Wide-Bite-Angle Diphosphinines
Organometallics, Vol. 27, No. 5, 2008 837
were performed on a Perkin-Elmer 2400 Series II CHNSO analyzer
at the Department of Chemical Engineering and Chemistry (TU/
e). 1H, 13C{1H}, and 31P{1H} NMR spectra were recorded on
Varian Mercury 200 and 400 and Bruker 500 spectrometers, and
all chemical shifts are reported relative to the residual proton
resonance in the deuterated solvents or referenced to an 85%
aqueous solution of H3PO4. Mass spectra were either run by
MALDI-TOF on a Bruker Autoflex spectrometer or by electrospray
impact on a Waters LCT Premier spectrometer.
Bis-Pyrylium Salt 3. Tetrafluoroboric acid (52% ethereal
solution, 8.04 g, 49 mmol) was added at 70 °C to a solution of
3.88 g (12.34 mmol) of 4,4′-diacetyl-o-terphenyl and 10.2 g (49
mmol) of 1,3-diphenyl-2-propen-1-one in 20 mL of 1,2-dichloro-
ethane. The mixture was heated for 2 h and was subsequently cooled
to room temperature. The red precipitate was filtered off, and the
bis-pyrylium salt was obtained as a dark red solid after recrystal-
1
lization from hot acetonitrile. Yield: 2.1 g (2.42 mmol), 20%. H
Figure 4. Potential energy diagram for the fragment Rh(4). The 3
kcal mol-1 over minimum energy threshold is marked as a straight
line.
NMR (DMSO-d6): δ (ppm) 7.67 (m, 8H), 7.73 (m, 8H), 7.82 (m,
4H), 8.54 (m, 12H, terphenyl H), 9.11 (s, 4H, heteroarom H). 13
C
NMR (DMSO-d6): δ (ppm) 115.5, 129.2, 129.5, 130.3, 130.4, 131.4,
131.6, 132.9, 135.5, 135.7, 139.0, 147.9, 165.3, 169.9, 170.4. 19F
NMR (DMSO-d6): δ (ppm) -148.2, -148.3 (1:3). Anal. Calcd for
C52H36B2F8O2 (Mr ) 866.46): C, 72.08; H, 4.19. Found: C, 72.45;
H, 4.15.
lead to a shorter P-P distance and formation of narrower bite
angle species (Scheme 3).
Terphenyl Bis-Phosphinine 4. A 2.6 g (10.4 mmol) amount of
P(SiMe3)3 was added dropwise at room temperature to a stirred
solution of 2.2 g (2.54 mmol) of 3, dissolved in 25 mL of
acetonitrile. The resulting black reaction mixture was heated to T
) 85 °C and refluxed for 8 h. Stirring was continued for 12 h at
room temperature, and subsequently all volatiles were removed
under vacuum. The resulting brown solid was chromatographed
with petroleum ether/ethyl acetate (4:1), affording 4 as a yellow
Conclusions
In summary, we have designed and synthesized successfully
a diphosphinine ligand that exhibits important structural features
for the preferred formation of trans complexes. Due to the linear
orientation of the lone-pair electrons of the phosphorus donors
in combination with an appropriate P-P distance, trans coor-
dination toward a Rh center and typical reactivities were
observed. Yet, in this most favorable case up to now, the final
test with the cis-enforcing precursor [Rh(nbd)2]BF4 did result
in the formation of several species at low temperature to which
unsymmetrical cis structures could be attributed. Consequently,
embedding the two phosphinine units into a rigid aryl backbone
should lead to an optimal structure and the development of truly
trans-spanning diphosphinines. Current investigations carried out
in our laboratories are thus focusing on bidentate diphosphinines
with reduced flexibility of the backbone and their impact on
homogeneous catalysis.7,16,22
solid. Yield: 400 mg (0.55 mmol, 22%). 1H NMR (C6D6): δ (ppm)
3
7.11–7.42 (m, 24H), 7.58 (m, 8H, terphenyl H), 8.00 (d, JH-P
)
4.4 Hz, 4H, heteroarom H). 13C NMR (CDCl3): δ (ppm) 124.2,
124.6, 127.1, 127.4, 127.6, 127.8, 127.9, 128.3, 128.7, 128.9, 129.0,
129.9, 130.5, 130.8 (m), 131.7 (m), 140.0, 141.5, 141.9 (2 × d,
JC-P ) 21.9, 23.0 Hz), 143.4, 144.1 (2 × d, JC-P ) 24.1, 13.8
Hz), 171.1, 171.6 (2 × d, JC-P ) 51.4, 51.8 Hz, C4). 31P NMR
(C6D6): δ (ppm) 184.2. Anal. Calcd for C52H36P2 (Mr ) 722.81):
C, 86.41; H, 5.02. Found: C, 86.21; H, 5.12. Single mass analysis
for C52H36P2: m/z 761.1945 (M + K).
