Classical and nonclassical polyhydride ruthenium(II) complexes stabilized by the tetraphosphine P(CH2CH2PPh2)3

The dichloride ((PP{sub 3})RuCl{sub 2}) (1) is selectively transformed into ((PP{sub 3})Ru(H)({eta}{sup 1}-BH{sub 4})) (2), ((PP{sub 3})Ru(H)Cl) (3), and ((PP{sub 3})Ru(H){sub 2}) (4) by reaction with NaBH{sub 4}, LiHBEt{sub 3}, and LiAlH{sub 4}, respectively (PP{sub 3} = P(CH{sub 2}CH{sub 2}PPh{sub 2}){sub 3}). Complex 2 is fluxional on the NMR time scale in ambient-temperature solutions due to equilibration of the BH{sub 4}{sup {minus}} hydrogens through cleavage of the Ru-H{sub b}-B bridge and interconversion of H{sub t} by rotation. The hydride-tetrahydroborate complex exhibits amphoteric nature: it reacts with protic acids, yielding the cis-hydride dihydrogen complex ((PP{sub 3})Ru(H)({eta}{sup 2}-H{sub 2}))Y (Y = PF{sub 6}, 6a; BPh{sub 4}, 6b), and with bases such as PEt{sub 3} or KO{sup t}Bu, converting to the dihydride 4. The latter compound can be obtained also by thermal decomposition of 2 in refluxing toluene or benzene. Complexes 6a,b can be prepared by reaction of the dihydride 4 with protic acids. In the solid state and in solution at low temperature ((PP{sub 3})Ru(H)({eta}{sup 2}-H{sub 2})){sup +} is octahedral, and the hydride and dihydrogen ligands occupy mutually cis positions. At ambient temperature in solution the complex is trigonal-bipyramidal and the equilibration of the hydrogens might proceed through an H{sub 3} unitmore » occupying an axial position trans to the bridgehead phosphorus atom of PP{sub 3}. 36 refs., 6 figs., 2 tabs.« less