Bis(η^5-pentamethylcyclopentadienyl)-bis[μ-2,3,4,5-tetramethyl-1-methylene-ScC^1:Sc'(η^5)-cyclopentadienyl]-discandium(III), [Sc_2(C_(10)H_(15))_2-(C_(10)H_(14)_2], M_r = 628.90, triclinic, Pl, ɑ = 8.641 (5), b= 9.478 (2), c = 12.338 (5) Å, ɑ = 75.58 (3), β = 80.39 (4), y = 63.75 (3)º, V = 875.8 (7) Å^3, Z = 1, D_x

= 1.19 g cm^(-3), λ(Mo Kɑ}=0.71073 Å, μ = 4.11 cm^(-1), F(000) = 340, room temperature, R (on F) = 0.046 for 2241 reflections with F_o^2 > 3σ(F_o^2). Two bis(pentamethylcyclopentadienyl)scandium molecules are joined across a center of symmetry. One of the Cp^* methyl groups has lost an H atom and that methylene group bonds to the symmetry-related Sc atom: Sc-C6' = 2.282 (5) Å. Other aspects of the bis-Cp^*Sc geometry are normal

Bercaw, John E.

Hajela, Sharad

Schaefer, William P.

Caltech Authors - Main

DAVID J. SZALDA AND ETSUKO FUJITA 1771 
90% d and l isomers it is possible that some of the 
isomers converted to the meso isomer between the 
preparation of the solution and the EXAFS meas-
urement. Since these isomers exist in equilibrium in 
solution and both racemic and meso forms crystallize 
from the same solution, care must be taken in 
analyzing and interpreting results using techniques 
such as EXAFS where bulk samples are used. 
This research was carried out at Brookhaven 
National Laboratory under contract DE-AC02-
76CH00016 with the US Department of Energy and 
supported by its Division of Chemical Sciences, 
Office of Basic Energy Sciences. 
Acta Cryst. (1992). C48, 1771-1773 
References 
BAILEY, M. F. & MAXWELL, I. E. (1966). J. Chem. Soc. Chem. 
Commun. pp. 908-910. 
BAILEY, M. F. & MAXWELL, I. E. (1972). J. Chem. Soc. Dalton 
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BERMAN, H. M., BERNSTEIN, F. C., BERNSTEIN, H. J., KOETZLE, T. 
F. & WILLIAMS, G. J. B. (1976). CRYSNET Manual. Informal 
Report BNL 21714. Brookhaven National Laboratory, New 
York, USA. 
FURENLID, L. R., RENNER, M. w., SZALDA, D. J. & FUJITA, E. 
(1991). J. Am. Chem. Soc. ll3, 883-892. 
JOHNSON, C. K. (1976). ORTEPII. Report ORNL-5138. Oak 
Ridge National Laboratory, Tennessee, USA. 
SHELDRICK, G. M. (1976). SHELX76. Program for crystal struc-
ture determination. Univ. of Cambridge, England. 
TAIT, A. M. & BUSCH, D. H. (1978). Inorganic Syntheses, Vol. 
XVIII, pp. 2-6. New York: John Wiley. 
Structure of a Permethylcyclopentadienyl-µ-tetramethylcyclopentadienylmethylene 
Scandium Dimer 
BY SHARAD lIAJELA, WILLIAM P. SCHAEFER AND JOHN E. BERCAW 
Division of Chemistry and Chemical Engineeringt and The Beckman Institute, Mail Code 139-74, 
California Institute of Technology, Pasadena, California 91125, USA 
(Received 26 December 1991; accepted 11 February 1992) 
Abstract. Bis( TJ 5-pentamethylcyclopentadienyl)-bis[µ-
2,3,4,5-tetramethyl-1-methylene-ScC1:Sc'( 775)-cyclo-
pentadienyl]-discandium(III), [Sei(C10H1 5)i-
(C10H14}i], M, = 628.90, triclinic, PI, a= 8.641 (5), b 
= 9.478 (2), c = 12.338 (5) A, a= 75.58 (3), f3 = 
80.39 (4), y = 63.75 (3)0 , V = 875.8 (7) A3, Z = 1, Dx 
=1.19gcm- 3, .A(MoKa}=0.71073A, µ= 
4.11 cm - 1, F(OOO) = 340, room temperature, R (on 
F) = 0.046 for 2241 reflections with F/ > 3u(F0 2). 
Two bis(pentamethylcyclopentadienyl)scandium mol-
ecules are joined across a center of symmetry. One of 
the Cp* methyl groups has lost an H atom and that 
methylene group bonds to the symmetry-related Sc 
atom: Sc-C6' = 2.282 (5) A. Other aspects of the 
bis-Cp*Sc geometry are normal. 
Introduction. Alkyl and hydride derivatives of perme-
thylscandocene are of interest both for their C-H 
bond-activation chemistry (Thompson, Baxter, Bulls, 
