On the synthesis and coordination properties of N-aryl-substituted 1, 3, 2-diazaphospholidine-4, 5-diimines

Article abstract of DOI:10.1002/zaac.201200542

New 1, 3, 2-diazaphospholidine-4, 5-diimines were synthesized by condensation of lithiated oxalamidines with PCl₃ or PhPCl ₂, and characterized by spectral and analytic data. The products react selectively with [(nbd)W(CO)₄], [Mo(CO)₆], or [(PhCN)₂PdCl₂] to give stable complexes, in which the heterocycle binds as chelating, bidentate ligand through the nitrogen atoms of the diimine unit. Formation of P-bound or dinuclear complexes was not observed. Reaction with PCl₃ or AsCl₃ in the presence of SnCl ₂ as reducing agent was unspecific. Evidence for the formation of bicyclic products arising from formal [4+1] cycloaddition between the diimine unit and a transient pnictogen(I) species was not obtained, and only a diimine complex of SnCl₄ was isolated in moderate yield. Single-crystal X-ray diffraction studies reveal that coordination of the diimine unit induces a substantial structural distortion of the ligand framework, which allows to explain the occurrence of substantial ³¹P coordination shifts despite the absence of a direct metal-phosphorus bond. Copyright

Full text of DOI:10.1002/zaac.201200542

ARTICLE
DOI: 10.1002/zaac.201200542
On the Synthesis and Coordination Properties of N-Aryl-substituted
1,3,2-Diazaphospholidine-4,5-diimines
Georgios Mourgas,[a] Ioannis Tiritiris,[b] Martin Nieger,[c] and Dietrich Gudat*[a]
Keywords: Phosphorus heterocycles; Nitrogen heterocycles; N-ligands; Coordination modes; Amidines
Abstract. New 1,3,2-diazaphospholidine-4,5-diimines were synthe-
sized by condensation of lithiated oxalamidines with PCl3 or PhPCl2,
and characterized by spectral and analytic data. The products react
selectively with [(nbd)W(CO)4], [Mo(CO)6], or [(PhCN)2PdCl2] to
give stable complexes, in which the heterocycle binds as chelating,
bidentate ligand through the nitrogen atoms of the diimine unit. Forma-
tion of P-bound or dinuclear complexes was not observed. Reaction
with PCl3 or AsCl3 in the presence of SnCl2 as reducing agent was
unspecific. Evidence for the formation of bicyclic products arising
from formal [4+1] cycloaddition between the diimine unit and a tran-
sient pnictogen(I) species was not obtained, and only a diimine com-
plex of SnCl4 was isolated in moderate yield. Single-crystal X-ray
diffraction studies reveal that coordination of the diimine unit induces
a substantial structural distortion of the ligand framework, which al-
lows to explain the occurrence of substantial 31P coordination shifts
despite the absence of a direct metal-phosphorus bond.
known to form stable chelate complexes with various transition
metals.[11] Consequently, 2 can be regarded as potential ditopic
ligand, whose rigid molecular skeleton orientates both donor
sites into opposite directions in space. Specimens of this type
have been denoted as Janus-head ligands[12] and are attracting
interest due to their ability to accommodate two different metal
atoms in close spatial proximity.[13]
Herein we report on the synthesis of further derivatives of
2 featuring both P–Cl and P–Ph substituents, and on first stud-
ies of the coordination properties of these species. Further-
more, we have also explored the feasibility of a [1+4] cycload-
dition between the 1,2-diimine unit and a transient P(I) spe-
cies[14] for the construction of a fused heterocyclic ring system
(Scheme 1).
Introduction
1,3,2-Diazaphospholidines (1) are N-heterocyclic phospha-
nes that make not only viable precursors for reactive phos-
phenium ions (in case of X = halide),[1] but attract currently
growing attention as ligands for catalytically active transition
metal complexes. P-Chloro- and P-phenyl-substituted diaza-
phospholidines have thus been applied in Suzuki-Miyaura[2] or
Mizoroki-Heck cross-coupling reactions.[3] Chiral diazaphos-
pholidines are useful ligands in enantioselective addition or
substitution reactions.[4] Bis-diazaphospholidines featuring two
rings connected via a suitable spacer unit have excellent che-
lating properties[4,5] and chiral derivatives thereof were used
in asymmetric hydroformylation[6] or allylic alkylation reac-
tions.[7]
The diazaphospholidine ligands used to date lack any func-
tional modification of their C2N2 backbone, and the phos-
phorus atom remains thus the only metal binding site in the
ring. We have recently prepared a 1,3,2-diazaphospholidine-
4,5-diimine (2),[8] which combines the P-donor function with
two exocyclic imine functionalities that make up an oxalamid-
ine unit.[9] Oxalamidines are, like diimines in general,[10] well
Scheme 1. R = Alkyl, Aryl; X = Cl, F, NMe2, Ph, OPh; R1 = 2,6-
iPr2C6H3 (Dipp), R2 = 2,6-Me2C6H3 (Dmp).
