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AD-A045 626 PRINCETON UNIV N J DEPT OF CHEMISTRY F/6 7/3 DETAILED STRUCTURE OF BIS-MICRON-(TRIMETHYLSILYLMETHYLIDYNE)TET--ETC(U) SEP 77 M H CHISHOLM» F A COTTON» M EXTINE N0001«»-76-C-0826
UNCLASSIFIED TR-77-02 NL
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OFFICE OF NAVAL RESEARCH
Contract N00014-76-C-0826
Task No. NR 056-625
TECHNICAL REPORT NO. 77-02
•• —.1 .•.,,-..,•.,.•„„,„,,. ..,,„ „,,,,, „p^,,
Detailed Structure of Bis-n-(trimethylsilylmethylidyne)
tetrakis-(trimethylsilylmethyl)ditungsten(W-W).
by M.H. Chisholm, a F.A. Cotton, M. Extine,
and CA. Murillo a
Prepared for Publication
in
Journal of Inorganic Chemistry
Departments of Chemistry Princeton University.. Princton, New Jersey 08540 and Texas A&M University College Station, Texas 77843
September 22, 1977
ß D C EQEH Off 14 W77
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Reproduction in whole or in part is permitted for any purpose of the United States government
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Approved for Public Release: Distribution Unlimited
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SECURITY CLASSIFICATION OF THIS PACE (Whan Data Ent.r.d)
REPORT DOCUMENTATION PAG
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c ass ION NO.
Detailed/Structure fid / Bis^p-(trimethylsily$Ldyne)tetrakis-
/ (trlmethylsilylmethyl) ditungsten(W-W)
/-rT^^JH./Chisholm, FJA. ./cotton, M./Extine [V^_ Jk C JA. /Murillo*J______ '
9. PERFORMING ORGANIZATION NAME ANO ADDRESS
Departments of Chemistry Princeton University, Princeton, N.J. Texas MM University, College Station.Tx, 1. CONTROLLING OFFICE NAME AND ADDRESS
Office of Naval Research Department of the Navy
U. MONITORING AGENCY NAME * AOORESSff/ dllttrtnl from Controlling Ollicm)
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IS. SUPPLEMENTARY NOTES
19. KEY WORDS (Contlmio on rmrmram alda II nacaamary and Idantlty by block nimbar)
Tungsten, Ditungsten, Alkyl, Alkylidyne, Metal-to-Metal Bond
j0. ABSTRACT (Contlnua on ravaraa alda II nmcmttary and Identity by block numbat)
'The crystal and molecular structures of a compound of composition W2(CSiMe3)2(CH2SiMe3)4 have been determined. The compound con- sists of dinuclear molecules which contain bridging alkylidyne groups, CSiMe3, which, along with the tungsten atoms form planar, rhombic rings, W-C-W-C. Two alkyl groups, CH2SiMe», are attached to each metal atom to form distorted tetrahedra about the metal atoms. There are two crystallographically Independent molecules,
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"*a each residing on a crystallographic inversion center. The two crystai;ographicalIy independent W-W distances, 2.521(2)"X, and 2.549(2)T, are consistent with the presence of W-W single bonds.j^The basic crystallographic data are as follows. Space group, P2!/a. Unit cell dimensions: a - 11.976(4)1; b » 18.989(5)Ä; c - 18.111(5)1; $ = 101.02(2)-«; V - 4043(2)Ä3; Z * 4.
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Submitted to Inorg. Chem. 9/77
Contribution from the Departments of Chemistry Texes A&M University, College Station, Texas 77843 Princeton University, Princeton, N. J. 08540
Detailed Structure of Bis-u-(trlmethylsilylaethylidyne)tetrakis~
(trimethylsilylmethyl)ditungsten(W-W)..
