Coordination Chemistry of Tetra- and Tridentate Ferrocenyl Polyphosphines: An Unprecedented [1,1′-Heteroannular and 2,3-Homoannular]-Phosphorus-Bonding Framework in a Metallocene Dinuclear Coordination Complex

• Published in: Inorganic chemistry 2008-03, Vol.47 (5), p.1607-1615
• Main Authors: Thomas, D. A, Ivanov, V. V, Butler, I. R, Horton, P. N, Meunier, P, Hierso, J.-C
• Format: Article
• Language: English
• Subjects: Chemical Sciences; Coordination chemistry
• ISSN: 0020-1669; 1520-510X
• DOI: 10.1021/ic7022105

Palladium(II) and nickel(II) halide complexes of the ferrocenyl polyphosphines 1,1′,2,3-tetrakis(diphenylphosphino)ferrocene (1), and 1,1′,2-tris(diphenylphosphino)-4-tert-butylferrocene (5) were prepared and characterized by multinuclear NMR. The metallo-ligand 1, the palladium [Pd2Cl4(1)] (3b) and nickel [NiCl2(5)] (6) coordination complexes were additionally characterized by X-ray diffraction crystallography. The behavior of 1 toward coordination to nickel and palladium was surprisingly different because the coordination of a second metal center after the initial 1,2-phosphorus-bonding of nickel was markedly difficult. The preference of nickel for 1,2-P coordination on 1,1′-bonding was confirmed by the exclusive formation of 6 from 5. The changes noted between the solid state structure of the ligand 1 and the structure obtained for the dinuclear palladium complex 3b reveal the rotational flexibility of this tetraphosphine. This flexibility is at the origin of the unique framework for a metallocenic dinuclear metal complex in which both coexist a 1,1′-heteroannular chelating P-bonding and a 2,3-homoannular chelating P-bonding with two palladium centers. Some reported specimens of ferrocenyl polyphosphines of constrained geometry have previously revealed that phosphorus lone pair overlap can lead to very intense “through-space” 31P31P nuclear spin−spin coupling constants (J PP) ( J. Am. Chem. Soc. 2004, 126 (35), 11077–11087 ] in solution phase. In these cases, an internuclear distance between heteroannular phosphorus atoms below 4.9 Å, with an adequate orientation of the lone-pairs in the solid state and in solution, was a necessary parameter. The flexibility of the new polyphosphines 1 and 5 does not allow that spatial proximity (internuclear distances between heteroannular phosphorus above 5.2 Å in the solid state); accordingly the expected through-space nuclear spin−spin coupling constants were not detected in any of their coordination complexes nor in 1.