(6,6‘-Dimethoxybiphenyl-2,2‘-diyl)bis(diphenylphosphine) (MeO-BIPHEP) as a Six-Electron Donor in [Ru(η5-C8H11)(MeO-BIPHEP)]+ Cations. Coordination of a Biaryl Double Bond, As Shown by 13C NMR and X-ray Crystallography

• Published in: Organometallics Vol. 16; no. 4; pp. 537 - 543
• Main Authors: Feiken, Nantko, Pregosin, Paul S, Trabesinger, Gerald, Scalone, Michelangelo
• Format: Journal Article
• Language: English
• Published: American Chemical Society 18.02.1997
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om960812x

The reaction of the MeO-BIPHEP complex Ru(OAc)2(1a) (1a = (6,6‘-dimethoxybiphenyl-2,2‘-diyl)bis(bis(3,5-di-tert-butylphenyl)phosphine), with HBF4 and 1,5-COD affords [Ru(η5-C8H11)(1a)]BF4 (4), in which 1a functions as a 6e donor to Ru(II) via an unexpected coordination of one of the biaryl double bonds. The isopropyl analog [Ru(η5-C8H11)(1b)]CF3CO2 (6; 1b = (6,6‘-dimethoxybiphenyl-2,2‘-diyl)bis(diisopropylphosphine)) was prepared by starting from [Ru(CF3CO2)2(1,5-COD)]2 and reveals the same η4-bonding mode. Both complexes were characterized by detailed multidimensional NMR studies, and the X-ray structure for 6 is reported. Although the 31P chemical shifts for this new η4-bonding mode are informative, the 13C resonance positions for the coordinated biaryl carbons are a more reliable criterion for recognizing this type of interaction. These chemical shift data are difficult to obtain using routine 13C measurements, and a long-range 13C,1H-correlation is recommended as the method of choice. Complex 4 exhibits dynamic behavior in solution, as shown by 2-D NOESY. This exchange process can be rationalized by assuming that the double bond dissociates; however, complex 6 does not show an analogous exchange process at ambient temperature.