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Organometallic Chemistry of [W2(OCH2tBu)8].

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Organometallic Chemistry of
1W, (OCH, tBu),] **
Malcolm H. Chisholm,* Kirsten Folting,
Matthew A. Lynn, William E. Streib, and
Darin B. Tiedtke
Dedicated to Professor Walter Siebert
on the occasion of his 60th birthday
The triple bond in [W,(OR),] compounds has provided access
to extensive organometallic and coordination chemistry.[’] The
recent preparation of [W,(OCH,~BU),]~’~
has allowed us to examine the chemistry derived from a d’-d2 (W=W)*+ center,
and herein we describe some preliminary findings. These are of
interest in their own right and make a fascinating comparison
with the chemistry already established for [W,(OR),] complexes
and other species with M=M bonds such as “OS,(CO),”~~~
and
[Cp:Re,(CO),] .[41 Several of the findings described herein are
summarized in Scheme 1. The new compounds have been fully
characterized and only selected data are given in the text and
footnotes.
[w,(OCH,tBu),] is believed to be a polymer containing
alkoxide-bridged (W=W)’+ units in the solid state and is insoluble in hydrocarbon solvents.[’] It does, however, readily dissolve in the presence of a Lewis base such as pyridine (py) to
form pni;(OCH,tBu),(py)]. When a suspension of [W,(OCH,tBu),ln in toluene is allowed to react with KH in the presence
of [18]crown-6, the rW,(OCH,tBu),(p-H)]- ion is formed:
(‘HNMR: 6 = 9.8 (W,(p-H), 1J(183W,H)= 119 Hz, Z = 24%)).
The addition of ethyne to [W,(OCH,tBu),], in toluene yields
a 1:1 adduct, 1, whose structure is shown in Figure
The
Scheme 1. Summary of the reactions of [W,(OR),I. R
[‘I
[**I
52
=
CH,tBu.
Prof. M. H. Chisholm, Dr. K. Folting, M. A. Lynn, Dr. W. E. Streib,
D. B. Tiedtke
Department of Chemistry and Molecular Structure Center
Indiana University, Bloomington, IN 47405 (USA)
Fax: Int. code +(812) 855-7148
e-mail: chisholm@indiana.edu
We thank the National Science Foundation for support of this work and
Dr. Theodore A. Budzichowski and Dr. Nadine E. Gruhn for helpful and encouraging discussions. D. B. T. acknowledges General Electric for a graduate fellowship and M. H. C for an Alexander yon Humboldt Stiftung.
0 VCH Verlagsgesellschaft mbH. 0-69451 Weinheim. 1997
Figure 1. An ORTEP drawing of the central W,(O),(p-C,) unit of 1, showmg the
pseudo confacial bioctahedral geometry and the twisted pethyne moiety. The standard deviations for the distances [A] shown are (3) to the last significant figure
solid-state structure provides a rare example of an organometallic compound with a bridging alkyne ligand that is neither perpendicular nor parallel to the M-M bond.[61By analogy with
the chemistry of “Os,(CO),” we might have anticipated a parallel structure: a dimetallacyclobutene. Indeed, simple calculations (EHMO and Fenske-Hall) based on [W,(OH),(C,H,)]
with a W,(OH), skeleton taken from the observed structure
suggest that by using the sum of the energies of the occupied
orbitals, which was employed by Calhorda and Hoffmann to
explain the bonding in the model complex [W,(NH,),Cl,(C,H,)]’-, the parallel structure is
However, ab
initio calculations (Gaussian 92 RHF)[’] on [W,(OH),(C,H,)]
reveal an optimized geometry with the C-C vector at an angle
of 67” to the W-W axis, which is in good agreement with the
observed structure. Calculations employing the
Fenske-Hall method show that the HOMOLUMO gap is maximized at a dihedral angle of
approximately 50°, thereby suggesting a second-order Jahn-Teller distortion is responsible for the observed structure. Full details of
the calculations will be reported later. In any
case, the distortion of the p-ethyne from perpendicular or parallel appears to be electronic
in nature rather than due to steric constraints
imposed by the alkoxide ligands, though the
potential energy surface is rather flat. The
latter is confirmed experimentally since the
ethynyl carbon atoms in the I3C,H, isotopomer show only one 183W-’3C coupling constant in the I3C{‘H} NMR spectrum: 6 = 191,
1J(183W,13C)= 57 Hz, Z = 25% even at
- 80 “C in [D,]toluene. Experimentally we cannot, therefore, distinguish between a rapid interconversion of the p-perpendicular and pparallel alkyne isomers and a dynamic process
in which the twisted p-alkyne oscillates about a
symmetric p-perpendicular position.
