[1]Molybdarenophanes: Strained metallarenophanes with aluminum, gallium, and silicon in bridging positions

Article abstract of DOI:10.1021/ja072747w

The first [1]molybdarenophanes were synthesized and structurally characterized. The aluminum and gallium compounds [(Me₂Ntsi) Al(η⁶-C₆H₅)₂Mo] (2a) and [(Me₂Ntsi)Ga(η⁶-C₆H₅) ₂Mo] (2b) [Me₂Ntsi = C(SiMe₃) ₂(SiMe₂NMe₂)] were obtained from [Mo(LiC ₆H₅)₂]·TMEDA and (Me₂Ntsi) ECl₂ [E = Al, Ga] in analytical pure form with isolated yields of 74% (2a) and 52% (2b). The silicon-bridged species [Ph₂Si- (η⁶-C₆H₅)₂Mo] (2c) was synthesized from [Mo(LiC₆H₅)₂]·TMEDA and Ph₂SiCl₂. Compound 2c was isolated as a crystalline material in an approximately 90% overall purity, from which a single crystal was used for X-ray analysis. The molecular structures of all three [1]molybdarenophanes 2a-c were determined by single-crystal X-ray analysis. The ring-tilt angle a was found to be 18.28(17), 21.24(10), and 20.23(29)° for 2a, 2b, and 2c, respectively. Variable temperature NMR measurements of 2a and 2b (-80 to 80°C; 500 MHz) showed a dynamic behavior of the gallium species 2b but not of compound 2a. The dynamic behavior of 2b was rationalized by assuming that the Ga-N donor bond breaks, inversion at the nitrogen atom occurs, and a rotation of the Me₂Ntsi ligand takes place followed by a re-formation of the Ga-N bond on the other side of the gallium atom. The analysis of the signals of meta and ortho protons of 2b gave approximate values of ΔG ^≠ of 59.6 and 59.1 kJ mol^-1, respectively. Compound 2b reacted with [Pt(PEt₃)₃] to give the ring-open product [(η⁶-C₆H₆)Mo{η⁶-C ₆H₅[GaPh(Me₂Ntsi)]}] (3b). The molecular structure of 3b was deduced from a single-crystal X-ray determination. The formation of the unexpected platinum-free product 3b can be rationalized by assuming that benzene reacted with 2b in a 1:1 ratio. Through a series of ¹H NMR experiments with 2b it was shown that small amounts of donor molecules (e.g., THF) in benzene are needed to form 3b; in the absence of a donor molecule, 2b is thermally stable.

Full text of DOI:10.1021/ja072747w

Published on Web 07/11/2007
[1]Molybdarenophanes: Strained Metallarenophanes with
Aluminum, Gallium, and Silicon in Bridging Positions
Clinton L. Lund,‡ Jo¨rg A. Schachner,‡ J. Wilson Quail,§ and Jens Mu¨ller*,‡
Contribution from the Department of Chemistry and Saskatchewan Structural Sciences Centre,
UniVersity of Saskatchewan, 110 Science Place, Saskatoon, Saskatchewan S7N 5C9, Canada
Received April 19, 2007; E-mail: jens.mueller@usask.ca
Abstract: The first [1]molybdarenophanes were synthesized and structurally characterized. The aluminum
and gallium compounds [(Me2Ntsi)Al(η6-C6H5)2Mo] (2a) and [(Me2Ntsi)Ga(η6-C6H5)2Mo] (2b) [Me2Ntsi )
C(SiMe3)2(SiMe2NMe2)] were obtained from [Mo(LiC6H5)2]‚TMEDA and (Me2Ntsi)ECl2 [E ) Al, Ga] in
analytical pure form with isolated yields of 74% (2a) and 52% (2b). The silicon-bridged species [Ph2Si-
(η6-C6H5)2Mo] (2c) was synthesized from [Mo(LiC6H5)2]‚TMEDA and Ph2SiCl2. Compound 2c was isolated
as a crystalline material in an approximately 90% overall purity, from which a single crystal was used for
X-ray analysis. The molecular structures of all three [1]molybdarenophanes 2a-c were determined by single-
crystal X-ray analysis. The ring-tilt angle R was found to be 18.28(17), 21.24(10), and 20.23(29)° for 2a,
2b, and 2c, respectively. Variable temperature NMR measurements of 2a and 2b (-80 to 80 °C; 500
MHz) showed a dynamic behavior of the gallium species 2b but not of compound 2a. The dynamic behavior
of 2b was rationalized by assuming that the Ga-N donor bond breaks, inversion at the nitrogen atom
occurs, and a rotation of the Me2Ntsi ligand takes place followed by a re-formation of the Ga-N bond on
the other side of the gallium atom. The analysis of the signals of meta and ortho protons of 2b gave
approximate values of ∆G* of 59.6 and 59.1 kJ mol-1, respectively. Compound 2b reacted with [Pt(PEt3)3]
to give the ring-open product [(η6-C6H6)Mo{η6-C6H5[GaPh(Me2Ntsi)]}] (3b). The molecular structure of 3b
was deduced from a single-crystal X-ray determination. The formation of the unexpected platinum-free
product 3b can be rationalized by assuming that benzene reacted with 2b in a 1:1 ratio. Through a
series of 1H NMR experiments with 2b it was shown that small amounts of donor molecules (e.g., THF) in
benzene are needed to form 3b; in the absence of a donor molecule, 2b is thermally stable.
Introduction
Since the discovery that ring-opening polymerization (ROP)
of sila[1]ferrocenophanes yield high molecular weight polymers,
many new strained[1]metallacyclophanes have been described
in the literature (Figure 1).1,2 Very recently, this area of
organometallic chemistry has witnessed important contributions
from several research groups. For example, a new class of
strained species derived from cycloheptatrienyl-cyclopenta-
dienyl sandwich compounds, [(η5-C7H7)(η5-C5H5)M] (M ) Ti,
Zr, Cr, V), had been prepared during the last 3 years (Figure
1).3-8 Braunschweig et al. reported on the synthesis of the first
Figure 1. [1]Metallacyclophanes.
strained manganese sandwich, a derivative of the parent com-
pound [(η6-C6H6)(η5-C5H5)Mn].9 The first [1]metallacyclo-
phanes with aluminum and gallium in bridging positions were
made accessible by our efforts using trisyl-type ligands with
donor abilities at the group 13 element [trisyl stands for
tris(trimethylsilyl)methyl, (Me3Si)3C]. To date, we have char-
acterized [1]ferrocenophanes,10-12 [1]chromarenophanes,12 and
[1]vanadarenophanes.12
‡ Department of Chemistry.
§ Saskatchewan Structural Sciences Center.
(1) Foucher, D. A.; Tang, B. Z.; Manners, I. J. Am. Chem. Soc. 1992, 114,
6246-6248.
