Bisphosphine ligands containing two o-N,N-dimethylanilinyl substituents at each phosphorus atom

Article abstract of DOI:10.1139/v02-127

The synthesis and complete characterization of the family of tetra(amine)bisphosphine ligands (o-NMe₂C₆H₄)₂P-(X)-P(o- NMe₂C₆H₄)₂, where X = CH₂ (dmapm), (CH

Full text of DOI:10.1139/v02-127

1600
Bisphosphine ligands containing two o-N,N-
dimethylanilinyl substituents at each phosphorus
atom
Nathan D. Jones, Patric Meessen, Martin B. Smith, Udo Losehand,
Steven J. Rettig, Brian O. Patrick, and Brian R. James
Abstract: The synthesis and complete characterization of the family of tetra(amine)bisphosphine ligands (o-
NMe2C6H4)2P-(X)-P(o-NMe2C6H4)2, where X = CH2 (dmapm), (CH2)2 (dmape), and CH(CH2)3CH (dmapcp), are de-
scribed. Crystal structure data are compared with known, analogous bisphosphines containing o-pyridyl or phenyl sub-
stituents in place of the o-dimethylanilinyl groups. Several short, intramolecular C-H···N distances in the anilinyl
derivatives may represent the presence of weak hydrogen bonds.
Key words: phosphine, amine, polydentate, hydrogen-bonding to N atoms.
Résumé : On décrit la synthèse et la caractérisation complète d’une famille de ligands tétra(amine)bisphosphine,
(o-NMe2C6H4)2P-(X)-P(o-NMe2C6H4)2, dans lesquels X = CH2 (dmapm), (CH2)2 (dmape) et CH(CH2)3CH (dmapcp).
On a comparé leurs structures cristallines à celles de bisphosphines connues, analogues, contenant des substituants
o-pyridyle ou phényle à la place des groupes o-diméthylanilinyles. Plusieurs distances intramoléculaires C-H···N dans
les dérivés anilinyles sont courtes et elles peuvent être le reflet de la présence de faibles liaisons hydrogènes.
Mots clés : phosphine, amine, polydentate, liaison hydrogène avec des atomes d’azote.
[Traduit par la Rédaction] Jones et al. 1606
Introduction
into an insoluble polymer via attachment through the N atom
(5, 7–9); (ii) to solubilize the catalyst in water (in which the
reactants and products are only slightly miscible) by
quaternization of the N atom via protonation or alkylation
(10–16); (iii) to water solubilize the catalyst via incorpora-
tion of a sulfonate group within an elaborated N-containing
functionality (17); and (iv) to extract the catalyst post-
reaction with aqueous acid in which the product does not
dissolve (18, 19).
Our group here has reported extensively on the use of
mono- and bis-phosphine ligands containing the o-pyridyl moi-
ety, with the goal of developing platinum metal complexes
rendered water soluble by protonation of the pyridyl N atom
(20); examples include the compound py2P(CH2)2Ppy2 and
the related py2P(C5H8)Ppy2, where py = o-pyridyl and C5H8
is a cyclopentane moiety bridging the two P atoms (cf. Fig. 1).
We have now extended this theme by replacing the o-pyridyl
group by the o-dimethylanilinyl group and report here on the
synthesis of the new ligands dmapm (1,1-bis(di(o-N,N-
dimethylanilinyl)phosphino)methane), dmape (1,2-bis(di(o-
N,N-dimethylanilinyl)phosphino)ethane), and dmapcp (rac-
The introduction of an amine moiety into a monophos-
phine compound for use as a P-N ligand has a long history
and dates from the 1940s; early examples include the 2-
pyridylphosphines made by Mann and co-workers (1) and o-
diphenylphosphino-N,N-dimethyl-aniline [Ph2P(o-C6H4NMe2)]
reported by Venanzi and co-workers (2); we have used the
latter extensively in some recent Ru chemistry (3). This
aminophosphine is just one example of a wide range of
bidentate, chelating P-N ligands (4). The incorporation of an
amine functionality into a bis(phosphine) ligand is more re-
cent and dates from about 25 years or so, an early example
being that of Achiwa who incorporated two PPh2 moieties
into proline derivatives (5). The amino-bisphosphine sys-
tems, which have been reviewed (6), have been developed
mainly with the aim of surmounting the severe problem in
homogeneous catalysis of separating the catalyst from the
reaction products. Approaches to solving this problem, in-
cluding representative literature references, have been: (i) to
“heterogenize” the homogeneous catalyst by incorporating it
Received 6 March 2002. Published on the NRC Research Press Web site at http://canjchem.nrc.ca on 28 November 2002.
