Diphosphanes derived from phobane and phosphatrioxa-adamantane: Similarities, differences and anomalies

Article abstract of DOI:10.1039/c1dt10335k

The homodiphosphanes CgP-PCg (1) and PhobP-PPhob (2) and the heterodiphosphanes CgP-PPhob (3), CgP-PPh₂ (4a), CgP-P(o-Tol) ₂ (4b), CgP-PCy₂ (4c), CgP-P^tBu₂ (4d), PhobP-PPh₂ (5a), PhobP-P(o-Tol)₂ (5b), PhobP-PCy₂ (5c), PhobP-P^tBu₂ (5d) where CgP = 6-phospha-2,4,8-trioxa-1,3,5,7-tetramethyladamant-9-yl and PhobP = 9-phosphabicyclo[3.3.1]nonan-9-yl have been prepared from CgP(BH₃)Li or PhobP(BH₃)Li and the appropriate halophosphine. The formation of 1 is remarkably diastereoselective, with the major isomer (97% of the product) assigned to rac-1. Restricted rotation about the P-P bond of the bulky meso-1 is detected by variable temperature ³¹P NMR spectroscopy. Diphosphane 3 reacts with BH₃ to give a mixture of CgP(BH₃)-PPhob and CgP-PPhob(BH₃) which was unexpected in view of the predicted much greater electron-richness of the PhobP site. Each of the diphosphanes was treated with dimethylacetylene dicarboxylate (DMAD) in order to determine their propensity for diphosphination. The homodiphosphanes 1 and 2 did not react with DMAD. The CgP-containing heterodiphosphanes 4a-d all added to DMAD to generate the corresponding cis alkenes CgPCH(CO₂Me)CH(CO₂Me)PR ₂ (6a-d) which have been used in situ to form chelate complexes of the type [MCl₂(diphos)] (7a-d) where M = Pd or Pt. The PhobP-containing heterodiphosphanes 3 and 5a-d react anomalously with DMAD and do not give the products of diphosphination. The X-ray crystal structures of the diphosphanes 2, 3, 4a, and 5a, the monoxide and dioxide of diphosphane 1, and the platinum chelate complex 7c have been determined and their structures are discussed.

Full text of DOI:10.1039/c1dt10335k

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PAPER
Diphosphanes derived from phobane and phosphatrioxa-adamantane:
similarities, differences and anomalies†
Deborah L. Dodds, Joelle Floure, Michael Garland, Mairi F. Haddow, Thomas R. Leonard, Claire L. McMullin,
A. Guy Orpen and Paul G. Pringle*
Received 26th February 2011, Accepted 11th April 2011
DOI: 10.1039/c1dt10335k
The homodiphosphanes CgP–PCg (1) and PhobP–PPhob (2) and the heterodiphosphanes CgP–PPhob
(3), CgP–PPh2 (4a), CgP–P(o-Tol)2 (4b), CgP–PCy2 (4c), CgP–PtBu2 (4d), PhobP–PPh2 (5a),
PhobP–P(o-Tol)2 (5b), PhobP–PCy2 (5c), PhobP–PtBu2 (5d) where CgP = 6-phospha-2,4,8-
trioxa-1,3,5,7-tetramethyladamant-9-yl and PhobP = 9-phosphabicyclo[3.3.1]nonan-9-yl have been
prepared from CgP(BH3)Li or PhobP(BH3)Li and the appropriate halophosphine. The formation of 1
is remarkably diastereoselective, with the major isomer (97% of the product) assigned to rac-1.
Restricted rotation about the P–P bond of the bulky meso-1 is detected by variable temperature 31
NMR spectroscopy. Diphosphane 3 reacts with BH3 to give a mixture of CgP(BH3)–PPhob and
P
CgP–PPhob(BH3) which was unexpected in view of the predicted much greater electron-richness of the
PhobP site. Each of the diphosphanes was treated with dimethylacetylene dicarboxylate (DMAD) in
order to determine their propensity for diphosphination. The homodiphosphanes 1 and 2 did not react
with DMAD. The CgP-containing heterodiphosphanes 4a–d all added to DMAD to generate the
corresponding cis alkenes CgPCH(CO2Me) CH(CO2Me)PR2 (6a–d) which have been used in situ to
form chelate complexes of the type [MCl2(diphos)] (7a–d) where M = Pd or Pt. The PhobP-containing
heterodiphosphanes 3 and 5a–d react anomalously with DMAD and do not give the products of
diphosphination. The X-ray crystal structures of the diphosphanes 2, 3, 4a, and 5a, the monoxide and
dioxide of diphosphane 1, and the platinum chelate complex 7c have been determined and their
structures are discussed.
of complexes of both of these classes of tertiary phosphines have
Introduction
shown that the phosphacycles constrain the bridgehead C–P–
C angles to be close to 90◦. The impact of the compressed
C–P–C angle on the s-donor/p-acceptor properties of CgPR and
PhobPR ligands is manifest from the IR and NMR spectra of
their complexes; compared to their acyclic analogues, CgPR and
PhobPR ligands are weaker s-donors and better p-acceptors.4–7
The unusual coordination properties CgPR and PhobPR may be
at the root of their many applications in catalysis.8,9
We have developed the reliable, one-pot route to compounds of
the type R2P–PR¢2 shown in eqn (1) and established that these
heterodiphosphanes are kinetically stable to metathesis and can
be employed in the stereospecific cis-diphosphination of Michael-
activated acetylenes to give a series of 1,2-diphosphinoethene
ligands.1 Contemporaneously, Gudat et al.2,3 reported on the
nature of the P–P bonding in highly polarised, heterodiphosphanes
and exploited the reactivity of the P–P bond in the synthesis of
diphosphines.
(1)
We are interested in phosphorus ligands in which the P
atom is in an unusual stereoelectronic environment and have
investigated phosphatrioxa-adamantane cage ligands (CgPR)4
and bicyclic phobane ligands (PhobPR).5 X-Ray structural studies
Here we report the synthesis and properties of diphosphanes of
the type CgP–PR2 and PhobP–PR2. The similarities of the CgP
and PhobP moieties are revealed in the crystal structures and 31
P
School of Chemistry, University of Bristol, Cantock’s Close, Bristol, UK,
BS8 1TS. E-mail: paul.pringle@bristol.ac.uk
† CCDC reference numbers 815349–815355. For crystallographic data in
CIF or other electronic format see DOI: 10.1039/c1dt10335k
NMR properties of the derived diphosphanes. However, there is
a contrast in the reactivity of CgP–PR2 and PhobP–PR2 towards
dimethylacetylene dicarboxylate.
