Mo and W dihalide complexes with uncommon trigonal-prismatic geometry imposed by the linear tetraphosphine ancillary ligand and their reactivities toward diazoalkanes

Article abstract of DOI:10.1021/ic700371b

New Mo and W tetraphosphine-dihalide complexes [MX₂(κ ⁴-P4)] (2, MX = MoCl, MoBr, WBr; P4 = meso-o-C₆H ₄(PPhCH₂CH₂-PPh₂)₂) with uncommon trigonal-prismatic geometries

Full text of DOI:10.1021/ic700371b

Inorg. Chem. 2007, 46, 4784−4786
Mo and W Dihalide Complexes with Uncommon Trigonal-Prismatic
Geometry Imposed by the Linear Tetraphosphine Ancillary Ligand and
Their Reactivities toward Diazoalkanes
Hidetake Seino, Daisuke Watanabe, Takeshi Ohnishi, Chirima Arita, and Yasushi Mizobe*
Institute of Industrial Science, The UniVersity of Tokyo, Komaba, Meguro-ku,
Tokyo 153-8505, Japan
Received February 27, 2007
New Mo and W tetraphosphine
(2, MX MoCl, MoBr, WBr; P4
PPh2)2) with uncommon trigonal-prismatic geometries have been
prepared. Treatment of ethyl diazoacetate with 2 (MX MoCl)
resulted in catalytic carbenoid-group coupling to give diethyl maleate
and fumarate, whereas reactions of 2 with trimethylsilyldiazoalkane
−
dihalide complexes [MX2(κ4-P4)]
meso-o-C6H4(PPhCH2CH2-
attractive features of P4 is that it forms two types of chelate
rings with different stabilities upon complexation. Thus, our
recent study has revealed that P4 can readily change the
coordination mode from κ4 to κ3, as well as κ2, by dissociat-
ing one or both of the outer phosphorus atoms.5 This hapticity
change may occur due to the steric strain arising from the
formation of three consecutive five-membered chelate rings
with P-M-P angles that are much smaller than 90°. The
chelate rings consisting of conformationally loose ethylene
groups are more likely to open than the relatively tightly
bound phenylene-containing chelate ring. In this paper, we
wish to describe further the influence of this ring strain in a
κ4-coordinating P4 ligand on the geometry and reactivities
of its Mo and W complexes.
)
)
)
formed the diazoalkane complexes trans-[MX(NN
4-P4)]+ (3+) and cis,mer-[MoCl2(NN
CHSiMe3)(
molecular structures of 2 (MX MoCl) and 3[PF6] (MX
were crystallographically determined.
d
CHSiMe3)-
3-P4)]. The
WBr)
(
κ
d
κ
)
)
Low-valent, early transition metal complexes are known
to display unique reactivities due to their strong electron-
donating abilities. The extensively studied Group 6 metal
complexes, bearing tertiary phosphine ligands, have been
shown to facilitate various bond-breaking and -making
reactions, as well as reducion of unsaturated molecules, such
as alkenes, alkynes, nitriles, and dinitrogen.1,2 However, the
systems investigated previously are limited mostly to mono-
and bidentate phosphine complexes, while studies involving
polydentate phosphines are still quite rare.3
We have discovered that reactions of the Mo complex
1a with excess amounts (2.5-3 equiv) of PhCH2Cl or
PhCH2Br take place at room temperature to form the dihalide
complexes [MoX2(κ4-P4)] (X ) Cl (2a), Br (2a′)) as green
crystals in moderate yields (eq 1).6 Dissociation of the dppe
Recently, we reported the preparation of the Mo and W
complexes [M(dppe)(κ4-P4)] (M ) Mo (1a), W (1b); dppe
) Ph2PCH2CH2PPh2) having the linear tetraphosphine lig-
and P4, i.e., meso-o-C6H4(PPhCH2CH2PPh2)2.4 One of the
* To whom correspondence should be addressed. E-mail: ymizobe@
iis.u-tokyo.ac.jp.
(1) (a) Pombeiro, A. J. L. New J. Chem. 1994, 18, 163. (b) Galindo, A.;
Gutie´rrez, E.; Monge, A.; Paneque, M.; Pastor, A.; Pe´rez, P. J.; Rogers,
R. D.; Carmona, E. J. Chem. Soc., Dalton Trans. 1995, 3801, and
references therein. (c) Seino, H.; Mizobe, Y.; Hidai, M. Chem. Rec.
