Synthesis, stability and reactivity of palladium(0) olefin complexes bearing labile or hemi-labile ancillary ligands and electron-poor olefins

Abstract

a b s t r a c tAn overview of the general features of electron-poor olefin stabilized palladium(0) complexes bearing labile and hemi-labile ancillary ligands is presented. In particular, we have summarized the synthetic methodologies, the ligands commonly used, and the characterization of such complexes. The behavior of these species in solution is also described with particular attention to their fluxional rearrangements and reactivity. Thus, olefin exchange reactions are described and a comprehensive order of coordinative capability of the most widely used electron-poor alkenes is presented. The reactions of the title complexes dealing with olefin isomerization, oxidative addition, and formation of palladacyclopentadiene derivatives are eventually reported together with their main structural characteristics.

Synthesis and reactivity toward olefin exchange and oxidative addition of some platinum(0) olefin complexes with thioquinolines as spectator ligands

“…In the search for analogies or differences with palladium derivatives, if any, we decided to investigate the oxidative addition of complexes 2a and 4a with allyl chloride and 3-chloro-1-phenylpropyne which are the most reactive species among the commercially available alkyl halides. Concomitantly, complexes 2a and 4a display the highest reactivity among the investigated Pt(0) species thanks to dmfu which is the most weakly coordinated olefin and hence the most prone to displacement [10].…”

“…Our group has gained a consolidated experience in the field of palladium(0) olefin complexes and in this respect a rank among the coordinative capabilities of different olefins and alkynes was assessed and the relative stability imparted to their derivatives clearly measured [10]. Remarkably, such a stability order was confirmed also in the case of the less investigated platinum derivatives [11].…”

“…Recently, the synthesis of the key intermediates in the homogeneous catalysis by d 10 PtL 2 involving NHC [8] or phosphine [9] ligands has represented the goal of some research groups. However, in our opinion the same target can also be reached by the wise catalytic application of olefin complexes of palladium(0) or platinum(0) from which the labile olefin can be easily displaced with the consequent release of a coordination site.…”

Reactions of palladium(0) olefin complexes stabilized by some different hetero- and homo-ditopic spectator ligands with propargyl halides

“…The separated stable pale-orange complex 1'b and the paleÀyellow 1j where characterized by 1 H and 13 C NMR and elemental analysis, which are in accord with the formulated structure. As for the NMR spectra, it is noteworthy that all the signals belonging to the spectator ligands are detected at different fields with respect to those of the free ligands, whereas the protons and carbons of the olefin shift significantly up-field upon coordination [10] (Dd H z 5, Dd C z 65 ppm, 1'b; Dd H z 2.4, Dd C z 80 ppm, 1j). In particular, in the case of complex 1'b, due to the heteroditopicity of the DPPQÀMe ligand, the two olefin protons are not equivalent and coupled with phosphorus of the ligand and therefore resonate as a multiplet.…”

Quantum mechanical study on the different fluxional mechanisms in a [Pd(η2-olefin) complex

“…The mechanisms put forward for the fluxional movements in olefin complexes of Pd are listed below [3,10,11].…”