Phosphaalkenyl germylenes and their gold, tungsten and molybdenum complexes

Article abstract of DOI:10.1039/c2cc17551g

The new bis(phosphaalkenyl) germanium(ii) compound (NHC)Ge(CClPMes*) ₂ reacts with L₂M(CO)₄ (M = Mo, W) to give bidentate complexes with an unexpected coordinating behaviour involving the Ge(ii) centre and one phosphorus atom, and with AuI or Me₂SAuCl to afford the monodentate complexes coordinated at the germanium(ii) atom.

Full text of DOI:10.1039/c2cc17551g

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COMMUNICATION
Phosphaalkenyl germylenes and their gold, tungsten and molybdenum
complexesw
Dimitri Matioszek,ab Tibor-Gabor Kocsor,abc Annie Castel,*ab Gabriela Nemes,*c
ab
Jean Escudie and Nathalie Saffond
´
Received 2nd December 2011, Accepted 17th February 2012
DOI: 10.1039/c2cc17551g
The new bis(phosphaalkenyl) germanium(II) compound
Q
(NHC)Ge(CCl PMes*)2 reacts with L2M(CO)4 (M = Mo, W)
to give bidentate complexes with an unexpected coordinating
behaviour involving the Ge(II) centre and one phosphorus atom,
and with AuI or Me2SAuCl to afford the monodentate complexes
coordinated at the germanium(II) atom.
During the last three decades, the stabilization and isolation of
compounds with group 14 elements in unusual or low oxidation
states has received considerable attention, particularly since the
discovery of the Arduengo-type carbene in 1991.1 The rapid
development of the chemistry of N-heterocyclic carbenes (NHC),
their use in transition metal catalysis2 and more recently as
organocatalysts3 have increased interest in their higher congeners
although they had been discovered earlier.4 However, among the
large number of stable monomeric germanium(II) compounds
reported to date,5 there are surprisingly few examples of stable
alkenyl group 14 divalent species; the last ones have generally
been obtained by hydrometallation reactions.5b,6
Scheme 1 Synthesis of compounds 1 and 2.
germylene 1 as a brown air-sensitive solid in a good yield
(Scheme 1). The 31P NMR spectrum indicates the formation
of only one isomer, probably the E/E form for steric reasons
(the intermediate lithium compound Mes*PQC(Li)Cl being
exclusively formed as the Z isomer), at 265.7 ppm, in the range
of well-known metallaphosphaalkenes.10 When the reaction
was performed with Cl2Geꢀdioxane instead of (NHC)GeCl2
and monitored by 31P NMR spectroscopy, the presence of a
signal at 297 ppm was observed which vanished after 3 h at
room temperature; however, by adding one equivalent of
NHC to the freshly prepared solution of 2, the compound 1
was obtained proving that the signal at 297 ppm corresponds to
the metastable 2. In both cases, it was not possible to prepare
the mono phosphaalkenyl-substituted germanium(II) compound:
using one equivalent of (NHC)GeCl2 or Cl2Geꢀdioxane yields
In previous studies, we highlighted the great interest of the
phosphaalkenyl moieties for access not only to novel derivatives7
but also for their ability to give various types of complexation.8
We therefore considered an extension of these studies to the
germanium divalent species. Herein, we describe the synthesis of
a bis(phosphaalkenyl) germanium(II) compound stabilized by
complexation with a carbene unit and its coordination reactions
to various transition-metals (tungsten, molybdenum and gold).
The reaction between two equivalents of the freshly prepared
phosphaalkenyl lithium Mes*PQC(Li)Cl8 and (NHC)GeCl2,9 in
THF solution at low temperature, gives the bis(phosphaalkenyl)
a
1
´
Universite de Toulouse, UPS, LHFA, 118 Route de Narbonne,
only the compound 1 or 2, respectively, as revealed by H and
31P NMR spectroscopy.
