Steric stabilisation of the P-P bond in a bulky tetraorganodiphosphine: synthesis, characterisation and X-ray structure determination of tetrakis(2,4,6-triisopropylphenyl)diphosphine

We report the synthesis and characterisation of tetrakis(2,4,6-triisopropyl phenyl)diphosphine. Synthesis is effected by the treatment of PCl3 with an excess of 2,4,6-triisopropylphenyllithium (or the equivalent Grignard reage nt) in 70% yield. While under normal circumstances the triarylphosphine wou ld be expected, excessive bulk prevents this, and the resulting diphosphine is, unusually, stable to P-P cleavage by further organolithium moieties. T he compound is stable, both thermally (m.p. 185 degrees C) and to air and w ater in the solid state, although conversion to the equivalent diorganophos phinate ester is effected by boiling ethanolic solutions in air. Crystallis ation from hexane/ethanol afforded pale yellow crystals of X-ray quality. T he molecule is characterised by m.p., IR, NMR, elemental analysis (C, H, P) and MS. The X-ray structure shows an antiperiplanar conformation with a P- P separation of 2.2461(16) Angstrom. Comparisons are made with other diphos phines, the title compound being only the fourth simple diphosphine to be s tructurally characterised. (C) 2000 Elsevier Science S.A. All rights reserv ed.