724733-25-9Relevant academic research and scientific papers
Chemistry of Fischer-type rhenacyclobutadiene complexes. II. Reactions with alkynes and sulfonium ylides, and rearrangements induced by nitriles and pyridine
Plantevin, Véronique,Wojcicki, Andrew
, p. 2013 - 2024 (2007/10/03)
Further investigations into the chemistry of the rhenacyclobutadiene complexes (CO)4Re(η2-C(R)C(CO2Me) C(X)) (1: R=Me, X=OEt (1a), O(CH2)3C=CH (1b), NEt2 (1c); R=CHEt2, X=OEt (1d); R=Ph, X=OEt (1e)) are reported. Reactions of 1 with alkynes at reflux temperature of toluene and at ambient temperature either under photochemical conditions or in the presence of PdO yield ring-substituted η5-cyclopentadienylrhenium tricarbonyl complexes, 2. The symmetrical alkynes R′C=CR′ (R′=Ph, Me, CO2Me) afford the pentasubstituted complexes (η5-C5(Me)(CO2Me) (OEt)(Ph)(Ph))Re(CO)3 (2d), (η5- C5(Me)(CO2Me)(OEt)(Me)(Me)) Re(CO)3 (2e), (η5-C5(Me) (CO2Me)(OEt) (CO2Me)(CO2Me)) Re(CO)3 (2f), and (η5-C5 (Me)(CO2Me) (NEt2)(CO2Me) (CO2Me)) Re(CO)3 (2i) on reaction with the appropriate 1, whereas the unsymmetrical alkynes R′C=CR″ (R′=Ph; R″=H, Me) give either only one, (η5- C5(Me)(CO2Me)(OEt) (Ph)H)Re(CO)3 (2a)), or both, (η5-C5(Me)(CO2Me) (OEt)(Ph)(Me))Re(CO)3 (2b) and (η5- C5(Me)(CO2Me)(OEt)(Me)(Ph)) Re(CO)3 (2c), (η5-C5(Ph) (CO2Me)(OEt) (Ph)H)Re(CO)3 (2g) and (η5-C5 (Ph)(CO2Me)(OEt)(H)(Ph)) Re(CO)3 (2h), of the possible products of [3 + 2] cycloaddition of alkyne to η2-C(R)C(CO2Me) C(X). Thermolysis of (CO)4Re(η2-C(Me) C(CO2Me) C(O(CH2)3C=CH)) (1b) containing a pendant alkynyl group proceeds to (η5-C5(Me) (CO2Me)(O(CH2) 3)H)Re(CO)3 (2j), a η5-cyclopentadienyl-dihydropyran fused-ring product. Competition experiments showed that each of PhC=CH and MeO2CC=CCO2Me reacts faster than PhC=CPh with 1a. The results with unsymmetrical alkynes are rationalized by steric properties of substituents at the C=C and Re=C bonds and by a preference of Re=C(Me) over Re=C(OEt) to undergo alkyne insertion. A mechanism is proposed that involves substitution of a trans CO by alkyne in 1, insertion of alkyne into Re=C bond to give a rhenabenzene intermediate, and collapse of the latter to 2. Complexes 1a and 1d undergo rearrangement in MeCN at reflux temperature to give rhenafuran-like products, (CO)4Re(κ2- OC(OMe)C(CH=CR2)C(OEt)) (R=H (3a) or Et (3b)). The reaction of 1d also proceeds in EtCN, PhCN, and t-BuCN at comparable temperature, but is slower (especially in t-BuCN) than in MeCN. In pyridine at reflux temperature, 1a undergoes a similar rearrangement, with CO substitution, to give (CO)3(py)Re(κ2-OC(OMe) C(CH=CEt2)C(OEt)) (4). A mechanism is proposed for these reactions. The sulfonium ylides Me2S=CHC(O)Ph and Me2S=C(CN)2 (Me2S=CRR′) react with 1a in acetonitrile at reflux temperature by nucleophilic addition of the ylide to the Re=C(Me) carbon, loss of Me2S, and rearrangement to a rhenafuran-type structure to yield (CO)4Re(κ2-OC(OMe)C(C(Me)=CRR′)C(OEt)) (R=H, R′=C(O)Ph (5a); R=R′=CN (5b)). All new compounds were characterized by a combination of elemental analysis, mass spectrometry, and IR and NMR spectroscopy.
