación de olefinas en ciclopropanos, aziridinas y epóxidos

1. Preparación de los pre-catalizadores. La reacción, a baja temperatura, de CuI y la sal potásica del ligando dihidrobispirazolilborato (KBp) en acetonitrilo (ec 1) permite el aislamiento de un sólido de color blanco cuyo análisis elemental se ajusta a la composición BpCu (1). CuI + KBp → BpCu + KCI (1) La reacción de 1 con un equivalente de bipiridilo (bipy), de 1,2-bis(difenilfosfina)etano (dppe) o de triciclohexilfosfina (PCy3) conduce a la formación y posterior aislamiento de los aductos de composición general BpCuL (L = bipy, 2; dppe, 3; PCy3, 4), como se indica en la ec 2: BpCu + L → BpCuL (2) L = bipy,2; dppe, 3; PCy 3, 4 En el caso de los ligandos monodentados piridina (py) o trifenilfosfina (PPh3), la adición de dos equivalentes permite aislar complejos de composición BpCuL2 (L = py, 5; PPh3, 6; ec 3): BpCu + 2L → BpCuL (3) L = py,5; PPh 3, 6 2. Ciclopropanación de olefinas en fase homogénea. Con objeto de conocer las posibilidades catalíticas en la reacción de ciclopropanación de olefinas de los mencionados complejos de cobre, se ha realizado un estudio completo modificando las condiciones de reacción, tras el cual es posible afirmar que estos complejos catalizan dicha transformación de forma eficiente a temperatura ambiente. (Tabla1).--------------------------------1. Synthesis of the catalyst precursors. The low-temperature reaction of CuI and the potassium salt of the Bp ligand, in acetonitrile (eq 1), leads to the isolation of a white solid of analytical composition BpCu (1). CuI + KBp → BpCu + KCI (1) The reaction of 1 with one molar equiv of Bioy, dppe or PCy3 affords the complexes of general composition BpCuL (L = bipy,2; dppe, 3; PCy3, 4), as depicted in eq 2. BpCu + L → BpCuL (2) L = bipy,2; dppe, 3; PCy 3, 4 When pyridine or triphenylphosphine are employed, two equiv are required to obtain the complexes BpCu + 2L → BpCuL (3) L = py,5; PPh 3, 6 2. Olefin Cyclopropanation reaction catalyzed by compelxes 1-6 under homogeneous conditions. Complexes 1-6 have been employed as the catalyst precursor in the reaction of ethyldiazoacetate with several olefins in order to test their catalytic capabilities in the general cyclopropanation reaction.The results shown in Table 1 are in accord with the existence of a moderate catalytic activity of such those complexes for this transformation

The TpxM Core in Csp3–H Bond Functionalization Reactions: Comparing Carbene, Nitrene, and Oxo Insertion Processes (Tpx = Scorpionate Ligand; M = Cu, Ag)

A comparison between three TpxM‐catalyzed (Tpx = scorpionate ligand; M = Cu, Ag) reactions leading to the functionalization of non‐activated, alkane Csp3–H bonds by carbene, nitrene or oxo insertion is presented. Analogies and differences in these transformations are discussed, including main reactive intermediates, selectivity trends and mechanistic interpretations.Support for this work was provided by the MINECO (CTQ2017-82893-C2-1-R)

Metal-Catalyzed Postpolymerization Strategies for Polar Group Incorporation into Polyolefins Containing C–C, C═C, and Aromatic Rings

Polymeric materials bearing polar groups constitute a class of macromolecules with interest in a number of uses. Because the direct synthesis employing polymerization strategies from polar monomers is very often precluded by catalyst poisoning or uncontrolled side reactions, the alternative postpolymerization route consisting in modifying a previously prepared polymer is continuously progressing. However, such a posteriori modification depends on the existence of potential reaction sites in the polymer. Because of this, polyolefins are the most challenging substrates to work with and, among them, the saturated ones. In this contribution, the current state of the art of the metal-catalyzed modification of polyolefins and subsequent polar group incorporation is provided.We acknowledge financial support from the Ministerio de Ciencia e Innovacion (CTQ2017-82893-C2-1-R), Junta de Andalucia (P18-RT-1536), and Universidad de Huelva (P.O.Feder UHU-1260216 and UHU-1254043). DYNASOL SLU is also highly appreciated for financial support. Funding for open access charge: Universidad de Huelva / CBU