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Scheme 1
Results and discussion
Diphosphanes
The cage-derived and phobane-derived diphosphanes 1–5 have
been prepared by the routes shown in Scheme 1. The diphos-
phane products have each been isolated in 65–75% overall yields
after purification and have been characterised by a combina-
1
tion of elemental analysis, mass spectrometry, 31P, H, and 13C
NMR spectroscopy (see Experimental section). In addition, the
X-ray crystal structures of several of the diphosphanes have
been determined (see below). Diphosphane 2 has been previously
reported as the product obtained adventitiously from the reaction
of PhobPH and 1-iodoheptafluoropropane.10
The two chiral PCg moieties present in 1 means that it exists
as rac and meso diastereoisomers. Treatment of CgP(BH3)Li with
CgPBr gave two products assigned to rac and meso isomers of
CgP(BH3)–PCg (1.BH3) on the basis of their characteristic 31P
NMR parameters {major product: d 13.8 (br d), -4.7 (d, JPP
=
363 Hz); minor product: d 14.3 (br d), -8.0 (d, JPP = 354 Hz)}.
The ratio of the 1.BH3 isomers was ca. 30 : 1 indicating that the
synthesis is surprisingly diastereoselective. After deprotection of
1.BH3 with Et2NH, the 31P NMR spectrum of the product 1
showed two signals in a ratio of ca. 30 : 1 with a sharp singlet at
d -15.1 and a broad singlet at d -17.5 (w1/2 = 70 Hz). Trituration
of the initially formed sample of 1 with MeOH gave the pure
Fig. 1 a. X-Ray crystal structure of CgP(O)–PCg (1a). Thermal ellipsoids
are shown at the 50% probability level. Hydrogen atoms have been omitted
for clarity. Oxygen O(4), has occupation of 42% on P(1) and 42% on
◦
˚
P(1A). Selected bond lengths [A] and angles [ ]: P1–P1A, 2.2618(6);
P1–C2, 1.8703(12); P1–C9, 1.8778(9); P1–O4, 1.4106(17); C2–P1–C9,
94.27 (5); C2–P1–P1A–C2A, -35.7(2); C2–P1–P1A–C9A, -135.2(2). b.
X-Ray crystal structure of CgP(O)–(O)PCg (1b). Thermal ellipsoids are
shown at the 50% probability level. Hydrogen atoms have been omitted
for clarity. Oxygen O(4) has occupation of 100% on P(1) and P(1A).
1
major isomer as shown by 31P, 13C and H NMR spectroscopy.
Evaporation of the methanol washings gave a small amount of a
solid that was relatively rich (40%) in the minor isomer of 1 and
this sample was further studied by variable temperature 31P NMR
(see below).
◦
˚
Selected bond lengths [A] and angles [ ]: P1–P1A, 2.3229(9); P1–C2,
1.8574(16); P1–C9, 1.8638(17); P1–O4, 1.4827(13); C2–P1–C9, 96.10(7);
C2–P1–P1A–C2A, 29.26(9); C2–P1–P1A–C9A, 132.70(8).
Attempts to grow crystals of the major isomer of 1 took
several days and unfortunately gave oxidised samples. Crystals
of the monoxide, CgP(O)–PCg (1a) and dioxide CgP(O)–(O)PCg
(1b) suitable for X-ray crystallography were grown from inde-
pendent samples by the slow evaporation of their solutions in
dichloromethane/hexane (1 : 1) and their structures are shown in
Fig. 1a and 1b. Both structures crystallised in the monoclinic space
group C2/c with 4 molecules per unit cell. The C2-symmetric
structure of 1a shown in Fig. 1a is of the a,a-enantiomer with
the b,b-enantiomer is equally present in the unit cell; the O(4) is
distributed 42% on each of P(1) and P(1A) with the remaining
16% of the structure modelled as the non-oxidised diphosphane
rac-1. The C–P–C angle at phosphorus is constrained by the cage
to be 94◦. The dioxide structure 1b, shown in Fig. 1b also shows
the a,a-enantiomer with the b,b-enantiomer equally present in
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the unit cell. The C–P–C angle of 96◦ in the dioxide 1b is slightly
larger than in the monoxide 1a.
or anti since the C2-symmetry of both of these conformations
would render the P atoms equivalent (see Scheme 2).
The crystal structures shown in Fig. 1a and 1b of the oxides of
1 were obtained from samples that were > 99% diastereomerically
pure by 31P NMR spectroscopy. Since both of the determined
structures (Fig. 1) are of rac isomers, we have assigned rac-1 to the
major diastereoisomer of 1 formed in its synthesis (Scheme 1).
The broad 31P NMR singlet obtained for the minor isomer of
1 (assigned to meso-1) at +25 ◦C in toluene (w1/2 70 Hz) became
sharper (w1/2 20 Hz) at +40 ◦C while at -60 ◦C it was resolved into
two doublets at d -12.0 and -29.2 (1JPP = 269 Hz). By contrast,
the sharp singlet for◦rac-1 remained invariant over the whole
range of -60 to +40 C. An estimate of 44 kJ mol-1 was made
for the energy barrier (DG‡) for the fluxional process in meso-1
based on an approximation of the coalescence temperature. The
fluxionality of meso-1 is consistent with slow rotation about the
P–P bond on the NMR timescale with a C1-symmetric rotamer
observed at low temperatures. It has been shown11 that the most
stable conformations adopted by diphosphanes (defined by the
{lone-pair–P–P–lone-pair} torsion angle) are anti (180◦) and
Crystals of PhobP–PPhob (2) suitable for X-ray crystallogra-
phy were obtained by slow evaporation of its CDCl3 solution.
Compound 2 crystallises in the triclinic space group P1 with 2
molecules in the unit cell. The molecular structure of 2 (Fig. 2)
shows an anti-periplanar arrangement of the phobane substituents
about the P–P bond.◦The C–P–C angle is constrained by the
phobane rings to be 93 .13 Molecule 2 has inversion symmetry, and
is described by two independent molecules in the asymmetric unit
(Z¢ = 2 ¥ 12 ).
¯
◦
t
gauche (60 ). Restricted rotation about the P–P bond in Bu2P–
PtBu2 has been reported11,12 with an accurately determined DG‡
of 52.7 kJ mol-1. Counterintuitively, the favoured rotamer for
t
Fig. 2 X-Ray crystal structure of PhobP–PPhob (2). Thermal ellipsoids
are shown at the 50% probability level. Hydrogen atoms and the
second PhobP–PPhob molecule have been omitted for clarity. Selected
the very bulky Bu2P–PtBu2 was unambiguously shown by 1H
and 13C NMR spectroscopy to have a gauche rather than an anti
conformation.11,12 If a gauche conformation was also adopted by
◦
˚
bond lengths [A] and angles [ ]: P1–P1A, 2.2277(9); P1–C1, 1.8640(18);
P1–C5, 1.8657(17); C1–P1–C5, 93.39(7); C1–P1–P1A–C1A, 180.00(5);
C1–P1–P1A–C5A, 83.89(7).
the similarly bulky meso-1 in solution, its variable temperature 31
P
NMR spectra described above could be rationalised as follows
(with the aid of the pictorial representation of the P–P rotation
given in Scheme 2). The two, enantiomeric, gauche rotamers of
meso-1 have C1-symmetry rendering the P nuclei inequivalent,
consistent with the AX pattern observed in its 31P NMR spectrum
at -50 ◦C; at high temperatures, the singlet for meso-1 arises
from the time-averaging of the P environments due to rapid
interconversion on the NMR timescale of the gauche rotamers via
the Ci-symmetric anti rotamer (see Scheme 2). The singlet in the
31P NMR spectrum of rac-1 observed at all temperatures could be
explained by the preferred rotamer in solution being either gauche
The addition of CgP(BH3)Li to PhobPCl or the addition of
PhobP(BH3)Li to CgPBr gave mixtures of isomers 3A and 3B
(Scheme 3) which have been identified in solution from their
characteristic 31P NMR spectra {3A: d 4.8 (br d, CgPBH3),
-28.7 (d, JPP = 320 Hz. PhobP); 3B: d 0.0 (br d, PhobPBH3),
-42.5 (d, JPP = 270 Hz, CgP)}. The initially formed compositions
of the 3A/3B mixtures reflected the location of the BH3 in
the starting material. Thus the reaction of CgP(BH3)Li with
PhobPCl after 10 min gave a 2 : 1 mixture of 3A : 3B whereas
addition of PhobP(BH3)Li to CgPBr after 10 min gave 3B
exclusively according to the 31P NMR spectra. The composition
of products from both routes changed over 16 h, and converged
on a ratio of ca. 1 : 10. Moreover, addition of 1 equiv. of
BH3·THF to 3 (described below) also gave 1 : 10 mixtures of 3A:
3B and therefore this is assumed to be the equilibrium propor-
tions.