The chemistry of strained [1]metallacyclophanes has essen-
tially been restricted to compounds that contain 3d transition
(2) Herbert, D. E.; Mayer, U. F. J.; Manners, I. Angew. Chem., Int. Ed. 2007,
46, 5060-5081.
(3) Elschenbroich, C.; Paganelli, F.; Nowotny, M.; Neumu¨ller, B.; Burghaus,
O. Z. Anorg. Allg. Chem. 2004, 630, 1599-1606.
(8) Bartole-Scott, A.; Braunschweig, H.; Kupfer, T.; Lutz, M.; Manners, I.;
Nguyen, T.-l.; Radacki, K.; Seeler, F. Chem.sEur. J. 2006, 12, 1266-
1273.
(4) (a) Tamm, M.; Kunst, A.; Bannenberg, T.; Herdtweck, E.; Sirsch, P.;
Elsevier, C. J.; Ernsting, J. M. Angew. Chem., Int. Ed. 2004, 43, 5530-
5534. (b) Tamm, M.; Kunst, A.; Bannenberg, T.; Randoll, S.; Jones, P. G.
Organometallics 2007, 26, 417-424.
(9) Braunschweig, H.; Kupfer, T.; Radacki, K. Angew. Chem., Int. Ed. 2007,
46, 1630-1633.
(5) Tamm, M.; Kunst, A.; Bannenberg, T.; Herdtweck, E.; Schmid, R.
Organometallics 2005, 24, 3163-3171.
(10) Schachner, J. A.; Lund, C. L.; Quail, J. W.; Mu¨ller, J. Organometallics
2005, 24, 785-787.
(6) Braunschweig, H.; Lutz, M.; Radacki, K. Angew. Chem., Int. Ed. 2005,
44, 5647-5651.
(11) Schachner, J. A.; Lund, C. L.; Quail, J. W.; Mu¨ller, J. Organometallics
2005, 24, 4483-4488.
(7) Braunschweig, H.; Lutz, M.; Radacki, K.; Schaumlo¨ffel, A.; Seeler, F.;
Unkelbach, C. Organometallics 2006, 25, 4433-4435.
(12) Lund, C. L.; Schachner, J. A.; Quail, J. W.; Mu¨ller, J. Organometallics
2006, 25, 5817-5823.
9
10.1021/ja072747w CCC: $37.00 © 2007 American Chemical Society
J. AM. CHEM. SOC. 2007, 129, 9313-9320
9313

A R T I C L E S
Scheme 1
Lund et al.
2). However, the signals of the gallane 2b sharpen at lower
temperature so that at -10 °C its pattern is similar to that of 2a
(Figure 2). We performed variable temperature NMR measure-
ments of 2a and 2b (-80 to 80 °C; 500 MHz). While the alane
2a does not show coalescences, the signals of meta and ortho
protons of 2b coalescence at 19.0 and 40.1 °C, respectively,
resulting in approximate values of ∆G* of 59.6 and 59.1 kJ
mol-1 17
. The dynamic behavior can be rationalized by assuming
metals in the sandwich moiety. Besides the zirconium compound
mentioned above,5 [1]ruthenocenophanes are the only strained
4d metal sandwich compounds known today.13 Surprisingly,
even though numerous examples of [1]chromarenophanes are
known, not a single [1]molybdarenophane is described in the
literature. Bis(benzene)molybdenum was first synthesized by
E.O. Fischer et al.14 Its dilithiation and subsequent reactions
with silicon dihalides resulted in sparingly characterized poly-
meric materials.15 In the course of the preparation of this
manuscript, Braunschweig et al. reported on the dilithiation of
[Mo(C6H6)2] and a structural determination of [Mo(LiC6H5)2-
(THF)6]. However, attempted syntheses of bora- and sila[1]-
molybdarenophanes were not successful.16
that the E-N donor bond breaks, inversion at the nitrogen atom
occurs, and rotation of the Me2Ntsi ligand takes place followed
by a re-formation of the E-N bond on the other side of the
bridging atom. This process is fast enough in the case of the
gallane 2b resulting in a time-averaged C2V species at higher
temperatures. The fact that compound 2a does not show
coalescence within the accessible temperature range matches
the expectation that Al-N donor bonds are stronger than Ga-N
donor bonds.
Suitable crystals for X-ray structural determinations of both
[1]molybdarenophanes were obtained by crystallization from
aromatic solvents. The alane was obtained as 2a‚1/2C6H5CH3
and the gallane as 2b‚C6H6 (Table 1 and Figures 3 and 4). The
group 13 element is situated in a spiro position and part of a
four-membered ring that deviates only slightly from planarity
(rms deviations from planarity are 0.0387 (2a) and 0.0330 Å
(2b)). Aluminum and gallium, respectively, are distorted
tetrahedrally coordinated by one N and three C atoms. Whereas
Al-C bonds are slightly shorter than the respective Ga-C
bonds, the Al-N bond of 2.021(4) Å is significantly shorter
than the Ga-N bond of 2.120(3) Å (Figure 3 and 4). Similar
sets of bond lengths had been determined for the [1]chromar-
enophanes and [1]vanadarenophanes.12 The difference of ca.
0.10 Å between the two E-N bond lengths renders the Ga-N
bond much weaker than the Al-N bond, a fact that fits to the
observed fluctuating behavior of 2b in solution.
Herein, we report on the first successful syntheses of
[1]molybdarenophanes, strained organometallic compounds with
aluminum, gallium, and silicon in bridging positions.
Results and Discussions
A reaction of freshly prepared [Mo(LiC6H5)2]‚TMEDA with
an intramolecularly coordinated alane or gallane (Me2Ntsi)ECl2
[Me2Ntsi ) C(SiMe3)2(SiMe2NMe2)] resulted in [1]molyb-
darenophanes in moderate isolated yields (Scheme 1).
Both [1]molybdarenophanes 2a and 2b show the expected
signal pattern for time-averaged Cs symmetric species in their
1
1H and 13C NMR spectra. The H NMR spectrum of the alane
2a, for example, displays two doublets at δ 3.75 and 4.43 (o-
H) and three pseudotriplets at δ 5.08, 5.16, and 5.57 (m-H, p-H)
with equal signal intensities (25 °C in C6D6). At similar
conditions, compound 2b (25 °C in C7D8) shows only four
instead of the expected five signals: three broad signals at δ
3.52 (o-H), 4.05 (o-H) and 5.24 (m-H), and one well resolved
pseudotriplet at δ 5.52 (p-H) (Figure 2). A similar sequence of
signals for ortho, meta, and para protons was found for the
alumina and galla[1]chromarenophanes.12 A definite proof that
the isolated products 2a and 2b are indeed strained [1]-
metallarenophanes comes from their 13C NMR data. The
aromatic ipso-C atoms resonate at δ 54.4 (2a) and 44.5 (2b)
which is a significant upfield shift compared to that of the
unstrained parent bis(benzene)molybdenum (δ 75.7). These
shifts are larger than those observed for alumina and galla[1]-
chromarenophanes equipped with the same stabilizing trisyl-
type ligand [δ 62.1 (Al) and 56.6 (Ga) relative to δ 74.8 for
Cr(C6H6)2].12 The larger shift is expected as [1]molyb-
darenophanes should be more highly strained than their chro-
mium analogues.
