Insertion Reactions of trans-Mo(dmpe)2(H)(NO) with Imines

Article abstract of DOI:10.1021/ic030139l

The insertion chemistry of the hydride complex trans-Mo(dmpe) ₂(H)(NO) (1) (dmpe = bis(dimethylphosphino)-ethane) with imines has been investigated. It was found that disubstituted aromatic imines RCH= NR′ (R, R′ = Ar) insert into the Mo-H bond of 1, while a series of various mono-and other disubstituted imines do not react. The insertion products trans-Mo(dmpe)₂(NO)[NR′(CH₂R)] (R = R′ = Ph (2); R = Cp₂Fe, R′ = Ph (3); R = Ph, R′ = Cp₂Fe (4); R = 1-naphthyl, R′ = Ph (5)) have been isolated and fully characterized by elemental analysis, IR and NMR spectroscopy, and mass spectrometry. The imine PhCH= NC₁₀H₇ (C₁₀H ₇ = 1-naphthyl) reacted with 1 establishing an equilibrium to produce the nonisolable complex trans-Mo(dmpe)₂(NO)[NC ₁₀H₇(CH₂Ph) (6). The equilibrium constant for this reaction has been derived from VT-NMR measurements, and the ΔH and ΔS values of this reaction were calculated to be -48.8 ± 0.4 kJ·mol^-1 and -33 ± 1 J·K^-1· mol^-1 reflecting a mild exothermic process and its associative nature. Single-crystal X-ray diffraction analyses were carried out on 2-5.

Full text of DOI:10.1021/ic030139l

Inorg. Chem. 2004, 43, 993−999
Insertion Reactions of trans-Mo(dmpe)2(H)(NO) with Imines
Fupei Liang, Helmut W. Schmalle, and Heinz Berke*
Anorganisch-Chemisches Institut der UniVersita¨t Zu¨rich, Winterthurerstrasse 190,
CH-8057 Zu¨rich, Switzerland
Received April 25, 2003
The insertion chemistry of the hydride complex trans-Mo(dmpe)2(H)(NO) (1) (dmpe ) bis(dimethylphosphino)-
ethane) with imines has been investigated. It was found that disubstituted aromatic imines RCHdNR′ (R, R′ ) Ar)
insert into the Mo−H bond of 1, while a series of various mono- and other disubstituted imines do not react. The
insertion products trans-Mo(dmpe)2(NO)[NR′(CH R)] (R ) R′ ) Ph (2); R ) Cp2Fe, R′ ) Ph (3); R ) Ph, R′ )
2
Cp2Fe (4); R ) 1-naphthyl, R′ ) Ph (5)) have been isolated and fully characterized by elemental analysis, IR and
NMR spectroscopy, and mass spectrometry. The imine PhCHdNC H (C H ) 1-naphthyl) reacted with 1
10
7
10 7
establishing an equilibrium to produce the nonisolable complex trans-Mo(dmpe)2(NO)[NC H (CH Ph)] (6). The
10
7
2
equilibrium constant for this reaction has been derived from VT-NMR measurements, and the ∆H and ∆S values
of this reaction were calculated to be −48.8 ± 0.4 kJ‚mol-1 and −33 ± 1 J‚K-1‚mol-1 reflecting a mild exothermic
process and its associative nature. Single-crystal X-ray diffraction analyses were carried out on 2−5.
Introduction
interest to develop transition metal hydride systems capable
of such insertions, since in contrast to main group compounds
transition metal species could be envisaged to provide access
to hydride species from a metal fragment and H2 and thus
could also operate on catalytic grounds. Such catalytic
hydrogenations are known, but as indicated above, they are
rare and quite often they lack activity and/or stability of the
catalytic species. This contrasts the situation of related
reductions of carbonyl functionalities with transition metal
hydrides.5a-eAnother avenue described by Noyori that in-
volves 2-propanol as the sacrificial hydrogen source can also
be utilized.5f Therefore, it was expected that by separate
Insertion reactions of imines into transition metal-
hydrogen bonds has been proposed to be a key step in
catalytic homogeneous hydrogenations of imines.1 However,
so far insertion of imines into LnM-H bonds leading to the
metal amido intermediates have been observed only in rare
cases as isolated steps.1b,2 In addition and in contrast to the
fact that main-group hydrides have frequently been utilized
in hydride reductions of the carbon-nitrogen double bond,3
applications of transition metal hydrides for related reductions
of imines are up to now limited.4 One reason for this obvious
lack of activity may be that in the majority of cases the
transition metal hydrogen bond possess too low polarity and
concomitant nucleophilicity to react with the relatively inert
CdN double bond. Nevertheless, it would be of great general
(3) (a) Oveman, L. E.; Freerks, R. L. J. Org. Chem. 1981, 46, 2833. (b)
Jamada, K.; Takeda, M.; Iwakuma, T. J. Chem. Soc., Perkin Trans.
1983, 265. (c) Polniaszek, R. P.; Kaufman, C. R. J. Am. Chem. Soc.
1989, 111, 4859. (d) Kavate, T.; Nakagawa, M.; Kakikawa T.; Hino,
T. Tetrahedron: Asymmetry 1992, 3, 227. (e) Sotomayor, N.;
Dominguez, E.; Lete, E. Synlett 1993, 431. (f) Tellitu, I.; Badia, D.;
Dominguez, E.; Garcia, F. J. Tetrahedron: Asymmetry 1994, 5, 1567.
(g) Kang, J.; Kim, J. B.; Cho, K. H.; Cho, B. T. Tetrahedron:
Asymmetry 1997, 8, 657.
* To whom correspondence should be addressed. E-mail:
hberke@aci.unizh.ch.
(1) (a) Willoughby, C. A.; Buchwald, S. L. J. Am. Chem. Soc. 1994, 116,
8952. (b) Obora, Y.; Ohta, T.; Stern, C. L.; Marks, T. J. J. Am. Chem.
Soc. 1997, 119, 3745. (c) James, B. R. Catal. Today 1997, 37, 209.
(d) Kobayashi, S.; Ishitani, H. Chem. ReV. 1999, 99, 1069. (e) Blaser,
H.-U.; Spindler, F. In ComprehensiVe Asymmetric Catalysis; Jacobsen,
E. N., Plaltz, A., Yamamoto, H., Eds.; Springer-Verlag: New York,
1999; Vol. 1, p 247. (f) Magee, M. P.; Norton, J. R. J. Am. Chem.