The equilibrium constant K1 is thus ca. 10 meaning that there
is little discrimination of BH3 for PhobP over the CgP sites in
3. This was unexpected since a PhobPZ would be predicted to be
electron-rich and therefore have a much higher Lewis basicity than
an analogous CgPZ. This prediction is logical but has not been
previously quantified. For this reason, we have carried out a 31P
NMR study of the equilibrium shown in eqn (2) in THF. Treatment
of CgPH.BH3 with PhobPH was monitored by 31P NMR. After
1 h, only about 3% of the non-boronated PhobPH remained and
after 16 h no PhobPH was detected leading to a calculated lower
limit on K2 of 10000. The explanation of the anomalously low
value of K1 may lie in steric effects; boranation of the PhobP in
3 may be destabilised by a steric clash of the BH3 with the CH3
groups on the a-C atoms of the CgP moiety.
Scheme 2 Newman projections depicting rotation about the P–P bonds
in meso-1 and rac-1 (from left to right, clockwise rotation of the front P
fragment). For simplicity, the chirality of the CgP unit is represented by
the stereogenic P atoms which have the same symmetry properties as the
chiral CgP moiety.
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Scheme 3
(2)
Treatment of any of the 3A/3B mixtures with Et2NH to
decomplex the BH3 gave the same product whose 31P NMR
spectrum at 121 MHz in CDCl3, CD2Cl2 or C6D6 was apparently a
singlet. Only at high field (202 MHz) was the inequivalence of the P
atoms in 3 exposed and analysis of the close AB pattern revealed
that the difference in chemical shift was just 0.14 ppm. The dP
values for 3 lie close to the average of the values for 1 and 2 and
it thus appears that the CgP and PPhob groups mutually perturb
their environments so that the P nuclei are in an almost identical
magnetic environment. The near-equivalence of the P nuclei in 3
may be a coincidence but it supports our contention (see below)
that CgP and PhobP have similar stereoelectronic properties and
is also consonant with the similar affinities for BH3 of the PhobP
and CgP donors in 3.
Fig. 4 X-Ray crystal structure of CgP–PPh2 (4a). Thermal ellipsoids are
shown at the 50% probability level. Hydrogen◦atoms have been omitted for
˚
clarity. Selected bond lengths [A] and angles [ ]: P1–P2, 2.2363(7); P1–C2,
1.8922(17); P1–C9, 1.8854(17); P2–C11, 1.8365(18); P2–C17, 1.8460(19);
C2–P1–C9, 92.36(8); C11–P2–C17, 102.13(8); C2–P1–P2–C11, 177.00(8);
C9–P1–P2–C11, 82.52(8).
Crystals of CgP–PPhob (3) suitable for X-ray diffraction were
grown by the slow evaporation of its saturated solution in
CH2Cl2/hexane (1 : 1). Compound 3 crystallises in the monoclinic
space group P21/c with 4 molecules per unit cell. The molecular
structure of 3 (Fig. 3) shows an anti-periplanar arrangement of
substituents about the P–P bond. The C–P–C angle is constrained
by the cage or phobane rings to be 92◦ and 93◦ respectively.
constrained to be 92◦ while the C–P–C angle at the PPh2 is 102◦
and more typical of a tertiary phosphine.
Crystals of PhobP–PPh2 (5a) suitable for X-ray crystallog-
raphy were obtained by slow evaporation of its solution in
CH2Cl2/hexane (1 : 1). Diphosphane 5a crystallises in the or-
thorhombic space group P212121 with 4 molecules per unit cell. The
molecular structure of 5a (Fig. 5) again shows an anti-periplanar
arrangement of the substituents about the P–P bond. The C–P–C
angle within the bicycle is constrained to be 93◦ while the C–
P–C angle at the PPh2 is 101◦ and is more typical of a tertiary
phosphine.
Fig. 3 X-Ray crystal structure of CgP–PPhob (3). Thermal ellipsoids are
shown at the 50% probability level. Hydrogen◦atoms have been omitted for
˚
clarity. Selected bond lengths [A] and angles [ ]: P1–P2, 2.2321(4); P1–C2,
1.8947(12); P1–C5, 1.8953(12); P2–C11, 1.8663(13); P2–C15, 1.8728(13);
C2–P1–C9, 91.95(5); C11–P2–C15, 92.84(6); C2–P1–P2–C11, 162.00(6);
C2–P1–P2–C15, -102.15(6).
Crystals of CgP–PPh2 (4a) suitable for X-ray crystallography
were obtained by slow evaporation of its diethyl ether solution.
Diphosphane 4a crystallises in the orthorhombic space group
Pca21 with 4 molecules per unit cell (two containing the a-
enantiomer, and two the b-enantiomer). The molecular structure
of 4a (Fig. 4) shows that the substituents are arranged in an
anti-periplanar manner. The C–P–C angle within the cage is
Fig. 5 X-Ray crystal structure of PhobP–PPh2 (5a). Thermal ellipsoids
are shown at the 50% probability level. Hydrogen ato◦ms have been omitted
˚
for clarity. Selected bond lengths [A] and angles [ ]: P1–P2, 2.2286(7);
P1–C1, 1.8760(2); P1–C5, 1.8610(2); P2–C9, 1.8390(2); P2–C15, 1.8340(2);
C1–P1–C5, 93.3(10); C9–P2–C15, 101.3(10); C1–P1–P2–C9, 95.93(11);
C5–P1–P2–C15, -161.14(10).
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The structures of 4a and 5a, with a PPh2 bound to a PCg
or PPhob, allow a comparison to be made between the cyclic
substituents. The P–P bond distances in 4a and 5a differ by less
(3)
˚
than 0.01 A and the C–P–C angles in the Ph2P are essentially the
same. This leads to the conclusion that stereoelectronically the PCg
and PPhob substituents appear to behave remarkably similarly in
these compounds.
Treatment of ligand 6a with [PtCl2(cod)] gave the chelate
complex 7a [eqn (4)] which has been fully characterised. The 1JPPt
values of 3315 Hz and 3766 Hz are typical of PPh2 and PtBu2
phosphines trans to chlorine15 and the large positive coordination
chemical shifts of +62.9 and +73.7 ppm are characteristic of
five-membered chelates.16 The other ligands 6b–d were very slow
to react with [PtCl2(cod)] or [PtCl2(NCtBu)2] with only traces
of complexes detected after several days, reflecting the great
bulk of these diphosphines that inhibits their coordination.
