Diphosphines with Strongly Polarized P-P Bonds
A R T I C L E S
achieved with POSTC7,37 and reconversion was realized again with
an INADEQUATE sequence preparing double-quantum coherence
in 2.8 ms. The reported effective dipole coupling constants are
average values from five experiments with different dephasing
periods (τtotal between 3 and 5 ms) and exhibit a standard deviation
of approximately 37 Hz. For the analysis of the DoDe values it
was necessary to include the chemical shift tensors into the fit
procedure38 because PostC7 under the chosen conditions does not
fully suppress the influence of the chemical shift. Chemical shifts
are referenced to ext. TMS (1H, 13C) or 85% H3PO4 (ꢀ ) 40.480747
MHz, 31P), and coupling constants are given as absolute values if
not indicated otherwise; i, o, m, p denote the positions in N-aryl
rings.
Computational studies aimed at exploring the potential energy
hypersurface of 7 and the influence of geometrical changes on 1JPP
were performed with the Gaussian 0339 program suite. DFT
calculations were generally carried out using Becke’s 3-parameter
exchange functional40 with the Lee-Yang-Parr correlation energy
functional (B3LYP)41 with 6-31g(d) basis sets for geometry
optimization and 6-31g(d,p) basis sets for the computation of
coupling constants. Numerical integrations were performed on an
ultrafine grid. Harmonic frequencies and zero-point energies (ZPE)
at optimized gas-phase structures were calculated at the same level
and served to identify local minima (only positive eigenvalues of
the Hessian matrix) or transition states (one negative eigenvalue)
on the potential energy surface. Further structure optimizations were
carried out at higher theoretical levels as specified in Table 3.
Natural population analyses42 were carried out with the NBO
module in Gaussian03. Listings of atomic coordinates and absolute
energies are given as Supporting Information. Evaluation of the
electron density at bond critical points was performed with the
program MORPHY.43
Additional calculations of the spin-spin coupling tensors were
done with the combined analytical/ finite perturbation approach of
ref 44, as implemented in the MAG-ReSpect program package.45
Kohn-Sham molecular orbitals obtained with Gaussian 03, the
B3LYP functional, IGLO-III basis set46 for phosphorus, and IGLO-
II basis sets46 for the other atoms were transferred to the MAG
module by suitable interface routines. A finite perturbation param-
eter of λ ) 10-3 au was used for the Fermi contact perturbation in
Gaussian 03. In addition to the FC contribution to the isotropic
coupling, this procedure provides also the FC/SD cross term that
dominates Janiso. From the general axes system of the molecular
framework, the J-tensor was subsequently transformed to an axis
system in which the P-P bond corresponds to the z-axis (large
“parallel component” of J-anisotropy), and the larger of the two
perpendicular components (Jyy) is in the P2-P1-N1 plane. This
orientation is consistent with that of the full measured anisotropic
coupling tensor and thus allowed us to obtain the pure dipolar
contribution by subtraction of the computed J-anisotropy from the
full coupling anisotropy. The SD contribution to the coupling, which
is not contained in the output of the MAG-ReSpect program, was
computed in Gaussian03 using the same basis set.
1-Chloro-3,5-dimethyl-2,4-diphenylphosphole 6. Butyllithium
(120 mmol, 48 mL of 2.5 M solution in hexane) was slowly added
to a cooled (-78 °C) solution of zirconocene dichloride (17.53 g,
60 mmol) and 1-phenylpropyne (13.92 g, 120 mmol) in THF (80
mL). The mixture was stirred for 0.5 h at -78 °C and then allowed
to warm to room temperature. The solvent was removed in vacuum,
and the residue dissolved in toluene (50 mL). The filtrate was
evaporated to dryness, and the residue was redissolved in THF(50
mL). The solution was cooled to -78 °C, and phosphorus trichloride
(8.25 g, 60 mmol) was slowly added. The mixture was then allowed
to warm to room temperature and stirred for 18 h. Solvents were
then removed in a vacuum, and the residue was extracted with
hexane (100 mL). Precipitated salts were removed by filtration, the
solvent was evaporated in a vacuum, and the residue was subjected
to fractionate distillation in vacuum. The product was obtained as
yellow oil, bp 82 °C/10-3 mbar, which solidified on standing (yield
12.97 g, 73%, mp 25 °C). 1H NMR (CD3CN) δ 7.52 - 7.11 (m, 10
3
4
H, Hphenyl), 2.01 (d, 3 H, JPH ) 11.2 Hz, CH3), 1.87 (d, 3 H, JPH
) 5.9 Hz, CH3); 31P{1H} NMR (CD3CN) δ 78.7 (s).