[W,(OCH,tBu),], reacts with ethene in
toluene to give green solutions and a similarly
colored crystalline compound. Crystals suitable for X-ray analysis have not yet been obtained but the NMR data leave
little ambiguity concerning the nature of the 1 : l adduct
[W2(OCH,tBu),(pz-C,H4)] (2). In contrast to “Os,(CO),”,
which forms a dirnetallacyclobutane upon reaction with
ethene,I3I the structure of 2 may be described as a confacial
bioctahedron, in which the q2-C,H4 unit occupies a terminal
site. Thus, addition occurs according to Equation (b) and not
by Equation (a). Compound 2 possesses eight inequivalent
0570-0833~97/3601-0052$15.00+ ,2510
Angew. Chem. Int. Ed. Engl. 1997,36, No. 112
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OCH,tBu ligands, which leads to sixteen doublets in the OCH,
region of the 'H NMR spectrum, and eight OCH, carbon resonances are observed in the 13C{'H} NMR spectrum. Similarly,
the q2-C,H4 ligand gives rise to four multiplets in the 'H NMR
spectrum. while the I3C{'H} NMR data of the '3C,H,-labeled
compound show two signals for inequivalent carbon atoms at
6 = 55 and 65 with 1J('3C,'3C) = 31 Hz. This C-C coupling
constant is significantly smaller than the value observed for free
ethene (67 Hz), and is consistent with the formation of a metallacyclopropane upon coordination of ethene. The W - W bond
is therefore oxidized by two electrons as depicted in Equation
(b). The rigid structure on the NMR time-scale arises from the
mutual competition of M-M and M dn-C, TI*bonding which
use different metal t,,-type orbitals.
Allene and [W,(OCH,tBu),], also form a 1 : 1 adduct in hydrocarbon solvents from which orange crystals of [W,(OCH,fBu),(p-q' ,q3-C3H4)](3) are obtained.[51The molecular structure of 3 in the solid-state is shown in Figure 2. The geometry
about W(l) may be viewed as octahedral, while that about W(2)
may be described as a distorted trigonal bipyramid in which the
q3-C3 unit occupies a single equatorial site with the rnethylene
units lying slightly above the trigonal plane. When the orange
crystals are dissolved in hydrocarbon solvents, green solutions
are obtained whose NMR data are very complex and are quite
inconsistent with the structure shown in Figure 2. Thus the 1 :1
eight inequivalent OCH,tBu ligands, and the q 2 - 0 13CPh, carbon resonance occurs at 6 = 100 with 1J(183W,13C)= 47 Hz,
I = 14%.
In the related reaction with thiobenzophenone the C=S bond
is cleaved rapidly, leading to the products [{ W(=CPh,)(OCH,tBu),(p-OCH,tBu3)},] (5) and [{W=S(OCH,tBu),},j
(6). The presence of the terminal alkylidene is evident from the
reaction involving Ph,I3C=S, which yields W='3CPh, with a
chemical shift of 6 = 261 and 1J(183W,13C)= 259 Hz, I = 14%.
The structure of 5 is based on an edge-shared bioctahedron. The
addition of EtOH to 5 led to the ethoxide complex
[{W=CPh,(OEt),(OCH,tBu)(p-OEt)},],
which was crystallographically characterized151and shown to have this structure.
we
Although the structure of [W=S(OtBu),] is
attempted an independent preparation of 6 by treating
[W,(OCH,tBu),], with elemental sulfur. While 6 is indeed
formed in this reaction in hydrocarbon solvents. a blue intermediate [W,(p-S)(OCH,tBu),] (7) was identified and crystallographically characterized (Figure 3). The molecular structure
of 7 can be described as a face-centered bioctahedron with a
symmetric W - S bridge and a W -W single bond (2.628
A).
Figure 3. An ORTEP drawing of 7, showing the confacial W,O,S core. Selected
distances [A] and angles I"]: W-W 2.628(1), W(l)-S(3) ?.?56(2), W(2)-S(3)
2.355(2); W(l)-S(3)-W(2) 67.82(5).