2001, 1, 349. (d) Hidai, M.; Mizobe, Y. Pure Appl. Chem. 2001, 73,
261. (e) Janak, K. E.; Tanski, J. M.; Churchill, D. G.; Parkin, G. J.
Am. Chem. Soc. 2002, 124, 13658, and references therein.
(2) (a) Mayer, J. M. AdV. Trans. Met. Coord. Chem. 1996, 1, 105. (b)
Crevier, T. J.; Mayer, J. M. J. Am. Chem. Soc. 1997, 119, 8485. (c)
Hascall, T.; Rabinovich, D.; Murphy, V. J.; Beachy, M. D.; Friesner,
R. A.; Parkin, G. J. Am. Chem. Soc. 1999, 121, 11402.
ligand and the presence of PhCH2CH2Ph in the reaction
mixture were confirmed. The W congener 1b reacted with
PhCH2Br more slowly than 1a to give the dibromide complex
[WBr2(κ4-P4)] (2b) in 42% yield, but the reaction of 1b with
PhCH2Cl did not proceed.
(4) (a) Arita, C.; Seino, H.; Mizobe, Y.; Hidai, M. Chem. Lett. 1999, 28,
611. (b) Arita, C.; Seino, H.; Mizobe, Y.; Hidai, M. Bull. Chem. Soc.
Jpn. 2001, 74, 561.
(5) (a) Seino, H.; Arita, C.; Hidai, M.; Mizobe, Y. J. Organomet. Chem.
2002, 658, 106. (b) Ohnishi, T.; Seino, H.; Hidai, M.; Mizobe, Y. J.
Organomet. Chem. 2005, 690, 1140.
(3) (a) Cotton, F. A.; Hong, B. Prog. Inorg. Chem. 1992, 40, 179. (b)
Mayer, H. A.; Kaska, W. C. Chem. ReV. 1994, 94, 1239. (c) Hierso,
J.-C.; Amardeil, R.; Bentabet, E.; Broussier, R.; Gautheron, B.;
Meunier, P.; Kalck, P. Coord. Chem. ReV. 2003, 236, 143.
4784 Inorganic Chemistry, Vol. 46, No. 12, 2007
10.1021/ic700371b CCC: $37.00
© 2007 American Chemical Society
Published on Web 05/10/2007

COMMUNICATION
Scheme 1
Figure 1. Molecular structure of 2a. Hydrogen atoms are omitted for
clarity. Bond distances (Å) and angles (deg): Mo-Cl(1), 2.4452(6);
Mo-Cl(2), 2.447(1); Mo-P(1), 2.4335(8); Mo-P(2), 2.4128(7); Mo-P(3),
2.3792(7); Mo-P(4), 2.4499(5); Cl(1)-Mo-Cl(2), 81.14(2); Cl(1)-Mo-
P(1), 86.02(2); Cl(1)-Mo-P(2), 88.46(2); Cl(2)-Mo-P(3), 88.00(2);
Cl(2)-Mo-P(4), 80.54(2); P(1)-Mo-P(2), 73.16(2); P(2)-Mo-P(3),
73.30(2); P(3)-Mo-P(4), 74.32(2); P(1)-Mo-P(4), 90.20(2).
also to be noted that these trans complexes are paramagnetic
due to the high-spin d4 electron configuration of such high-
symmetry structures. The presence of three consecutive
strained chelate rings is the likely reason why complexes of
structure type 2 disfavor an octahedral geometry of trans or
even cis configuration. In the solid-state structure of 2a, the
P-Mo-P angles in the three five-membered chelate rings
fall in the range 73-75°, and the sum of these values at
∼221° is much smaller than 270° required to locate all four
P atoms at the equatorial sites in the idealized octahedron.
Even the meridional arrangement of two adjacent chelate
rings results in a distortion between the mutually trans P
atoms, as observed in the octahedral complex 1 (see the
artwork in eq 1), in which the trans P-M-P angles within
P4 are at 152.63(9)° and 152.55(7)° for M ) Mo and W,
respectively.4 Therefore, it is likely that the tetradentate P4
ligand determines the geometry of 2 not electronically but
by its intrinsic steric constraints.