The extent of strain in metallacyclophanes is usually il-
lustrated by a set of angles (Figure 5). The tilt angles R, which
is a measure of the deviation of the two phenyl rings from
coplanarity, is the most commonly used parameter to compare
different [1]metallacyclophanes. Compounds 2a and 2b with
tilt angles R of 18.28(17) and 21.24(10)° are expectedly higher
tilted than their chromium counterparts [R ) 11.81(9) (Al) and
13.24(13)° (Ga)].12 Dimethylsila[1]ferrocenophane, the most
thoroughly investigated [1]metallacyclophane, shows with R )
20.8(5)°18 a similar distortion as 2a and 2b.
For most new [1]metallacyclophanes, silicon-bridged species
were the first ones which were explored. On the basis of the
promising results we obtained with the synthesis of 2a and 2b,
we performed initial experiments targeted at silicon-bridged [1]-
molybdarenophanes. As already mentioned in the introduction,
independent from our efforts, Braunschweig and co-worker’s
targeted these species, but their attempted synthesis of sila[1]-
molybdarenophanes failed and 1,1′-disubstituted bis(benzene)-
molybdenum compounds were isolated instead.16 The authors
speculated that the targeted [1]molybdarenophanes were ther-
mally instable, which prevented their isolation; no direct
evidence for the formation of these ansa species were found.
Following the procedure for the synthesis of 2a-b, we reacted
As mentioned above, the peaks in the proton NMR spectrum
of 2b are broader and not as well resolved as those of 2a (Figure
(13) Vogel, U.; Lough, A. J.; Manners, I. Angew. Chem., Int. Ed. 2004, 43,
3321-3325.
(14) Fischer, E. O.; Stahl, H. O. Chem. Ber. 1956, 89, 1805-1808.
(15) Green, M. L. H.; Treurnicht, I.; Bandy, J. A.; Gourdon, A.; Prout, K. J.
Organomet. Chem. 1986, 306, 145-165.
(16) Braunschweig, H.; Buggisch, N.; Englert, U.; Homberger, M.; Kupfer, T.;
Leusser, D.; Lutz, M.; Radacki, K. J. Am. Chem. Soc. 2007, 129, 4840-
4846.
(17) Sandstro¨m, J. Dynamic NMR Spectroscopy; Academic Press: London, 1982.
(18) Finckh, W.; Tang, B. Z.; Foucher, D. A.; Zamble, D. B.; Ziembinski, R.;
Lough, A.; Manners, I. Organometallics 1993, 12, 823-829.
9
9314 J. AM. CHEM. SOC. VOL. 129, NO. 30, 2007

[1]Molybdarenophanes
A R T I C L E S
Figure 2. 1H NMR spectra in the region of the arene protons of 2a at 25 °C (bottom), of 2b at 25 °C (middle), and 2b at -10 °C (top) taken in C7D8 (small
singlet at δ 4.58 (room temp) and 4.61 (-10 °C) is due to [Mo(C6H6)2]).
Table 1. Crystal and Structural Refinement Data for Compounds 2a-c, and 3b
2a‚
1/2toluene
2b
‚
benzene
2c
3b
empirical formula
formula weight
wavelength, Å
crystal system
space group
Z
C53H88Al2Mo2N2Si6
1167.63
0.71073
triclinic
P1h
1
C29H46GaMoNSi3
658.60
0.71073
triclinic
P1h
2
C24H20MoSi
432.43
0.71073
monoclinic
P21/c
4
C29H46GaMoNSi3
658.60
0.71073
triclinic
P1h
2
a, Å
b, Å
c, Å
9.0050(4)
9.7930(5)
17.0803(8)
98.873(3)
97.435(2)
96.174(3)
1463.15(12)
1.325
9.2069(3)
13.3959(4)
13.5754(3)
110.073(2)
90.698(2)
96.944(2)
1558.49(8)
1.403
7.8790(5)
18.5687(13)
14.5051(9)
90
120.590(4)
90
1826.8(2)
1.572
173(2)
9.2936(5)
9.7991(5)
17.2637(10)
90.071(4)
102.786(3)
92.141(4)
1532.06(14)
1.428
R, deg
â, deg
γ, deg
vol, Å3
d (calcd), mg/m3
temp, K
173(2)
173(2)
173(2)
abs coefficient, mm-1
θ range, deg
refln collected
independent refln
abs correction
ref method
0.617
2.26 to 26.02
17573
5736 [R(int) ) 0.0959]
ψ-scan
full-matrix
least-squares on F2
5736/99/321
1.072
1.400
2.58 to 27.54
22845
7144 [R(int) ) 0.0607]
ψ-scan
full-matrix
least-squares on F2
7144/38/296
1.041
0.788
2.81 to 23.25
9175
2624 [R(int) ) 0.1586]
none
full-matrix
least-squares on F2
2624/0/235
1.056
1.424
3.12 to 24.41
15565
5028 [R(int) ) 0.1303]
ψ-scan
full-matrix
least-squares on F2
5028/0/327
1.065
data/restraints/params
GOF on F2
final R indices [I > 2σ(I)]
R1 ) 0.0540
wR2 ) 0.1220
R1 ) 0.0935
wR2 ) 0.1459
0.717 and -0.819
R1 ) 0.0441
wR2 ) 0.0986
R1 ) 0.0655
wR2 ) 0.1107
0.826 and -0.628
R1 ) 0.0633
wR2 ) 0.1002
R1 ) 0.1169
wR2 ) 0.1167
0.480 and -0.563
R1 ) 0.0690
wR2 ) 0.1584
R1 ) 0.1053
wR2 ) 0.1785
1.317 and -0.943
R indices (all data)
largest diff. peak and hole, e.Å-3
1
[Mo(LiC6H5)2]‚TMEDA with Ph2SiCl2. According to the H
NMR spectrum of the reaction mixture the targeted diphenylsila-
[1]molybdarenophane (2c) was unequivocally formed among
other products. On the basis of the published NMR data for
1,1′-disubstituted bis(benzene)molybdenum compounds,16 com-
pound 2c is formed in an approximate 1:1 mixture with [Mo-
{C6H5(SiPh2Cl)}2]. The separation of pure 2c from this mixture
proved to be very difficult. To date, we have successfully
crystallized 2c from benzene, resulting in single crystals suitable
for X-ray structural analysis. However, the overall purity of
isolated 2c was estimated to be >90% (see Experimental
Section). This first silicon-bridged [1]molybdarenophane (2c)
was unequivocally identified by 1H and 13C NMR spectroscopy.
