This tutorial review devoted to ligand chemistry deals with the design and properties of ferrocenyl polyphosphines, an original class of multidentate ligands. The development of a varied library of ferrocenyl tetra-, tri- and diphosphine ligands is reviewed. The multidentate nature of these species has led to unique spectroscopic and catalytic properties, in which the spatial proximity of phosphorus atoms is crucial. Regarding their catalytic applications, the key issues of catalyst longevity and ultralow catalyst loadings are discussed. Another part is concerned with fundamental advances gained in physical chemistry for structure elucidation by the study of the intriguing "through-space" NMR spin-spin J couplings existing within several of these polyphosphines.

Abstract:The diastereoselective synthesis of dialkylated ferrocenyl bis(phosphane)s bearing aryl, alkyl, and hetero-or polycyclic substituents on the phosphino groups is reported, together with their characterization in the solid state by X-ray structure analysis and in solution by multinuclear NMR spectro-

The present study deals with the conformational control of the metallocene backbone within ferrocenyl polyphosphane ligands and their performance in the highly topical palladium-catalyzed heteroaromatics arylation by direct C-H activation. New substituted cyclopentadienyl rings were synthesized, which allowed the assembling of original tri-and diphosphanes. The bulky cyclopentadienyl lithium salts diphenylphosphino-3-(triphenyl)methylcyclopentadienyllithium (4) and 1,2-bis(diphenylphosphino)-4-(triphenyl)methylcyclopentadienyllithium (5) were prepared in excellent yield. The assembling of these new hindered cyclopentadienyl salts (Cp) with other Cp fragments was performed in order to prepare ferrocenyl ligands with controlled conformation. A comparison of conformations of 1,1′,2-tris(diphenylphosphino)-3′,4-di-tert-butylferrocene (3) and 1,1′,2-tris(diphenylphosphino)-3′-(triphenyl)methyl-4tert-butylferrocene (6) allowed us to determine, for the first time, the conditions of an efficient control of the orientation of the phosphino substituents on the ferrocene backbone in the absence of an ansabridge. The characterization of these metallo-ligands, by multinuclear NMR in solution and by X-ray diffraction in the solid state, focused on nonbonded J PP spin-spin couplings. These unusual couplings are especially useful for assessing the conformation of the ferrocene backbone in solution. The palladium complexes of the triphosphane ligand 6 and the diphosphane 1,1′-bis(diphenylphosphino)-3,3′-di(triphenyl)methylferrocene ( 7) were successfully used in the direct C-H activation of electron-rich heteroaromatics for coupling to demanding aryl bromides, whether electron rich and/or sterically congested. Products such as 2-butyl-5-(4-methoxyphenyl)furan (10), 2-butyl-5-o-tolylfuran (11), and thiophene analogues (12 and 13) were obtained in yields higher than 90%. The NMR examination of the reaction of [PdCl(η 3 -C 3 H 5 )] 2 with ligands 6 and 7 allowed us to determine the coordination chemistry of the precatalysts. The allylic palladium complexes 8 and 9 confirmed the unusual conformation present in 6. As a consequence, the selective and "genuinely" tridentate bonding of a triphosphane to one palladium center is reported. This seldom observed coordination mode is a direct consequence of the successful ferrocene backbone conformation control.