Soc. 2001, 123, 1778. (g) Herrera, V.; Mun˜oz, B.; Landaeta, V.;
Canudas, N. J. Mol. Catal., A 2001, 174, 141. (h) Xiao, D.; Zhang,
X. Angew. Chem., Int. Ed. 2001, 3425. (i) Samec, J. S. M.; Ba¨ckvall,
J.-E. Chem.sEur. J. 2002, 8, 2955.
(4) Palagyi, J.; Nagy-Magos, Z.; Marko, L. Transition Met. Chem. 1985,
10, 336.
(5) (a) Darensbourg, M. Y.; Slater, S. G. J. Am. Chem. Soc. 1981, 103,
5914. (b) Slater, S. G.; Lusk, R.; Schumann, B. F.; Darensbourg, M.
Y. Organometallics 1982, 1, 1662. (c) Gaus, P. L.; Kao, S. C.;
Darensbourg, M. Y.; Arndt, L. W. J. Am. Chem. Soc. 1984, 106, 4752.
(d) Gaus, P. L.; Kao, S. C.; Youngdahl, K.; Darensbourg, M. Y.; Arndt,
L. W. J. Am. Chem. Soc. 1985, 107, 2428. (e) Tooley, P. A.; Ovalles,
C.; Kao, S. C.; Darensbourg, D. J.; Darensbourg, M. Y. J. Am. Chem.
Soc. 1986, 108, 5465. (f) Noyori, R.; Hashiguchi, S. Acc. Chem. Res.
1997, 30, 97.
(2) (a) Fryzuk, M. D.; Piers, W. E. Organometallics 1990, 9, 986. (b)
Debad, J. D.; Legzdins, P.; Lumb, S. A.; Batchelor, R. J.; Einstein,
W. B. Organometallics 1995, 14, 2543.
10.1021/ic030139l CCC: $27.50 © 2004 American Chemical Society
Published on Web 01/09/2004
Inorganic Chemistry, Vol. 43, No. 3, 2004 993

Liang et al.
Scheme 1
studies of stoichiometric imine insertions into transition
metal-hydrogen bonds fundamental knowledge could be
acquired of how to tune hydrides toward better catalytic
performance among other possibilities via their coordination
sphere.
In previous investigations we found that the insertion
reaction of the hydride mer-Mo(CO)(H)(NO)(PMe3)3 related
to 1 with N-benzylideneaniline is accessible; however, the
reaction product could not be isolated and thus the structure
of the product could not be definitely established.6 We
attributed the difficulty in the isolation of the product to an
incomplete transformation caused by a too low activity of
the hydride. Enforced reaction conditions led to decomposi-
tions. Prompted by this failure, we set out to study the
synthesis and reactivity of hydrides with an enhanced polar
character in the transition metal-hydrogen bond. In recent
years our group has studied the chemistry of activated
transition metal hydrides.7 Systematic investigations allowed
the conclusion that strong trans-influence ligands such as
nitrosyl and carbyne groups tune the LnM-H bond toward
greater ionicity (hydridicity). A similar effect was seen upon
increase of the number of strongly σ-donating cis phosphine
substituents.8 Following these lines we have recently prepared
the complex trans-Mo(dmpe)2(H)(NO) (dmpe ) bis(dim-
ethylphosphino)ethane),9 a hydride complex with four cis
phosphorus donors in the coordination sphere of the molyb-
denum center. It was found that this hydride indeed displayed
the requested enhanced hydridic character.
(NO)(PMe3)3,6 presumably reflecting the increased hydridic
character of 1. However, the reaction took much longer time
compared to the reaction of 1 with the CdO double bond of
ketones,9 for which the reactions lasted only 2-3 h indicating
a general reluctance of imine double bonds to undergo
insertion reactions. The insertion product 2 could easily be
isolated as analytically pure yellow crystals in 81% yield
after diffusion of pentane into a toluene solution of 2.
1 reacted also with N-ferrocenylideneaniline, N-ben-
zylideneferrocenylamine, and N-1-naphthylideneaniline to
produce the isolable amide complexes 3-5, respectively
(Scheme 1). However, all these reactions proceeded much
slower than the reaction of N-benzylideneaniline. For ex-
ample, reactions of 1 with N-ferrocenylideneaniline and N-1-
naphthylideneaniline in toluene took about 5 days at room
temperature. Heating facilitated the reactions, and at 65 °C
they came to an end overnight. These reactivity differences
were presumably due to enhanced steric influences of the
substituents at the CCdN atom. The bulkier ferrocenyl and
naphthyl groups in N-ferrocenylideneaniline and N-1-naph-
thylideneaniline hinder the hydride transfer step more.
Reaction of 1 with N-benzylideneferrocenylamine took even
3 days to come to completion at 65 °C revealing that still
more enforced conditions are required, in particular when
compared to the reaction of its isomer, N-ferrocenylidene-
aniline. This difference in reactivity between these two
compounds can presumably again be attributed to steric
crowding at the nitrogen atom. In the transition state the
ferrocenyl substituent at the forming amido faces decisive
steric repulsion with the Mo(dmpe)2(NO) fragment.
Results and Discussions
Reaction of trans-Mo(dmpe)2(H)(NO) (1) with Imines.
Hydride 1 was synthesized by a procedure already reported
by us.9 Treatment of 1 with equimolar amounts of N-
benzylideneaniline in toluene afforded the corresponding
amido complex 2 (Scheme 1). The insertion reaction was
found to proceed smoothly at room temperature and was
complete after 24 h. The reaction conditions are much milder
than those for the analogous reaction of mer-Mo(CO)(H)-
(6) Liang, F.; Jacobsen, H.; Schmalle, H. W.; Fox, T.; Berke, H.
Organometallics 2000, 19, 1950.
(7) (a) van der Zeijden, A. A. H.; Veghini, D.; Berke, H. Inorg. Chem.
1992, 31, 5106. (b) van der Zeijden, A. A. H.; Berke, H. HelV. Chim.
Acta 1992, 75, 513. (c) Nietlispach, D.; Bakhmutov, V. I.; Berke, H.
J. Am. Chem. Soc. 1993, 115, 9191. (d) Bakhmutov, V. I.; Bu¨rgi, T.;
Burger, P.; Ruppli, U.; Berke, H. Organometallics 1994, 13, 4203.
(e) Nietlispach, D.; Veghini, D.; Berke, H. HelV. Chim. Acta 1994,
77, 2197. (f) Shubina, E. S.; Belkova, N. V.; Krylov, A. N.; Vorontsov,
E. V.; Epstein, L. M.; Gusev, D. G.; Niedermann, M.; Berke, H. J.
Am. Chem. Soc. 1996, 118, 1105. (g) Belkova, N. V.; Shubina, E. S.;
Ionidis, A. V.; Epstein, L. M.; Jacobsen, H.; Messmer, A.; Berke, H.