For example, a large splitting between the resonances of ortho,
meta, and para protons at δ 4.04 (d), 4.98 (pst), and 5.46 (pst)
(Figure 6), respectively, clearly shows that a strained C2V
symmetrical [1]molybdarenophane had been formed.
Via 2D correlated NMR spectroscopy, 13C NMR signals could
be assigned to ortho, meta, and para carbon atoms and, more
importantly, the signal of the ipso-C atom was detected at δ
32.0. The upfield shift of the resonance of the ipso-C atom with
respect to the unstrained parent bis(benzene)molybdenum (δ
75.7) clearly supports the conclusion from the proton spectra.
To obtain structural details, a single-crystal X-ray analysis
of 2c was undertaken (Table 1 and Figure 7). The silicon atom
in 2c is nearly ideally tetrahedrally surrounded by four carbon
9
J. AM. CHEM. SOC. VOL. 129, NO. 30, 2007 9315

A R T I C L E S
Lund et al.
The tilt angle R is the most commonly used parameter to
illustrate the degree of strain in metallacyclophanes (Figure 5).
For the aluminum-bridged [1]molybdarenophanes 2a the R angle
of 18.28(17)° means a 55% (6.5°) increase compared to its
chromium analogue [(Me2Ntsi)Al(C6H5)2Cr] (R ) 11.81(9)°).12
Similarly, the gallium species 2b with R ) 21.24(10)° shows
an increase of 60% (8.0°) with respect to its chromium
counterpart (R ) 13.24(13)°).12 Compound 2c exhibits a tilt
angle R of 20.23(29)° which is only a 40% (5.8°) increase
compared to its chromium analogue19 (R ) 14.4°). On the basis
of the increases found for 2a and 2b, a tilt angle between
22-23° would be expected for compound 2c.
The interest in novel [1]metallacyclophanes is partly driven
by their potential usefulness for ring-opening polymerizations
(ROPs). However, the known examples of ROPs of strained
metallarenophanes are rare. Manners et al. had shown that ther-
mal or anionic copolymerization of dimethylsila[1]chrom-
arenophane with dimethylsila[1]ferrocenephane can be per-
formed.20 A few years later, dimethylsila[1]chromarenophane
was polymerized using Karstedt’s catalyst, but the poor solubil-
ity of the resulting polymers prevented a full characterization.21
To investigate if a metallarenophane is prone to undergo transi-
tion-metal mediated ROP, platinum complexes like [Pt(1,5-
COD)2]22,23 and [Pt(PEt3)3]23-28 had been used with the intent
of isolating a compound in which a PtLx moiety is inserted into
the ipso-C bridging-element bond. Compounds of this type have
thrown some light on the transition-metal mediated ROP.23 The
first isolatable compound was [Fe(η5-C5H4)2Pt(PEt3)2SiMe2]
obtained from dimethylsila[1]ferrocenophane and [Pt(PEt3)3].24,25
On this basis, we intended to find out if the new [1]molyb-
darenophanes might undergo transition-metal mediated poly-
merizations and we did a series of experiments with the gallium-
bridged species 2b. Surprisingly, compound 2b reacts with
[Pt(PEt3)3] in refluxing benzene to give the new ring-opened
product 3b (Figure 8). As deduced from a single-crystal X-ray
analysis, 3b is a platinum-free species (Table 1 and Figure 8).
Its formation can be rationalized by assuming that benzene
reacted with the [1]molybdarenophane 2b in a 1:1 ratio. We
performed a series of NMR experiments to elucidate the role
Figure 3. Molecular structure of 2a with thermal ellipsoids at the 50%
1
probability level. H atoms and
/ a molecule of toluene are omitted for
2
clarity. Selected bond lengths [Å] and angles [deg]: Al1-N1 ) 2.021(4),
Al1-C1 ) 2.005(5), Al1-C7 ) 2.012(5), Al1-C13 ) 2.048(5), C1-
Al1-C7 ) 98.2(2), C7-Al1-C13 ) 125.10(19), C1-Al1-C13 ) 122.0-
(2), C7-Al1-N1 ) 111.7(2), C1-Al1-N1 ) 113.90(19), C13-Al1-N1
) 86.16(19).
Figure 4. Molecular structure of 2b with thermal ellipsoids at the 50%
probability level. H atoms and one molecule of benzene are omitted for
clarity. Selected bond lengths [Å] and angles [deg]: Ga1-N1 ) 2.120(3),
Ga1-C1 ) 2.029(4), Ga1-C7 ) 2.023(4), Ga1-C13 ) 2.054(3), C1-
Ga1-C7 ) 93.74(14), C7-Ga1-C13 ) 125.85(14), C1-Ga1-C13 )
128.35(14), C7-Ga1-N1 ) 114.54(15), C1-Ga1-N1 ) 109.96(16),
C13-Ga1-N1 ) 84.50(14).
1
of the platinum complex. H NMR experiments with 2b and
[Pt(PEt3)3] in C6H6 and C6D6, respectively, clearly revealed that
the nonsubstituted benzene ring of the bis(arene)molybdenum
moiety of 3b exclusively comes from the solvent. From a
competing experiment between C6H6 and C6D6, it was shown
that both ligands are incorporated into 3b with the same rate,
attesting that C-H activation is not part of a rate determining
step. If [Pt(PEt3)3] was not added, the galla[1]molybdarenophane
Figure 5. Common angles to describe [1]metallacylophanes. Values for
2a2b in [deg]: R ) 18.28(17) [21.24(10)], θ ) 98.2(2) [93.74(14)], and δ
) 167.31(20) [164.20(17)].
atoms, which can be illustrated by the narrow range of 102.6-
(4)-111.6(4)° found for the six C-Si-C angles. Expectedly,
the θ angle of 102.6(4)° (C1-Si1-C7) is the most distorted
C-Si-C angle. The four Si-C bonds are split into a set of
two shorter bonds (Si1-C13 ) 1.867(8) and Si1-C19 ) 1.851-
(9) Å) and two longer bonds (Si1-C1 ) 1.901(9) and Si1-C7
) 1.897(9) Å). Even though the differences between the two
sets are small, they are significant and can be rationalized as
being a consequence of the strain exerted on the bonds of silicon
to the ipso-C atoms of the coordinated phenyl rings. In
agreement with this interpretation is the fact that the less strained
diphenylsila[1]chromarenophane19 shows a less pronounced
difference between the two sets of Si-C bonds (1.882(4)/1.882-
(4) Å compared to 1868(4)/1.870(5) Å).
(19) Elschenbroich, C.; Hurley, J.; Metz, B.; Massa, W.; Baum, G. Organo-
metallics 1990, 9, 889-897.
