Preparation, characterisation and reactivity of a series of classical and non-classical rhenium hydride complexes‡
Abstract
Hydride complexes [ReH(CO)4L] 1, [ReH(CO)3L2] 2, [ReH(CO)2L3] 3 and [ReH(CO)L4] 4 [L = P(OEt)3 a, PPh(OEt)2 b, PPh2(OEt) c or PPh2(OMe) d] were prepared by treating [ReH(CO)5] with the appropriate phosphite under UV irradiation or reflux. The complexes were characterised by IR, 1H, 13C and 31P NMR spectroscopy and by crystal structure determinations of 1d and 2d. Protonation of the monocarbonyls [ReH(CO)L4] 4 in CD2Cl2 with HBF4·Et2O resulted in an equilibrium mixture of the classical dihydride complexes [ReH2(CO)L4]+BF4– and their non-classical tautomers [Re(η2-H2)(CO)L4]+BF4–. The dihydride [ReH2(CO){PPh(OEt)2}4]BPh4 was also isolated as a solid by protonation of [ReH(CO){PPh(OEt)2}4] in ethanol. Thermally unstable [Re(η2-H2)(CO)4L]+, [Re(η2-H2)(CO)3L2]+ and [Re(η2-H2)(CO)2L3]+ 7 cations were also prepared by protonation of the corresponding monohydrides 1, 2 and 3 and fully characterised in solution. The unsaturated complexes [Re(CO)2L3]BPh4 and [Re(CO)L4]BPh4 11 and the triflate [Re(η1-OSO2CF3)(CO)3L2] were obtained from the η2-H2 derivatives by evolution of H2. The new complexes [Re(CCPh)(CO)3L2], [Re(CCPh)(CO)L4] 13, [Re(4-MeC6H4CN)(CO)2L3]BPh4, [Re(4-MeC6H4NC)(CO)2L3]BPh4 and [Re(4-MeC6H4NC)(CO)L4]BPh4 were prepared by treating the triflate compounds or the unsaturated compounds [Re(CO)2L3]BPh4 and [Re(CO)L4]BPh4 with Li+CCPh– or with the appropriate ligand.