M. H. Chisholm,la F. A. Cotton,lb* M. Extine,lb and C. A. Murillo
ABSTRACT
The crystal and molecular structures of a compound of composition
W (CSiMe ) (CH-SiMe»), have been determined. The compound consists of dlnuclear
molecules which contain bridging alkylidyne groups, CSlMe., which, along with
the tungsten atoms form planar, rhombic rings, W-C-W-C. Two alkyl groups,
CH2SlMe , are attached to each metal atom to form distorted tetrahedra about
the metal atoms. There are two crystallographically independent molecules,
each residing on a crystallographic inversion center. The two crystallographically e o
Independent W-W distances, 2.521(2)A and 2.549(2)A, are consistent with the
presence of W-W single bonds. The basic crystallographic data are as follows. e o
Space group, P2./a. Unit cell dimensions: a - 11.976(4)A; b » 18.989(5)A;
c - 18.111(5)A; $ - 101.02(2)°; V - 4043(2)A3; Z - 4.
-.Mi. I .„.Jt.,,...,,.,, •,. ~^--. .„.,-...,..., ..„ •- -*•••••"'-* -•••-••• *- .
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-2-
j INTRODUCTION I
2 3 In a previous study we attempted, to prepare W2(CH2SlMe.)6 from the reaction
between WC1, and Me.SiCH.MgCl (1:4 mole ratio) and fortuitously isolated a new
2 compound which we formulated, on the basis of noncrystallographic evidence,
as bis-u-(trimethylsilylmethylldyne)tetrakls(trimethylsilylmethyl)ditungsten,
W (CSlMe ) (CH SiMe ) , I. We proposed this structure by analogy to that
4 found for Nbj(CSlMe3)2(CH2SlMe.), but explicitly noted that the ditungsten
compound should contain a metal-to-metal bond. W.(CSiMe_)2(CH2SiMe,), has also
been prepared Independently, and the same structure proposed.
We report here the results of a single crystal x-ray study on I that con-
firms the structure proposed for it.
EXPERIMENTAL SECTION
2 The method we used for the preparation of I has been described previously.
Crystals of I were grown from pentane at ca. -78°C. Reactions of I with C-H-,
MeCCMe, PhCCH, MeOjCC-COjMe, C-H., CJi,, 1,3-butadiene, and C02 were carried
out in 5 mm NMR tubes in toluene-d«. Gaseous reagents were added to solutions
of I using vacuum line techniques. Other reagents were added to the NMR tubes
by syringe. The progress of the reactions was monitored via H NMR spectroscopy.
No attempt was made to isolate any of the products of these reactions.
X-Ray Crystallography. Crystal Selection and Data Collection.
Considerable difficulty was encountered in (i) mounting crystals of W (CSiMe.).-
(CH.SlMe.), in such a manner that they did not decompose and (ii) once they
were mounted, finding a crystal of suitable quality. Finally, a platelike
crystal measuring ca. 0.17 x 0.34 x 0.56 urn was mounted by wedging it into a
nitrogen-filled capillary in a glove box. The ends of the capillary were
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-3-
sealed with a small hand torch. The crystal was mounted with Its longest
dimension nearly coincident with the + axis. Omega scans of several Intense
low-angle reflections had peak widths at half-height of ca. 0.2°. Lattice
constants and axial photographs Indicated that the crystal belonged to the
monoclinic system. The unit cell constants, determined from the setting angles
of 15 reflections having 21°<26MoKa<27° are: a - 11.976(4)A, b - 18.989(5)A,
c - 18.111(5)A, ß - 101.02(2)°, and V - 4043(2)A3. The observed volume was
consistent with that expected for Z • 4. The systematic absences observed
during data collection, OkO (k - 2n+l) and hO£ (h * 2n+l) uniquely determined
the space group to be P2-/a (equiv. positions + {x,y,z; l/2-x,l/2+y,-z}) a non-
standard setting of P2 /c (No. 14).
The data were collected at 25°C with a Snytex PI autodiffractometer e
equipped with a graphite crystal monochromster and using MoKct (X * 0.710730A)
radiation. Variable scan rates from 4.0 to 24.0°/min were used for symmetric
0/26 scans ranging from 1.0° below to 1.0° above the calculated MoKct -Ka„
doublet. The ratio of scan to background time was 0.5. A total of 5313
unique, non-systematically absent reflections having 0°<29 <45.0° were
recorded. The intensities of three standard reflections were monitored
frequently throughout data collection and showed no decrease In intensity.
