Further improvements in the preparation of disecondary phosphines PhHP(CH2)nPHPh, n = 2, 3, and their tetracarbonyltungsten complexes: Analysis of their multinuclear NMR spectra

Article abstract of DOI:10.1021/om990027v

The disecondary phosphines PhHP(CH₂)_n-PHPh, n = 2, 3, have been prepared in high yields (80%) after short reaction times (6 h) and converted into the meso- and rac-diastereomers of [{PhHP(CH₂)_nPHPh}-W(CO)_4<

Full text of DOI:10.1021/om990027v

2912
Organometallics 1999, 18, 2912-2914
F u r th er Im p r ovem en ts in th e P r ep a r a tion of
Disecon d a r y P h osp h in es P h HP (CH2)n P HP h , n ) 2, 3, a n d
Th eir Tetr a ca r bon yltu n gsten Com p lexes: An a lysis of
Th eir Mu ltin u clea r NMR Sp ectr a
Ron S. Dickson, Patricia S. Elmes, and W. Roy J ackson*
Department of Chemistry, Monash University, Clayton, Victoria 3168, Australia
Received J anuary 19, 1999
Summary: The disecondary phosphines PhHP(CH2)n-
PHPh, n ) 2, 3, have been prepared in high yields (80%)
after short reaction times (6 h) and converted into the
meso- and rac-diastereomers of [{PhHP(CH2)nPHPh}-
NMR spectra. 12/13C isotope effects on δ(31P) are ob-
served in the 13C NMR spectra of the tungsten com-
plexes and measured for R-CH2 and equatorial carbonyl
carbon atoms.
W(CO)4], n ) 2, 3. 12/ 13C isotope effects on 31P shieldings
2
and | J P-P| couplings have been calculated from the 13
C
Resu lts a n d Discu ssion
NMR spectra of the complexes.
Disecon d a r y Dip h osp h in es. The disecondary phos-
phines 1,2-bis(phenylphosphino)ethane and 1,3-bis-
(phenylphosphino)propane were prepared by a double
cleavage of P-Ph bonds of the appropriate bis(diphen-
ylphosphino)alkane with lithium under ultrasonic ir-
radiation, followed by aqueous hydrolysis of the bis-
(lithium phenylphosphide) and purification by distillation.
We have found a combination of ultrasonic irradiation,
low reaction temperature (10 °C), and an excess of
lithium very effective for the synthesis of disecondary
phosphines on a multigram scale in high yields (>80%)
after short reaction times (<6 h). (See Scheme 1.)
31P{1H} NMR spectroscopy showed both reaction prod-
ucts to be an equimolar mixture of racemic (RR,SS) and
meso (RS) diastereomers. Each pair of diastereomers
has been separated by cis coordination to tungsten
carbonyl.
Dip h osp h in e Tu n gsten Tetr a ca r bon yl Com -
p lexes. The reaction of tungsten hexacarbonyl with 1,2-
bis(phenylphosphino)ethane (1; n ) 2) in toluene at 160
°C resulted in a clear yellow solution showing only two
components, in equal amounts, by 31P NMR at δ 4.9 and
δ 2.5. Both meso and racemic forms of [{PhHP(CH2)2-
PHPh}W(CO)4] crystallized from toluene as analytically
pure, colorless crystals with different morphologies. By
contrast, [{PhHP(CH2)2PHPh}W(CO)4] diastereomers
isolated from the same reactants heated under reflux
in diglyme were reported as impure brown crystals with
lower melting points.4 The racemic (RR/SS) diastere-
omer (3; n ) 2) crystallized first and was identified by
the presence of two 13CO resonances in the 13C{1H}
NMR spectrum, whereas the meso (RS) diastereomer
(2; n ) 2) displayed three 13CO resonances.