(20) Hultzsch, K. C.; Nelson, J. M.; Lough, A. J.; Manners, I. Organometallics
1995, 14, 5496-5502.
(21) Berenbaum, A.; Manners, I. J. Chem. Soc., Dalton Trans. 2004, 2057-
2058.
(22) Sheridan, J. B.; Temple, K.; Lough, A. J.; Manners, I. J. Chem. Soc., Dalton
Trans. 1997, 711-713.
(23) Temple, K.; Ja¨kle, F.; Sheridan, J. B.; Manners, I. J. Am. Chem. Soc. 2001,
123, 1355-1364.
(24) Sheridan, J. B.; Lough, A. J.; Manners, I. Organometallics 1996, 15, 2195-
2197.
(25) Reddy, N. P.; Choi, N.; Shimada, S.; Tanaka, M. Chem. Lett. 1996, 649-
650.
(26) Temple, K.; Lough, A. J.; Sheridan, J. B.; Manners, I. J. Chem. Soc., Dalton
Trans. 1998, 2799-2805.
(27) Chan, W. Y.; Berenbaum, A.; Clendenning, S. B.; Lough, A. J.; Manners,
I. Organometallics 2003, 22, 3796-3808.
(28) Tamm, M.; Kunst, A.; Herdtweck, E. Chem. Commun. 2005, 1729-1731.
9
9316 J. AM. CHEM. SOC. VOL. 129, NO. 30, 2007

[1]Molybdarenophanes
A R T I C L E S
Figure 6. 1H NMR spectrum in the region of the arene protons of 2c at 25 °C.
and that is what makes the compound a common starting
material for half-sandwich complexes.29,30 However, the sub-
stitution of benzene in [Mo(C6H6)2] by other arenes requires
forcing thermal conditions (160 °C; 48 h).31 The respective
ligand substitution in the galla[1]molybdarenophane 2b which
yields 3b is catalyzed by the donor species, and it seems that
the reaction occurs at relatively mild conditions because of the
high strain of 2b.
Summary and Conclusion
The first [1]molybdarenophanes with aluminum, gallium, and
silicon in bridging positions have been synthesized. Surprisingly
the gallium species 2b with an R tilt angle of 21.24(10)° is
significantly higher strained than its aluminum counterpart 2a
(R ) 18.28(17)). This is counterintuitive because the slightly
smaller Al atom should result in a slightly larger tilt angle R.32
To date, for all known cases, the tilt angles R are larger for
galla- than for alumina[1]metallacyclophanes.10-12 Compounds
2a and 2b follow the same trend but show with 3.0° so far the
largest difference; the reasons for the structural differences are
unknown. In the presence of donor ligands like PEt3, COD, and
THF, respectively, the otherwise thermally robust gallium
species 2b adds one equivalent of benzene to give the unstrained
complex 3b. The reaction with THF proceeds cleanly to give
the ring-open product 3b exclusively, showing that THF acts
as a catalyst only. At this point we can only speculate about
the mechanism of this catalyzed benzene addition. It seems
likely that the σ-donor ligand coordinates to the molybdenum
atom and weakens the coordination of the phenyl group so that
benzene eventually replaces the σ-donor ligand and the η6-
phenyl group. This is an unprecedented reactivity of a bis-
(benzene)molybdenum derivative and a similar ring-opening
reaction of [1]metallacyclophanes is not reported in the literature.
In contrast to many other [1]metallacyclophanes, the gallium
compound 2b does not insert a PtLx moiety into E-C(ipso)
bonds, which might be due to a steric protection of these bonds
by two bulky SiMe3 groups.
Figure 7. Molecular structure of 2c with thermal ellipsoids at the 50%
probability level. H atoms are omitted for clarity. Selected bond lengths
[Å] and angles [deg]: Si1-C1 ) 1.901(9), Si1-C7 ) 1.897(9), Si1-C13
) 1.867(8), Si1-C19 ) 1.851(9), C1-Si1-C7 ) 102.6(4), C1-Si1-C13
) 111.3(4), C1-Si1-C19 ) 111.0(4), C7-Si1-C13 ) 111.6(4), C7-
Si1-C19 ) 109.3(4), C13-Si1-C19 ) 110.8(4), R ) 20.23(29), δ )
165.29 (see Figure 5).
Figure 8. Molecular structure of 3b with thermal ellipsoids at the 50%
probability level. H atoms are omitted for clarity. Selected bond lengths
[Å] and angles [deg]: Ga1-N1 ) 2.148(6), Ga1-C1 ) 2.001(7), Ga1-
C14 ) 1.994(8), Ga1-C13 ) 2.096(7), C1-Ga1-C14 ) 109.2(3), C13-
Ga1-C14 ) 119.9(3), C1-Ga1-C13 ) 117.2(3), C14-Ga1-N1 )
112.8(3), C1-Ga1-N1 ) 112.2(3), C13-Ga1-N1 ) 83.2(3).
2b did not react with benzene at all: the strained species 2b
did not change after heating to 65 °C in C6D6 for 7 days. The
reaction of [Pt(COD)2] with 2b gave also product 3b. On the
basis of these findings, we tested if the platinum complex or
just free donor ligands are needed for the transformation. NMR
experiments of 2b in C6D6 with 0.3-0.5 equiv amounts of PEt3,
COD, and THF, respectively, all resulted in the formation of
3b. However, only in the case of THF did the reaction proceed
exclusively from 2b to 3b, with no signs of any byproducts.
For PEt3 and COD, the 1H NMR spectra revealed the formation
of byproducts, which we could not identify so far. For [Mo-
(C6H6)2] it is known that the benzene ligands are relatively labile
The first silicon-bridged [1]molybdarenophane (2c) shows
with R ) 20.23(29)° a smaller angle than expected. Our finding
that bis(lithiobenzene)molybdenum and Ph2SiCl2 results in the
targeted sila[1]molybdareanophane 2c is in contrast to a recent
(29) Davis, R.; Kane-Maguire, L. A. P. In ComprehensiVe Organometallic
Chemistry; Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon
Press: Oxford, 1982; Vol. 3, pp 1204-1210.
(30) Morris, M. J. In ComprehensiVe Organometallic Chemistry; Abel, E. W.,
Stone, F. G. A., Wilkinson, G., Eds.; Pergamon Press: Oxford, 1995; Vol.
5, pp 529-531.
(31) Asirvatham, V. S.; Ashby, M. T. Organometallics 2001, 20, 1687-1688.
(32) Al: 1.25 Å and Ga: 1.26 Å (singly bonded, 3-fold-coordinated elements),
see: Holleman-Wiberg. Inorganic Chemistry, 1st English ed.; Academic
Press: San Diego, London, 2001.
