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Phosphino-Triazole Ligands for Palladium-Catalyzed Cross-Coupling', Organometallics, Vol University of Birmingham Phosphino-Triazole Ligands for Palladium- Catalyzed Cross-Coupling Zhao, Yiming; Van Nguyen, Huy; Male, Louise; Craven, Philip; Buckley, Benjamin R.; Fossey, John S. DOI: 10.1021/acs.organomet.8b00539 License: Creative Commons: Attribution (CC BY) Document Version Publisher's PDF, also known as Version of record Citation for published version (Harvard): Zhao, Y, Van Nguyen, H, Male, L, Craven, P, Buckley, BR & Fossey, JS 2018, 'Phosphino-Triazole Ligands for Palladium-Catalyzed Cross-Coupling', Organometallics, vol. 37, no. 22, pp. 4224-4241. https://doi.org/10.1021/acs.organomet.8b00539 Link to publication on Research at Birmingham portal Publisher Rights Statement: checked for eligibility 30/11/2018 Organometallics 2018, 37, 22, 4224-4241 10.1021/acs.organomet.8b00539 General rights Unless a licence is specified above, all rights (including copyright and moral rights) in this document are retained by the authors and/or the copyright holders. The express permission of the copyright holder must be obtained for any use of this material other than for purposes permitted by law. •Users may freely distribute the URL that is used to identify this publication. •Users may download and/or print one copy of the publication from the University of Birmingham research portal for the purpose of private study or non-commercial research. •User may use extracts from the document in line with the concept of ‘fair dealing’ under the Copyright, Designs and Patents Act 1988 (?) •Users may not further distribute the material nor use it for the purposes of commercial gain. Where a licence is displayed above, please note the terms and conditions of the licence govern your use of this document. When citing, please reference the published version. Take down policy While the University of Birmingham exercises care and attention in making items available there are rare occasions when an item has been uploaded in error or has been deemed to be commercially or otherwise sensitive. If you believe that this is the case for this document, please contact [email protected] providing details and we will remove access to the work immediately and investigate. Download date: 24. Sep. 2021 This is an open access article published under a Creative Commons Attribution (CC-BY) License, which permits unrestricted use, distribution and reproduction in any medium, provided the author and source are cited. Article Cite This: Organometallics 2018, 37, 4224−4241 pubs.acs.org/Organometallics Phosphino-Triazole Ligands for Palladium-Catalyzed Cross-Coupling † † ‡ † § Yiming Zhao, Huy van Nguyen, Louise Male, Philip Craven, Benjamin R. Buckley, † and John S. Fossey*, † ‡ School of Chemistry and X-ray Crystallography Facility, School of Chemistry, University of Birmingham, Edgbaston, Birmingham, West Midlands B15 2TT, United Kingdom § Department of Chemistry, Loughborough University, Loughborough, Leicestershire LE11 3TU, United Kingdom *S Supporting Information ABSTRACT: Twelve 1,5-disubtituted and fourteen 5-sub- stituted 1,2,3-triazole derivatives bearing diaryl or dialkyl phosphines at the 5-position were synthesized and used as ligands for palladium-catalyzed Suzuki−Miyaura cross-cou- pling reactions. Bulky substrates were tested, and lead-like product formation was demonstrated. The online tool SambVca2.0 was used to assess steric parameters of ligands and preliminary buried volume determination using XRD- obtained data in a small number of cases proved to be informative. Two modeling approaches were compared for the determination of the buried volume of ligands where XRD data was not available. An approach with imposed steric restrictions was found to be superior in leading to buried volume determinations that closely correlate with observed reaction conversions. The online tool LLAMA was used to determine lead-likeness of potential Suzuki−Miyaura cross-coupling products, from which 10 of the most lead-like were successfully synthesized. Thus, confirming these readily accessible triazole-containing phosphines as highly suitable ligands for reaction screening and optimization in drug discovery campaigns. ■ INTRODUCTION are not always employed as innocent bystander linkage motifs. fi 1−4 Triazoles of this type have been used as analogues of peptide Click chemistry, as de ned by Sharpless and co-workers, 16 has transformed the face, and accessibility to the nonspecialist linkages (Figure 1, 2), such peptidomimetics are physiolog- of molecular linking strategies. Among click approaches, the ically stable, and their modular synthesis allows access to a 17,18 highly regioselective copper-catalyzed, Huisgen cycloaddition broad range of biologically relevant applications. The reaction to form 1,4-triazoles (Figure 1, 1) by Meldal and utility of further synthetic transformations has been probed, particularly in the derivatization at the 5-position (Figure 1, 3).19,20 Downloaded via UNIV OF BIRMINGHAM on November 30, 2018 at 09:26:51 (UTC). Copper-catalyzed triazole formation has been exploited in a 21 See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles. wide range of scenarios and has been the subject of various − mechanistic studies,22 26 leading to the proposal of a binuclear transition state involving two copper atoms. 