Inorg. Chem. 1997, 36, 1522. (h) Gusev, D. G.; Llamazares, A.; Artus,
G.; Jacobsen, H.; Berke, H. Organometallics 1999, 18, 75. (i) Messmer,
A.; Jacobsen, H.; Berke, H. Chem.sEur. J. 1999, 5, 3341. (j)
Bannwart, E.; Jacobsen, H.; Furno, F.; Berke, H. Organometallics
2000, 19, 3605. (k) Furno, F.; Fox, T.; Schmalle, H. W.; Berke, H.
Organometallics 2000, 19, 3620. (l) Ho¨ck, J.; Jacobsen, H.; Schmalle,
H. W.; Artus, G. R. J.; Fox, T.; Amor, J. I.; Ba¨th, F.; Berke, H.
Organometallics 2001, 20, 1533. (m) Furno, F.; Fox, T.; Alfonso, M.;
Berke, H. Eur. J. Inorg. Chem. 2001, 1559.
A related, but presumably more enhanced, steric hindrance
now being related also to the product can be derived from
the difference in reactivity of the two isomers N-1-naphth-
ylideneaniline and N-benzylidene-1-naphthylamine. In con-
trast to the reaction with N-1-naphthylideneaniline, the
reaction of 1 with N-benzylidene-1-naphthylamine turns out
to be an equilibrium (Scheme 1) preventing the amido
complex 6 from being isolated from the reaction mixture.
(8) (a) Berke, H.; Burger, P. Comments Inorg. Chem. 1994, 16, 279. (b)
Jacobsen, H.; Berke, H. In Recent AdVences in Hydride Chemistry;
Poli, R., Peruzzini, M., Eds.; Elsevier: Amsterdam, 2001; p 89.
(9) Liang, F.; Schmalle, H. W.; Fox, T.; Berke, H. Organometallics 2003,
22, 3382.
994 Inorganic Chemistry, Vol. 43, No. 3, 2004

Reactions of trans-Mo(dmpe)2(H)(NO) with Imines
Table 1. Imines Tested for Insertion with 1
a
b
c
Me2CdNCHMe2; Me2CdNPh; Ph(Me)CdNPh; Ph2CdNPh; Ph2CdNH
PhCHdNCH2Ph; PhCHdNMe
2-methy-2-oxazoline; 1,5-diazabicyclo[2.2.2]octane; (Me2N)2CdNH
a 10:1 stoichiometric ratio of the imine and 1. However, no
insertion reaction was observed for all these imines under
the given conditions. The imines listed in Table 1 can be
classified into three categories: C-disubstituted imines (entry
a); C-phenyl- and N-alkyl-substituted imines (entry b); imines
with a π-donor atom at the carbon terminus of the CdN
moiety (entry c). These negative observations presumably
allow us to generalize that hydride 1 preferably reacts with
1,2-diaryl-substituted imines.
1
Figure 1. 1D-NOE H NMR spectrum of the equilibrium reaction of 1
with (1-naphthyl)CH2dNPh to yield 6 (Scheme 1) (C7D8, room tempera-
ture).
The possibility of an acceleration of such imine insertions
of 1 in the presence of protic substrates, as it was found in
many cases of insertion reactions of aldehydes or ketones
with transition metal hydrides,5,10 has been additionally
probed. The relatively acidic OH species phenol, methyl
alcohol, and ethyl alcohol were added to the reaction systems
of 1 and the imines. However, insertions have not been
detected; rather reactions of 1 with the acids occurred leading
to evolution of dihydrogen and formation of the correspond-
ing alkoxide complexes for both “reactive” and “nonreactive”
imines of Table 1.
Characterization of Complexes 2-5. The insertion
products 2-5 could be isolated as analytically pure com-
pounds and have been fully characterized by elemental
analysis, IR and NMR spectroscopy, and mass spectrometry.
Selected spectroscopic features are discussed below.
Besides the signals for the phenyl ring protons of the
amido moiety appearing in the range of 6.47-7.05 ppm and
those for the methylene and methyl protons of the dmpe
ligands between 1.05 and 1.35 ppm, the 1H NMR spectrum
of 2 shows a singlet at 4.28 ppm (C6D6) belonging to the
newly formed N bound CH2 group. In the 13C{1H} NMR
the signal of this Cmethylene atom was found at 59.0 ppm as a
quintet due to coupling with the four chemically equivalent
dmpe phosphorus nuclei (3JCP ) 6 Hz). In contrast to the
other sharp singlets for the Cphenyl atoms, a broadened signal
was observed at 119.5 ppm for the phenyl Cipso atom. The
Figure 2. van’t Hoff plot for the equilibrium reaction of 1 with
(1-naphthyl)CH2dNPh (Scheme 1). K values are from 31P NMR in C7D8.
But the formation of 6 can clearly be deduced from the NMR
1
spectra of the reaction mixture. In the H NMR spectrum
(C7D8) a singlet at 4.67 ppm can be attributed to the -NCH2-
protons. This assignment has been confirmed by an 1D-NOE
experiment. When the signal at 4.67 ppm was irradiated,
exchange with signals at 8.1 and -4.72 ppm (resonances
for the -CH) group of the imine and the HMo atom,
respectively) could be identified (Figure 1). The 31P{1H}
spectrum displays besides the signal for 1 a singlet at 24.8
ppm, which belongs to 6.
The temperature dependence of the equilibrium constant
K of this reaction to 6 has been determined by NMR in C7D8.
A van’t Hoff plot is drawn out in Figure 2, which allowed
for the calculation of DH and DS amounting to -48.8 (
0.4 kJ‚mol-1 and -33 ( 1 J‚K-1‚mol-1, respectively. The
reaction is therefore only mildly exothermic, which is
presumably similar but still a bit less on the exothermic side
than the other cases of investigated inserting imines. ∆H for
the reaction to 6 is smaller than that of 1 with Mo(dmpe)2-
(NO)[(µ-OCH)Re2(CO)9],9 where a Mo-O bond is newly
installed. This can be attributed to a generally smaller Mo-N
bond energy in comparison with the Mo-O bond.
3
broadening is anticipated to be due to a small J coupling
with the phosphorus nuclei.
