A phosphanyl-substituted benzo-1,3,2-dioxaborol as ambiphilic bifunctional Lewis donor-acceptor unit

Article abstract of DOI:10.1002/ejic.200800024

Condensation of 3-[(diphenylphosphanyl)methyl]benzene-1,2-diol (1) with phenyl boronic acid gave a phosphane-functionalised benzo-1,3,2-dioxaborol 3. The ability of this species to act as a Lewis base through the P-centered donor and as a Lewis acid throu

Full text of DOI:10.1002/ejic.200800024

FULL PAPER
DOI: 10.1002/ejic.200800024
A Phosphanyl-Substituted Benzo-1,3,2-Dioxaborol as Ambiphilic Bifunctional
Lewis Donor–Acceptor Unit
Samir Chikkali,[a] Silja Magens,[b] Dietrich Gudat,*[a] Martin Nieger,[c] Ingo Hartenbach,[a]
and Thomas Schleid[a]
Keywords: Phosphanes / Boranes / Lewis acids / Lewis bases / Donor–acceptor systems
Condensation of 3-[(diphenylphosphanyl)methyl]benzene-
1,2-diol (1) with phenyl boronic acid gave a phosphane-func-
tionalised benzo-1,3,2-dioxaborol 3. The ability of this spe-
cies to act as a Lewis base through the P-centered donor and
as a Lewis acid through the B-centered acceptor sites was
demonstrated by the reactions with (cod)PdCl2 and some ni-
trogen donors (4-dimethylaminopyridine, diaza-[2.2.2]-bicy-
clooctane, pyridine). These reactions yielded either palla-
dium–phosphane complexes or amine–borane adducts that
were characterised by spectroscopic data and, in some cases,
by single-crystal X-ray diffraction studies. Reactions of a Pd
complex of the phosphane-functionalised benzo-1,3,2-di-
oxaborol 3 with dabco, or of the dmap adduct of 3 with (cod)-
PdCl2, gave materials that were characterised by analytical
data and solid-state NMR spectroscopic data as triple Lewis
acid/base complexes and that contain both PǞPd and BǟN
dative bonds. Even though these adducts were unstable in
solution, the results of these experiments demonstrate the
ability of 3 to act as a bifunctional donor/acceptor ligand,
which is of potential use as a building block for main chain
organometallic polymers or multimetallic complexes.
(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2008)
able to act as a bifunctional ambiphilic ligand through the
P-centred donor and B-centred acceptor sites. We describe
here the synthesis of ambiphilic ligands of this type and
present a first investigation of their reaction behaviour
towards Lewis acids and bases. The results of these studies
may open a new avenue towards the construction of me-
tallopolymers and multimetallic complexes (Scheme 1).[7]
Introduction
Tertiary phosphanes that carry additional Lewis acid
functionalities are receiving increasing interest as ambi-
philic bifunctional ligands. The reaction behaviour of these
species has been found to depend significantly on the Lewis
acidity of the acceptor moiety: ligands for which the ac-
ceptor is a strong Lewis acid form stable metal complexes
through PǞM–ClǞB or PǞMǞB interactions[1] or un-
dergo unusual reactions such as the activation of dihydro-
gen.[2] In contrast, species featuring Lewis acid sites of
moderate acceptor power may serve as templates for direct-
ing catalytic reactions by precoordination of substrates with
complementary donor functionalities.[3,4]
Scheme 1.
Having recently begun to explore the chemistry of the
catechol phosphane 1,[5] we have demonstrated that its reac-
tion with boric acid B(OH)3 proceeds selectively at the diol
unit to give the borate-templated anionic diphosphane 2, Results and Discussion
which may bind as a trans-spanning bidentate ligand to a
Catechol phosphane 1 was synthesised as previously re-
univalent metal ion such as Ag+.[6] With regard to this be-
haviour, it was anticipated that reaction of 1 with phenyl
boronic acid PhB(OH)2 might give rise to an ambiphilic
phosphane-functionalised dioxaborol 3, which may then be
ported[5] by hydrophosphanation of dihydroxy benzalde-
hyde with diphenylphosphane, followed by reduction of the
resulting phosphane oxide with LiAlH4. Reaction of 1 with
1 equiv. phenyl boronic acid in CH2Cl2 for 1 h at room tem-
perature and subsequent evaporation of volatiles gave a
quantitative yield of a white solid which was identified as
analytically pure dioxaborol 3 by elemental analysis and
spectroscopic (NMR, MS) data. The broad 11B NMR sig-
nal [δ(11B) = 31.7 ppm] and the sharp 31P{1H} NMR signal
[δ(31P) = –11 ppm] are found in regions that are characteris-
[a] Institut für Anorganische Chemie, Universität Stuttgart,
Pfaffenwaldring 55, 70550 Stuttgart, Germany
E-mail: gudat@iac.uni-stuttgart.de
[b] Institut für Organische Chemie, Universität Stuttgart,
Pfaffenwaldring 55, 70550 Stuttgart, Germany
[c] Laboratory of Inorganic Chemistry, University of Helsinki,
A. I. Virtasen aukio 1, Helsinki, Finland
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S. Chikkali, S. Magens, D. Gudat, M. Nieger, I. Hartenbach, T. Schleid
FULL PAPER
tic for tricoordinate boronic esters[8] and free phosphanes, 25% (by integration of suitable NMR signals) of the cis
respectively, and indicate the absence of any inter- or intra- isomers. The 11B NMR spectrum of 6 contains a single
molecular phosphorus/boron donor–acceptor interactions. broad line [δ(11B) = 29 ppm], which does not change with
The ability of 3 to act as a bifunctional ligand was nonethe- time. This suggests that δ(11B) of both isomers does not
less demonstrated by the outcome of its reactions with cy- differ significantly. The signal is slightly more shielded than
clooctadiene palladium dichloride (4) and dimethylamino- that of 3, but still remains in the characteristic region of
pyridine (dmap, 5a) or diazabicyclo-[2.2.2]-octane (dabco, boronic esters with a trigonal-planar coordinated boron
5b).