Burger, Nolan, Santarsiero, Schaefer & Bercaw, 
1987) and as model systems for Ziegler-Natta 
catalysis (Burger, Thompson, Cotter & Bercaw, 
1990). A notable feature of these complexes is their 
ability to activate the primary C-H bonds of mol-
t Contribution No. 8551. 
0108-2701192/l 01771-03$06.00 
ecules such as CH4 , CH3CH2CH3, Si(CH3) 4 and 
P(CH3h (Thompson et al., 1987). During the course 
of some recent mechanistic studies, we have observed 
that the cyclopentylmethyl derivative, CpfScCHr 
(cyc/o-C5H8) [Cp* = 775-C5(CH3)5], slowly and 
cleanly decomposes in cyclohexane to give methyl-
cyclopentane and a yellow crystalline precipitate. 
The 1 H NMR spectrum of the yellow product is 
consistent with a compound containing one Cp* and 
one (TJ5,77 1)-C5(CH3) 4CH2, the latter arising via 
metallation of a Cp* ligand (i.e. a 'tuck-in' complex). 
This same tuck-in complex has been previously 
obtained from thermolysis of CpfScCH3 (Thompson 
et al., 1987); however, the solid product obtained 
previously was not crystalline and was postulated to 
be oligomeric based on its solubility properties. We 
report herein the structure of the complex which 
crystallizes as the dimer, [Cp*Sc{µ-(77 5,TJ1)-
C5(CH3)4CH2}h, when allowed to form slowly at 
room temperature. 
Experimental. A parallelepiped, 0.4 x 0.2 x 0.05 mm, 
crystal was used for data collection on a CAD-4 
diffractometer with w scans. 25 reflections with 24 < 
28 < 28° were used for determination of the unit cell. 
No absorption correction was applied to the data 
© 1992 International Union of Crystallography 
1772 
Table 1. Final refined positional ( x 104), equivalent 
isotropic displacement (A2 x 104) and isotropic 
displacement (A 2) parameters 
Ueq = (113).l:;.l:1 U;1a;*a/a;.a1; H atoms refined with isotropic 
displacement parameters, B. 
Sc 
Cl 
C2 
C3 
C4 
C5 
C6 
C7 
C8 
C9 
CIO 
Cll 
Cl2 
Cl3 
Cl4 
Cl5 
Cl6 
Cl7 
Cl8 
Cl9 
C20 
H6A 
H6B 
x 
3717 (.8) 
3923 (4) 
3513 (4) 
1831 (4) 
1223 (4) 
2516 (4) 
5429 (4) 
4619 (5) 
706 (5) 
-558 (4) 
2290 (4) 
3154 (4) 
2251 (4) 
3485 (4) 
5129 (4) 
4929 (4) 
2318 (5) 
332 (5) 
3157 (5) 
6805 (5) 
6366 (5) 
6294 (36) 
5132 (33) 
y 
1165 (.7) 
2104 (3) 
3428 (3) 
3845 (3) 
2744 (4) 
1685 (3) 
1412 (4) 
4333 (4) 
5401 (4) 
2824 (5) 
480 (4) 
217 (4) 
1905 (4) 
2559 (4) 
1276 (4) 
-173 (4) 
-943 (5) 
2804 (4) 
4283 (4) 
1458 (5) 
-1823 (4) 
1604 (32) 
2166 (32) 
z 
3300 (.5) 
4991 (2) 
4061 (2) 
3769 (3) 
4459 (3) 
5216 (2) 
5718 (3) 
3583 (3) 
3035 (3) 
4496 (3) 
6200 (3) 
1759 (2) 
1524 (2) 
1263 (2) 
1334 (2) 
1624 (2) 
2048 (3) 
1391 (3) 
740 (3) 
1009 (3) 
1620 (3) 
5299 (23) 
6200 (22) 
Uoq or B 
300 (l) 
301 (7) 
344 (7) 
377 (8) 
394 (8) 
331 (7) 
340 (7) 
495 (9) 
611 (11) 
611 (11) 
466 (8) 
397 (8) 
410 (8) 
414 (8) 
435 (9) 
408 (9) 
625 (10) 
616 (10) 
647 (11) 
713 (12) 
653 (11) 
2.7 (7) 
2.8 (6) 
Table 2. Selected bond distances (A) and angles (0 ) 
Cp* represents the centroid of the five ring atoms. 
Sc-C6' 2.282 (5) C6'- Sc- Cp•l 107.9 
Sc-Cp•1 2.181 C6'-Sc-Cp•2 108.6 
Sc-Cp•2 2.212 Cp•l-Sc-Cp•2 141.6 
C6--Cl l.507 (4) C6-Cl--CZ 127.9 (3) 
C6-H6..4 0.90 (3) C6-- Cl- CS 124.7 (3) 
C6-H6B 0.96 (3) H6A-C6-Cl 107.3 (19) 
H6B-C6-Cl 104.8 (17) 
H6B-C6--H6..4 98.1 (26) 
collection; (sin8/A)max = 0.59 A- 1; h from -10 to 10, 
k from - 11 to 11, I from - 14 to 14. Three standard 
reflections (300, 023, 030) showed no variations 
greater than expected from counting statistics. 6239 
reflections were measured, of which 3068 were 
independent; goodness of fit for merging was 0.98; 
Rmt for 2682 reflections with exactly two observa-