(PP)Rh(CO)Cl (5). A mixture of 4 (100.0 mg, 0.14 mmol) and
[Rh(CO)2Cl]2 (27.0 mg, 0.07 mmol) was cooled to T ) -40 °C,
and CH2Cl2 (2.5 mL) was slowly added. The dark orange solution
was slowly warmed to room temperature and subsequently filtered
over Al2O3 (neutral)/Celite. Compound 5 was obtained as an orange
solid after evaporating the solvent. Yield: 88.0 mg (1.0 mmol, 71%).
1H NMR (CD2Cl2): δ (ppm) 7.16 (d, JH-H ) 9.3 Hz, 4H), 7.31 (d,
JH-H ) 9.7 Hz, 2H), 7.33 (d, JH-H ) 9.7 Hz, 2H), 7.48–7.51 (m,
6H), 7.55–7.59 (m, 6H), 7.70 (m, 2H), 7.76 (d, JH-H ) 7.4 Hz,
Experimental Section
General Considerations. All manipulations were carried out
under an argon atmosphere, using modified Schlenk techniques, or
in a Braun glovebox unless otherwise stated. All glassware was
dried prior to use by heating under vacuum. All common solvents
and chemicals were commercially available and were purchased
from Aldrich Chemical Co. P(SiMe3)3,14 4,4′-diacetyl-o-terphenyl,13
[Rh(CO)2I]2,17 and 1,3-diphenyl-2-propen-1-one23 were prepared
according to the literature. The Rh precursors were obtained as a
generous gift from Umicore AG & Co. Kg (Germany). MeI was
degassed using the freeze–pump–thaw method. The solvents were
taken from custom-made solvent purification columns filled with
Al2O3. The elemental analyses were obtained from H. Kolbe,
Mikroanalytisches Laboratorium, Mülheim a.d. Ruhr, Germany, or
6H), 7.85 (d, JH-H ) 7.7 Hz, 4H), 8.31 (pseudo-t, JH-H, JP-H
)
10.8 Hz, 2H, heteroarom H), 8.36 (pseudo-t, JH-H, JP-H ) 10.9
Hz, 2H, heteroarom H). 13C NMR (CD2Cl2): δ (ppm) 127.7 (CH),
127.9 (CH), 128.0, 128.1, 128.3 (CH), 128.4 (CH), 128.7, 128.8
(CH), 128.9, 129.0, 129.1 (CH), 129.3, 130.5 (d, JCP ) 47.7 Hz,
CH), 135.8 (heteroarom CH), 136.4 (heteroarom CH), 139.1, 139.2,
140.5, 140.6, 141.1, 141.3, 141.8, 142.2, 163.1, 183.5 (m, CO).
31P NMR (CD2Cl2): δ (ppm) 166.6 (d, JP-Rh ) 173.1 Hz). Yellow-
orange crystals of 5 are obtained by slow crystallization from
CH2Cl2 at low temperature. Anal. Calcd for C53H36ClOP2Rh (Mr
) 889.17): C, 71.59; H, 4.08. Found: C, 71.71; H, 4.38.
(22) For phosphinines as ligands in homogeneous catalysis, see also:
(a) Reetz, M. T.; Li, X. Angew. Chem., Int. Ed. 2005, 44, 2962. (b) Reetz,
M. T.; Mehler, G. Tetrahedron Lett. 2003, 44, 4593. (c) DiMauro, E. F.;
Kozlowski, M. C. J. Chem. Soc., Perkin Trans. 1 2002, 439. (d) Breit, B.
J. Mol. Catal. A: Chem. 1999,143, 143. (e) Breit, B.; Winde, R.; Harms,
K. J. Chem. Soc., Perkin Trans. 1 1997, 18, 2681. (f) Knoch, F.; Kremer,
F.; Schmidt, U.; Zenneck, U.; Le Floch, P.; Mathey, F. Organometallics
1996, 15, 2713.
Reaction of 5 with MeI. To a solution of 5, prepared from 4
(30 mg, 0.042 mmol) and [Rh(CO)2Cl]2 (8.0 mg, 0.021 mmol), in
CH2Cl2 (0.8 mL) was added MeI (48 mg, 0.34 mmol, 8 equiv) at
room temperature. The halogen metathesis under formation of 6
was recorded by means of 31P NMR spectroscopy over a period of
(23) Shadakshari, U.; Nayak, S. K. Tetrahedron 2001, 57, 8185.