The 31P{1H} NMR spectra of the isomeric complexes 3
and 4 are very similar and comparable to 2 (24.8 ppm)
indicated by singlets at 25.1 (3) and at 24.8 ppm (4), while
1
the H and 13C{1H} NMR spectra show greater deviations
reflecting the structural differences of both complexes. The
1H NMR spectra of 3 and 4 in C6D6 display characteristic
singlets at 4.06 and 3.34 ppm, respectively, which are
assigned to their methylene protons. Their marked difference
in chemical shift may be related to the difference in
pyramidalization at the amido atom (vide infra). For 4 two
signals belonging to the protons of the two Cp rings (the
The screening of the insertion capability of 1 with imines
was extended to a series of other imines listed in Table 1.
All these reactions were carried out as NMR experiments at
room temperature or at 60-70 °C for 2 days in C7D8 with
(10) (a) Kundel, P.; Berke, H. J. Organomet. Chem. 1987, 335, 353. (b)
van der Zeijden, A. A. H.; Bosch, H. W.; Berke, H. Organometallics
1992, 11, 2051. (c) Ho¨ck, J.; Fox. T.; Schmalle, H.; Berke, H. Chimia
1999, 53, 350. (d) Messmer, A. Ph.D. Thesis, University of Zurich,
1999.
Inorganic Chemistry, Vol. 43, No. 3, 2004 995

Liang et al.
Figure 4. ORTEP plot of the structure of 2. Displacement ellipsoids are
drawn with 50% probability. All hydrogen atoms except for H13a and H13b
are omitted for clarity.
Table 2. Selected Bond Lengths (Å) and Bond Angles (deg) of 2
Mo(1)-N(1)
Mo(1)-N(2)
Mo(1)-P(1)
Mo(1)-P(2)
Mo(1)-P(3)
Mo(1)-P(4)
N(1)-O(1)
1.7916(15)
2.2421(14)
2.4982(5)
2.4781(6)
2.5020(6)
2.4946(5)
1.2255(19)
1.385(2)
N(1)-Mo(1)-P(1)
N(1)-Mo(1)-P(2)
N(1)-Mo(1)-P(3)
N(1)-Mo(1)-P(4)
N(1)-Mo(1)-N(2)
C(20)-N(2)-Mo(1)
C(13)-N(2)-Mo(1)
C(20)-N(2)-C(13)
P(1)-Mo(1)-P(2)
P(3)-Mo(1)-P(4)
86.32(5)
84.97(5)
87.87(5)
85.62(5)
177.46(6)
130.00(12)
115.72(11)
113.46(15)
77.997(19)
79.500(18)
N(2)-C(20)
N(2)-C(13)
1.463(2)
Figure 3. VT-1H NMR spectra for the -NCH2- group of 5 in C7D8.
Hz. The 31P{1H} NMR spectrum shows a singlet at 24.8 ppm.
All these latter NMR data of 5 are comparable to those of
the amido complexes 2-4.
substituted Cp ring is denoted as Cp′) are found as a singlet
at 3.88 ppm and a multiplet at 3.80 ppm with an intensity
ratio of 5:4 (Cp and Cp′), whereas the related resonances
for 3 appear as a singlet at 4.09 ppm and two triplets at 3.97
and 3.84 ppm, respectively. In the 13C{1H} NMR spectra of
3 and 4 the resonances for the Cmethylene atoms are found with
a small chemical shift difference at 53.5 and 55.8, respec-
tively. The ferrocenyl unit of 3 shows no P coupled signal
exhibiting four singlets at 93.6 (Cp), 69.2, 68.8, and 65.8
ppm (all Cp′), while the resonances for the ferrocenyl rings
of 4 show two singlets at 68.3 (Cp) and 60.9 ppm and a
quintet at 62.3 ppm (both Cp′). The splitting of the latter
signal confirms the vicinity of the Cp′ Cipso atom of 4 to the
metal phosphine moiety. Conversely and as expected from
the substituent exchanged structure of both isomers, the Cipso
atom of the phenyl group of 3 shows P coupling (quintet at
120.6 ppm), while the signals for the other aromatic C nuclei
appear as singlets, as do all Cphenyl resonances of 4.
Crystal Structures of Complexes 2-5. Crystals of 2
suitable for X-ray diffraction analysis were obtained by slow
diffusion of pentane into a solution of the complex in toluene
at room temperature. An ORTEP plot of 2 is given in Figure
4. The complex has a pseudooctahedral coordination geom-
etry around the Mo center. The NNO-Mo-P bond angles
(Table 2) show that the phosphine ligands bend toward the
nitrosyl group. This bending may be attributed to the steric
repulsion9 between the Mo(dmpe)2(NO) fragment and the
amido moiety. Presumably based on the same effect, an
elongation of about 0.04 Å for the Mo-P bonds (Table 2,
average 2.4932 Å) can be observed in comparison with the
previously reported other complexes containing an Mo-
(dmpe)2(NO) fragment.9 The relatively long Mo(1)-N(2)
(amido) bond length of 2.2421(14) Å in 2 can be primarily
ascribed to the trans influence of the NO group. The N(2)-
C(20) bond distance of 1.385(2) Å and the N(2)-C(13)
distance of 1.463(2) Å are comparable to those found for
N-C(sp2) and N-C(sp3) bonds in amido complexes.11 The
amido nitrogen exhibits a planar rather than a pyramidal
geometry12 with a sum of the three bond angles of around
N(2) of 359.2°.
1
In the H NMR spectrum of 5 (C6D6) the resonances of
the -NCH2- protons were found as two broad singlets at
4.84 and 4.57 ppm, respectively, which is different from the
corresponding resonances of 2-4 featuring just singlets. The
appearance of two signals for 5 indicates hindered rotation
of the naphthyl moiety rendering the two hydrogen atoms
to be diasterotopic, and indeed their resonances display
temperature-dependence (Figure 3). At low-temperature two
doublets with a geminal coupling (2JHH ) 17 Hz at -40 °C)
can be observed. At high temperature fast rotation of the
naphthyl moiety on the NMR time scale occurs, which leads
to equivalency of the two hydrogen atoms of the CH2 group.
In the 13C{1H} NMR spectrum of 5 (C6D6, room temperature)
the resonance of the N bound methylene group appears at
56.2 ppm as a quintet with a C-P coupling constant of 7
To further support and compare the structure of the
isomericcomplexes 3 and 4 both complexes have been
(11) (a) Laplaza, C. E.; Odom, A. L.; Davis, W. M.; Cummins, C. C. J.
Am. Chem. Soc. 1995, 117, 4999. (b) Laplaza, C. E.; Johnson, M. J.
