Dialkylscandium complexes supported by β-diketiminato ligands: Synthesis, characterization, and thermal stability of a new family of organoscandium complexes

Article abstract of DOI:10.1021/om010131o

Several diorganoscandium complexes stabilized by the β-diketiminato ligands (Ar)NC(R)-CHC(R)N(Ar) (Ar = 2,6-iPr-C₆H₃; R = CH₃ (ligand a), R = tBu (ligand b)) have been synthesized. Reaction of the lithium salts of the ligands with ScCl₃·3THF leads to the complexes LScCl₂(THF)_n, which may be readily alkylated to form the dialkyl derivatives. Most are isolated as base-free, four-coordinate complexes. Several have been characterized via X-ray crystallography, and a detailed discussion of their structures is presented. Steric interactions between Ar and the Sc-alkyl groups force the scandium to adopt an out-of-plane bonding mode. In solution, this is manifested via a fluxional process which equilibrates the two diastereotopic alkyl groups and ligand groups as well. The barriers to this process roughly correlate with the steric bulk of the alkyl substituents. At elevated temperatures, the dialkyl derivatives LScR₂ undergo a metalation process whereby one of the alkyl groups is eliminated as RH, and a ligand iPr group is metalated in the methyl position. These reactions are first order in scandium complex, and activation parameters of ΔH? = 19.7(6) kcal mol^-1 and ΔS? = -17(2) cal mol^-1 K^-1 were measured for the loss of Me₄Si from (Ligb)-Sc(CH₂SiMe₃)₂.

Full text of DOI:10.1021/om010131o

Organometallics 2001, 20, 2533-2544
2533
Dia lk ylsca n d iu m Com p lexes Su p p or ted by
â-Dik etim in a to Liga n d s: Syn th esis, Ch a r a cter iza tion ,
a n d Th er m a l Sta bility of a New F a m ily of
Or ga n osca n d iu m Com p lexes
Paul G. Hayes,† Warren E. Piers,*,†,1 Lawrence W. M. Lee,† Lisa K. Knight,†
Masood Parvez,† Mark R. J . Elsegood,‡,2 and William Clegg‡
Departments of Chemistry, University of Calgary, 2500 University Drive NW, Calgary,
Alberta T2N 1N4, Canada, and University of Newcastle, Newcastle upon Tyne NE1 7RU, U.K.
Received February 9, 2001
Several diorganoscandium complexes stabilized by the â-diketiminato ligands (Ar)NC(R)-
CHC(R)N(Ar) (Ar ) 2,6-iPr-C6H3; R ) CH3 (ligand a ), R ) tBu (ligand b)) have been
synthesized. Reaction of the lithium salts of the ligands with ScCl3‚3THF leads to the
complexes LScCl2(THF)n, which may be readily alkylated to form the dialkyl derivatives.
Most are isolated as base-free, four-coordinate complexes. Several have been characterized
via X-ray crystallography, and a detailed discussion of their structures is presented. Steric
interactions between Ar and the Sc-alkyl groups force the scandium to adopt an out-of-
plane bonding mode. In solution, this is manifested via a fluxional process which equilibrates
the two diastereotopic alkyl groups and ligand groups as well. The barriers to this process
roughly correlate with the steric bulk of the alkyl substituents. At elevated temperatures,
the dialkyl derivatives LScR2 undergo a metalation process whereby one of the alkyl groups
is eliminated as RH, and a ligand iPr group is metalated in the methyl position. These
reactions are first order in scandium complex, and activation parameters of ∆Hq ) 19.7(6)
kcal mol-1 and ∆Sq ) -17(2) cal mol-1 K-1 were measured for the loss of Me4Si from (Ligb)-
Sc(CH2SiMe3)2.
In tr od u ction
dimerize or oligomerize, or to retain molecules of donor
ligand in the metal's coordination sphere. Indeed, this
is also a long standing set of problems for organoyttrium
and organolanthanide chemistry.5 The circumvention of
these problems is mainly a question of ligand choice;
desirable ligands offer enough steric bulk and electron
donation to prevent the aforementioned chemical prob-
lems, but not so much as to shut down organometallic
reactivity. Thus, while some examples of LScR2 com-
plexes exist in the literature,6 the ligand modifications
necessary to achieve these targets have also resulted
in rather uninteresting compounds from an organome-
tallic reactivity point of view.
We recently turned to the â-diketiminato ligand
framework as a promising template for developing the
organometallic chemistry of the ScR2 molecular frag-
ment.7 This family of ligands, imine analogues of the
ubiquitous “acac” grouping of ligands, has been known
for some time,8 but their coordination chemistry has
only recently begun to be developed. When the nitrogen
substituents are sterically bulky, they are particularly
suited to stabilizing organometallic compounds of Lewis
Organoscandium chemistry has to date been domi-
nated by complexes with a dianionic complement of
ancillary ligands and one hydrocarbyl ligand.3,4 While
much elegant chemistry of fundamental importance has
been uncovered, the inherent limitations of only one
reactive organyl group has been a roadblock toward
further development of the organometallic chemistry of
scandium in comparison to the group 4 elements, where
dialkyl derivatives are plentiful.
The difficulty in synthesizing well-defined compounds
of general formula LScR2, where L is a monoanionic
ancillary ligand, stems from the tendency of these types
of compounds to undergo redistribution reactions, to
* To whom correspondence should be addressed. Phone: 403-220-
5746. FAX: 403-289-9488. E-mail: wpiers@ucalgary.ca.
† University of Calgary.
‡ University of Newcastle.
(1) Phone: 403-220-5746.Fax: 403-289-9488.E-mail: wpiers@ucalgary.ca.
S. Robert Blair Professor of Chemistry 2000-2005.
(2) Present address: University of Loughborough, Department of
Chemistry, Loughborough, Leicestershire LE1 3TU, U.K.