Figure 2. An ORTEP drawing of 3, showing the pseudo-octahedral geometry at
W(1) and the pseudo-trigonal-bipyramidal geometry at W(2) (0(6)-W(2)-0(48)
167.4(2)'). Selected dlstances [A] and angles ["I: W(l)-W(2) 2.97(1), W(l)-C(4)
2.1 l(1). W(2)-C(4) 2.25(1), W(2)-C(3) 2.35 (1). W(2)-C(5) 2.27(1); C(3)-C(4)C(5) 108.7(6)
allene adduct 3 must exist in equilibrium with another isomer
(or isomers), one of which is believed to be analogous to the
q2-ethene adduct described previously.
Benzophenone and [W,(OCH,tBu),], react to give a 1 :1 adduct, 4, whose structure is proposed (based on spectroscopic
properties) to be analogous to the fully characterized compound
[ ~ , ( O - C - C , H , ) ~ ( ~ ~ - ~.['I C ~Specifically
H~)]
for 4, there are
Angew. Chem. Inr. Ed. Engl. 1997,36, No. 112
An 0x0 analog of 7, namely [W,(p-O)(OCH,tBu),] (8), has
been synthesized and ~haracterizedc~]
as a purple, hydrocarbonsoluble, crystalline solid from the reaction between [W,(OCH,tBu),] and pyridine N-oxide in toluene. The W- W distance of 2.55 8, in 8 is notably shorter than that in 7 and reflects
the fact that the W-p-0 distances (av 1.95(1)A) are much
shorter than the W-p-S distances (av 2.35(1) A). The reaction
of 8 with 0, yields [W=O(OCH,tBu),j.
[W,(OCH,fBu),J, and carbon monoxide react in hydrocarbon solvents to form a 1 :1 adduct. The proposed structure of
[W,(OCH,tBu),(CO)] (9) is shown in Scheme 1 and a simple
orbital interaction diagram is given in Scheme 2. In contrast to
[W,(OR),] complexes, the formation of a terminal carbonyl
with ketene-like character is quite striking: b = 323 for I3CO
with 1J(183W,13C)= 220 Hz, 1 = 1 4 % ; V(13CO) =1817 cm-'.
The proposed structure of this monocarbonyl adduct allows the
partitioning of electrons between the two tungsten atoms such
that the W atom bearing the CO ligand is a d4 pseudo-trigonal
bipyramidal metal center. Thus, as shown in Scheme 2, the (dxz,
dJ4 orbitals may back-bond to the CO TI*ligand and at the
same time they may mix with the formally vacant t,, orbitals of
like symmetry at the other metal center. In the absence of accu-
Q VCH Verlagsgesellschaft mbH. 0-69451 Weinheim,1997
0570-0833/97/3601-0053$ 15.00+ .X/0
53
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purple solution. Crystallization from toluene gave X-ray quality purple crystals of
8 in 87% yield.
9: Carbon monoxide (0.103 mmol) was added to a suspension of [W,(OCH,rBu),]
( 1 0 0 m g , 9 . 3 9 ~ 1 O ~ ~ m m o l ) i n d r y . d e g a shexanes(10mL)at
sed
-196°C by using
a calibrated gas manifold. Recrystallization in dry, degassed Et,O gave dark red
crystalsof9in81 % yield. "C('H} NMR(125 MHz,C,D,, -65"C):S = 320(CO.
iJ(ix'W,i3C) = 227 Hz (14%)). 35.4, 35 1, 35.0, 34.8, 34.5. 34.1 (CH,, in relative
ratios of 1 :2.1 1 : 1.2), 28.0. 27.4. 27.2, 27.0, 26.8 (C(CH,),. in a 1 : 1 :2:2:2 ratio).
IR: i.(i3CO)=1817cm-'. B("C"O) =1770cm-'.
'
Received: May 2, 1996
Revised version: October 9, 1996 [Z9091 IE]
German version: Angen. Chem. 1997, 109, 52-54
Keywords: 0 ligands
tungsten
Scheme 2. Orbital scheme of 9.
rate data for the W-W distance, the relative importance of the
Wdx-Wdx bonding- cannot be determined.
In summary, our preliminary investigation of the chemistry of
the W=W bond in [W,(OCH,tBu),] reveals some fascinating
chemistry that is notably different from that established for
~ ' ~ for
] related d3-d3
other M = M bonded c ~ m p l e x e s ~and
(W = W)6f-containing compounds supported by alkoxide ligands."'