* Prof. Dr. D. Gudat
Fax: +49-71168564241
E-Mail: gudat@iac.uni-stuttgart.de
[a] Institut für Anorganische Chemie
University of Stuttgart
Pfaffenwaldring 55
Results and Discussion
70550 Stuttgart, Germany
[b] Institut für Organische Chemie
University of Stuttgart
The 1,3,2-diazaphospholidine-4,5-diimines (5, 6) were pre-
pared using the same procedure that had previously been re-
ported for 2.[8] Oxalamidine precursors 3 and 4 were synthe-
sized as described by Beckert et al..[15] In order to avoid prob-
lems arising from the formation of mixtures of constitutional
isomers, we choose specimen with identical substituents on all
Pfaffenwaldring 55
70550 Stuttgart, Germany
[c] Laboratory of Inorganic Chemistry
Department of Chemistry
University of Helsinki
P.O Box 55 (A.I. Virtasen aukio1)
00014 Helsinki, Finland
Z. Anorg. Allg. Chem. 2013, 639, (3-4), 517–523
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
517

G. Mourgas, I. Tiritiris, M. Nieger, D. Gudat
ARTICLE
nitrogen atoms. Conversion into the target heterocycles 5 and
6 was accomplished by metalation with two equivalents of bu-
tyllithium at –78 °C, followed by slow addition of the appro-
priate dichlorophosphane (Scheme 2). The products were iso-
lated as moisture and air sensitive, pale yellow powders, and
characterized by analytical and spectroscopic data. The P-
chloro derivative 6 displays sharp signals in the 1H NMR spec-
trum, whereas the signals of the P-phenyl derivative 5 are sig-
nificantly broadened, presumably as a consequence of hin-
dered rotation of the N-aryl moieties.[8] The 31P chemical shifts
of 5 (δ31P = 90.1) and 6 (δ31P = 134.6, cf. δ31P = 134 for 2[8]
)
are smaller than those of other known 1,3-diarylated 2-phenyl-
(δ31P around 110[16]) or 2-chloro-1,3,2-diazaphospholidines
(δ31P = 137–155[17]), respectively; this common trend suggests
that the shielding is presumably a characteristic signature of
the imine substitution.
Figure 1. Molecular structure of 5. Thermal ellipsoids are drawn at
50% probability level, hydrogen atoms are omitted for clarity. Selected
bond lengths /Å and angles /°: P1–C38 1.824(2), P1–N5 1.727(1), P1–
N2 1.737(1), C3–C4 1.510(2), C3–N2 1.404(2), C4–N5 1.383(2), C3–
N3 1.268(2), C4–N4 1.268(2), N2–P1–C38 104.34(7), N5–P1–C38
102.67(8), N2–P1–N5 89.66(7).
+30 ppm but no sign of coupling to a magnetically active 183
W
nucleus, (ii) two equally intense 13C NMR signals attributable
to the carbon atoms of carbonyl ligands at δ13C = 213, 191,
(iii) a shift of the ν(C=N) band in the IR spectrum from
1651 cm–1 to 1565 cm–1 in 5, and (iv) a characteristic pattern
of ν(CO) vibrational modes between 1830–1985 cm–1[18] in-
dicative of a cis-W(CO)4 unit. These findings led to the hy-
pothesis that the metal atom binds via the diimine unit rather
than the phosphorus lone-pair, which was corroborated by the
independent synthesis of 7 via base-induced condensation of a
preformed amidine complex [(3)W(CO)4] with PhPCl2. For-
mation of an analogous molybdenum complex 8 was also ob-
served in the reaction of 5 with [Mo(CO)6] but required longer
reaction times.
Scheme 2. Synthesis of 1,3,2-diazaphospholidin-4,5-diimines 5, 6 (3,
5: R = Dmp, X = Ph; 4, 6: R = Mes, X = Cl).
Single crystals of 5 were obtained from toluene at –20 °C
and characterized by a single-crystal X-ray diffraction study
(Figure 1). The crystal contains isolated molecules whose most
obvious attribute is the different configuration of the two imine
double bonds. This structural motif had already been noted for
2,[8] and serves presumably to minimize steric strain between
the bulky N-aryl moieties. The coordination around the endo-
cyclic nitrogen atoms has to be described as essentially planar
[sum of bond angles 354.0(2)° for N2 and 359.1(2)° for N5].
The phosphorus atom exhibits the same pyramidal coordina-
tion [sum of bond angles 296.7(2)°] as in other diazaphosphol-
idines.[8,17] The C3–C4 distance [1.510(2) Å] represents a typi-
cal single bond value. The P1–N2 and P1–N5 distances
[1.727(1)–1.737(1) Å] are slightly longer than in 2, whereas
the difference in the formal carbon–nitrogen single [C4–N5/
C3–N2 1.383(2)–1.404(2) Å] and double bond lengths
[C3–N3/C4–N4 1.268(2) Å] is somewhat less pronounced.
These features suggest that π conjugation in the amidine units
has increased at the expense of the n(N)–σ*(PX) hyperconju-
gative interaction in the NPN unit.
Scheme 3. Synthesis of 1,3,2-diazaphospholidine-4,5-diimine com-
plexes 7–9 (5, 7, 8: R = Dmp, X = Ph; 6, 9: R = Mes, X = Cl;
(L)2M(CO)4 = (norbornadiene)W(CO)4, Mo(CO)6).
In order to explore the coordination properties of com-
pounds 5 and 6 we chose to study reactions with low valent
metal carbonyls {[(nbd)W(CO)4], [Mo(CO)6]; nbd
=
norbornadiene} and [(PhCN)2PdCl2], whose central metal
The molecular structures of complexes 7 and 8 were con-
atoms [Mo(0), W(0), PdII] are known to form stable complexes firmed by single-crystal X-ray diffraction studies on samples
with both phosphane and diimine donors. Complex 7 obtained by crystallization from toluene at –20 °C. The molec-
(Scheme 3) was obtained after refluxing 5 with [(nbd)W(CO)4] ular structure of 7 is displayed in Figure 2; the structure of 8
in toluene for 2 h. The product was isolated after work-up is essentially identical and is not shown. The octahedral coor-
as red, crystalline solid and characterized by analytical and dination environment at the metal atom is distinguished by a
spectroscopic data. Prominent spectral features include the ob- strong deflection of the two mutually trans-positioned carb-
servation of (i) a 31P NMR signal with a coordination shifts onyls from an ideal linear arrangement [C1C–W–C1D
Δδ31P(coord) = δ31P(complex) – δ31P(ligand) of approx. 164.9(2)° for 7, 164.6(2)° for 8]. This distortion exceeds that
518
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 517–523

N-Aryl-substituted 1,3,2-Diazaphospholidine-4,5-diimines
in other [(diimine)M(CO)4] complexes, where C–M–C angles
range between 170 and 172°,[11,19] and is presumably attribut-
able to repulsive interactions between the carbonyls and the N-
aryl groups. The M–N distances and the flat envelope confor-
mation of the chelate ring are similar as in other known di-
imine complexes (M–N 2.21–2.28 Å[11,19]). The metal coordi-
nation induces lengthening of P–N distances [1.748(4)–
1.757(3) Å] and further levelling of formal carbon–nitrogen
single [1.375(6)–1.386(7) Å] and double bonds [1.282(7)–
1.302(8) Å] as compared to 5 [P–N 1.727(1)–1.737(1) Å;
C–N 1.383(2)–1.404(2) Å, C=N 1.268(2) Å]. In combination
with the pronounced red shift of the ν(C=N) mode in the IR
spectrum, these features suggest that the metal coordination
further enhances the π electron conjugation in the amidine
moieties, but diminishes the hyperconjugation in the NPN unit
of the ligand. As these changes must be considered to exert a
perceptible change in the local electron distribution around the
phosphorus atom, it is easily understood how even the remote
binding of a metal atom can induce a substantial 31P coordina-
tion shift.