atom.[8] The proton NMR spectra of both complexes dis-
Reaction of 0.5 equiv. 4 with 3 in thf produced a yellow play the expected signals for the phenyl and catechol pro-
solution. The formation of two reaction products that were tons. The signals for the aliphatic CH2 protons are clearly
later identified as cis- and trans isomers of complex 6 distinguishable and appear as doublets [δ = 4.34, J =
4
(Scheme 2) by 31P NMR spectroscopy was established. The 11.6 Hz (6); δ = 4.23, J = 11.6 Hz (7); J = |2JPH + JPЈH|]
same product mixture was alternatively accessible from re- for the cis isomers and as slightly more shielded pseudotrip-
action of the complexes cis/trans-7, which were easily ob- lets [δ = 4.20, J = 7.5 Hz (6); δ = 4.13, J = 8.4 Hz (7)] for
tained from an analogous reaction of 1 and 4 with 2 equiv. the trans isomers.
phenyl boronic acid. Isolation of the pure complexes trans-
Suitable crystals for a single-crystal X-ray diffraction
6 and trans-7 was accomplished by recrystallisation of the study of 7 were grown from a concentrated thf solution at
crude products remaining after evaporation of all volatiles +4 °C. The complex crystallises as a thf solvate with two
from the reaction mixtures from thf at +4 °C. The composi- solvent molecules per unit of 7 in a monoclinic unit cell
tion and identity of both products was established by ana- (space group P21). Each molecule of 7 displays two strong
lytical and spectroscopic studies and confirmed by single- OH···O hydrogen bonds (O4···O7 2.69 Å, O2···O5 2.70 Å)
crystal X-ray diffraction studies.
with the oxygen atoms of two solvent molecules (see Fig-
ure 1), whereas the remaining solvent molecules are trapped
in the periphery of the complex and display no significant
intermolecular interactions. A further pair of hydrogen
bonds (O2···O3#/O2#···O3 2.71 Å) connects two OH
groups of adjacent molecules and leads to the formation of
zig-zag chains of complexes connected by hydrogen bonds.
The palladium atom in each complex displays a square-
planar coordination geometry and is surrounded by two
mutually trans-positioned chlorine and phosphorus atoms
[P2–Pd1–P1 178.0(1)°, Cl1–Pd1–Cl2 178.6(1)°]. The dis-
tances between the metal and the phosphorus [Pd1–P1
2.337(1) Å, Pd1–P2 2.331(1) Å] and chlorine atoms [Pd1–
Scheme 2. Synthesis of the palladium complexes 6, 7 and the N-
donor complexes 8a,b [cod = 1,5-cyclooctadiene, Do = 4-dimethyl-
aminopyridine (in 8a) or diazabicyclo-(2.2.2)-octane (in 8b)].
The 31P NMR spectra of freshly prepared solutions of
crystalline samples of 6 and 7 display single sharp lines at
very similar chemical shifts [δ(31P) = 20.5 (trans-6),
19.1 ppm (trans-7)] that are characteristic of similar trans-
configured palladium diphosphane complexes.[9] The onset
of trans-/cis isomerisation leads to the appearance of ad-
ditional signals attributable to the cis isomers [δ(31P) = 30.6
(cis-6), 31.2 ppm (cis-7)] and produces within several hours
Figure 1. Molecular structure of trans-7 with two out of four sol-
vent molecules. O2# and O3# denote oxygen atoms of adjacent
molecules. Thermal ellipsoids are drawn at the 50% probability
level and H atoms except those of the OH groups have been omit-
ted for clarity. Hydrogen bonds are drawn as thin lines. Selected
bond lengths [Å] and bond angles [°]: Pd1–Cl1 2.299(1), Pd1–Cl2
2.306(1), Pd1–P1 2.337(1), Pd1–P2 2.331(1), Cl1–Pd1–P2 93.2(1),
Cl2–Pd1–P2 86.5(1), Cl1–Pd1–P1 85.1(1), Cl2–Pd1–P1 95.3(1), P2–
Pd1–P1 178.0(1), Cl1–Pd1–Cl2 178.6(1). Intermolecular distances
an equilibrium mixture that contains approximately 20– [Å]: O2···O5 2.695(6), O2···O3# 2.713(6), O4···O7 2.693(6).