(3) Reviews: (a) Piers, W. E.; Shapiro, P. J .; Bunel, E. E.; Bercaw,
J . E. Synlett 1990, 74. (b) Meehan, P. R.; Aris, D. R.; Willey, G. R.
Coord. Chem. Rev. 1999, 181, 121. (c) Edelmann, F. T. In Comprehen-
sive Organometallic Chemistry II; Abel, E. W., Stone, F. G. A.,
Wilkinson, G.;, Lappert, M. F., Eds.; Elsevier Science: New York, 1995;
Vol. 4. (d) Cotton, S. A. Polyhedron 1999, 18, 1691.
(5) Bambirra, S.; Brandsma, M. J . R.; Brussee, E. A. C.; Meetsma,
A.; Hessen, B.; Teuben, J . H. Organometallics 2000, 19, 3197 and
references therein.
(6) (a) Blackwell, J .; Lehr, C.; Sun, Y.; Piers, W. E.; Pearce-
Batchilder, S. D.; Zaworotko, M. J .; Young, V. G., J r. Can. J . Chem.
1997, 75, 702. (b) Fryzuk, M. D.; Giesbrecht, G. R.; Rettig, S. J .
Organometallics 1996, 15, 3329.
(7) Lee, L. W. M.;. Piers, W. E.; Elsegood, M. R. J .; Clegg, W.; Parvez,
M. Organometallics 1999, 18, 2947.
(8) McGeachin, S. G. Can. J . Chem. 1968, 46, 1903.
(4) Recent papers: (a) Herberich, G. E.; Englert, U.; Fischer, A.; Ni,
J .; Schmitz, A. Organometallics 1999, 18, 5496. (b) Abrams, M. B.;
Yoder, J . C.; Loeber, C.; Day, M. E.; Bercaw, J . E. Organometallics
1999, 18, 1389. (c) Yoder, J . C.; Day, M. W.; Bercaw, J . E. Organome-
tallics 1998, 17, 4946. (d) Fryzuk, M. D.; Geisbrecht, G. R.; Rettig, S.
J . Can. J . Chem. 2000, 78, 1003.
10.1021/om010131o CCC: $20.00 © 2001 American Chemical Society
Publication on Web 05/15/2001

2534 Organometallics, Vol. 20, No. 12, 2001
Hayes et al.
acidic metals in group 2,9 group 4,10 and group 13.11
Herein we describe the synthesis of several â-diketimi-
nato-supported bis(hydrocarbyl)scandium derivatives,
where use of 2,6-iPrC6H3 aryl groups on nitrogen offers
adequate steric protection to the metal center. While a
bis-Cp* scandocene derivative containing a â-diketimi-
nato ligand has been reported,12 the compounds re-
ported here are the first of scandium supported by a
â-diketiminato ancillary ligand.
Sch em e 1
Resu lts a n d Discu ssion
Syn th esis a n d Gen er a l P r op er ties. The â-diketim-
inato ligands employed in this study incorporate the
bulky 2,6-diisopropylphenyl group as the substituent on
nitrogen and differ only in the nature of the backbone
substituent R. The “a ” series of compounds utilizes
methyl groups in these positions, while the “b” series
exploits the bulkier tert-butyl group, which renders the
aryl groups more sterically active about the metal center
by pushing them forward and holding them more
upright with respect to the N-C-C-C-N plane of the
ligand.10b,13 The lithium salts of these ligands10b may
be used in conjunction with ScCl3‚3THF to attach the
â-diketiminato framework to the scandium metal
(Scheme 1). For the methyl-substituted ligand, dichlo-
ride 1a retains one THF donor, while the more sterically
demanding tBu-adorned ligand precludes THF ligation
and the “base-free” dichloride complex 1b is obtained.
This is consistent with the greater steric demands of
the b ligand, as are the somewhat more forcing condi-
tions required to institute this donor into the scandium
coordination sphere.
Ta ble 1. UV-Vis Da ta for 1a , 2a , 4a , 5a , a n d 1b-6b
compd
λ
ꢀ
compd
λ
ꢀ
1a
2a
4a
5a
6a
322
318
348
346
344
3800
20 600
4300
28 900
19 400
1b
2b
3b
4b
5b
6b
358
366
366
366
367
370
10 800
11 000
20 800
11 300
22 100
22 200
the a series, that producing the dimethyl derivative 2a ,
is the THF ligand in the starting dichloride retained.
For the dibenzyl, dineopentyl, and bis((trimethylsilyl)-
methyl) examples, the alkyl group is large enough to
preclude THF coordination; compounds 4a -6a are
isolated base-free as formally eight-electron complexes,
assuming the diketiminato ligand donates four electrons
to the scandium center (vide infra). In the tBu-
substituted b series, all of the dialkyl complexes remain
base-free, even when exposed to THF, attesting again
to the greater steric saturation about the metal center
with this ligand. Notably, the diethyl derivative 3b is
also accessible and stable toward decomposition path-
ways involving â-elimination (vide infra).
Dichlorides 1 serve as starting materials for the
preparation of a variety of base-free dialkylscandium
derivatives. Reactions between the dichlorides and 2
equiv of R′Li or PhCH2MgCl occur under mild conditions
(room temperature, 0.5-2 h) to give the products in
moderate to good yields. Only in one reaction involving
(9) (a) Gibson, V. C.; Segal, J . A.; White, A. J . P.; Williams, D. J . J .
Am. Chem. Soc. 2000, 122, 7120. (b) Bailey, P. J .; Dick, C. M. E.; Fabre,
S.; Parsons, S. J . Chem. Soc., Dalton Trans. 2000, 1655. (c) Caro, C.
F.; Hitchcock, P. B.; Lappert, M. F. Chem. Commun. 1999, 1433. (d)
Chisholm, M. H.; Huffman, J . C.; Phomphrai, K. J . Chem. Soc., Dalton
Trans. 2001, 222.
