1236844-79-3Relevant academic research and scientific papers
Congested ferrocenyl polyphosphanes bearing electron-donating or electron-withdrawing phosphanyl groups: Assessment of metallocene conformation from NMR spin couplings and use in palladium-catalyzed chloroarenes activation
Mom, Sophal,Beaupérin, Matthieu,Roy, David,Royer, Sylviane,Amardeil, Régine,Cattey, Hélène,Doucet, Henri,Hierso
experimental part, p. 11592 - 11603 (2012/01/06)
The synthesis of novel substituted cyclopentadienyl salts that incorporate both a congested branched alkyl group (tert-butyl, (triphenyl)methyl, or tri(4-tert-butyl)phenylmethyl) and a phosphanyl group is reported. The introduction of either electron-withdrawing or electron-donating substituents (furyl, i-propyl, cyclohexyl, tert-butyl) on P atoms was generally achieved in high yield. The modular synthesis of ferrocenyl polyphosphanes from an assembly of these cyclopentadienyl salts was investigated, leading to the formation of new triphosphanes (denoted as 9-12) and diphosphanes (denoted as 14-16). The resulting phosphanes are not sensitive to air or moisture, even when electron-rich substituents are present. This set of polyphosphanes displays varied conformational features, which are discussed in the light of their multinuclear NMR characterization in solution and of the X-ray solid state structure of the representative triphosphane 1,2-bis(diphenylphosphanyl)- 1′-(diisopropylphosphanyl)-3′-(triphenyl)methyl-4-tert-butyl ferrocene, 11. In particular, the existence of a range of significantly different nonbonded ("through-space", TS) spin-spin coupling constants between heteroannular P atoms, for the triphosphanes of this class, allowed their preferred conformation in solution to be appraised. The study evidences an unanticipated flexibility of the ferrocene platform, despite the presence of very congested tert-butyl and trityl groups. Herein, we show that, contrary to our first belief, the preferred conformation for the backbone of ferrocenyl polyphosphanes can not only depend on the hindrance of the groups decorating the cyclopentadienyl rings but is also a function of the substituents of the phosphanyl groups. The interest of these robust phosphanes as ligands was illustrated in palladium catalysis for the arylation of n-butyl furan with chloroarenes, using direct C-H activation of the heteroaromatic in the presence of low metal/ligand loadings (0.5-1.0 mol %). Thus, 4-chlorobenzonitrile, 4-chloronitrobenzene, 4-chloropropiophenone, and 4-(trifluoromethyl) chlorobenzene were efficiently coupled to n-butyl furan, using Pd(OAc) 2 associated to the new diphosphane ligands 1,1′- bis(diisopropylphosphanyl)-3,3′-di(triphenyl)methyl ferrocene (15) or 1,1′-bis(dicyclohexylphosphanyl)-3,3′-di(triphenyl)methylferrocene (16), which respectively hold the electron-rich -Pi-Pr2 and -PCy 2 groups.
N-heterocyclic carbenes: Useful ligands for the palladium-catalysed direct C5 arylation of heteroaromatics with aryl bromides or electron-deficient aryl chlorides
Ozdemir, Ismail,Goek, Yetkin,Oezeroglu, Oezlem,Kaloglu, Murat,Doucet, Henri,Bruneau, Christian
experimental part, p. 1798 - 1805 (2010/08/13)
New Pd-N-heterocyclic carbene complexes have been prepared and employed for palladium-catalysed direct arylation of heteroaromatic derivatives by using aryl halides. These catalyst precursors promote the coupling of challenging aryl halides such, as deactivated or congested aryl bromides and also activated aryl chlorides. This procedure employs only 1 mol-% of an air-stable palladium complex. This is a practical advantage over the procedures that employ palladium attached to air-sensitive phosphane ligands, which are often used to promote the coupling of such, aryl halides.
