The iminophosphorane Ph3P=NSiMe3 as a synthon for M-Caryl σ bonds (M = In, Fe, Ge) implementing imino sidearm donation

Article abstract of DOI:10.1021/om0009738

Lithiation of triphenyl((trimethylsilyl)imino)phosphorane, Ph₃P=NSiMe₃ (1), with MeLi gives the ortho-metalated species [Li(o-C₆H₄PPh₂NSiMe₃)]₂ ·Et₂O (2). It has all the requirements of an organometallic ligand capable of sidearm donation: the deprotonated orthophenyl carbon atom leads to metal-carbon σ bonds in reactions with metal halides, and the Ph₂P=NSiMe₃ moiety donates an electron pair to that metal via the imine nitrogen atom. In reactions with InCl₃ the In(III) organometallic complex [In(o-C₆H₄PPh₂NSiMe₃)₃] (3) was obtained, while with FeCl₂ a new example of the rare iron(II) 14-VE complexes [Fe(o-C₆H₄PPh₂NSiMe₃)₂] (4) was obtained. Reaction of 2 with Ph₃GeCl gave [Ph₃Ge(o-C₆H₄PPh₂NSiMe₃)] (5). While in 4 both imino sidearms coordinate to the metal, because of steric crowding only two of the three present coordinate in 3. Because of the low Lewis acidity of the tetraorganogermanium moiety the imino sidearm does not donate to the central germanium atom in 5.

Full text of DOI:10.1021/om0009738

2730
Organometallics 2001, 20, 2730-2735
Th e Im in op h osp h or a n e P h 3P dNSiMe3 a s a Syn th on for
M-Ca r yl σ Bon d s (M ) In , F e, Ge) Im p lem en tin g Im in o
Sid ea r m Don a tion
Stefan Wingerter,† Matthias Pfeiffer,† Thomas Stey,† Monica Bolboaca´,‡
Wolfgang Kiefer,‡ Vadapalli Chandrasekhar,§ and Dietmar Stalke*,†
Institut fu¨r Anorganische Chemie der Universita¨t Wu¨rzburg, Am Hubland,
D-97074 Wu¨rzburg, Germany, Institut fu¨r Physikalische Chemie der Universita¨t Wu¨rzburg,
Am Hubland, D-97074 Wu¨rzburg, Germany, and Department of Chemistry,
Indian Institute of Technology, Kanpur, Kanpur-208 016, India
Received November 15, 2000
Lithiation of triphenyl((trimethylsilyl)imino)phosphorane, Ph3PdNSiMe3 (1), with MeLi
gives the ortho-metalated species [Li(o-C6H4PPh2NSiMe3)]2‚Et2O (2). It has all the require-
ments of an organometallic ligand capable of sidearm donation: the deprotonated ortho
phenyl carbon atom leads to metal-carbon σ bonds in reactions with metal halides, and the
Ph2PdNSiMe3 moiety donates an electron pair to that metal via the imine nitrogen atom.
In reactions with InCl3 the In(III) organometallic complex [In(o-C6H4PPh2NSiMe3)3] (3) was
obtained, while with FeCl2 a new example of the rare iron(II) 14-VE complexes [Fe(o-C6H4-
PPh2NSiMe3)2] (4) was obtained. Reaction of 2 with Ph3GeCl gave [Ph3Ge(o-C6H4PPh2-
NSiMe3)] (5). While in 4 both imino sidearms coordinate to the metal, because of steric
crowding only two of the three present coordinate in 3. Because of the low Lewis acidity of
the tetraorganogermanium moiety the imino sidearm does not donate to the central
germanium atom in 5.
Ch a r t 1. Am in o Sid ea r m Don a tion (a ) ver su s
Im in o Sid e Ar m Don a tion (b)
In tr od u ction
The concept of sidearm donation has been very
effectively pioneered and utilized by van Koten and co-
workers,1-3 with the recent consummation of this
concept being the design of cartwheel types of ligands,
C6[3,5-(CH2Y)2C6H3]6 (Y ) NMe2, P(O)Ph2, PPh2, SPh),
for supporting multimetallic assemblies.3 The approach
of sidearm donation4 involves R-metalated aryl ligands
substituted with CH2Y, where the heteroatom in the
group Y provides intramolecular coordination to the
metal, thereby providing extra stabilization (Chart 1).
In the design of most of these ligands the group Y is
linked to the aromatic moiety by the means of an alkyl
bridge. Schmidbaur and co-workers have shown that the
iminophosphorane Ph3PdNSiMe3 in its reactions with
triphenylaluminum or -gallium first affords a complex
where the group 13 metal is coordinated through the
imino nitrogen atom.5,6 More recently we have shown
that ortho lithiation of the iminophosphorane Ph3Pd
NSiMe3 (1) affords a new type of sidearm donating
ligand, [Li(o-C6H4PPh2NSiMe3)]2‚Et2O (2).7 The lithia-
tion and reactivity of the trimethyl((trimethylsilyl)-
imino)phosphorane8 Me3PdNSiMe3 and the structure
of the tetrameric complex [(LiCH2)Me2PdNSiMe3]4 have
been studied by Dehnicke et al.9 The coordinating
nitrogen atom of the sidearm is an imino nitrogen
(NSiMe3) that is connected to the aromatic group
through the intervening phosphorus atom. In previous
studies we have shown the utility of this ligand in
stabilizing diarylstannylenes and plumbylenes in their
monomeric forms,10 besides demonstrating their effect-
iveness as a chelating ligand for Zn(II) and organo-
copper(I) compounds.11 While with Sn(II), Pb(II), and
Zn(II) two ligands per metal ion are coordinated, with
Cu(I) only one ligand is involved. In all known com-
† Institut fu¨r Anorganische Chemie der Universita¨t Wu¨rzburg.
