Stable Au(III) Complexes Bearing Hemilabile P^∧N and C^∧N Ligands: Coordination of the Pendant Nitrogen upon Oxidation of Gold

Abstract

The oxidation of Au(I) complexes featuring two hemilabile ligands was investigated. The phosphine-amine (P ∧ N) and mesoionic N-heterocyclic carbenepyridine (C ∧ N) ligands were shown to stabilize the ensuing Au(III) complexes by chelation. Oxidation of (MeDalphos)AuCl with PhICl 2 directly affords the corresponding P ∧ N-chelated cationic Au(III) complex without requiring a chloride abstractor. The C ∧ N hemilabile ligand is shown to efficiently chelate Au(III), but not Au(I). Cationization of the (C ∧ N)AuCl complex 3 affords the dinuclear complex 4 with the C ∧ N ligand bridging two Au centers. Oxidation of 3 with PhICl 2 does not spontaneously enforce coordination of the pyridine side arm, as with the P ∧ N ligand. However, cationization of the resulting AuCl 3 complex 5 with a chloride abstractor successfully promoted pyridine chelation. The structures of all complexes have been ascertained by NMR spectroscopy and X-ray diffraction analyses.

Hemilabile MIC^N ligands allow oxidant-free Au(i)/Au(iii) arylation-lactonization of γ-alkenoic acids

“…The Au(I) centers adopted a linear dicoordinate arrangement, showing an aurophilic interaction (Au•••Au length of 2.8212(4) Å). Analogously to Bourissou's (MICˆN)Au(I) complex, 64 the formation of a dimeric Au(I) species was favored rather than a mononuclear Au(I) having both the MIC and py or pym pendant groups coordinated.…”

“…40 More recently, Bourissou and coworkers reported the reactivity of a Au(I) complex containing a N3-alkylated mesoionic 1,2,3-triazol-5-ylidene bearing a pendant pyridine group. 64 However, the complex did not undergo oxidative addition towards iodobenzene, thus precluding its exploitation in oxidant-free reactivity. In fact, the formation of a dimeric Au(I) species was observed instead of the formation of the oxidative addition Au(III) product.…”

Ligand-enabled oxidation of gold(i) complexes with o-quinones

“…12 The reaction proceeds similarly with the related tetrabromo and tetrauoro o-benzoquinones to give the corresponding Au(III) catecholate complexes 5b,c. Again, no reaction was observed with the less oxidizing parent and 3,5-t 16 The higher stability of the P^N-ligated complexes 5a-c enabled to grow crystals and carry out X-ray diffraction analyses (Fig. 2 and Table 1).…”

“…Very similar data were observed for the related [(P^N)AuCl2]SbF6 complex ( 31 P: 109.8 ppm; 1 H: 3.92 ppm; 13 C: 59.1 ppm; 15 N: 82.3 ppm). 16 Scheme 2. Oxidation of the (P^N)-ligated Au(I) complex 4 with tetrahalo obenzoquinones (isolated yields in parentheses).…”

Mechanistic Investigation into the Gold-Catalyzed Decarboxylative Cross-Coupling of Iodoarenes

“…Gold­(I/III) redox catalysis − is in its infancy relative to gold­(I) catalysis − or the well-established redox catalysis of other late transition metals (e.g., Pd or Ir). The comparatively high oxidation potential for most gold­(I) complexes has largely prevented the incorporation of gold-mediated oxidative addition into catalytic cycles. − Notwithstanding this challenge, a growing number of reports demonstrate that some gold­(I) complexes can be oxidized with alkyl iodides, − aryl diazonium salts, − hypervalent iodine species, ,,,,− and other reagents. ,, The gold­(I)-mediated oxidative addition with aryl halides was recently enabled through the use of bidentate or hemilabile ligands. − Even with these advances in fundamental reactivity, it is challenging to develop catalytic cross-coupling reactions that rely upon gold-mediated redox events. ,,− ,,,− ,− …”