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An Ambiphilic Bifunctional Lewis Donor-Acceptor Unit
Cl1 2.299(1) Å, Pd1–Cl2 2.306(1) Å] are normal and match the phenyl and catechol protons, further resonances that are
commonly found bond lengths[10] in trans-diphosphane attributable to the donor moieties. For 8a, the number and
palladium
dihalides
(Pd–P
2.34Ϯ0.03 Å,
Pd–Cl multiplicity of these signals is as expected (AAЈXXЈ spin
2.30Ϯ0.02 Å).
system and intense singlet for the aromatic and N-methyl
The complex 6 crystallises as a solvate with four mole- protons, respectively), whereas 8b displays only a single res-
cules of thf in a monoclinic unit cell in the space group onance accounting for all twelve protons of the donor moi-
P21/c (Figure 2). The discrete complexes have a crystallo- ety. The same effect is also observable in the 13C spectrum
graphic Ci symmetry and show no significant intermo- and indicates that the adduct exhibits a fluxional structure
lecular interactions. The palladium atom lies on a crystallo- in solution, which arises from chemical exchange between
graphic centre of symmetry and displays, as in 7, a square- the coordinating and non-coordinating nitrogen donor sites
planar coordination geometry with the phosphorus and in the dabco unit. Even though the available spectroscopic
chlorine atoms in
a trans arrangement. The Pd–Cl data provide no further information, it appears most likely
[2.298(1) Å] and Pd–P distances [2.332(1) Å] are identical that the exchange follows a dissociative mechanism and in-
to those in 7 within experimental error. The benzodiox- volves intermediate cleavage of the donor–acceptor bond.
aborol units display the same arrangement as that of the Formation of a thermodynamically and kinetically labile
catechol rings in 7 and point away from each other. The donor–acceptor adduct was also observed upon treatment
boron atom displays a trigonal-planar geometry in which of 3 with the weaker Lewis base pyridine. Quantitative
the endocyclic O1–B–O2 angle [110.9(5)°] is reduced and transformation of the free dioxaborol into the pyridine
the C20–B–O1/O2 angles [125.2(5)/123.8(5)°] are appropri- complex (as judged from the upfield shift of the 11B NMR
ately enlarged with respect to the ideal angle of 120°. The signal) required, in this case, the addition of a large excess
B1–O1/O2 [1.395(6)/1.402(6) Å] and B1–C20 [1.543(8) Å] of the Lewis base (approximately 6 equiv.), and the resulting
distances are in close agreement with the corresponding complex could not be isolated.
bond lengths in 2-phenyl-1,3,2-benzodioxaborol.[11]
Recrystallisation of 8a from a concentrated dichloro-
methane solution to which a few drops of thf had been
added produced colourless single crystals (space group
P21/c) of a solvate containing one molecule of thf per for-
mula unit. The crystal contains discrete molecules of 8a
(Figure 3) without significant intermolecular interactions.
The boron atom displays a distorted tetrahedral coordina-
tion geometry, which is characterised by a reduction in the
O1–B–O2 [105.2(5)°] and O1/O2–B–N1 angles [107.9(5)/
105.2(5)°] and a widening of the O1/O2–B–C20 [111.9(5)/
114.7(6)°] and C20–B–N1 [111.5(5)°] angles relative to the
tetrahedral angle of 109.4°.[12] The increase in the boron
coordination number relative to that of 3 induces a marked
lengthening of the B–O1/O2 and B–C20 bonds by some 8–
9 and 6 pm, respectively, which is in good agreement with
literature data.[11] The length of the formal donor–acceptor
bond [B–N1 1.609(9) Å] and the coplanar arrangement of
Figure 2. Molecular structure of trans-6. Thermal ellipsoids are
drawn at the 50% probability level and the H atoms and solvent
molecules (thf) have been omitted for clarity. Selected bond lengths
[Å] and bond angles [°]: Pd1–Cl1 2.298(1), Pd1–P1 2.332(1), B1–
O1 1.395(6), B1–O2 1.402(6), B1–C20 1.543(8), Cl1–Pd1–P1
86.3(1), Cl1–Pd1–P1# 93.7(1), P1–Pd1–P1# 180.0, Cl1–Pd–Cl1#
180.0, C20–B1–O1 125.2(5), C20–B1–O2 123.8(5), O1–B–O2
110.9(5).
The Lewis base complexes 8a,b were prepared by treating
a thf solution of 3 with 1 equiv. of the appropriate donor
and isolated in a quantitative yield after evaporation of the
solvent. Both species were characterised by analytical and
spectroscopic data, and the identity of 8a was further con-
firmed by a single-crystal X-ray diffraction study. The at-
tachment of the donor to the boron atom was indicated by
a pronounced upfield shift of the 11B NMR signals [δ(11B)
= 11 (8a), 15 ppm (8b)], which appear now in a spectral
region characteristic for tetracoordinate boron atoms;[8] the
Figure 3. Molecular structure of 8a. Thermal ellipsoids are drawn
at the 50% probability level and the H atoms and solvent molecules
(thf) have been omitted for clarity. Selected bond lengths [Å] and
bond angles [°]: B1–O1 1.475(8), B1–O2 1.498(8), B1–N1 1.609(9),
B1–C20 1.614(10), C7–P1 1.859(7), P1–C8 1.814(7), P1–C14
1.846(6), O1–B1–O2 105.2(5), O1–B1–N1 107.9(5), O2–B1–N1
105.2(5), O1–B1–C20 111.9(5), O2–B1–C20 114.7(6), N1–B1–C20
111.5(5), C8–P1–C14 101.5(3), C8–P1–C7 104.1(3), C14–P1–C7
31P NMR chemical shifts remain similar to that of free 3.
1
The H NMR spectra of 8a,b show, beside the signals for 96.7(3).