F-31062 Toulouse, France. E-mail: castel@chimie.ups-tlse.fr
b CNRS, LHFA, UMR 5069, F-31062 Toulouse Cedex 9, France
c Universitatea Babes--Bolyai, Facultatea de Chimie s-i Inginerie
Chimica˘, str. Kogalniceanu, nr; 1, RO-400084, Cluj-Napoca,
Romania. E-mail: sgabi@chem.ubbcluj.ro
Compound 1 is soluble in THF, diethyl ether and toluene
but rapidly decomposes in chlorinated solvents (chloroform,
dichloromethane). It is stable up to 60 1C in THF or toluene in
contrast with the recently reported (MeMesNacnac)GeC-
(tBu)QPH which has been obtained by hydrogermylation of
a phosphaalkyne.11 Suitable crystals for X-ray crystallography
were obtained from a saturated toluene solution at ꢁ24 1C.
The structure of 1 is shown in Fig. 1 with selected bond lengths and
angles.z These data confirm the presence of the E/E configuration
d Service Commun Rayons X, Institut de Chimie de Toulouse,
ICT- FR2599, Universite´ Paul Sabatier, UPS,
118 Route de Narbonne, F-31062 Toulouse Cedex 9, France
w Electronic supplementary information (ESI) available: Experimental
procedure and physicochemical data for compounds 1, 3–6,
X-ray data for 1, 3, 5 and 6. CCDC 857220 for 1, 857221 for 3,
857222 for 5, 857223 for 6. For ESI and crystallographic data in CIF
or other electronic format see DOI: 10.1039/c2cc17551g
c
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Chem. Commun., 2012, 48, 3629–3631 3629

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two resonances, one at 267.2 ppm with additional satellites due
to the coupling with tungsten (1JP–W = 214.7 Hz) and the second
one at 281.9 ppm suggesting that the two phosphaalkenyl
fragments are not equivalent with only one phosphorus atom
directly bonded to tungsten. In addition, the 1H NMR spectrum
reveals a non-equivalence of the (NHC) isopropyl units with four
signals for the methyl groups and two signals for the methine
protons. These non-equivalences can result not only from the
presence of two different phosphaalkenyl ligands causing chirality
at the germanium atom but also from a restricted rotation around
the Ge–Ccarbene bond which is slow on the NMR time scale.
The 13C NMR spectra show the same complexity with the
non-equivalence not only of the isopropyl groups, but also of
the carbons of the Mes* moiety. In addition, four doublets
(coupling with the phosphorus atom) were observed for CO
groups. For each compound, the IR spectrum exhibits four
CO stretching vibrations of similar intensity characteristic of a
L2W(CO)4 moiety.10,14 The NMR and IR spectra of the
molybdenum complex 4 present the same features which
differ only with respect to chemical shifts (for example d
31P (C6D6) = 280.2 (PMo); 296.2 (P)). The X-ray crystallography
study of 3 (suitable crystals were obtained from CH2Cl2
at ꢁ24 1C) confirms the coordination of only one phosphorus
atom, the second C(Cl)QPMes* ligand remaining ‘‘pendent’’.
The tungsten centre is octahedrally coordinated with two
carbonyl groups occupying the apical positions and forms a
planar four-membered ring with P1, C2 and Ge1 atoms
(P1–C2–Ge1–W1 torsion angle of only 0.39(17)1) (Fig. 2).
The germanium atom adopts a distorted tetrahedral geometry
with a small endocyclic W1–Ge1–C2 bond angle (89.94(10)1),
significantly smaller than that in the complex reported by
Fig. 1 Molecular structure of compound 1 in the solid state (50%
probability level for the thermal ellipsoids). For clarity, hydrogen
atoms and crystallization solvent (toluene) are omitted. Me, iPr and
Mes* groups are simplified. Selected bond distances [A] and bond
angles [1]: Ge1–C1 2.087(2), Ge1–C2 2.014(2), Ge1–C3 2.011(2),
P1–C2 1.675(3), P2–C3 1.676(3), Cl1–C2 1.762(2), Cl2–C3 1.770(3);
C1–Ge1–C2 96.04(9), C1–Ge1–C3 105.76(10), C2–Ge1–C3 100.39(10).
in which the germanium center is tri-coordinate and exhibits a
distorted-pyramidal geometry (sums of bond angles 302.191).