‡ Institut fu¨r Physikalische Chemie der Universita¨t Wu¨rzburg.
§ Indian Institute of Technology.
(1) For reviews see: (a) van Koten, G. Pure Appl. Chem. 1989, 61,
1681. (b) J astrzebski, J . T. B. H.; van Koten, G. Adv. Organomet. Chem.
1993, 35, 241.
(2) Knapen, J . W. J .; Van der Made, A. W.; de Wilde, J . C.; van
Leeuwen, P. W. N. M.; Wijkens, P.; Grove, D. M.; van Koten, G. Nature
1994, 372, 659.
(3) Dijkstra, H. P.; Steenwinkel, P.; Grove, D. M.; Lutz, M.; Spek,
A. L.; van Koten, G. Angew. Chem. Int. Ed. 1999, 38, 2186.
(4) Review on the concept of intramolecular coordination: Gruter,
G.-J . M.; van Klink, G. P. M.; Akkerman, O. S.; Bickelhaupt, F. Chem.
Rev. 1995, 95, 2405.
(7) Steiner, A.; Stalke, D. Angew. Chem., Int. Ed. Engl. 1995, 34,
1752.
(8) Schmidbaur, H.; J onas, G. Chem. Ber. 1967, 100, 1120.
(9) Mu¨ller, A.; Neumu¨ller, B.; Dehnicke, K. Chem. Ber. 1996, 129,
253.
(10) Wingerter, S.; Gornitzka, H.; Bertermann, R.; Pandey, S. K.;
Rocha, J .; Stalke, D. Organometallics 2000, 19, 3890.
(11) Wingerter, S.; Gornitzka, H.; Bertrand, G.; Stalke, D. Eur. J .
Inorg. Chem. 1999, 173.
(5) Schmidbaur, H.; Wolfsberger, W. Chem. Ber. 1967, 100, 1000.
(6) Schmidbaur, H.; Wolfsberger, W. Chem. Ber. 1967, 100, 1016.
10.1021/om0009738 CCC: $20.00 © 2001 American Chemical Society
Publication on Web 05/22/2001

Ph3PdNSiMe3 as a Synthon for M-Caryl σ Bonds
Organometallics, Vol. 20, No. 13, 2001 2731
pounds the imino nitrogen atom is occupied by coordi-
nation to the metal ion. To explore the general scope of
this ligand system with a view to understanding its
coordination behavior toward diverse types of metals
and metalloids, we have carried out the reactions of
[Li(o-C6H4PPh2NSiMe3)]2‚Et2O (2) with indium, germa-
nium, and iron halides. In the choice of these reactions
we had the following questions in mind:
(i) How is the formal P-N double bond affected by
ortho phenyl ring metalation and metal coordination?
(ii) Can a metal ion accommodate more than two of
these bulky ligands?
(iii) Under what conditions would the imino nitrogen
not participate in sidearm donation?
(iv) What would be the mode of linkage to a typical
transition-metal ion such as Fe(II)?
The results of these investigations are discussed in
the following account.
F igu r e 1. FT-Raman (1a, 2a) and FT-infrared (1b, 2b)
spectra of Ph3PdNSiMe3 (1) and [Li(o-C6H4PPh2NSiMe3)]2‚
Et2O (2). Complete assignment is given in Table 2 of the
Supporting Information.
Resu lts a n d Discu ssion
Ra m a n a n d In fr a r ed Sp ectr oscop ic In vestiga -
t ion s a n d Th eor et ica l Ca lcu la t ion s of P h 3P d
NSiMe3 (1) a n d [Li(o-C6H4P P h 2NSiMe3)]2‚Et2O (2).
Ortho metalation of Ph3PdNSiMe3 (1) and imido group
metal sidearm coordination is in all known cases ac-
companied by P-N bond lengthening. This effect should
be detectable in vibrational spectroscopic experiments,
as not all organometallic species can be obtained as
single crystals. The Raman and infrared spectra of
Ph3PdNSiMe3 (1) and [Li(o-C6H4PPh2NSiMe3)]2‚Et2O
(2) were recorded and the vibrational modes assigned
by DFT calculations. The geometrical parameters of
Ph3PdNSiMe3 (1) and the model compound [Li(o-C6H4-
PH2NSiH3)]2‚H2O (2*) were calculated at the BPW91/
6-31G* and BPW91/6-31+G* levels of theory. The
geometry was computed without any symmetry restric-
tion. Analytical harmonic vibrational modes have also
been calculated for both structures to confirm that a
local minimum on the potential energy surface was
found. The computed geometry of both Ph3PdNSiMe3
(1) and the model compound [Li(o-C6H4PH2NSiH3)]2‚
H2O (2*) match the experimental solid-state structures,
especially at the BPW91/6-31+G* level of theory. The
PdN bond length in the lithium complex (1.562(2) Å,
calculated 1.573(4) Å) is 0.02 Å longer than that of the
iminophosphorane 1. The P-C bond lengths do not
differ significantly for the lithium compound 2 compar-
ing to the starting material 1 (1.802(2)-1.812(3) Å,
calculated 1.818(3)-1.821(4) Å).
