Coordination Chemistry and Methylation of Mixed-Substituted Tetraphosphetanes (RP-PtBu)₂ (R=Ph, Py)

Synthesis of mixed-substituted tetraphosphetanes (RP-PtBu)₂ (R=Ph (4), Py (5); Py=2-pyridyl) is achieved from the condensation of dipyrazolylphosphanes RPpyr₂ (R=Py (1), Ph (3); pyr=3,5-dimethylpyrazolyl) as P₁ -building block (R-P) and tBuPH₂ in an equimolar ratio. Compound 5 is of special interest since the presence of two pyridyl-substituents as well as the P₄ -core allows for a rich coordination chemistry with coinage metal salts [Cu(MeCN)₄ ][OTf], Ag[OTf] and in situ formed [Au(tht)][OTf] (tht=tetrahydrothiophene). Both tetraphosphetanes undergo alkylation reaction with MeOTf to give a series of tetraphosphetanium and tetraphosphetanediium triflate salts with additional methylation of the pyridyl-moiety in case of 5 resulting in interesting novel cyclic trications. Harsh reaction condition and an excess of MeOTf converts 5 into the cyclic trication [-P(^Me Py)PMe₂ P(^Me Py)PtBu-]³⁺ (13³⁺ ; ^Me Py=1-methylpyridiniumyl) through the elimination of isobutene. This salt undergoes a complicated rearrangement reaction involving a P-P/P-P bond metathesis to form trication [-P(MePy)₃ PtBu-]³⁺ (17³⁺ ) when reacted with Me₂ PPMe₂ .