By X-ray crystallography, the structure of 2a has been
determined unequivocally as shown in Figure 1. The Mo
center in 2a has a trigonal-prismatic geometry, in which one
of the rectangular faces is capped by the tetradentate P4
ligand. The three edges of the prism are defined by the pairs
of the outer P atoms (P(1) and P(4)), the inner P atoms (P(2)
and P(3)), and the chloride ligands. The twist angles φ are
only 2°, 4°, and 4° with respect to these edges, respectively,
where the values of φ have been defined previously by Stiefel
and co-worker with the limiting values being 0° and 60° for
trigonal-prismatic and octahedral structures.7 The dihedral
angle between two basal triangles is 12°. Well-resolved NMR
signals indicate that all complexes of 2 are diamagnetic, and
the 31P{1H} NMR spectra of these complexes, which exhibit
two signals each assignable to the outer and the inner P
nuclei, confirm the Cs symmetry.
Most reactions of trans-[MX2(tP)4] are proposed to be
initiated by dissociation of phosphine or, less commonly,
the X- ligands,2 and therefore, the complexes with bidentate
phosphine ligands such as trans-[MX2(dppe)2] are less
reactive than monophosphine complexes. In the case of 2,
the 16-electron metal center is not as sterically protected and
directly accessible, since the P4 ligand covers only one
hemisphere of the metal. Thus, reactions of 2 with ethyl
diazoacetate rapidly occurred at room temperature to form
unstable complexes, which spontaneously decomposed to
give a mixture of diethyl maleate and diethyl fumarate. When
a 10-fold molar amount of ethyl diazoacetate was treated
with 2a, a total of ∼2.8 mol (per mol of 2a) of these
carbenoid-coupling products was detected in a molar ratio
of ca. 2:3. To our knowledge, Mo complexes that can
catalyze the carbenoid coupling of diazo compounds are quite
rare.10 Indeed, trans-[MoCl2(dppe)2] did not react with ethyl
diazoacetate. Since neither the detection of any intermediary
It is noteworthy that trigonal-prismatic structure is uncom-
mon for six-coordinate Mo(II) and W(II) complexes.8 All
the other structurally determined complexes of the type
[MX2(tP)4] (M ) Mo, W; X ) halogens; tP ) tertiary
phosphine ligand) adopt a trans octahedral geometry.9 It is
(6) The following method was used to synthesize 2a. To a red suspension
of 1a (2.51 g, 1.94 mmol) in benzene (230 mL) was added PhCH2Cl
(0.70 mL, 6.1 mmol). After the mixture had been stirred in the dark
at room temperature for 48 h, deposited green microcrystals of 2a
were filterd off, washed with benzene and diethyl ether, and dried in
vacuo to give 1.25 g (73% yield). 1H NMR (CD2Cl2): δ 2.2-2.5 (m,
4H, PCH2), 2.8-3.0, 3.45-3.65 (m, 2H each, PCH2), 6.15-7.75 (m,
34H, aromatic). 31P{1H} NMR (CD2Cl2): δ 101.8, 141.9 (AA′XX′
pattern: JAX + JAX′ ) 56 Hz). Complexes 2a′ and 2b are prepared
from the cooresponding 1 and PhCH2Br in an analogous manner. 2a′:
82% yield. 1H NMR (CD2Cl2): δ 2.2-2.4, 2.55-2.75, 3.0-3.2, 4.05-
4.25 (m, 2H each, PCH2), 6.0-7.75 (m, 34H, aromatic). 31P{1H} NMR
(CD2Cl2): δ 98.7, 142.0 (AA′XX′ pattern: JAX + JAX′ ) 53 Hz). 2b:
42% yield. 1H NMR (CD2Cl2): δ 1.9-2.1, 2.25-2.5, 2.55-2.8, 3.25-
3.45 (m, 2H each, PCH2), 6.3-7.8 (m, 34H, aromatic). 31P{1H} NMR
(CD2Cl2): δ 55.6 (br with 183W satellites, JPW ) 246 Hz), 105.1 (br
with 183W satellites, JPW ) 258 Hz).
(7) Stiefel, E. I.; Brown, G. F. Inorg. Chem. 1972, 11, 434.
(8) (a) Templeton, J. L.; Ward, B. C. J. Am. Chem. Soc. 1980, 102, 6568.