The data were reduced to a set of relative IF I values. The intensities were o'
corrected for absorption effects (u * 62.1 cm ); transmission coefficients
ranged from 0.160 to 0.394 with an average of 0.285. The 2396 data having
I>3o(I) were retained as observed and used in subsequent structure solution
and refinement.
6 • Structure Solution and Refinement. The positions of the 32 unique non-
hydrogen stom8 were determined by standard heavy atom methods. The structure
was refined to convergence using anisotropic thermal parameters for the tungsten
and silicon atoms and Isotropie thermal parameters for the carbon atoms. The
«till lllll - • .»l.rii im i • •• in -<•„ •• i .^^l^*m*^^*a****^M^^_ ., .. .. ... .....,., .^„.... ...... „..,., „...^. .^.
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-4-
final discrepancy Indices were
Rl - EllF0l- Fc /Fc
0.070
R2- aw||Fo|-lFc||2/L|Fo|2>1/2- 0.083
The estimated standard deviation of an observation of unit weight was 1.48.
A final difference Fourier map showed no peaks of chemical significance. The
o largest 7 peaks in the map were within ca. 1A of the tungsten atoms and
presumably reflect the inadequacies of the absorption correction.
A table of observed and calculated structure factors (11 pages) is
available as supplementary material. See any current masthead page for
ordering information.
RESULTS AND DISUCSSION
Reactivity. I is a highly reactive, air sensitive compound. It reacts
in solution at room temperature with acetylene, dimethylacetylene, phenyl-
-vj'-tylörte, ccj.fcthylacetylenedicarboxylate, allene, ethylene and 1,3-butadiene.
Nc -,>_.:tJ- va«*. ^v' erved with CO«. The above reactions were carried out in
»**..". <i 'bes and monitored via u NMR spectroscopy.
It 13 interesting to note that the corresponding Nb (CSille ) (CH2SiMe.)4
compound is comparatively inert, although it too is quite sensitive to
moisture and oxygen.
Solid State Structure of W-(CSlMe-);(CH,SiMe,),. The compound is composed
of discrete molecules in the solid state. Each molecule possesses crystal-
lographically imposed C. symmetry and the asymmetric unit consists of halves
of two different molecules. The atomic positional and thermal parameters
are given in Table I. The molecular structure of molecule I is shown in
Figure 1 along with the atomic labelling scheme. A figure for molecule II is
not given since the two molecules are essentially identical. The atoms of
—^npB-mrTnrn— . . n .11 M !Uj.i..•_•«i.u' '.n... ...*»
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-5-
tnolecule II are numbered using sets ofnumbers tbat follow those for
molecule I. For example, the carbon atoms C(13), C(14),...(C24) correspond
to C(l), C(2),...C(12) of molecule I. Bond distances and angles for both
molecules are given In Tables II and III. A comparison of pertinent molecular
dimensions for W2(CH,SlMe )g, I, and Nb2(CSiMe3)2(CH2SiMe3)4 Is given In
Table IV.
The W (CSiMe )2(CH SIMe ), molecule has a structure very similar to that
of the niobium analog, although It may be noted that the two compounds are not
lsomorphous. Each metal atom is coordinated to two terminal alkyl groups and
to two bridging alkylidyne groups. The C(l)-W(l)-C(l) * and C(5)-W(l)-C(9)
planes are nearly perpendicular to each other and the three bonds to the
bridging "carbyne" carbons are essentially coplanar. The only important
differences between the Nb, and W structures are due to the presence of the
metal-metal bond in the tungsten compound.
The effects of the W-W bond on the molecular dimensions are very evident
in three places. First, of course, there are the metal-metal distances them-
selves. The Nb-Nb distance, though it is as short, or shorter than, a number
7 ° of Mo-Mo single bond distances, which range from ca. 2.5 to ca. 3.3A, is
consistent with the absence of direct Nb-Nb bonding and is determined by the
rather strong and short bonds to the bridging carbon atoms. The mean W-W
o distance, 2.535A, is very much shorter and is consistent with the presence of
a single bond between the tungsten atoms. W-W single bonds, like those between
molybdenum atoms, may vary enormously in length but the values observed here
are near the short end of the range and leave no doubt that a W-W bond exists.