The compounds are all white to pale yellow solids
which exhibit intense LMCT absorptions in the UV-
visible spectra taken in hexane (Table 1). Maximum
absorptions for five-coordinate compounds 1a and 2a
are at shorter wavelength than the four-coordinate
species due to the different geometry and greater
electronic saturation at the metal. λmax for the dialkyl
members of the a series is about 10-15 nm lower
(higher energy) than the values for the b series.
The mixed-alkyl derivative LbSc(CH3)CH2SiMe3 (8b)
was prepared via the pathway shown in Scheme 2. A
solution of 1b and 2b in a 1:1 ratio underwent almost
complete comproportionation to give solutions which
were comprised of about 85% of the mixed methyl-
chloro derivative 7b and residual starting materials.
This appears to be an equilibrium ratio, as the addition
of B(C6F5)3 as a catalyst14 did not drive the reaction
further toward the mixed species. Alkylation of the
(10) (a) Qian, B.; Scanlon, W. J .; Smith, M. R., III. Organometallics
1999, 18, 1693. (b) Budzelaar, P. H. M.; van Oort, A. B.; Orpen, A. G.
Eur. J . Inorg. Chem. 1998, 1485. (c) Kakaliou, L.; Scanlon, W. J .; Qian,
B.; Back, S. W.; Smith, M. R., III; Motry, D. H. Inorg. Chem. 1999, 38,
5964. (d) Rahim, M.; Taylor, N. J .; Xin, S.; Collins, S. Organometallics
1998, 17, 1315. (e) Lappert, M. F.; Liu, D. S. J . Organomet. Chem.
1995, 500, 203. (f) Hitchcock, P. B.; Lappert, M. F.; Liu, D.-S. J . Chem.
Soc., Chem. Commun. 1994, 2637. (g) Kim, W.-K.; Fevola, M. J .; Liable-
Sands, L. M.; Rheingold, A. L.; Theopold, K. H. Organometallics 1998,
17, 4541. (h) Vollmerhaus, R.; Rahim, M.; Tomaszewski, R.; Xin, S.;
Taylor, N. J .; Collins, S. Organometallics 2000, 19, 2161.
(11) (a) Hardman, N. J .; Eichler, B. E.; Power, P. P. Chem. Commun.
2000, 1991. (b) Cui, C.; Roesky, H. W.; Schmidt, H.-G.; Noltemeyer,
M.; Hao, H.; Cimposesu, F. Angew. Chem., Int. Ed. 2000, 39, 4274. (c)
Yalpani, M.; Ko¨ster, R.; Boese, R. Chem. Ber. 1992, 125, 15. (d)
Radzewich, C. E.; Coles, M. P.; J ordan, R. F. J . Am. Chem. Soc. 1998,
120, 9384. (e) Cosledan, F.; Hitchcock, P. B.; Lappert, M. F. Chem.
Commun. 1999, 705. (f) Radzewich, C. E.; Guzei, I. A.; J ordan, R. F.
J . Am. Chem. Soc. 2000, 122, 8673. (g) Qian, B.; Ward, D. L.; Smith,
M. R., III. Organometallics 1998, 17, 3070. (h) Cui, C.; Roesky, H. W.;
Hao, H.; Schmidt, H. G.; Noltemeyer, M. Angew. Chem., Int. Ed. 2000,
39, 1815. (i) Qian, B.; Baek, S. W.; Smith, M. R., III. Polyhedron 1999,
18, 2405.
(12) Bercaw, J . E.; Davies, D. L.; Wolczanski, P. T. Organometallics
1986, 5, 443.
(13) A similar phenomenon is observed and used in related amidi-
nate ligands: Dagorne, S.; Guzei, I. A.; Coles, M. P.; J ordan, R. F. J .
Am. Chem. Soc. 2000, 122, 274.
(14) Zhang, S.; Piers, W. E.; Gao, X.; Parvez, M. J . Am. Chem. Soc.
2000, 122, 5499.

A New Family of Organoscandium Complexes
Organometallics, Vol. 20, No. 12, 2001 2535
Ta ble 2. Selected Metr ica l P a r a m eter s for
F ive-Coor d in a te Str u ctu r es 1a a n d 2a
Sch em e 2
parama
1a
2a
Bond Distances (Å)
2.175(4)
Sc-N(1)
Sc-N(2)
Sc-O(1)
Sc-E(1)
Sc-E(2)
Sc-C(4)
Sc-C(5)
Sc-C(6)
N(1)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-N(2)
2.201(6)
2.190(7)
2.228(5)
2.210(9)
2.245(9)
3.116(9)
3.383(9)
3.098(9)
1.337(9)
1.385(10)
1.414(10)
1.311(9)
2.107(4)
2.203(4)
2.3556(17)
2.3795(18)
3.066(5)
3.327(6)
3.062(6)
1.312(7)
1.399(8)
1.387(7)
1.363(6)
Bond Angles (deg)
131.47(8)
94.85(13)
92.33(12)
104.53(13)
123.79(13)
86.77(17)
175.31(16)
95.82(16)
121.1(4)
E(1)-Sc-E(2)
N(1)-Sc-E(1)
N(1)-Sc-E(2)
N(2)-Sc-E(1)
N(2)-Sc-E(2)
N(1)-Sc-N(2)
N(1)-Sc-O(1)
N(2)-Sc-O(1)
Sc-N(1)-C(4)
N(1)-C(4)-C(3)
N(1)-C(4)-C(5)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
C(5)-C(6)-C(7)
C(5)-C(6)-N(2)
C(7)-C(6)-N(2)
C(6)-N(2)-Sc
123.8(4)
96.4(3)
93.1(3)
105.9(3)
130.1(3)
85.2(3)
175.5(3)
93.7(2)
121.5(6)
119.6(8)
124.0(8)
116.4(8)
129.3(8)
113.3(8)
124.7(8)
122.0(8)
122.6(6)
120.2(5)
123.5(5)
116.3(5)
130.4(5)
116.3(5)
122.9(5)
120.7(5)
122.4(3)
F igu r e 1. ORTEP diagram of the five-coordinate complex
2a (30% ellipsoids).