Dedicated to Tris Chivers, a close friend, fellow cricketer, squash player, and chemistry colleague for 35 years (at least for BRJ!).
N.D. Jones, P. Meessen,1 M.B. Smith,2 U. Losehand, S.J. Rettig,3 B.O. Patrick, and B.R. James.4 Department of Chemistry,
The University of British Columbia, Vancouver, BC V6T 1Z1, Canada.
1Present address: BASF AG, D-67056 Ludwigshafen, Germany.
2Present address: Department of Chemistry, Loughborough University, Leicestershire, LE11 3TU, U.K.
3Deceased 27 October 1998.
4Corresponding author (e-mail: brj@chem.ubc.ca).
Can. J. Chem. 80: 1600–1606 (2002)
DOI: 10.1139/V02-127
© 2002 NRC Canada

Jones et al.
1601
Fig. 1. Tetra(o-N,N-dimethylanilinyl)bisphosphines.
1,1-Bis(di(o-N,N-dimethylanilinyl)phosphino)methane,
dmapm
To a solution of n-BuLi in hexanes (1.6 M, 16.5 mL,
26.4 mmol), cooled to –40°C on a dry ice – CH3CN bath,
was added o-bromo-N,N-dimethylaniline (5.05 g, 25.2 mmol)
in Et2O (20 mL) via cannula over 20 min. The yellow solu-
tion was stirred for 15 min and a white precipitate formed.
The slurry was allowed to warm to room temperature (r.t.)
and stirring was continued for 1 h. After the solution was
cooled again to –40°C, 1,1-bis(dichlorophosphino)methane
(1.33 g, 6.09 mmol) in Et2O (15 mL) was added over 5 min.
The resulting orange slurry was stirred for 15 min and then
allowed to warm to r.t. Stirring was continued for 1 h and
then HCl (~1 M, 50 mL) was added. The organic layer was
removed and KOH (~2 M) was added dropwise to the aque-
ous layer to neutrality. The aqueous fraction was extracted
with CH2Cl2 (3 × 20 mL) and the combined extracts were
dried over MgSO4. After removal of the solvent in vacuo,
EtOH (15 mL) was added. The slurry was refluxed for 0.5 h,
cooled to r.t., and the mixture filtered to give a white powder
that was washed with cold EtOH (3 × 5 mL) and dried in
1,2-bis(di(o-N,N-dimethylanilinyl)phosphino)cyclopentane),
illustrated in Fig. 1. Tóth and co-workers (11–15) have
made related ligands, but bearing para-C6H4(NMe2) sub-
stituents, including chiral derivatives for catalytic asymmet-
ric hydrogenation in water, once the N atoms have been
quaternized; with these systems, simultaneous coordination
to the same metal centre by both the P and N atoms of the
same ligand is not possible, and there are no reports of
bridging by these para-substituted ligands. Our new ortho-
substituted ligands make the N atoms available for coordina-
tion to the same metal as the P atoms, as well as for provid-
1
vacuo. Yield: 1.84 g (54%). H NMR ꢀ: 2.23 (t, 2H, CH2,
2JHP = 4.2), 2.68 (s, 24H, NCH3), 7.02 (pt, 2H, Ar), 7.11
(pd, 4H, Ar), 7.25 (pt, 4H, Ar), 7.40 (pd, 4H, Ar). 13C{1H}
NMR ꢀ: 28.0 (t, CH2, 1JCP = 26.2), 45.3 (s, NCH3), 119.7 (s,
CH), 124.2 (s, CH), 128.6 (s, CH), 132.3 (s, CH), 139.2 (s,
CN), 157.1 (m, CP). 15N NMR ꢀ: –343.7 (s, NMe2). 31P{1H}
NMR ꢀ: –36.0 (s). CI-MS m/z: 557 ([M–H]+). Anal. calcd.
for C33H42N4P2: C 71.2, H 7.6, N 10.1; found: C 71.0, H
7.8, N 9.9. Crystals of dmapm suitable for X-ray diffraction
were grown from an acetone solution layered with hexanes.
ing convenient
(P-N) environments; the extensive
coordination chemistry of these ligands, particularly within
Ru, Pd, and Pt systems, and their applications in catalysis (6,
21) will be published elsewhere. One benefit of excluding
coordination chemistry from this article is that the findings
presented amount to a contribution in main group chemistry,
Tris Chivers’s forte!