FT-Raman and infrared spectroscopy was employed
to elucidate the coordination behavior of the lithiated
triphenyl((trimethylsilyl)imino)phosphorane compound
2 in relation to the parent starting material 1. The
assignment of the vibrational modes was performed
with the help of DFT calculations. The infrared and
Raman spectra of Ph3PdNSiMe3 (1) and [Li(o-C6H4-
PPh2NSiMe3)]2‚Et2O (2), in the range from 400 to 1800
cm-1, are presented in Figure 1.
One of the most relevant features of the vibrational
spectra of organometallic compounds are the metal-
carbon stretching vibrations, since they are directly
related to the most substantial property of the molecule,
that is the M-C bond strength.12 However, the assign-
ment of the ν(M-C) vibrational modes is often quite
complicated due to the presence of other bands in the
same region or of their low intensities. In our case, the
lithium-carbon stretching vibration appears only in the
infrared spectrum of [Li(o-C6H4PPh2NSiMe3)]2‚Et2O (2)
as a weak band at 956 cm-1. The assignment of the ν-
(Li-C) vibration was based on the results of theoretical
calculations. Significant changes in the position and
relative intensities of some bands could be observed in
the Raman spectrum of 2. Thus, the band at 684 cm-1
(calculated 687 cm-1) assigned in the spectrum of 1 to
the νa(Si-C) vibration is shifted to lower wavenumbers
by 6 cm-1 and the intensity is increased due to convolu-
tion of the νs(Li-N) vibration in the same spectral
range.13 The band around 1100 cm-1 assigned to the ν-
(P-Ph) vibration14 is more intense in the spectrum of
lithium compound 2. The new shoulder that appears in
the spectrum of 2 at 739 cm-1 was attributed to the νs-
(Li-O) vibration.12 In the Raman spectrum of [Li(o-
C6H4PPh2NSiMe3)]2‚Et2O (2) the broad band at about
1331 cm-1 (calculated 1332 cm-1) was assigned to the
ν(PdN) stretching mode.15 In comparison to the corre-
sponding vibration of Ph3PdNSiMe3 (1), this band is
shifted to higher wavenumbers by 10 cm-1, due to the
N-Li coordination. The shift of the ν(PdN) vibration
confirms our observation that the iminophosphorane
units coordinate through the imino nitrogen atoms.
Syn th esis of 3-5. The reactions of the lithiated
iminophosphorane 2 with indium trichloride, ferrous
dichloride, or triphenylgermanium chloride proceed
quite smoothly by the complete replacement of chlorine
atoms, with the elimination of lithium chloride and with
the formation of three, two, or one M-Caryl σ bonds to
afford products 3-5 respectively (eqs 1-3).
X-r a y Cr yst a l St r u ct u r e of [In (o-C6H 4P P h 2-
NSiMe3)3] (3). The molecular structure of the complex
(12) Nakamoto, K. Infrared and Raman Spectra of Inorganic and
Coordination Chemistry, 5th ed.; Wiley: New York, 1997; Part A
(Theory and Applications in Inorganic Chemistry), p 148.
(13) Ismail, Z. K.; Hauge, R. H.; Margrave, J . L. J . Chem. Phys. 1972,
57, 5137.
(14) Pikl, R.; Duschek, F.; Fickert, C.; Finsterer, R.; Kiefer, W. Vib.
Spectrosc. 1997, 14, 189.
(15) Colthup, N. B.; Daly, L. H.; Wiberley, S. E. Introduction to
Infrared and Raman Spectroscopy; Academic Press: New York,
London, 1964; p 305.

2732 Organometallics, Vol. 20, No. 13, 2001
Wingerter et al.
Figu r e 2. Solid-state structure of [In(o-C6H4PPh2NSiMe3)3]
(3). Selected bond lengths (Å) and angles (deg) are pre-
sented in Table 1.
equatorial bond angles, the axial bond angle N1-In-
N3 also deviates from the ideal value of 180° to 168.82-
(6)°. A related indium compound, In(o-C6H4CH2NMe2)3, 16
which contains the sidearm donating dimethylamino
group, is isostructural with 3, suggesting that the
deviation from regular trigonal-bipyramidal geometry
in 3 is probably a reflection of the short bite of the
chelate spanning the equatorial-axial positions.
The In-C bond distances in 3 (2.169(2)-2.228(3) Å)
are similar to the In-Caryl distances observed in other
organoindium compounds such as (t-Bu)2In(2,6-i-Pr2-
C6H3)SiPh3 (2.222(6) and 2.223(6) Å)17 and Me2In(C6H4-
NEt2) (2.205(8) Å).18 The In-N bond distances observed
in 3 (N1, 2.696(3) Å; N3, 2.487(2) Å) are considerably
longer than those observed in more covalent situations,
as found, for example, in [In{N(SiMe3)2}3] (2.049(1) Å).19
However, these can be still considered as reasonably
strong interactions, considering the sum of the covalence
radii of In (1.5 Å) and N (0.7 Å).20 Also, In-Ncoord
distances found in other compounds In(o-C6H4CH2-
16
NMe2)3 (2.504, 2.565 Å) are consistent with trends
observed in the present instance. In comparison, the
distance between In1 and the third imino nitrogen N2
in 3 is 3.542(2) Å, clearly indicating the absence of any
interaction between the two atoms.