Copper‐Catalyzed Selective Pyrrole Functionalization by Carbene Transfer Reaction

1H‐Pyrroles can be directly functionalized by means of the incorporation of carbene groups from diazo compounds, in a process catalyzed by TpxCu complexes (Tpx=hydrotrispyrazolylborate ligand). The reactions take place with a complete selectivity toward the formal insertion of the carbene into the Cα−H bond, leading to alkylated pyrroles, with no modification of the Cβ−H, N−H or C=C bonds of the pyrrole unit. Alkyl substituents at C‐ring as well as alkyl, aryl, allyl or alkyne substitution at N atom are tolerated, the strategy affording 20 new pyrrole derivatives. The observance of partial deuteration at the methylene group when the reaction is carried out with added D2O serves to discard the direct insertion of the carbene group into the Csp2−H bond, the alternative electrophilic attack to the pyrrole ring being feasible.Support for this work was provided by the MINECO (CTQ2017- 82893-C2-1-R and PO FEDER 2014-2020, UHU-1254043). AMR thanks MINECO for a FPU fellowship

Pyrrole Functionalization by Copper‐Catalyzed Nitrene Transfer Reactions

The catalytic functionalization of pyrroles by incorporation of a nitrene group is reported. The Cα‐H bond of 1H‐pyrrole is amidated upon the formal insertion of the NTs (Ts=p‐toluenesulfonyl) group catalyzed by TpBr3Cu(NCMe) (TpBr3=hydrotris(3,4,5‐tribromo‐pyrazolyl)borate). N‐substituted pyrroles also verify the same transformation. The mechanism proposal is similar to that previously described for benzene amidation with the same catalyst and PhI=NTs, which takes place through aziridine formation, ring opening and 1,2‐hydrogen shift. A cascade reaction involving the coupling of 2,5‐dimethylfuran, 1,2,3‐trimethyl‐pyrrole and a nitrene NTs group is also described, leading to a 1,2‐dihydropyridine‐imine compound.Support for this work was provided by the MINECO (CTQ2017‐82893‐C2‐1‐R and PO FEDER 2014‐2020, UHU‐1254043). AMR and MRR thanks MEC for a FPU fellowships

Mechanistic Studies on Gold-Catalyzed Direct Arene C–H Bond Functionalization by Carbene Insertion: The Coinage-Metal Effect

The catalytic functionalization of the Csp 2-H bond of benzene by means of the insertion of the CHCO2Et group from ethyl diazoacetate (N2=CHCO2Et) has been studied with the series of coinage metal complexes IPrMCl (IPr = IPr = 1,3-bis(diisopropylphenyl)imidazol-2-ylidene) and NaBArF 4 (BArF 4 = tetrakis(3,5-bis(trifluoromethyl)phenyl)borate). For Cu and Ag, these examples constitute the first of such metals toward this transformation, that also provides ethyl cyclohepta-2,4,6-trienecarboxylate as by-product from the so-called Buchner reaction. In the case of methyl-substituted benzenes, the reaction exclusively proceeds onto the aromatic ring, the Csp 3-H bond remaining unreacted. A significant coinage metal effect has been observed, since the gold catalyst favors the formation of the insertion product into Csp 2-H bond whereas copper and silver preferentially induce the formation of the cycloheptatriene derivative. Experimental studies and theoretical calculations have explained the observed selectivity in terms of the formation of a common Wheland intermediate, resembling an electrophilic aromatic substitution, from which the reaction pathway evolves into two separate routes to each product.We thank the Spanish MINECO for CTQ2014-52769-C3-1-R, CTQ2014-57761-R, RED INTECAT CTQ2014-52974-REDC and Severo Ochoa Excellence Accreditation 2014-2018 SEV-2013-0319 and the ICIQ Foundation for financial support

