[35279-80-2]  · C12H12O8Pd  · Tetramethoxycarbonylpalladacyclopentadiene  · (MW 390.66)

(catalyst for intramolecular enyne cyclizations,1 [2 + 2 + 2] cycloadditions,1 allene-alkyne cross-condensations,2 and enyne metatheses3)

Alternate Name: [1,2,3,4-tetrakis(methoxycarbonyl)-1,3-butadien-1,4-diyl]palladium.

Physical Data: 170 °C (dec); brown, microcrystalline complex which exists as a polymeric structure.4

Solubility: very sol complexing solvents (phosphines, benzonitrile); sparingly sol noncomplexing solvents,4 but will dissolve in benzene and 1,2-dichloroethane upon addition of one equivalent of a phosphine.1

Analysis of Reagent Purity: 1H NMR (PhCN) d 6.23 (s, 6H), 6.34 (s, 6H).4

Preparative Methods: synthesized from Dimethyl Acetylenedicarboxylate and Tris(dibenzylideneacetone)dipalladium in virtually quantitative yield.4 The active complex is usually generated by addition of a phosphine ligand to break up the insoluble polymer.1

Intramolecular Enyne Cyclization.

In an attempt to observe intermediates in the Pd2+ catalyzed cyclization of 1,6-enynes, the title reagent (1) was used as an electron-deficient catalyst; an intramolecular carbometalation and subsequent cyclization were observed (eq 1).1

[2 + 2 + 2] Cycloaddition.

When cyclization of a 1,6-enyne was performed in the presence of an acetylene, a [2 + 2 + 2] cycloaddition resulted (eq 2).1 Further experimentation supported a [2 + 2 + 2] cyclization mechanism rather than a Diels-Alder reaction.1

Allene-Alkyne Cross-Condensation.

When (1) is exposed to a combination of an allene and an alkyne, a cross-condensation occurs.2 Regio- and stereocontrol can be obtained by an appropriate choice of ligand (eq 3). Even sterically hindered allenes can be used (eq 4).2

Intramolecular Enyne Metathesis.

By changing the CO2Me groups to CO2CH2CF3 (TCPCTFE) or CO2CH2CF2CF2CF3 (TCPCHFB) groups, one obtains a catalyst that effects intramolecular enyne metatheses, accomplishing the installation of a bridgehead alkene within a bridged bicycle (eq 5).3 The difference in reactivity between (1) and TCPCTFE or TCPCHFB, shown in eq 6, demonstrates the synthetic utility of this type of catalyst.3

1. Trost, B. M.; Tanoury, G. J. JACS 1987, 109, 4753.
2. Trost, B. M.; Kottirsch, G. JACS 1990, 112, 2816.
3. Trost, B. M.; Trost, M. K. JACS 1991, 113, 1850.
4. Moseley, K.; Maitlis, P. M. CC 1971, 1604.

Steven D. Paget

The Ohio State University, Columbus, OH, USA

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