Experimental Section
1: Ethyne (0.225 mmol) was added by using a calibrated gas manifold to a suspension of [W,(OCH,tBu),] (120 mg, 0.113 mmol) in dry, degassed hexanes (10 mL)
at - 196 "C. Recrystallization in dry, degassed toluene afforded X-ray quality dark
red crystals of 1 in 86% yield. I3C{'H) NMR (125 MHz, C,D,, 24°C): 6 =191
(iJ(1s'W,13C) = 56 Hz (25%)).
2: Ethene (0.103 mmol) was added to a suspension of [W,(OCH,rBu),] (100 mg,
9.39 x lo-, mmol)indry,degassed hexanes(l0mL)at -196"Cbyusingacalibrated gas manifold. Recrystallization in dry, degassed toluene gave dark green crystals
of 2 in 78% yield. 'HNMR (500 MHz, C,D,, -65°C): 6 = 5.3-3.3 16 doublets
(1H per doublet), 1.48 (9H), 1 3 0 (9H), 1.20 (9H), 1.26 (9H), 1.09 (18H), 0.90
(9H), 0.88 (9H); I3C{'H} NMR (125 MHz, C,D,, -65°C): 6 = 64.3, 55.1
(H,C=CH,, 1J(i3C,'3C) = 31 Hz), 36.1, 35.3, 35.0, 34.7, 34.5, 34.4, 33.5, 33.3
(CH,), 28.5, 27.9, 27.7, 27.6, 27.5, 27.3, 26.7 (C(CH,),).
3: AIlene (0.129mmol) was added to a suspension of [W,(OCH,tBu),l (125mg.
0.1 17 mmol) in dry, degassed hexanes (10 mL) at - 196°C by using a calibrated gas
manifold. Upon warming to 23 "C, the solution became deep green. Crystallization
in hexanes gave X-ray quality pale orange crystals of 3 in 8 2 % yield.
4: ~,(OCH,tBu),] (100 mg, 9.39 x lo-, mmol) and benzophenone (34 mg,
0.19 mmol) were dissolved in dry, degassed hexanes (10 mL) at 24°C to give a forest
green solution. Crystallization in Et,O gave crystals of 4 in 79% yield. "C{ 'H)
= 47 Hz
NMR (125 MHz, C,D,, 24'C): 6 = 100 (Ph-C(0)-Ph, LJ(183W,13C)
(14 Yo)).
5 and 6: [W,(OCH,tBu),] (150mg, 0.141 mmol) and thiobenzophenone (56 mg,
0.28 mmol) were dissolved in dry, degassed hexanes (10 mL) at 24°C to give a
brown solution. "C{'H} NMR (125 MHz, C,D,, 24°C): 6 = 263 (W=CPh,,
= 259 Hz(14%)). Compounds5and 6cocrystallize in hexanes. Com1J(183W,13C)
pound 6 can be prepared independently [lo] and identified spectroscopically.
Addition of ethanol to 5 resulted in the formation of the mixed alkoxide complex,
[{W=CP~,(OE~),(OCH,IB~)(~-OE~)}~]
which was identified crystallographically
~51.
7: [W,(OCH,tBu),] (100 mg, 9.39 x lo-, mmol) and elemental sulfur (3.0 mg,
1.2 x lo-' mmol) were dissolved in dry, degassed hexanes (10 mL) at 24°C to give
a brown solution. Crystallization from hexanes gave X-ray quality pale blue crystals
of 7 in 78% yield.
8: [W,(OCH,tBu),] (120 mg, 0.113 mmol) and pyridine N-oxide (10.7 mg,
0.1 13 mmol) were dissolved in dry, degassed toluene (10 mL) at 24 "C to give a
54
0 VCH Verlagsgesellschaft mbH, 0-69451 Weinherm, 1997
. organometallic chemistry
S ligands
-
[I] M. H. Chisholm, J Chem. SOC.
Dalron Trans. 1996, 1781.
121 T A. Budzichowski, M. H. Chisholm, K. Folting, J. C. Huffman, W. E. Streib,
J Am. Chem. Soc. 1995. 117, 7428.
[3] The Os,(CO), template binds alkynes to give p-parallel 1,2-dimetaIlacyclobutenes, Os,(CO),(p-C,R,) (M. R. Burke, J Takats, J. Organomer. Chem.