Nevertheless a crystal of the platinum complex 7c suitable for
X-ray crystallography was obtained from slow evaporation of the
reaction mixture of 6c and [PtCl2(NCtBu)2] and its X-ray crystal
structure determined (see below). The palladium complexes 7b
and 7d were synthesised by treatment of the labile [PdCl2(NCPh)2]
with ligands 6b and 6d and have been fully characterised.
Diphosphinations
We have previously shown that a range of diphosphanes readily
add to dimethylacetylene dicarboxylate (DMAD) under ambient
conditions to give diphosphines.1 It was noted that the rate of this
reaction was a function of the diphosphane: (i) with homodiphos-
phanes, the lower the steric bulk, the greater the rate, e.g. Ph2P–
PPh2 adds rapidly to DMAD whereas neither (o-Tol)2P–P(o-Tol)2
t
nor Bu2P–PtBu2 adds even at elevated temperatures; (ii) with
heterodiphosphanes, the greater the electronegativity difference
between the PR2 groups, the greater the rate, e.g. (o-Tol)2P–PtBu2
adds rapidly whereas no reaction was observed between DMAD
and (o-Tol)2P–PPh2 or Cy2P–PtBu2. The mechanism proposed in
Scheme 4 involves nucleophilic attack by the diphosphane on
the Michael activated acetylene (step i, Scheme 4) followed by
cleavage of the P–P bond involving electrophilic attack on the
allene group in the betaine intermediate (step ii, Scheme 4).2
This mechanism can be used to rationalise the reactivities of the
diphosphanes towards diphosphination of DMAD in terms of the
nucleophilicity and electrophilicity of the diphosphane, both of
which should increase with the polarity and decrease with the size
of the diphosphane.
(4)
Complex 7c crystallises as a toluene solvate in the triclinic space
¯
group P1 with 2 molecules per unit cell (see Fig. 6).
Scheme 4
Similar reasoning to the above can explain why the non-
polar and very bulky CgP–PCg (1) does not react with DMAD.
The unsymmetrical CgP-containing diphosphanes 4a–c all react
smoothly at room temperature with DMAD to give diphos-
phinoethene ligands 6a–d which have been characterised by
31P NMR spectroscopy in solution only and used in situ. The
cis alkene structure is assigned in each case [eqn (3)] on the
Fig. 6 X-Ray crystal structure of 7c.C6H5CH3. Thermal ellipsoids
are shown at the 50% probability level. Hydrogen atoms and sol-
vent of crystallisation have been omitted for clarity. Selected bond
3
basis of the similarity of the JPP values to those we previously
lengths [A] and angles [◦]:Pt1–P1, 2.2233(9); Pt1–P2, 2.2180(8);
˚
reported for similar diphosphinoethenes1 and the formation of
chelate complexes (see below). The cis geometry is consistent
with the Michael addition mechanism above (Scheme 4); a radical
mechanism would be expected to yield a mixture of cis and trans
alkene isomers.14
Pt1–Cl1, 2.3463(8); Pt1–Cl2, 2.3559(9); P1–C2, 1.895(3); P1–C9, 1.870(3);
P1–C11, 1.856(3); P2–C12, 1.843(3); P2–C17, 1.841(3); P2–C23, 1.841(3);
P2–Pt1–P1, 88.35(3); C11–P1–C2, 112.84(12); C11–P1–C9, 102.33(11);
C2–P1–C9, 95.13(12); C17–P2–C12, 103.16(12); C17–P2–C23, 109.28(13);
C12–P2–C23, 105.85(12); P1–C11–C12–P2, 4.2(3).
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None of the PhobP-containing diphosphanes 2, 3, 5a–d added
to DMAD to give diphosphines under the same conditions that
the CgP–PR2 (4a–d) added readily. The lack of any reaction of
the PhobP–PPhob (2) with DMAD even in refluxing toluene is
understandable in terms of its lack of polarity and the steric bulk.
All of the other PhobP–PR2 diphosphanes reacted with DMAD
(some rapidly even at -40 ◦C) to give a mixture of several products
in each case, none of which have been identified. The 31P NMR
spectra have signals in the P(V) region and none of these show PP
coupling indicating that the products are the result of P–P bond
rupture. In view of the structural and spectroscopic similarities
between the CgP- and PhobP-containing species noted here, the
very different reactions of the CgP–PR2 and PhobP–PR2 with
DMAD was unexpected.
THF (10 cm3) at -78 ◦C. The reaction mixture was stirred for 1 h
to give a yellow solution which was added dropwise over 20 min
to a solution of CgPBr (2.00 g, 5.90 mmol) in THF (10 cm3)
cooled to -78 ◦C. The reaction mixture was stirred overnight
and allowed to warm to room temperature. The resulting 31P
NMR spectrum showed a mixture of boronated and unboronated
diphosphane. Diethylamine (1.73 g, 2.40 cm3, 17.1 mmol) was
added and the reaction stirred for 1 h before volatile solvents
were removed in vacuo. MeOH (25 cm3) was added to the white
solid. After stirring overnight, filtration afforded a white solid
which was dried in vacuo to yield rac-CgP–PCg (1.66 g, 3.8 mmol,
65%). From the MeOH filtrate a further crop of product as a 3 : 2
mixture of rac:meso isomers was obtained (0.22 g, 0.53 mmol,
9%). Crystals of partially oxidised 1 (see Results and discussion)
suitable for X-ray diffraction were grown by slow evaporation of a
hexane/CH2Cl2 (1 : 1) solution. Elemental analysis for rac-1, calcd
for C20H32O6P2: C, 55.81; H, 7.49. Found: C, 55.96; H, 7.53%. EI
mass spectrum: m/z 430.1 (M+). HRMS (EI) calcd for C20H32O6P2:
430.1674, found: 430.1678. 31P NMR (CDCl3): -15.0 (s). 1H NMR
(400 MHz, CDCl3): 2.43 (1H, d, 1JHH = 13.4 Hz, CH2), 2.26 (1H,
d, 1JHH = 13.4, CH2), 2.11–2.05 (2H, m, CH2), 1.94–1.81 (4H, m,
CH2), 1.72–1.69 (4H, m, CH3), 1.58–1.48 (8H, m, CH3), 1.41–1.38
(12H, s, CH3). 13C NMR (75 MHz, CDCl3): 96.7 (t, 3JCP = 0.7 Hz,
CO), 96.3 (s, CO), 75.0 (t, 1JCP = 20 Hz, PC), 74.2 (t, 1JCP = 6 Hz,
PC), 47.0 (t, 2JCP = 8 Hz, CH2), 41.2 (t, 2JCP = 3 Hz, CH2), 28.7 (t,
2JCP = 7 Hz, CH3), 28.3 (t, 2JCP = 13 Hz, CH3), 28.1 (s, CH3), 27.7
(s, CH3).
