Synthesis of phosphine substituted β-diketiminate based isomeric Ge(II) complexes

Article abstract of DOI:10.1039/b915403e

Treatment of phosphine substituted β-diketiminate lithium, Ph ₂PC[C(Me)N(Dipp)]₂LiOEt₂ (1) (Dipp = 2,6- ⁱPr₂C₆H₃) with dioxane· GeCl₂resulted in a five-membered N,P chelate complex, Ph₂ PC[C(Me)N(Dipp)]₂GeCl (2). An isomer of 2 CH{[C(CH₂PPh ₂)N(Dipp)][C(Me)N(Dipp)]}GeCl (5) was obtained from the germanium complex L′Ge (L′ = CH[C(CH₂) N(Dipp)][C(Me)N(Dipp)])Ge (4) and Ph₂PCl. In 5 the PPh₂ group remains uncoordinated. Both complexes were characterized by X-ray structural analysis and in the case of 5 both enantiomers crystallize in the same unit cell. The Royal Society of Chemistry 2010.

Full text of DOI:10.1039/b915403e

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Synthesis of phosphine substituted b-diketiminate based isomeric
Ge(II) complexes†‡
N. Dastagiri Reddy,*a Anukul Jana,b Herbert W. Roesky,*b Prinson P. Samuelb and Carola Schulzkec
Received 29th July 2009, Accepted 2nd October 2009
First published as an Advance Article on the web 9th November 2009
DOI: 10.1039/b915403e
Treatment of phosphine substituted b-diketiminate lithium, Ph2PC[C(Me)N(Dipp)]2LiOEt2 (1)
(Dipp = 2,6-iPr2C6H3) with dioxane·GeCl2resulted in a five-membered N,P chelate complex,
Ph2PC[C(Me)N(Dipp)]2GeCl (2). An isomer of 2 CH{[C(CH2PPh2)N(Dipp)][C(Me)N(Dipp)]}GeCl
=
(5) was obtained from the germanium complex L¢Ge (L¢ = CH[C( CH2)N(Dipp)][C(Me)N(Dipp)])Ge
(4) and Ph2PCl. In 5 the PPh2 group remains uncoordinated. Both complexes were characterized by
X-ray structural analysis and in the case of 5 both enantiomers crystallize in the same unit cell.
(A) has led in some cases to the formation of either coordination
Introduction
polymers7 or bimetallic systems,8 without affecting chelation (D),
while in most cases they have remained spectators.9
b-Diketiminate ligands occupy a distinct position in metal-
coordination chemistry, which is evident from the number of
articles published every year on these systems.1 What makes them
important is their tunability, which is both electronic and steric.
The steric environment provided by these ligands, especially the
2,6-diisopropylphenyl substituted diketiminate, has been exploited
in main-group chemistry for synthesizing species with low valent
elements2 and active metals.3 Both steric and electronic factors
have been utilized in developing efficient homogeneous catalysts4
and model systems of biological relevance.5 Barring one example6
(Fig. 1, B, Dipp = 2,6-diisopropylphenyl) b-diketiminate ligands
usually form chelate complexes with metals through the N atoms
(C). Incorporation of groups like –CN and –NO2 at the R3 position
Phosphines have been well known for stabilizing transition
metals especially the late and heavier ones.10 Introducing a
phosphine moiety at the R2 or R3 position would lead to potential
ligands for synthesizing heterobimetallic systems involving main-
group elements and late transition metals. Recently, there have
been reports on phosphine substituted b-diketiminate ligands,
in which phosphine moieties occupy the R3 position.11 We have
been interested in heterobimetallic germylenes,12 which are po-
tential catalysts for olefin polymerization. In continuation of our
research in such systems, we explored the reaction of a phosphine
substituted (at the R3 position) b-diketiminate ligand 1 with
dioxane·GeCl2. In parallel, we have also designed and executed
a synthetic route, via germylene, for making b-diketiminate Ge(II)
complex with a free phosphine moiety at the R2 position. These
reactions have led to the formation of isomers, however, with
different coordination modes, which will be discussed here in
detail.
Results and discussion
An equimolar reaction of 1 and the dioxane complex of GeCl2 in
ether gives a pale yellow colored product in almost quantitative
yield. The product 2 was structurally characterized as an N,P
chelate complex of germanium (Scheme 1), which has been isolated
and purified by washing it with n-hexane. Compound 2 is formed
Fig. 1
exclusively and shows a single resonance at d 15.16 ppm in the 31
P
NMR spectrum.