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S. Chikkali, S. Magens, D. Gudat, M. Nieger, I. Hartenbach, T. Schleid
FULL PAPER
the Me2N group and the pyridine ring of the donor moiety
are similar as in other known dmap–borane complexes
(average B–N bond length 1.62Ϯ0.03 Å[12]). The P–C bond
lengths and the pyramidal coordination geometry [sum of
C–P–C angle 303(1)°] are normal.
The findings described above stimulated us to investigate
whether 3 is also capable of forming two complementary
donor–acceptor interactions at the same time and can thus
act as a µ2-bridging ligand that can connect to a Lewis acid
and a Lewis base. The controlled synthesis of such a species
featuring multiple donor–acceptor bonds between different
Lewis acid/base pairs represents a challenge as it requires
the fine-tuning of the functionalities involved in order to
select the desired and to suppress the undesired Lewis acid/
base pairings. Since self complexation of 3 seems to be un-
favourable and PdII (even if it can form stable complexes
with nitrogen donors) normally has a preference to bind
phosphorus donor ligands, it appears that pairing of Pd–P/
B–N donor/acceptor sites is on the whole preferable, and
selective simultaneous coordination of a nitrogen donor
and a transition-metal (Pd) acceptor fragment to 3 should
thus be feasible.
The synthesis of the targeted adducts was attempted by
two different ways. In one approach, a thf solution of the
dioxaborol–amine adduct 8a was treated with 0.5 equiv.
(cod)PdCl2 in order to accomplish the formation of ad-
ditional Pd–P dative bonds. The reaction produced a yellow
precipitate, which was isolated by filtration and gave analyt-
ical data that are compatible with the expected composition
[PdCl2(8a)2]. The product failed to redissolve without de-
composing in organic solvents (see below) and was there-
fore further characterised by solid-state NMR spectroscopy.
The 11B MAS-NMR spectrum consists of a single, relatively
narrow (∆ν1/2 = 500 Hz) line, which is centred at 6 ppm and
displays the shape of a quadrupolar powder pattern (Fig-
ure 4 top). The position of this line provides clear evidence
that the tetrahedral coordination at boron is retained. The
31P{1H} CP/MAS-NMR spectrum displays a complex
pattern of several superimposed lines (Figure 4 middle),
Figure 4. 11B MAS NMR (top) and 31P{1H} CP/MAS-NMR (mid-
dle) spectrum of the solid adduct [PdCl2(8a)2] (middle). 31P{1H}
CP/MAS-NMR spectrum of the adduct 6·–1.2dabco (bottom).
which indicates that the solid contains chemically nonequiv- equiv. dabco per molecule of 6. The 11B MAS-NMR spec-
alent phosphane units in several distinguishable local envi- trum gave a signal that is centred at 5 ppm and displays a
ronments. Analysis of the isotropic chemical shifts – all similar lineshape as that of the previously mentioned
lines are in the range between 31 and 43 ppm – confirms dmap complex, thus disclosing that the tetracoordinate en-
that all signals are attributable to metal-coordinated phos- vironment at boron persists. Furthermore, the 31P{1H} CP/
phane ligands and that free phosphane moieties are absent. MAS-NMR spectrum shows a broad, unstructured line
The 11B and 31P NMR spectroscopic data, in combination, which extends over the region between 20 and 40 ppm (Fig-
further support the assignment of the product as complex ure 4 bottom) and indicates that the phosphorus coordina-
[PdCl2(8a)2]. The observed complexity of the 31P NMR tion to palladium likewise remains intact. On the basis of
spectrum is readily accounted for if one considers that a these data, we formulated the product as a chainlike,[13]
complex of this type may exist as a mixture of cis- and trans oligomeric array of alternating PdCl2 and dabco units that
isomers, each of which may form two diastereomers (owing are bridged by the ambiphilic bidentate donor 3. The chain
to the chiral nature of the tetracoordinate boron atoms) and structures are held together by dative PǞPd and BǟN in-
a variety of distinguishable rotamers.
teractions and are presumably terminated by dabco frag-
In a second approach, complex 6 was treated with ments.