Torsion Angles (deg)
C(6)-N(2)-C(20)-C(25)
C(6)-N(2)-C(20)-C(21)
C(4)-N(1)-C(8)-C(9)
C(4)-N(1)-C(8)-C(13)
82.2(6)
-100.9(6)
90.0(6)
99.0(9)
mixture with LiCH2SiMe3 gave samples of 8b contami-
nated with 2b and 6b. The mixed-alkyl species 8b could
be obtained about 95% pure via successive recrystalli-
zations; discussion of the solution structure of this
compound is presented below. Interestingly, 8b cannot
be prepared via redistribution between the two dialkyls
2b and 6b, even in the presence of catalytic B(C6F5)3;
evidently, a ligand capable of bridging the scandium
centers is required for this process.
-81.0(11)
94.1(11)
-89.1(10)
-92.6(7)
a
E ) Cl for 1a and C for 2a .
X-r a y Cr ysta l Str u ctu r es. Several of the derivatives
prepared as shown in Scheme 1 have been structurally
characterized.
The structure of the five-coordinate dichloride 1a was
reported in a preliminary account;7 the structural
features of the dimethyl congener are comparable, and
an ORTEP diagram of 2a is shown in Figure 1. Table 2
gives selected metrical data for both of these compounds
for comparison; full details for 2a and all of the other
compounds reported herein can be found in the Sup-
porting Information. The scandium center in 2a has a
distorted-trigonal-bipyramidal geometry, with N(1) and
O(1) occupying the apical sites (N(1)-Sc(1)-O(1) )
175.5(3)°). Perusal of the Sc(1) to ligand atom distances
(bonding distances to N(1) and N(2) and nonbonding
distances to the three carbon atoms) suggests that the
ligand is essentially symmetrically bound to the scan-
dium center; additionally, the five ligand atoms are
virtually coplanar, with the highest deviation from the
plane defined by these atoms being 0.064(8) Å for C(6).
The scandium atom sits 0.815 Å out of this plane (cf.
0.694 Å for 1a ), somewhat less than the values for this
parameter observed for the four-coordinate complexes
discussed below. The torsion angles included in Table
2 are an indication as to how “upright” the aryl moieties
F igu r e 2. ORTEP diagram of the four-coordinate complex
1b (30% ellipsoids).
are with respect to the NCCCN ligand plane. The values
are close to 90((10)°, indicating that the rings are
essentially perpendicular to the ligand plane.
The molecular structures of the THF-free, four-
coordinate derivatives 1b-4b and 6a ,b have also been
determined; ORTEP diagrams of these compounds
showing the structures from various perspectives are
given in Figures 2-7, and Table 3 lists selected metrical
parameters for these complexes. The scandium centers
adopt distorted-tetrahedralgeometries wheretheN-Sc-N

2536 Organometallics, Vol. 20, No. 12, 2001
Hayes et al.
F igu r e 3. ORTEP diagram of the four-coordinate complex
2b (30% ellipsoids). Only the ipso carbons of the N aryl
groups are shown for clarity.
F igu r e 5. ORTEP diagram of the four-coordinate complex
4b (30% ellipsoids). Only the ipso carbons of the N aryl
groups are shown for clarity.
F igu r e 4. ORTEP diagram of the four-coordinate complex
3b (30% ellipsoids). Only the ipso carbon of the forward N
aryl group is shown for clarity.
F igu r e 6. ORTEP diagram of the four-coordinate complex
6a (30% ellipsoids).
angles are ∼92-96° for the b series complexes and are
about 4-5° less at 90.71(4)° for 6a . The widening of the
N-Sc-N angle in the tBu-substituted compounds is a
compensation for the increased steric interaction be-
tween the bulky aryl groups and the scandium alkyl
ligands in the b series caused by the larger C(4)-N(1)-
C(8) and C(6)-N(2)-C(20) angles (by ∼4-7°) compared
to those in 6a . C(1)-Sc-C(2) angles hover around the
ideal tetrahedral angle of 109°, and the bond distances
to scandium are typical of Sc-N, Sc-C, or Sc-Cl single
bonds.3b For the diethyl derivative 3b (Figure 4) large
Sc-C(1)-C(38) and Sc-C(2)-C(39) angles of 119.4(5)
and 129.0(5)°, respectively, suggest that â-agostic in-
teractions are absent. Similarly, normal Sc-C(1)-C(38)
and Sc-C(2)-C(44) angles of 127.0(4) and 115.3(5)° in
the dibenzyl compound 4b (Figure 5) argue against any
η2 bonding of these ligands to scandium.
In all of these compounds, the scandium atom is
situated out of the ligand plane significantly (by ∼1.1-
1.25 Å; see Table 3), rendering the alkyl or chloride
substituents inequivalent. In this paper and others,15
F igu r e 7. ORTEP diagram of the four-coordinate complex
6b (30% ellipsoids).
we refer to the substituent which occupies the site
“underneath” the â-diketiminato ligand as the endo
group, while the other is defined as the exo site; the
(15) Knight, L. K.; Piers, W. E.; McDonald, R. Chem. Eur. J . 2000,
6, 4322.