1986, 302, C25) and ethene to give the 1,2-dimetallacyclobutene Os,(CO),( p C 2 H 4 )(F. H. Grevels. W. E. Klotzbiickner, F. Seils, K. Schaffner, J. Takats,
J Am. Chem. SOC.1990,112,1995). Seealso J. Takats, Polyhedron 1988,7,931;
R. M. Bullock, T. J. Hembre, J. R. Norton, J Am. Chem. Sac 1988,110,7868;
R. T. Hembre, C. P. Scott, J. R. Norton, [bid. 1987, 109, 3468.
[4] C. P. Casey, R. S. Carino, R. K. Hayashi, K. D. Schadetsky, J. Am. Chem. Soc.
1996. 118, 1617.
[5] Summary of the crystal data for 1 M , = 1090.85, monoclinic, space group
P2,/a, a=18.836(4). h=11.518(2), c=23.620(5)& p=99.87(5)", V =
5048.33 A3, pCalsd
= 1.435 gcm-'. The structure was solved by using a combination ofdirect methods (MULTAN78)and Fourier techniques. The positions
of the tungsten atoms were obtained from an initial E-map. The positions of
the remaining non-hydrogen atoms were obtained from subsequent iterations
of least-squares refinement followed by a difference Fourier calculation.
Hydrogen atoms were included in fixed, calculated positions with thermal
parameters fixed at one plus the isotropic thermal parameter of the carbon
atom to which it was bonded. The final R ( F ) was 0.0651 for the 470 total
variables and 7250 reflections considered observed. Summary of the crystal
data for 3: M , =1104.88. triclinic, space group P i , a = 19.620(3), b =
18.252(3), ~=15.179(3)A, z = 92.20(2), B =113.17(2), 7 = 93.03(2)",
V = 5068.27 A'. pcalcd
= 1.448 gem-,. The final R(F) was 0.0256 for the 479
total variables and 5856 reflections considered observed. Summary of the crystal data for [{W=CPh,(OEt),-(OCH,iBu)(p-OEt)),l. M , = 1329.06, triclinic,
space group Pi, a = 12.408(4), h =13.295(4), c = 9.453(3) A, a = 93.86(2),
B = 94.34(2), 7 = 69.91(1)2, V = 1459.02A', pCalcd
= 1.513 gcm-'. The final
R(F) was 0 0408 for the 335 total variables and 4717 reflections considered
observed. Summary of the crystal data for 7. M , = 1096.88, triclinic, space
group P i . a =14.755(6), b =14.888(6). c =12.172(5) A, I = 92.20(2),
/l =113.17(2),7 =113.17(2)', V = 2449 60
pCalcd
= 1 487 g ~ m - The
~ . final
R ( F ) was 0.0294 for the 461 total variables and 5524 reflections considered
observed. Summary of the crystal data for 8. M , = 1080.81, triclinic, space
group P i , n = 12.221(1), b = 19.820(2), c = 11.593(1)A, a = 91.56(1),
O, =111.49(1), 7 =72.05(1)'. V = 2474.00p\', ps.,od=1.451 gcm-'. The final
R ( F ) was 0.0228 for the 461 total variables and 6890 reflections considered
observed. Further details of the crystal structure investigations may be obtained from the Fachinformationszentrum Karlsruhe, D-76344 EggensteinLeopoldshafen (Germany), on quoting the depository number CSD-59380.
[6] D. M. Hoffman, R. Hoffmann, C. R. Fisel, J. Am. Chem. Soc. 1982, 104, 3858.
[7] M. J. Calhorda, R. Hoffmann, Organomernllics 1986, 5,2181
[S] M. J. Frisch, G. W Trucks. H B. Schlegel, P. M. W. Gill, B. W. Johnson, M. W.
Wong, J. B. Foresman, M. A. Robb, M. Head-Gordon, E. S. Repiogle, R.
Gomperts, J. L. Andres, K. Raghavachari, J. S. Binkley, C. Gonzalez, R. L.
Martin, D. J. Fox, D. J. DeFrees, J. Baker, J. J P. Stewart, J. A. Pople, Gaussian
92/DFT, Revision G.2, Gaussian, Inc. Pittsburgh. PA, 1993.
[9] J. T. Barry. S. T. Chacon, M. H. Chisholm, J. C . Huffman, W E. Streib, J Am.
Chem. SOC.1995, 117. 1974.
[lo] M. H. Chisholm, J. C. Huffman, J. W. Pasterczyk, Poijhedron 1987, 6, 1551.
OS70-0833/97/3601-0054$15.00+ 2510
A',
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