“…30 min). The formation of [Re 2 (μ-H)(μ-CHC(H)Ph)(CO) 8 ] , from the reaction with styrene was slightly slower, reaching completion in about 20 min at 298 K. In the case of acetaldehyde, the reaction was still highly selective, but much slower, requiring about 2.5 h for the complete transformation of 3 into [Re 2 (μ-H)(μ-η 2 -C(Me)O)(CO) 8 ] …”
The reaction of [Re2(μ-H)2(CO)8] (1) with diazomethane at 193 K in THF-d
8 gives the
unstable [Re2(μ-H)(μ-CH3)(CO)8] derivative (2) containing a methyl group arising from the
insertion of CH2 into a Re−H−Re bond. Isotopic perturbation of the equilibria by partial
deuteration demonstrated that the methyl bridges the Re−Re bond in an unsymmetrical
way, with a fast exchange between one agostic and two terminal C−H bonds. At temperatures
higher than 253 K, 2 decomposes, in THF solution, with CH4 elimination to give the novel
red complex 1,2-eq,eq-[Re2(CO)8(THF)2] (3), which was characterized by NMR spectroscopy
and X-ray analysis. In the solid form a staggered conformer of C
2 symmetry was found. 13C
NMR analysis revealed the presence, in wet THF, of the aquo complexes [Re2(CO)8(THF)(H2O)] (4) and [Re2(CO)8(H2O)2] (5), whose formation is favored at low temperature (ΔH° for
the formation of 5 from 4: −14.4(2) kJ mol-1). In solution, due to the lability of the THF
ligands, 3 behaves as a “lightly stabilized” Re2(CO)8 fragment, capable of activating different
E−H bonds. Reaction with HCl in THF leads to [Re2(μ-H)(μ-Cl)(CO)8], while with H2 the
unsaturated starting material [Re2(μ-H)2(CO)8] is obtained. In THF solution, at room
temperature, reactions with phenylacetylene, styrene, and acetaldehyde give the derivatives
of C−H activation [Re2(μ-H)(μ-C⋮CPh)(CO)8], [Re2(μ-H)(μ-CHC(H)Ph)(CO)8], and [Re2(μ-H)(μ-η2-C(Me)O)(CO)8]. Moreover, the activation of an sp3 C−H bond in ethyl acetate occurs
slowly when 3 is dissolved in the reactant itself, the resultant product being [Re2(μ-H)(μ-η2-CH2C(O)OEt)(CO)8].
“…30 min). The formation of [Re 2 (μ-H)(μ-CHC(H)Ph)(CO) 8 ] , from the reaction with styrene was slightly slower, reaching completion in about 20 min at 298 K. In the case of acetaldehyde, the reaction was still highly selective, but much slower, requiring about 2.5 h for the complete transformation of 3 into [Re 2 (μ-H)(μ-η 2 -C(Me)O)(CO) 8 ] …”
The reaction of [Re2(μ-H)2(CO)8] (1) with diazomethane at 193 K in THF-d
8 gives the
unstable [Re2(μ-H)(μ-CH3)(CO)8] derivative (2) containing a methyl group arising from the
insertion of CH2 into a Re−H−Re bond. Isotopic perturbation of the equilibria by partial
deuteration demonstrated that the methyl bridges the Re−Re bond in an unsymmetrical
way, with a fast exchange between one agostic and two terminal C−H bonds. At temperatures
higher than 253 K, 2 decomposes, in THF solution, with CH4 elimination to give the novel
red complex 1,2-eq,eq-[Re2(CO)8(THF)2] (3), which was characterized by NMR spectroscopy
and X-ray analysis. In the solid form a staggered conformer of C
2 symmetry was found. 13C
NMR analysis revealed the presence, in wet THF, of the aquo complexes [Re2(CO)8(THF)(H2O)] (4) and [Re2(CO)8(H2O)2] (5), whose formation is favored at low temperature (ΔH° for
the formation of 5 from 4: −14.4(2) kJ mol-1). In solution, due to the lability of the THF
ligands, 3 behaves as a “lightly stabilized” Re2(CO)8 fragment, capable of activating different
E−H bonds. Reaction with HCl in THF leads to [Re2(μ-H)(μ-Cl)(CO)8], while with H2 the
unsaturated starting material [Re2(μ-H)2(CO)8] is obtained. In THF solution, at room
temperature, reactions with phenylacetylene, styrene, and acetaldehyde give the derivatives
of C−H activation [Re2(μ-H)(μ-C⋮CPh)(CO)8], [Re2(μ-H)(μ-CHC(H)Ph)(CO)8], and [Re2(μ-H)(μ-η2-C(Me)O)(CO)8]. Moreover, the activation of an sp3 C−H bond in ethyl acetate occurs
slowly when 3 is dissolved in the reactant itself, the resultant product being [Re2(μ-H)(μ-η2-CH2C(O)OEt)(CO)8].
