MEASUREMENT OF HETERONUCLEAR COUPLING-CONSTANTS IN ORGANOMETALLIC COMPLEXES USING HIGH-RESOLUTION 2D NMR

H-1-P-31 coupling constants across the central metal atom (2J(P-M-H)) were measured in a series of octahedral hydridometal phosphine complexes [MRH(PP3), PP3 = P(CH2CH2CH2P(CH3)2)3; M = Ru, Fe; R = H, Cl, 1-pentenyl, cyclopentenyl, 2-methyl-1-butenyl, 3,3-dimethyl-1-butenyl] using a selective two-dimensional NMR experiment. The use of band-selective pulses focused on a narrow frequency range in the H-1 NMR spectrum (encompassing the metal-bound hydride resonances) provided spectra with high resolution as well as removed the need for suppression of intense signals arising from protic organic solvents. The magnitude of 2J(P-M-H) was found to depend on the relative disposition of the coupled nuclei and about the central metal atom, as well as the nature of the metal. For FeRH(PP3) complexes, the magnitude of 2J(P-M-H(cis)) > 2J(P-M-H(trans)), while for analogous Ru complexes, 2J(P-M-H(trans)) > 2J(P-M-H(cis)). Irrespective of whether the metal center is Fe or Ru, the sign of 2J(P-M-H(trans)) is opposite that of 2J(P-M-H(cis)) and 2J(P-M-P(cis)), but the same as 2J(P-M-P(trans)).