(b) Burrow, T. E.; Hughes, D. L.; Lough, A. J.; Maguire, M. J.; Morris,
R. H.; Richards, R. L. J. Chem. Soc., Dalton Trans. 1995, 1315. (c)
Baker, P. K.; Drew, M. G. B.; Parker, E. E.; Robertson, N.; Underhill,
A. E. J. Chem. Soc., Dalton Trans. 1997, 1429. (d) Fomitchev, D. V.;
Lim, B. S.; Holm, R. H. Inorg. Chem. 2001, 40, 645.
(9) (a) Carmona, E.; Mar´ın, J. M.; Poveda, M. L.; Atwood, J. L.; Rogers,
R. D. Polyhedron 1983, 2, 185. (b) Bakir, M.; Cotton, F. A.; Cudahy,
M. M.; Simpson, C. Q.; Smith, T. J.; Vogel, E. F.; Walton, R. A.
Inorg. Chem. 1988, 27, 2608. (c) Pietsch, B.; Dahlenburg, L. Inorg.
Chim. Acta 1988, 145, 195. (d) Filippou, A. C.; Schnakenburg, G.;
Philippopoulos, A. I. Acta Crystallogr. 2003, E59, m602.
Inorganic Chemistry, Vol. 46, No. 12, 2007 4785

COMMUNICATION
essentially linear W-N-N linkage, the bent N-N-C array
(122.2(5)°), and the NdC double bond length (1.255(8) Å)
suggest that this ligand is best interpreted by a hydrazone-
like structure as a 2σ,4π electron donor to the W(IV) center.
These characteristics are quite similar to those of the
numerous diazoalkane complexes of the analogous ligand
environment trans-[MX(NNdCRR′)(tP)4]+ and the related
complexes such as cis,mer-[MX2(NNdCRR′)(tP)3], which
have been derived from the dinitrogen complexes [M(N2)2-
(tP)4].13 For 3b+, strong trans influence of the diazoalkane
ligand presumably results in the trans geometry in spite of
the larger strain due to the planar coordination of κ4-P4. In
3b+, to reduce this strain, the P-Mo-P angle in each chelate
ring is slightly widened to 80-81° from those in 2, and all
the W-P bonds are bent toward the bromide ligand by ca.
10° to decrease the wide P(1)-W-P(4) angle to some extent
(111.66(4)°).14
Figure 2. Structure of the cationic part of 3b[PF6]. The major conformer
of the disordered SiMe3 group is shown. Hydrogen atoms are omitted for
clarity. Bond distances (Å) and angles (deg): W-Br, 2.6626(5); W-P(1),
2.494(1); W-P(2), 2.437(1); W-P(3), 2.426(1); W-P(4), 2.506(1);
W-N(1), 1.757(4); N(1)-N(2), 1.324(6); N(2)-C(47), 1.255(8); Si-C(47),
1.854(6); Br-W-P, 78.80(3)-81.14(3); Br-W-N(1), 178.0(1); P(1)-W-
P(2), 80.03(4); P(1)-W-P(3), 154.81(4); P(1)-W-P(4), 111.66(4); P(2)-
W-P(3), 80.51(4); P(2)-W-P(4), 154.80(4); P(3)-W-P(4), 81.05(4);
P-W-N(1), 98.3(1)-100.8(1); W-N(1)-N(2), 173.2(4); N(1)-N(2)-
C(47), 122.2(5); Si-C(47)-N(2), 121.7(5).
Reactions of the Mo complex 2a with Me3SiCHN2 were
also carried out which disclosed the formation of two types
of diazoalkane complexes depending on the reaction condi-
tions. When the reaction was conducted in benzene or THF
at room temperature, rapid formation of the neutral diazo-
alkane complex cis,mer-[MoCl2(NNdCHSiMe3)(κ3-P4)] (4a)
was observed. Although the isolation of pure 4a was
hampered by its instability, spectroscopic data suggest that
the diazoalkane ligand is analogous to that in 3b[PF6]. By
contrast, stirring a CH2Cl2 solution of 2a and Me3SiCHN2
afforded the quite stable cation 3a+, which was isolated as
3a[PF6] in good yield after anion metathesis with K[PF6].
The formation of the neutral κ3-P4 complex in the case of
Mo may be due to the less electron-rich nature of Mo, when
compared to W, and this should stabilize the neutral species.