1,2-Bis(di(o-N,N-dimethylanilinyl)phosphino)ethane, dmape
The synthesis of this compound follows that of dmapm.
Thus, reaction of n-BuLi (1.6 M, 17.4 mL, 27.8 mmol), o-
bromo-N,N-dimethylaniline (5.56 g, 27.8 mmol), and 1,2-
bis(dichlorophosphino)ethane (1.61 g, 6.94 mmol) gave
Experimental
General
Unless otherwise noted, synthetic procedures were per-
formed using standard Schlenk techniques under a dry Ar or N2
atmosphere. The precursors 1,1-bis(dichlorophosphino)methane
and 1,2-bis(dichlorophosphino)ethane were purchased from
commercial sources and stored in an N2-filled glovebox,
while 1,2-bis(dichlorophosphino)cyclopentane was made ac-
cording to a literature procedure (22) and stored in a
Schlenk tube under Ar. N,N-Dimethyl-o-bromoaniline was
made by reaction of o-bromoaniline and dimethylsulfate ac-
cording to a literature procedure (23); all other reagents were
purchased from commercial sources and used as supplied.
Solvents were dried and distilled under N2 prior to use.
NMR spectra were recorded on a Bruker AV300 spec-
trometer (300.13 MHz for 1H, 75.46 MHz for 13C,
40.56 MHz for 15N, 121.49 MHz for 31P) at 300 K in
CDCl3. Residual solvent proton (1H, ꢀ 7.24 relative to exter-
nal SiMe4), solvent carbon (13C, ꢀ 77.0 relative to external
SiMe4), external MeNO3 (15N), or external P(OMe)3 (31P, ꢀ
141.00 relative to 85% aq H3PO4), were used as references
(s = singlet, d = doublet, t = triplet, p = pseudo). Downfield
shifts were taken as positive. All J-values are given in Hz.
Mass spectral and elemental analyses were conducted in the
UBC Chemistry Department (B.C., Canada) by G. Eigendorf
using a Kratos Concept II HQ mass spectrometer and by
P. Borda using a Carlo Erba 1108 analyzer, respectively.
1
2.44 g (61%) of a white powder. H NMR ꢀ: 1.91 (pt, 4H,
2
CH2, JHP = 4.1), 2.62 (s, 24H, NCH3), 6.94 (m, 8H, Ar),
7.09 (m, 4H, Ar), 7.22 (m, 4H, Ar). 13C{1H} NMR ꢀ: 24.3
(s, CH2), 45.2 (s, NCH3), 119.8 (s, CH), 124.1 (s, CH),
128.8 (s, CH), 132.3 (s, CH), 136.9 (pt, CN, J = 9.5), 157.7
(pt, CP, J = 6.6). 15N NMR ꢀ: –343.8 (s, NMe2).
31P{1H} NMR ꢀ: –28.9 (s). CI-MS m/z: 571 ([M – H]+).
Anal. calcd. for C34H44N4P2: C 71.6, H 7.8, N 9.8; found: C 71.0,
H 7.6, N 9.5. Crystals of dmape suitable for X-ray diffrac-
tion were grown from a CH2Cl2 solution layered with EtOH.
Rac-1,2-bis(di(o-N,N-dimethylanilinyl)phosphino)cyclo-
pentane, dmapcp
The synthesis of this compound corresponds to that
of dmapm. Thus, reaction of n-BuLi in hexanes (1.6 M,
23.0 mL, 36.8 mmol), o-bromo-N,N-dimethylaniline (6.83 g,
34.1 mmol), and 1,2-bis(dichlorophosphino)cyclopentane
(2.33 g, 8.57 mmol) at –40°C gave 2.72 g (52%) of a white
1
powder. H NMR ꢀ: 1.51 (m, 2H, C(4)H2), 1.70 (m, 2H,
C
(3/5)HH), 2.23 (m, 3H, C(3/5)HH, CH), 2.55 (s, 12H, NCH3),
2.60 (s, 12H, NCH3, obscures CH protons), 6.49 (m, 2H,
Ar), 6.71 (m, 2H, Ar), 6.96–7.28 (m, 12H, Ar). The 13C{1H}
NMR spectrum shows a complicated pattern of signals due
to coupling to phosphorus. Chemical shifts are presented
© 2002 NRC Canada

1602
Can. J. Chem. Vol. 80, 2002
Fig. 2. Molecular structure of dmapcp (50% ellipsoids); H2 and H3b are labelled because they are discussed in the text.