The Ge–C bond lengths (2.011(2) and 2.014(2) A) are among
the shortest described in the literature (2.012–2.067 A)11,12 for
germylenes. The PQC distances (1.675(3) A and 1.676(3) A)
lie in the expected range10 and the Ge–Ccarbene bond (2.087(2) A)
compares well with those of (NHC)GeMes2 (2.078(3) A)9 and of
the recently described (NHC)Ge[Sn(SiMe3)3]2 (2.082(4) A).13
One of the great interests of 1 is to have multiple coordination
sites (the divalent metal center, the CQP double bonds and the
phosphorus atoms) potentially leading to mono-, bi- or tridentate
derivatives. In order to gain more insight into the ability of 1 to
coordinate transition-metal, reactions with [codW(CO)4] (cod =
1,5-cyclooctadiene) and [nbdMo(CO)4] (nbd = 2,5-norbornadiene)
were firstly examined. Displacement of the ligand (cod or nbd)
occurred easily in THF at 60 1C (Scheme 2).
Complexes 3 and 4 were isolated in good yields (73% and
67%, respectively) as brown or yellow powders. They are
soluble in common organic solvents, especially in chlorinated
solvents where they are perfectly stable in comparison with the
non-coordinated germylene 1. The 31P NMR spectra of 3 showed
Fig. 2 Molecular structure of compounds 3 and 5 in the solid state
(50% probability level for the thermal ellipsoids). For clarity, hydrogen
atoms and crystallization solvent (dichloromethane) are omitted. Me,
iPr and Mes* groups are simplified. Selected bond distances [A] and bond
angles [1]: 3: Ge1–C1 2.042(3), Ge1–C2 2.010(4), Ge1–C3 1.970(4),
P1–C2 1.674(4), P2–C3 1.672(4), C2–Cl1 1.736(4), C3–Cl2 1.746(3),
W1–P1 2.4952(10), W1–Ge1 2.6508(4); P1–W1–Ge1 66.42(2),
P1–C2–Ge1 99.56(17), C3–Ge1–C2 104.09(15), C3–Ge1–C1 100.57(14),
C1–Ge1–C2 112.45(14), C3–Ge1–W1 126.53(10), C2–Ge1–W1 89.94(10),
C1–Ge1–W1 121.33(10), Ge1–C3–P2 125.76(19), P1–C2–Ge1–W1 0.39(17).
5: Ge1–C1 2.031(3), Ge1–C2 1.974(3), Ge1–C3 1.969(3), Ge1–Au1 2.3449(3),
Au1–Cl3 2.3128(9), P1–C2 1.668(3), P2–C3 1.665(3), Cl2–C3 1.752(3),
Cl1–C2 1.743(3); Cl3–Au1–Ge1 177.07(3), C1–Ge1–C2 102.17(12),
C1–Ge1–C3 110.53(12), C2–Ge1–C3 106.66(12), C1–Ge1–Au1 113.79(9),
C2–Ge1–Au1 116.06(9), C3–Ge1–Au1 107.38(9).
Scheme 2 Synthesis of metallo-germylenes 3–6.
3630 Chem. Commun., 2012, 48, 3629–3631
c
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A. Filippou et al. (97.81(1)1).15 The Ge–W bond length
(2.6508(4) A) is one of the longest to be reported in germylene
complexes,16 and is close to the value of a germanium–tungsten
single bond 2.681(3) A.17 It is also to note the shortening of the
Ge–Ccarbene distance (2.042(3) A) compared to that of the
starting germylene (2.087(2) A).
