Evaluating heteroleptic copper(I)-based complexes bearing π-extended diimines in different photocatalytic processes

Abstract

A series of 12 new copper-based photocatalysts of the type Cu(N^N)(P^P)BF4 were synthesized bearing π-extended diimine ligands. The complexes have red shifted absorptions and larger extinction coefficients than complexes prepared with a parent diimine, dmp. The complexes were evaluated for their ability to promote three different photochemical transformations. Although the complexes were inactive in a reductive PCET process, the complexes afforded good yields in both SET and ET processes. Interestingly, homoleptic copper-complexes derived from the π-extended diimines were significantly more active in SET processes than analogous complexes with simpler diimines.

Photoactive Copper Complexes: Properties and Applications

“…Indeed, as the diphosphine ligand lowers the energy of the orbital HOMO, the energy gap between the ground and excited states becomes larger, which reduces the nonradiative deactivation pathways due to the energy gap law. Sterically hindered diimines with 2,9-substituted phenanthrolines are, however, required to further increase the emission intensities and lifetimes, as seen for example with [Cu(dmp)(DPEphos)] + ([Cu( NN 2 )( PP 1 )] + , entry 20 in Table ), emitting at 570 nm with a lifetime of 14.3 μs in deaerated dichloromethane …”

“…Following the report of the Collins group on the remarkably efficient synthesis of various heteroleptic copper complexes and their applications in photoredox catalysis, , Itoh and co-workers reported in 2018 the use of [Cu(dmp)(Binap)]PF 6 ([Cu( NN 2 )( PP 41 )]PF 6 ) for the visible light-catalyzed ATRA reaction of tetrabromomethane onto alkenes . The same year, the Soo group studied the properties of a family of panchromatic bis(arylimino)acenaphthene copper complexes, allowing to carry out diverse reactions under inexpensive white light sources .…”

Heteroleptic Copper(I)-Based Complexes Incorporating BINAP and π-Extended Diimines: Synthesis, Catalysis and Biological Applications

“…Although the complexes of dppz and bdppz had larger excited-state reduction potentials, it is possible that the complexes with ligands with larger π-surfaces could be more unstable in solution. The stability of various copper complexes with diimines having large π-surfaces was previously shown to decrease with the size of the ligand in other photocatalytic processes [26]. However, it should be noted that amongst other BINAP-derived complexes, the Cu(dpq)(BINAP)BF 4 (66% of 2) was superior in the Appel-type reaction to other structurally similar complexes such as Cu(dmp)(BINAP)BF 4 (18% of 2) and Cu(phen)(BINAP)BF 4 (45% of 2), suggesting that the dpq offered some beneficial reactivity (Figure 4).…”

“…Our bank of available diimines and bisphosphines has since expanded to allow for development of improved complexes for energy transfer processes [25]. Among the diimine structures evaluated were those that possessed extended π-surfaces, which unfortunately did not afford heteroleptic complexes with remarkable activities in photocatalysis [26]. However, previous studies were limited to wide-bite-angle bisphosphines, as the preparation of the corresponding complexes with BINAP was problematic (Figure 1).…”

Photophysical properties of homobimetallic Cu(i)–Cu(i) and heterobimetallic Cu(i)–Ag(i) complexes of 2-(6-bromo-2-pyridyl)-1H-imidazo[4,5-f][1,10]phenanthroline

“…19,30,[38][39][40][41][42][43][44][45][46] Second, the introduction of substituents at the ortho positions of the a-diimine coordination sites is a good way to gain better emission, because it can increase the steric hindrance of the coordination sites and reduce the quenching of luminescence caused by the attack of solvent molecules, especially water molecules. 4,15,37,[47][48][49][50][51] For instance, a highly luminescent Cu(I) complex has been reported by introducing two methyl groups to the 6,6 0 -positions of 4,4 0dimethyl-2,2 0 -bipyridine (dmbpy). 37 Its luminescence quantum yield was 6 times that of the Cu(I) analogue with dmbpy.…”