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

摘要

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" (PP)-P-31-P-31 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 angstrom, 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 angstrom 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.