The 1H NMR spectrum of 2 exhibits as many as eight
doublets for isopropyl methyl groups and four multiplets for
methyne protons due to the unsymmetrical nature of the molecule.
Interestingly, two of the methyne protons of the isopropyl groups
are quite shielded (d 1.68 and 2.53 ppm). Upon examination of
the orientation of methyne protons in the solid state we have
found that two protons are in close proximity to the center of
the phenyl groups of the phosphine moiety and hence fall in the
shielding region of the ring current (see ESI †for orientation). This
observation suggests complex 2 has the same structure both in the
solid and solution state.
aDepartment of Chemistry, Pondicherry University, Pondicherry, 605014,
India. E-mail: ndreddy.che@pondiuni.edu.in; Fax: 91413 2655987; Tel: 91
413 26554484
bInstitut fu¨r Anorganische Chemie, Tammannstrasse 4, Go¨ttingen, 37077,
Germany. E-mail: hroesky@gwdg.de; Fax: 49 551 393373; Tel: 49 551
393001
cSchool of Chemistry, Trinity College Dublin, Dublin 2, Ireland
† Electronic supplementary information (ESI) available: ORTEP diagram
of 2 showing proximity of methyne protons to phenyl groups. CCDC
reference numbers 741341 & 741342. For ESI and crystallographic data in
CIF or other electronic format see DOI: 10.1039/b915403e
‡ Dedicated to Prof. Richard A. Walton on the occasion of his 70th
birthday.
234 | Dalton Trans., 2010, 39, 234–238
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b-diketiminate ligand 1 is in a unusual coordination mode in
its As(III) and Sb(III) complexes (Fig. 3, I). The Al(III) forms an
N,N’ chelate complex, in which the –PPh2 remains uncoordinated
(Fig. 3, II).11b It is evident from their observation that the mode of
coordination depends upon the nature of the metal. In addition
to the coordination modes observed so far (I and II in ref. 11b, III
in this paper), there is also another mode possible (IV).
Scheme 1
Single crystals of 2 were obtained from n-hexane solution, and
a molecular structure with selected bond distances and bond
angles is given in Fig. 2. Surprisingly, a thorough search for N,P
chelate complexes of germanium in CCDC resulted in one four-
membered ring compound13 and two six-membered rings,14 and
no five-membered rings were reported. Ge–N and Ge–P bond
distances are in the range of those reported for such complexes.15
The five-membered ring is slightly puckered and no four atoms in
the ring fall in one plane. The N(1)–C(26), C(27)–C(28) bond
lengths, typical of single bonds, and C(26)–C(27), C(28)–N(2)
bond lengths, typical of double bonds, support the formulation
given for 2 in Scheme 1.
Fig. 3
Recently, from the work of Driess and coworkers3j as well as
from our results16 we have learnt that the germylene 4 can be
utilized for effecting substitution at the a carbon of the ligand
back-bone. In order to introduce the Ph2P group at this position
we have employed Ph2PCl. A quantitative reaction has occurred
when a solution of 4 in n-hexane is treated with Ph2PCl. Product
5 was characterized by NMR and single crystal X-ray studies
(Scheme 2).
Scheme 2
As shown in Fig. 4, the N,N’-chelation mode of the ligand is
retained and the Ph2P group does not interact with Ge(II). As with
the previously reported b-diketiminate Ge(II) complexes,3j,17 Ge
deviates away from the plane of the ring, and Ge–N and Ge–Cl
bonds are also typical of such complexes. As given in Fig. 4, unlike
in 2, all the C–C and C–N bond lengths of the b-diketiminate
skeleton in 5 are almost equal.
Fig. 2 Molecular structure of 2. Thermal ellipsoids are shown at 50%
probability. Hydrogen atoms are omitted for clarity. Selected bond lengths
◦
˚
(A) and bond angles ( ): Ge(1)–N(1) 1.9700(16), Ge(1)–Cl(1) 2.2934(8),
Ge(1)–P(1) 2.4300(11), N(1)–C(26) 1.361(2), C(26)–C(27) 1.385(3),
C(27)–C(28) 1.473(3), N(2)–C(28) 1.285(2); N(1)–Ge(1)–Cl(1) 95.63(6),
N(1)–Ge(1)–P(1) 80.49(5), Cl(1)–Ge(1)–P(1) 93.16(3), C(26)–N(1)–Ge(1)
123.02(12), N(1)–C(26)–C(27) 121.52(16), C(27)–P(1)–Ge(1) 97.91(7),
C(26)–C(27)–P(1) 114.08(14), N(2)–C(28)–C(27) 117.44(16).