Figure 3. Molecular structure of 9. Thermal ellipsoids are drawn at
50% probability level, hydrogen atoms are omitted for clarity. Selected
bond lengths /Å and angles /°: P1–Cl3 2.075(1), P1–N4 1.721(1), P1–
N3 1.718(1), C1–N3 1.376(1), C2–N4 1.378(1), C1–C2 1.498(1), C1–
N1 1.289(1), C2–N2 1.282(1), N2–Pd1 2.046(1), N1–Pd1 2.052(1),
Pd1–Cl2 2.278(1), Pd1–Cl1 2.280(1), N4–P1–Cl3 101.55(2), N3–P1–
Cl3 101.01(2), N4–P1–N3 91.40(2), N2–Pd1–N1 80.96(2), Cl1–Pd1–
N1 93.92(2), Cl2–Pd1–N2 93.43(1), Cl2–Pd1–Cl1 92.08(2).
As expected, the palladium atom is coordinated by two
chlorides and the nitrogen atoms of the diimine unit, and exhi-
bits the typical square-planar coordination expected for a cen-
tral PdII(d8) atom. The structural features of the diimine-palla-
dium moiety match those of related diimine complexes like
[20]
[bis(2,6-diisopropyl-phenyl)-1,4-diazabutadiene]-PdCl2
or
2,6-iPr-BIAN-PdCl2 (BIAN = bis-iminoacenaphthen).[21] The
structural features of the ligand are closely similar to those of
compounds 7 and 8. As there, the coordination environment at
the endocyclic nitrogen and phosphorus atoms can be de-
scribed as planar [sum of bond angles 356.5(1)° at N4 and
358.3(6)° at N3] and pyramidal [sum of bond angles 294.0(6)°
at P1], respectively. A further shortening of the P–Cl bond
[P1–Cl3 2.075(1) Å] with respect to 2 [P–Cl 2.127(2) Å[8]] is
offset by a lengthening of the adjacent P–N bonds [P1–N4
1.721(1) Å, P1–N3 1.718(1) Å vs. 1.700(4) Å and 1.708(5) Å
in 2[8]] and a similar bond length equalization in the amidine
as for 7 and 8.
Figure 2. Molecular structure of 7 (M =W). Thermal ellipsoids are
drawn at 50% probability level, hydrogen atoms are omitted for clarity.
Selected bond lengths /Å and angles /° (values in brackets denote ap-
propriate data for 8, M = Mo): P1–C6 1.824(4) [1.832(6)], P1–N5
1.756(5) [1.750(5)], P1–N2 1.748(4) [1.757(5)], C3–N2 1.384(7)
[1.378(8)], C4–N5 1.375(6) [1.386(7)], C3–C4 1.484(8) [1.480(8)],
C3–N3 1.302(6) [1.292(7)], C4–N4 1.282(7) [1.297(7)], N4–M1
2.254(4) [2.297(5)], N3–M1 2.247(4) [2.282(5)], M1-C1A 1.973(6)
[1.957(7)], M1-C1B 1.964(6) [1.970(7)], M1-C1C 2.042(5) [2.038(6)],
M1-C1D 2.026(6) [2.032(7)], N5–P1–C6 100.9(2) [101.2(2)], N2–P1–
C6 105.0(2) [105.2(2)], N5–P1–N2 90.1(2) [90.0(2)].
31P NMR spectroscopic monitoring revealed that all studied
reactions of 5 and 6 with metal complexes proceeded quite
selectively and (apart from minor and varying amounts of hy-
Knowing that 2-chloro-1,3,2-diazaphospholidines can bind drolysis products) quantitatively; in particular, we were unable
central PdII atoms via the free electron pair at phosphorus,[2] to observe any signals attributable to complexes with P-coordi-
we also examined the appropriate reaction of the P-chloro de- nated ligands or, when an excess of metal complex was em-
rivative 6. Reaction with [(PhCN)2PdCl2] in refluxing toluene ployed, dinuclear complexes with μ-bridging coordination of
and evaporation of the solvent gave an orange, moisture and diazaphospholidine-diimines.
air sensitive solid, which was characterized by analytical and
The high affinity of Lewis-acidic metal fragments towards
spectroscopic data. Observation of a 31P NMR signal with a the diimine moiety prompted us to investigate also the prospect
similar positive coordination shift [Δδ31P(coord) = 26] as 7 of using 5 to trap transient phosphorus(I) electrophiles in a
and 8 suggested that the product might likewise be described [4+1] cycloaddition. This approach allowed to convert open
as a diimine complex 9 (Scheme 3). This hypothesis was fi- diimines in a single step into appropriate phosphorus heterocy-
nally confirmed by a single-crystal X-ray diffraction study cles[14,22] and may in the presented case give direct access to
(Figure 3).
