Abstract
AbstractThe preferred conformation of aminophosphanes with bulky amino groups (1–20) was determined by NMR spectroscopy in solution, in two cases in the solid state (11,17) and in one case (11) by X‐ray crystallography. Trimethylsilylaminodiphenylphosphanes Ph2PN(R)SiMe3 (R = Bu (1), Ph (2), 2‐pyridyl (3), 2‐pyrimidyl (4), Me3Si (5)), amino(chloro)phenylphosphanes Ph(Cl)PNRR′ (R = Bz, R′ = Me (6), R = Bz, R′ = tBu (7), R = Et, R′ = Ph (8)), amino(chloro)tert‐butylphosphanes tBu(Cl)PNRR′ (R = R′ = iPr (9), R = Me, R′ = tBu (10), R = Bz, R′ = tBu (11), R = H, R′ = tBu (12), R = Et, R′ = Ph (13), R = iPr, R′ = Ph (14), R = Bu, R′ = Ph (15), R = Bz, R′ = Ph (16), R = R′ = Ph (17), R = R′ = Me3Si (18)), 3‐tert‐butyl‐2‐chloro‐1,3,2‐oxazaphospholane (19), and benzyl(tert‐butyl)aminodichlorophosphane (20) were studied by 1H, 13C, 15N, 29Si, and 31P NMR spectroscopy. In all cases, the more bulky substituent at the nitrogen atom prefers the syn‐position with respect to the assumed orientation of the phosphorus lone pair of electrons. Many of the derivatives studied adopt this preferred conformation even at room temperature. Numerous signs of coupling constants 1J(31P, 15N), 2J(31P, 13C), and 2J(31P, 29Si) were determined. Low temperature NMR spectra were measured for derivatives for which rotation about the PN bond at room temperature is fast, showing the presence of two rotamers at low temperature. The respective conformation of these rotamers could be assigned by 13C, 15N, and 31P NMR spectroscopy. Isotope‐induced chemical shifts 1Δ15/14N(31P) were determined for all compounds at natural abundance of 15N by using Hahn‐echo extended polarization transfer experiments. The molecular structure of 11 in the solid state reveals pyramidal surroundings of the nitrogen atom and mutual trans‐positions of the tert‐butyl groups at phosphorus and nitrogen. © 2002 Wiley Periodicals, Inc. Heteroatom Chem 13:667–676, 2002; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.10084
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