2 equiv. dabco. This reaction likewise produced a yellow so-
Attempts aiming at recrystallisation of the crude prod-
lid, which was isolated in the same manner as before and ucts remained unsuccessful. Both materials were found to
1
may be formulated according to analytical and H NMR dissolve only in strongly donating solvents such as dmf or
spectroscopic data as an adduct containing approx. 1.2 dmso, and NMR spectra of these solutions gave evidence
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An Ambiphilic Bifunctional Lewis Donor-Acceptor Unit
for the occurrence of decomposition processes. Thus,
whereas the 11B NMR spectrum of a freshly prepared dmf
solution of the dmap adduct [PdCl2(8a)2] still displays a sin-
gle resonance with a similar chemical shift as that in the
solid state [δ(11B) = 10.6 ppm], the 31P{1H} NMR spectrum
shows, in addition to two signals at δ = 18.4 and 37.9 ppm,
which can be assigned to the phosphane ligands in the
trans- and cis-P2PdCl2 fragments, resonances that can be
assigned to the free phosphane 3 and a new product with
an AX-type spin system. The se signals at δ(31P) = 80.6 and
27.9 ppm (JPP = 30.7 Hz) are assigned to a cis-configured
palladium complex with two different phosphane li-
gands.[14] The same signals (except that for 3) were also vis-
ible in the 31P{1H} NMR spectrum of the dabco adduct. In
this case, however, the 11B NMR spectrum differed from
the spectrum of the solid in that a signal at much lower
field is observed [δ(11B) = 21–29 ppm, depending on the age
of the solution), the position of which clearly indicates the
Experimental Section
General Remarks: All manipulations were carried out under a dry
argon atmosphere, and solvents were dried by standard procedures
unless otherwise mentioned. The catechol phosphane 1 was pre-
pared as reported earlier.[5] Cyclooctadiene palladium dichloride
was prepared according to the literature,[16] and phenyl boronic
acid, 1,4-diazabicyclo-[2.2.2]-octane and dimethylaminopyridine
were commercially available and were used without further purifi-
cation. Solution NMR spectra were recorded on a Bruker Avance
400 spectrometer (1H: 400.1 MHz, 11B: 128.4 MHz, 13C:
100.5 MHz, 31P: 161.9 MHz) at 303 K unless mentioned otherwise;
chemical shifts were referenced to external tms (1H, 13C), 85%
H3PO4 (Ξ
=
40.480747 MHz, 31P), or BF3.OEt2 (Ξ
=
32.083974 MHz, 11B). Solid-state MAS-NMR spectra were re-
corded on a Bruker Avance 400 MHz NMR instrument with spin-
ning speeds between 3 and 14 kHz. Cross-polarisation with a ramp-
shaped contact pulse and mixing time between 3 and 5 ms was used
for signal enhancement in the CP/MAS experiments. 11B NMR
spectra were recorded without CP by using a Hahn-echo pulse se-
quence. Coupling constants are given as absolute values; prefixes i,
o, m, p denote phenyl ring positions of P-C6H5 substituents, C6H3
represents the catechol ring protons. EI-MS: Varian MAT 711,
70 eV. ESI-MS: Bruker Daltonics micrOTOF-Q. Elemental analy-
ses: Perkin–Elmer 2400CHSN/O Analyser; deviations from calcu-
lated values are, in the case of solvates, attributable to nonstiochio-
metric amounts of solvent. Melting points were determined in
sealed capillaries.
1
presence of a three-coordinate boron atom. The H NMR
spectrum displays signals attributable to the free amine (in-
tegration of suitable resonances allowed the confirmation
of a ratio of 1:1.2 for catechol phosphane/amine). The ob-
served spectroscopic data indicate that in solution extensive
dissociation of the solid adduct into 6 and dabco occurs;
direct evidence of the formation of a bifunctional adduct of
the ambiphile 3 is, however, provided by an ESI-MS analy-
sis, which displays, among several other signals, a low inten-
sity peak at m/z = 1211 with an isotope pattern indicative
of the composition [(dabcoǞ3Ǟ)2PdCl2 + H+]. Whereas
the dabco adduct is thus considered to dissociate in solution
primarily through cleavage of the dative B–N bond, the
data of the dmap complex suggest that in this case decom-
Diphenyl-(2-phenylbenzo[1,3,2]dioxaborol-4-ylmethyl)phosphane (3):
Phenyl boronic acid (245 mg, 2 mmol) was added to a solution of
1 (620 mg, 2 mmol) in CH2Cl2 (20 mL), and the reaction mixture
was stirred for 1 h. The volatiles were evaporated in vacuo to give
a quantitative yield of spectroscopically pure 3 as a colourless solid.
C25H20BO2P (394.22): calcd. C 76.12, H 5.11; found C 75.50, H
1
5.11. H NMR (CDCl3): δ = 8.00 (m, 2 H, BC6H5), 7.57 (m, 1 H,
plexation of the phosphane (presumably accompanied by BC6H5), 7.45 (m, 6 H, PC6H5), 7.35–7.25 (m, 6 H, BC6H5, PC6H5),
7.07 (ddd, 3JHH = 7.6 Hz, 4JHH = 1.3 Hz, JPH = 1.3 Hz, 1 H, C6H3),
the formation of halide bridges or coordination of dmap)
occurs. The formation of an unsymmetrical phosphane in
6.93 (t, 3JHH = 7.9 Hz, 1 H, C6H3), 6.82 (ddd, 3JHH = 7.6 Hz, 4JHH
= 1.3 Hz, JPH = 1.3 Hz, 1 H, C6H3), 3.62 (s, 2 H, CH2) ppm.
both cases suggests that additional processes, which pre-
13C{1H} NMR (CDCl3): δ = 148.0 (d, JPC = 1.7 Hz, C6H3), 146.9
sumably include cleavage of the dioxaborol ring,[14] also
(d, JPC = 4.0 Hz, C6H3), 138.1 (s, Ph), 137.8 (s, Ph), 134.9 (s, Ph),
133.0 (s, Ph), 132.7 (s, Ph), 132.1 (s, Ph), 128.7 (s, Ph), 128.3 (d,
take place.
JPC = 6.5 Hz, o-C), 128.0 (s, Ph), 123.8 (d, JPC = 7.5 Hz, m-C),
122.7 (d, JPC = 8.3 Hz, i-C), 122.4 (d, JPC = 1.4 Hz, p-C), 110.1 (d,
1
JPC = 2.5 Hz, p-C), 28.7 (d, JPC = 16.5 Hz, CH2) ppm. 31P{1H}
Conclusions
NMR (CDCl3): δ = –11.1 (s) ppm. 11B NMR (CDCl3): δ = 31.7
(br.) ppm. MS (EI, 70 eV): m/z (%) = 394.1 (100) [M+], 185.0
[Ph2P+].
