112173-19-0Relevant academic research and scientific papers
Secondary methoxycarbene complexes [(η5-C5Me5)M(CO)2(CHOMe)] + (M = Fe, Ru): Dynamic NMR studies and electrophilic properties
Guerchais, Véronique,Lapinte, Claude,Thépot, Jean-Yves,Toupet, Loic
, p. 604 - 612 (2008/10/08)
The anionic complex [(η5-C5Me5)Ru(CO)2] -K+ (3), a precursor of (η5-C5Me5)Ru(CO)2(CH 2OMe) (2), is conveniently obtained by reduction of [(η5-C5Me5)Ru(CO)2]2 by using a dispersion of potassium in boiling THF overnight. The methoxymethyl complexes (η5-C5Me5)M(CO)2(CH 2OMe) (1, M = Fe; 2, M: Ru) undergo an α-hydride abstraction with Ph3C+PF6- giving specifically the corresponding secondary methoxycarbene complexes [(η5-C5Me5)M(CO)2(CHOMe)] +PF6- (4, M = Fe; 5, M = Ru). Monitoring the above reaction by variable-temperature 1H and 13C NMR experiments shows that the carbene complexes 4 and 5 are formed at -80°C as a mixture of cis and trans isomers in a 90:10 and 95:5 kinetic ratio, respectively; upon warming, the cis form irreversibly isomerizes into the more sterically favored trans isomer. NOE studies on 5 indicate that isomerism in these systems arises from restricted carbene carbon-oxygen bond rotation. Complex 4a (4+CF3SO3-) is also formed in the reaction of 1 with Me3SiOSO2CF3 that proceeds by an intermolecular hydride transfer from the unreacted methoxymethyl complex 1 to the methylene cation intermediate [(η5-C5Me5)Fe(CO)2(=CH 2)]+. Reaction of 4 (-80°C) with PPh3 gives the unstable α-methoxyphosphonium salt [(η5-C5Me5)Fe(CO)2(CHOMePPh 3)]+PF6- (8) which was characterized at -20 °C by 1H, 31P, and 13C NMR spectroscopy. The preferred conformation of 8 is discussed. The [:CHOMe] ligand of 4 or 5 inserts into the Si-H bond of Et3SiH and Me2PhSiH, giving the methoxymethylsilanes 10 and 11, whereas 4 converts Ph3SiH into Ph3SiMe and Ph3SiOMe via a hydride/methoxide exchange. The new alkene complexes [(η5-C5Me5)M(CO)2(CH 2=CHR)]+PF6- (12, M = Fe, R = H; 13, M: Fe; R = Ph; 14, M = Ru, R = H; 15, M = Ru, R = Ph) are synthesized when the insertion reaction is carried out in the presence of CH2=CHR. Complex 15a (15+CF3SO3-) can be also obtained from 2 upon treatment with Me3SiOSO2CF3 in the presence of styrene. The X-ray crystal structure of 15a shows that it crystallizes in the monoclinic space group P21/c with unit cell parameters a = 8.533 (4) A?, b = 23.663 (7) A?, c = 11.480 (6) A?, β = 100.77 (7)°, and Z = 4. The structure was solved and refined (4333 reflections) to the final values for the residual R = 0.053 and Rw = 0.061.
