NEW DIHYDROGEN COMPLEXES - THE SYNTHESIS AND SPECTROSCOPIC PROPERTIES OF IRON(II), RUTHENIUM(II), AND OSMIUM(II) COMPLEXES CONTAINING THE MESO-TETRAPHOS-1 LIGAND

The synthesis and properties of dihydrogen complexes trans-[MH(H-2)L](+), M = Fe, Ru, Os, which contain the ligand mesotetraphos-1, S,R-Ph(2)PCH(2)CH(2)P(Ph)CH2CH2P(Ph)CH(2)CH(2)PPh(2) (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-beta-Os(Cl)(2)L with H-2 (1 atm) and NaBPh(4) (1 mol) in THF or by the reaction of trans-OsH(CI)L with NaBPh(4) and H-2. 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 T-1(min) data to be 0.88, 0.89, and 0.99 Angstrom for the complexes of Fe, Ru, Os, respectively. The presence of the H-D bond in the isotopomers trans-[MH(KD)L]+ and trans-[MD(HD)L](+) is also confirmed by the observation of (1)J(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(H-2)(dppe)(2)](+) or to the trihydride Re(H)(3)L. Described also are the properties of the precursor complexes including cis-beta- and trans-Ru(Cl)(2)L and derivatives of the dihydrogen complexes trans-[MH(L')L](+), L' = CH3CN (on Ru and Os), PMe(2)Ph (on Ru), and CO (on Os). Trends in the NMR properties of isostructural complexes are reported.