Flash Communication: A Ferrous Adduct of a Phosphanylidene-σ⁴-phosphorane

The sterically encumbered phosphanylidene-σ4-phosphorane Mes*PPMe3 (Mes* = 2,4,6-tBu3C6H2) smoothly displaces Et2O in [(tBupyrr2py)Fe(OEt2)] (1-OEt2) (tBupyrr2py2– = 3,5-tBu2-bis(pyrrolyl)pyridine) to form a rare example of a η1-phospha-Staudinger adduct of Fe, namely, [(tBupyrr2py)Fe(Mes*PPMe3)] (1-Mes*PPMe3) in 64% yield. Complex 1-Mes*PPMe3 is a ferrous, S = 2 system and quite thermally stable, but in the presence of B(C6F5)3 and photolysis, it forms the phosphaindan ferrous adduct [(tBupyrr2py)Fe(phosphaindan)] (1-phosphaindan) (phosphaindan = HPCH2C(Me2)-2,4-tBu2C6H2) along with Me3PB(C6F5)3. In the absence of Lewis acid, photolysis of 1-Mes*PPMe3 results instead in the formation of free phosphaindan and the PMe3 ferrous adduct [(tBupyrr2py)Fe(PMe3)] (1-PMe3) thus suggesting that dissociation of the phosphanylidene-σ4-phosphorane precedes the formation of a transient phosphinidene fragment Mes*P. All phosphorus adducts of 1 were crystallographically characterized and show quite similar Fe–P distances (2.4685(5) for 1-Mes*PPMe3; 2.5062(7) for 1-phosphaindan; and 2.4323(8) Å for 1-PMe3).