Coordination Chemistry and Methylation of Mixed‐Substituted Tetraphosphetanes (RP−P t Bu) 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(MePy)PMe2P(MePy)PtBu‐]3+ (13 3+; MePy=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)3PtBu‐]3+ (17 3+) when reacted with Me2PPMe2.
Choose your donor: A convenient route towards mixed‐substituted tetraphosphetanes was established, enabling the synthesis of (PhP‐PtBu)2 and (PyP‐PtBu)2 (Py=2‐pyridyl) in good yields. The coordination chemistry of (PyP‐PtBu)2 was investigated by reacting it with coinage metal triflate salts. Further methylation studies on both tetraphosphetanes revealed an interesting chemistry of multiply charged, cylic polyphosphanes.