New dihydrogen complexes: the synthesis and spectroscopic properties of iron(II), ruthenium(II), and osmium(II) complexes containing the meso-tetraphos-1 ligand

Abstract

The synthesis and properties of dihydrogen complexes trans-[MH(H₂)L]⁺, M = Fe, Ru, Os, which contain the ligand meso-tetraphos-1, S,R-Ph₂PCH₂CH₂P(Ph)CH₂CH₂P(Ph)CH₂CH₂PPh₂ (L) are described. There are interesting possibilities of isomerism in such trans complexes because the axial binding sites at the metal are different, one being surrounded by four phenyl groups and the other by two phenyl groups. The osmium complex is prepared in an unusual reaction of cis-β-Os(Cl)₂L with H₂ (1 atm) and NaBPh₄ (1 mol) in THF or by the reaction of trans-OsH(Cl)L with NaBPh₄ and H₂. The iron and ruthenium complexes were made by a reaction of HBF₄ with complexes trans-M(H)₂L that have inequivalent trans hydrides. The ruthenium complex was also prepared starting from isomers of trans-RuH(Cl)L. The H—H distance in the rapidly spinning dihydrogen ligand has been calculated from T₁(min) data to be 0.88, 0.89, and 0.99 Å for the complexes of Fe, Ru, Os, respectively. The presence of the H—D bond in the isotopomers trans-[MH(HD)L]⁺ and trans-[MD(HD)L]⁺ is also confirmed by the observation of ¹J_HD coupling constants of 32, 33.5, and 26.4 Hz for Fe, Ru, and Os, respectively. There is no rapid intramolecular H atom exchange in these complexes in contrast to those with di-tert-phosphine ligands like [MH(H₂)(dppe)₂]⁺ or to the trihydride Re(H)₃L. Described also are the properties of the precursor complexes including cis-β- and trans-Ru(Cl)₂L and derivatives of the dihydrogen complexes trans-[MH(L′)L]⁺, L′ = CH₃CN (on Ru and Os), PMe₂Ph (on Ru), and CO (on Os). Trends in the NMR properties of isostructural complexes are reported.