Conclusion
We have synthesised a new series of P–P bonded diphosphanes
incorporating PCg and PPhob moieties and discovered that the
synthesis of CgP–PCg is over 95% diastereoselective for the
rac-isomer. Structural similarities between the PCg and PPhob
substituents are evident from the 31P NMR spectral data for
CgP–PPhob and the X-ray crystal structures of CgP–PPh2 and
PhobP–PPh2. Moreover the similar affinity of BH3 for both P
sites in CgP–PPhob is testament to the similarity of their Lewis
basicities in this molecule and may be a consequence of a mutual
perturbation of their donor properties and steric congestion in
the borane adducts. These similarities are counterbalanced by the
contrasting reactions of CgP–PR2 and PhobP–PR2 with DMAD
that have been observed.
Preparation of PhobP–PPhob (2)
To a solution of PhobPH (0.10 g, 0.76 mmol) in THF (5 cm3),
BH3·THF (1 M solution in THF, 1.00 cm3, 1.00 mmol) was added
at 0 ◦C and the mixture stirred for 1 h. All volatiles were then
removed in vacuo and the remaining white solid dissolved in THF
Experimental section
Unless otherwise stated, all work was carried out under a dry
nitrogen atmosphere, using standard Schlenk line techniques. Dry
N2-saturated solvents were collected from a Grubbs system17 using
filtration through an alumina column impregnated with deoxy-
genated catalysts in flame and vacuum dried glassware. NMR
spectra were measured on a Jeol Eclipse 300 or a Jeol GX 400
spectrometer. Unless otherwise stated 1H, 13C, and 31P NMR spec-
tra were recorded at 400, 100, and 121 MHz, respectively at +23 ◦C
unless otherwise stated. NMR chemical shifts are in ppm to high
frequency of an external reference, TMS (for 1H and 13C) and 85%
H3PO4 (for 31P). Mass spectra were recorded by the University of
Bristol Mass Spectrometry Service on a VG Analytical Autospec
(EI) or VG Analytical Quattro (ESI) spectrometers. Elemental
analyses were carried out by the Microanalytical Laboratory of the
School of Chemistry, University of Bristol. The starting materials
CgPH·BH3,3 CgPBr,3 PhobPH·BH3,4 PhobPBr,4 (o-Tol)2PCl,18
[PtCl2(1,5-cod)],19 [PtCl2(ButCN)2]20 and [PdCl2(NCPh)2]21 were
made according to literature methods. All other phosphines were
purchased from Strem, Aldrich or Acros. Commercial reagents
were used as supplied unless otherwise stated. Ph2PCl and Et2NH
were distilled prior to use. After purification all phosphines were
stored under argon in a glove box at room temperature. All
complexes were stored in air at room temperature.
n
(5 cm3). BuLi (1.6 M solution in hexanes, 0.58 cm3, 0.91 mmol)
was added dropwise at -78 ◦C. After 30 min, the resulting solution
was allowed to warm to room temperature and stirred for a further
1 h. The solutionwas recooledto -78 ◦C and a solution of PhobPCl
(0.13 g, 0.76 mmol) in THF (5 cm3) added dropwise over 2 min and
the mixture then allowed to warm to room temperature overnight.
The solvent was removed in vacuo to give a white solid which was
redissolved in THF (5 cm3) and stirred overnight with an excess of
HNEt2 (0.25 g, 0.34 ml, 3.6 mmol). The solvent and excess HNEt2
were then removed in vacuo. The resulting solid was dissolved in
Et2O (10 cm3) and washed with water (3 ¥ 5 cm3). The organic
phase was dried over MgSO4 and reduced to dryness in vacuo
to yield diphosphane 2 as a white powder (0.11 g, 0.40 mmol,
53%). Crystals of 2 suitable for X-ray diffraction were grown by
slow evaporation of it CDCl3 solution. Elemental analysis calcd
for C16H28P2: C, 68.06; H, 10.00. Found: C, 67.85; H, 10.21%. 31
P
NMR (162 MHz; CDCl3): d -45.9. 1H NMR (CDCl3): d 2.62–1.14
(m). 13C (CDCl3) d 33.1 (t, JCP = 6 Hz), 27.7 (br s), 24.6 (d, JCP
=
4 Hz), 23.4 (br s), 22.6.
Preparation of CgP–PPhob (3)
Preparation of CgP–PCg (1)
To a solution of CgPH (0.22 g, 1.0 mmol) in THF (10 cm3),
nBuLi (4.10 cm3, 1.6 M in hexane, 6.49 mmol) was added dropwise
over 10 min to a solution of CgPH.BH3 (1.61 g, 5.89 mmol) in
BH3·THF (1 M solution in THF, 1.20 cm3, 1.20 mmol) was
◦
added at 0 C and the mixture stirred for 1 h. All volatiles were
7142 | Dalton Trans., 2011, 40, 7137–7146
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removed in vacuo and the remaining white solid redissolved in THF
m, CH), 8.04 (1H, m, CH), 6.99–6.86 (6H, m, CH), 2.56 (1H, m,
(10 cm3). nBuLi (1.6 M solution in hexanes, 0.70 cm3, 1.12 mmol)
CH2), 2.52 (3H, s, CH3), 2.42 (3H, s, CH3), 1.97 (1H, dd, JHH
6.6 Hz, JHP 13.1 Hz, CH2), 1.71–1.58 (2H, dd, JHH = 3.7 Hz, JHP
=
=
◦
was added dropwise over 2 min at 0 C to give a straw-coloured
solution which was then added to a cooled solution (-78 ◦C)
of PhobCl (0.18 g, 1.00 mmol) in THF (10 cm3). The resulting
solution was allowed to warm to room temperature overnight.
The volatiles were then removed in vacuo to give a white solid
which was redissolved in THF (20 cm3) and stirred overnight with
an excess of HNEt2 (0.25 g, 0.34 cm3, 3.6 mmol). The solvent and
excess HNEt2 were removed in vacuo and the residue then dissolved
in Et2O (5 cm3) and washed with water (3 ¥ 5 cm3). The organic
phase was dried over MgSO4 and then reduced to dryness in vacuo
to yield diphosphane 3 as a white powder (0.11 g, 0.40 mmol,
53%). Crystals of 3 suitable for X-ray diffraction were grown by
slow evaporation of a hexane/CH2Cl2 (1 : 1) solution. ESI mass
spectrum: m/z 357 [M - H]+. 31P NMR (202 MHz, C6D6): d -34.7
13.2 Hz + dd, JHH = 3.4, JHP = 12.0 Hz, CH2), 1.49 (3H, s, CH3),
1.38 (3H, s, CH3), 1.11 (3H, d, JHP = 12.0 Hz, CH3), 1.00 (3H, d,
JHP = 11.7 Hz, CH3). 13C NMR (CDCl3): d 142.8 (dd, JCP = 38
and 28 Hz), 135.8 (dd, JCP = 21 and 6 Hz), 135.4 (d, JCP = 8 Hz),
135.2 (d, JCP = 4 Hz), 130.5 (dd, JCP = 5 and 5 Hz), 128.9, 126.1,
96.8, 96.4, 74.9 (dd, JCP = 17 and 9 Hz), 74.2 (dd, JCP = 31 and
7 Hz), 46.3 (d, JCP = 16 Hz), 40.3 (d, JCP = 13 Hz), 29.2 (d, JCP
=
20 Hz), 28.2 (d, JCP = 9 Hz), 27.8, 21.6 (d, JCP = 23 Hz), 21.3 (d,
JCP = 22 Hz).