elusive bicyclic heteropentalenes. In contrast to our expecta-
Z. Anorg. Allg. Chem. 2013, 517–523
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 519

G. Mourgas, I. Tiritiris, M. Nieger, D. Gudat
ARTICLE
tions, 5 did not react with PI3, and reaction with excess PBr3
The molecular structure of 11 bears some similarity with
in the presence of cyclohexene proceeded via metathesis to those of other structurally characterized SnIV-diimine com-
give a mixture of unreacted PBr3 (δ31P = 227), PhPBr2 (δ31P plexes.[25] The values of Sn–Cl distances [2.376(1)–
= 150[23]), and a product, which we assign as P-bromo-1,3, 2- 2.422(1) Å] and N–Sn–N angles [74.43(6)°] match the analo-
diazaphospholidine-4,5-diimine (10) (δ31P = 145, Scheme 4). gous features of [(dipp-BIAN)SnCl4] (12) (Sn–Cl 2.353–
Even if this species could not be isolated, the assignment is 2.406 Å, N–Sn–N 74.3°[25]) or [(bipy)SnCl4] (Sn–Cl 2.359–
backed by the independent synthesis of the same product by 2.409 Å[26]). On the contrary, the Sn–N distances of some
reaction of 3 with BuLi and PBr3.
2.54–2.56 Å are substantially larger than those of typical
NǞSnIV donor-acceptor bonds (2.18–2.30 Å in 12 or related
octahedral tin tetrahalide complexes[25,26]). We consider this
finding quite remarkable given that a similar difference be-
tween the M(CO)4 complexes 7 and 8 and [(dipp-BIAN)
M(CO)4] is absent, and attribute this deviation tentatively to
the different properties of the central metal atoms in both types
of complexes: the zerovalent metal atoms in 7, 8 may engage
in both NǞM σ dative and MǞN π retrodative interactions,
whereas the central SnIV atom in 11 is essentially a Lewis
acceptor, and the NǞM σ-bonding contribution dominates.
Under these circumstances, the electron withdrawing effect of
the endocyclic nitrogen atoms next to the diimine unit can be
considered to make an oxalamidine like 5 a weaker donor than
alkyl- or aryl-substituted diimines. Inspection of the metric pa-
rameters in the ligand of 11 reveals further that the equalization
of the single and double bonds in the amidine units and the
lengthening of P–N bonds are even more pronounced than in
7–9. As a compensation, the P1–C6 bond 1.798(2) Å] is
shorter than a normal single bond of 1.836Ϯ0.010 Å.[27]
The outcome of the spectroscopic studies reveals that the
reaction between 5 and PCl3/SnCl2 is rather unspecific and
follows (in view of the detection of both PhPCl2 and 11 among
the products) in part a metathesis and in part a redox pathway.
Even if it must be assumed that some PCl3 is thus reduced,
the imine moiety of 5 does not trap the suspected low valent
phosphorus fragment but rather the SnCl4 formed as oxidation
product. The reason for this deviation from the reported reac-
tivity of other diimines[14,22] is not totally clear. However, we
assume that the need to isomerize one of the C=N bonds in 5
prior to formation of a chelate adduct and a lower σ-donor
strength of the imino-nitrogen atoms are obstacles that do not
completely prevent the formation of chelate complexes with
strong and persistent Lewis acids, but may severely interfere
with the stabilization and capture of a fragile and transient
phosphorus(I) species.
Scheme 4. (R = Dmp).
Reaction of 5 with PCl3 in the presence of SnCl2 as reducing
agent[14,24] produced a red solution. A 31P NMR survey
showed a signal attributable to PhPCl2 (δ31P = 161) along with
further signals around 130–135 and 99–106 ppm, respectively.
Work-up produced a moderate yield (37%) of an orange, crys-
talline product, which was identified by means of a single-
crystal X-ray diffraction study as the tin(IV) complex 11
(Scheme 4). Complex 11 was also obtained as the only isolable
product from the analogous reaction of 5 with AsCl3 and SnCl2
(Figure 4).
Conclusions
1,3,2-Diazaphospholidine-4,5-diimines were prepared by
condensation of lithiated oxalamidines with PCl3 or phenyl
dichlorophosphane, respectively. The heterocycles form stable
metal complexes by acting as chelating bidentate N-donor li-
gands through their diimine unit, but showed no activity as P-
donors. Complex formation induces a structural distortion of
the ligand framework, which indicates that π delocalization in
the amidine units is enhanced at the expense of hyperconjuga-
tive interactions in the NPN moiety. These effects allow ex-
plaining the large 31P coordination shifts upon metal binding
at the remote nitrogen atoms, and may also be assumed to
Figure 4. Molecular structure of 11. Thermal ellipsoids are drawn at
50% probability level, hydrogen atoms are omitted for clarity. Selected
bond lengths /Å and angles /°: P1–C6 1.798(3), P1–N2 1.754(1), P1–
N5 1.752(1), C4–N5 1.350(1), C3–N2 1.350(1), C4–C3 1.516(1), C3–
N3 1.294(1), C4–N4 1.291(1), Sn1–N4 2.540(2), Sn1–N3 2.564(2),
Sn-Cl1 2.421(3), Sn1–Cl2 2.385(2), Sn1–Cl3 2.382(2), Sn1–Cl4
2.375(2), N2–P1–C6 103.48(4), N5–P1–C6 101.84(5), N2–P1–N5
89.03(4), N4–Sn1–N3 74.43(2).
