Metallacycles

Rhodafuran from a methoxy(alkenyl)carbene. A methoxy(alkenyl)carbenerhodium complex [RhCp*Cl{C(OMe)CHCPh2}(PMe3)]PF6 (2) has been synthesized and used as the starting material for the study of the effect of the metal center (Rh vs. Ir) in the formation of new rhodacycle complexes. While η3 and η5 indenylrhodium complexes have been achieved by the C–H bond activation of a phenyl ring, insertion of terminal alkynes into the rhodium–carbene bond led to the first example of the synthesis of rhodafuran complexes through rhoda-1,3,5-hexatriene intermediates. This new method represents an efficient process to obtain metallafuran complexes.

Cyclometalated Iridium Complexes from Intramolecular C–H Activation. The (methoxy)alkenylcarbeneiridium complexes [IrCp*Cl{═C(OMe)CH═CR1R2}L]PF6 (R1 = CH3, R2 = CH3, Ph; R1 = Ph, R2= H; L = PPh2Me, PMe3) can undergo an intramolecular C–H activation of one of the substituents R of the alkenyl fragment to give new five-membered-ring cyclometalated iridium complexes. In this work it is shown that the arrangement of substituents in the alkenyl fragment determines the size of the ring in the iridacycle complexes. The iridacyclopenta-1,3-diene complexes [IrCp*{═C(OMe)CH═CRCH2}L]PF6 (L = PPh2Me, R = CH3 (2a), Ph (4a); L = PMe3, R = CH3 (2b), Ph (4b)) can be deprotonated to give the iridacyclopenta-2,4-diene complexes [IrCp*{C(OMe)═CHCR═CH}L] (L = PPh2Me, R = CH3(6a), Ph (7a); L = PMe3, R = CH3 (6b), Ph (7b)).
Catalytic Roles

The Catalytic Role of Extra Molecules in the Aminolysis or Heterolytic Cleavage of an Iridium Alkoxycarbene Complex. A theoretical analysis was performed on reactions involving iridium alkoxycarbene complex [IrCp*Cl{=C(OCH3)CHCPh2}(PPh2Me)]PF6 (Cp* = pentamethylcyclopentadienyl), which can undergo aminolysis or heterolytic cleavage of the carbon(sp3)–oxygen bond. The energy barriers of these pathways were estimated and the reasons for the reactivity of the system evaluated. Aminolysis or heterolytic cleavage of the carbon(sp3)–oxygen bond is the result of a subtle equilibrium between electronic, steric, and cooperative effects. Cooperative effects facilitate the proton transfer that occurs in aminolysis through formation of a bridge by one or several molecules. These molecules act as catalysts that decrease the energy barrier and change the favored pathway, so that the environment is a key factor in the reactivity of this complex.

[IrCp*(NCMe)2(PPh2Me)][PF6]2 as Catalyst for the Meyer–Schuster Rearrangement of Arylpropargylic Alcohols under Mild Conditions. The novel iridium complex [IrCp*(NCMe)2(PPh2Me)][PF6]2 (I) efficiently catalyzed the Meyer–Schuster rearrangement of selected arylpropargylic alcohols into α,β‐unsaturated aldehydes under mild conditions and without the need of a co‐catalyst. A mechanism involving a (hydroxy)alkenylcarbene intermediate is proposed.