In tr od u ction
As part of our interest in heterobimetallic catalysts,
it became necessary to prepare significant amounts of
the disecondary phosphines PhHP(CH2)nPHPh, n ) 2,
3, and their tetracarbonyltungsten complexes.1 Interest
in this class of phosphines has increased in recent years
in view of their use as ligands and as precursors for
multidentates and macrocycles.2
Several alternative syntheses for disecondary phos-
phines are known.3 Recent research on the method of
lithium cleavage of ditertiary phosphines indicates that
improved yields of disecondary phosphines PhHP(CH2)n-
PHPh (1; n ) 2-4, 6) are obtained when the reaction
temperature is lowered to 0 °C.4 Unfortunately, reduc-
ing the reaction temperature to minimize P-CH2 bond
cleavage and subsequent formation of Ph2PH increases
reaction times significantly (200 h for n ) 2). Ultrasonic
irradiation of diphosphines with lithium at 0 °C has
been reported to accelerate the reductive cleavage
without any contamination from side reactions and has
been used for small-scale (300 mg) preparations of bis-
(alkylphenylphosphino)alkanes.5
We have prepared the disecondary phosphines PhHP-
(CH2)nPHPh (1; n ) 2, 3) in high yields (80%), faster
and more conveniently than previously reported.4 In
addition, our reactions of these phosphines with tung-
sten hexacarbonyl have produced colorless, purer com-
plexes than previously isolated4 and allowed the sepa-
ration and identification of all meso and racemic
diastereomers on a multigram scale. Multinuclear NMR
2
spectra are reported for all diastereomers and | J P-P
|
31P NMR of an aliquot from the reaction of 1,3-bis-
(phenylphosphino)propane (1; n ) 3) with tungsten
hexacarbonyl in toluene at 160 °C indicated the pres-
ence of four products. Single phosphorus resonances at
δ -34.1 and δ -30.4 from the expected diastereomers
were obtained in a 1.3:1 ratio as 54% of the total P, as
well as two multiplets attributed to polymeric products
at δ -24.5 and δ -15.5 in a 1:2.9 ratio and 46% of the
total P. Repetition of this reaction afforded the same
products in different ratios. The solution deposited
couplings obtained by computer analysis of 13C{1H}
(1) Dickson, R.S.; Elmes, P. S.; Fallon, G. D.; J ackson, W. R.
Organometallics, submitted for publication.
(2) Steltzer, O.; Langhans, K. P. In The Chemistry of Organophos-
phorus Compounds; Hartley, F. R., Ed.; Wiley: New York, 1990; Vol.
1, Chapter 8.
(3) Kosolapoff, G. M.; Maier, L. Organic Phosphorus Compounds;
Wiley-Interscience: New York, 1972; Vol. 1, p 17.
(4) Kimpton, B. R.; McFarlane, W.; Muir, A. S.; Patel, P. G.;
Bookham, J . L. Polyhedron 1993, 12, 2525.
(5) Chou, T.; Tsao, C.; Hung, S. C. J . Org. Chem. 1985, 50, 4329.
10.1021/om990027v CCC: $18.00 © 1999 American Chemical Society
Publication on Web 06/25/1999

Notes
Organometallics, Vol. 18, No. 15, 1999 2913
Sch em e 1
hexagonal crystals of analytically pure meso-[{(RS)-
PhHP(CH2)3PHPh}W(CO)4] (2; n ) 3) (98% isomeric
purity) again identified by three resonances in the 13C
NMR spectrum. Isomeric purity was increased to 99.5%
(31P NMR analysis) by flash chromatography. The rac-
[{(RR/SS)PhHP(CH2)3PHPh}W(CO)4] complex (3; n )
3), which was less readily isolated, was obtained as a
white solid in 85% isomeric purity and identified by the
presence of two 13CO resonances.
NMR An a lysis. The 31P{1H} NMR spectrum for each
of the diastereomeric tungsten carbonyl complexes
consists of a single resonance flanked by 183W satellites.
A downfield shift of the ligand P resonances of ca. 50
ppm for the five-membered chelate rings (31P NMR: δ
2.5 (meso), 4.9 (racemic)) and of ca. 20 ppm for the six-
membered rings (31P NMR: δ -30.4 (meso), -33.9
(racemic)) was observed on chelation (31P NMR: ca. δ
-46 for 1,2-diphosphine, ca. δ -53 for 1,3-diphosphine).