Scheme 1.
and the number of lines in each signal are given in parenthe-
ses following the peak frequencies. 13C{1H} NMR ꢀ: 24.6
(1, C(4)H2), 29.9 (3, C(3/5)H2), 40.4 (3, C(1/2)H), 45.0 (2,
NCH3), 119.9 (2, CH), 124.1 (2, CH), 128.5 (1, CH), 133.1
(2, CH), 137.9 (9, CN), 157.8 (7, CP). 15N NMR ꢀ: –338.8
(s, NMe2). 31P{1H} NMR ꢀ: –25.6 (s). CI-MS m/z 611 ([M–
H]+). Anal. calcd. for C37H48N4P2: C 72.8, H 8.0, N 9.2;
found: C 72.9, H 8.1, N 9.1. Crystals of dmapcp suitable for
X-ray diffraction were grown from a CH2Cl2 solution lay-
ered with EtOH. The labelling of the C atoms in the NMR
corresponds to that shown in the crystal structure (Fig. 2).
which N,N-dimethyl-2-lithioaniline is first generated by re-
action of n-BuLi with N,N-dimethyl-2-bromoaniline, and
then this is exposed to 0.25 mol equiv of the appropriate
tetra(chloro)bisphosphine; Scheme 1 summarizes the method
for dmapm. The compounds were isolated from the reaction
mixture by extraction with dilute aq HCl and purified after
neutralization by recrystallization from boiling EtOH. The
syntheses are analogous to those used for syntheses of the
related (pyridyl) mono- and bis(phosphine) ligands (20, 29–
31). Of note, owing to the activating nature of the NMe2
groups, the lithium exchange in step one of the synthesis
proceeds with higher yields than for the deactivated pyridyl
halides in the corresponding tetra(pyridyl)bisphosphine ana-
logues (>50 vs. ~30%) (20). The new ligands are white,
microcrystalline powders that are indefinitely air- and mois-
ture-stable in the solid state and for prolonged periods in
metal-free solution. They are freely soluble in chlorinated
solvents and in dilute aq HCl, partially soluble in alcohols
and Et2O, and insoluble in hexanes.
X-ray crystallography of dmapm, dmape, and dmapcp
Suitable crystals were selected, mounted on a glass fibre
using Paratone-N oil, and the unit frozen to –100°C. All
measurements were made on a Rigaku/ADSC CCD area de-
tector with graphite monochromated Mo Kꢁ radiation. Se-
lected crystallographic data appear in Table 1.5 In each case
the data were processed and corrected for Lorentz and polar-
ization effects and absorption (24). Neutral atom scattering
factors for all non-hydrogen atoms were taken from the In-
ternational Tables for X-ray Crystallography (25, 26). All
structures were solved by direct methods (27) and expanded
using Fourier techniques (28). All non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were not refined,
but were included in calculated positions (with C—H =
0.98 Å) that were updated as the refinement progressed.
The precursor 1,2-bis(dichlorophosphino)cyclopentane
was made by reaction of cyclopentene, white phosphorus,
and PCl3 (22). This procedure results almost exclusively in
the trans product and, because of this, dmapcp is produced
as a racemic mixture of R,R- and S,S-enantiomers, as with
Results and discussion
Synthesis
The compounds dmapm, dmape, and dmapcp were pre-
pared in a low-temperature, two-step, one-pot procedure in
5 Supplementary data (full crystal data and details on data collection and refinement have been deposited, along with tables of atomic coordi-
nates, anisotropic thermal parameters, all bond lengths and angles, and torsion angles) may be purchased from the Depository of Unpub-
lished Data, Document Delivery, CISTI, National Research Council Canada, Ottawa, ON K1A 0S2, Canada
(http://www.nrc.ca/cisti/irm/unpub_e.shtml for information on ordering electronically). CCDC 185016–185018 contain the supplementary
data for this paper. These data can be obtained, free of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (or from the Cambridge Crys-
tallographic Data Centre, 12 Union Road, Cambridge, U.K.; fax +44 1223 336033; or deposit@ccdc.cam.ac.uk).