520
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 517–523

N-Aryl-substituted 1,3,2-Diazaphospholidine-4,5-diimines
(s, 2 H, CH) ppm (+)-EI-MS (70 eV): m/z (%) = 622.3 (40) [M+],
607.3 (100) [M+-CH3]. IR (KBr): ν˜ = 1666 (s, br) (C=N) cm–1.
reduce the nucleophilic character of the phosphorus atom,
which offers a viable explanation for the one-sided coordina-
tion behavior. Reaction of a diazaphospholidine-4,5-diimine
with AsCl3 or PCl3 in the presence of SnCl2 did not proceed
via formal [1+4] cycloaddition of the diimine unit with a tran-
sient pnictogen(I) species to give a heteropentalene, but rather
via formation of a low yield of a diimine-SnCl4 complex. It
General Procedure for the Preparation of Compounds 7 and 8:
Ligand 5 (3.05 g, 5 mmol) was dissolved in toluene (20 mL) and
[(nbd)W(CO)4] (2.7 g, 7 mmol) or [Mo(CO)6] (1.85 g, 7 mmol) were
added in one portion. The reaction mixture was refluxed for 2 d and
turned eventually dark red to violet. The solution was cooled to room
remains to be established if this deviation from a common re- temperature and filtered through Celite. The filtrate was evaporated to
dryness and the residue recrystallized from toluene at –20 °C.
action pattern for diimines is due to the unfavorable steric or
electronic predisposition of the starting material or the destabi-
lization of the expected bicyclic product by increased ring
strain.
2-Phenyl-tetra-(2,6-dimethylphenyl)-1,3,2-diazaphospholidine-
4,5-diimine-tetracarbonyltungsten (7): Yield: 2.56 g, (57%); m.p.
175 °C. C44H41N4O4PW (904.63): calcd. C 58.42, H 4.57, N 6.19%,
found C 57.97, H 4.22, N 5.88%. 31P{1H} NMR (CDCl3, 300 K): δ =
1
120.9 (s). H NMR (CDCl3, 300 K): δ = 1.92 (s, 6 H, CH3), 2.24 (s,
3
Experimental Section
6 H, CH3), 2.64 (s, 6 H, CH3), 2.68 (s, 6 H, CH3), 6.38 (d, 2 H, JHH
3
3
= 7.8 Hz, CH), 6.48 (d, 2 H, JHH = 7.3 Hz, CH), 6.65 (t, 2 H, JHH
=
All manipulations were carried out in an atmosphere of dry argon using
standard vacuum line techniques. Solvents were dried by standard pro-
cedures. Oxalamidines 3 and 4 were prepared as described in refer-
ence[15]. All other chemicals were commercially available and used as
received. NMR spectra were recorded with a Bruker Avance 250 (1H,
250.1 MHz; 13C, 62.8 MHz; 31P, 101.2 MHz) spectrometer at 303 K;
chemical shifts are referenced to external SiMe4 (1H, 13C) or 85%
H3PO4 (31P). Coupling constants are given in absolute values. Elemen-
tal analyses were determined with a Perkin-Elmer 2400 CHN/O Ana-
lyzer; large deviations between found and calculated values are pre-
sumably due to incomplete combustion and formation of metal carbide
(8) or hydrolysis during sample preparation (9). Melting points were
determined in sealed capillaries with a Büchi Melting Point B-545
apparatus. IR spectra were recorded with a Nicolet 6700 FTIR spec-
trometer equipped with a Smart orbit unit with a diamond crystal and
a MCTA-detector.
3
7.5 Hz, CH), 6.79–6.91 (m, 4 H, CH), 6.99 (d, 2 H, JHH = 7.10 Hz,
CH), 7.48 (m, 2 H, m-Ph), 7.61 (m, 1 H, p-Ph), 7.84 (m, 2 H, o-Ph)
ppm. IR (KBr): ν˜ = 1985 (s), 1909 (m), 1867 (m), 1830 (s) (CO),
1565 (m) (C=N) cm–1.
2-Phenyl-tetra-(2,6-dimethylphenyl)-1,3,2-diazaphospholidine-
4,5-diimine-tetracarbonylmolybdenum (8): Yield 2.20 g (54%),
m.p. 183 °C. C44H41MoN4O4P (816.73): calcd. C 64.71, H 5.06, N
6.86%, found C 64.12, H 4.97, N 6.83%. 31P{1H} NMR (CDCl3,
300 K): δ = 118.2 (s). 1H NMR (CDCl3, 300 K): δ = 1.28 (s, 6 H,
CH3), 2.23 (s, 6 H, CH3), 2.66 (s, 6 H, CH3), 2.69 (s, 6 H, CH3), 6.37
3
3
(d, 2 H, JHH = 7.7 Hz, CH), 6.46 (d, 2 H, JHH = 7.5 Hz, CH), 6.63
3
(t, 2 H, JHH = 7.5 Hz, CH), 6.77–6.89 (m, 4 H, CH), 6.98 (d, 2 H,
3JHH = 7.4 Hz, CH), 7.46 (m, 2 H, m-Ph), 7.60 (m, 1 H, p-Ph), 7.84
(m, 2 H, o-Ph) ppm.
2-Chloro-tetramesityl-1,3,2-diazaphospholidine-4,5-diimine-
palladium(II)chloride (9): Ligand 5 (3.1 g, 5 mmol) was dissolved in
toluene (20 mL) and [(PhCN)2PdCl2] (2.68g, 7 mmol) was added in
one portion. The reaction mixture was refluxed for 2 d. The solution
was cooled to room temperature, filtered through Celite, and the filtrate
was evaporated to dryness. Recrystallization of the residue in toluene
at –20 °C gave 9 as orange solid. Yield 2.56 g (57%), m.p. 288 °C.
C38H44Cl3N4PPd (800.54): calcd. C 57.01, H 5.54, N 7.00%, found C
56.04, H 5.64, N 6.38%. 31P{1H} NMR (CDCl3, 300 K): δ = 160.0
General Procedure for the Preparation of Compounds 5 and 6:
Oxalamidine 3 (502 mg, 1.0 mmol) or 4 (558 mg, 1.0 mmol) were dis-
solved in THF (10 mL) and the solution cooled to –78 °C. Butyllithium
(1.5 mL of a 1.6 m solution, 2.4 mmol) were subsequently added. The
solution was stirred for 30 min. PhPCl2 (215 mg, 1.2 mmol) or PCl3
(165 mg, 1.2 mmol) was added, and the mixture was stirred for further
12 h. Solvents were removed in vacuo, the residue taken up in toluene
or Et2O (10 mL), and filtered through Celite. The products were ob-
tained after removal of the solvent under reduced pressure as air and
moisture sensitive, pale yellow powders that could be purified by
recrystallization.