Rare Gold-Catalyzed 4-exo-dig Cyclization for Ring Expansion of Propargylic Aziridines toward Stereoselective (Z)‑Alkylidene Azetidines, via Diborylalkyl Homopropargyl Amines

We report an uncommon 4-exo-dig cyclization of N-tosyl homopropargyl amines, catalyzed by [AuCl(PEt3)]/AgOTf, to prepare stereoselective (Z)-2-alkylidene-1-tosylazetidine compounds. The reaction outcome contrasts with the gold-catalyzed cyclization of N-tosyl homopropargyl amines containing a methyl group at the propargylic position that provides substituted 2,3-dihydropyrroles via a 5-endo-dig mechanism. The access to N-tosyl homopropargyl amines is possible by the regioselective nucleophilic attack of α-diboryl alkylidene lithium salts to propargylic aziridinesThe authors thank Ministerio de Economía y Competitividad and Fondo Europeo de Desarrollo Regional (FEDER) through Projects PID2022-141693NB-I00, PID2020-113797RB-C21, and RED2022-134074-T, founded by MCIN/AEI/10.13039/ 501100011033 and “ERDF-A Way of Making Europe

Heterogeneous Olefin Aziridination Reactions Catalyzed by Polymer-Bound Tris(triazolyl)methane Copper Complexes

Efficient olefin aziridination has been achieved with a tris(triazolyl)methane copper catalyst supported onto polystyrene. Aryl, alkyl and methoxycarbonyl-substituted olefins are converted into N-tosylaziridines in good to high yields. The solid catalyst is readily separated by filtration and recycled, allowing its reuse with no significant loss of the catalytic activity

Trispyrazolylborate Ligands Supported on Vinyl Addition Polynorbornenes and Their Copper Derivatives as Recyclable Catalysts

Polynorbornenes prepared by vinyl addition poly- merization and bearing pendant alkenyl groups serve as skeletons to support trispyrazolylborate ligands (Tpx) built at those alkenyl sites. Reaction with CuI in acetonitrile led to VA-PNB–TpxCu(NCMe) (VA-PBN = vinyl addition polynorbor- nene) with a 0.8–1.4 mmol incorporation of Cu per gram of polymer. The presence of tetracoordinated copper(I) ions was been assessed by FTIR studies on the corresponding VA-PNB-TpxCu(CO) adducts, in agreement with those on discrete TpxCu(CO). The new materials were employed as heteroge- neous catalysts in several carbene- and nitrene-transfer reac- tions, showing a behavior similar to that of the homogene- ous counterparts but also being recycled several times main- taining a high degree of activity and selectivity. This is the first example of supported Tpx ligands onto polymeric sup- ports with catalytic applications.MINECO (CTQ2017-82893-C2-1-R, CTQ2016-80913-P and Red Intecat CTQ2016-81923-REDC)Junta de Castilla y León (VA051P17, VA062G18)European Union (CHAOS COST ACTION CA-15106)

Catalytic Nitrene Transfer To Alkynes: A Novel and Versatile Route for the Synthesis of Sulfinamides and Isothiazoles

A novel transformation is reported for the reaction of terminal or internal alkynes with the nitrene precursor PhI=NTs (Ts=p-toluenesulfonyl) in the presence of catalytic amounts of Tp(Br3)Cu(NCMe) (Tp(Br3)=hydrotris(3,4,5-tribromo-pyrazolylborate). Two products containing an imine functionality have been isolated from the reaction mixtures, identified as sulfinamides and isothiazoles. The former correspond to the formal reduction of the sulfone group into sulfoxide, whereas the latter involves the insertion of an alkyne carbon atom into the aromatic ring of the N-tosyl moiety.Support for this work was provided by the MINECO (CTQ2014-52769-C3-R-1, CTQ2014-57761-R, Severo Ochoa Excellence Accreditation 2014-2018 SEV-2013-0319, Red Intecat CTQ2014-52974-REDC) and by a FPU fellowship (M.R.R.). We thank Prof. Antonio Echavarren for helpful comments and discussions