Tricyclohexylphosphine (PCy₃) | CAS 2622-14-2 | ≥97%

Tricyclohexylphosphine (PCy₃) is a bulky, strongly electron-donating trialkylphosphine widely used as a supporting ligand in homogeneous catalysis. Its three cyclohexyl groups make it both a powerful σ-donor — with high basicity, the conjugate acid having a pKₐ of about 9.7 — and a sterically demanding ligand characterised by a large Tolman cone angle near 170°. This combination of strong donation and steric bulk stabilises low-coordinate metal complexes and can favour the coordinatively unsaturated species in catalytic cycles.

Olefin-metathesis catalysis

PCy₃ is a defining ligand of ruthenium olefin-metathesis chemistry: two PCy₃ ligands feature in the first-generation Grubbs ruthenium benzylidene catalyst, and one is retained in the second-generation system alongside an N-heterocyclic carbene. In Grubbs-type catalysts, initiation proceeds predominantly through dissociation of one PCy₃ ligand to generate a 14-electron ruthenium species, which binds the olefin and proceeds through a metallacyclobutane intermediate. Because phosphine loss is the gateway to the active catalyst, ligand structure controls initiation: larger cone angles accelerate dissociation and stronger donation slows it, so PCy₃ sets a particular balance of initiation rate and resting-state stability. This makes it both a practical component of working catalysts and a benchmark in studies of how phosphine structure governs metathesis activity.

Cross-coupling and aryl chloride activation

As an electron-rich, sterically demanding trialkylphosphine, PCy₃ accelerates oxidative addition and helps bring relatively unreactive substrates — including aryl chlorides — within reach of palladium- and nickel-catalysed cross-coupling. The well-defined nickel precatalyst bis(tricyclohexylphosphine)nickel(II) dichloride, NiCl₂(PCy₃)₂, is a documented catalyst precursor for Suzuki–Miyaura coupling of aryl tosylates with arylboronic acids and for Kumada and Negishi couplings. PCy₃-ligated palladium, such as Pd(PCy₃)₂Cl₂, catalyses Buchwald–Hartwig amination of aryl chlorides with secondary amines. A more specialised example is nickel/PCy₃-catalysed silaborative carbon–carbon bond cleavage of vinylcyclopropanes, in which PCy₃ is uniquely effective among phosphines and the ring opens selectively to give boryl-substituted allylsilanes.

Hydrogenation and coordination chemistry

PCy₃ is a component of Crabtree's iridium hydrogenation catalyst, valued for the homogeneous hydrogenation of highly substituted alkenes that resist less active systems, and for hydrogen-transfer chemistry. The ligand also supports well-defined, electron-rich low-valent complexes that serve as reference points in organometallic mechanism: bis(tricyclohexylphosphine)palladium(0), Pd(PCy₃)₂, is a coordinatively unsaturated L₂Pd(0) centre whose oxidative addition of aryl halides has been studied in detail, and analogous nickel(0) and platinum(0) phosphine species support the study of oxidative addition, reductive elimination and small-molecule activation. Its well-defined donor strength and cone angle make PCy₃ a recurring reference ligand in mechanistic and ligand-comparison work.