The effects of introducing sterically demanding aryl substituents in [Cu(N^N)(P^P)]⁺complexes

Abstract

The syntheses and characterizations of six [Cu(N^N)(POP)][PF] and [Cu(N^N)(xantphos)][PF] compounds (POP = bis(2-(diphenylphosphino)phenyl)ether, xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene), in which N^N is a bpy ligand (1-Naphbpy, 2-Naphbpy, 1-Pyrbpy) bearing a sterically hindered 1-naphthyl, 2-naphthyl or 1-pyrenyl substituent in the 6-position, are reported. Single-crystal structure determinations of five complexes confirm a distorted tetrahedral environment for copper(i) and a preference for the N^N ligand to be oriented with the sterically-demanding aryl group being remote from the (CH)O unit of POP or the xanthene 'bowl' of xantphos. The angle between the ring planes of the bpy range from 5.8 to 26.0° and this is associated with interactions between the aryl unit and the phenyl substituents of the P^P ligand. In solution at room temperature, the complexes undergo dynamic behaviour which has been investigated using variable temperature 2D NMR spectroscopy. The [Cu(N^N)(xantphos)] complexes exist as a mixture of conformers which interconvert through inversion of the xanthene bowl-shaped unit; the preference for one conformer over the other is significantly changed on going from N^N = Phbpy to 1-Pyrbpy (Phbpy = 6-phenyl-2,2'-bipyridine). The electrochemical and photophysical properties of the [Cu(N^N)(POP)][PF] and [Cu(N^N)(xantphos)][PF] compounds are presented; the compounds are orange emitters but the introduction of the 1-naphthyl, 2-naphthyl or 1-pyrenyl substituents result in poor photoluminescence quantum yields.

Remote Modification of Bidentate Phosphane Ligands Controlling the Photonic Properties in Their Complexes: Enhanced Performance of [Cu(RN‐xantphos)(N^N)][PF6] in Light‐Emitting Electrochemical Cells

“…We have previously commented upon comparable orientational preferences of asymmetrical 6‐substituted bpy ligands in [Cu(xantphos)(6‐Rbpy)] + cations. [ 10,11,26 ]…”

[Cu(POP)(N^S)][PF6] and [Cu(xantphos)(N^S)][PF6] compounds with 2-(thiophen-2-yl)pyridines

“…We have previously reported detailed investigations of the orientation preferences of asymmetrical 6substituted-2,2 0 -bipyridine (6-Rbpy) ligands in [Cu(xantphos)(6-Rbpy)][PF 6 ]. 40,41 In [Cu(xantphos)(2)][PF 6 ] and [Cu(xantphos)(4)] [PF 6 ], the N^S ligand is oriented with the 6-methyl substituent of the pyridine ring lying over the xanthene 'bowl' (Fig. 3).…”

Intra-Cation versus Inter-Cation π-Contacts in [Cu(P^P)(N^N)][PF6] Complexes

“…As previously discussed [9][10][11] 6 ], well-resolved 1D 13 C{ 1 H} NMR spectra were not obtained and the 13 C chemical shifts were identified by using the HMQC and HMBC spectra. NMR spectra are shown in Figures S7-S27 (see Supporting Information).…”

“…A search of the Cambridge Structural Database (CSD, v. 5.40 with February 2019 updates [29]) for {Cu(xantphos)(bpy)}-containing compounds (excluding {Cu(xantphos)(phen)}) revealed 33 entries of which only six contained N^N/P^P ligand π-stacking interactions, always face-to-face stacking of the bpy domain and a PPh2 phenyl ring. These six structures have CSD refcodes EVADOW [15], EVADUC [15], EVAFEO [15], EVAFOY [15], VAWDUV [11] and VICREH [13]. In two other structures (CSD refcodes HIJQUP [30] and VANYUH [31]), inefficient bpy…phenyl π-stacking occurs with angles between the least squares planes of the rings of 38.3° (HIJQUP) and 27.3° (VANYUH).…”

“…[Cu(PˆP)(NˆN)] + complexes containing the wide bite-angle bisphosphanes 4,5-bis(diphenylphosphanyl)-9,9-dimethyl-9H-xanthene (xantphos, IUPAC PIN (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane)) and bis (2-(diphenylphosphanyl)phenyl)ether (POP, IUPAC PIN oxydi(2,1-phenylene)]bis(diphenylphosphane)) (Scheme 1) have been widely investigated and show particular promise as materials exhibiting high photoluminescence quantum yields (PLQYs). alkyloxy [10], alkylthio [10], aryl [9,11], halo [12] or trifluoroalkyl [13] [9] and [Cu(xantphos)(6-PhSbpy)][PF6] (38%) (6-Mebpy = 6-methyl-2,2'-bipyridine, 6-Etbpy = 6-ethyl-2,2'-bipyridine, 6,6'-Me2bpy = 6,6'-methyl-2,2'-bipyridine, 6-PhSbpy = 6-phenylthio-2,2'-bipyridine) [10]. A recurring feature of the solid-state structures of [Cu(xantphos)(6-Xbpy)] + complexes is the accommodation of the X group within the bowl-shaped cavity of the xanthene unit.…”