C
53H78Cl2GeN2O4P2W, 3(CH2Cl2),
M
=
%
1451.23, triclinic, P1,
a = 12.0774(6), b = 14.8952(8), c = 21.9932(16) A, a = 100.256(3),
b = 96.379(3), g = 113.219(2)1, V = 3505.3(4) A3, Z = 2, 63975
reflections collected, 140 94 unique (Rint = 0.0361), R1 (observed data) =
0.0347, wR2 (all data) = 0.0930. 5ꢀ2.5(CH2Cl2): C49H78AuCl3GeN2P2,
%
2.5(CH2Cl2), M = 1345.30, triclinic, P1, a = 11.3212(6), b = 15.4945(7),
c = 18.5887(10) A, a = 79.533(2), b = 87.667(2), g = 77.006(2)1, V =
=
3124.4(3) A3, Z = 2, 65 805 reflections collected, 15 160 unique (Rint
The germylene 1 gives an immediate and very clean reaction
with one equivalent of ClAuSMe2 or AuI leading quantitatively
to the gold complexes 5 or 6 (Scheme 2) which were isolated as
brown or orange powders soluble in all common solvents.
Surprisingly, these complexes are very stable towards oxidation
0.0365), R1 (observed data) = 0.0325, wR2 (all data) = 0.0790.
6ꢀ1.5(C6H6): C49H78AuCl2GeIN2P2, 1.5(C6H6), M = 1341.59, mono-
clinic, C2/c, a = 12.1895(9), b = 37.193(3), c = 27.7641(18) A, b =
95.446(3)1, V = 12530.3(16) A3, Z = 8, 124 173 reflections collected,
12 726 unique (Rint = 0.0988), R1 (observed data) = 0.0452, wR2
(all data) = 0.0917.
1
and hydrolysis. The 31P and H NMR spectra are consistent
1 A. J. Arduengo III, R. L. Harlow and M. Kline, J. Am. Chem.
Soc., 1991, 113, 361.
with the presence of a symmetrical species in each case. Indeed,
only one phosphorus signal was observed for each compound at
293.0 (5) and 292.6 ppm (6), and the 1H NMR signals (methine
protons and methyl groups of (NHC) isopropyl units) are
equivalent. Suitable crystals for X-ray crystallography were
grown from dichloromethane (for 5) and from benzene (for 6)
at room temperature. Their molecular structures with the main
geometrical parameters are shown in Fig. 2 (for 5) and in the
ESIw (for 6). These complexes are isomorphous and their
structures show the sole formation of Ge(II)–Au(I) adducts.
To date, there is only one gold germylene complex obtained from
pyridyl-azaallyl germanium(II) chloride and AuI.18 Generally, the
germylenes R2Ge gave insertion reactions in the Au–halogen
bond leading to R2XGe–Au complexes with a s Au–Ge bond.19
In our case, the steric hindrance of the phosphaalkenyl moieties
probably prevents this reaction. Moreover, we never observed the
coordination of the phosphorus atom although the phosphine
gold complexes are very well known.20 The gold atom presents
an almost linear coordination with bond angles Ge1–Au1–Cl3
of 177.07(3)1 in 5 and Ge1–Au1–I1 of 176.75(2)1 in 6. The
Ge–Au distances of 2.3449(3) A in 5 and 2.3641(6) A in 6,
respectively, are similar to those previously reported for
Ge(II)–Au distances 2.346(2) A.18
2 F. Glorius, N-Heterocyclic Carbenes in Transition Metal Catalysis,
Springer, Berlin, 1st edn, 2006.
3 N. Marion, S. Diez-Gonzalez and S. P. Nolan, Angew. Chem., Int. Ed.,
2007, 46, 2988.
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Org. Chem., 1982, 37, 1375; (b) W. A. Herrmann, M. Denk,
J. Behm, W. Scherer, F.-R. Klingan, H. Bock, B. Solouki and
M. Wagner, Angew. Chem., Int. Ed., 1992, 31, 1485.
5 (a) S. Nagendran and H. W. Roesky, Organometallics, 2008, 27, 457;
(b) S. K. Mandal and H. W. Roesky, Chem. Commun., 2010, 6016;
(c) M. Asay, C. Jones and M. Driess, Chem. Rev., 2011, 111, 354.
6 (a) A. Jana, D. Ghoshal, H. W. Roesky, I. Objartel, G. Schwab
and D. Stalke, J. Am. Chem. Soc., 2009, 131, 1288; (b) A. Jana,
H. W. Roesky and C. Schulzke, Dalton Trans., 2010, 39, 132.
7 P. M. Petrar, G. Neme-s, I. Silaghi-Dumitrescu, H. Ranaivonjatovo,
H. Gornitzka and J. Escudie
´
, Chem. Commun., 2007, 4149.
