78409-02-6Relevant academic research and scientific papers
Nitrogen Nuclear Magnetic Resonance Spectroscopy as a Probe of Bonding, Bending and Fluxionality of the Imido Ligand
Bradley, Donald C.,Hodge, Stephen R.,Runnacles, John D.,Hughes, Mark,Mason, Joan,Richards, Raymond L.
, p. 1663 - 1668 (2007/10/02)
Nitrogen-14 and -15 NMR studies of imido (NR)-ligands have been made for 37 complexes of Ta, Mo, W, Re and Os, including bent NR ligands, with evidence of bent-linear fluxionality in solution, in concert with an OR or a second NR ligand.A striking difference from diazenido (N=NR) or nitrosyl ligands is the small difference in nitrogen shift for linear and bent NR ligands, the latter appearing across the whole range for NR ligands of the metals studied (with R = H, Me, Et, But, CH2But, aryl or SiMe3) in complexes with co-ordination numbers ranging from four to seven, and OR, Cl, F, NHR, NR2, N(SiMe3)2, S2CNEt2, phosphine, diphosphine or oxo coligands.This range δN -90 to 156, resembles that of the linear ligating nitrogen in N2 and NO ligands; the shielding is higher than in nitrides, with low-energy n(N) ---> ?* paramagnetic circulations, and lower than in bridging imides and amides.The deshielding on bending is much smaller than for N=NR or NO ligands because the imido lowest-unoccupied molecular orbitals (LUMOs), mainly ?* (MN) or ?* (MN), are higher lying than the ?* (NN) and ?* (NO) LUMOs.Another difference in the imido ligand is the closer parallelism of the nitrogen and the metal shielding, both of which increase with (? + ?)-acceptor ability of the coligands (increasing the ligand-field splitting).In The (thf = tetrahydrofuran) series, similarly, the nitrogen shielding increases in the sequence X = OMe Me H F Cl NO2, with increase in (? + ?)-acceptor ability of the aromatic group.The overall pattern of imido-nitrogen shielding, including the periodicity of the metal dependence (the shielding increasing down the group of the metal, but decreasing across the row) thus resembles that of other ?-donor ligands such as oxo and fluoro but differs from that of ?-acceptor nitrogen ligands, such as N2, N=NR or NO.
Organoimido-complexes of Tungsten-(VI) -(V), and -(IV): Crystal and Molecular Structures of and .
Bradley, Donald C.,Hursthouse, Michael B.,Malik K. M. Abdul,Nielson, Alastair J.,Short Richard L.
, p. 2651 - 2656 (2007/10/02)
Reaction of RNCO (R = Ph or Et) with WOCl4 gave the tungsten (VI) imido-compounds which, in further reactions gave (thf = tetrahydrofuran) and 3>.In the presence of phosphine ligands (L = PPh3 or PMe2Ph; L2 = Ph2PCH2CH2PPh2), in boiling benzene, reduction occured forming the paramagnetic tungsten (V) compounds 2>.More powerful reduction (sodium amalgam) in the presence of ligands (L = PMe3, PMe2Ph, and CNBut) gave the tungsten (IV) compounds 3>.Other reactions led to cleavage of the organoimido-group from the tungsten.An X-ray structure determination of showed the meridional configuration of chlorines with mutually trans-phosphines.The short W-N bond length (1.742 Angstroem) and practically linear WNC (172.3 degree) suggest that the imido-group is acting as a four electron ligand.Structure determination of shows that the three phosphines are meridional, and all cis to the W=-N-Ph unit.Although the imido-function seems to exert a small trans-lengthening influence on the relevant W-Cl bond in the trichloride, this effect does not seem to be present in the dichloride.
