Kolter M, Koszinowski K. Stability and Unimolecular Reactivity of Palladate(II) Complexes [L
n PdR
3 ]
- (L=Phosphine, R=Organyl, n=0 and 1).
Chemistry 2016;
22:15744-15750. [PMID:
27717040 DOI:
10.1002/chem.201603431]
[Citation(s) in RCA: 11] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2016] [Indexed: 11/08/2022]
Abstract
The reduction of PdII precatalysts to catalytically active Pd0 species is a key step in many palladium-mediated cross-coupling reactions. Besides phosphines, the stoichiometrically used organometallic reagents can afford this reduction, but do so in a poorly understood way. To elucidate the mechanism of this reaction, we have treated solutions of Pd(OAc)2 and a phosphine ligand L in tetrahydrofuran with RMgCl (R=Ph, Bn, Bu) as well as other organometallic reagents. Analysis of these model systems by electrospray- ionization mass spectrometry found palladate(II) complexes [Ln PdR3 ]- (n=0 and 1), thus pointing to the occurrence of transmetallation reactions. Upon gas-phase fragmentation, the [Ln PdR3 ]- anions preferentially underwent a reductive elimination to yield Pd0 species. The sequence of the transmetallation and reductive elimination, thus, constitutes a feasible mechanism for the reduction of the Pd(OAc)2 precatalyst. Other species of interest observed include the PdIV complex [PdBn5 ]- , which did not fragment via a reductive elimination but lost BnH instead.
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