title: Comparison of the catalytic activity for the Suzuki-Miyaura reaction of (η(5)-Cp)Pd(IPr)Cl with (η(3)-cinnamyl)Pd(IPr)(Cl) and (η(3)-1-t-Bu-indenyl)Pd(IPr)(Cl).
abstract: Complexes of the type (η(3)-allyl)Pd(L)(Cl) and (η(3)-indenyl)Pd(L)(Cl) are highly active precatalysts for the Suzuki-Miyaura reaction. Even though allyl and indenyl ligands are similar to cyclopentadienyl (Cp) ligands, there have been no detailed comparative studies exploring the activity of precatalysts of the type (η(5)-Cp)Pd(L)(Cl) for Suzuki-Miyaura reactions. Here, we compare the catalytic activity of (η(5)-Cp)Pd(IPr)(Cl) (IPr = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene, Cp) with two commercially available catalysts (η(3)-cinnamyl)Pd(IPr)(Cl) (Cin) and (η(3)-1-t-Bu-indenyl)Pd(IPr)(Cl) ( (tBu) Ind). We show that Cp gives slightly better catalytic activity than Cin, but significantly inferior activity than (tBu) Ind. This order of activity is rationalized by comparing the rates at which the precatalysts are activated to the monoligated Pd(0) active species along with the tendency of the starting precatalysts to comproportionate with monoligated Pd(0) to form inactive Pd(I) dimers. As part of this work the Cp supported Pd(I) dimer (μ-Cp)(μ-Cl)Pd2(IPr)2 (Cp (Dim) ) was synthesized and crystallographically characterized. It does not readily disproportionate to form monoligated Pd(0) and consequently Cp (Dim) is a poor catalyst for the Suzuki-Miyaura reaction.
authors.affiliation: The Department of Chemistry, Yale University, P. O. Box 208107, New Haven, Connecticut, 06520, USA.
authors.forename: Patrick R
authors.initials: PR
authors.lastname: Melvin
authors.affiliation: The Department of Chemistry, Yale University, P. O. Box 208107, New Haven, Connecticut, 06520, USA.
authors.forename: Nilay
authors.initials: N
authors.lastname: Hazari
authors.affiliation: The Department of Chemistry, Yale University, P. O. Box 208107, New Haven, Connecticut, 06520, USA.
authors.forename: Hannah M C
authors.initials: HM
authors.lastname: Lant
authors.affiliation: The Department of Chemistry, Yale University, P. O. Box 208107, New Haven, Connecticut, 06520, USA.
authors.forename: Ian L
authors.initials: IL
authors.lastname: Peczak
authors.affiliation: The Department of Chemistry, Yale University, P. O. Box 208107, New Haven, Connecticut, 06520, USA.
authors.forename: Hemali P
authors.initials: HP
authors.lastname: Shah
keywords: NHC ligands; Suzuki–Miyaura reaction; cross-coupling; homogeneous catalysis; palladium