Synthesis and structural features of complexes [(P∩P)2Rh][hfacac] containing hexafluoroacetyl- acetonate as a noncoordinating anion

Abstract

The synthesis and characterization of complexes [(P∩P)2Rh][hfacac] (P∩P = chelating bidentate phosphine ligand R2P(CH2)nPR2 (2a-g), hfacac = hexafluoroacetylacetonate anion) (4) is reported. The molecular structures of 4a (R = Ph, n = 1) and 4f (R = Cy, n = 2) in the solid state were determined by single-crystal X-ray diffraction. The complexes crystallize in the monoclinic space groups C2/c (No. 15) and P21/n (No. 14), respectively. No coordinative interaction between the rhodium center of the cation [(P∩P)2Rh]+ (4a+, 4f+) and the hfacac anion is evident in either cases. In the crystal structure of 4a, hydrogen bonds between the oxygen atoms of the hfacac anion and methylene protons of the CH2 bridges of the phosphine ligand lead to highly symmetric chains of regularly alternating cations and anions. The coordination geometry around the rhodium center in 4a+ is ideally square-planar, whereas 4f+ is significantly distorted towards a tetrahedron with an angle between the two P2Rh moieties of 18.6°. The cation 4b+ (R = Cy, n = 1) was investigated in form of the tetrafluoroborate salt for comparison. The compound [{Cy2P(CH2)PCy2}2Rh][BF4] crystallizes as a THF solvate (4b′) in the triclinic space group P[Formula: see text] (No. 2) containing ideally square-planar [(P∩P)2Rh]+ cations. Key words: rhodium, chelating ligands, coordination modes, 1,3-diketonates, phosphorus ligands.