1,2,3-Triazole derivatives have been employed as nitrogen-coordinating − ligands,27 e.g. in N,N′-,28 34 N,S-,29 N,Se-29 and cyclo- − metalated35 37 bidentate coordination complexes. Further- more, tris-triazoles, such as TBTA (Figure 2, 4) and its Figure 1. Upper: copper-catalyzed azide−alkyne cycloaddition analogues, have been used as ligands for reactions including (CuAAC). Lower: examples of 1,2,3-triazole-containing structures. the CuAAC by both Fokin38 and Zhu39 and their co-workers, demonstrating exceptional ligand-mediated reaction acceler- Sharpless,4,5 has grown in popularity and has been employed in ation. 6 Alkylation of a 1,2,3-triazole derivative, to furnish a 1,3,4- increasingly varied applications over the intervening years. fi The copper-catalyzed azide−alkyne cycloaddition (CuAAC) is trisubstituted triazolium salt, is the rst step in the synthesis of − ubiquitous,5,7 9 and often referred to as “the click reaction”, a newer class of N-heterocyclic carbene (NHC) reported in and the product 1,2,3-triazoles, bearing 1,4-substition patterns, with reliable fidelity and yields being synonymous with click Received: July 30, 2018 − chemistry (Figure 1, 1).8,10 15 However, the resulting triazoles Published: October 17, 2018 © 2018 American Chemical Society 4224 DOI: 10.1021/acs.organomet.8b00539 Organometallics 2018, 37, 4224−4241 Organometallics Article Figure 2. Examples of triazole-containing or -derived ligands. 2008 by Albrecht and co-workers40 and later extended by Lee − and Crowley41 43 as ligands for gold and by Grubbs and Bertrand as ligands for ruthenium-mediated catalysis (Figure 2, 5).44 The ready access to a range of ligand scaffolds through the CuAAC has led the triazole−NHC platform to continue to − gain in popularity.45 49 These reports demonstrate the 1,2,3- triazole unit is a legitimate candidate for further exploitation as a key component in ligand design and catalyst development.50 The co-authors of this report have investigated triazoles as − chemosensors51 53 and as products of asymmetric syn- Figure 3. Representative examples of bulky phosphine ligands − thesis.54 58 Furthermore, an interest in boronic acid derivatives including: upper: S-Phos (7)andX-Phos(8); middle left: − as chemosensors,59 64 including the use of cross-coupling heteroaromatic phosphine derivative (9); middle right and lower reactions as a means of sensing,65 means the co-authors of this row: Phosphino-ferrocene derivatives displaying planar chirality. report are familiar with boronic acids and esters.66 As such, a desire to bring together these streams of research under one access to highly active palladium-ligand conjugates for cross- umbrella has led to the research reported in this manuscript. coupling some of the least active substrates. Herein, the development of bulky and highly active triazole- 1,4-Disubstituted-1,2,3-triazoles have been used in the containing phosphine ligands for palladium-catalyzed Suzuki− assembly of phosphorus-containing species that have the Miyaura cross-coupling reactions is explored (Scheme 1). potential to be employed as ligands. Ready access to libraries of products using CuAAC reactions has permitted the develop- 3 Scheme 1. Outline of a General Palladium-Catalyzed ment of phosphines connected to triazoles with sp linkages to Suzuki−Miyaura Formation of Biaryl 6 the 1-N and 4-C positions. Examples include those reported by Dubrovnia, Börner and co-workers (Figure 4, 13),95 Gandel- man and co-workers who prepared PCP′ pincer complexes from bis-phosphinotriazoles (Figure 4, 14),96 and Kann and Palladium-catalyzed cross-coupling reactions are well-stud- ied and offer ready access to an extensive range of (bi)aryl − motifs (Scheme 1, 6).67 76 The suite of palladium-catalyzed cross-coupling chemistry available for the construction of biologically relevant products has transformed the field of medicinal chemistry, yet cross-coupling between sterically hindered and lead-like building blocks, particularly with aryl chlorides, remains challenging.77 Developments in palladium-catalyzed chemistry have been heavily influenced by ligand design and optimization. Among the superior ligands for palladium-catalyzed cross-coupling − reactions are bulky alkyl phosphines,78
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