It was shown that the phosphanyl-substituted benzodi-
oxaborol 3 may react both as a Lewis base and as a Lewis
acid by forming stable adducts through dative PǞPd and
BǟN bonds, respectively. Even bifunctional coordination
Palladium Bis[diphenyl-(2-phenylbenzo-1,3,2-dioxaborol-4-ylmeth-
yl)phosphane] Dichloride (6): (a) Phenyl boronic acid (122 mg,
1 mmol) was added to a solution of 7 (397 mg, 0.5 mmol) in thf.
with simultaneous formation of both types of donor–ac- The reaction mixture was stirred for 2 h at room temperature. The
volatiles were then evaporated in vacuo to produce a yellow powder
of spectroscopically pure 6 in quantitative yield. Suitable crystals
for a single-crystal X-ray diffraction study were obtained by
recrystallisation from a minimum amount of thf at +4 °C. Yield:
333 mg (69%). M.p. 240 °C (dec.). (b) (cod)PdCl2 (32.5 mg,
0.11 mmol) was added to solution of 3 (90 mg, 0.22 mmol) in thf.
The mixture was stirred for 2 h at room temperature. The volatiles
were then evaporated under reduced pressure to produce a yellow
powder, which was recrystallised from thf. The crystalline product
was collected by filtration and dried in vacuo. Yield: 83 mg (75%).
M.p. 240 °C (dec.). C50H40B2Cl2O4P2Pd (965.76): calcd. C 62.19,
ceptor interactions is, in principle, feasible, although the re-
sulting complexes could only be characterised by spectro-
scopic data in the solid state and were found to dissociate or
decompose in solution. Provided that the interplay between
donor and acceptor centres is further optimised and the
stability of the donor–acceptor interaction increased, the
extension of this chemistry may allow the rational design of
metallopolymers[15] or multimetallic complexes with a wide
structural complexity and diversity. Investigations to ac-
complish these goals are currently under way.
Eur. J. Inorg. Chem. 2008, 2207–2213
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2211

S. Chikkali, S. Magens, D. Gudat, M. Nieger, I. Hartenbach, T. Schleid
H 4.18; found C 61.2, H 4.68. H NMR (CDCl3): δ = 7.8–7.3 (m, Reaction of 6 with dabco: The donor dabco (16 mg, 0.14 mmol) was
FULL PAPER
1
2
C6H5), 7.1–6.7 (m, C6H3), 4.3 (d, JPH = 11.5 Hz, CH2 of cis iso-
mer), 4.2 (t, ΣJPH = 7.8 Hz, CH2 of trans isomer) ppm. 13C{1H}
NMR (CDCl3, only data of trans isomer given): δ = 147.9 (t, ΣJCP
added to a solution of 6 (70 mg, 0.07 mmol) in thf (6 mL). The
resulting mixture was stirred for 1 h during which a yellow precipi-
tate was formed. The volatiles were evaporated under reduced pres-
= 5.0 Hz, C6H3), 147.7 (t, JPC = 1.2 Hz, C6H3), 135.0 (s, Ph), 133.9 sure. The residue was suspended in thf (5 mL), and diethyl ether
3
(t, JPC = 6 Hz, m-C), 132.2 (s, Ph), 130.8 (s, Ph), 128.0 (s, Ph), (20 mL) was added. The supernatant liquid was decanted off, and
127.9 (t, JPC = 5 Hz, i-C), 125.3 (br., B–C), 124.8 (t, JPC = 2.4 Hz,
C6H3), 122.4 (s, C6H3), 119.0 (t, JPC = 2.0 Hz, C6H3), 110.8 (t, JPC
the remaining precipitate dried in vacuo to give 56 mg of a yellow–
orange powder. M.p. 167 °C. C50H40B2Cl2O4P2Pd·1.2dabco: calcd.
C 62.44, H 4.98, N 3.05; found C 61.39, H 5.14, N 2.92. 11B MAS
1
= 1.6 Hz, C6H3), 25.0 (t, JPC = 13 Hz, CH2) ppm. 31P{1H} NMR
(CDCl3): δ = 30.6 (cis isomer), 20.4 (trans isomer) ppm. 11B NMR NMR (solid): δiso = 5 ppm. 31P{1H} CP/MAS NMR (solid): see
(CDCl3): δ = 29.1 (br.) ppm.
Figure 4 bottom.
Palladium Bis[diphenyl-(2,3-dihydroxyphenylmethyl)phosphane] Di-
chloride (7): To a solution of 1 (200 mg, 0.64 mmol) in thf (20 mL)
was added (cod)PdCl2 (93 mg, 0.32 mmol). The reaction mixture
was stirred for 2 h at room temperature and then concentrated un-
der reduced pressure to half the total volume. Shiny yellow needle-
like crystals were obtained on stirring this solution overnight at
+4 °C. The crystals were isolated by filtration and dried in vacuo.
Yield: 240 mg (95%). M.p. 176 °C. C38H34Cl2O4P2Pd·thf (866.07):
calcd. C 58.25, H 4.89; found C 58.06, H 5.27. 1H NMR (CD3CN):
[PdCl2(8a)2]: (cod)PdCl2 (110 mg, 0.39 mmol) was added to a
stirred solution of 8a (400 mg, 0.78 mmol) in thf (20 mL). A yellow
precipitate began to separate after 5 min, and stirring was contin-
ued for 1 h. Diethyl ether (40 mL) was then added, and the yellow
precipitate was filtered off. Drying in vacuo for 3 h gave 352 mg
(yield 75%) of product. M.p. 191 °C. C64H60B2Cl2N4O4P2Pd
(1210.10): calcd. C 63.53, H 5.00, N 4.63; found C 63.00, H 4.92,
N 4.64. 11B MAS- and 31P{1H} CP/MAS-NMR spectra are dis-
played in Figure 4 top and middle. The solution NMR spectra of
freshly prepared samples showed signals attributable to a mixture
of cis/trans isomers of [PdCl2(8a)2] [11B NMR: δ = 10.6 ppm;
31P(1H) NMR: δ = 37.9 (cis isomer), 18.4 (trans isomer) ppm] in
addition to signals for decomposition products. The intensity of
the signal for the decomposition products increased upon standing.
