FULL PAPER Palladacyclopentadiene Complexes with Mono- and Didentate Imidato Ligands: Synthesis, Hemilabile Behaviour and Catalytic Application in the Stille Reaction Jose ´ Luis Serrano,* [a] Ian J. S. Fairlamb,* [b] Gregorio Sa ´nchez,* [c] Luis Garcı ´a, [a] Jose ´ Pe ´rez, [a] Jorge Vives, [c] Gregorio Lo ´pez, [c] Catherine M. Crawforth, [b] and Richard J. K. Taylor [b] Keywords: Catalysis / Cross-coupling / N,O ligands / Palladium / Stille reactions The binuclear hydroxo complex [NBu 4 ] 2 [Pd 2 {C 4 (COOMe) 4 } 2 - (μ-OH) 2 ](1) has been prepared by addition of two equiva- lents of NBu 4 OH to polymeric [Pd{C 4 (COOMe) 4 }] n . Complex 1 has been successfully employed as a precursor to three novel binuclear imidate-bridged complexes [NBu 4 ] 2 [Pd 2 - {C 4 (COOMe) 4 } 2 (μ-imidate) 2 ] [imidate = succinimidate (suc) 2, phthalimidate (pht) 3 or maleimidate (mal) 4] in which the imidate group displays a bidentate N,O-coordination mode. The hemilabile behaviour of the imidate ligands has been investigated by reaction with a variety of P, N and S ligands, affording the corresponding mononuclear derivatives [NBu 4 ][Pd{C 4 (COOMe) 4 }(imidate)L] [L = PPh 3 (2a, 3a or 4a), P(p-C 6 H 4 F) 3 (2b, 3b or 4b), PBu 3 (2c, 3c or 4c), py (2d, 3d or Introduction Over the last twenty five years great advances in the de- velopment of palladium-catalysed carbon-carbon and carbon-heteroatom bond-forming processes have been ob- served. [1] Palladium-catalysed reactions, such as Stille [2] and Suzuki coupling, have made significant contributions to synthetic chemistry, not least in the synthesis of important natural products and materials. [3] For this reason, highly active, efficient and selective Pd catalysts are continually been sought after. The scope of the Suzuki and Stille reac- tions — the reaction of organohalides with organoboronic acids or organostannanes, respectively — has been substan- tially expanded upon in recent years. The design of electron- rich palladium species possessing strong σ-donor ligands [a] Departamento de Ingenierı ´a Minera, Geolo ´gica y Cartogra ´fica, A ´ rea de Quı ´mica Inorga ´nica, Universidad Polite ´cnica de Cartagena, 30203 Cartagena, Spain E-mail: jose.serrano@upct.es [b] Department of Chemistry, University of York, York, Heslington, York, YO10 5DD, UK E-mail: ijsf1@york.ac.uk [c] Departamento de Quı ´mica Inorga ´nica, Universidad de Murcia, 30071 Murcia, Spain E-mail: gsg@um.es 2706  2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim DOI: 10.1002/ejic.200300962 Eur. J. Inorg. Chem. 2004, 2706-2715 4d), p-MeC 6 H 4 NH 2 (2e, 3e or 4e), tetrahydrothiophene (2f, 3f or 4f)] with terminal N-bonded imidate ligands. The char- acterization of the new complexes involved spectroscopic methods (IR, FAB, 1 H, 13 C, 19 F and 31 P NMR) and X-ray crys- tallographic analysis for 1, 4b and 4e. The mononuclear de- rivatives are shown to catalyse the Stille cross-coupling of benzyl bromide 7 with ethyl Z-vinylstannyl carboxylate (8) in high yields. Yields and reaction times are dependent on the presence and type of imidate ligand, which suggests an im- portant role for it in the catalytic cycle. ( Wiley-VCH Verlag GmbH and Co. KGaA, 69451 Weinheim, Germany, 2004) that mediate mild cross-coupling reactions of activated and deactivated organohalide substrates with appropriate nucle- ophiles has contributed to this effort. [4] To date, however, palladacyclopentadiene complexes have not been used in classic carbon-carbon bond-forming processes, although they have been implicated in a number of other catalytic processes. [5] In this paper, we wish to describe the synthesis of a new class of palladacyclopentadiene complexes that contain im- idato ligands (succinimide, maleimide and phthalimide). We have studied in previous work [6] the hemilabile behav- iour [7] of such ligands in complexes with a classical cyclo- metallated backbone. The precursors employed in this case were the well-known complexes with bridging acetate groups. However, regarding the desired palladacyclopenta- diene compounds we envisaged that they could be syn- thesised from binuclear hydroxypalladium complexes, the chemistry of which has been studied recently, [8] by means of a simple acid-base reaction with protic electrophiles. [9] Thus, the preparation of the new organometallic di-μ-hydroxo complex 1 containing a palladacyclopentadiene backbone, its use as a precursor of binuclear di-μ-imidate palladacy- clopentadiene complexes 2-4, and their hemilabile behav- iour towards monodentate ligands, such as acetonitrile,