tions was 0.032. All reflections were used in solution 
and refinement of the structure. The Sc-atom posi-
tion was determined from a Patterson map and the C 
atoms were all found in a subsequent Fourier map. 
H atoms were placed at idealized positions based on 
difference maps calculated in their expected planes 
(C-H = 0.95 A). H atoms on C6 were found in a 
three-dimensional difference map and their positions 
and isotropic displacement parameters were refined, 
but all other H-atom parameters were fixed. Posi-
tional and anisotropic displacement parameters of 
the Sc and C atoms, plus the C6 H-atom parameters 
and a scale factor were refined. For all 2856 reflec-
tions with F/ > 0, R (on F) = 0.062, wR (on F 2) = 
0.010, S = 2.19 for 3068 reflections and 198 param-
eters. Weights were calculated as 1/u2(.f;,2); variances 
[o-2(.F;,2)]-were derived from counting statistics plus an 
additional term, (0.0141)2; variances of the merged 
data by propagation of e.s.d. plus another additional 
term, (0.0141)2• Maximum shift/e.s.d. in the final 
cycle was 0.02. Maximum and minimum heights in 
final difference Fourier map were 0.40 and 
-0.35 e A- 3, respectively. Atomic scattering factors 
were obtained from Cromer & Waber (1974), and the 
dispersion correction for Sc from Cromer (1974). 
Computer programs used were those of the CRYM 
crystallographic computing system (Duchamp, 1964) 
and 0 RTEP (Johnson, 1976). Final refined param-
eters of the atoms are given in Table 1 *with selected 
distances and angles in Table 2. Fig. 1 shows a 
*Lists of assigned H-atom parameters, anisotropic dis-
placement parameters, complete distances and angles, and 
observed and calculated structure factors have been deposited 
with the British Library Document Supply Centre as Supplemen-
tary Publication No. SUP 55184 (19 pp.). Copies may be obtained 
through The Technical Editor, International Union of Crystallog-
raphy, 5 Abbey Square, Chester CHI 2HU, England. [CIF refer-
ence: HH0622] 
Fig. 1. An ORTEPII (Johnson, 1976) drawing of the dimer with 
50% probability ellipsoids showing the numbering system. H 
atoms are not shown. 
Fig. 2. An ORTEPII (Johnson, 1976) packing drawing showing 
the contents of a unit cell, with the unit cell outlined. Atoms are 
shown as 50% probability ellipsoids; H atoms are not shown. 
SHARAD HAJELA, WILLIAM P. SCHAEFER AND JOHN E. BERCAW 1773 
labeled drawing of the dimer; crystal packing is 
shown in Fig. 2. 
Discussion. The dimer is joined across an inversion 
center by an (77 5,77 1)-Cp* group which bridges the 
two symmetry-related Sc atoms. The 77 1-methylene 
(C6) has been formed as the result of C-H acti-
vation of a Cp* methyl group. A somewhat surpris-
ing result is that, in all other regards, the bonding is 
very similar to that determined for Cp!ScCH3 
(Thompson et al., 1987). The (775,77 1)-ring remains 
planar with a maximum deviation of only 0.22 A 
from the least-squares plane calculated for Cl 
through ClO. The geometry about C6 is essentially 
tetrahedral; the angles Cl-C6-Sc', Cl-C6-H6A, 
Cl-C6-H6B and H6A-C6-H6B are 118.9, 
107.3, 104.8 and 98.1°, respectively, giving an aver-
age value of 107.3 (8.6) 0 • The H6A-C6-H6B angle 
is slightly compressed (98.1°) while the Cl-C6-Sc' 
angle is somewhat opened (118.9°). The Sc'···H6A 
and Sc' .. ·H6B distances are 2.76 (3) and 2.79 (3) A 
indicating that there is no agostic interaction for the 
a-H atoms with the Sc center. The Cp*-Sc-Cp* 
angle (141.8°) is approximately the same as for Cp! 
Acta Cryst. (1992). C48, 1773-1776 
ScCH3 (144.7°) suggesting that formal replacement 