2
δ = 7.8–7.1 (m, Ph), 7.0–7.65 (m, C6H3), 4.23 (d, JPH = 11.6 Hz,
CH2 of cis isomer), 4.13 (t, Σ2JPH = 8.0 Hz, CH2 of trans isomer);
3.77 (m, 4 H, thf), 1.93 (m, 4 H, thf) ppm. 13C{1H} NMR (CD3CN,
only data of trans isomer given): δ = 145.3 (t, ΣJCP = 2.1 Hz, C6H3),
144.6 (t, ΣJCP = 5.8 Hz, C6H3), 134.8 (t, JPC = 6.1 Hz, i-C), 131.7
(s, Ph), 130.3 (m, ΣJPC = 45.9 Hz, C6H3), 128.9 (t, ΣJPC = 10.2 Hz,
Ph), 123.8 (t, ΣJPC = 5.8 Hz, C6H3), 120.9 (t, ΣJPC = 2.6 Hz, C6H3),
120.4 (s, C6H3), 114.7 (t, ΣJCP = 2.8 Hz, C6H3), 68.3 (s, thf), 26.2 (s,
thf), 25.3 (t, JPC = 13.9 Hz, CH2) ppm. 31P{1H} NMR (CD3CN): δ
= 32.2 (cis isomer), 18.7 (trans isomer) ppm.
Crystal Structure Study: The single-crystal X-ray diffraction studies
of trans-6, trans-7 and 8a were carried out on a Bruker-Nonius
Kappa-CCD diffractometer at 123(2) K using Mo-Kα radiation (λ
= 0.71073 Å). Direct Methods (SHELXS-97[17]) were used for
structure solution, and full-matrix least-squares refinement on F2
(SHELXL-97[17]). H atoms were localised by difference Fourier
synthesis and refined by using a riding model.
Diphenyl-(2-phenylbenzo[1,3,2]dioxaborol-4-ylmethyl)phosphane-3-
(dimethylaminopyridine) (8a): The donor dmap (244 mg, 2 mmol)
was added to a solution of 3 (790 mg, 2 mmol) in CH2Cl2. The
reaction mixture was stirred for 1 h. Evaporation of the solvent
under reduced pressure and drying of the colourless residue in
vacuo gave 980 mg of 8a (yield 95%). M.p. 167 °C. C32H30BN2O2P
(516.39): calcd. C 74.43, H 5.86, N 5.43; found C 74.20, H 5.93, N
5.41. 1H NMR (CDCl3): δ = 8.25 (m, 2 H, dmap), 7.55–7.40 (m, 6
6: Yellow-orange crystals, C50H40B2Cl2O4P2Pd·2thf, M = 1109.89,
crystal size 0.20ϫ0.10ϫ0.05 mm, monoclinic, space group P21/c
(No. 14): a = 11.7333(7) Å, b = 22.9485(17) Å, c = 10.3897(5) Å, β
= 111.424(4) °, V = 2604.2(3) Å3, Z = 2, ρ(calcd.) = 1.415 Mgm–3,
F(000) = 1144, µ = 0.572 mm–1, 22106 reflections (2θmax = 50°),
4480 unique [Rint = 0.102], 322 parameters, 66 restraints, R1
[IϾ2σ(I)] = 0.048, wR2 (all data) = 0.088, GooF = 0.862, largest
diff. peak and hole 0.672 and –0.429 eÅ–3.
3
H, C6H5), 7.40–7.20 (m, 9 H, C6H5), 6.62 (ddd, JHH = 7.6 Hz,
4JHH = 1.3 Hz, JPH = 1.3 Hz, 1 H, C6H3), 6.50 (m, 2 H, dmap),
3
3
6.48 (dd, JHH = 7.6 Hz, 7.8 Hz, 1 H, C6H3), 6.39 (ddd, JHH
=
7.6 Hz, 4JHH = 1.3 Hz, JPH = 1.3 Hz, 1 H, C6H3), 3.5 (s, 2 H, CH2),
3.01 (s, 6 H, dmap) ppm. 31P{1H} NMR (CDCl3): δ = –17.2 ppm.
11B NMR (CDCl3): δ = 11.1 (br.) ppm.
7: Yellow–orange crystals, C38H34Cl2O4P2Pd·4thf, M = 1082.31,
crystal size 0.5ϫ0.3ϫ0.1 mm, monoclinic, space group P21: a =
10.2633(2) Å, b = 22.7369(4) Å, c = 11.6400(2) Å, β = 112.586(1)°,
V = 2507.93(8) Å3, Z = 2, ρ(calcd.) = 1.433 Mgm–3, F(000) = 1128,
µ = 0.595 mm–1, 42973 reflections (2θmax = 56.54°), 12092 unique
[Rint = 0.113, Rσ = 0.087], 749 parameters, 1 restraint to fix the
origin, flack parameter x = 0.51(2), therefore refined as inversion
twin, R1 [IϾ2σ(I)] = 0.053, wR2 (all data) = 0.126, GooF = 1.032,
largest diff. peak and hole 1.27 and –1.46 eÅ–3.
