C−C Cross‐Couplings from a Cyclometalated Au(III) C∧ N Complex: Mechanistic Insights and Synthetic Developments

• Published in: Chemistry : a European journal Vol. 27; no. 57; pp. 14322 - 14334
• Main Authors: Bonsignore, Riccardo, Thomas, Sophie R., Rigoulet, Mathilde, Jandl, Christian, Pöthig, Alexander, Bourissou, Didier, Barone, Giampaolo, Casini, Angela
• Format: Journal Article
• Language: English
• Published: WEINHEIM Wiley 13.10.2021; Wiley Subscription Services, Inc; John Wiley and Sons Inc
• Subjects: Benzylpyridines; Chemical reactions; Chemistry; Chemistry, Multidisciplinary; Coordination; Couplings; Cross coupling; Crystallography; Gold; gold cyclometalated complexes; Intermediates; Magnetic resonance spectroscopy; NMR; NMR spectroscopy; Nuclear magnetic resonance; Nucleophiles; organometallics; Physical Sciences; Reagents; reductive elimination; Science & Technology; Tin; Two dimensional analysis; GOLD(III) COMPLEXES; ORGANIC-SYNTHESIS; PHOTOREDOX; REACTIVITY; BOND FORMATION; OXIDATIVE ADDITION; gold cyclometalated complexes; H ACTIVATION; organometallics; cross-coupling; BASIS-SETS; reductive elimination; NMR spectroscopy; DUAL GOLD
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/chem.202102668

In recent years, the reactivity of gold complexes was shown to extend well beyond π‐activation and to hold promises to achieve selective cross‐couplings in several C−C and C−E (E=heteroatom) bond forming reactions. Here, with the aim of exploiting new organometallic species for cross‐coupling reactions, we report on the Au(III)‐mediated C(sp2)−C(sp) occurring upon reaction of the cyclometalated complex [Au(CCH2N)Cl2] (1, CCH2N=2‐benzylpyridine) with AgPhCC. The reaction progress has been monitored by NMR spectroscopy, demonstrating the involvement of a number of key intermediates, whose structures have been unambiguously ascertained through 1D and 2D NMR analyses (1H, 13C, 1H‐1H COSY, 1H‐13C HSQC and 1H‐13C HMBC) as well as by HR‐ESI‐MS and X‐ray diffraction studies. Furthermore, crystallographic studies have serendipitously resulted in the authentication of zwitterionic Au(I) complexes as side‐products arising from cyclization of the coupling product in the coordination sphere of gold. The experimental work has been paralleled and complemented by DFT calculations of the reaction profiles, providing valuable insight into the structure and energetics of the key intermediates and transition states, as well as on the coordination sphere of gold along the whole process. Of note, the broader scope of the cross‐coupling at the Au(III) CCH2N centre has also been demonstrated studying the reaction of 1 with C(sp2)‐based nucleophiles, namely vinyl and heteroaryl tin and zinc reagents. These reactions stand as rare examples of C(sp2)−C(sp2) cross‐couplings at Au(III). The mechanism of C(sp2)−C(sp) coupling templated by the Au(III) cyclometalated complex [Au(CCH2N)Cl2] has been investigated. By tuning the reaction conditions and monitoring its progress by NMR, a number of intermediate species involved in the reductive elimination process could be isolated and characterised by different spectroscopic and analytical methods, including XRD, as well as by DFT studies.