Similar large downfield shifts have been observed
previously on forming five-membered chelates.6
significant C backbone contribution.1J W-P couplings of
223 and 213 for the disecondary phosphine five- and six-
membered chelate rings also parallel trends found for
the analogous ditertiary phosphine chelates, where
1J W-P decreases from 229 to 222 as chelate ring size
increases from 5 to 6.
The magnitude of the chemical shift difference at P
(νoδ) due to 12C-PA-W-PB-13C isotopic substitution
was estimated for the ligand (1; n ) 2) and for the
complexes (2 and 3, n ) 2 and 3). The values for the
ligand were 3.5 Hz at CH2 and 2.4 Hz at the ipso-phenyl
C for spectra recorded at 100.6 MHz and are comparable
to the values of 4.5 and 4.2 Hz recorded previously at
125.8 MHz.4 All of the complexes gave smaller values
of νoδ, viz., 1.15-1.3 Hz at the R-CH2 (2 and 3; n ) 2,
3), and 0.9 Hz at the equatorial CO carbons (2 and 3; n
) 2). These represent 12/13C isotope effects upon δ(31P)
of 0.007-0.008 ppm for the directly bonded CH2 groups
and of 0.004 ppm for the equatorial carbonyl carbons
in the complexes.
The 13C{1H} NMR spectra of the complexes display
symmetrical six-line multiplets for the R-CH2 groups
and equatorial carbonyls (2 and 3; n ) 2) and sym-
metrical five-line multiplets with unresolved central
lines for the equatorial carbonyls (2 and 3; n ) 3) and
ipso, ortho, and meta phenyl-ring carbons. Computer
simulation of the spectra as the X spectra of an ABX
spin system7 (A, B ) 31P, X ) 13C) yielded |J P-P| and
|J P-C| coupling constants as well as the chemical shift
differences νoδΑΒ arising from the 12/13C isotopic substi-
tution, viz., 12C-PA-W-PB-13C. The results have been
submitted as Supporting Information.
Exp er im en ta l Section
Gen er a l P r oced u r es. All operations involving secondary
phosphine ligands and solutions of their tungsten complexes
were carried out under an atmosphere of dry, oxygen-free
argon or nitrogen using dry, deoxygenated solvents. Ditertiary
phosphines and lithium wire (99.9%) were purchased from
Aldrich. Tetrahydrofuran (THF) was distilled from Na/benzo-
phenone prior to use. Ultrasonic reactions were performed
using a conventional cleaning bath (Branson B2200 E2, output
60 W).
NMR spectra were measured at field strengths of 4.7 and
9.4 T on Bruker AC200 or DRX400 spectrometers, respectively.
2
The J P-P coupling of 6.4 Hz calculated for each of
The H NMR spectra were measured at 200 or 400 MHz, 13C
1
the meso- and rac-[{PhHP(CH2)2PHPh}W(CO)4] (2 and
3; n ) 2) diastereomers is considerably less than the
couplings of 20.5 and 26.5 Hz computed for meso- and
rac-[{PhHP(CH2)3PHPh}W(CO)4] (2 and 3; n ) 3) and
differ from the literature values of 12.6, 14.9, and 14.5
for meso- and rac-[{PhHP(CH2)2PHPh}W(CO)4] and
meso-[{PhHP(CH2)3PHPh}W(CO)4], respectively.4 They
at 100.6 MHz, and 31P at 162 MHz. Chemical shifts are
referenced from Me4Si for 1H and 13C and from 85% H3PO4
for 31P; in all cases, a positive chemical shift denotes a shift to
higher frequency. N is the splitting of the principal doublet of
the signals in the 13C{1H} NMR. Iterative calculations and
simulated NMR spectra were performed on an Aspect 3000
computer using the PANIC program from Bruker. PANIC is
a minicomputer version of the LAOCOON9 type programs.
