Xantphos | CAS 161265-03-8 | ≥98%

Xantphos (4,5-Bis(diphenylphosphino)-9,9-dimethylxanthene; (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphine)) is the prototypical wide-bite-angle bidentate diphosphine of the van Leeuwen xanthene family. The rigid 9,9-dimethylxanthene backbone preorganises the two -PPh2 donors at a natural bite angle of ~111°, substantially wider than narrow-bite-angle diphosphines such as dppe (~85°) and dppp (~91°), placing the ligand in the regime in which several metal-catalysed reductive-elimination steps are kinetically accelerated relative to competing pathways. The ligand binds in κ2-P,P fashion at most late transition metals and switches between cis-chelating, bis-equatorial and unusual trans-chelating coordination modes at palladium and rhodium depending on oxidation state, coligands and the catalytic step. As with all tertiary aryl phosphines, slow oxidation to phosphine oxide occurs on prolonged air exposure; for catalytic use it is best handled and stored under inert atmosphere.

Pd-catalysed C-heteroatom cross-coupling and carbonylation. The wide bite angle and rigid backbone make Xantphos one of the privileged ligands for challenging Pd-catalysed Buchwald–Hartwig C–N coupling, including the coupling of aryl bromides and chlorides with primary anilines, primary aliphatic amines, hindered amides, ureas, sulfonamides and aminoazoles, where the kinetic acceleration of C–N reductive elimination at wider P–M–P angles also minimises bis-arylation. Typical conditions pair Xantphos with Pd2(dba)3, Pd(OAc)2 or palladacycle precatalysts in 1,4-dioxane or toluene with Cs2CO3 or NaOtBu base. The same ligand supports Pd-catalysed C–S, C–O and C–P bond-forming chemistry, and the (Xantphos)Pd system is a general platform for atmospheric-pressure carbonylation of aryl bromides — alkoxycarbonylation to aryl methyl esters, aminocarbonylation to benzamides and to Weinreb amides — proceeding via cis-coordinated (Xantphos)Pd(acyl) intermediates characterised by X-ray crystallography. Cu(Xantphos)I / Pd(OAc)2 dual-metal systems, in which the phosphine binds to copper rather than palladium, are also reported for Sonogashira-type alkynylation.

Rh-catalysed linear-selective hydroformylation. Xantphos is the benchmark ligand for Rh-catalysed hydroformylation of terminal olefins to linear aldehydes, where the wide bite angle enforces bis-equatorial coordination of the diphosphine in the trigonal-bipyramidal Rh(I) hydride complex and strongly favours the linear alkyl intermediate over the branched isomer. With Rh(acac)(CO)2 / Xantphos under 10–30 bar syngas at 80–120 °C, 1-octene is hydroformylated with very high regioselectivity for the linear n-nonanal product and isomerisation to internal alkenes suppressed. Closely related xanthene-backbone diphosphines (DPEphos ~102°, sixantphos ~108°, thixantphos ~110°, nixantphos) cover the bite-angle/regioselectivity gradient defined by the van Leeuwen group.

Coordination chemistry, Cu(I) photoluminescence and mechanism studies. Xantphos forms well-defined complexes across much of the d-block, including Pd, Pt, Rh, Ir, Ru, Ni, Mn, Cu, Ag and Au, providing rigid wide-bite-angle scaffolds for the study of oxidative addition, reductive elimination, migratory insertion and β-hydride elimination. Heteroleptic cationic [Cu(Xantphos)(N^N)]+ complexes, where N^N is a substituted 2,2′-bipyridine or 1,10-phenanthroline, are a well-established class of thermally activated delayed fluorescence (TADF) emitters with high solid-state photoluminescence quantum yields reported for suitably substituted systems, of interest for light-emitting electrochemical cells and Cu(I)-based OLED active layers. Related (Xantphos)Pd(CF3)(Ph) and (Xantphos)Rh-acyl complexes are widely used as benchmark systems for mechanistic studies of carbon-carbon and carbon-heteroatom reductive elimination.