A New Family of Organoscandium Complexes
Organometallics, Vol. 20, No. 12, 2001 2537
Ta ble 3. Selected Metr ica l P a r a m eter s for F ou r -Coor d in a te Str u ctu r es 1b-4b a n d 6a ,b
parama
1b
2b
3b
4b
6a
6b
Bond Distances (Å)
Sc-N(1)
Sc-N(2)
Sc-E(1)
Sc-E(2)
Sc-C(4)
Sc-C(5)
Sc-C(6)
2.046(6)
2.099(6)
2.352(3)
2.326(3)
2.628(7)
2.700(7)
2.738(7)
1.333(9)
1.433(10)
1.422(10)
1.319(9)
1.295(6)
2.1029(10)
2.125(5)
2.118(5)
2.244(6)
2.204(6)
2.777(7)
2.832(6)
2.767(7)
1.318(6)
1.418(7)
1.423(7)
1.338(7)
1.240(5)
2.091(5)
2.118(5)
2.265(6)
2.203(7)
2.722(7)
2.796(7)
2.796(7)
1.361(8)
1.399(8)
1.431(9)
1.325(8)
1.244(4)
2.1130(10)
2.1320(10)
2.2446(13)
2.1954(14)
2.8732(12)
3.0793(13)
2.9176(12)
1.3417(16)
1.4049(17)
1.4188(17)
1.3288(16)
1.1152(14)
2.091(5)
2.144(5)
2.229(7)
2.202(7)
2.808(7)
2.934(7)
2.890(7)
1.349(8)
1.400(9)
1.447(8)
1.325(7)
1.146(6)
2.1451(10)
2.2197(15)
2.2219(16)
2.7289(12)
2.8775(12)
2.8770(12)
1.3622(15)
1.3962(16)
1.4475(16)
1.3127(15)
1.2621(12)
N(1)-C(4)
C(4)-C(5)
C(5)-C(6)
C(6)-N(2)
N2C3 plane-Sc
Bond Angles (deg)
E(1)-Sc-E(2)
N(1)-Sc-E(1)
N(1)-Sc-E(2)
N(2)-Sc-E(1)
N(2)-Sc-E(2)
N(1)-Sc-N(2)
Sc-N(1)-C(4)
C(6)-N(2)-Sc
N(1)-C(4)-C(3)
N(1)-C(4)-C(5)
C(3)-C(4)-C(5)
C(4)-C(5)-C(6)
C(5)-C(6)-C(7)
C(5)-C(6)-N(2)
C(7)-C(6)-N(2)
C(4)-N(1)-C(8)
C(6)-N(2)-C(20)
115.00(12)
113.5(2)
112.2(2)
116.0(2)
102.2(2)
95.9(2)
100.0(5)
104.2(5)
126.4(8)
120.0(8)
113.0(8)
134.8(8)
112.6(7)
119.7(8)
127.7(8)
125.3(7)
126.9(7)
109.46(6)
110.80(5)
123.27(6)
112.64(5)
107.17(5)
92.20(4)
101.77(7)
110.28(8)
124.60(10)
121.33(11)
113.71(10)
133.43(11)
113.28(10)
119.23(10)
127.50(10)
124.47(10)
127.52(10)
117.6(3)
111.4(2)
109.2(2)
113.2(2)
108.9(2)
94.00(16)
105.1(3)
104.1(3)
126.8(5)
121.2(5)
111.9(5)
136.4(5)
113.4(5)
120.5(5)
125.9(5)
125.6(5)
127.4(5)
114.4(3)
109.7(2)
105.7(3)
123.9(2)
105.6(3)
94.7(2)
102.0(4)
106.3(4)
125.2(6)
120.3(6)
114.2(6)
136.1(7)
112.6(6)
120.0(6)
127.4(6)
124.4(6)
127.5(5)
114.84(5)
117.18(5)
107.58(5)
113.12(5)
110.91(5)
90.71(4)
110.55(8)
112.86(8)
119.86(11)
123.53(11)
116.61(11)
130.74(12)
115.39(11)
123.28(11)
121.33(11)
120.06(10)
120.73(10)
109.4(3)
119.3(2)
105.3(3)
120.2(2)
107.3(2)
93.5(2)
107.4(4)
110.6(4)
124.6(6)
120.9(6)
114.2(6)
134.7(6)
112.0(6)
120.2(6)
127.8(6)
125.5(5)
126.3(6)
Torsion Angles (deg)
C(6)-N(2)-C(20)-C(25)
C(6)-N(2)-C(20)-C(21)
C(4)-N(1)-C(8)-C(9)
C(4)-N(1)-C(8)-C(13)
95(1)
98.31(15)
89.3(7)
98.2(8)
99.9(1)
94.2(8)
-92.0(10)
115.1(9)
-69.6(11)
-87.90(15)
124.69(13)
-59.56(16)
-95.4(7)
104.1(7)
-80.8(7)
-88.8(9)
110.7(8)
-74.3(9)
-83.5(1)
109.5(2)
-74(2)
-91.5(9)
105.7(7)
-82.0(8)
a
E ) Cl for 1b and C for 2b-4b and 6a ,b.
Ch a r t 1
differences are best illustrated by the view of 3b shown
in Figure 4 and that of 4b in Figure 5.
Several factors can potentially contribute to the extent
to which out-of-plane bonding is present in these
â-diketiminato complexes. For example, some authors
have invoked a six-electron η5-bonding mode to account
for out-of-plane bonding modes in the group 4 metal
coordination chemistry of these ligands, in analogy with
η5-pentadienyl complexes.10 However, a DFT treatment
of the bonding of these ligands to Cu(I) centers recently
presented by Tolman and Solomon et al.16 suggest that
a description akin to that found in η5-pentadienyl
bonding is not applicable. Tolman and Solomon show
that five occupied orbitals are associated with the
â-diketimide ligand (Chart 1). In this orbital set, the
2b1, 1a2, and 1b1 orbitals are out-of-plane π orbitals
which could function as donors in “pentadienyl-like”
bonding to a metal, while the two in-plane orbitals (5b2
and 6a1) are associated with the nitrogen lone pairs.
In principle, then, the â-diketimide ligand can function
as a 10-electron donor; in practice, the out-of-plane 1a2
and 1b1 orbitals are low in energy and do not figure
into the ligand-metal bonding picture significantly. The
majority of the bonding occurs through the in-plane
orbitals 5b2 and 6a1, which form σ-bonds to the metal
center; such in-plane bonding means that the ligand
functions as a 4-electron donor.17 The flexibility of the
ligand backbone and the σ-symmetry of these orbitals
allow metals to move out of the ligand plane without
(16) Randall, D. W.; DeBeer George, S.; Holland, P. L.; Hedman,
B.; Hodgson, K. O.; Tolman, W. B.; Solomon, E. L. J . Am. Chem. Soc.