A.; Peters, J. C.; Odom, A. L, Kim, E.; Cummins, C. C.; George, G.
N.; Pickering, I. J. J. Am. Chem. Soc. 1996, 118, 8623.
(12) (a) Chiu, K. W.; Wong, W.-K.; Wilkinson, G. Polyhedron 1982, 1,
37. (b) Dewey, M. A.; Arif, A. M.; Gladysz, J. A. J. Chem. Soc.,
Chem. Commun. 1991, 712.
996 Inorganic Chemistry, Vol. 43, No. 3, 2004

Reactions of trans-Mo(dmpe)2(H)(NO) with Imines
Table 4. Selected Bond Lengths (Å) and Bond Angles (deg) of 4a
Mo(1)-N(1)
Mo(1)-N(2)
Mo(1)-P(1)
Mo(1)-P(2)
Mo(1)-P(3)
Mo(1)-P(4)
N(1)-O(1)
N(2)-C(20)
N(2)-C(13)
Fe-C(20)
1.787(3)
2.240(2)
2.4987(8)
2.4900(8)
2.4999(9)
2.4756(8)
1.218(3)
1.367(4)
1.479(4)
2.230(3)
2.015(3)
2.083(3)
2.060(4)
2.052(4)
1.6915(4)
1.6576(4)
N(1)-Mo(1)-P(1)
N(1)-Mo(1)-P(2)
N(1)-Mo(1)-P(3)
N(1)-Mo(1)-P(4)
N(2)-Mo(1)-P(1)
N(2)-Mo(1)-P(2)
N(2)-Mo(1)-P(3)
N(2)-Mo(1)-P(4)
C(20)-N(2)-Mo(1)
C(13)-N(2)-Mo(1)
C(20)-N(2)-C(13)
P(1)-Mo(1)-P(2)
P(3)-Mo(1)-P(4)
Cp(1)-Fe-Cp(2)
87.10(9)
86.67(9)
83.85(9)
84.53(9)
93.34(7)
94.66(7)
95.78(7)
94.14(7)
124.8(2)
115.73(19)
112.8(2)
79.49(3)
79.09(3)
177.06(3)
Fe-C(22)
Fe-C(24)
Fe-C(27)
Fe-C(29)
Figure 5. ORTEP plot of the structure of 3. Displacement ellipsoids are
drawn with 50% probability. The benzene solvate molecule and all hydrogen
atoms except for H13a and H13b are omitted for clarity.
Fe-Cp(1)
Fe-Cp(2)
a Cp(1) and Cp(2) refer to the centers of the gravity of the cyclopenta-
dienyl rings C(14)-C(18) and C(19)-C(23), respectively.
adopts a practically planar geometry at this atom with a sum
of the three angles around N(2) of 359.5°. The amido
nitrogen atom of 4 however shows a slight pyramidalization
with a sum of the angles around N(2) of 353°. For the
ferrocenyl fragment the Fe-C distances of 3 (2.031(3)-
2.071(3) Å) are comparable to those of 4 (2.015(3)-2.083(3)
Å) and to those found in ferrocene and its derivatives.13 The
Fe-C distances of the Cipso atom of 4 (Fe-C(20), 2.230(3)
Å) and the same one of 3 (Fe-C(14), 2.109(2) Å) are
significantly elongated especially in 4, which may be ascribed
to steric repulsion with the substituents, i.e., the Mo(dmpe)2-
(NO) fragment and the other residue of the amido group.
Similar steric effects have previously been seen in complexes
with congested substituents at the ferrocene ring.14
Figure 6. ORTEP plot of the structure of 4. Displacement ellipsoids are
drawn with 50% probability. All hydrogen atoms except for H13a and H13b
are omitted for clarity.
Table 3. Selected Bond Lengths (Å) and Bond Angles (deg) of 3a
The bulky naphthyl moiety in 5 has been found to affect
the 1H NMR spectrum of newly formed -NCH2- group due
to hindered rotation in solution. It was therefore of interest
to see to what preferred conformation the spectral properties
might be attributable to. 5 was subjected to an X-ray
diffraction study. Suitable crystals were obtained by cooling
a toluene solution to -30 °C for several weeks. Under the
given conditions 5 crystallized as toluene solvate. The
asymmetric unit of 5 contains two independent molecules,
and in each molecule the Mo center is pseudooctahedrally
coordinated similar to those of compounds 2-4. The
structural model of one of both independent molecules is
shown in Figure 7. Selected bond distances and angles of
both molecules are given in Table 5. A comparison of the
bond distances and the bond angles around the Mo centers
of 5 with those of 2-4 does not reveal significant deviations
in the essential parts of the coordination geometries. Even
the related bond lengths and angles around the practically
planar amido nitrogen atom of 5 are almost the same as those
of 2 and 3. All these observations suggest that the bulkiness
naphthyl moiety does not lead to significant changes of the
structural parameters of 5 in the solid state. The conforma-
tions of the aromatic rings are very similar in both indepen-
Mo-N(1)
Mo-N(2)
Mo-P(1)
Mo-P(2)
Mo-P(3)
Mo-P(4)
N(1)-O(1)
N(2)-C(24)
N(2)-C(13)
Fe-C(14)
Fe-C(16)
Fe-C(18)
Fe-C(21)
Fe-C(22)
Fe-Cp(1)
Fe-Cp(2)
1.813(2)
2.253(2)
2.4916(7)
2.4733(7)
2.5056(7)
2.4965(7)
1.193(3)
1.388(3)
1.472(3)
2.109(2)
2.031(3)
2.071(3)
2.061(3)
2.047(3)
1.6649(4)
1.6591(4)
N(1)-Mo-P(1)
N(1)-Mo-P(2)
N(1)-Mo-P(3)
N(1)-Mo-P(4)
N(2)-Mo-P(1)
N(2)-Mo-P(2)
N(2)-Mo-P(3)
N(2)-Mo-P(4)
C(24)-N(2)-Mo
C(13)-N(2)-Mo
C(24)-N(2)-C(13)
P(1)-Mo-P(2)
P(3)-Mo-P(4)
Cp(1)-Fe-Cp(2)
82.91(8)
85.32(8)
86.87(8)
87.21(8)
95.07(6)
95.90(6)
92.05(6)
94.90(6)
128.96(17)
117.28(15)
113.3(2)
78.95(2)
79.15(3)
176.71(3)
a Cp(1) and Cp(2) refer to the centers of the gravity of the cyclopenta-
dienyl rings C(14)-C(18) and C(19)-C(23), respectively.