Investigations to further explore the coordination chemistry
of these complexes and their utility in molecular transforma-
tions are in progress.
metal-carbene species nor the carbene-group transfer to
alkenes or aldehydes has been achieved,11 the study has been
extended to the reactions with different diazoalkanes.
Treatment of W complex 2b with the mildly reactive
diazoalkane Me3SiCHN2 at room temperature gave the
cationic diazoalkane complex trans-[WBr(NNdCHSiMe3)-
-
(κ4-P4)]Br (3bBr), which was isolated as the PF6 salt
3b[PF6] in 55% yield (Scheme 1).12 Crystallographic study
of 3b[PF6] has revealed that the cation 3b+ has a highly
distorted octahedral structure, where the terminal N-bound
diazoalkane ligand and bromide are located mutually trans,
as shown in Figure 2. The κ4-P4 ligand occupies the
equatorial coordination sites in a fashion that the phenyl
groups attached to the inner P atoms are oriented syn to the
diazoalkane ligand. A short W-N distance at 1.757(4) Å
indicates the presence of W-N multiple bonding, and the
Acknowledgment. This work was supported by a Grant-
in-Aid for Scientific Research on Priority Area (No. 18065005,
“Chemistry of Concerto Catalysis”) from the Ministry of
Education, Culture, Sports, Science, and Technology, Japan,
and by CREST of JST (Japan Science and Technology
Agency).
Supporting Information Available: Crystallographic data of
2a‚2(THF) and 3b[PF6] in CIF format and detailed experimental
information. This material is available free of charge via the Internet
at http://pubs.acs.org.
(10) Doyle, M. P.; Dorow, R. L.; Tamblyn, W. H. J. Org. Chem. 1982,
47, 4059.
(11) (a) Lebel, H.; Marcoux, J. F.; Molinaro, C.; Charette, A. B. Chem.
ReV. 2003, 103, 977. (b) Maas, G. Chem. Soc. ReV. 2004, 33, 183. (c)
Merlic, C. A.; Zechman, A. L. Synthesis 2003, 1137. (d) Kirmse, W.
Angew. Chem., Int. Ed. 2003, 42, 1088.
(12) Selected spectroscopic data are as follows. 3b[PF6]: 1H NMR
(CDCl3): δ -0.28 (s, 9H, SiMe3), 5.62 (s, 1H, NdCH). 31P{1H} NMR
(CDCl3): δ 40.3 (AA′XX′ pattern with 183W satellites, JPW ) 306
Hz), 81.5 (AA′XX′ pattern with 183W satellites, JPW ) 268 Hz), JAX
+ JAX′ ) 157 Hz. IR (KBr): ν(NdC) 1573 cm-1. 3a[PF6]: 1H NMR
(CDCl3): δ -0.25 (s, 9H, SiMe3), 5.49 (s, 1H, NdCH). 31P{1H} NMR
(CDCl3): δ 66.5, 101.9 (AA′XX′ pattern: JAX + JAX′ ) 148 Hz). IR
(KBr): ν(NdC) 1573 cm-1. 4a: 1H NMR (C6D6): δ -0.35 (s, 9H,
SiMe3), 6.58 (s, 1H, NdCH). 31P{1H} NMR (C6D6): δ -10.4 (d, J
) 40 Hz), 49.9 (d, J ) 205 Hz), 53.8 (ddd, J ) 205, 40, 5 Hz), 103.8
IC700371B
(13) Reviews: (a) Mizobe, Y.; Ishii, Y.; Hidai, M. Coord. Chem. ReV.
1995, 139, 281. (b) Hidai, M.; Ishii, Y. Bull. Chem. Soc. Jpn. 1996,
69, 819. (c) Dartiguenave, M.; Menu, J. M.; Dyedier, E.; Dartiguenave,
Y.; Siebald, H. Coord. Chem. ReV. 1998, 178-180, 623.
(14) Similar distortions of the square-planar geometry of divalent Group
10 metal complexes with the meso/rac-Ph2PCH2CH2P(Ph)CH2-
CH2P(Ph)CH2CH2PPh2 ligand have been discussed: Bachmann, C.;
Oberhauser, W.; Bru¨ggeller, P. Polyhedron 1996, 15, 2223, and
references therein.
(d, J ) 5 Hz). IR (KBr): ν(NdC) 1585 cm-1
.
4786 Inorganic Chemistry, Vol. 46, No. 12, 2007