Synthesis, characterization, and structure of the complex [FeH(H2BH2){CH3C(CH2PPh2)3}]

Abstract

By reaction of [Fe(H₂O)₆][BF₄]₂ with 1,1,1-tris(diphenylphosphinomethyl)ethane, tppme, and an excess of sodium tetrahydroborate, in boiling tetrahydrofuran, the red crystalline complex [FeH(H₂BH₂)(tppme)] has been synthesized. Its crystal structure has been determined from counter diffraction data [orthorhombic, space group Pn2₁a, a= 20.803(7), b= 16.964(5), c= 10.242(3)Å, and Z= 4] and refined by full-matrix least squares to R and R′ of 0.042 and 0.041 respectively for 1 191 reflections having I 3σ(I). The iron atom is six-co-ordinated by the three phosphorus atoms of the ligand, two hydrogen atoms of the BH₄ group, and a hydridic hydrogen atom. Variable-temperature ₁H and ₃₁P n.m.r. studies have shown that at low temperature (<253 K) the molecule is rigid also in solution. On raising the temperature, scrambling of the three metal-bound hydrogens occurs and the ligand phosphorus atoms, co-ordinated to the metal, become magnetically equivalent.