I. Silaghi-Dumitrescu,
8 R. Septelean, G. Nemes, J. Escudie
´
,
H. Ranaivonjatovo, P. M. Petrar, H. Gornitzka, L. Silaghi-Dumitrescu
and N. Saffon, Eur. J. Inorg. Chem., 2009, 628.
9 P. A. Rupar, V. N. Staroverov, P. J. Ragogna and K. M. Baines,
J. Am. Chem. Soc., 2007, 129, 15138.
´
10 R. Septelean, G. Nemes, J. Escudie, I. Silaghi-Dumitrescu,
H. Ranaivonjatovo, H. Gornitzka, L. Silaghi-Dumitrescu and
S. Massou, Eur. J. Inorg. Chem., 2006, 4237.
11 S. L. Choong, W. D. Woodul, C. Schenk, A. Stasch,
A. F. Richards and C. Jones, Organometallics, 2011, 30, 5543.
12 (a) P. Jutzi, A. Becker, H. G. Stammler and B. Neumann, Organo-
metallics, 1991, 10, 1647; (b) G. L. Wegner, R. J. F. Berger, A. Schier
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L. Pu, M. M. Olmstead and P. P. Power, Organometallics, 1997,
16, 1920.
In summary, the first bis(phosphaalkenyl) germanium(II)
compound was isolated and fully characterized, including
X-ray diffraction analysis. An unexpected coordinating behaviour
involving the Ge(II) centre and one phosphorus atom was
observed with tungsten and molybdenum complexes whereas
the sole coordination of the germanium centre occurred with
gold complexes. The reactivity study of 1 with other types of
transition metal complexes is now under investigation in order
to determine the factors influencing the type of complexes.
We are grateful to the CNRS (ANR-08-BLAN-0105-01)
and Romanian Agency UEFISCDI (PCCE-140/2008) for
financial support of this work. T. K. thanks also POSDRU
(contract 88/1.5/S/60185—Investing in people!).
´
13 N. Katir, D. Matioszek, S. Ladeira, J. Escudie and A. Castel,
Angew. Chem., Int. Ed., 2011, 50, 5352.
14 B. Hutchinson and K. Nakamoto, Inorg. Chim. Acta, 1969, 3, 591.
15 A. C. Filippou, N. Weidemann, A. I. Philippopoulos and
G. Schnakenburg, Angew. Chem., Int. Ed., 2006, 45, 5987.
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2010, 29, 3039; (b) R. Aysin, P. Koroteev, A. Korlyukov, A. Zabula,
S. Bukalov, L. Leites, M. Egorov and O. Nefedov, Russ. Chem. Bull.,
2010, 59, 348; (c) G. Huttner, U. Weber, B. Sigwarth, O. Scheidsteger,
H. Lang and L. Zsolnai, J. Organomet. Chem., 1985, 282, 331;
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B. V. Mork, R. S. Simons and P. P. Power, J. Am. Chem. Soc.,
2000, 122, 650; (b) A. C. Filippou, P. Portius, J. G. Winter and
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¨
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Notes and references
z Details
of
the
X-ray
C49H78Cl2GeN2P2, 2(C7H8),
diffraction 1ꢀ2(C7H8):
%
1084.83, triclinic, P1, a =
studies:
M
=
13.9844(4), b = 14.0830(4), c = 18.5657(6) A, a = 79.5190(10),
b = 75.8570(10), g = 63.2850(10)1, V = 3156.09(16) A3, Z =
2, 48 874 reflections collected, 12 787 unique (Rint
R1 (observed data) = 0.0458, wR2 (all data) = 0.1262. 3ꢀ3(CH2Cl2):
=
0.0490),
19 U. Anandhi and P. R. Sharp, Inorg. Chim. Acta, 2006, 359, 3521.
20 E. R. T. Tiekink and J.-G. Kang, Coord. Chem. Rev., 2009, 253, 1627.
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 3629–3631 3631