subjected to crystallographic analyses. Diffusion of pentane
into a benzene solution afforded suitable crystals of 3, which
crystallized as a benzene solvate. Suitable crystals of 4 were
obtained by diffusion of pentane into a toluene solution. The
ORTEP drawings of 3 and 4 are depicted in Figures 5 and
6, respectively. Selected bond lengths and angles are given
in Table 3 for 3 and in Table 4 for 4. Overall, the related
bond distances and angles around the molybdenum centers
of 3 and 4 are very close suggesting in particular similar
binding strengths of the amido nitrogen atom to Mo in the
two complexes. The only structural differences that can be
detected, which are presumably too small and therefore not
relevant in terms of thermodynamics, are the pyramidal
angles at the nitrogen atoms of the amido units. 3 again
(13) (a) Bracci, M.; Ercolani, C.; Floris, B.; Bassetti, M.; Chiesi-Villa, A.;
Guastini, C. J. Chem. Soc., Dalton Trans. 1990, 1357. (b) Silver, J.;
Miller, J. R.; Houlton, A.; Ahmet, M. T. J. Chem. Soc., Dalton, Trans.
1994, 3355. (c) Barranco, E. M.; Gimeno, M. C.; Jones, P. G.; Laguna,
A.; Villacampa, M. D. Inorg. Chem. 1999, 38, 702.
(14) Roberts, R. M. G.; Silver, J.; Yamin, B. M.; Drew, M. G. B.; Eberhardt,
U. J. Chem. Soc., Dalton Trans. 1988, 1549.
Inorganic Chemistry, Vol. 43, No. 3, 2004 997

Liang et al.
dence that ligand tuning may be quite an effective approach
to optimize reactivity in transition metal hydride chemis-
try.7,15
Experimental Section
All reactions and manipulations were performed under an
atmosphere of dry nitrogen using conventional Schlenk techniques
or a glovebox. Solvents were dried according to standard procedures
and freshly distilled under nitrogen prior to use. trans-Mo(dmpe)2-
(H)(NO) (1) was prepared as described previously.9 Other reagents
were purchased from Fluka or Aldrich. NMR spectra were recorded
on the following spectrometers: Varian Gemini-300 instrument,
1H at 300.1 MHz, 13C at 75.4 MHz, 31P at 121.5 MHz, 11B at 96.2
MHz; Bruker DRX-500 instrument, 1H at 500.2 MHz, 13C at 125.8
MHz, 31P at 202.5 MHz, 11B at 160.5 MHz. δ(1H) and δ(13C) are
relative to SiMe4, δ(31P) is relative to 85% H3PO4, and δ(11B) is
relative to BF3‚OEt2. IR spectra were recorded on a Biorad FTS-
45 instrument. Mass spectra were run on a Finnigan-MAT-8400
mass spectrometer. Elemental analyses were performed on a Leco
CHN(S)-932 instrument.
trans-Mo(dmpe)2(NO)[NPh(CH2Ph)] (2). A 0.025 g (0.059
mmol) sample of 1 was dissolved in ca. 0.7 mL of C7D8. To this
solution was added 0.011 g (0.061 mmol) of N-benzylideneaniline.
After 24 h the reaction was complete (NMR monitoring). The
solvent was removed, and the residue was dissolved in ca. 0.5 mL
of toluene. Diffusion of pentane into this solution afforded yellow
crystals of 2. Yield: 0.029 g (81%). IR (cm-1, THF): 1538 (NO).
1H NMR (C6D6): δ 7.05 (m, 7H, Ph), 6.67 (m, 2H, Ph), 6.47 (t,
3JHH ) 7.5 Hz, 1H, Ph), 4.28 (s, 2H, NCH2), 1.35 (s, 12H, PMe),
1.05 (s, 12H, PMe′), 1.25 (m, 8H, PCH2). 13C{1H} NMR (C6D6):
δ 158.9, 144.6, 128.1, 127.4, 127.1, 125.3, 119.5 (br), 110.3
Figure 7. ORTEP plot of the structure of 5. Displacement ellipsoids are
drawn with 50% probability. The benzene solvate molecules and all
hydrogen atoms except for H19a and H19b are omitted for clarity.
Table 5. Selected Bond Lengths (Å) and Bond Angles (deg) of 5
Mo(1)-N(1)
Mo(1)-N(2)
Mo(1)-P(1)
Mo(1)-P(2)
Mo(1)-P(3)
Mo(1)-P(4)
N(1)-O(1)
1.778(4)
N(1)-Mo(1)-P(1)
N(1)-Mo(1)-P(2)
N(1)-Mo(1)-P(3)
N(1)-Mo(1)-P(4)
N(1)-Mo(1)-N(2)
C(13)-N(2)-Mo(1)
C(19)-N(2)-Mo(1)
C(13)-N(2)-C(19)
P(1)-Mo(1)-P(2)
P(3)-Mo(1)-P(4)
N(3)-Mo(2)-P(5)
N(3)-Mo(2)-P(6)
N(3)-Mo(2)-P(7)
N(3)-Mo(2)-P(8)
N(3)-Mo(2)-N(4)
C(42)-N(4)-Mo(2)
C(48)-N(4)-Mo(2)
C(42)-N(2)-C(48)
P(5)-Mo(2)-P(6)
P(7)-Mo(2)-P(8)
87.92(13)
79.40(13)
85.39(13)
88.41(13)
178.90(16)
130.0(3)
115.9(3)
113.5(4)
79.88(5)
80.13(5)
84.42(13)
85.24(14)
80.89(13)
90.31(14)
177.50(17)
129.9(3)
115.7(3)
113.5(4)
80.07(5)
79.18(5)
2.251(4)
2.4883(14)
2.5142(14)
2.4888(13)
2.4778(14)
1.240(5)
N(2)-C(13)
N(2)-C(19)
Mo(2)-N(3)
Mo(2)-N(4)
Mo(2)-P(5)
Mo(2)-P(6)
Mo(2)-P(7)
Mo(2)-P(8)
N(3)-O(2)
1.373(6)
1.468(6)
1.770(4)
2.251(4)
2.4974(13)
2.4592(14)
2.5241(14)
2.4916(14)
1.230(5)
N(4)-C(42)
N(4)-C(48)
1.394(6)
1.468(6)
3
1
(8 s, Ph), 59.0 (quint, JCP ) 6.4 Hz, NCH2), 30.3 (quint, JCP
)
10 Hz, PCH2), 17.0 (m, PMe). 31P{1H} NMR (C6D6): δ 24.8 (s).
EI-MS: m/z 609 (55, M+), 458 (71, [M+ - dmpe]), 426 (88, [M+
- PhCH2NPh]), 396 (22, [M+ - PhCH2NPh - NO]). Anal. Calcd
for C25H44MoN2OP4: C, 49.34; H, 7.30; N, 4.60. Found: C, 49.69;
H, 7.33; N, 4.70.