The P-N bond distances of 1.570(2) Å (P1-N1),
1.582(2) Å (P3-N3), and 1.550(2) Å (P2-N2) are
consistent with the structure of 3. The shortest distance
involves the imino nitrogen that does not participate in
coordination.
X-r a y Cr ysta l Str u ctu r e of [F e(o-C6H4P P h 2NSi-
Me3)2] (4). Although a large number of organoiron
compounds containing 18 valence electrons are known,21
the corresponding compounds with 14 valence electrons
3 is shown in Figure 2. The asymmetric unit of this
complex also contains two noncoordinating toluene
molecules.
The complex 3 is monomeric, and the central indium
atom is five-coordinated in a distorted-trigonal-bipyra-
midal geometry. The coordination environment around
indium is composed of three equatorial aryl substituents
and two apical imino nitogens which function as side-
arm donors. The third imino nitrogen is not involved in
coordination to the indium atom. The sum of the
equatorial bond angles is 358.85°. However, there is
considerable variation in the individual equatorial
C-In-C angles besides their deviation from the ideal
value of 120°. Thus, the largest angle is seen for C202-
In-C302, 141.23(9)°, while the other two angles C102-
In-C202 and C302-In-C102 are 110.31(9) and 107.31-
(9)°, respectively. Similar to the distortion in the
(16) Schumann, H.; Seuss, T. D.; Hemling. Private communication
to the CCDC.
(17) Petrie, M. A.; Ruhlandt-Senge, K.; Hope, H.; Power, P. P. Bull.
Soc. Chim. Fr. 1993, 130, 851.
(18) Schumann, H.; Hartmann, U.; Wassermann, W.; Dietrich, A.;
Go¨rlitz, F. H.; Pohl, L.; Hostalek, M. Chem. Ber. 1990, 123, 2093.
(19) J olly, W. L. In Modern Inorganic Chemistry, 2nd ed.; McGraw-
Hill: New York, 1991.
(20) Pauling, L. In Die Natur der Chemischen Bindung, 3rd ed.;
Verlag Chemie: Weinheim, Germany, 1968.

Ph3PdNSiMe3 as a Synthon for M-Caryl σ Bonds
Organometallics, Vol. 20, No. 13, 2001 2733
Figu r e 3. Solid-state structure of [Fe(o-C6H4PPh2NSiMe3)2]
(4). Selected bond lengths (Å) and angles (deg) are pre-
sented in Table 1.
F igu r e 4. Solid-state structure of [Ph3Ge(o-C6H4PPh2-
NSiMe3)] (5). Selected bond lengths (Å) and angles (deg)
are presented in Table 1.
are not very abundant. A few examples that are known
include [Fe(C6Cl5)2(PEt2Ph)2],22 [FeR2(bpy)2] (R
)
Me, Et),23 [FeR2(dippe)2],24 [Fe(CH2Ph)2(TMEDA)],25
[Fe(Trip)2(PyH)2],26 etc. Furthermore, the number of
homoleptic iron(II) compounds containing alkyl or aryl
ligands are also quite rare, a few examples being the
dimers [{FeR2}2] (R ) Mes,27 2,4,6-i-Pr3C6H2 28) and the
monomer [Fe(2,4,6-t-Bu3C6H2)2].29 Recently Leung et al.
have reported homoleptic Fe(II) compounds containing
intramolecular sidearm coordinating nitrogen atoms.30
Compound 4 reported in this study belongs to this class
of 14-VE type of molecules. The molecular structure of
4 is shown in Figure 3.
The structure of the complex is isostructural with the
other 14-VE complex prepared with the o-C6H4PPh2-
NSiMe3 ligand, viz., [Zn(o-C6H4PPh2NSiMe3)2]. The
coordination environment around Fe(II) is comprised of
two carbon atoms and two nitrogen atoms arranged in
a distorted-tetrahedral geometry. The bond angles
around Fe vary from 88.70(10)° (N1-Fe1-C2) to
126.90(12)° (N1-Fe1-N1A). The Fe-C distance ob-
served (2.071(3) Å) is one of the shortest Fe-C distances
found for organoiron(II) compounds, which vary between
2.021 and 2.227 Å.22-30 The Fe-N bond distances
observed for 4 (2.111(2) Å) are similar to those observed
for compounds containing sidearm donation.30 The P-N
bond distance in 4 is slightly longer (1.591(2) Å) in
comparison with the ligand in 2 (1.562(2) Å)6 and is in
the range for observed trends in PdN distances.31-34
X-r a y Cr ysta l Str u ctu r e of [P h 3Ge(o-C6H4P P h 2-
NSiMe3)] (5). The X-ray structure of 5 is shown in
Figure 4. In the asymmetric unit of 5 a solvent diethyl
ether molecule is also present which does not show any
interaction with the organogermanium complex.