Syn th esis of 1,2-Bis(p h en ylp h osp h in o)eth a n e (1; n )
2). In a typical procedure, a mixture of 1,2-bis(diphenylphos-
phino)ethane (7.90 g, 19.8 mmol) and freshly cut Li wire (1.40
g, 200 mmol) in THF (250 mL) contained in a double-walled
flask with the outer jacket containing ethylene glycol was
irradiated in an ultrasonic bath maintained at 10 °C by
addition of crushed ice.10 The reaction was monitored by TLC
(alumina, hexane/ethyl acetate, 9:1) and was complete in 5 h.
2
are instead very similar in magnitude to the J P-P
couplings of +5.5 and -21.5 reported for the analogous
tertiary phosphine chelates [{Ph2P(CH2)2PPh2}W(CO)4]
and [{Ph2P(CH2)3PPh2}W(CO)4], respectively.8 The sen-
sitivity of these P-P couplings to ring size suggests a
(6) Garrou, P. E. Chem. Rev. 1981, 81, 229.
(7) Emsley, J . W.; Feeney, J .; Sutcliffe, L. H. High-Resolution
Nuclear Magnetic Resonance Spectroscopy; Pergamon Press: Oxford,
1965; Vol. 1, p 357.
(8) Andrews, G. T.; Colquhoun, I. J .; McFarlane, W. Polyhedron
1983, 2, 783.
(9) Castellano, S.; Bothner-By, A. R. J . Chem. Phys. 1962, 36, 1951.

2914 Organometallics, Vol. 18, No. 15, 1999
Notes
The deep-red solution was cannulated from excess Li and
cooled in an ice-water bath before hydrolysis with deoxygen-
ated water (30 mL). The phosphine was extracted with diethyl
ether (60 mL); the extracts were combined and washed with
cold HCl (2 M, 2 × 10 mL), followed by cold water, until any
acidity was completely removed. The organic layer was dried
(Na2CO3) and filtered, and the solvent removed under reduced
pressure. The residual viscous liquid was purified by Kugel-
rohr distillation to give the required compound as a colorless
oil (3.9 g, 80%), bp (oven) 160 °C/1 mm (lit. 161 °C/0.8 mm).11
31P{1H} NMR (toluene-d8) indicated an equimolar mixture of
two diastereomers: δ -45.8, -46.4 (lit. δ -45.6, -45.9).4 1H
and 13C{1H} NMR data were similar to literature data.4
Syn th esis of 1,3-Bis(p h en ylp h osp h in o)p r op a n e (1; n
) 3). In a similar manner, ultrasonic irradiation of a mixture
of 1,3-bis(diphenylphosphino)propane (9.40 g, 22.8 mmol) and
Li wire (1.63 g, 228 mmol) in THF (200 mL), followed by
aqueous hydrolysis and Kugelrohr distillation, gave the title
compound as a clear oil (5.0 g, 84%), bp (oven) 200 °C/1 mm
(lit. 191-200 °C/5 mm).12 31P{1H} NMR (toluene-d8): δ -52.8,
-52.9. The two diastereomers were present in equimolar ratio,
lit. δ -51.9,-52.0. 41H and 13C{1H} NMR data were similar to
literature data.4
337 Hz, PH), 7.46 (m, 6H, aromatic m-H and p-H), 7.69 (m,
4H, aromatic o-H). 13C{1H} NMR: δ 26.0 (m, N ) 44.2 Hz,
CH2), 129.1 (m, N ) 10.1 Hz, C3, 5), 130.7 (m, N ) 2.1 Hz,
C4), 130.9 (m, N ) 43.4 Hz, C1, ipso-C), 132.6 (m, N ) 11.9
2
2
Hz, C2, 6), 198.9 (t, J P-C ) 5.7 Hz, COax), 201.6 (t, J P-C
)
:
8.0 Hz, COax), 206.6 (m, N ) 18.6 Hz, COeq). IR (CH2Cl2) cm-1
ν(CO) 2020, 1917 (sh), 1899, 1883 (infl).
