TY - JOUR
T1 - Reactions of alkynes with [RuCl(cyclopentadienyl)] complexes
T2 - The important first steps
AU - Dutta, Barnali
AU - Curchod, Basile F E
AU - Campomanes, Pablo
AU - Solari, Euro
AU - Scopelliti, Rosario
AU - Rothlisberger, Ursula
AU - Severin, Kay
PY - 2010/7/26
Y1 - 2010/7/26
N2 - Cyclopentadienyl-ruthenium half-sandwich complexes with η2-bound alkyne ligands have been suggested as catalytic intermediates in the early stages of Ru-catalyzed reactions with alkynes. We show that electronically unsaturated complexes of the formula [RuCl(Cp̂)(η2-RC=CR')] can be stabilized and crystallized by using the sterically demanding cyclopentadienyl ligand Cp̂ (Cp̂ = η5-l-methoxy-2,4tert-butyl-3-neopentyl-cyclopentadienyl). Furthermore we demonstrate that [RuCl2(Cp̂)]2 is an active and regioselective catalyst for the [2+2+2] cyclotrimerization of alkynes. The first elementary steps of the reaction of mono(η2- alkyne) complexes containing {RuCl(Cp*)} (Cp* = η5- C5Me5) and (RuCl(Cp̂)} fragments with alkynes were investigated by DFT calculations at the M06/6-31G* level in combination with a continuum solvent model. Theoretical results are able to rationalize and complement the experimental findings. The presence of the sterically demanding Cp̂ ligand increases the activation energy required for the formation of the corresponding di(η2alkyne) complexes, enhancing the initial regioselectivity, but avoiding the evolution of the system towards the expected cyclotrimerization product when bulky substituents are present. Theoretical results also show that the electronic structure and stability of a metallacyclic intermediate is strongly dependent on the nature of the substituents present in the alkyne.
AB - Cyclopentadienyl-ruthenium half-sandwich complexes with η2-bound alkyne ligands have been suggested as catalytic intermediates in the early stages of Ru-catalyzed reactions with alkynes. We show that electronically unsaturated complexes of the formula [RuCl(Cp̂)(η2-RC=CR')] can be stabilized and crystallized by using the sterically demanding cyclopentadienyl ligand Cp̂ (Cp̂ = η5-l-methoxy-2,4tert-butyl-3-neopentyl-cyclopentadienyl). Furthermore we demonstrate that [RuCl2(Cp̂)]2 is an active and regioselective catalyst for the [2+2+2] cyclotrimerization of alkynes. The first elementary steps of the reaction of mono(η2- alkyne) complexes containing {RuCl(Cp*)} (Cp* = η5- C5Me5) and (RuCl(Cp̂)} fragments with alkynes were investigated by DFT calculations at the M06/6-31G* level in combination with a continuum solvent model. Theoretical results are able to rationalize and complement the experimental findings. The presence of the sterically demanding Cp̂ ligand increases the activation energy required for the formation of the corresponding di(η2alkyne) complexes, enhancing the initial regioselectivity, but avoiding the evolution of the system towards the expected cyclotrimerization product when bulky substituents are present. Theoretical results also show that the electronic structure and stability of a metallacyclic intermediate is strongly dependent on the nature of the substituents present in the alkyne.
KW - Alkynes
KW - Cyclotrimerization
KW - Density functional calculations
KW - Organometallic chemistry
KW - Ruthenium
UR - http://www.scopus.com/inward/record.url?scp=77954835196&partnerID=8YFLogxK
U2 - 10.1002/chem.201000855
DO - 10.1002/chem.201000855
M3 - Article (Academic Journal)
C2 - 20583066
AN - SCOPUS:77954835196
SN - 0947-6539
VL - 16
SP - 8400
EP - 8409
JO - Chemistry - A European Journal
JF - Chemistry - A European Journal
IS - 28
ER -