The germanium atom is surrounded by four co-
valently bound carbon atoms. The sidearm nitrogen N1
is at a distance of 3.111(4) Å from the central germa-
nium atom, Ge1. Although the angle N1‚‚‚Ge1-C34 is
173.8°, close enough to be an axial angle, we discount
the possibility of the sidearm nitrogen interacting with
germanium on the following grounds. (1) Ge1 is out of
plane by a considerable 0.47 Å from an equatorial plane
defined by Ge1, C2, C22, and C28. (2) The sum of the
equatorial bond angles is 343.2°, in comparison to the
ideal value of 360.0° (Figure 5). (3) The bond distances
found in situations where the sidearm nitrogen is
believed to participate in coordination to germanium are
considerably smaller than those observed in the present
instance. Thus, for example, in the compound MePh-
ClGe(o-C6H4CH2NMe2) the Ge-N bond distance ob-
served is between 2.479 and 2.508(11) Å.35 This latter
value corresponds to a value for a dative NfGe bond.
For covalent Ge-N bonds the distances are even
smaller. For example, for [Cl3Ge-NdPMe3]n (n ) 1, 2)
the values observed are 1.837(7) and 1.972(1) Å.36
Similarly for [Ge{N(SiMe3)2}2] the Ge-N bond distances
found are 1.877(8) and 1.873(5) Å.37
The Ge-C bond distances found for 5, 1.943(5)-1.974-
(5) Å are quite similar to those observed for other
tetraarylgermanium compounds: tetra-o-tolylgerma-
nium (average Ge-C ) 1.966 Å),38 Ge(C6F5)4 (1.957(4)
Å),39 and Ge(C6H5)4 (1.954 Å).40 The P-N bond distance
in 5 is 1.538(4) Å, and its similarity with that of Ph3Pd
(21) Koerner von Gustorf, E. A.; Grevels, F. W.; Fischer, I. The
Organic Chemistry of Iron; Academic: London, 1978.
(22) Chatt, J .; Shaw, B. L. J . Chem. Soc. 1961, 185.
(23) (a) Yamamoto, A.; Morifuji, K.; Ikeda, S.; Saito, T.; Uchida, Y.;
Misono, A. J . Am. Chem. Soc. 1968, 90, 1878. (b) Lau, W.; Huffman,
J . C.; Kochi, J . K. Organometallics 1982, 1, 155.
(24) Hermes, A. R.; Girolami, G. S. Organometallics 1987, 6, 763.
(25) Hill, D. H.; Parvez, M. A.; Sen, A. J . Am. Chem. Soc. 1994, 116,
2889.
(26) Mu¨ller, H.; Seidel, W.; Go¨rls, H. Z. Anorg. Allg. Chem. 1996,
622, 1269.
(27) Mu¨ller, H.; Seidel, W.; Go¨rls, H. J . Organomet. Chem. 1993,
445, 133.
(28) (a) Klose, A.; Solari, E.; Ferguson, R.; Floriani, C.; Chiesi-Villa,
A.; Rizzoli, C. Organometallics 1993, 12, 2414. (b) Klose, A.; Solari,
E.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.; Re, N. J . Am. Chem. Soc.
1994, 116, 9123.
(29) (a) Mu¨ller, H.; Seidel, W.; Go¨rls, H. Angew. Chem., Int. Ed. Engl.
1995, 34, 325. (b) Wehmschulte, R. J .; Power, P. P. Organometallics
1995, 14, 3264.
(30) Leung, W.-P.; Lee, H. K.; Wenig, L.-H.; Luo, B.-S.; Zhou, Z.-Y.;
Mak, T. C. W. Organometallics 1996, 15, 1785.
(31) Niecke, E.; Gudat, D. Angew. Chem., Int. Ed. Engl. 1991, 30,
217.
(32) Chandrasekhar, V.; Thomas, K. R. J . Struct. Bonding (Berlin)
1993, 81, 41.
(33) Chandrasekhar, V.; Vivekanandan, K.; Nagendran, S.; Senthil
Andavan, G. T.; Weathers, N. R.; Yarbrough, J . C.; Cordes, A. W. Inorg.
Chem. 1998, 37, 6192.
(34) Chandrasekhar, V.; Thomas, K. R. J . Appl. Organomet. Chem.
1993, 7, 1.
(35) Breliere, C.; Carre, F.; Corriu, R. J . P.; De Saxce, A.; Poirier,
M.; Royo, G. J . Organomet. Chem. 1981, 205, C1.
(36) Meller, A.; Ossig, G.; Marringele, W.; Noltemeyer, M.; Stalke,
D.; Herbst-Irmer, R.; Freitag, S.; Sheldrick, G. M. Z. Naturforsch. 1992,
47B, 162.
(37) Chorley, R. W.; Hitchcock, P. B.; Lappert, M. F.; Leung. W.-P.;
Power, P. P.; Olmstead, M. M. Inorg. Chim. Acta 1992, 198-200, 203.
(38) Belsky, V. K.; Simonenko, A. A.; Reikhsfeld, V. O. J . Organomet.
Chem. 1992, 427, 23.
(39) Charisse´, M.; Roller, S.; Dra¨ger, M. J . Organomet. Chem. 1992,
427, 23.
(40) Chieh. P. C. J . Chem. Soc. A 1971, 3243.