The washings and filtrate were combined and concentrated
to afford further white precipitate (0.35 g, 9%). 31P NMR: δ
4.9 (30.5%), δ 2.5 (69.5%). Discolored residual material con-
taining both diastereomers in the same proportions was
obtained on complete evaporation of the solvent.
m eso/r a c-Tetr a ca r bon yl(1,3-bisp h en ylp h osp h in op r o-
p a n e)tu n gsten (2, 3; n ) 3). Reaction of tungsten hexacar-
bonyl (1.58 g, 4.5 mmol) and 1,3-bis(phenylphosphino)propane
(1.16 g, 4.5 mmol) in toluene (5 mL) resulted in a clear, pale-
yellow solution. 31P NMR analysis of the crude product showed
four phosphorus resonances at δ -34.1 (s, 30%), -30.6 (s, 24%),
-24.5 (m, 12%), and -15.5 (m, 34%). Colorless hexagonal
crystals which gradually deposited on cooling were separated,
washed with methanol, dried under vacuum (0.01 mm), and
identified by 13C NMR as meso-[{(RS)-PhHP(CH2)3PHPh}-
W(CO)4] (2; n ) 3), mp 209.5-210 °C. Anal. Found: C, 40.95;
H, 3.2; P, 10.85. Calcd for C19H18O4P2W: C, 41.0; H, 3.3; P,
11.1. MS(EI): m/z 558 (186W) [M+]. 31P{1H} NMR (CDCl3): δ
-30.4 (s, J W-P ) 212.1 Hz), isomeric purity 99.5%. 1H NMR
(CDCl3): δ1.80 (m, 3H, CH2), 2.46 (m, 1H, CH2), 2.74 (m, 2H,
CH2), 5.89 (m, 2H, J P-H ) 328 Hz, PH), 7.44 (m, 6H, aromatic
m-H and p-H), 7.64 (m, 4H, aromatic o-H). 13C{1H} NMR: δ
Syn th esis of Tu n gsten Tetr acar bon yl Com plexes. These
were prepared by heating tungsten hexacarbonyl with the
appropriate disecondary phosphine and toluene in a sealed,
evacuated, glass pressure reaction tube (100 mL) at 160 °C
for 40 h. After cooling and venting, an aliquot was removed
for analysis by 31P NMR spectroscopy before isolation of
products proceeded.
2
24.0 (t, J P-C ) 1.8 Hz, â-CH2), 27.4 (m, N ) 27.4 Hz, R-CH2),
meso/ra c-Tetracarbonyl(1,2-bisphenylphosphinoethane)-
tu n gsten (2, 3; n ) 2). Reaction of tungsten hexacarbonyl
(2.40 g, 6.8 mmol) and 1,2-bis(phenylphosphino)ethane (1.68
g, 6.8 mmol) in toluene (5 mL) gave a clear, pale-yellow
solution. The 31P NMR spectrum of the crude product showed
only two resonances at δ 4.9 and 2.5 of equal intensity. The
solution rapidly deposited colorless platelets, which were
separated, washed, dried, and identified by 13C NMR as rac-
[{(RR/SS)-PhHP(CH2)2PHPh}W(CO)4] (3; n ) 2). Yield: 1.24
g (34%). Mp: 176.5-178 °C. Anal. Found: C, 39.9; H, 3.0; P,
11.4. Calcd for C18H16O4P2W: C, 39.9; H, 3.0; P, 11.4. MS(EI):
128.9 (m, N ) 9.8 Hz, C3,5), 130.2 (m, N ) 1.8 Hz, C4), 132.3
(m, N ) 11.2 Hz, C2,6), 133.4 (m, N ) 48.3 Hz, C1, ipso-C),
199.3 (t, 2J P-C ) 6.9 Hz, COax), 203.4 (t, 2J P-C ) 8.4 Hz, COax),
204.8 (m, N ) 14.1 Hz, COeq). IR (CH2Cl2) cm-1: ν(CO) 2019,
1919, 1893, 1868 (sh).