The 31P NMR chemical shifts of 2 (15.16 ppm) and 5
(-13.47 ppm) are diagnostic of the coordination mode in these
complexes. The complexes 2 and 5 are chiral and the chirality is
due to the presence of the out of plane Ge–Cl bond as well as the
way the ligand coordinates in 2, and the unsymmetrical nature of
the ligand in 5. Interestingly, in 5 both enantiomers are present in
the same unit cell (Fig. 4).
The chelation mode of the b-diketiminate in 2 was unex-
pected, since we were aiming at complex 3 (Scheme 1) in which
the phosphine moiety remains a spectator. However, recently
it has been demonstrated by Burford and coworkers that the
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Fig. 4 Molecular structure of 5, showing both the enantiomers. Thermal ellipsoids are drawn at 50% probability. Hydrogen atoms are omitted for clarity.
◦
˚
Selected bond lengths (A) and bond angles ( ): Ge(1)–N(1) 1.984(3), Ge(1)–N(2) 1.967(3), Ge(1)–Cl(1) 2.3250(11), N(1)–C(14) 1.348(4), C(14)–C(15)
1.400(5), C(15)–C(16) 1.387(5), N(2)–C(16) 1.351(5); N(2)–Ge(1)–N(1) 91.35(12), N(2)–Ge(1)–Cl(1) 93.70(9), N(1)–Ge(1)–Cl(1) 94.61(8).
Table 1 Crystal data for complexes 2 and 5
Experimental
2 C41H50ClGeN2P, 5 C41H50ClGeN2P,
General considerations
Empirical formula, CCDC-No. 741342
741341
All manipulations were performed in a dry and oxygen-free
atmosphere (N2 or Ar) by using Schlenk-line and glove-box
techniques. Solvents were purified with the M-Braun solvent
drying system. Compounds 111b (used MeLi in ether) and 416a were
prepared by literature methods. Other chemicals were procured
and used as received. 1H, 13C, and 31P NMR spectra were recorded
on a Bruker 500 or 300 MHz instrument and referenced to the
T/K
133(2)
Triclinic
¯
P1
133(2)
Orthorhombic
P212121
10.060(2
25.670(5)
29.272(6)
90
90
90
7559(3)
8
1.247
Crystal system
Space group
˚
a/A
11.003(2)
11.678(2)
16.335(3)
86.03(3)
87.29(3)
67.40(3)
1932.7(7)
2
˚
b/A
˚
c/A
a (◦)
b (◦)
g (◦)
1
deuterated solvent in the case of the H and 13C NMR spectra.
31P NMR spectra were referenced to 85% H3PO4. Elemental
analyses were performed by the Analytisches Labor des Institut fu¨r
Anorganische Chemie der Universita¨t Go¨ttingen. Melting points
were measured in sealed glass tubes with a Bu¨chi melting point B
540 instrument and are not corrected.
3
˚
V/A
Z
rc/Mg m-3
1.220
0.932
748
m/mm-1
0.954
2992
F(000)
Crystal size/mm
0.49 ¥ 0.36 ¥ 0.34 0.50 ¥ 0.12 ¥ 0.10
1.89–27.04
17957/8316
[R(int) = 0.0832] [R(int) = 0.1146]
q range [◦]
1.39–26.02
59909/14663
Reflections collected/unique
Crystallographic details. Suitable crystals of 2 and 5 were
mounted on a glass fiber and data were collected on an IPDS
II Stoe image-plate diffractometer (graphite monochromated
Reflections observed [I > 2s(I)] 7725
12018
Data/restraints/parameters
R1, wR2 [I > 2s(I)]a
R1, wR2 (all data)a
GoF
8316/0/425
14663/0/847
0.0480, 0.0861
0.0635, 0.0911
1.000
˚
0.0439, 0.1177
0.0467, 0.1199
1.068
Mo-Ka radiation, l = 0.71073 A) at 133(2) K. The data were
integrated with X-Area. The structures were solved by Direct
Methods (SHELXS-97)18 and refined by full-matrix least square
methods against F2 (SHELXL-97). All non-hydrogen atoms were
refined with anisotropic displacement parameters. The hydrogen
atoms were placed in calculated positions and refined by using a
riding model. Crystallographic data are given in Table 1.
Residual density
max./min./e A
1.211/-1.222
0.453/-0.492
-3
˚
ꢀ
ꢀ
ꢀ
ꢀ
a R1 = ꢀFo| - |Fcꢀ/ |Fo|. wR2 = [ w(Fo - Fc2)2/ w(Fo2)2]0.5
.