2734 Organometallics, Vol. 20, No. 13, 2001
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles (d eg) of 3-5
Wingerter et al.
3 (M ) In)
4 (M ) Fe)
5 (M ) Ge)
Bond Distances and Angles
M-C
2.228(3)
2.696(3)
1.570(2)
1.804(3)
1.821(3)-1.827(3)
1.820(3)
126.0(2)
110.8(2)
109.3
2.192(2)
2.169(2)
2.487(2)
1.582(2)
1.806(3)
2.071(3)
2.111(2)
1.591(2)
1.802(3)
1.811(3)-1.810(3)
1.807(3)
128.15(14)
108.06(12)
110.54(11)
118.28(12)
88.70(10)
120.8(2)
1.974(5)
3.111(4)a
1.538(4)
1.818(5)
1.824(5)
1.822(5)
128.8(2)
112.7(2)
M-N
3.542(2)a
P-N
1.550(2)
1.819(3)
1.828(3)-1.832(3)
P-C(C6H4M)
P-C(C6H5)
av(P-C)
P-N-Si
N-P-C(C6H4M)
M-N-P
1.818(2)-1.822(3)
134.4(2)
116.2(2)
125.4(2)
109.9(2)
109.2(2)
124.2(2)
81.8
M-N-Si
CR-M-NR
C-C(M)-C
122.7
76.5
115.1(2)
115.9(2)
116.7(2)
117.0(4)
Deviations (Å)
0.010
0.151
metalated C from C5H4 plane
M from C6H4 plane
0.031
0.038
0.006
0.314
0.003
0.055
0.0
0.181
a
Nonbonding distances.
NSiMe3 (1.542(2) Å)41 also supports the notion of the
noncoordinating imino nitrogen atom.
Str u ctu r a l Com p a r ison s. Table 1 summarizes some
of the important metric parameters for the compounds
3-5.
trends have also been seen in the other metal complexes
prepared from 2. In 5, where there is no coordination
from the nitrogen, the PdN bond distance is the shortest
one found (1.538(4) Å). The P-C distances do not vary
significantly, however, and also are not diagnostic of the
imino nitrogen coordination.
In the lithium derivative 2 and the organometallic
complexes 3 and 4 the participation of the sidearm imino
nitrogen in coordination to the metal leads to the
formation of five-membered metallacycle structures. In
5 formation of such a metallacycle is precluded because
of the absence of coordination by the imino nitrogen.
This is almost certainly due to the relatively weak Lewis
acidic nature of a tetraaryl-substituted germanium
center.
In examples of neutral or anionic pentacoordinate
germanium compounds the central germanium is sur-
rounded by at least one or more highly electronegative
atoms such as halogens or oxygen atoms which increase
the Lewis acidity and facilitate higher coordination
around germanium.35,42-44
In the other cases (2-4) where the iminophosphorane
functions as a chelating ligand, the maximum number
of ligands accommodated around the central metal ion
is 3, e.g., in the case of the indium complex 2. However,
even in the latter, the imino nitrogen coordination is
restricted to only two ligands, with the third ligand
bound to the indium only through a M-Caryl σ-bond.
Thus, in all the examples that we have studied so far
with 2 as the starting material, the number of five-
membered metallacycles formed does not exceed 2. It
would be interesting if a similar situation would prevail
with f-block metal ions.
An important indicator for the involvement of the
imino nitrogen in coordination (apart from the M-N
bond distance) is the extent of lengthening of the PdN
bond. Thus, if one takes the distance found in Ph3Pd
NSiMe3 (1) as the reference (1.542(2) Å), the distance
increases steadily in proceeding from 2 to 4: 2 (1.562-
(2) Å), 3 (1.570(2), 1.582(2) Å), and 4 (1.591(2) Å). These
Con clu sion
The questions risen in the Introduction can be an-
swered as follows:
(i) All analytical tools employed in this paper indicate
the lengthening of the PdN bond upon NfM dative
bonding. Spectroscopic infrared and Raman investiga-
tions indicate for the ν(PdN) vibration a shift to higher
wavenumbers (M ) Li). Density functional theory
calculations (M ) Li) and X-ray structure determina-
tions (M ) Li, Fe, In) find longer P-N bonds in the
intramolecular metal complexed compounds than in the
starting material. If the imino sidearm is not employed
in metal coordination (M ) Ge), the PdN bond is as
short as in the starting material. We will further
elaborate this analytical combination to scale the shift
of the ν(PdN) vibration to bond distance changes in the
solid state, to deduce from the vibrational spectra the
role of the metal imide coordination.
(ii) Not until now has a metal complex with more than
two of these bulky ligands been observed. However, the
large trivalent indium atom clearly can accommodate
three ligands. The imino sidearm is flexible enough to
fill vacant coordination sites or to act as a pendent
spectator.
(iii) As in most coordination compounds, the presence
of a dative bond is predominantly governed by steric
conditions (i.e. the radius of the metal). In the indium
complex there is not enough room for the third imino
group to coordinate the metal, but in the germanium
complex there would be plenty of space. Although the
orientation of the three phenyl groups indicates the
release of a vacant coordination site, the imino group
would not coordinate, as the Lewis acidity of the central
germanium atom is not high enough because electron-
withdrawing substituents are missing.