of a methyl ligand with a bulkier (77 5,77 1)-Cp* group 
as the alkyl does not significantly perturb the 
Sc-Cp* bonding. 
This work was supported by the USDOE Office of 
Basic Energy Sciences (Grant No. DE-FG03-
85ER113431). 
References 
BURGER, B. J., THOMPSON, M. E., CoTIER, W. D. & BERCAW, J.E. 
(1990). J. Am. Chem. Soc. 112, 1566-1577. 
CROMER, D. T. (1974). International Tables for X-ray Crystallog-
raphy, Vol. IV, pp. 149-151. Birmingham: Kynoch Press. 
(Present distributor Kluwer Academic Publishers, Dordrecht.) 
CROMER, D. T. & WABER, J. T. (1974). International Tables for 
X-ray Crystallography, Vol. IV, pp. 99-101. Birmingham: 
Kynoch Press. (Present distributor Kluwer Academic 
Publishers, Dordrecht.) 
DUCHAMP, D. J. (1964). CRYM crystallographic computing 
system. Am. Crystallogr. Assoc. Meet., Bozeman, Montana. 
Paper Bl4, p. 29. 
JOHNSON, C. K. (1976). ORTEPII. Report ORNL-3794, third 
revision. Oak Ridge National Laboratory, Tennessee, USA. 
THOMPSON, M. E., BAXTER, S. M., BULLS, A. R., BURGER, B. J., 
NOLAN, M. C., SANTARSIERO, B. D., SCHAEFER, W. P. & 
BERCAW, J. E. (1987). J. Am. Chem. Soc. 109, 203-219. 
A Silicon-Bridged Bis(substituted Cp) Yttrium Complex 
BY RICHARD E. MARSH, WILLIAM P. SCHAEFER, E. BRYAN COUGHLIN AND JOHN E. BERCAW 
Division of Chemistry and Chemical Engineering* and The Beckman Institute, Mail Code 139-74, 
California Institute of Technology, Pasadena, California 91125, USA 
(Received 9 December 1991; accepted 11 February 1992) 
Abstract. rac-Bis(tetrahydrofuran)lithium [bis(2-
trimethylsilyl-4-tert-butyl-rJ5-cyclopentadienyl)di-
methylsilane]dichloroyttrate, [Li(C4H80)2][Y(C26H48-
Si3)Cli], Mr= 755.87, triclinic, PI, a= 13.110 (8), b 
= 17.163 (15), c = 20.623 (14) A, a= 104.02 (7), /3 = 
99.38 (5), y = 100.24 (6)0 , v = 4326 (6) A3 , z = 4, 
Dx = 1.16 g cm- 3, A.{Mo Ka)= 0.71073 A, µ = 
15.86 cm - 1, F(OOO) = 1608, room temperature, R = 
0.056 for 6136 reflections with F'a2 > 3u(F0 2). There 
are two virtually identical molecules in the asym-
metric unit. In each, the Y atom is tetrahedrally 
coordinated to a substituted Si-bridged bis(cyclo-
pentadienyl) ligand and to two Cl ions in the cleft. 
The Li atom is 2.35 A from each Cl ion, and two 
molecules of tetrahydrofuran are connected to the 
Li, completing its tetrahedral coordination. 
*Contribution No. 8539. 
0108-2701/92/101773-04$06.00 
Introduction. The Ziegler-Natta polymerization of 
olefins has occupied the attention of chemists for 
nearly four decades. Recently, the development of 
homogeneous transition-metal catalyst systems has 
afforded the possibility of mechanistic investigations 
into various key steps of polymer initiation, pro-
pagation and chain termination. Brintzinger and co-
workers have developed a series of ansa-zirconocene 
catalysts which possess a C2 symmetric ligand 
arrangement about the metal center (Roll, 
Brintzinger, Rieger & Zolk, 1990; Wiesenfeldt, 
Reinmuth, Barsties, Evertz & Brintzinger, 1989). 
Moreover, activation of these ansa-zirconocene cata-
lysts with methylalumoxane results in production of 
highly isospecific polymers. Work in this laboratory 
has centered on the study of well defined single-
component Ziegler-Natta-type catalyst systems 
(Piers, Shapiro, Bunel & Bercaw, 1990). We report 
© 1992 International Union of Crystallography 


Structure of a Permethylcyclopentadienyl-μ-tetramethylcyclopentadienylmethylene Scandium Dimer

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Structure of a Permethylcyclopentadienyl-μ-tetramethylcyclopentadienylmethylene Scandium Dimer

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