Heteroleptic copper(I) complexes incorporating sterically demanding diazabutadiene ligands (DABs). Synthesis, spectroscopic characterization and solid state structural analysis

Sterically demanding pyridine-quinoline anchoring ligands as building blocks for copper(i)-based dye-sensitized solar cell (DSSC) complexes

“…Our results compare well with the τ 4 values of 0.67 and 0.66 reported for [Cu(L)(phen)] + and [Cu(L)(dmp)] + (L = 6,6′-dimesityl-2,2′-bipyridine; dmp = 2,9-dimethyl-1,10-phenanthroline) respectively, where a distorted trigonal pyramidal geometry has been proposed. 41 This is also in good agreement with the reported τ 4 value of 0.59, for [Cu(pqcame) 2 ][PF 6 ], 27 albeit the new compounds are slightly less distorted. Notably, complex 7 , with a methyl group at the C8 of the quinoline ring, displays a geometry index τ 4 = 0.49 implying a severe distortion from the ideal tetrahedral geometry.…”

“…[24][25][26] Methylation at the 6′ and 8 positions of the anchoring ligand may act as a protecting scaffold for the copper(I) metal center. In this respect, stereochemical protection can be potentially offered by the benzo ring of the quinoline moiety, as was reported for [Cu( R DAB dipp ) (L COOMe )][PF 6 ] ( R DAB dipp = 1,4-diaza-1,3-butadienes, R = H, Me; dipp = 2,6-diisopropylphenyl; L COOMe = methyl-2-( pyridin-2-yl)quinoline-4-carboxylate) complexes, 27 and for the case of a number of ruthenium(II) complexes. 15,28,29 Accordingly, simple organic diimine ligand precursors, analogues of pqca, substituted with methyl at the 6′ (6′-Mepqca), the 8 (8-Mepqca), and both the 8 and 6′ positions (8,6′-Me 2 pqca) of the pyridyl ring and the quinoline moiety, constitute the basis of this work.…”

“…24–26 Methylation at the 6′ and 8 positions of the anchoring ligand may act as a protecting scaffold for the copper( i ) metal center. In this respect, stereochemical protection can be potentially offered by the benzo ring of the quinoline moiety, as was reported for [Cu( R DAB dipp )(L COOMe )][PF 6 ] ( R DAB dipp = 1,4-diaza-1,3-butadienes, R = H, Me; dipp = 2,6-diisopropylphenyl; L COOMe = methyl-2-(pyridin-2-yl)-quinoline-4-carboxylate) complexes, 27 and for the case of a number of ruthenium( ii ) complexes. 15,28,29…”

“…They were isolated as low melting solids (126 °C–154 °C), according to the improved synthesis reported for the pqcame ligand. 27 The 1 H NMR spectra of 6′-Mepqcame , 8-Mepqcame and 8,6′-Me 2 pqcame recorded in CDCl 3 are included in the ESI (Fig. S10–S18†), displaying the characteristic singlet resonance for the methyl group protons at δ 2.71 (6′-Me), 2.92 (8-Me) and 2.92/2.69 ppm (8,6′-Me) respectively.…”

“…The FT-IR spectra of 6-8 are characterised by a strong asymmetric stretching vibration typical of the ν as (CvO) of the ester moiety at ∼1730 cm −1 , shifted to higher wave numbers compared with 1-4, which is in good agreement with the vibration mode reported for the [Cu( pqcame) 2 ][PF 6 ] complex, at 1726 cm −1 . 27 The NMR spectra of 6-8 were recorded in CDCl 3 and assignment was based on routine two-dimensional (2D) NMR techniques (ESI, Fig. S31-S39 †).…”