Scott Winston

C–H activation with N-heterocyclic carbene complexes of iridium and rhodium

The first example of intramolecular, room temperature activation of a C–H bond in N-pyridine functionalised heterocyclic carbene complexes of iridium is reported.

Stable N-functionalised ‘pincer’ bis carbene ligands and their ruthenium complexes; synthesis and catalytic studies

Deprotonation of 2,6-bis(arylimidazolium)pyridine dibromide with KN(SiMe3)2 gave thermally stable 2,6-bis(arylimidazol-2-ylidene)pyridine, which was further used to prepare ruthenium ‘pincer’ complexes; the latter show catalytic activity in transfer hydrogenation of carbonyl compounds.

N-Functionalised heterocyclic carbene complexes of silver

N-Functionalised imidazol-2-ylidene carbene complexes of AgI have been prepared by interaction of the corresponding imidazolium salt with Ag2O in dichloromethane or 1,2-dichloroethane in the presence of molecular sieves or with Ag2CO3 in 1,2-dichloroethane. In an analogous way disilver(I) complexes of o-phenylenedimethylenebis(imidazol-2-ylidene) have been obtained. Their structures, as determined by X-ray crystallography, indicate that the carbene ligand acts as monodentate from the carbene end or as a bridge between two different metal atoms. In one case the silver is coordinated by two carbene ligands. In the majority of the structurally characterised complexes the metal centres adopt linear geometries with M–C(carbene) bond lengths in the range of 207–210 pm characteristic of a single bond.

Uranium complexes with dianionic O-methylated calix[4]arene ligands

Introduction of the dianionic 25,27-O-dimethylated 5,11,17,23-tetra-tert-butylcalix[4]arene spectator, L2−, to a uranium (IV) centre gave the cyclic trimeric complex 1, which was structurally characterised; complex 1 serves as a useful starting material for further derivatisation.

Synthesis and structural characterisation of stable pyridine- and phosphine-functionalised N-heterocyclic carbenes

Stable, uncoordinated (1-[2-(6-trimethylsilyl)pyridyl]-3-[(2,6- diisopropyl)phenyl]imidazol-2-ylidene), I, and (1-[beta-(diphenylphosphino)ethyl]-3-[(2,6-diisopropyl)phenyl]imidazol- 2-ylidene), II, have been synthesised; in the solid state they adopt a conformation with the lone pairs in a mutually anti arrangement.

Chelating and ‘pincer’ dicarbene complexes of palladium; synthesis and structural studies

A series of ‘pincer’ 2,6-pyridyl dicarbene complexes of the type [(C–N–C)PdX]+, 4a, 4b, 2,6-lutidinyl dicarbene complexes of the type [(C⁁N⁁C)PdX]+, 4c, 4d, 1,3-xylyl dicarbene complexes of the type [(C⁁C⁁C)PdX], 5a,5b,5c and 1,2-xylyl dicarbene complexes [(CC)PdX2], 8, where carbene is 3-arylimidazol-2-ylidene, aryl = mesityl, 2,6-Pri2C6H3, X = Br or Cl, have been prepared by (i) transmetallation from the corresponding silver complexes, i.e. [(C–N–C)Ag2Cl2], [(C⁁N⁁C)Ag2Cl2] and [(CC)Ag2Cl2] to palladium, (ii) substitution of cod in (cod)PdX2 by the ‘pincer’ (C–N–C) (iii) palladation of bis-imidazolium salts [C(H)⁁C(H)⁁C(H)] in the presence of base. The crystal structures show that the ligands act as chelates in 4–5, while in 8 as both chelate and bridging.

Functionalised and chelate heterocyclic carbene complexes of palladium; synthesis and structural studies

A series of picolyl-functionalised, [(C^N)PdXY], 1a, 2a, 3a and 4, pyridyl-functionalised, [(C–N)PdXY], 5a, 6, 7 and 8, methoxymethyl-functionalised, [(C^O)Pd(μ-X)X]2, 10, and trans-[(C^O)2PdX2], 11, and diethylcarbamoylmethyl-functionalised, trans-[(C^amide)2PdX2], 12, N-heterocyclic carbene (NHC) complexes of palladium(II), (C^N) = (3-R1)[1-(α-picolyl)imidazol-2-ylidene, (C–N) = (3-R1)[1-(2-pyridyl)imidazol-2-ylidene, R1 = But, mesityl, 2,6-Pri2C6H3, (C^O) = (3-R1)(1-methoxymethyl)imidazol-2-ylidene, R1 = 2,6-Pri2C6H3, (C^amide) = (3-R1)(1-diethylcarbamoylmethyl)imidazol-2-ylidene, R1 = 2,6-Pri2C6H3, Y = Me, X = Br or Cl, have been synthesised by interaction of (1,5-cod)PdXY or (1,5-cod)PdX2 with the corresponding silver NHC complexes, or (in certain cases) with the free functionalised NHC ligands. Derivatives of 1a, 2a, 3a and 5a were prepared by substitution of the halide X by weakly coordinating anions. The majority of the complexes described here were characterised by spectroscopic and diffraction methods and show that the (C–N) and (C^N) ligands act as chelates, while the methoxymethyl- and diethylcarbamoylmethyl-functions in 10, 11 and 12, respectively, are dangling. Derivatives of 5a in which the pyridine ring is substituted with electron withdrawing or bulky substituents show only minor variation of the pyridine–palladium distances.

Alkyliminomethyl)phenylamido and related complexes of zirconium and titanium

A range of trialkylsilylamido complexes of zirconium in which the silylamido functional group is attached to an o-(alkyliminomethyl)- or an o-(alkyliminoethyl)-substituted aromatic ring have been synthesised by salt elimination or aminolysis reactions and characterised by spectroscopic and diffraction methods. The monoanionic ligands (L), formally isoelectronic to the cyclopentadienyl ligand, can be introduced to zirconium by reaction of LLi with ZrCl4 under a variety of conditions giving rise to complexes of type LZrCl3 and L2ZrCl2, by reaction of LLi with Zr(NMe2)2Cl2(THF)2, and Zr(NEt2)2Cl2(THF)2 giving rise to LZrCl(NMe2)2Cl and LZrCl(NEt2)2Cl, respectively, or by reaction of LH with Zr(NMe2)4 giving rise to LZr(NMe2)3. LZr(NMe2)2Cl and LZr(NEt2)2Cl can be transformed to LZrCl3 by reaction with Me3SiCl, while LZr(NMe2)3 on heating rearranges to dimeric imido complexes by elimination of amidosilanes. Aminolysis of Zr(NMe2)2Cl2(THF)2 with LH results in a formal insertion of the imino CN into the Zr-amido bond. The combination of enolisable imine and a bulky silyl amide gave rise to a new mixed donor ligand system comprising of one silylamido and one eneamido group. Finally aminolysis of Ti(NMe2)Cl2 with LH resulted in the isolation of a C3 symmetric triamido titanium complex.