54477-77-9Relevant academic research and scientific papers
Ab Initio and Experimental Studies on the Structure and Relative Stability of the cis-Hydride-η2-Dihydrogen Complexes [{P(CH2CH2PPh2)3}M (H)(η2-H2)]+ (M = Fe, Ru)
Bianchini, Claudio,Masi, Dante,Peruzzini, Maurizio,Casarin, Maurizio,Maccato, Chiara,Rizzi, Gian Andrea
, p. 1061 - 1069 (2008/10/09)
Ab initio calculations (DMOL method) including the estimate of the total energy and the full optimization of the geometrical parameters have been used to study the electronic structures and the coordination geometries of the model systems [{P(CH2CH2PH2)3}M (H) (L)]+ (M = Fe, L = H2, C2H4, CO, N2; M = Ru, L = H2). Single crystal X-ray analyses have been carried out on the complexes [(PP3)Fe (H)(η2-H2)]BPh4·0.5THF (1·0.5THF), [(PP3)Fe (H)(CO)]BPh4·THF(3·THF), and [(PP3)Ru (H)(η2-H2)]BPh 4·0.5THF(5·0.5THF) [PP3 = P(CH2CH2PPh2)3]. Crystal data: for 1·0.5THF, triclinic P1 (No. 2), a = 17.626(3) A?, b = 14.605(3) A?, c = 12.824(4) A?, α = 90.09(2)°, β = 103.87(2)°, γ = 107.46(2)°, Z = 2, R = 0.082; for 3·THF, triclinic P1 (No. 2), a = 12.717(2) A?, b = 14.553(1) A?, c = 17.816(2) A?, α = 72.90(1)°, β = 76.82(2)°, γ = 89.71(1)°, Z = 2, R = 0.067; for 5·0.5THF, monoclinic P2/1a (No. 14), a = 19.490(5) A?, b = 19.438(2) A?, c = 16.873(5) A?, β= 110.96(2)°, Z = 4, R = 0.074. On the basis of theoretical calculations, X-ray analyses, and multinuclear NMR studies, all of the complexes of the formula [(PP3)M (H) (L)]BPh4 [M = Fe, L = H2 (1), C2H4 (2), CO (3), N2 (4); M = Ru, L = H2 (5), C2H4 (6)] are assigned a distorted octahedral structure where the hydride (trans to a terminal phosphorus donor) and the L ligand occupy mutually cis positions. The theoretical calculations indicate that the H2 ligand in the η2-dihydrogen-hydride derivatives 1 and 5 is placed in the P-M-H plane (parallel orientation) and that there is an attractive interaction between the H and H2 ligands. XPS measurements, performed on the iron complexes, show that the Fe → L back-bonding interaction plays a leading role in 3. It is concluded that the stronger metal-H2 bond in the dihydrogen-hydride complex 1, as compared to the Ru analog 5, is due to the greater d(metal) → σ*(H-H) back-donation as well as a more efficient interaction between the terminal hydride and an H of the dihydrogen ligand. This cis effect is suggested to contribute to the relative stability of the iron complexes, which increases in the order C2H4 2 2 CO.
Chemoselective hydrogen-transfer reduction of α,β-unsaturated ketones catalyzed by isostructural iron(II), ruthenium(II), and osmium(II) cis hydride η2-dihydrogen complexes
Bianchini, Claudio,Farnetti, Erica,Graziani, Mauro,Peruzzini, Maurizio,Polo, Alfonso
, p. 3753 - 3761 (2008/10/08)
The nonclassical trihydrides [(PP3)M(H)(η2-H2)]BPh4 (M = Fe, Ru, Os) are efficient catalyst precursors for the reduction of α,β-unsaturated ketones via hydrogen-transfer from secondary alcohols [PP3 = P(CH2CH2PPh2)3]. α,β-Unsaturated ketones bearing bulky substituents at the double bond (i.e. benzylideneacetone) are chemoselectively reduced to allylic alcohols by using either the iron or the ruthenium catalyst. In contrast, the osmium system catalyzes the reduction of α,β-unsaturated ketones to saturated ketones via isomerization of the initially produced allylic alcohols. A number of reducible substrates including various unsaturated and saturated ketones, aldehydes, alkenes, and alkynes have been studied in order to get information on the steric and electronic factors which may affect the interaction of the substrate with the metal center and, thus, control the selectivity of the hydrogen-transfer reductions. Evidence is provided for the formation of an η1-O-benzylideneacetone complex of the formula [(PP3)Os(H){η1-OCMe-(CH=CHPh)}]BPh4 which has been characterized by multinuclear NMR spectroscopy. The latter compound and the related complex [(PP3)Os(H)(η1-OCMe2)]BPh4 have been used in a number of reactions. As a result, valuable information has been obtained which allows one to propose catalytic cycles for the hydrogen-transfer reduction of α,β-unsaturated ketones to unsaturated alcohols assisted by the Fe and Ru complexes, and for the isomerization of allylic alcohols to saturated ketones catalyzed by the Os complex.