“…Two isomers of the nanocarbonyl photoproduct, eq -Re 2 (CO) 9 and ax -Re 2 (CO) 9 , were characterized by using matrix isolation and liquid-noble-gas techniques . Moreover, 366 nm photolyses of Re 2 (CO) 10 in solutions of olefin yield hydridoalkenyldirhenium octacarbonyl complexes, (μ-H)(μ-alkenyl)Re 2 (CO) 8 , as major photoproducts. , Carbonyls with semibridging CO have been generated under various conditions; the equivalent Re complex, (b) b-Re 2 (CO) 9 , has not been observed, however, in the photochemistry of Re 2 (CO) 10 . …”
The mechanism of (&mgr;-H)(&mgr;-alkenyl)Re(2)(CO)(8) formation upon UV irradiations of Re(2)(CO)(10) in presence of olefin (styrene, trans-stilbene, 4-methyl-1-cyclohexane, and ethylene) was investigated by laser flash photolyses. Such photoproducts result from reactions of the olefin with eq-Re(2)(CO)(9). No reactions of Re(CO)(5) leading to hydride alkenyl products were observed. Dependences of the reaction rate on olefin concentration and solvent revealed an additional intermediate formed after the addition of the olefin to eq-Re(2)(CO)(9) and before the appearance of the &mgr;-hydrido-&mgr;-alkenyl products.
“…Obwohl ungesättigte Kohlenwasserstoffe photo chemisch mit 1 bevorzugt [Re2(CO)8(//-H)(y u-^12-olefinyl)]-Komplexe ergeben [18][19][20], ist dieses Reaktionsverhalten bei Allenen eher atypisch. So konnten zu 5 analoge Komplexe bei den Um set zungen von [Re2(CO)10] mit Allen und methylsub stituierten Allen-Derivaten nicht gefunden werden [23].…”
Section: -»6unclassified
“…Da bislang lediglich Photoreaktionen von [Re2(C O )l0] mit konjugierten Dienen, Trienen und Tetraenen beschrieben wurden [18][19][20][21][22], schien es reizvoll, dessen Photoreaktivität auch gegenüber kum ulierten Dienen näher zu untersuchen [23]. Im folgenden soll über die Ergebnisse mit Phenylallen als Reaktionspartner berichtet werden.…”
Decacarbonyldirhenium (1) and phenylallene (2) form upon U V irradiation four dinuclear complexes: Decacarbonyl-//-^l:l-(3,4-diphenyl-1,5-hexadien-2,5-diyl)-dirhenium (3), enneacarb on yl-//V :3-(3-phenyl-2-propen-l,2-diyl)-dirhenium (4), octacarb on yl-//-h yd rid o-/iV 2-(3-phenyl-l,2-propadien-l-yl)-dirhenium (5) and octacarbonyl-/i-?72 2-(phenyl-l,2-propadiene)-dirhenium (6). The thermolabile complex 4 looses CO and forms the phenylallene bridged compound 6. Similarly 5 is rearranged to 6 by transfer o f the hydrido ligand to the 3-phenyl-1,2-propadien-l-yl bridge. The formation o f 3 and 4 can be rationalized via pentacarbonyl-phenylpropenediyl-rhenium radicals which dimerize to give 3 or add pentacarbonylrhenium radicals, loose CO and form 4. The crystal and molecular structure o f 3 was deter mined by X-ray structure analysis. In the solid state the molecule is present in the ± ap confor mation. In solution at 233 K the ± a p , +sc, and -s c conform ations are equally populated. By a hindered rotation around a CC single bond, the three conformers are interconverted with a rotation barrier o f J G * 25g = 52.3 ± 1 k J -m o L 1.
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