Further fractional crystallization from toluene gave white
precipitates which were mixtures of the meso/ rac-diastereo-
mers. 31P{1H} NMR: δ -30.4 (33%), δ -33.9 (67%). Removal
of the toluene and addition of acetone/methanol to the residue
gave an off-white precipitate of mainly rac-[{(RR/SS)PhHP-
(CH2)3PHC6H5}W(CO)4]. Mp: 123-5 °C. Anal. Found: C; 40.2;
H, 3.3. Calcd for C19H18O4P2W: C, 41.0; H, 3.3. 31P{1H} NMR
(CDCl3): δ -33.9 (s, J W-P ) 212.9 Hz) (88%), δ -30.4 (12%).
No further purification of the racemic diastereomer was
attempted, as the compound appeared to decompose with
handling. 1H NMR (CDCl3): δ 2.01 (m, 2H, CH2), 2.19 (m, 2H,
CH2), 2.38 (m, 2H, CH2), 6.06 (m, 2H, J P-H ) 339 Hz, PH),
7.46 (m, 6H, aromatic m-H and p-H), 7.66 (m, 4H, aromatic
m/z 544 (186W) [M+]. 31P{1H} NMR (CDCl3): δ 4.9 (s, J W-P
222.7 Hz) and 4% meso-diastereomer δ 2.5. H NMR (CDCl3):
)
1
δ 1.40 (m, 2H, CH2), 2.87 (m, 2H, CH2), 6.00 (m, 2H, J P-H
)
334 Hz, PH), 7.47 (m, 6H, aromatic m-H and p-H), 7.73 (m,
4H, aromatic o-H). 13C{1H} NMR: δ 26.7 (m, N ) 43.0 Hz,
CH2), 129.1 (m, N ) 10.3 Hz, C3, 5), 130.5 (m, N ) 46.5 Hz,
C1, ipso-C), 130.8 (m, N ) 2.0 Hz, C4), 133.1 (m, N ) 12.1 Hz,
2
C2, 6), 200.3 (t, J P-C ) 7.2 Hz, COax), 206.6 (m, N ) 18.3 Hz,
2
o-H). 13C{1H} NMR: δ 22.0 (t, J P-C ) 1.8 Hz, â-CH2), 26.9
COeq). IR (CH2Cl2) cm-1: ν(CO) 2020, 1918 (sh), 1899.
A second quantity of material which crystallized from
solution as opaque aggregates was filtered, washed, dried, and
confirmed by 13C NMR as meso-[{(RS)-PhHP(CH2)2PHPh}-
W(CO)4] (2; n ) 2). Yield: 0.25 g (7%). Mp: 168-9 °C. Anal.
Found: C, 40.0; H, 3.0; P, 11.1. Calcd for C18H16O4P2W: C,
39.9; H, 3.0; P, 11.4. MS(EI): m/z 544 (186W) [M+]. 31P{1H}
(m, N ) 28.6 Hz, R-CH2), 128.9 (m, N ) 9.7 Hz, C3,5), 130.3
(m, N ) 1.9 Hz, C4), 132.5 (m, N ) 11.2 Hz, C2,6), 133.3 (m,
N ) 43.9 Hz, C1, ipso-C), 201.3 (t, 2J P-C ) 7.3 Hz, COax), 204.7
(m, N ) 14.5 Hz, COeq).
Su p p or tin g In for m a tion Ava ila ble: A table of calculated
coupling constants, J PP and J PC, for complexes 2 and 3, n ) 2
and 3, as well as selected observed and simulated NMR reso-
nances from 13C{1H} spectra (100.6 MHz) of [{(RS)-PhHP(CH2)n-
PHPh}W(CO)4] diastereomers (2; n ) 2, 3). This material is
available free of charge via the Internet at http://pubs.acs.org.
1
NMR (CDCl3): δ 2.5 (s, J W-P ) 222.6 Hz). H NMR (CDCl3):
δ 2.04 (m, 2H, CH2), 2.35 (m, 2H, CH2), 6.13 (m, 2H, J P-H
)
(10) Sa fety Con sid er a tion . Reactions involving lithium metal and
immersion in an ultrasonic bath containing water should not be carried
out using single-walled flasks for fear of breakage.
(11) Issleib, K.; Weidmann, H. Chem. Ber. 1968, 101, 2197.
(12) Issleib, K.; J acob, D. Chem. Ber. 1961, 94, 107.
OM990027V