Ligand PPh3 compounds with

Low oxidation states - An important characteristic of transition metal chemistry is the formation of compounds with low (often zero or negative) oxidation states. This has little parallel outside the transition elements. Such complexes are frequently associated with ligands like carbon monoxide or alkenes. Compounds analogous to Fe(CO)s, [Ni(cod)2] (cod = 1,4-cyclooctadiene) or [Pt(PPh3]3] are very rarely encountered outside the transition-metal block. The study of the low oxidation compounds is included within organometallic chemistry. We comment about the nature of the bonding in such compounds in Chapter 6. 

Substantially more work has been done on reactions of square-planar nickel, palladium, and platinum alkyl and aryl complexes with isocyanides. A communication by Otsuka et al. (108) described the initial work in this area. These workers carried out oxidative addition reactions with Ni(CNBu )4 and with [Pd(CNBu )2] (. In a reaction of the latter compound with methyl iodide the complex, Pd(CNBu )2(CH3)I, stable as a solid but unstable in solution, was obtained. This complex when dissolved in toluene proceeds through an intermediate believed to be dimeric, which then reacts with an additional ligand L (CNBu or PPh3) to give PdL(CNBu )- C(CH3)=NBu I [Eq. (7)]. 

The chemical structure of the polymers was confirmed by NMR and elemental analysis, and spectroscopically characterized in comparison with monodisperse low molecular weight model compounds. Scheme 5 outlines the approach to the model compounds. Model compounds 31-34 were synthesized by complexation of the ruthenium-free model ligands 29/30 with 3/4. The model ligands were synthesized in toluene/diisopropylamine, in a similar fashion as the polycondensation using Pd(PPh3)4 and Cul as catalyst (Sonogashira reaction) [34,47-49]. 

The number of theoretical investigations of transition metal complexes with carbodiphosphoranes and related divalent carbon(O) ligands is rather small. Quantum chemical calculations of the nickel complexes (CO) Ni-C(PPh3)2 with n = 2, 3 have been pubhshed together with experimental work which describes the S3mthesis and X-ray structure analyses of the compounds [107]. The first systematic... 

New outstanding results were obtained in the preparation of compounds with either two C(PPh3)2 ligands at the same metal (Fig. 22) or of a complex with one carbodiphosphorane coordinated to two metal fragments as shown in Fig. 23. 

Unusual ortho metallation of one or two phenyl groups of C(PPh3)2 is observed by reacting with some second and third row group 9 and 10 transition metal compounds. As mentioned before, transition metal precursors were compounds with either vacant coordination sites or easily removable ligands. Doubly ortho metalated compounds can also be seen as pincer carbodiphosphoranes. 

Fig. 32 Pt compounds with additional chelating ligands and one r bonded C(PPh3)(CO) ligand...

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