(41) Weller, F.; Kang, H.-C.; Massa, W.; Ru¨benstahl, T.; Kunkel, F.;
Dehnicke, K. Z. Naturforsch. 1995, 50B, 1050.
(42) Holmes, R. R.; Day, R. O.; Sau, A. C.; Poutasse, C. A.; Holmes,
J . M. Inorg. Chem. 1985, 24, 193.
(43) Sau, A. C.; Day, R. O.; Holmes, R. R. J . Am. Chem. Soc. 1980,
102, 7972.
(iv) The imino sidearm donation can be employed to
stabilize a rare example of a 14-VE iron complex.
(44) Day, R. O.; Holmes, J . M.; Sau, A. C.; Holmes, R. R. Inorg.
Chem. 1982, 21, 281.

Ph3PdNSiMe3 as a Synthon for M-Caryl σ Bonds
Organometallics, Vol. 20, No. 13, 2001 2735
0.3 mm. The infrared spectra were recorded in the range from
400 to 4000 cm-1 with a Bruker IFS 120HR spectrometer and
an MCD detector. The spectra were obtained with a 2 cm-1
resolution.
Exp er im en ta l Section
All manipulations were performed under an inert gas
atmosphere of dry N2 with Schlenk techniques or in an argon
glovebox. All solvents were dried over Na/K alloy and distilled
prior to use. NMR spectra were obtained in benzene-d6 as
solvent with SiMe4 or H3PO4 as the external reference on a
Bruker AM 250. Mass spectra were recorded on a Finnigan
Mat 8230 or Varian Mat CH5 spectrometer. Elemental analy-
ses were performed by the Analytisches Laboratorium des
Instituts fu¨r Anorganische Chemie der Universita¨t Wu¨rzburg.
The lithiated aminoiminophosphorane 2 was prepared accord-
ing to literature procedures.6
Ca lcu la tion s. The DFT calculations were performed using
GAUSSIAN98.45 All calculations of harmonic wavenumbers
were performed by using a fully optimized geometry as
reference geometry. The DFT geometry optimization was
carried out with a combination of exchange and correlation
functionals which gave the best results in test calculations:
Becke’s 1988 exchange functional46 in combination with the
Perdew-Wang 91 gradient-corrected correlation functional47
(BPW91). The 6-31G* and 6-31+G* basis sets for all atoms
have been employed in the geometry optimization and the
vibration calculations.
[In (o-C6H4P P h 2NSiMe3)3] (3). The lithiated iminophos-
phorane 2 (1.10 g, 1.40 mmol) and indium trichloride (0.21 g,
0.93 mmol) were taken up in diethyl ether (20 mL) and stirred
at room temperature for 24 h. Removal of solvent under
vacuum afforded a white residue, which was taken up in
toluene (20 mL); this mixture was stirred at room temperature
for 3 days. The mixture was filtered, and the filtrate was
concentrated and kept for crystallization at room temperature.
After 3 days colorless crystals suitable for X-ray analysis were
obtained. The mother liquor, after the removal of crystals, was
evaporated to dryness under vacuum to afford a solid. It was
washed with pentane (20 mL) and dried. The crystals and the
white solid were found to be the same and correspond to the
title compound. Yield: 0.51 g, 47%. Mp (DTA): 175 °C dec.
1H NMR (C6D6): δ 0.50 (s, 27H, SiMe3), 7.10-8.70 (m, 42H,
Cr ysta llogr a p h ic Mea su r em en ts. Data for all structures
were collected at low temperatures using oil-coated shock-
cooled crystals48 on an Enraf-Nonius CAD4 diffractometer
using graphite-monochromated Mo KR radiation (λ ) 0.710 73
Å). A semiempirical absorption correction was applied. The
structures were solved by Patterson or direct methods with
SHELXS-90.49 All structures were refined by full-matrix least-
squares procedures on F2, using SHELXL-93.50 All non-
hydrogen atoms were refined anisotropically, and a riding
model was employed in the refinement of the hydrogen atom
positions. Further details on the structure investigation can
be obtained from the Director of the Cambridge Crystal-
lographic Data Centre, 12 Union Road, GB-Cambridge
CB2 1EZ, U.K. (fax, (+44)1223-336-033; e-mail, deposit@
ccdc.cam.ac.uk), by quoting the supplementary publication
numbers 159642 (3), 159643 (4), and 159644 (5).
3
Ph H). 13C NMR (C6D6): δ 3.24 (d, J C,P ) 3.2 Hz, SiMe3),
124.3-135.3 (m, Ph C), 166.0 (s, In-C). 31P NMR (C6D6): δ
-20.3. MS (70 eV, EI): m/z (%) 334 (100) [C6H4PPh2NSiMe2+],
Anal. Calcd for C63H69InN3P3Si3: C, 65.2; H, 5.99; N, 3.62.
Found: C, 66.1; H, 6.13; N, 3.49.
[F e(o-C6H4P P h 2NSiMe3)2] (4). A mixture of 2 (1.50 g, 1.91
mmol) and FeCl2 (0.24 g, 1.91 mmol) was taken up in THF
(25 mL). The resulting red-brown solution was stirred at room
temperature for 24 h. To this solution was added toluene (25
mL), this mixture was filtered over Celite, and the clear red
filtrate was kept at -40 °C. After a couple of weeks red crystals
corresponding to the title compound were isolated. Total
Ack n ow led gm en t. We thank the Deutsche Fors-
chungsgemeinschaft (SFB 347, Projects D4 and C2) and
the Fonds der Chemischen Industrie. D.S. kindly ac-
knowledges the support of Bruker axs-Analytical
X-ray Systems, Karlsruhe, Germany, and CHE-
METALL, Frankfurt/Main, Germany.