Preparation of 2-(2′,3′,4′,5′-Tetraethylphospholyl)-dihydro-
1,3,2-diazaphospholes 4b,c,f,g. Lithium (10 mmol) was added to
a solution of 1-chloro-2,3,4,5-tetraethylphosphole (5 mmol) in THF
(20 mL). The mixture was stirred for 3 h at room temperature before
unreacted metal was removed by filtration. The remaining solution
was slowly added to a cooled (-78 °C) solution of the appropriate
2-chloro-dihydro-1,3,2-diazaphosphole (5 mmol) in THF (50 mL).
The solution was then allowed to warm to room temperature and
stirred for 1 h at this temperature. Solvent was then removed under
reduced pressure, and the residue was treated with hexane (50 mL).
The formed suspension was filtered over Celite, and the filtrate
evaporated to dryness. The crude product was purified by recrys-
tallization from appropriate solvents.
4b: recrystallization from hexane at -20 °C, yield 2.65 g (88%),
mp 92 °C; 1H NMR (C6D6) δ 7.21-7.07 (m, 6 H, m/p-H), 6.18 (d,
2 H, 3JPH ) 0.4 Hz, N-CH), 3.71 (sept, 2 H, 3JHH ) 6.7 Hz, CH),
3.70 (sept, 2 H, 3JHH ) 6.7 Hz, CH), 2.32 (q, 4 H, 3JHH ) 7.5 Hz,
CH2), 1.74 (m, 4 H, 3JHH ) 7.5 Hz, 3JPH ) 11.0 Hz, 4JPH ) 0.7 Hz,
CH2), 1.39 (d, 6 H, 3JHH ) 6.7 Hz, CH3), 1.16 (d, 6 H, 3JHH ) 6.7
Hz, CH3), 1.02 (t, 12 H, 3JHH ) 6.7 Hz, CH3); 13C{1H} NMR (C6D6)
δ 151.9 (dd, JPC ) 7.3, 1.4 Hz, i-C), 147.0 (dd, JPC ) 3.1, 1.8 Hz,
o-C), 142.7 (dd, 1JPC ) 21.0 Hz, 2JPC ) 14.4 Hz, Cphosphole), 137.8
(dd, JPC ) 7.0, 1.4 Hz, Cphosphole), 127.8 (d, 5JPC ) 1.5 Hz, p-CH),
4
124.5 (d, JPC ) 0.5 Hz, m-CH), 122.3 (dd, JPC ) 9.2, 1.3 Hz,
4
5
N-CH), 28.9 (dd, JPC ) 6.5 Hz, JPC ) 1.2 Hz, CH), 25.7 (s,
(37) Hohwy, M.; Jakobsen, H. J.; Ede´n, M.; Levitt, M. H.; Nielsen, N. C.
J. Chem. Phys. 1998, 108, 2686.
6
7
3
CH3), 23.3 (dd, JPC ) 2.0 Hz, JPC ) 2.0 Hz, CH3), 21.2 (d, JPC
) 1.5 Hz, CH2), 21.0 (dd, JPC ) 22.0, 1.4 Hz, CH2), 18.7 (dd, 3JPC
) 4JPC ) 2.8 Hz, CH3), 16.5 (d, 4JPC ) 1.2 Hz, CH3); MS (EI, 70
eV, 370 K) m/e (%) 601.2 (0.1) [M]+, 407.2 (100) [M - C12H20P]+,
195.1 (40) [M - C26H36N2P]+. C38H56N2P2 (602.82): C 75.71, H
9.36, N 4.65; found C 75.11, H 9.27, N 4.47.