2000, 122, 11632.
(17) In another DFT treatment of LM-R cations (M ) Ti, V, Cr),
in-plane bonding was determined to be the ground-state bonding
mode: Deng, L.; Schmid, R.; Ziegler, T. Organometallics 2000, 19, 3069.

2538 Organometallics, Vol. 20, No. 12, 2001
Hayes et al.
Sch em e 3
significant disruption of these bonding interactions, but
potentially turning on π-bonding interactions between
the 2b1 ligand orbital and an orbital of appropriate
symmetry on the metal. This out-of-plane 2b1 orbital
is associated with the two ligand nitrogens and the
central ligand backbone carbon. Indeed, those structures
which have been described as η5 structures for Ti and
Zr complexes are characterized by a significant pucker-
ing of this central backbone carbon toward the metal,
suggesting a 6-electron, 2σ-π bonding description is
most appropriate. For the present scandium complexes,
although they are electron-deficient, the rather long
distances from the scandium center to the ligand
backbone carbons C(4), C(5), and C(6) and the lack of
distinct puckering of C(5) toward the Sc center (Table
3) suggest that a tendency toward a 2σ-π bonding mode
is not the overriding cause of scandium’s deviation from
the ligand plane in these complexes.
Another potential contributing factor to out-of-plane
bonding could be the size of the metal ion the â-diketim-
inato ligand is chelating. If the metal ion is too large
for the ligand’s maximum bite angle, it could alleviate
the situation by popping up out of the ligand plane. This
phenomenon accounts for out-of-plane binding of metals
with an ionic radius >1.0 Å in porphyrin compounds18
or the extent to which metals deviate from the N4 plane
in related tmtaa complexes.19 While we do not observe
any in-plane bonding to scandium in this series of
compounds, the ionic radius of Sc3+ is similar to that of
Zr4+, for which several η2 σ-bound â-diketiminato ligand
complexes have been characterized,10c,d,h suggesting
that, in principle, â-diketiminato ligands can accom-
modate relatively large metal ions.
In light of the above discussion, it appears the most
important factor dictating the adoption of an out-of-
plane bonding mode is the steric interaction between
the N-aryl groups and the other substituents on the
metal. Several four-coordinate complexes of ligand a
with metal ions ranging from Ti and V(III)10b to Cu-
(II)16,20 and Zn(II)21 and into the p block with Al(III)11
have been structurally characterized, and all assume
the out-of-plane bonding mode to varying degrees.
Interestingly, in lower coordinate complexes of this
ligand, in-plane postures are assumed.9,10b,22
To our knowledge, the complexes reported herein are
the first four-coordinate compounds of the more steri-
cally demanding ligand b which have been prepared and
structurally characterized.23 The successful preparation
of 1b stands in contrast to the failed attempts to attach
this ligand to Ti(III) or V(III);10b evidently the slightly
larger effective ionic radius of Sc(III) compared to the
Ti(III) and V(III) ions24 is enough to allow for complex-
ation. While the Sc(III) ion can be accommodated by this
ligand, the unfavorable interactions between the aryl
Ta ble 4. In ter n a l Com p a r ison of Liga n d Bon d
Dista n ces (Å) for F ou r -Coor d in a te Dia lk yl
Com p lexes LScR2
2b
6b
4b
6a
3b
Sc-N(2)
Sc-N(1)
∆
2.1451(10) 2.144(5) 2.118(5) 2.1320(10)
2.1029(10) 2.091(5) 2.091(5) 2.1130(10)
2.118(5)
2.125(5)
-0.007
0.0422
0.053
0.027
0.019
N(1)-C(4) 1.3622(15) 1.349(8) 1.361(8) 1.3417(16)
N(2)-C(6) 1.3127(15) 1.325(7) 1.325(8) 1.3288(16)
1.318(6)
1.338(7)
-0.02
∆
0.0495
0.024
0.036
0.0129
C(5)-C(6) 1.4475(16) 1.447(8) 1.431(9) 1.4188(17)
C(4)-C(5) 1.3962(16) 1.400(9) 1.399(8) 1.4049(17)
1.423(7)
1.418(7)
0.005
∆
0.0513
0.047
0.032
0.0139
Sc-C(6)
Sc-C(4)
∆
2.8770(12) 2.890(7) 2.796(7) 2.9176(12)
2.7289(12) 2.808(7) 2.722(7) 2.8732(12)
2.767(7)
2.777(7)
-0.01
0.1481
0.082
0.074
0.0444
isopropyl groups and the metal substituents cause the
metal to assume its position out of plane. As the metal
dips below the ligand plane, the N-aryl groups tilt
upward, allowing the N-Sc σ bonding interactions to
be maintained. This structural perturbation alleviates
steric interactions by permitting the isopropyl groups
on the side of the ligand plane opposite the metal to
rotate inward toward the metal, above the exo R group.
The isopropyl groups on the same side of the metal
center rotate away from the endo substituent. This
phenomenon is best illustrated by the view of 6b in
Figure 7. When another ligand is present on scandium,
as in the five-coordinate compounds 1a and 2a , the aryl
groups cannot rotate in this fashion without encounter-
ing the fifth ligand and the deviation of scandium from
the ligand plane is less (∼0.69 Å) in these complexes.
