Rhodium-Stabilized <i>o</i>-Quinone Methides: Synthesis, Structure, and Comparative Study with Their Iridium Congeners

The parent o-quinone methide (o-QM) cannot be observed in condensed phases above −100 °C, but in this work, o-QM and its dimethyl derivative are stabilized by complexation to Cp*Rh. Precursor oxo-dienyl rhodium complexes [(η5-Cp*)Rh(η5-2-alkyl-oxodienyl)][BF4] (5a,b) were isolated as yellow microcrystalline solids in 85−90% yields and fully characterized. In addition the X-ray molecular structure of 5b is reported. Selective alkyl deprotonation by t-BuOK in CH2Cl2 provided the first series of rhodium−o-QM complexes [(η5-Cp*)Rh(η4-(R)2C7H4O)] (R = H, 6a; R = Me, 6b). The o-QM is stabilized through η4-coordination to the metal center, as shown by the X-ray structure of 6b. Structural and reactivity studies on 6a,b show that the rhodium−o-QM complexes are less stable than their iridium congeners.