(38) Bak, M.; Rasmussen, J. T.; Nielsen, N. C. J. Magn. Reson. 2000, 147,
296.
(39) Frisch, M. J. et al. Gaussian 03, ReVision E.01; Gaussian Inc.:
Pittsburgh, PA, 2003.
(40) Becke, A. D. J. Chem. Phys. 1993, 98, 5648.
(41) Lynch, B. J.; Fast, P. L.; Harris, M.; Truhlar, D. G. J. Phys. Chem. A
2000, 104, 4811.
(42) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985,
83, 735.
(43) Popelier, P. L. A. Comput. Phys. Commun. 1996, 93, 212.
(44) (a) Malkin, V. G.; Malkina, O. L.; ErikssonL. A.; Salahub, D. R., In
Modern Density Functional Theory: A Tool for Chemistry; Theoretical
and Computational Chemistry; Seminario, J. M., Politzer, P., Eds.;
Elsevier: Amsterdam, 1995; Vol. 2. (b) Malkina, O. L.; Salahub, D. R.;
Malkin, V. G. J. Chem. Phys. 1996, 105, 8793.
(45) Malkin, V. G.; Malkina, O. L.; Reviakine, R.; Arbuznikov, A. V.;
Kaupp, M.; Schimmelpfennig, B.; Malkin, I.; Repisky´, M.; Ko-
morovsky´, S.; Hrobarik, P.; Malkin, E.; Helgaker, T.; Ruud, K.
ReSpect, Version 2.1; 2006.
(46) Kutzelnigg, W., Fleischer, U., Schindler, M. In NMR-Basic Principles
and Progress; Diehl, P., Fluck, E., Gu¨nther, H., Kosfeld, R., Eds.;
Springer-Verlag: Heidelberg, Germany, 1990; Vol. 23, p 165.
4c: recrystallization from hexane/THF (10:1) at -20 °C, yield
2.39 g (88%), mp 132 °C; 1H NMR (C6D6) δ 6.80 (s, 4 H, m-CH),
2.44 (q, 4 H, 3JHH ) 7.5 Hz, CH2), 2.32 (s, 12 H, o-CH3), 2.13 (s,
3
6 H, p-CH3), 1.79 (m, 2 H, JHH ) 7.5 Hz, CH2), 1.77 (m, 2 H,
3
3JHH ) 7.5 Hz, CH2), 1.42 (s, 6 H, NCCH3), 1.17 (t, 6 H, JHH
)
7.5 Hz, CH3), 1.13 (t, 6 H, JHH ) 7.5 Hz, CH3); 13C{1H} NMR
3
1
(C6D6) δ 149.7 (dd, JPC ) 10.9, 3.0 Hz, i-C), 144.3 (dd, JPC
)
25.3 Hz, 2JPC ) 17.1 Hz, Cphosphole), 137.7 (dd, 3JPC ) 4.5 Hz, 4JPC
5
) 1.6 Hz, o-C), 137.6 (d, JPC ) 1.3 Hz, p-C), 135.2 (dd, JPC
)
7.1, 1.1 Hz, Cphosphole), 129.8 (s, m-CH), 124.8 (dd, JPC ) 8.6, 0.7
Hz, N-C), 21.6 (d, 2JPC ) 13.7 Hz, CH2), 21.4 (d, 3JPC ) 8.4 Hz,
CH2), 21.1 (s, o-CH3), 19.4 (d, 3JPC ) 1.4 Hz, CH3), 19.3 (s, CH3),
3
17.7 (s, p-CH3), 11.4 (d, JPC ) 3.7 Hz, NC-CH3); MS (EI, 70
eV, 400 K) m/e (%) 545.3 (0.1) [M - H]+, 351.1 (100) [M -
9
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