1
(s). H NMR (CDCl3, 300 K): δ = 2.06 (s, 18 H, CH3), 2.17 (s, 6 H,
CH3), 2.44 (s, 6 H, CH3), 2.64 (s, 6 H, CH3), 6.22 (s, 2 H, CH), 6.47
(s, 2 H, CH), 6.64 (s, 2 H, CH), 6.80 (s, 2 H, CH) ppm. IR (KBr):
ν˜ = 1620 (s), 1601 (s) (C=N) cm–1.
2-Phenyl-tetrakis-(2,6-dimethylphenyl)-1,3,2-diazaphospholidine-
4,5-diimine (5): Yield 505 mg (83 %); m.p. 134.5 °C. C40H41N4P
(608.75): calcd. C 78.92, H 6.88, N 9.20%; found: C 78.73, H 6.82,
N 9.19%. 31P{1H} NMR (CDCl3, 300 K): δ = 90.1 (s). 1H NMR
(CDCl3, 300 K): δ = 1.66 (broad s, 6 H, CH3), 1.84 (broad s, 6 H,
CH3), 2.26 (s, 6 H, CH3), 2.66 (s, 6 H, CH3), 6.38–7.07 (m, 12 H,
CH), 7.37–7.58 (m, 3 H, m/p-C6H5), 7.78–7.92 (m, 2 H,, o-C6H5) ppm.
(+)-EI-MS (70 eV): m/z (%) = 608.3 (65) [M+], 593.3 (100)
[M+-CH3], 531.3(7) [M+-Ph]. IR (KBr): ν˜ = 1651 (s, br) (C=N) cm–1.
2-Phenyl-tetra-(2,6-dimethylphenyl)-1,3,2-diazaphospholidine-
4,5-diimine-tetrachlorotin (11): PCl3 (1 mmol, 72 mg, 47 μL) was
added drop wise to a stirred solution of anhydrous SnCl2 (190 mg,
1 mmol) in THF (15 mL). This mixture was added to a solution of 5
(608 mg, 1 mmol) in THF (15 mL). The yellow solution turned orange.
The reaction mixture was stirred overnight and evaporated to dryness.
The remaining, light orange residue was extracted with acetonitrile and
filtered through Celite. The filtrate was concentrated to a volume of
10 mL and stored at 4 °C. The product precipitated as orange, crystal-
2-Chloro-tetramesityl-1,3,2-diazaphospholidine-4,5-diimine (6): line solid, which was collected by filtration. Yield 320 mg (37%), m.p.
Yield 390 mg (63 %); m.p. 178 °C. C38H44ClN4P·CH3CN (664.23):
calcd. C 72.33, H 7.13, N 10.54%; found C 71.90, H 6.99, N 9.63%.
31P{1H} NMR (CDCl3, 300 K): δ = 134.6 (s). 1H NMR (CDCl3, 300 K): δ = 99.5 (s). 1H NMR (CDCl3 300 K): δ = 1.21 (s, 6 H, CH3),
167 °C. C42H44Cl4N4PSn·CH3CN (910.33): calcd. C 55.41, H 4.87, N
7.69%, found: C 55.03, H 4.61, N 7.18%. 31P{1H} NMR (CDCl3,
300 K): δ = 1.73 (s, 6 H, p-CH3), 2.04 (s, 6 H, o-CH3), 2.09 (s, 6 H,
p-CH3), 2.20 (s, 6 H, p-CH3), 2.34 (s, 6 H, o-CH3), 2.41 (s, 6 H, o-
CH3), 6.23 (s, 2 H, CH), 6.54 (s, 2 H, CH), 6.70 (s, 2 H, CH), 6.85
2.32 (s, 6 H, CH3), 2.77 (s, 6 H, CH3), 2.79 (s, 6 H, CH3), 6.39 (d, 2
3
3
H, JHH = 7.5 Hz, CH), 6.51 (d, 2 H, JHH = 7.4 Hz, CH), 6.73–6.91
3
3
(m, 4 H, CH), 6.96 (d, 2 H, JHH = 7.5 Hz, CH), 7.04 (d, 2 H, JHH
=
Z. Anorg. Allg. Chem. 2013, 517–523
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim www.zaac.wiley-vch.de 521

G. Mourgas, I. Tiritiris, M. Nieger, D. Gudat
ARTICLE
7.0 Hz, CH), 7.53 (m, 2 H, m-Ph), 7.68 (m, 1 H, p-Ph), 7.85 (m, 2 H,
o-Ph). 13C{1H} NMR (CDCl3): δ = 19.8, 21.9, 22.0, 22.1, 22.7 (CH3),
126.9, 128.5, 128.8, 129.3, 129.35, 129.41, 129.45, 129.51, 131.1,
131.5, 135.6, 136.47, 136.52, 136.55, 136.99, 137.0 (CAryl), 151.6
(C=N) ppm. (+)-ESI-MS: m/z = 833.11 [M – Cl]+, 609.32 [M-SnCl3]+.
Acknowledgements
Financial support by the Deutsche Forschungsgemeinschaft, the Acad-
emy of Finland (M. N.), and the COST action CM802 (phoscinet) is
gratefully acknowledged. We thank J. Trinkner and K. Wohlbold (Insti-
tut für Organische Chemie, University of Stuttgart) for recording the
mass spectra.
X-ray Crystallography: Crystallographic data were collected with a
Bruker-Nonius KappaCCD diffractometer at T = 123(2) (5, 7, 8, and
11) or 100(2) K using Mo-Kα radiation (λ = 0.71073 Å). Direct meth-
ods (Patterson methods for 7) (SHELX-97[28]) were used for structure
solution, and non-hydrogen atoms were refined anisotropically
(SHELX-97[28], full-matrix, least-square on F2). Hydrogen atoms were
refined with a riding model. A semi-empirical absorption correction
was applied for 7, 8, and 11.