Diphenyl-(2-phenylbenzo[1,3,2]dioxaborol-4-ylmethyl)phosphane-3-
[1,4-azabicyclo(2.2.2)octane] (8b): The donor dabco (160 mg,
1.4 mmol) was added to a solution of 3 (550 mg, 1.4 mmol) in thf.
The reaction mixture was stirred for 1 h. Evaporation of the solvent
under reduced pressure and drying of the colourless residue
in vacuo gave 664 mg of 8b (yield 92%). M.p. 132 °C.
C31H32BN2O2P·thf (578.50): calcd. C 72.67, H 6.97, N 4.84; found
C 71.97, H 6.76, N 4.49. 1H NMR (CDCl3): δ = 7.66 (m, 2 H,
BC6H5), 7.48 (m, 4 H, PC6H5), 7.36–7.21 (m, 9 H, BC6H5, PC6H5),
8a: Colourless crystals, C32H30BN2O2P·thf, M = 588.46, crystal size
0.12ϫ0.06ϫ0.03 mm, monoclinic, space group P21/c (No. 14): a
= 14.7942(4) Å, b = 9.5746(4) Å, c = 22.8934(7) Å, β = 93.558(2) °,
V = 3236.57(19) Å3, Z = 4, ρ(calcd.) = 1.208 Mgm–3, F(000) =
1248, µ = 0.122 mm–1, 10492 reflexes (2θmax = 50°), 5703 unique
[Rint = 0.145], 390 parameters, 96 restraints, R1 [IϾ2σ(I)] = 0.120,
wR2 (all data) = 0.227, GooF = 1.103, largest diff. peak and hole
0.385 and –0.335 eÅ–3.
2
6.68–6.51 (m, 3 H, C6H3), 3.73 (m, thf), 3.51 (d, JPH = 1 Hz, 1 H,
CH2), 2.80 (s, 12 H, dabco), 1.83 (m, thf) ppm. 13C{1H} NMR
(CDCl3): δ = 150.9 (d, JPC = 1.7 Hz, C6H3), 149.6 (d, JPC = 4.3 Hz,
1
C6H3), 139.2 (d, JPC = 16 Hz, i-C), 133.5 (s, Ph), 133.0 (d, JPC
=
18.6 Hz, m-C), 128.4 (s, p-C), 128.3 (d, JPC = 6.4 Hz, o-C), 128.1
(s, Ph), 127.3 (s, Ph), 121.2 (d, JPC = 8.0 Hz, C6H3), 119.5 (d, JPC
= 9.2 Hz, C6H3), 119.3 (d, JPC = 1.5 Hz, C6H3), 107.7 (d, JPC
=
CCDC-672200 (6), CCDC-672366 (7), CCDC-672201 (8a) contain
2.5 Hz, C6H3), 44.8 (s, dabco), 28.8 (d, 1JPC = 14.8 Hz, CH2) ppm. the supplementary crystallographic data for this paper. These data
31P{1H} NMR (CDCl3): δ = –12.0 ppm. 11B NMR (CDCl3): δ = can be obtained free of charge from The Cambridge Crystallo-
14.9 (br.) ppm.
2212
graphic Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
www.eurjic.org
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 2207–2213

An Ambiphilic Bifunctional Lewis Donor-Acceptor Unit
[8]
P. Diehl, E. Fluck, R. Kosfeld, Nuclear Magnetic Spectroscopy
of Boron Compounds, Springer Verlag, Berlin, 1978, p. 144.
Acknowledgments
[9]
D. J. Brauer, P. Machnitzki, T. Nickel, O. Stelzer, Eur. J. Inorg.
Chem. 2000, 65–73.
Result of a query in the CSD for complexes trans-[Pd-
We thank Dr. J. Opitz, J. Trinkner and K. Wohlbold (Institut für
Organische Chemie, Universität Stuttgart) for recording the mass
spectra. M. N. thanks the DAAD for financial support. This work
was financially supported by the Deutsche Forschungsgemein-
schaft.
[10]
[11]
[12]
(PR3)2X2].
F. Zettler, H. D. Hausen, H. Hess, Acta Crystallogr. 1974, 3,
1876–1878.
W. Clegg, A. J. Scott, F. E. S. Souza, T. B. Marder, Acta Crys-
tallogr. 1999, 5, 1885–1888. Result of a query in the CSD for
compounds dmapǞBX3.
A mixture of chainlike and cyclic structures cannot be ruled
out.
In view of the fact that chelate complexes of P,O-chelating
phosphanes normally display a strong deshielding of δ(31P) (see
ref.[9]), it appears likely that cleavage of the dioxaborol ring and
additional coordination of a phenolate moiety of one phos-
phane ligand to Pd has occurred.
The synthesis of a related P–M/B–N coordination polymer
arising from interaction of a phosphaazaadamantane ruthe-
nium complex and phenyl boroxine was recently reported: B. J.
Frost, C. A. Mebi, P. W. Gingrich, Eur. J. Inorg. Chem. 2006,
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Received: January 9, 2008
Published Online: March 27, 2008
Eur. J. Inorg. Chem. 2008, 2207–2213
© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
2213