2
◦
Synthesis of 2. To
a
cooled (-30 ◦C) suspension of
Mp. 288–290 C. H NMR (300.01 MHz, C6D6) d 0.62 (d, 3H,
CH(CH3)2), 0.71 (d, 3H, CH(CH3)2), 0.81–0.84 (two doublets, 6H,
CH(CH3)2), 1.17–1.21 (two doublets, 6H, CH(CH3)2), 1.28 (d, 3H,
CH(CH3)2), 1.54 (d, 3H, CH(CH3)2), 1.68 (m, 1H, CH(CH3)2),
1.77 (s, 3H, CCH3), 1.91 (s, 3H, CCH3), 2.53 (m, 1H, CH(CH3)2),
3.02 (m, 1H, CH(CH3)2), 3.98 (m, 1H, CH(CH3)2), 6.95–7.20 (m,
12H, Ph), 7.82–7.90 (m, 2H, Ph), 8.03–8.11 (m, 2H, Ph) ppm;
1
dioxane·GeCl2 complex (1.50 g, 6.47 mmol) in ether (40 mL) was
added a suspension of 1 (4.44 g, 6.51 mmol) in ether (40 mL)
using a L-bent tube. The resultant mixture was stirred at room
R
temperature overnight and filtered using Celiteꢀ. All the volatiles
were removed from the filtrate and 50 mL of n-hexane was added
to the residue. The mixture was stirred well for about 30 min and
filtered to obtain a yellow colored powder (2.82 g). The filtrate
was kept at room temperature and after one day pale yellow
colored crystals were obtained (1.50 g). Total yield 4.32 g (94%).
1
13C{ H} NMR (75.47 MHz, C6D6) d 21.64, 21.80, 23.03, 23.77,
24.06, 24.29, 24.32, 24.43, 24.49, 24.57, 24.62, 26.81, 27.61, 28.35,
28.54, 28.91, 91.37, 92.03, 123.30–147.32 (28 resonances), 167.45,
236 | Dalton Trans., 2010, 39, 234–238
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1
167.48, 173.62, 173.97 ppm; 31P{ H} NMR (121.50 MHz, C6D6)
(h) N. J. Hardman, R. J. Wright, A. D. Phillips and P. P. Power, J. Am.
Chem. Soc., 2003, 125, 2667–2679.
d 15.16 ppm. Elemental analysis for C41H50ClGeN2P (%): Calcd.:
3 (a) V. Jancik, L. W. Pineda, A. C. Stu¨ckl, H. W. Roesky and R. Herbst-
Irmer, Organometallics, 2005, 24, 1511–1515; (b) S. Singh, A. Pal, H. W.
Roesky and R. Herbst-Irmer, Eur. J. Inorg. Chem., 2006, 4029–4032;
(c) G. Bai, H. W. Roesky, J. Li, M. Noltemeyer and H.-G. Schmidt,
Angew. Chem., 2003, 115, 5660–5664; G. Bai, H. W. Roesky, J. Li,
M. Noltemeyer and H.-G. Schmidt, Angew. Chem., Int. Ed., 2003, 42,
5502–5506; (d) Y. Peng, H. Fan, H. Zhu, H. W. Roesky, J. Magull and
C. E. Hughes, Angew. Chem., 2004, 116, 3525–3527; Y. Peng, H. Fan, H.
Zhu, H. W. Roesky, J. Magull and C. E. Hughes, Angew. Chem., Int. Ed.,
2004, 43, 3443–3445; (e) V. Jancik and H. W. Roesky, Angew. Chem.,
2005, 117, 6170–6172; V. Jancik and H. W. Roesky, Angew. Chem., Int.
Ed., 2005, 44, 6016–6018; (f) P. M. Gurubasavaraj, S. K. Mandal, H. W.
Roesky, R. B. Oswald, A. Pal and M. Noltemeyer, Inorg. Chem., 2007,
46, 1056–1061; (g) C. Cui, S. Kopke, R. Herbst-Irmer, H. W. Roesky, M.
Noltemeyer, H.-G. Schmidt and B. Wrackmeyer, J. Am. Chem. Soc.,
2001, 123, 9091–9098; (h) H. Zhu, J. Chai, Q. Ma, V. Jancik, H. W.
Roesky, H. Fan and R. Herbst-Irmer, J. Am. Chem. Soc., 2004, 126,
10194–10195; (i) S. Nembenna, H. W. Roesky, S. K. Mandal, R. B.