References
[1] S. Fleming, M. K. Lupton, K. Jekot, Inorg. Chem. 1972, 11,
2534–2535.
[2] a) L. Ackermann, H. K. Potuchi, A. Althammer, R. Born, P.
Mayer, Org. Lett. 2010, 12, 1004–1007; b) L. Ackermann, J. H.
Spatz, C. J. Gschrei, R. Born, A. Althammer, Angew. Chem. 2006,
118, 7789–7792; Angew. Chem. Int. Ed. 2006, 45, 7627–7630.
[3] P. Wucher, L. Caporaso, P. Röesle, F. Ragone, L. Cavallo, S.
Mecking, I. Göttker-Schnetmann, Proc. Natl. Acad. Sci. USA
2011, 108, 8955–8959.
[4] a) H. Tye, D. Smyth, C. Eldred, M. Wills, Chem. Commun. 1997,
1053–1054; b) T. Pfretschner, L. Kleemann, B. Janza, K. Harms,
T. Schrader, Chem. Eur. J. 2004, 10, 6048–6057.
[5] A. J. Robbie, A. R. Cowley, M. W. Jones, J. R. Dilworth, Polyhe-
dron 2011, 30, 1849–1856.
[6] S. Breeden, D. J. Cole-Hamilton, D. F. Foster, G. J. Schwarz, M.
Wills, Angew. Chem. 2000, 112, 4272–4274.
5: C40H41N4P; M = 608.74; crystal size 0.50ϫ0.30ϫ0.10 mm;
monoclinic, space group P21/n, a = 12.754(1), b = 17.673(2),
c = 15.083(2) Å, β = 97.52(1)°, V = 3370.5(6) Å3, Z = 4, ρ =
1.200 Mg·m–3, μ = 0.116 mm–1, θmax = 27.48°; 24618 reflections, 7527
independent reflections (Rint = 0.040), 414 parameters, R1 = 0.048
[I Ͼ 2σ(I)], wR2 = 0.112 (all data), S = 1.03, largest diff. peak/hole
0.331/–0.323 e·Å–3.
7: C44H41N4O4PW·0.5toluene;
M
=
950.69; crystal size
0.25ϫ0.10ϫ0.05 mm; monoclinic, space group P21/c, a = 11.303(2),
b = 21.281(4), c = 17.298(3) Å, β = 101.79(2)°, V = 4073.1(13) Å3,
Z = 4, ρ = 1.550 Mg·m–3, μ = 2.926 mm–1, θmax = 27.48°; 35093
reflections, 9382 independent reflections (Rint = 0.088), 511 param-
eters, 14 restrains, R1 = 0.048 [I Ͼ 2σ(I)], wR2 = 0.095 (all data), S =
1.03, largest diff. peak/hole 1.467/–1.503 e Å3.
[7] I. C. F. Vasconcelos, G. K. Anderson, N. P. Rath, C. D. Spilling,
Tetrahedron: Asymmetry 1998, 9, 927–935.
[8] G. Mourgas, Z. Benkö, D. Förster, M. Nieger, D. Gudat, Arkivoc
2012, 50–59.
[9] Functional 4-oxo- or 4-imino-1,3,2-diazaphospholidines, which
might possibly act as ambident P,O- or P,N-donors are likewise
known but their coordination properties have not been explored:
a) Yu. G. Gololobov, L. I. Nesterova, Zh. Obshch. Khim. 1980,
50, 683–684; b) E. E. Korshin, R. M. Eliseenkova, T. A. Zyabli-
kova, L. G. Zakharova, A. G. Akhmadullin, V. D. Nusinovich,
Ya. A. Levin, Izvest. Akad. Nauk Ser. Khim. 1993, 1116–1121; c)
E. E. Korshin, L. I. Sabirova, T. A. Ziablikova, I. E. Ismaev,
Ya. A. Levin, Izvest. Akad. Nauk Ser. Khim. 1994, 480–484; d) L.
He, Y. Luo, M. Ding, A. Lu, X. Liu, T. Wu, F. Cai, Heteroat.
Chem. 2001, 12, 497–500.
8: C44H41MoN4O4P·0.5toluene;
M
=
862.78; crystal size
0.32ϫ0.08ϫ0.04 mm; monoclinic, space group P21/c, a = 11.352(1),
b = 21.305), c = 17.312(2) Å, β = 101.79(2)°, V = 4098.6(8) Å3, Z =
4, ρ = 1.398 Mg·m–3, μ = 0.409 mm–1, θmax = 25.00°; 22936 reflec-
tions, 7193 independent reflections (Rint = 0.112), 512 parameters, 14
restrains, R1 = 0.067 [I Ͼ 2σ(I)], wR2 = 0.161 (all data), S = 1.03,
largest diff. peak/hole 1.029/–0.918 e Å3.
[10] Review: G. van Koten, K. Vrieze, Adv. Organomet. Chem. 1982,
21, 151–239.
[11] a) M. Döring, H. Görls, R. Beckert, Z. Anorg. Allg. Chem. 1994,
620, 551–560; b) M. Döring, P. Fehling, H. Görls, W. Imhof, J.
Prakt. Chem. 1999, 341, 748–756; c) P. Fehling, M. Döhring, F.
Knoch, R. Beckert, H. Görls, Chem. Ber. 1995, 128, 405–412.
