[17830-50-1] · C40H32O3P2Pd · (Maleic anhydride)bis(triphenylphosphine)palladium · (MW 729.08)
(zerovalent palladium complex which catalyzes the dimerization of 1,3-dienes and 1,2-dienes5-9)
Alternate Name: bis(triphenylphosphine)(maleic anhydride)palladium.
Physical Data: mp 147-151 °C (dec).1
Solubility: sol THF, acetone, chloroform; low sol benzene.
Form Supplied in: not widely available.
Preparative Methods: reaction of Tetrakis(triphenylphosphine)palladium(0) with Maleic Anhydride at rt in benzene,1 benzene/THF,2,3 or THF3 yields the title complex as a stable monomeric species, which is purified by crystallization from methanol/hexane.2 The title reagent has also been synthesized from the putative bis(triphenylphosphine)palladium.4
Handling, Storage, and Precautions: stable in air for many hours in the solid state.2
(Maleic anhydride)bis(triphenylphosphine)palladium (1) is a zerovalent palladium complex that has been used extensively as a catalyst for the dimerization of conjugated dienes.5-7 For example, complex (1) efficiently promotes the coupling of 1,3-Butadiene to form linear dimers (eq 1).5 These reactions are most commonly carried out in benzene, THF, and acetone. In the presence of protic nucleophiles such as MeOH or Morpholine, the dimerizations take place with addition of the protic component (eq 2). Further studies have demonstrated that (1) catalyzes the reaction of 1,3-dienes with acyloin derivatives to yield mainly the product of O-alkylation (eq 3).6
The title reagent promotes the co-cyclization of conjugated dienes with isocyanates (eq 4).7
Allenes can be condensed with dienes,8 amines, enamines, and activated methylenes,9 using reagent (1). Secondary amines react efficiently with allenes in the presence of 0.2 mol % of (1) to provide substituted 1,3-dienes (eq 5). Primary amines give the corresponding bis(dienyl)amines, albeit in lower yields. Carbon acids also react with allenes in the same way to yield substituted dienes (eq 6). In all these reactions, complex (1) was the palladium reagent of choice due of its ease of preparation, good stability, and high reactivity.9
In the presence of an acid catalyst, reagent (1) promotes the addition of cyclic amines to homoconjugated dienes such as norbornadiene (eq 7).10
Reagent (1) catalyzes the hydrosilation of allenes and dienes. The reaction between allene and triethylsilane gives the 1:1 addition product, allyltriethylsilane, in 48% yield.9 The analogous reaction with 1,3-dienes yields the linear dimer of the diene (eq 8).11 Catalysis of a Si-Si/Si-Si metathesis reaction, which proceeds very slowly at 200 °C, can be catalyzed by reagent (1) (eq 9).12
Christophe Michoud & Viresh H. Rawal
The Ohio State University, Columbus, OH, USA