Oswald, A. Pal, R. Herbst-Irmer, M. Noltemeyer and H.-G. Schmidt,
J. Am. Chem. Soc., 2006, 128, 13056–13057; (j) M. Driess, S. Yao,
M. Brym and C. van Wu¨llen, Angew. Chem., 2006, 118, 4455–4458;
M. Driess, S. Yao, M. Brym and C. van Wu¨llen, Angew. Chem., Int.
Ed., 2006, 45, 4349–4352; (k) L. W. Pineda, V. Jancik, H. W. Roesky, D.
Neculai and A. M. Neculai, Angew. Chem., 2004, 116, 1443–1445; L. W.
Pineda, V. Jancik, H. W. Roesky, D. Neculai and A. M. Neculai, Angew.
Chem., Int. Ed., 2004, 43, 1419–1421; (l) M. Stender, A. D. Phillips and
P. P. Power, Inorg. Chem., 2001, 40, 5314–5315; (m) Y. Ding, H. Hao,
H. W. Roesky, M. Noltemeyer and H.-G. Schmidt, Organometallics,
2001, 20, 4806–4811; (n) Y. Ding, Q. Ma, I. Uson, H. W. Roesky, M.
Noltemeyer and H.-G. Schmidt, J. Am. Chem. Soc., 2002, 124, 8542–
8543; (o) Y. Ding, Q. Ma, H. W. Roesky, R. Herbst-Irmer, I. Uso´n,
M. Noltemeyer and H.-G. Schmidt, Organometallics, 2002, 21, 5216–
5220.
C, 69.37; H, 7.10; N, 3.95. Found: C, 69.65; H, 7.66; N, 3.96.
Synthesis of 5. To a cooled (-60 ◦C) solution of 4 (1.40 g,
2.86 mmol) in n-hexane (30 mL) was added a solution of Ph2PCl
(0.64 g, 2.90 mmol) in n-hexane (20 mL). The solution turned
yellow and a yellow precipitate started forming while the mixture
was brought to rt. After stirring the mixture overnight it was
filtered and the precipitate was dried under vacuum (0.80 g).
Keeping the filtrate at rt for one day also afforded orange yellow
crystals along ◦with some powder (1.02 g). Total yield 1.82 g (90%).
1
Mp. 173–175 C. H NMR (500.13 MHz, C6D6) d 1.09 (d, 3H,
CH(CH3)2), 1.15 (d, 3H, CH(CH3)2), 1.26–1.32 (three doublets,
9H, CH(CH3)2), 1.39 (s, 3H, CCH3), 1.42 (d, 3H, CH(CH3)2), 1.47
(d, 3H, CH(CH3)2), 1.52 (d, 3H, CH(CH3)2), 3.14 (q, 2H, CH2),
3.23 (m, 1H, CH(CH3)2), 3.39 (m, 1H, CH(CH3)2), 3.93 (m, 1H,
CH(CH3)2), 4.03 (m, 1H, CH(CH3)2), 4.92 (d, 1H, CH), 6.88–8.05
1
(several multiplets, 16H, Ph) ppm; 13C{ H} NMR (125.77 MHz,
C6D6) d 23.32, 23.97, 24.22, 24.47, 24.82, 24.89, 26.77, 27.75,
28.21, 28.28, 28.66, 29.18, 29.41, 37.12, 37.31, 101.86, 101.92,
124.00–147.21 (23 resonances), 164.31, 166.16 ppm; 31P{ H}
1
NMR (121.50 MHz, C6D6) d -13.47 ppm. Elemental analysis for
C41H50ClGeN2P (%): Calcd.: C, 69.37; H, 7.10; N, 3.95. Found: C,
69.45; H, 7.08; N, 3.34.
Conclusions
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In summary, we have synthesized two isomeric b-diketiminate
based Ge(II) complexes by two entirely different methods and they
have been structurally characterized. Ligand 1 has shown versatile
coordination modes and the way in which it coordinates to Ge(II)
in 2 is the first of its kind. The presence of a free phosphine moiety
in complex 5 can be exploited to coordinate further with other
metals to obtain heterometallic Ge(II) complexes. Currently, we
are exploring the route to incorporate two phosphine moieties in
the backbone of the b-diketiminate ligand.
Acknowledgements
This work was supported by the Deutsche Forschungsgemein-
schaft. NDR thanks the Alexander von Humboldt Stiftung and
Department of Science & Technology, New Delhi for financial
support.
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