Preparation of CgP–PCy2 (4c)
Diphosphane 4c was prepared similarly to 4a from CgPH.BH3
(1.03 g, 4.47 mmol) and Cy2PCl (1.04 g, 0.99 cm3, 4.47 mmol)
as a white solid in 38% yield. The sample was 91% pure, with 2%
P2Cy4 and 5% P2Cg2. HRMS (ESI): calcd for C22H39O4P2 429.2332,
found: 429.2318. 31P NMR (C6D6): d -2.9 (d, JPP = 311 Hz, PCy2),
-27.4 (d, JPP = 311 Hz, PCg); 1H NMR (300 MHz; C6D6): d 2.61–
0.83 (42H, m). 13C NMR (75 MHz; C6D6): d 96.7, 96.3, 75.1, 74.6
1
(d, JPP = 200 Hz), -34.8 (d, JPP = 200 Hz). H NMR (CDCl3): d
2.62–0.44 (24H, m, alkyl CH, CH2), 1.20 (3H, s, CH3), 1.14 (3H,
s, CH3). 13C (CDCl3) d 95.6, 95.3, 73.0–72.6 (m), 47.2, 44.6 (dd,
JCP = 8 and 7 Hz), 38.5 (dd, JCP = 7 and 5 Hz), 31.9 (dd, JCP
=
7 and 6 Hz), 31.6 (dd, JCP = 7 and 6 Hz), 28.9 (dd, JCP = 12 and
10 Hz), 27.6 (dd, JCP = 7 and 6 Hz), 26.8 (d, JCP = 2 Hz), 26.7 (dd,
JCP = 6 and 4 Hz), 26.0 (dd, JCP = 9 and 6 Hz), 24.3 (dd, JCP = 9
and 6 Hz), 21.9 (t, JCP = 3 Hz), 21.5, 10.0.
(m), 47.8 (d, JCP = 17 Hz), 40.8 (d, JCP = 6 Hz), 33.0 (d, JCP
=
22 Hz), 32.4, 32.2 (d, JCP = 3 Hz), 31.8 (quintet, JCP = 8 Hz), 31.2
(m), 31.0 (d, JCP = 2 Hz), 30.5 (d, JCP = 25 Hz), 29.0 (d, JCP
13 Hz), 28.5 (dd, JCP = 20 and 6 Hz), 28.0–27.3 (m), 26.5 (d, JCP
3 Hz), 26.3–25.9 (m).
=
=
Preparation of CgP–PPh2 (4a)
◦
To a cooled (-78 C) solution of CgPH.BH3 (0.51 g, 2.2 mmol)
Preparation of CgP–PtBu2 (4d)
n
in THF (10 cm3), BuLi (1.6 M in hexanes, 1.50 cm3, 2.4 mmol)
was added dropwise. After 30 min, the solution was allowed to
warm to room temperature and left to stir for 2 h. The solution
was then added to a cooled (-78 ◦C) solution of Ph2PCl (0.49 g,
0.41 cm3, 2.2 mmol) in THF (10 cm3) and then allowed to
warm to room temperature overnight. The 31P NMR spectrum
showed a mixture of boronated and non-boronated diphosphane.
Diethylamine (0.48 g, 0.70 cm3, 11.1 mmol) was added and the
solution stirred overnight. The solvent was then removed in vacuo
and methanol added (10 cm3) to the residue. The resulting white
solid product was filtered off, washed with methanol (3 ¥ 5 cm3)
and dried in vacuo (0.21 g, 0.53 mmol, 24%). This ligand was also
characterised by X-ray crystallography. HRMS (ESI) calcd for
C22H27O4P2 417.1394, found 417.1379. 31P NMR (C6D6) dP -18.5
Diphosphane 4d was prepared similarly to 4a from CgPH.BH3
(1.01 g, 4.41 mmol) and But2PCl (0.80 g, 0.84 cm3, 4.41 mmol) as
a white solid in 23% yield. HRMS (ESI): calcd for C18H35O3P2
361.2069, found 361.2056. 31P NMR (C6D6): d 43.7 (d, JPP
=
379 Hz, PBut2), -9.08 (d, JPP = 379 Hz, PCg). H NMR (300
MHz; CDCl3): d 2.80 (1H, d, JHP = 12.9 Hz, CH2), 2.12 (1H, ddd,
JHP = 1.2 and 12.9 Hz, JHH = 6.8 Hz, CH2), 1.81 and 1.74 (2H, d,
JHP = 12.9 Hz, dd, JHP = 12.9 Hz, JHH = 4.2 Hz, CH2), 1.65 (3H, d,
JHP = 12.0 Hz, CH3), 1.54 (3H, d, JHP = 12.9 Hz, CH3), 1.42–1.35
(24H, m, CCH3 + 2CH3); 13C NMR (75 MHz; CDCl3): d 96.6,
1
96.2, 75.2 (m), 74.6, 48.5 (d, JCP = 19 Hz), 40.7, 36.5 (d, JCP
=
38 Hz), 33.2 (d, JCP = 14 Hz), 31.7 (m), 29.9 (d, JCP = 12 Hz), 28.6
(m), 27.9 (d, JCP = 12 Hz).
1
(d, JPP = 189 Hz, PCg), -32.3 (d, JPP = 189 Hz, PPh2). H NMR
(C6D6) dH 7.98 (2H, t, JHH = 7.0 Hz, CH), 7.79 (2H, t, JHH = 7.0 Hz,
CH), 7.07–6.96 (6H, m, CH), 2.47 (1H, d, JHP = 13.2 Hz, CH2),
1.90 (1H, dd, JHP = 13.2 Hz, JHH = 6.22 Hz, CH2), 1.73–1.59 (2H,
Preparation of PhobP–PPh2 (5a)
To a cooled solution (0 ◦C) of Ph2PH (0.37 g, 0.34 cm3, 2.0 mmol)
in THF (8 cm3), BH3·THF (1 M solution, 2.20 cm3, 2.20 mmol) was
added dropwise over 5 min and the solution then allowed to warm
to room temperature. After 2 h the solution was cooled to -78 ◦C
and nBuLi (1.6 M solution in hexanes, 1.40 cm3, 2.24 mmol) was
added dropwise over 2 min. After 30 min, the resulting solution
was allowed to warm to room temperature an◦d stirred for a further
1 h. The solution was then recooled to -78 C and a solution of
PhobPCl (0.35 g, 1.98 mmol) in THF (5 cm3) added dropwise
over 5 min and the mixture stirred overnight. The solvent was
removed in vacuo to give a brown oil. The crude product was stirred
overnight with an excess of HNEt2 (0.50 g, 0.68 cm3, 7.2 mmol) in
THF (10 cm3). In situ 31P NMR showed all the borane protecting
group had been removed. The volatiles were then removed in vacuo
m, CH2), 1.52 (3H, s, CH3), 1.37 (3H, s, CH3), 1.11 (3H, d, JHP
=
11.7 Hz, CH3), 0.90 (3H, d, JHP = 12.1 Hz, CH3). 13C NMR (75
MHz, C6D6) d 135.6–134.7 (m, ArCH), 96.7 (s, OCO), 96.3 (s,
OCO), 74.6–73.6 (m, PCO), 45.7 (d, JCP = 15 Hz, CH2), 40.0 (d,
JCP = 11 Hz, CH2), 29.1–28.5 (m, CH3), 27.9 (d, JCP = 16 Hz, CH3).