Close inspection of the metrical parameters associated
with the ligand backbone reveals that contributions to
the ground-state structure from an amido-imide reso-
nance structure (II; Scheme 3) in addition to the
symmetric, delocalized resonance contributor I may be
significant. Bond distances within the ligands for the
dialkyl complexes suggest that bonding of the ligand to
the metal is not entirely symmetrical for some of the
compounds. As Table 4 shows, the phenomenon is most
extreme for the dimethyl derivative 2b and least
pronounced for diethyl complex 3b. For 2b, the Sc-N(1)
distance is slightly shorter than the Sc-N(2) distance
and N(2)-C(6) and C(4)-C(5) are shorter than N(1)-
C(4) and C(5)-C(6), respectively, indicating an alternat-
ing, more localized distribution of electrons in the
ligand. The ligand “plane” is also somewhat disrupted;
C(6) deviates significantly by 0.321 Å from the plane
defined by the other four ligand atoms, which are
essentially coplanar. This is seen most clearly in the
view of 2b given in Figure 3. The distortions within the
ligands diminish as one progresses across Table 4; for
the last entry, 3b, the ligand is more symmetrically
bound to the metal center, indicative of a delocalized
electron distribution. The extent to which II contributes
(18) Brothers, P. J . Adv. Organomet. Chem. 2000, 46, 223.
(19) Cotton, F. A.; Czuchajowska, J . Polyhedron 1990, 21, 2553.
(20) Holland, P. L.; Tolman, W. B. J . Am. Chem. Soc. 2000, 120,
6331.
(21) (a) Cheng, M.; Lobkovsky, E. B.; Coates, G. W. J . Am. Chem.
Soc. 1998, 120, 11018. (b) Cheng, M.; Attygalle, A. B.; Lobkovsky, E.
B.; Coates, G. W. J . Am. Chem. Soc. 1999, 121, 11583.
(22) Holland, P. L.; Tolman, W. B. J . Am. Chem. Soc. 1999, 121,
7270.
(23) Budzelaar, who introduced ligand b, has reported its three-
coordinate lithium salt (THF adduct), which assumes an in-plane
bonding mode.
(24) Shannon, R. D. Acta Crystallogr. 1976, A32, 751.

A New Family of Organoscandium Complexes
Organometallics, Vol. 20, No. 12, 2001 2539
Ta ble 5. 1H NMR Da ta for LSc(CH2R)2 Com p lexesa
b
c
compd
1a e
HL
RL
Ar H
7.21
7.05
7.16
7.25
7.26
7.15
7.12
CH iPrd
CH3 iPr
1.17, 1.39
1.26, 1.43
1.20, 1.40
1.41, 1.47
1.43, 1.50
1.06, 1.22
1.18, 1.23
Sc-CH2
R
5.32
6.01
5.06
5.85
5.70
5.01
5.62
5.00
5.58
5.00
5.68
5.87
5.73
5.69
5.74
1.65
1.17
1.67
1.21
1.13
1.58
1.04
1.63
1.11
1.59
1.10
1.10
1.09
1.05
1.03
3.56
3.10
3.45
3.52
3.38
3.08
2.50, 3.65
3.47
2.86, 4.12
3.31
2.70, 3.95
3.15, 3.43
3.12, 3.55
2.87, 3.91
2.73, 3.79
1b
2a f
-0.15
2b
3b
4a
4b
0.11
0.32g
1.25
2.10
2.12
0.87
0.75, 0.78
0.18
6.70-7.16
6.70-7.20
1.03
5a
7.16
7.00-7.20
7.16
1.17, 1.47
1.23, 1.23, 1.46, 1.74
1.16, 1.44
5bh
1.35
0.08
0.13
6a
6b
7b
8b
7.07
1.20, 1.75
0.00
0.16
6.99-7.07
6.97-7.10
6.85-7.09
6.85-7.09
1.27, 1.37, 1.37, 1.46
1.27, 1.30, 1.32, 1.48
1.18, 1.38, 1.73, 1.74
1.18, 1.34, 1.46, 1.69
-0.08, -0.09i
0.12, 0.03
0.12, 0.01
0.00
0.09
0.50
exoMe-8bj
endoMe-8bj
a
b
Spectra accumulated in C6D6 and at room temperature unless otherwise noted. Ligand backbone proton. c Ligand backbone
substituent:, a , R1 ) CH3; b, R1 ) Bu. J H-H ) 6.8(1) Hz. e Coordinated THF resonances at 1.49 and 3.48 ppm. f Coordinated THF
resonances at 1.23 and 3.40 ppm. J H-H ) 8.20 Hz. Solvent C7D8, T ) 242 K. CH3. Solvent C7D8, T ) 200 K.
Ta ble 6. 13C{1H} NMR Da ta for LSc(CH2R)2 Com p lexesa
t
d
g
h
i
j
b
i
compd
C4/6
C5
Cipso
CAr
CPr
RL
Sc-C
R
1a c
1b
162.3
174.3
167.8
174.1
174.2
167.9
174.8
99.8
90.8
96.1
92.7
92.5
95.7
91.3
143.3
142.8
143.0
143.4
143.8
143.2
143.2
124.2, 126.6, 143.3
124.3, 127.0, 141.1
124.4, 126.9, 142.7
124.2, 126.1, 141.1
124.2, 126.0, 141.5
124.7, 126.9, 142.2
124.7, 125.1, 126.9, 141.2,
141.9
24.7, 25.0, 28.6
24.4, 26.9, 29.9
25.2, 25.4, 28.6
24.5, 26.9, 29.7
26.6, 26.7, 29.2
24.8, 24.9, 28.8
24.6, 25.3, 26.2, 27.0,
28.9, 29.8
24.4
44.7, 32.3
24.1
44.6, 32.6
44.7, 32.4
24.2
2a d
2b
24.8
27.6
3b
40.8
13.2
4a
61.6
57.5, 64.3
149.3, 120.3, 124.9, 129.6
151.6, 149.0, 128.5, 128.7,
126.0, 125.2, 119.8, 119.7
35.4, 34.9
4be
45.0, 32.3
5a
167.1
174.9
94.3
93.0
143.0
144.2
124.6, 126.8, 142.3
124.7, 125.1, 126.7, 141.9,
142.3
25.0, 25.3, 28.8
25.1, 25.6, 26.7, 27.5,
28.8, 29.9
24.6
45.3, 33.0
72.3
5bf
69.9, 75.5
35.6, 35.3, 36.6, 35.4
6a
167.9
175.6
95.7
93.6
141.8
143.2
124.7, 127.1, 142.6
124.7, 125.1, 127.0, 142.0,
142.4
24.9, 25.7, 28.6
24.7, 25.4, 26.5, 28.4,
28.8, 29.4
24.4
44.8, 32.7
44.9
41.8, 48.7
3.4
3.4, 4.7
6bg
7b
8b
174.2
174.5
92.1
93.3
143.0
143.2
124.1, 124.3, 126.6, 141.1,
24.0, 24.1, 26.3, 26.6,
44.6, 32.2
44.7, 32.3
25.8
141.4
29.1, 29.7
124.5, 124.6, 127.0, 141.2,
141.8
24.4, 24.6, 25.1, 26.6,
27.0, 29.6
27.3, 45.5
3.9
a
b
Spectra accumulated in C6D6 or C7D8 and at room temperature, unless otherwise noted. For the b series, the values are for the
quaternary and primary Bu carbons, respectively. c Coordinated THF resonances at 67.0 and 24.8 ppm. Coordinated THF resonances
t
d
at 67.0 and 24.8 ppm. e T ) 265 K. f T ) 242 K. T ) 233 K.