© 2002 NRC Canada

Jones et al.
1603
Table 1. Crystallographic data for dmapm, dmape, and dmapcp.
dmapm
dmape
dmapcp
Formula
C33H42N4P2
C34H44N4P2
C37H48N4P2
Formula weight
Crystal system
Space group
a (Å)
b (Å)
c (Å)
ꢁ (°)
ꢂ (°)
ꢃ (°)
V (Å3)
556.67
Monoclinic
Cc(#9)
12.076(2)
19.674(2)
14.341(3)
90
114.142(8)
90
3109.1(8)
4
570.70
Triclinic
P1(#2)
610.73
Orthorhombic
P212121(#19)
11.975(1)
14.9163(2)
19.8124(5)
90
90
90
3539.2(3)
4
1.146
8.1849(4)
15.500(1)
19.882(2)
73.501(4)
81.052(1)
79.9046(9)
2364.9(3)
3
Z
Dcalcd. (g cm–3)
1.189
1.202
(Mo Kꢁ) (mm–1)
T (°C)
0.168
–100
0.167
–100
0.153
–93
Total data collected
Independent reflections
R1 (on F2, all data)
wR2 (on F2, all data)
14209
5977
0.073
21881
10698
0.077
9864
9864
0.0942
0.097
0.083
0.0705
the 1,2-bis(diphenylphosphino)cyclopentane analogue, dppcp
(22); the chirality designators refer to the absolute configu-
rations of the methine C atoms 1 and 2 in the backbone of
the ligand (Figs. 1 and 2).
Table 2. Selected bond lengths (Å) and angles (°) for dppm
and dmapm with estimated standard deviations in parentheses.
dppma
dmapm
Bond lengths (Å)
P1—C17
P2—C17
P1—C9
P1—C1
P2—C18
P2—C26
P1···P2
Bond angles (°)
ꢄ<P1, ꢄ<P2b
P1-C17-P2
C1-P1-C17
C17-P2-C26
Characterization
1.846(5)
1.868(5)
1.828(5)
1.842(5)
1.839(6)
1.842(5)
2.97(1)
1.854(3)
1.844(3)
1.835(2)
1.856(2)
1.843(3)
1.843(3)
3.099(3)
The dmapm, dmape, and dmapcp compounds have been
fully identified by means of NMR spectroscopy of all the
nuclei present (1H, 13C, 31P, and 15N), mass spectrometry, el-
emental analysis, and molecular structure determination by
low-temperature X-ray diffraction.
The compounds show the expected chemical shifts in their
1H NMR signals, but the multiplicity of the backbone pro-
tons needs comment. Whereas the CH2 in dmapm gives the
expected triplet due to H–P coupling (2JHP = 4.2 Hz), the
protons in dmape appear as a pseudo triplet, resulting from
the overlapping of the expected doublet of doublets, as in the
o-pyridyl analogue, dpype (30). In the case of the
racemic dmapcp, only multiplets were observed for the
cyclopentyl protons, and these are assigned by comparison
with data for the o-pyridyl analogue, dpypcp (20); the as-
signments of the 13C{1H} signals are tentative and are also
based on well-established data for dpypcp (20). The 31P{1H}
NMR spectra show singlets at ꢀ –36.0 (dmapm), –28.9
(dmape), and –25.6 (dmapcp); the values for the last two are
about 20 ppm to higher fields than those of the o-pyridyl an-
alogues (20, 30). The 15N NMR signals for the NMe2-type
ligands appear in the ꢀ –340 region.
It is constructive to consider structural features of
dmapm, dmape, and dmapcp along with those of their phenyl
analogues: bis(diphenylphosphino)methane, dppm (32), 1,2-
bis(diphenylphosphino)ethane, dppe (33), and dppcp (see
above) (22), and those we have determined for the pyridyl
analogues dpype (20) and dpypcp (20, 34), respectively. As
far as we are aware, the pyridyl analogue of dmapm has not
been reported. The molecular structures of the three new
compounds are, not surprisingly, very similar to those of
their phenyl and pyridyl analogues.
