TY - JOUR
T1 - Synthesis, structures and properties of luminescent (C^N^C)gold(III) alkyl complexes: Correlation between photoemission energies and C-H acidity
AU - Fernandez Cestau, Julio
AU - Bertrand, Benoit
AU - Pintus, Anna
AU - Bochmann, Manfred
PY - 2017/9/11
Y1 - 2017/9/11
N2 - The reaction of (C^Npz^C)AuCl with C-H acidic compounds H2CR1R2 in the presence of base readily affords the corresponding alkyl complexes (C^Npz^C)AuCHR1R2 [2a, R1 = R2 = CN; 3a, R1 = R2 = C(O)Me; 4, R1 = R2 = CO2Et; 5, R1 = R2 = C(O)Ph; 6a, R1 = H, R2 = C(O)Me]. The analogous pyridine-pincer complexes 2b, 3b and 6b were obtained similarly [C^Npz^C = 2,6-bis(4′-tBuC6H3)2pyrazine dianion; C^Npy^C = 2,6-bis(4′-tBuC6H3)2pyridine dianion]. The reactions of (C^Npz^C)AuOAcF (7a) and (C^Npy^C)AuOAcF (7b) with MeMgI gave the methyl complexes (C^Npz^C)AuMe (8a) and (C^Npy^C)AuMe (8b), respectively. The crystal structures of 2a, 2b, 3a, 6a, and 7a have been determined. The photophysical properties of the new complexes and those of the previously reported gold hydride (C^Npz^C)AuH (AuH) are reported. The lower-energy absorption and the emission maxima follow the energy sequence 2a < 3a < 4 < 5 < 6a < AuH ≈ 8a for the pyrazine series, and 2b < 3b < 6b ≈ 8b for the pyridine series. These values provide a correlation with the pKa values of the corresponding ancillary ligand precursors. In agreement with DFT calculations, the emissions are assigned to 3IL(C^N^C)/3ILCT {(C6H4tBu-4’)→pz/py*} transitions, dominated by the HOMO and the LUMO orbitals. The LUMO is located in the heterocycle (py/pz) in trans position to the ancillary ligand, which makes this orbital more sensitive to the electronic nature of the ancillary ligand than the HOMO. The calculations establish that the charge transfer from the tBuC6H3 ligand fragments to the central heterocycle ring in the dominant transition explains the modulation of the properties with the σ-donor characteristics of the alkyl or hydride ligands.
AB - The reaction of (C^Npz^C)AuCl with C-H acidic compounds H2CR1R2 in the presence of base readily affords the corresponding alkyl complexes (C^Npz^C)AuCHR1R2 [2a, R1 = R2 = CN; 3a, R1 = R2 = C(O)Me; 4, R1 = R2 = CO2Et; 5, R1 = R2 = C(O)Ph; 6a, R1 = H, R2 = C(O)Me]. The analogous pyridine-pincer complexes 2b, 3b and 6b were obtained similarly [C^Npz^C = 2,6-bis(4′-tBuC6H3)2pyrazine dianion; C^Npy^C = 2,6-bis(4′-tBuC6H3)2pyridine dianion]. The reactions of (C^Npz^C)AuOAcF (7a) and (C^Npy^C)AuOAcF (7b) with MeMgI gave the methyl complexes (C^Npz^C)AuMe (8a) and (C^Npy^C)AuMe (8b), respectively. The crystal structures of 2a, 2b, 3a, 6a, and 7a have been determined. The photophysical properties of the new complexes and those of the previously reported gold hydride (C^Npz^C)AuH (AuH) are reported. The lower-energy absorption and the emission maxima follow the energy sequence 2a < 3a < 4 < 5 < 6a < AuH ≈ 8a for the pyrazine series, and 2b < 3b < 6b ≈ 8b for the pyridine series. These values provide a correlation with the pKa values of the corresponding ancillary ligand precursors. In agreement with DFT calculations, the emissions are assigned to 3IL(C^N^C)/3ILCT {(C6H4tBu-4’)→pz/py*} transitions, dominated by the HOMO and the LUMO orbitals. The LUMO is located in the heterocycle (py/pz) in trans position to the ancillary ligand, which makes this orbital more sensitive to the electronic nature of the ancillary ligand than the HOMO. The calculations establish that the charge transfer from the tBuC6H3 ligand fragments to the central heterocycle ring in the dominant transition explains the modulation of the properties with the σ-donor characteristics of the alkyl or hydride ligands.
U2 - 10.1021/acs.organomet.7b00439
DO - 10.1021/acs.organomet.7b00439
M3 - Article
VL - 36
SP - 3304
EP - 3312
JO - Organometallics
JF - Organometallics
SN - 0276-7333
IS - 17
ER -