dent molecule structures, which allows to conclude that the
given arrangement of Figure 7 (Ph approximately in plane
with the plane at N2, naphthyl plane approximately perpen-
dicular to it) is a low-energy conformation possessing also
a high weight in solution. The two N-bound hydrogens (H19a
and H19b) show quite different chemical environments,
which are expected to be responsible for the observed
trans-Mo(dmpe)2(NO)[NPh(CH2Cp2Fe)] (3). A mixture of
0.027 g (0.063 mmol) of 1 and 0.022 g (0.076 mmol) of
N-ferrocenylideneaniline was dissolved in ca. 0.7 mL of C7D8 in
an NMR tube. The resulting solution was monitored by NMR. After
5 days at room temperature the reaction was complete and the
solvent was removed in vacuo. The remaining residue was dissolved
in ca. 0.5 mL of benzene. Diffusion of pentane into the benzene
1
splitting of their H NMR signals.
solution gave orange crystals of 3. Yield: 0.037 g (82%). IR (cm-1
,
Conclusions
1
THF): 1536 (NO). H NMR (C6D6): δ 7.24-7.11 (m, 4H, Ph),
Relatively rare insertion reactions of several imines were
demonstrated to occur with the activated hydride trans-
Mo(dmpe)2(H)(NO) producing the corresponding amido
complexes. In these reactions trans-Mo(dmpe)2(H)(NO)
displayed hydride-transfer capabilities presumably due to the
strongly polar character of the Mo-H bond.9 By variation
of the type of the inserting imine it became apparent that a
supposedly weak Mo-N(amide) bond generates a borderline
situation and despite the high reactivity of the hydride applied
this may set thermodynamic restrictions to the insertion
abilities of the imine component. Superimposed kinetic
factors, like the steric congestion in the transition state of
the insertion reaction, could also hinder the reaction or even
set further limits to the range of applicable inserting imines.
Overall the generally high propensity of trans-Mo(dmpe)2-
(H)(NO) to allow hydride-transfer processes provides evi-
6.56 (tt, 3JHH ) 6.9 Hz, 4JHH ) 1.4 Hz, 1H, Ph), 4.09 (s, 5H, Cp),
3
4.06 (s, 2H, NCH2), 3.97 (t, 2H, JHH ) 2.0 Hz, Cp), 3.84 (t, 2H,
3JHH ) 2.0 Hz, Cp′), 1.34 (s, 12H, PMe), 1.08 (s, 12H, PMe′),
1.21 (m, 8H, PCH2). 13C{1H} NMR (C6D6): δ 161.6, 128.5, 127.3,
3
110.5 (4s, Ph), 120.6 (quint, JCP ) 3 Hz, Ph), 93.6, 69.2, 68.8,
3
1
65.8 (4s, Cp), 53.5 (quint, JCP ) 6 Hz, NCH2), 30.3 (quint, JCP
) 9 Hz, PCH2), 17.0 (m, PMe). 31P{1H} NMR (C6D6): δ 25.1 (s).
EI-MS: m/z 716 (27, M+), 566 (82, [M+ - dmpe]), 426 (34, [M+
- Cp2FeCH2NPh]), 396 (16, [M+ - Cp2FeCH2NPh - NO]). Anal.
Calcd for C29H48FeMoN2OP4: C, 48.61; H, 6.77; N, 3.91. Found:
C, 48.93; H, 7.14; N, 3.92.
trans-Mo(dmpe)2(NO)[N(Cp2Fe)(CH2Ph)] (4). A mixture of
0.021 g (0.049 mmol) of 1 and 0.018 g (0.062 mmol) of
N-benzylideneferrocenylamine was dissolved in ca. 0.7 mL of C7D8
in an NMR tube. The resulting solution was heated to 65 °C. After
3 days the reaction was complete (NMR monitoring). The solvent
was removed in vacuo. The residue was extracted with diethyl ether.
998 Inorganic Chemistry, Vol. 43, No. 3, 2004

Reactions of trans-Mo(dmpe)2(H)(NO) with Imines
Table 6. Crystallographic Data and Structure Refinement Parameters for 2-5
2
3
4
5
formula
color
C25H44MoN2OP4
yellow
C35H54FeMoN2OP4
orange
C29H48FeMoN2OP4
red
C43H62MoN2OP4
yellow
cryst dimens (mm)
temp (K)
cryst syst
space group (No.)
a (Å)
0.36 × 0.27 × 0.21
0.53 × 0.49 × 0.21
0.22 × 0.11 × 0.08
0.27 × 0.20 × 0.11
183(2)
183(2)
123(2)
183(2)
monoclinic
P21/n (14)
monoclinic
P21/a (14)
orthorhombic
P212121 (19)
9.8225(4)
monoclinic
P21/c (14)
9.1592(6)
15.9501(7)
12.2334(8)
14.0645(7)
13.0005(7)
21.3405(14)
b (Å)
16.2028(10)
c (Å)
â (δꢀγ)
20.6001(13)
21.9336(14)
20.5507(9)
31.069(2)
96.615(8)
92.755(8)
90
92.466(8)
V (Å3
)
2989.4(3)
4
608.44
1.352
0.673
1272
3769.5(4)
4
3270.7(3)
4
716.36
1.455
1.048
1488
8611.8(10)
8
Z
fw
794.47
842.77
d(calcd) (g cm-3
)
)
1.400
1.300
abs coeff (mm-1
0.917
0.487
F(000)
1656
3552
2θ scan range (deg)
no. of unique data
no. of data obsd [I > 2s(I)]
abs corr
5.34 < 2θ < 60.62
5.66 < 2θ < 60.56
5.24 < 2θ < 60.56
3.86 < 2θ < 51.78
8864
11 191
9700
16 609
6060
8237
7617
8642
numerical
Patterson
306
numerical
Patterson
365
numerical
Patterson
352
numerical
Patterson
935
solution method
no. of params refined
R, wR2 (%) all data
4.90, 4.86
2.75, 4.73
1.030
5.21, 11.61
3.53, 9.75
1.014
4.47, 5.71
2.98, 5.53
1.062
9.48, 11.17
4.70, 10.46
0.993
R1, wR2 (obsd) (%)a
goodness-of-fit
a R1 ) ∑(Fo - Fc)/∑Fo, I > 2σ(I); wR2 ) {∑w(Fo - Fc )2/∑w(Fo )2}1/2
.