9
J. AM. CHEM. SOC. VOL. 129, NO. 30, 2007 9317

A R T I C L E S
Lund et al.
report.16 The authors reported that 1,1′-disubstituted bis(ben-
zene)molybdenum compounds were formed and speculated that
the targeted [1]molybdareanophanes were thermally instable and,
therefore, could not be obtained. We have proven that the most
strained [1]molybdareanophane, the gallium-bridged species 2b,
is thermally robust when heated in benzene. Besides the
sensitivity toward donor molecules, all [1]molybdarenophanes
are very sensitive toward oxygen. In all cases the highest
to the residual protons of the deuterated solvent (C6D6 at δ 7.15; C7D8
at δ 2.10); 13C chemical shifts were referenced to C6D6 at δ 128.00
and C7D8 at δ 20.40. 27Al NMR spectra were referenced to [Al(acac)3]
dissolved in C6D6. An unequivocal assignment of signals of the bis-
(benzene)molybdenum moiety of compound 2c was done with the help
of 1H/1H-COSY, HMQC, and HMBC spectroscopy. Mass spectra were
measured on a VG 70SE (m/z > 10% are listed for signals of the most
abundant ions). Elemental analyses were performed on a Perkin-Elmer
2400 CHN elemental analyzer using V2O5 to promote complete
combustion.
1
resolved H NMR spectra with the smallest peak width were
obtained from freshly synthesized samples. Prolonged handling
of the species using Schlenk techniques usually resulted in H
Improved Synthesis of [Mo(C6H6)2] (Based on ref 39). MoCl5
(7.4072 g, 27.082 mmol), AlCl3 (18.522 g, 138.91 mmol), Al (1.821
g, 67.44 mmol), mesitylene (1.0 mL), and benzene (70 mL) were set
to reflux for 76 h. All volatiles were removed in vacuum and the brown
solid was broken up into small pieces and added to N2 saturated aqueous
solution (175 mL) containing KOH (51.090 g, 910.60 mmol) and
NaS2O4 (11.152 g, 64.051 mmol) over 1 h at -20 to -30 °C. The
solution was decanted off and the brown solid was dried on high
vacuum. The solid was continually extracted with boiling benzene (150
mL) to give a dark green solution. All volatiles were removed to give
a green solid. The solid was washed with hexanes (60 mL) and dried
to give a bright green solid (3.2742 g, 48%). 1H NMR (500 MHz): δ
4.58 (s).
Synthesis of [{(Me2NMe2Si)(Me3Si)2C}Al(η6-C6H5)2Mo] (2a).
[Mo(C6H6)2] (0.7830 g, 3.105 mmol), cyclohexane (30 mL), TMEDA
(1.875 g, 16.13 mmol), and nBuLi (6.0 mL, 2.6 M in hexanes, 15.6
mmol) were added one after the other, and the mixture was heated
(2.5 h, 50 °C) during which the slurry changed color from green to
dark red. The solution was syringed off, and the remaining red solid
was dried in high vacuum to give [Mo(LiC6H5)2]‚TMEDA (0.811 g,
2.13 mmol). A slurry of this compound in benzene (20 mL, 0 °C) was
added to a solution of 1a (0.770 g, 2.15 mmol) in benzene (10 mL, 0
°C) and stirred for 1 h at room temperature. LiCl was filtered off,
followed by concentration of the filtrate to appoximately 5 mL, and
crystallization at 6 °C gave green crystals of 2a‚C6H6 (0.969 g, 74%).
1H NMR (500 MHz, C6D6): δ ) 0.14 (s, 6H, SiMe2), 0.45 (s, 18 H,
SiMe3), 1.97 (s, 6H, NMe2), 3.75 (d, 2H, o-H), 4.43 (d, 2H, o-H), 5.08
(pst, 2H, m-H), 5.16 (pst, 2H, m-H), 5.57 (pst, 2H, p-H). 13C NMR
(C6D6): 3.0 (SiMe2), 8.1 (SiMe3), 40.5 (NMe2), 54.4 (ipso-C), 74.4
(o-C), 74.5 (o-C), 82.5 (p-C), 83.1 (m-C), 83.8 (m-C). 27Al NMR
1
NMR spectra with unstructured and broad signals for the
aromatic protons of the coordinated phenyl groups. In extreme
cases, these peaks disappeared in the baseline, while all other
signals remained undisturbed. These observations can be
rationalized by assuming that small amounts of oxygen result
in small amounts of paramagnetic Mo(I) cations. A fast electron
exchange between the neutral and oxidized [1]molybdarenophanes
spreads, on time average, the paramagnetic impurity evenly over
all species so that only the aromatic protons are affected.
Electron transfer of this type were found for bis(benzene)-
chromium derivatives before.12,19,33
Recently, a novel type of ring-opening polymerization, coined
photocontrolled ROP, was described.34,35 Within this method,
a ROP of a sila[1]ferrocenophane is initiated by Cp-, but the
polymerization only occurs under irradiation. Photocontrolled
ROP is a living polymerization that can be stopped and
continued by turning the light off and on, respectively. Photons
weaken the Fe-Cp bond allowing the addition of Cp-. It is the
only example of ROP where the ring-opening happens at the
transition-metal side of the precursor. On the basis of our
findings, it is feasible that one can develop a similar but “dark”
version of the photocontrolled ROP for [1]molybdarenophanes
with benzene instead of Cp- as a starter and THF instead of
photons as activator.
Experimental Section
(C6H6): 148 (w1//2 ) 1800 Hz). MS (70 eV): m/z (%) 364 (10) [M+
Mo - C6H6 - C6H5], 295 (14), [M+ - Mo - C6H6 - 2SiMe3 ]+, 246
(60) [MH+ - Mo - Al - C6H6 - 2 C6H5 - CH3], 230 (19) [M+
-
General Procedures. All manipulations were carried out using
standard Schlenk techniques. Solvents were dried using a Braun sol-
vent purification system and stored under nitrogen over 4 Å molec-
ular sieves. All solvents for NMR spectroscopy were degassed prior
to use and stored under nitrogen over 4 Å molecular sieves.
[Mo(LiC6H5)2]‚TMEDA,15 AlCl2[C(SiMe3)(SiMe2NMe2)] (1a),36 and
GaCl2[C(SiMe3)(SiMe2NMe2)] (1b)36 were synthesized as described in
the literature. [Pt(PEt3)3] was prepared from [Pt(PEt3)4]37 in situ by
heating to 60 °C under high vacuum in an NMR tube. [Pt(COD)2] was
prepared via a modified procedure by substituting potassium in place
of lithium.38 An improved synthesis of [Mo(C6H6)2] with respect to a
-
Mo - Al - C6H6 - 2 C6H5 - 2 CH3], 219 (18) [C9H27Si3]+, 217
(16) [C9H25Si3]+, 203 (42) [C8H23Si3]+, 154 (31) [C12H10]+, 129 (30)
[C5H13Si2]+, 102 (34) [C4H12NSi]+, 91 (12) [C7H7]+, 78 (100)
[C6H6]+, 73 (35) [C3H9Si]+, 58 (19) [C2H6Si]+. Anal. Calcd for
C29H46AlMoNSi3 (615.8603): C, 56.56; H, 7.53; N, 2.27; Found: C,
55.73; H, 7.35; N, 2.62. Crystals of 2a‚1/2C7H8 suitable for X-ray
diffraction were grown from toluene at 6 °C.