Since VP-W bonds have lengths 52.30A and Re—Re bonds (there are no well-
defined W=-W bonds for comparison) are in the range 2.45-2.49A, it is
i- • • .1 -. K„.H,,MM,,11<*-I* ,..,«,... ,., ,^.: „..•,.,iJ,.,.„^.- •„... .,.-_- ,..,.£,.^.. _,.^..^^ „..,., ._^.....^. •_.,.,... ^....„.i. ..„,,,_ . ...^ >--..- —-
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<^IBMfcfc^_^ ____________________________ _^____ . —
not likely that there la significant multiple character to the W-W bond
here.
The other two results of the M-M bond existing in I but not in its Nb
analog are (a) a considerable contraction of the M-C-M angle in the W compound,
and (b) an expansion of the ring angles at the W atoms. In the Nb compound
the Nb-C-Nb angle is >90° (94.4(4)°) while in the W compound the mean tf-C-W
angle is <90° (84.5(10)°). Because the rings are planar the ring angles at the
metal atoms are necessarily the complements of those at the bridging carbon
atoms.
An interesting but somewhat puzzling feature of this structure is the
apparent lack of symmetry in the bridges. This is suggested by the inequality
of W-C bond lengths and also by the inequality in the W-C-Si angles. On the
basis of the discrepancies in distances alone, one would not be justified in
asserting that asymmetry exists, since the two independent discrepancies are 0 o •
only 0.12A and 0.08A while the esd in each individual bond length is ca. 0.03A.
However, the discrepancies in the angles are 16° in each case, while each
individual angle has an esd of 2°, thus making it likely that there is some
real asymmetry, although it may be a lot smaller than the discrepancies just
mentioned would imply. Of course, very small discrepancies might result from
intra- or intermolecular packing forces. This is an attractive idea, since
there is no evident electronic reason to expect, or even rationalize, asymmetric
bridging. In the case of the niobium compound there was similar, borderline
evidence for asymmetry of the bridges.
Acknowledgement. We are grateful to the National Science Foundation for
support at Texas A&M University and the Office of Naval Research at Princeton
University.
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REFERENCES
1. (a) Princton University, (b) Texas A&M University.
2. M. H. Chishoim, F. A. Cotton, M. Extine and B. R. Stults, Inorg. Chen., 15, 2252 (1976).
3. W. Mowat, A. J. Shortland, G. Yagupsky, M. Yagupsky, N. J. Hill, and G. Wilkinson, J. Chem. Soc., Dalton Trans., 533 (1972).
4. F. Huq, W. Mowat, A. C. Skapski and G. Wilkinson, Chem. Comm., 1477 (1971).
5. R. A. Anderson, A. L. Gayler and G. Wilkinson, Angew. Chem. Int. Ed. Engl., 15, 609 (1976).
6. All data reduction, structure-solving and refinement programs were those of the Enraf-Nonius structure-determination package, and were executed on the PDD 11/45 compouter system at the Molecular Structure Corporation, College Station, Texas 77801