2
2
2
Concentration and cooling to -30 °C of the extracts afforded 4 as
red crystals. Yield: 0.30 g (85.7%). IR (cm-1, THF): 1538 (NO).
1H NMR (C6D6): δ 7.31 (d, br, 5H, Ph), 3.88 (s, 4H, Cp), 3.80
(m, 5H, Cp′), 3.34 (s, 2H, NCH2), 1.40 (m, 8H, PCH2), 1.30 (s,
12H, PMe), 1.25 (s, 12H, PMe′). 13C{1H} NMR (C6D6): δ 144.6,
134.2, 127.9, 126.1 (4s, Ph), 68.3 (s, Cp), 62.3 (quint, 3JCP ) 6 Hz
Total exposure times for the four compounds were 23, 16, 17, and
23 h in the order of the complexes given above. After integrations
and corrections for Lorentz and polarization effects, a total of 7998
reflections for 2, 7996 for 3 and 5, and 8000 for 4 were selected
out of the whole limiting sphere for the cell parameter refinements.
A total of 31 734, 43 436, 34 154, and 49 914 reflections were
collected, of which 8864, 11 191, 9700, and 16 609 reflections were
unique (Rint ) 5.22%, 3.85%, 5.23%, and 9.11%); data reduction
and numerical absorption correction used 18, 11, 9, and 11 indexed
crystal faces.16
The structures were solved by Patterson method using the
Program SHELXS-97,17 and they were refined with SHELXL-97.18
The absolute configuration for 4 was determined by using Flack’s
x-parameter refinement.19 The absolute structure parameter x was
0.538(18); i.e., merohedrical twinning was observed with an
appoximate twin ratio of 1:1. The X-ray data collections and the
processing parameters are given in Table 6.
3
Cp′), 60.9 (s, Cp′), 55.8 (quint, JCP ) 6 Hz, NCH2), 30.7 (quint,
1JCP ) 10 Hz, PCH2), 17.7 (quint, 1JCP ) 5 Hz, PMe), 17.2 (quint,
1JCP ) 5 Hz, PMe′). 31P{1H} NMR (C6D6): δ 24.8 (s). Anal. Calcd
for C29H48FeMoN2OP4: C, 48.61; H, 6.77; N, 3.91. Found: C,
49.01; H, 7.09; N, 3.92.
trans-Mo(dmpe)2(NO)[NPh(CH2-1-naphthyl)] (5). A 0.029 g
(0.068 mmol) sample of 1 was dissolved in ca. 0.7 mL of C7D8,
and 0.017 g (0.073 mmol) of N-1-naphthylideneaniline was added.
After 6 days at room temperature the reaction was complete (NMR
monitoring). The solvent was removed in vacuo, and the residue
was recrystallized from diethyl ether at -30 °C to give yellow solid
of 5. Yield: 0.035 g (78%). IR (cm-1, THF): 1540 (NO). 1H NMR
(C6D6): δ 8.13-6.49 (m, 12H, naphthyl, Ph), 4.84 (s, br, 1H,
NCH2), 4.57 (s, br, 1H, NCH2), 1.34 (s, br, 24 H, PMe), 1.23 (m,
8 H, PCH2). 13C{1H} NMR (C6D6): δ 159.1, 138.4, 134.4, 132.6,
129.6, 126.0, 125.8, 125.4, 125.1, 124.5, 122.8, 110.3 (12 s,
Acknowledgment. We are grateful to the Swiss National
Science Foundation and the Funds of the University of Zurich
for financial support.
Supporting Information Available: Tables of crystal data and
structure refinement parameters, atomic coordinates, bond lengths,
bond angles, anisotropic displacement parameters, and hydrogen
coordinates for 2-5. This material is available free of charge via
the Internet at http://pubs.acs.org.
3
1
naphthyl, Ph), 56.2 (quint, JCP ) 7 Hz, NCH2), 30.3 (quint, JCP
) 9 Hz, PCH2), 17.0 (br, PMe). 31P{1H} NMR (C6D6): δ 24.8 (s).
EI-MS: m/z 659 (40, M+), 508 (50, [M+ - dmpe]), 426 (60, [M+
- C10H7CH2NPh]), 396 (28, [M+ - C10H7CH2NPh - NO]). Anal.
Calcd for C29H46MoN2OP4: C, 52.88; H, 7.05; N, 4.25. Found:
C, 53.04; H, 7.06; N, 4.27.
IC030139L
X-ray Crystal Structure Analyses. The intensity diffraction data
were collected at 183(2) K (2, 3, 5) and 123(2) K (4) using an
imaging plate detector system (Stoe IPDS) with graphite-mono-
chromated Mo KR radiation. A total of 190, 167, 167, and 220
images were exposed at constant times of 3.00, 1.50, 2.00, and
2.20 min/image for compounds 2-5, respectively. The crystal-to-
image distances were set to 50 mm, except of compound 5, that
had a necessary large distance of 70 mm. The corresponding θmax
values were 30.31, 30.28, 30.34, and 25.89°, respectively. φ-oscil-
lation (2, 5) or rotation scan modes (3, 4) were selected for the φ
increments of 1.0, 1.2, 1.2, and 0.7° per exposure in each case.
(15) (a) Darensbourg, M. Y.; Ash, C. E. AdV. Organomet. Chem. 1987,
27, 1. (b) Dedieu, A., Eds. Transition Metal Hydrides; VCH Publish-
ers: Weinheim, Germany, New York, 1992. (c) Xin X.; Moss, J. R.
Coord. Chem. ReV. 1999, 181, 27.
(16) Stoe IPDS software for data collection, cell refinement and data
reduction, versions 2.87-2.92; Stoe & Cie: Darmstadt, Germany,
1997-1999. Verson 2.92 was used for 5.
(17) SHELXS-97: Sheldrick, G. M. Acta Crystallogr. 1990, 46A, 467.
(18) SHELXL-97: Sheldrick, G. M. Programme for the Refinement of
Crystal Structures; University of Go¨ttingen: Go¨ttingen, Germany,
1997.
(19) (a) Flack, H. D. Acta Crystallogr. 1983, A39, 876. (b) Flack, H. D.;
Bernardinelli, G. Acta Crystallogr. 1999, A55, 908.
Inorganic Chemistry, Vol. 43, No. 3, 2004 999