A halide-free pyridinium-substituted η3-cycloheptatrienide-Pd complex.

We report the synthesis and characterization of a novel 4-(dimethylamino)pyridinium-substituted η3-cycloheptatrienide-Pd complex which is free of halide ligands. Diacetonitrile{η3-[4-(dimethylamino)pyridinium-1-yl]cycloheptatrienido}palladium(II) bis(tetrafluoroborate), [Pd(C2H3N)2(C14H16N2)](BF4)2, was prepared by the exchange of two bromide ligands for noncoordinating anions, which results in the empty coordination sites being occupied by acetonitrile ligands. As described previously, exchange of only one bromide leads to a dimeric complex, di-µ-bromido-bis({η3-[4-(dimethylamino)pyridinium-1-yl]cycloheptatrienido}palladium(II)) bis(tetrafluoroborate) acetonitrile disolvate, [Pd2Br2(C14H16N2)2](BF4)2·2CH3CN, with bridging bromide ligands, and the crystal structure of this compound is also reported here. The structures of the cycloheptatrienide ligands of both complexes are analogous to the dibromide derivative, showing the allyl bond in the ß-position with respect to the pyridinium substituent. This indicates that, unlike a previous interpretation, the main reason for the formation of the ß-isomer cannot be internal hydrogen bonding between the cationic substituents and bromide ligands.

A Lewis acid ß-diiminato-zinc-complex as all-rounder for co- and terpolymerisation of various epoxides with carbon dioxide.

A ß-diiminato-zinc-N(SiMe3)2 complex (1) was synthesised and fully characterised, including an X-ray diffraction study. The activity of catalyst 1 towards the coupling reaction of CO2 and various epoxides, including propylene oxide (PO), cyclohexene oxide (CHO), styrene oxide (SO), limonene oxide (LO), octene oxide (OO) and epichlorohydrin (ECH), was investigated. Terpolymerisation of CO2, PO and LO, as well as CO2, CHO and PO, was successfully realised, resulting in polymers with adjustable glass transition temperatures and transparencies. Reaction conditions such as temperature, pressure and catalyst concentration were varied to find the optimal reaction values, especially regarding LO/CO2. In situ IR experiments hinted that at 60 °C and a critical LO concentration, polymerisation and depolymerisation are in an equilibrium (ceiling effect). Pressurising catalyst 1 with carbon dioxide resulted in a dimeric catalyst (2) with a OSiMe3 group as a new initiator. Homopolymerisation of different epoxides was carried out in order to explain the reactivity concerning copolymerisation reaction of CO2 and epoxides.

A Pd4Br4 macrocycle trapped by cocrystallization from a highly dynamic equilibrium of η(3)-cycloheptatrienide complexes.

In the coordination chemistry of palladium, dimers bridged via halides are a common motif. Higher oligomers, however, are still rare. We report the structure of an alternating eight-membered [Pd4Br4](4-) ring framed by cycloheptatrienide ligands, which was obtained by cocrystallization of dimers and tetramers of the complex salt bromido{η(3)-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II) tetrafluoroborate, namely bis[di-µ-bromido-bis({η(3)-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II))] cyclo-tetra-µ-bromido-tetrakis({η(3)-[3-(2,6-diisopropylphenyl)imidazolium-1-yl]cycloheptatrienido}palladium(II)) octakis(tetrafluoroborate) dichloromethane octasolvate, [Pd4Br4(C22H26N2)4][Pd2Br2(C22H26N2)2]2(BF4)8·8CH2Cl2. These dimers and tetramers form a highly dynamic equilibrium in solution which was studied by low-temperature NMR spectroscopy. In the light of the presented results, tetrameric Pd(II) species can be assumed to co-exist as a second species in many cases where by current knowledge only a dimeric compound would be expected.