Reaction of the dimer [(η5-C5Me5)RhCl(μ2-Cl)]2 with 2 or 4 equiv of the water-soluble phosphine 1,3,5-triaza-7-phosphatricyclo[3.3.1.1]decane (pta) affords [Rh(η5-C5Me5)(pta)Cl2] and [Rh(η5-C5Me5)(pta)2Cl]Cl, respectively. Both complexes have been characterized in solution by NMR spectroscopy and in the solid state by single-crystal X-ray diffraction, the latter as the chloride and BPh4 - salts. In addition, the rhodium(I) complexes [Rh(η5-C5Me5)(CO)(pta)] and [Rh(η5-C5H5)(pta)2] have been prepared from [Rh(η5-C5Me5)(CO)2] and [Rh(η5-C5H5)(PPh3)2], respectively, by reaction with pta. An in vitro evaluation of these compounds, together with [Os(η6-C10H14)(pta)Cl2] and the well-characterized antimetastasis drug [Ru(η6-C10H14)(pta)Cl2], RAPTA-C, was undertaken using HT29 colon carcinoma, A549 lung carcinoma, and T47D breast carcinoma cells. In the HT29 cell line, the two nearest congeners to [Ru(η6-C10H14)(pta)Cl2], viz., [Rh(η5-C5Me5)(pta)Cl2] and [Os(η6-C10H14)(pta)Cl2], demonstrated very similar cytotoxicity profiles. [Rh(η5-C5Me5)(pta)Cl2] proved significantly more cytotoxic in A549 cells and [Rh(η5-C5Me5)(pta)2Cl]Cl 3-fold more cytotoxic in T47D cells, both relative to RAPTA-C. These data suggest that the development of organometallic anticancer drugs based on the neighboring elements to ruthenium should not be overlooked.

The hydration of phenylacetylene in the presence of the complex mer,trans-(PNP)RuCl 2 (PPh 3 ) in THF at 60°C leads to the cleavage of the C-C triple bond with formation of the carbonyl complex fac,cis-(PNP)RuCl 2 (CO) and toluene [PNP ) CH 3 CH 2 CH 2 N(CH 2 CH 2 PPh 2 ) 2 ]. A study under different experimental conditions, the use of model and isotope labeling experiments, and the detection of several intermediates, taken altogether, show that the C-C bond cleavage reaction comprises a number of steps, among which the most relevant to the mechanism are 1-alkyne to vinylidene tautomerism, conversion of a vinylidene ligand to hydroxycarbene by intramolecular attack of water, deprotonation of hydroxycarbene to σ-acyl, deinsertion of CO from the acyl ligand, and hydrocarbon elimination by protonation of the metal-alkyl moiety. The following intermediate species have been isolated and characterized: the vinylidene fac,cis-(PNP)RuCl 2 {CdC(H)Ph}, the (aquo)(σ-alkynyl) complex fac-(PNP)RuCl-(CtCPh)(OH 2 ), and the (benzyl)carbonyl mer-(PNP)RuCl(η 1 -CH 2 Ph)(CO). Other intermediates such as the σ-acyl mer-(PNP)RuCl(η 1 -COCH 2 Ph)(CO) have been intercepted by addition of appropriate reagents, while the independent synthesis of the aminocarbene complex fac,cis-(PNP)RuCl 2 {C(NC 5 H 10 )(CH 2 Ph)} and its reaction with water have provided evidence for the intermediacy of a hydroxycarbene species in the C-C bond cleavage reaction.

A new family of Cs‐ and C1‐symmetric 2,6‐bis(imino)pyridyl ligands has been synthesised. These ligands, which differ from their known counterparts in the contemporaneous presence of alkyl and aryl substituent at the ketimine nitrogen atoms, form stable, five‐coordinate complexes with FeCl2 and CoCl2. All ligands and catalysts have been fully characterised both in the solid state and in solution. A single‐crystal X‐ray analysis of [CoCl2{2‐[CMe=N−(2,6‐dimethylphenyl)]‐6‐(CMe=N−C6H11)C5H3N}]·H2O shows the metal centre to adopt a highly distorted square‐pyramidal geometry. In combination with methylaluminoxane (MAO), both iron and cobalt compounds act as effective and selective (> 99%) catalysts for the oligomerisation of ethylene to a Schulz−Flory distribution of α‐olefins, with the α factor ranging from 0.61 to 0.91. The iron catalysts exhibit TOFs as high as 7·105 mol C2H4 (mol of cat × h)−1 and are much more active than their cobalt analogues. Experiments at different ethylene pressures with the iron catalysts showed that both the propagation rate and the chain transfer rate are first order in ethylene pressure. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2003)

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