The use of electron-poor phosphine-substituted cobaltocenium salts as ligands for the biphasic hydroformylation in ionic liquids has been investigated. Using improved oxidation methods, 1,1′-bis(diphenylphosphino)cobaltocenium nitrate, 1,1′-bis(diphenylphosphino)cobaltocenium hexafluorophosphate, and 1,1′-bis[1-methyl(1-diphenylphosphino)ethyl]cobaltocenium hexafluorophosphate have been synthesized. 1,1′-Bis(diphenylphosphinocobaltocenium hexafluorophosphate in particular proved to be a very suitable ligand for the biphasic hydroformylation of 1-octene in 1-butyl-3-methylimidazolium hexafluorophosphate (BMIM PF 6 ), enabling high catalyst activity, high selectivity to the n-product, and no detectable catalyst leaching. In contrast to aqueous biphasic systems, the ionic liquid BMIM PF 6 provides for the rhodium catalyst a low-coordinating medium with limited but sufficient solubility for 1-octene to allow high reaction rates. † Dedicated to Prof. Willi Keim on the occasion of his 65th birthday.

Ph 3 PAgCtCPh] 4 ‚3.5THF (2) can be prepared by the reaction of CpAgPPh 3 (1) with lithium phenylacetylide (1:1 equiv). Similarly [Me 3 PAgCtCSiMe 3 ] ∞ (4) can be prepared by the reaction of CpAgPMe 3 (3) and lithium (trimethylsilyl)acetylide (1:1 equiv). Both complexes have been characterized by elemental analyses, solid-state IR spectroscopy, 1 H and 31 P NMR spectroscopy, and low-temperature X-ray diffraction studies. The structure of 2 consists of a tetranuclear "flat-butterfly" core, with the two "hinge" silver atoms σ-bonded to two acetylide fragments, which then π-complex the apical Ag(PPh 3 ) 2 fragments. In 4, the smaller steric bulk of the phosphine employed allows this complex to crystallize as a polymer. Rather than being constructed from simple [R 3 PAg(acetylide)] units, both 2 and 4 are formed by the aggregation of (acetylide) 2 Agand Ag(PR 3 ) 2 + fragments. The preparation of complexes 2 and 4 demonstrates the synthetic utility of nucleophilic substitution of CpAgPR 3 in the synthesis of Ag organometallics. The different structural alternatives adopted by 2 and 4 point to the steric bulk of the phosphine ligands being the major influence on the structure of Ag acetylide complexes.

An efficient ruthenium-catalyzed transfer dehydrogenation of amines to imines was achieved under mild conditions using 2,6-dimethoxy benzoquinone (2) or cat. 2/MnO2 as oxidant.

Nucleophilic substitution of the cp (q-C,H5) ligand of [Cu(cp)(PPh,)] with LiL (L = 1,3-benzoxazoline-2thionate) gave the heterobimetallic complex [(Ph,P),CuL,Li(thf),]*thf 1 (thf = tetrahydrofuran), the ligandtransfer reaction of which with CuCl, generated the tetrameric cage complex [{CuL(PPh,)},] 2. The crystal structures of these complexes revealed that the association of the metal centres occurs by a variety of ligand co-ordination modes (p-S, N; N, p-S; p3-S). Electrochemical measurements have been used to probe the nature of the species present in solution.

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