Synthesis of [{(Me2NMe2Si)(Me3Si)2C}Ga(η6-C6H5)2Mo] (2b).
[Mo(C6H6)2] (0.9116 g, 3.615 mmol), cyclohexane (30 mL), TMEDA
(2.180 g, 18.76 mmol), and nBuLi (7.0 mL, 2.6 M in hexanes, 18 mmol)
were added one after another, and the mixture was heated (2.5 h, 50
°C) during which the slurry changed color from green to dark red. The
solution was syringed off and the remaining red solid was dried in
high vacuum (0.835 g, 2.20 mmol). A slurry of this compound in
benzene (30 mL, 0 °C) was added to a solution of 1b (0.884 g, 2.20
mmol) in benzene (10 mL, 0 °C). After stirring for 2 h at room
temperature, LiCl was filtered off, the filtrate was concentrated (5 mL),
and crystallization at 6 °C gave green crystals of 2b‚C6H6 (0.747 g,
52%). 1H NMR (500 MHz, C7D8, -10 °C): δ ) 0.19 (s, 6H, SiMe2),
0.45 (s, 18 H, SiMe3), 1.99 (s, 6H, NMe2), 3.49 (d, 2H, o-H), 4.09 (d,
2H, o-H), 5.23 (pst, 2H, m-H), 5.32 (pst, 2H, m-H), 5.56 (pst., 2H,
p-H). 13C NMR (C7D8, -10 °C) : 2.8 (SiMe2), 7.3 (SiMe3), 11.7 (CSi3),
41.2 (NMe2), 44.5 (ipso-C), 73.8 (o-C), 73.9 (o-C), 83.6 (p-C), 84.5
1
common method described in reference39 is reported below. H, 13C,
and 27Al NMR spectra were recorded on a Bruker 500 MHz Avance
1
at 25 °C, unless noted differently. H chemical shifts were referenced
(33) Elschenbroich, C.; Zenneck, U. J. Organomet. Chem. 1978, 160, 125-
137.
(34) Chan, W. Y.; Lough, A. J.; Manners, I. Organometallics 2007, 26, 1217-
1225.
(35) Tanabe, M.; Vandermeulen, G. W. M.; Chan, W. Y.; Cyr, P. W.; Vanderark,
L.; Rider, D. A.; Manners, I. Nat. Mater. 2006, 5, 467-470.
(36) Al-Juaid, S. S.; Eaborn, C.; El-Hamruni, S. M.; Hitchcock, P. B.; Smith, J.
D. Organometallics 1999, 18, 45-52.
(37) Yoshida, T.; Matsuda, T.; Otsuka, S. In Inorganic Synthesis; Angelici, R.
J., Ed.; John Wiley & Sons: New York, 1990; Vol. 28, p 120-123.
(38) Spencer, J. In Inorganic Synthesis; Shriver, D. F., Ed.; John Wiley &
Sons: New York, 1979; Vol. 19, p 213-215.
(39) Silverthorn, W. E. In Inorganic Synthesis; Mcgraw-Hill: New York;
London, 1977; Vol. 17, p 54-57.
9
9318 J. AM. CHEM. SOC. VOL. 129, NO. 30, 2007

[1]Molybdarenophanes
A R T I C L E S
(m-C), 85.5 (m-C). MS (70 eV): m/z (%) 406 (100) [M+ - Mo -
C6H6 - C6H5], 361 (22) [M+ - Mo - C6H6 - C6H5 - 3CH3], 292
After 160 h the starting compound 2b showed no signs of decom-
position or transformation. After 832 h 4% of 2b had been transformed
to 3b.
(13) [M+ - Mo - Ga - C6H6 - C6H5 - 3CH3], 246 (87) [MH+
-
Mo - Ga - C6H6 - 2 C6H5 - CH3], 230 (74) [M+ - Mo - Ga -
C6H6 - 2C6H5 - 2CH3], 223 (13) [C12H10Ga]+, 217 (35) [C9H25Si3]+,
203 (31) [C8H23Si3]+, 201 (15) [C8H21Si3]+, 187 (25) [C7H19Si3]+, 175
(14) [C8H23Si2]+, 154 (15) [C12H10]+, 128 (28) [C5H12Si2]+, 102 (26)
[C4H12NSi]+, 78 (93) [C6H6]+, 73 (31) [C3H9Si]+. Anal. Calcd for
C29H46GaMoNSi3 (658.6017): C, 52.89; H, 7.04; N, 2.13; Found: C,
52.26; H, 7.10; N, 2.37.
Tube 4: 2b‚C6H6 (26.4 mg, 0.0401 mmol) and [Pt(PEt3)4] (26.6 mg,
0.0398 mmol) were weighed into an NMR tube, C6D6 (1.0 mL) was
added, and the tube was flame sealed. After 304 h the starting compound
2b had been consumed.
Tube 5: [Pt(COD)2] (11.0 mg, 0.027 mmol) was dissolved in C6D6
(1.0 mL), compound 2b‚C6H6 (15.3 mg, 0.023.2 mmol) was added to
the solution, and the tube was flame sealed. After 304 h the starting
compound 2b had been consumed.
Synthesis of [Ph2Si(η6-C6H5)2Mo] (2c). [Mo(C6H6)2] (1.1062 g,
4.387 mmol), cyclohexane (30 mL), TMEDA (2.589 g, 22.28
mmol), and nBuLi (7.8 mL, 2.86 M, 22.3 mmol) were added one
after another, and the mixture was heated (2.5 h, 50 °C) during which
the slurry changed color from green to dark red. The solution was
syringed off, and the remaining red solid was dried in high vacuum
(1.383 g, 3.637 mmol). A slurry of this compound in benzene (30 mL,
0 °C) was prepared, and Ph2SiCl2 (0.917 g, 3.622 mmol) was added
dropwise during 10 min. The solution was warmed to ambient
temperature and stirred for 1 h. An 1H NMR spectrum from an aliquot
of the reaction mixture revealed that 2c had been formed. Crystallization
from benzene at 6 °C gave 2c as a red-brown crystalline solid (0.415
g, app. 23%), from which a single crystal was used for the X-ray
structural analysis. However, according to 1H NMR spectroscopy this
crystalline fraction showed an approximate overall purity of 90% (see
Tube 6: 2b‚C6H6 (19.4 mg, 0.029 mmol) was placed in a NMR
tube and THF (1.2 µL, 0.01 mmol), and C6D6 (1.0 mL) were added,
followed by flame sealing the tube. After 448 h the starting compound
2b had been cleanly converted to 3b.