306.3(6), 303.7(6)
106.2(3)
101.7(2)
301.5(3), 303.4(3)
113.9(1)
95.9(1)
103.2(2)
98.9(1)
aData taken from ref. 32.
bSum of angles at P1 and P2.
Table 2 lists some geometrical parameters for dmapm and
dppm, and Fig. 3 shows the molecular structure of dmapm,
which shows minor differences to that of dppm. The in-
creased steric bulk of the NMe2 substituents in dmapm leads
to a different rotation of the arene moieties that induces two
sub van der Waals contacts between N and H atoms in adja-
cent N,N-dimethylanilinyl moieties on each side of the mole-
cule (N1···H23 = 2.65 Å and N4···H14 = 2.50 Å vs. the van
der Waals contact of 2.75 Å (35)); the corresponding C···N
bond lengths are 3.61 and 3.45 Å (larger than the 3.30 Å
value for the sum of the radii), and the corresponding N···C-
H angles are about 147 and 163°. These interactions may
represent weak C-H···N hydrogen bonds, which do exist
(35). This steric hindrance forces the molecule to “stretch”,
which leads to a 7° wider P-C-P angle (113.9°) and a longer
P···P distance (3.099 Å) with respect to dppm. Also, the cor-
responding C-P-C angles are compressed in comparison to
© 2002 NRC Canada

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Can. J. Chem. Vol. 80, 2002
Table 3. Selected bond lengths (Å) and angles (°) for dppe, dpype, and dmape with estimated standard deviations in parentheses.
dppea
dpypeb
dmape(CS)
dmape(C1)
Bond lengths (Å)
P3—C35
P3—C44
P3—C36
C35—C35*
P3···P3*
1.829(3)
1.825(7)
1.819(3)
1.521(7)
4.436(13)
1.842(3)
1.845(3)
1.849(3)
1.527(6)
4.453(9)
1.849(2)
1.837(2)
1.844(2)
1.538(4)
4.481(6)
P1—C1
P1—C3
P1—C11
C1—C2
P1···P2
1.858(2)
1.847(2)
1.846(2)
1.526(3)
4.508(6)
Bond angles (°)
ꢂ<P1, ꢂ<P2c
P1-C35-C35*
304.2(12)
110.9(4)
301.6(9)
110.4(3)
300.0(5)
110.7(2)
ꢂ<P1, ꢂ<P2
P1-C1-C2
P2-C2-C1
P-C-C-P
301.7(2), 301.3(2)
110.9(1)
113.7(1)
P-C-C-P
0.0
0.0
0.0
7.0
aData taken from ref. 33; weighted mean of two independent measurements.
bData taken from ref. 20.
cSum of angles at P1 and P2.
fected by the different aromatic substituents, but the average
P—C(aromatic) bond lengths are longer in dmape (av 1.844 Å)
and dpype (av 1.847 Å) than in dppe (av 1.822 Å), presum-
ably reflecting electronic differences between the ipso car-
bons in the anilinyl and pyridyl moieties compared with
those in the phenyl groups (the same difference is seen on
comparing data for dmapm and dppm, see Table 2). The
CS molecule shows a short N6···H42 contact (2.53 Å) with
C—N = 3.49 Å and an N···H-C angle of 165°, again indica-
tive of a weak H-bonding interaction.
Fig. 3. Molecular structure of dmapm (50% ellipsoids); H14 is
labelled because it is discussed in the text.
In the case of dmapcp, the backbone is puckered owing to
the steric demand of the cyclopentyl ring (P-C-C-P, 168°)
(Fig. 2). The four N,N-dimethylanilinyl moieties lead to
steric crowding, inducing sub van der Waals contacts (and
possible H-bonding) between two of the N atoms and the
closest H atoms of the cyclopentyl backbone (N4···H3b
(2.67 Å), C—N (3.49 Å), N···H–C (140.7°); and N1···H2
(2.53 Å), C—N (3.33 Å), N···H–C (136.4°)). These contacts
might explain the relatively long P—C(aliphatic) bonds (1.882
and 1.879 Å) and the increased P—P distance (4.505 Å)
compared with data for dppcp and dpypcp (Table 4). Ac-
cordingly, the P—C(aromatic) bonds of the strained N,N-
dimethylanilinyl moieties are also slightly elongated com-
pared with those of the non-interacting N,N-dimethylanilinyl
groups: P1—C6 (1.852) vs. P1—C14 (1.837 Å) and P2—
C30 (1.847) vs. P2—C22 (1.831 Å). The P—C(aliphatic) bonds
are about 0.04 Å longer than the P—C(aromatic) bonds.