Preparation of CgP–P(o-Tol)2 (4b)
Diphosphane 4b was prepared similarly to 4a from CgPH.BH3
(1.02 g, 4.45 mmol) and (o-Tol)2PCl (1.11 g, 4.45 mmol) as a white
solid in 41% yield. HRMS (ESI): calcd for C24H31O3P2 429.1756,
found 429.1743. 31P NMR (C6D6): d -23.8 (d, JPP = 207 Hz, PCg),
-50.4 (d, JPP = 207 Hz, P(o-Tol)2). 1H NMR (CDCl3): d 8.16 (1H,
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and the residue dissolved in Et2O (5 cm3) and washed with water
(3 ¥ 5 cm3). The combined organic phase was dried over MgSO4
and reduced to dryness in vacuo to yield diphosphane 5a as a white
gummy solid (0.44 g, 1.4 mmol, 67%). Crystals of 5a suitable for
X-ray diffraction were grown from a CH2Cl2 : hexane (1 : 1) solu-
tion. Elemental analysis calcd for C20H24P2: C, 70.17; H, 7.07%.
Found: C, 69.47; H, 7.41. HRMS (ESI): calcd for C20H25P2(O)
343.1383, found 343.1375. 31P NMR (162 MHz; CDCl3): d -15.3
Preparation of [PtCl2(6a)] (7a)
A solution of 6a, prepared from CgP–PPh2 (0.103 g, 0.256 mmol)
and DMAD (0.031 cm3, 0.036 g, 0.256 mmol) in CH2Cl2 (2
cm3) was added dropwise to a stirred solution of [PtCl2(1,5-cod)]
(0.096 g, 0.26 mmol) in CH2Cl2 (2 cm3). After 1 h, the solution
was reduced to ca. 1 cm3 and then Et2O was added dropwise to
precipitate the white solid product 7a which was filtered off and
dried in vacuo (0.114 g, 0.141 mmol, 55%). Elemental analysis calc
for 7a. 1.5CH2Cl2: C, 37.86; H, 3.77. Found: C, 38.19; H, 3.78%.
1
(d, JPP = 166 Hz), -36.7 (d, JPP = 166 Hz). H NMR (CDCl3):
d 7.65–7.18 (10H, m, ArH), 2.77–1.42 (14H, m, PhobylCH). 13
C
31P NMR (CDCl3): d 51.8 (s, JPtP = 3766 Hz, PPh2), 47.2 (s, JPtP
=
(CDCl3) d 136.6 (dd, JCP = 10 and 19 Hz), 134.3 (d, JCP = 7 Hz),
128.7, 128.6, 32.8 (d, JCP = 11 Hz), 28.1 (d, JCP = 13 Hz), 25.0 (dd,
JCP = 13 and 4 Hz), 23.3 (d, JCP = 4 Hz), 22.6.
1
3315 Hz, PCg). H NMR (CDCl3): d 7.94 (2H, m, ArCH), 7.72
(2H, m, ArCH), 7.45–7.63 (6H, m, ArCH), 3.88 (3H, s, OCH3),
3.52 (3H, s, OCH3), 2.93 (1H, d, JHP = 14.2 Hz, CH2), 1.93 (dd,
JHP = 18.9 and 14.29 Hz), 1.85 (dd, JHP = 26.6 and 13.9 Hz), 1.69
(4H, d, JHP = 16.37 Hz), 1.52 (6H, t, JHH = 8.67 Hz), 1.39 (3H, s).
13C NMR (CDCl3): d 166.0 (dd, JCP = 24 and 5 Hz), 161.1 (dd,
JCP = 22 Hz and 6 Hz), 156.0 (t, JCP = 24 Hz), 151.0 (t, JCP = 24 Hz),
134.1 (dd, JCP = 12 and 42 Hz), 132.8 (dd, JCP = 25 and 2 Hz), 128.9
(dd, JCP = 15 and 13 Hz), 125.3 (dd, JCP = 75 and 70 Hz), 97.9,
Preparation of PhobP–P(o-Tol)2 (5b)
Diphosphane 5b was made similarly to 5a from PhobPH (0.10 g,
0.76 mmol) and (o-Tol)2PCl (0.19 g, 0.76 mmol) in 69% yield as
a white solid. Elemental analysis calcd for C22H28P2: C, 74.56; H,
7.96. Found: C, 74.46; H, 7.81. HRMS (ESI): calcd for C20H25P2(O)
371.1688, found 371.1704. 31P NMR (CDCl3): d -18.4 (d, JPP
=
97.7, 76.4, 76.2, 53.8, 53.3, 40.6 (t, JCP = 5.5 Hz), 28.0 (d, JCP
8 Hz), 27.0, 26.7, 25.4 (d, JCP = 4 Hz).
=
171 Hz), -56.3 (d, JPP = 171 Hz). 1H NMR (CDCl3): d 7.74–6.99
(8H, m, ArH), 2.77–1.42 (14H, m, PhobylCH), 2.46 (6H, s, CH3).
13C (CDCl3) d 142.7 (br d, JCP = 25 Hz), 137.2 (br s), 134.1 (d,
Preparation of [PdCl2(6b)] (7b)
JCP = 16 Hz), 129.9 (d, JCP = 5 Hz), 128.3, 125.9, 32.8 (d, JCP
13 Hz), 28.8 (2C, dd, JCP = 12 and 4 Hz), 24.6 (dd, JCP = 17 and
5 Hz), 23.3 (d, JCP = 5 Hz), 22.6 (ArCH3, s), 21.6 (d, JCP = 19 Hz).
=
A solution of 6b, prepared from CgP–P(o-Tol)2 (0.053 g,
0.12 mmol) and DMAD (0.015 cm3, 0.018 g, 0.12 mmol) in CH2Cl2
(2 cm3) was added dropwise to a solution of [PdCl2(NCPh)2] (0.038
g, 0.099 mmol) in CH2Cl2 (2 cm3). After 1 h, the solution was re-
duced to ca. 1 cm3 and then Et2O was added dropwise to precipitate
the yellow solid product 7b which was filtered off and dried in vacuo
Preparation of PhobP–PCy2 (5c)
Diphosphane 5c was made similarly to 5a from Cy2PH (0.21 g,
0.99 mmol) and PhobPCl (0.18 g, 0.99 mmol) in 41% yield as a
waxy white solid. It was characterised by 31P NMR spectroscopy
only (CDCl3): d -22.4 (d, 1JPP = 179 Hz), -33.6 (d, 1JPP = 179 Hz).