Tube 7: 2b‚C6H6 (25.8 mg, 0.039 mmol) was placed in a NMR
tube and COD (2.4 µL, 0.02 mmol) and C6D6 (1.0 mL) were added,
followed by flame sealing the tube. After 448 h the starting compound
2b had been consumed.
Tube 8: [Pt(PEt3)4] (28.3 mg, 0.042 mmol) was converted to
[Pt(PEt3)3] as described above and 2b‚C6H6 (28.1 mg, 0.043 mmol)
was added. The compounds were dissolved in C6H6 (0.50 mL, 5.6
mmol) and C6D6 (0.50 mL, 5.6 mmol), and the tube was flame sealed.
After 216 h the reaction was stopped because it was determined that
no deuterium isotope effect was present.
1
Supporting Information). H NMR (500 MHz, C6D6): δ ) 4.04 (d,
4H, o-H), 4.98 (pst, 4H, m-H), 5.46 (pst, 2H, p-H), 7.20 (m, 6H, m-H,
p-H), 7.97 (pst, 4H, o-H). 13C NMR (C6D6): 32.0 (ipso-C), 74.1
(o-C), 85.1 (p-C), 85.6 (m-C), 128.9 (p-C), 130.5 (m-C), 134.4
(ipso-C), 134.5 (o-C).
Crystal Structure Determination. The crystal data of 2a-c, and
3b were collected at -100 °C on a Nonius Kappa CCD diffractom-
eter, using the COLLECT program.40 Cell refinement and data
reductions used the programs DENZO and SCALEPACK.41 SIR9742
was used to solve the structure and SHELXL-9743 was used to
refine the structure. ORTEP-3 for Windows44 was used for molecular
graphics and PLATON45 was used to prepare material for publication.
H atoms were placed in calculated positions with Uiso constrained to
be 1.2 times Ueq of the carrier atom for aromatic protons. Uiso is
constrained to be 1.5 times Ueq for methyl protons. For compound 2a,
a solvent toluene molecule was found disordered around a center of
symmetry. It was modeled with a rigid toluene molecule. The
temperature factors of the C atoms of the toluene were allowed to refine
but were restrained by SIMU, DELU, and ISOR commands in the
refinement. For compound 2b, a solvent benzene molecule was found
disordered around a center of symmetry. It was modeled by two rigid
benzene molecules with the sum of their occupancies equal to 1.0. The
temperature factors of the C atoms of the benzene were allowed to refine,
but were restrained by SIMU, DELU, and ISOR commands in the
refinement.
Synthesis of [(η6-C6H6)Mo{η6-C6H5[GaPh(Me2Ntsi)]}] (3b).
[Pt(PEt3)4] (0.3751 g, 0.5618 mmol) was placed in a Schlenk flask and
heated to 60 °C under vacuum (10-2 Torr) to give [Pt(PEt3)3] as a red
oil.37 Benzene (5 mL) and 2b (0.3698 g, 0.5615 mmol) were added.
After stirring for 1 h at ambient temperature, the solution was heated
to 65 °C for 87 h. The mixture was monitored by 1H NMR spectroscopy
with a gradual disappearance of 2b and the appearance of new signals.
All volatiles were removed and the resulting black solid was extracted
with benzene (5 mL). The benzene was removed and the greenish solid
was dissolved in a 1:1 mixture of Et2O and toluene (5 mL) and kept at
1
-30 °C to give green crystals (0.105 g, 28%). H NMR (500 MHz,
C6D6): δ ) 0.19 (br. s, 6 H, SiMe2), 0.35 (s, 18H, SiMe3), 2.22 (s, 6H,
NMe2), 4.47 (s, 6H, Ph), 4.53 (br. d, 2H, o-H), 4.60 (br. s, 2H, m-H),
4.67 (pst, 1H, p-H), 7.21 (pst, 1H, p-H), 7.29 (pst, 2H, m-H), 7.68 (d,
2H, o-H).
1H NMR Experiments with 2b. [Pt(PEt3)3] was prepared from
[Pt(PEt3)4]37 in situ by heating to 60 °C under high vacuum in an
NMR tube. PEt3 (1.0 M in THF) was purchased from Aldrich. Samples
were prepared in a glovebox and subsequently flame sealed by freezing
the samples in liquid nitrogen and evacuating the tubes under high
vacuum (10-2 mbar). All NMR tubes were heated for prolonged time
at an oil bath temperature of 65 °C and monitored by 1H NMR
spectroscopy.
Tube 1: [Pt(PEt3)4] (37.4 mg, 0.0560 mmol) was weighed into a
NMR tube, and the off-white solid was converted to the red oil
[Pt(PEt3)3] by heating the NMR tube to 60 °C under high vacuum.
Compound 2b‚C6H6 (37.5 mg, 0.0569 mmol) in C6D6 (1 mL) was added
to the red oil, and the tube was flame sealed. After 1336 h approximately
80% of the starting compound 2b had been consumed.
Tube 2: PEt3 (0.016 mL, 1.0 M in THF, 0.016 mmol) was placed
in a NMR tube, and THF was removed under reduced pressure.
Compound 2b‚C6H6 (28.6 mg, 0.0434 mmol) in C6D6 (1 mL) was
added, and the tube was flame sealed. After 1168 h the starting
compound 2b had been consumed.
Compounds 2c and 3b gave crystals of poor quality. The maximum
observable diffraction angles were low (23.25° and 24.41°) and the
merging R values were high (0.159 and 0.13). A full sphere of data
was collected in both cases. The presence of a heavy atom (Mo) in
both structures contributes strongly to the poor bond precision for
the lighter atoms because the Mo atom dominates the scattering. In
both structures all non-hydrogen atoms refined anisotropically with no
restraints to reasonable positions giving reasonable bond lengths
and bond angles, thus clearly establishing the connectivity of the
molecules.
(40) Nonius; Nonius BV: Delft, The Netherlands, 1998.
(41) Otwinowski, Z.; Minor, W. In Macromolecular Crystallography, Part A;
Carter, C. W., Sweet, R. M., Eds.; Academic Press: London, 1997; Vol.
276, p 307-326.
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A R T I C L E S
Lund et al.
Acknowledgment. We thank the Natural Sciences and Engi-
neering Research Council of Canada (NSERC Discovery Grant,
J.M.), the Saskatchewan Structural Sciences Centre, and the
University of Saskatchewan for their generous support. We
thank the Canada Foundation for Innovation (CFI) and the
government of Saskatchewan for funding of the X-ray and NMR
facilities in the Saskatchewan Structural Sciences Centre (SSSC).
Supporting Information Available: Crystallographic data for
2a-c, and 3b in CIF file format; 1H and 13C NMR spectra for
2c. This material is available free of charge via the Internet at
http://pubs.acs.org.
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