1
yield: 0.91 g, 63%. Mp (DTA): 97 °C dec. H NMR (C6D6): δ
0.08 (broad signal, 18H, SiMe3), 6.89 (broad signal, 28H, Ph
H).31P NMR (C6D6): δ 1.24 (broad signal). MS (70 eV, EI): m/z
(%) 404.1 (2.63) [Ph3PNSiMe3‚Fe], 334.1 (100) [Ph3PNSiMe2],
318.1 (6.1) [Ph3PNSiMe], Anal. Calcd for C42H46FeN2P2Si2: C,
67.0; H, 6.16; N, 3.72. Found: C, 67.4; H, 6.14; N, 3.90.
[P h 3Ge(o-C6H4P P h 2NSiMe3)] (5). A mixture of 2 (0.16 g;
0.20 mmol) and triphenylgermanium chloride (0.14 g; 0.41
mmol) were taken up in diethyl ether (15 mL) and stirred at
room temperature. The reaction mixture at first turned yellow.
After 1 day precipitation of a white solid was noticed. The
reaction mixture was stirred for a further 2 days and the
solvent stripped off in vacuo to afford a white solid. It was
taken up in toluene (10 mL), and this mixture was stirred for
12 h and filtered over Celite to remove LiCl. The filtrate was
stored at room temperature. After several days colorless
crystals were obtained. Yield: 0.07 g, 27%. Mp (DTA): 123
Su p p or tin g In for m a tion Ava ila ble: Tables of calculated
geometric data, complete IR/Raman band assignments for 1
and 2, and crystal data, fractional coordinates, bond lengths
and angles, anisotropic displacement parameters, and hydro-
gen atom coordinates of the structures 3-5. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM0009738
(45) Frisch, M. J .; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J . R.; Zakrzewski, V. G.; Montgomery, J . A.,
J r.; Stratmann, R. E.; Burant, J . C.; Dapprich, S.; Millam, J . M.;
Daniels, A. D.; Kudin, K. N.; Strain, M. C.; Farkas, O.; Tomasi, J .;
Barone, V.; Cossi, M.; Cammi, R.; Mennucci, B.; Pomelli, C.; Adamo,
C.; Clifford, S.; Ochterski, J .; Petersson, G. A.; Ayala, P. Y.; Cui, Q.;
Morokuma, K.; Malick, D. K.; Rabuck, A. D.; Raghavachari, K.;
Foresman, J . B.; Cioslowski, J .; Ortiz, J . V.; Stefanov, B. B.; Liu, G.;
Liashenko, A.; Piskorz, P.; Komaromi, I.; Gomperts, R.; Martin, R. L.;
Fox, D. J .; Keith, T.; Al-Laham, M. A.; Peng, C. Y.; Nanayakkara, A.;
Gonzalez, C.; Challacombe, M.; Gill, P. M. W.; J ohnson, B. G.; Chen,
W.; Wong, M. W.; Andres, J . L.; Head-Gordon, M.; Replogle, E. S.;
Pople, J . A. Gaussian 98, revision A.7; Gaussian, Inc.: Pittsburgh, PA,
1998.
1
°C dec. H NMR (C6D6): δ 0.38 (s, 9 H, SiMe3), 6.93-7.82 (m,
29 H, Ph H). 31P NMR (C6D6): δ 8.4. MS (70 eV, EI): m/z (%)
334 (100) [C6H4PPh2NSiMe2+]. Anal. Calcd for C39H38GeNPSi:
C, 71.8; H, 5.87; N, 2.15. Found: C, 73.0; H, 5.71; N, 2.34.
Ra m a n Sp ectr oscop ic Exp er im en ts. The FT-Raman
spectra of the polycrystalline samples were recorded at room
temperature using a Bruker IFS 120HR spectrometer equipped
with a FRA 106 Raman module. The spectral resolution was
2 cm-1. Radiation of 1064 nm from a Nd:YAG laser with an
output power of 600 mW was employed for excitation. A Ge
detector cooled with liquid nitrogen was used.
(46) Becke, A. D. Phys. Rev. 1988, A38, 3098.
(47) Perdew, J . P.; Wang, Y. Phys. Rev. 1992, B45, 13244.
(48) (a) Hope, H. Acta Crystallogr., Sect. B 1988, 44, 22. (b) Kottke,
T.; Stalke, D. J . Appl. Crystallogr. 1993, 26, 615. (c) Kottke, T.; Lagow,
R. J .; Stalke, D. J . Appl. Crystallogr. 1996, 29, 465. (d) Stalke, D. Chem.
Soc. Rev. 1998, 27, 171.
(49) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467.
(50) Sheldrick, G. M. Program for Crystal Structure Refinement;
Universita¨t Go¨ttingen, Go¨ttingen, Germany, 1996.
For infrared measurements the samples were mixed with
KBr in order to obtain thin pellets with a thickness of about