The unit cell of the dmapcp crystal chosen for the analysis
shows that only the S,S enantiomer is present (chiral space
group P212121), implying a spontaneous resolution has taken
place; other crystals must contain only R,R enantiomers, but
no attempt was made to separate these by the Pasteur
method of inspection. The analogous dppcp and dpypcp sys-
tems crystallize with both enantiomers in the unit cell. Apart
from the slight distortions mentioned above, the S,S enantio-
mers of the three compounds exhibit a very similar overall
molecular geometry (Table 4).
those of dppm (C1-P1-C17 (95.9°) and C17-P2-C26 (98.9°) vs.
101.7° and 103.2°), which leads to slightly more “pyrami-
dal” P atoms as defined by the sum of the angles at P1 and
P2 (av 302.5 vs. av 304.9°). The P—C bond lengths within
the two molecules are essentially the same.
The asymmetric unit cell of dmape contains 1.5 crystallo-
graphically independent molecules, 1 being in a general po-
sition and 1 lying on a centre of symmetry. The main
difference (see Fig. 4) is that in the CS molecule one of the
phosphine groups is twisted 180° with respect to the other,
whereas in the dissymmetric molecule both phosphine moi-
eties are facing the same side, the N,N-dimethylanilinyl sub-
stituents taking gauche positions with respect to each other.
The corresponding bond lengths and angles within each mol-
ecule differ only marginally (Table 3). While the centro-
symmetric molecule exhibits a planar backbone with a P-C-
C-P torsion angle constrained by symmetry to be –180°, the
CS molecule is slightly puckered with a corresponding tor-
sion angle of 173°. The CS molecule exhibits geometry very
similar to that of the also centrosymmetrical analogues dppe
and dpype. The pyramidal geometry at the P atom is not af-
Coordination chemistry
As alluded to in the Introduction, the new ligands have re-
vealed diverse coordination chemistry (6, 21). Established
bonding modes include: (i) P,P-, P,N-, and P,P,N-coordination
within d8 square planar systems, including interconversions
© 2002 NRC Canada

Jones et al.
1605
Fig. 4. Structures of the dissymmetric (C1) and symmetric (CS) molecules of dmape (50% ellipsoids); H42 is labelled because it is dis-
cussed in the text.
Table 4. Selected bond lengths (Å) and angles (°) for dpcp, dpypcp, and dmapcp with estimated standard de-
viations in parentheses.
dppcpa
dpypcpb
dmapcp
Bond lengths (Å)
P1—C1
P1—C6
P1—C14
P2—C2
P2—C22
P2—C30
C1—C2
P1···P2
1.866(2)
1.836(2)
1.833(2)
1.857(2)
1.833(2)
1.831(2)
1.546(2)
4.448(6)
1.862(2)
1.850(2)
1.847(2)
1.863(2)
1.834(2)
1.854(2)
1.546(3)
4.457(7)
1.882(3)
1.852(3)
1.837(3)
1.879(3)
1.831(3)
1.847(3)
1.537(3)
4.505(9)
Bond angles (°)
ꢂ<P1, ꢂ<P2c
P1-C1-C2
P2-C2-C1
P-C-C-P
306.4(3), 304.6(3)
109.2(1)
109.8(1)
304.2(3), 303.8(3)
109.0(1)
109.9(1)
302.4(3), 299.1(3)
108.5(1)
111.3(1)
161.7
–164.3
168.2
aData taken from ref. 22.
bData taken from ref. 34.
cSum of angles at P1 and P2.
between types sometimes involving loss of initially coordi-
nated ancillary halides; (ii) P,P,N,N-coordination with
the dmapm ligand that bridges metal–metal bonded systems
of formally d8 centres; and (iii) P,P,N,N- and P,P,N,N,N,N-
coordination modes within RuII-d6 octahedral systems.
These findings will be reported in future publications.
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