7. F. A. Cotton, £. Less-Common Metals, 54, 3 (1977).
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Table II. Bond Distances (A)
-10-
Atoms Distance
2.549(2)
Atoms Distance
W(l)-W(l)' Sl(2)-C(8) 1.82(3)
1.93(3) -C(D 1.85(3) Sl(3)-C(9)
-car 1.97(2) -C(10) 1.85(4)
-C(5) 2.13(3) -C(ll) 1.86(4)
-C(9) 2.05(3) -C(12) 1.75(5)
W(2)-W(2)' 2.521(2) S(4)^C(13) 1.97(3)
-C(13) 1.82(3) -C(14) 1.87(7)
-C(13)' 1.90(3) -C(15) 1.80(7)
-C(17) 2.11(4) -C(16) 1.86(7)
-C(21) 2.13(3) Sl(5)-C(17) 1.84(3)
Si(l)-C(l) 1.91(3) -C(18) 1.89(5)
-C(2) 1.88(3) -C(19) 1.77(9)
• -C(3) 1.93(3) -C(20) 1.99(8)
-C(4) 1.92(3) Si(6)-C(21) 1.83(4)
Sl(2)-C(5) 1.87(3) -C(22) 1.91(6)
-C(6) 1.88(3) -C(23) 1.96(7)
-C(7) 1.90(4) -C(24) 1.93(5)
Numbers in parentheses are estimated standard deviations in the least
significant! digits.
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tH
o o CJ CJ CJ u cj cj u CJ U CJ CJ CJ CJ CJ s CO
f-l tH f-l <-t CM CM CM CM CM CM en CO co co CO co /**. ^N 8 •H CO
•H CO CO
•H CO
•H CO
•H CO
•rl CO
fl CO
«H CO
1-1 CO
«H CO
i-l CO
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•H CO
•H CO CO CJ CJ
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CJ
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m
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CM tH «»
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so «sr CM CM
^-^ f <r sO O tH OS H tH
«sr r» MT tH © tH
CO sO o «sr m CM en 00 -» -» CM CM Os tH <-t o
<»\ s*\ >~\ <—> /^ <~» /«s f«s <"* <•>» en en P» en p* tH r» tH tH CM tH inejsfHinosmosostHtHHcM
CJCJCJCJUCJCJCJCJOCJCJCJCJCJ CJUCJ
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ft CM
ft CM
ft CM
ft CM
ft CM
ft CM
ft CM
ft
ft ft ft ft tH* tHtHtHtHmcMCMCMCM
UCJ CJ CJ CJ CJ ft ft ft ft
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-12-
Q
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S ««-» •"N <-N »>-» § co <n r» -H o r-l i-4 i-4 CM u >—' >•/ >_' s^ < u u
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x"\ *"S /-* ^s H CM <n «» >•»• •w ^-^ iH «H T4 •-» 01 01 Ol CJ
m <-s
§ <-s ^s »-N -a* i-4 m o% >_/
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00 •-4 «n o> O
5 i-4 <H o i-4 H •H 1-4 1-4
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S
U O CJ
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c-> r* /-s *-» H -H iH 1-4 >•• v—- •w >_' U o u U
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e 3 4J « cd
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l»MMil tll«ll-|i IT I • r- ••••"—• — — •-• •.- -•• '•••• - •
•It.. u.* i». ^n'.P*^'»^'.-..^<W..'«*.r'«^-«^ ,.,__ ___ r-.
-13-
Table IV. Average Bond Lengths (A) In W2(CSiMe3)2(CH2SiMe3)4, W2(CH2SiMe3)6>a
and Nb2(CSlMe3)2(CH2SlMe3)4.b
Compound Bonds Average Range
W2VR4
*2R6
ND2R2 R4
W-W
w-ct
Si-C
W-W
w-ct
Si-C
Nb-Nb
Nb-Ct
Nb-Cb
Sl-C
2.535 2.521(2)-2.549(2)
2.11(4) 2.05(3)-2.13(3)
1.89(7) 1.82(3)-1.97(2)
1.88(6) 1.75(5)-1.99(8)
2.255(2) 2.254(2)-2.255(2)
2.14(6) 2.03(4)-2.23(3)
1.89(6) 1.80(5)-2.04(4)
2.897(2)
2.160(9)
1.975 1.954(9)-1.995(9)
1.86(1) —
"Cf. Ref. 2
bCf. Ref. 4.
CR» - CSiMe3, R - CH-SIMe», C - terminal carbon, C. - bridging carbon.
Numbers in parentheses are either the standard deviation from the mean bond
lengths or the estimated standard deviations of the individual bond lengths.
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-14- V
Figure l. A view of Molecule I using 402 probability ellpsoids and showing
the atom labelling scheme. Molecule II is essentially identical.
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