Diborane Reductions of CO2 and CS2 Mediated by Dicopper μ-Boryl Complexes of a Robust Bis(Phosphino)-1,8-Napthyridine Ligand

12 January 2024, Version 1
This content is a preprint and has not undergone peer review at the time of posting.


A symmetrical dinucleating 1,8-naphthyridine ligand featuring phosphino side arms linked through fluorene-9,9-diyl moieties (PNNPFlu) was synthesized and used to obtain the cationic organodicopper complexes 2, [(PNNPFlu)Cu2(µ‐Ph)][NTf2]; [NTf2] = bis(trifluoromethane)sulfonimide, and 6, [(PNNPFlu)Cu2(µ‐CCPh)][NTf2], as well as the µ‐tert-butoxide 3, [(PNNPFlu)Cu2(µ‐OtBu)][NTf2]. Complex 3 reacted with diboranes to afford dicopper µ‐boryl species (4, with µ‐Bcat; cat = catecholate and 5, with µ‐Bpin; pin = pinacolate). Complexes 4 and 5 are more reactive in C–H bond activations of terminal alkynes and toward activations of CO2 and CS2, in comparison to dicopper µ‐boryl complexes supported by a 1,8-naphthyridine-based ligand with two di(pyridyl) side arms. The molecular structures (determined by X-ray crystallography) and DFT analysis indicate that the higher reactivity of 4 and 5 relate to changes in the coordination sphere of copper, rather than to perturbations on the Cu–B bonding interactions. Addition of xylyl isocyanide (CNXyl) to 4 gave 7, [(PNNPFlu)Cu2(µ‐Bcat)(CNXyl)][NTf2], demonstrating that the lower coordination number at copper is chemically significant. Reactions of 4 and 5 with CO2 yielded the corresponding dicopper borate complexes (8, [(PNNPFlu)Cu2(µ‐OBcat)][NTf2]; 9, [(PNNPFlu)Cu2(µ‐OBpin)][NTf2]), with 4 demonstrating catalytic CO2 reduction in the presence of excess diborane. Related reactions of 4 and 5 with CS2 provided the insertion products 10, {[(PNNPFlu)Cu2]2[µ‐S2C(Bcat)2]}[NTf2]2 and 11, [(PNNPFlu)Cu2(µ,κ2‐S2CBpin)][NTf2], respectively. These insertion products feature Cu–S–C–B linkages analogous to those of proposed, analogous CO2 insertion intermediates.



Supplementary materials

Supporting Information
Experimental methods, details of synthesis, details of crystallography, details of calculations, NMR spectra, IR spectra


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