Carbenes samarium

Cantat T, Jaroschik F, Nief F, Ricard L, Mezailles N, Le Floch P (2005) New mono- and bis-carbene samarium complexes synthesis, X-ray crystal structures and reactivity. Chem Commun 5178-5180. doi 10.1039/b510327d... 

Thermolysis of 219a and 219b produced the benzofulvenes 221 as expected. However, the formation of 222 from 219c can best be accounted for by regarding the biradical 220a as the carbene 220b to allow an intramolecular C-H insertion reaction. The presence of a carbonyl group in 219 also permits the use of samarium(II) iodide, samarium(III) chloride, boron trifluoride and trifluoroacetic acid to promote the Schmittel cyclization reaction. 

Barbier reaction Samarium(II) iodide, 270 Benzoannelation Chromium carbene complexes, 82 Dicarbonylcyclopentadienylcobalt, 96 Ethyl (Z)-3-bromoacryIate, 130 Grignard reagents, 138 Methyl acrylate, 183 Methyllithium, 188 Ruthenium(III) chloride, 268 Benzoin condensation Benzyltriethylammonium chloride, 239 3-EthyIbenzothiazolium bromide, 130 Benzoylation (see also Acylation) Cadmium, 60 Dibutyltin oxide, 95 Birch reduction Birch reduction, 32... 

The first lanthanide-NHC complexes were isolated by Arduengo and coworkers in 1994.62 A stable carbene displaces THF in bis(pentamethylcy-clopentadienyl)-samarium-THF to form the samarium(II)-NHC complex 55 (Scheme 29). The addition of a second equivalent of NHC resulted in the isolation of the bis(NHC) adduct 56. Compound 56 was characterised in the solid state by single crystal X-ray diffraction and exhibits samarium-NHC bond distances of 2.837(7) A and 2.845(7) A, which are longer than the M-C bond in a-bonded alkyl lanthanide complexes. 

Chromium carbene complexes. phloroglucinols Malonyl dichloride. phthalides Thallium(III) trifluoroacetate. pinacols Samarium(II) iodide. Tetra-w-butylammonium fluoride. 

Having arrived at uranium as the coordinated metal, we are already past the lanthanides. It is necessary to take a break here and turn towards rare earth metal complexes with amino functionalised carbenes. Amongst the earliest examples are samarium and yttrium complexes of our already familiar amino functionalised imidazolium zwitteiion from Figure 4.28. 

Investigations into the coordination chemistry of ylides and iminophosphor-anes continue apace, an interesting development being the use of iminophos-phorane fragments as the pendant arms on new pincer ligands which help to stabilise unusual samarium and zirconium carbene complexes. 

Organolanthanide carbene complexes have been elusive for a long time. With the use of Arduengo-type heterocyclic carbenes this interesting class of compounds has become readily available. The (imidazol-2-ylidene) samarium complexes shown in Scheme 105 were obtained from l,3,4,5-tetramethylimidazol-2-ylidene and Cp 2Sm(THF) in different molar ratios.519... 

Cp 2Sm(THF)2 reacts with l,3-diisopropyl-4,5-dimethylimidazoline-2-ylidene, C3N2Me2Pr 2 (= Pr -carben), forming Cp 2Sm(Pr -carben). In the carbene ring the values for the C-N distances alternate between 1.395(4) and 1.348(4) A. The Sm-C, C-C, and the exocyclic N-C bond lengths are in the normal range.585 Several related samarium(n) and ytterbium(ll) carbene complexes have been synthesized analogously. 

A computational study of cyclopropanation reactions of the divalent samarium carbenoid ISmCH2I with ethylene has been presented. The ISmCH2I species was found to have a samarium carbene complex character with... 

Furthermore, in contrast to P-diketiminato ligands, the methanide group of bis-(phosphinimino)methanides can be deprotonated again to give bis(phosphinimino)-methandiides which act as dianionic A, A-ligand systems. As shown by Cavell et al., this ligand forms a pincer carbene-type complex with samarium, which exhibits a... 

---