9: C38H44Cl3N4PPd; M = 800.49; crystal size 0.15ϫ0.15ϫ0.16 mm;
monoclinic, space group P21/c, a = 13.4754(6), b = 20.1664(11), c =
15.0554(8) Å, β = 105.715(3)°, V = 3938.4(3) Å3, Z = 4, ρ =
1.350 Mg·m–3, μ = 0.745 mm–1, θmax = 28.34°, 9778 reflections/7193
independent reflections (Rint = 0.0969), 436 parameters, 0 restrains, R1
= 0.0674 [I Ͼ 2σ(I)], wR2 = 0.0974 (all data), S = 1.211, largest diff. [12] Reviews: a) M. Veith, Chem. Rev. 1990, 90, 3–16; b) M. Veith,
peak/hole 0.457/–0.364 e·Å–3. A highly disordered solvent molecule
S. Weidner, K. Kunze, D. Käfer, J. Hans, V. Huch, Coord. Chem.
(toluene) was removed with the SQUEEZE routine of Platon[29]
.
Rev. 1994, 137, 297–322; c) F. Baier, Z. Fei, H. Gornitzka, A.
Murso, S. Neufeld, M. Pfeiffer, I. Rüdenauer, A. Steiner, T. Stey,
D. Stalke, J. Organomet. Chem. 2002, 661, 111–127.
[13] Review: I. Kuzu, I. Krummenacher, J. Meyer, F. Armbruster, F.
Breher, Dalton Trans. 2008, 5836–5865.
[14] G. Reeske, C. R. Hoberg, N. J. Hill, A. H. Cowley, J. Am. Chem.
Soc. 2006, 128, 2800–2801; G. Reeske, A. H. Cowley, Inorg.
Chem. 2007, 47, 1426–1430.
11: C40H41Cl4N4PSn·acetonitrile;
M
=
910.28; crystal size
0.30ϫ0.15ϫ0.10 mm; monoclinic, space group P21/n, a = 12.482(1),
b = 26.391(3), c = 12.623(1) Å, β = 104.99(1)°, V = 4016.7(6) Å3,
Z = 4, ρ = 1.505 Mg·m–3, μ = 0.980 mm–1, θmax = 27.48°; 41753
reflections, 9150 independent reflections (Rint = 0.033), 487 param-
eters, R1 = 0.028 [I Ͼ 2σ(I)], wR2 = 0.061 (all data), S = 1.10, largest [15] D. Lindauer, R. Beckert, J. Prakt. Chem. 1995, 337, 143–152.
diff. peak/hole 0.658/–0.490 e Å3.
[16] V. A. Jones, S. Sripang, M. Thornton-Pett, T. P. Kee, J. Or-
ganomet. Chem. 1998, 567, 199–218.
[17] a) M. R. Marre, M. Sanchez, J. F. Brazier, R. Wolf, Can. J. Chem.
1982, 60, 456–468; b) C. A. Caputo, J. T. Price, M. C. Jennings,
R. McDonald, N. D. Jones, Dalton Trans. 2008, 3461–3469; c)
O. Puntigam, I. Hajdok, M. Nieger, M. Niemeyer, S. Strobel, D.
Gudat, Z. Anorg. Allg. Chem. 2011, 637, 988–994.
[18] a) H. tom Dieck, I. W. Renk, Chem. Ber. 1971, 104, 110–130; b)
W. Majunke, D. Leibfritz, T. Mack, H. tom Dieck, Chem. Ber.
1975, 108, 3025–3029.
Crystallographic data (excluding structure factors) for the structures in
this paper have been deposited with the Cambridge Crystallographic
Data Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK.
Copies of the data can be obtained free of charge on quoting the
depository numbers CCDC-914696 (5), -914697 (7), -914713 (8),
-914555 (9), and -914698 (11), (Fax: +44-1223-336-033; E-Mail:
deposit@ccdc.cam.ac.uk, http://www.ccdc.cam.ac.uk)
522
www.zaac.wiley-vch.de
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2013, 517–523

N-Aryl-substituted 1,3,2-Diazaphospholidine-4,5-diimines
[19] a) V. Kirim, P. Roesky, Z. Anorg. Allg. Chem. 2004, 630, 466–
469; b) I. L. Fedushkin, A. A. Skatova, A. N. Lukoyanov, N. M.
Khvoinova, A. V. Piskunov, A. S. Nikipelov, G. K. Fukin, K. A.
Lysenko, E. Irran, H. Schumann, Dalton Trans. 2009, 4689–4694.
[20] N. M. Comerlato, G. L. Crosetti, R. A. Howie, P. C. D. Tibultino,
J. L. Wardell, Acta Crystallogr., Sect. E 2001, 57, 295–297.
[25] a) N. J. Hill, G. Reeske, J. A. Moore, A. H. Cowley, Dalton
Trans. 2006, 4838–4844; b) A. V. Piskunov, A. V. Lado, G. K.
Fukin, E. V. Baranov, L. G. Abakumova, V. K. Cherkasov, G. A.
Abakumov, Heteroat. Chem. 2006, 17, 481–490.
[26] V. N. Zakharov, A. V. Yatsenko, A. L. Kamyshnyi, L. A. Aslanov,
Koord. Khim. 1991, 17, 789–794.
[21] D. N. Coventry, A. S. Batsanov, A. E. Goeta, J. A. K. Howard, [27] F. H. Allen, O. Kennard, D. G. Watson, L. Brammer, A. G. Orpen,
T. B. Marder, Polyhedron 2004, 23, 2789–2795.
[22] J. W. Dube, G. J. Farrar, E. L. Norton, K. L. S. Szekely, B. F. T.
Cooper, C. L. B. MacDonald, Organometallics 2009, 28, 4377–
4384.
R. Taylor, J. Chem. Soc. Perkin Trans. 2 1987, S1–S19.
[28] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112–122.
[29] A. L. Spek, Platon, A Multipurpose Crystallographic Tool,
Utrecht University, Utrecht, The Netherlands, 2004.
[23] A. Hinke, W. Kuchen, Chem. Ber. 1983, 116, 3003–3010.
[24] A. Schmidpeter, S. Lochschmidt, W. S. Sheldrick, Angew. Chem.
Int. Ed. Engl. 1982, 21, 63–64.
Received: December 11, 2012
Published Online: February 7, 2013
Z. Anorg. Allg. Chem. 2013, 517–523
© 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
523