Contents 1. Abbreviations 747 2. Introduction 747 3. Stoichiometric Reactions with Carbon-Carbon 747 Bond Formation 4-Catalytic Reactions with Carbon-Carbon Bond 751 Formation 4.1. Reactions with Alkynes 751 4.2. Reactions with Alkenes 754 4.3. Reactions with Conjugated Dienes 755 4.4. Reactions with Methylenecyclopropanes 758 4.5. Reactions with Allene 759 4.6. Reactions with Aromatic Compounds 759 4.7. Electrochemical Reactions 759 5. The Relevance of C02 Complexes 760 6. Concluding Remarks 761 7. References 762

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Several aspects of the catalytic telomerization of 1,3-butadiene and C02 have been examined with the aims of studying the catalytic properties of reversible C02-carrier complexes and of selectively producing the 5-lactone 2-ethylidene-6-hepten-5-olide (3). When using Pd(II) complexes containing a cyclometalated ligand and a functional phosphine, only the specific C02 carriers [(o-C6H4CH2NMe2)Pd{R2PC(C02Et)=C(0)OH}] (2a, R = Ph; 2b, R = Cy) showed catalytic activity. They represent the first examples of C02 carriers having a catalytic activity in C02 chemistry. The complex isolated at the end of the reaction was identified as the cyclometalated phosphine carboxylate complex [(o-C6H4CH2NMe2)Pd|R2PCH2C(0)0|] (8). Another new catalytic system consisting of [Pd(MeCN)4] [BF4]2 associated to a phosphine ligand, p-hydroquinone, and triethylamine was tested under various conditions. Yield and selectivity of the six-membered ring lactone 3 are functions of the basicity and the bulk of the phosphine ligand. The yield of C02 telomers can be increased up to 76% (based on butadiene) by addition of acetophenone to the latter catalytic system containing PPh3. Furthermore, isomeric telomers of formula C9HI2Ó2 formed during catalysis can be converted into the 5-lactone 3, leading to an overall selectivity of 96%.

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208 0 VCH Verlagsgesellschaff mbH. 0-6940 Weinheim, 1989 0570-0833/89/0202-0208 $ 02.50/0 Angew. Chem. Int. Ed. Engl. 28 (1989) No. 2