(0.026 g, 0.035 mmol, 35%). 31P NMR (CDCl3): d 61.5 (d, JPP
=
7 Hz) 68.5 (d, JPP = 10 Hz) 68.9 (d, JPP = 7 Hz) 69.3 (d, JPP = 10 Hz).
Preparation of [PdCl2(6d)] (7d)
Preparation of PhobP–PtBu2 (5d)
A solution of 6d, prepared from CgP–PtBu2 (0.051 g, 0.141 mmol)
and DMAD (0.017 cm3, 0.020 g, 0.141 mmol) in CH2Cl2 (2 cm3)
was added dropwise to a solution of [PdCl2(NCPh)2] (0.043 g,
0.112 mmol) in CH2Cl2 (2 cm3). After 1 h, the solution was reduced
to ca. 1 cm3 and then Et2O was added dropwise to precipitate the
yellow solid product 7d which was filtered off and dried in vacuo
(0.035 g, 0.051 mmol, 46%). Elemental analysis calc for 7d: C,
42.40; H, 5.93. Found: C, 42.74; H, 5.66%. 31P NMR (CDCl3): d
68.0 (d, JPP = 9 Hz, PCg) 122.6 (d, JPP = 9 Hz, PBut2).
Diphosphane 5d was made similarly to 5a from PhobPH (1.00 g,
7.64 mmol) and Bu2PCl (1.37 g, 7.64 mmol) in 44% yield as a
t
white powder. Elemental analysis calcd for C16H32P2: C, 67.11;
H, 11.26. Found: C, 66.84; H, 11.04%. HRMS (ESI): calcd for
C16H33P2(O) 303.2001, found 303.2012. 31P NMR (CDCl3): d 16.7
(d, 1JPP = 199 Hz), -30.7 (d, 1JPP = 199 Hz). 1H NMR (CDCl3): d
2.77–1.10 (14H, m, PhobylCH), 1.23 (18H, d, CH3), JHP = 10 Hz).
13C (CDCl3) d 33.6 (dd, PCCH3, JCP = 27 and 8 Hz), 33.4 (d, JCP
=
13 Hz), 31.5 (dd, CCH3, JCP = 19 and 3 Hz), 27.8 (dd, JCP = 8 and
5 Hz), 27.3 (dd, JCP = 19 and 3 Hz), 22.8 (d, JCP = 5 Hz), 22.7.
Crystal structure determinations
X-Ray diffraction experiments on 1a, 2, 3, and 5a were carried
out at 100 K on a Bruker Kappa Apex II CCD diffractometer,
whilst 1b, 4a and 7c (as its toluene solvate) were carried out at
173 K on a Bruker SMART diffractometer, both using Mo-Ka
Diphosphination reactions to generate diphosphines 6a–d
Diphosphination reactions were carried out in toluene (1 cm3) by
mixing equimolar amounts (0.26 mmol) of diphosphane 4a–d and
DMAD at room temperature and the progress of the reactions
were monitored by 31P NMR spectroscopy. The products were
then used in situ for the preparation of complexes 7a–d. For 6a:
d -11.1 (d, JPP = 162 Hz, PPh2), -26.5 (d, JPP = 162 Hz, PCg).
For 6b: d -25.1 (d, JPP = 171 Hz, PCg), -26.7 (d, JPP = 171 Hz,
˚
radiation (l = 0.71073 A). All data collections were performed
using a single crystal coated in inert oil and mounted on a glass
fibre. Intensities were integrated22 from several series of exposures
in j and w calculated by the Apex II23 program after unit cell
determination for structures 1, 2, 3, and 5a, for structures 1b, 4a
and 7c·C6H5CH3 intensities were integrated24 from several series
of exposures measuring 0.3◦ in w. Absorption corrections were
based on equivalent reflections using SADABS,25 and structures
P(o-Tol)2). For 6c: d -6.2 (d, JPP = 169 Hz, PCy2), -28.9 (d, JPP
=
169 Hz, PCg). For 6d: d 27.9 (d, JPP = 185 Hz, PBut2), -31.6 (d,
JPP = 185 Hz, PCg).
7144 | Dalton Trans., 2011, 40, 7137–7146
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Table 1 Crystallographic data
Compound
1a
1b
2
3
4a
5a
7c·C6H5CH3
Colour, habit
Size/mm
Empirical formula C20H32O6.84P2
Colourless nugget Colourless block Colourless plate Colourless plate Colourless block Colourless nugget Colourless block
0.14 ¥ 0.11 ¥ 0.10 0.20 ¥ 0.20 ¥ 0.10 0.15 ¥ 0.14 ¥ 0.03 0.41 ¥ 0.19 ¥ 0.09 0.30 ¥ 0.20 ¥ 0.12 0.10 ¥ 0.09 ¥ 0.07 0.49 ¥ 0.26 ¥ 0.20
C20H32O8P2
462.40
C16H28P2
282.32
C18H30O3P2
356.36
C22H26O3P2
400.37
C20H24P2
326.33
C35H52Cl2O7P2Pt
912.70
M
443.77
Crystal system
Monoclinic
C 2/c
Monoclinic
C 2/c
Triclinic
P 1
Monoclinic
P 21/c
Orthorhombic
P ca21
25.664(5)
11.194(2)
7.1808(14)
90.00
90.00
90.00
2062.8(7)
4
0.230
Orthorhombic
P 212121
8.7796 (3)
12.3250(4)
16.0889(5)
90.00
90.00
90.00
1740.96(10)
4
0.245
Triclinic
P 1
¯
¯
Space group
˚
a/A
13.019(3)
8.4223(19)
20.509(5)
90.00
107.483(12)
90.00
2144.9(9)
4
0.241
12.0015(10)
12.7265(11)
14.6537(13)
90.00
104.510(2)
90.00
2166.8(3)
4
0.246
6.5859(7)
9.9499(11)
11.4318(12)
89.916(5)
89.400(5)
86.605(6)
747.76(14)
2
19.9995(5)
10.3237(2)
8.6944(2)
90.00
92.516(1)
90.00
1793.39(7)
4
0.255
11.051(3)
12.288(3)
15.346(4)
66.679(6)
85.658(9)
80.770(11)
1888.7(19)
2
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
V/A-3
Z
m/mm-1
T/K
0.273
100
15568/3456
3.986
173
20066/8550
100
20939/3160
173
6949/2494
100
29347/4112
173
22827/4751
100
11481/3999
Reflections:
total/independent
Rint
0.0446
0.0396, 0.0621
0.0223
0.0362, 0.0483
1.309, -0.258
0.0279
0.0391, 0.0435
1.809, -0.206
0.0302
0.0303, 0.0356
0.357, -0.331
0.0392
0.0339, 0.0357
0.455, -0.200
0.0487
0.0397, 0.0497
0.340, -0.311
0.0508
0.0222, 0.0239
1.102, -1.533
Final R1
Largest peak, hole 0.377, -0.268
(e A-3)
rc/g cm-3
1.374
1.417
1.254
1.320
1.289
-0.01(7)
1.245
-0.18(10)
1.605
Flack parameter
2
were refined against all Fo data with hydrogen atoms riding in
calculated positions using SHELXTL.26 A freely refining variable
was used to model the occupancy of O4 in 1a. Crystal structure
and refinement data are given in Table 1.
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Acknowledgements
We thank Rhodia, EPSRC and CCDC for studentships COST
action CM0802 ‘PhoSciNet’ for support and Johnson-Matthey
for a loan of precious metal compounds.
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7146 | Dalton Trans., 2011, 40, 7137–7146
This journal is
The Royal Society of Chemistry 2011
©