g
to the structure thus does not appear to correlate well
with the steric properties of the alkyl group and the
energetic difference between I and II is likely small.
Solu tion Str u ctu r es a n d Dyn a m ic Beh a vior .
Solution NMR spectra for the dialkyl structures dis-
cussed above should be reflective of the low symmetry
inherent to the out-of-plane bonding mode observed.
Because rotation of the N-aryl groups is precluded due
to the steric properties of these ligands, the isopropyl
methyl groups pointing inward at the metal are in
different chemical environments than those directed
away from the molecular core, and two signals would
be expected for an in-plane solution structure. As the
metal deviates from the ligand plane, “top-bottom”
asymmetry is introduced and four separate doublets for
the isopropyl methyl groups would be predicted. Also,
distinct resonances for the two different (endo and exo)
alkyl substituents would be expected for this structure.
copy on these complexes reveals coalescence behavior
consistent with equilibration of two equivalent out-of-
plane structures via a C2v symmetric, in-plane transition
state. Figure 8 shows an illustrative series of spectra
using 3b as an example; the proposed fluxional process
is also depicted. In the fast-exchange regime, the ethyl
groups are equivalent, and only one and two resonances
are observed for the isopropyl methine and methyl
groups, respectively. As the sample is cooled, signals for
the now inequivalent ethyl groups emerge and the
pattern for the ligand isopropyl moieties morphs into
what would be expected for a structure akin to that
found in the solid state as discussed above. The barrier
for this process can be extracted from the NMR data;25
a ∆Gq value of 10.6(5) kcal mol-1 at the coalescence
temperature of 240 K was measured for the diethyl
compound 3b.
The barriers for this process in each of the four-
coordinate compounds was measured using variable-
1
Tables 5 and 6 give the H and 13C{1H} NMR data
1
for all of the dialkyl derivatives reported herein, as well
as the two dichloride precursors. As can be seen, for
most of these compounds, spectra consistent with a
symmetrical, in-plane structure are observed at room
temperature. For bis((trimethylsilyl)methyl) complex
temperature H NMR spectroscopy, and the results are
shown in Table 7. In addition, barriers normalized to
298 K are given. Although there are some anomalies,
generally the barriers track the steric bulk of R, with
higher barriers observed as R gets larger. This is
1
6b, however, the H NMR spectrum at room tempera-
ture is broad and featureless, a manifestation of dy-
namic behavior. Indeed, variable-temperature spectros-
(25) Sandstro¨m, J . Dynamic NMR Spectroscopy; Academic Press:
New York, 1982.

2540 Organometallics, Vol. 20, No. 12, 2001
Hayes et al.
Sch em e 4
Sch em e 5
F igu r e 8. Representative series of 1H NMR spectra of
diethyl complex 3b (400 MHz, C7D8), depicting the coales-
cence behavior of the spectrum and the postulated dynamic
process accounting for this behavior.
Ta ble 7. F r ee En er gies of th e F lu xion a l P r ocess in
LScR2
changes diastereomeric rather than equivalent struc-
tures (Scheme 4). As samples of8b are cooled, coalescence
behavior is observed (255 K) and signals for the two
isomers exoMe-8b and endoMe-8b emerge at 210 K; the
isomers are present in a 2.8:1 ratio. The assignment of
the major species as the exoMe diastereomer was made
on the basis of a low-temperature ROESY experiment,
which clearly showed correlation between the methyl
group and the lower isopropyl methine group pointing
inward toward the exo position in the major isomer.
Because of this relatively close contact, the exo position
is the most sterically crowded, and positioning of the
larger CH2SiMe3 group in the endo site is favored on
this basis.
a
b
compd
R
Tc (K)
∆Gq (kcal mol-1
)
∆Gq
Tc
norm
4a
5a
6a
1b
2b
3b
4b
5b
6b
CH2Ph
187
275
210
263
213
240
298
242
303
8.2c
12.3
9.5
12.3
9.6
10.6
13.4
10.7
13.7
5.2c
11.4
6.7
10.8
6.9
8.6
13.4
8.7
CH2CMe3
CH2SiMe3
Cl
CH3
CH2CH3
CH2Ph
CH2CMe3
CH2SiMe3
13.9
a
b
In kcal mol-1
.
In kcal mol-1, normalized to 298 K. c Upper
limit due to inability to observe the low-temperature-limit spec-
trum of 4a .
The four-coordinate dialkyl complexes are somewhat
thermally unstable in benzene solution, initially under-
going a metalation process with one of the C-H bonds
of an aryl isopropyl group and eliminating 1 equiv of
R-H (Scheme 5). For dialkyls in the a series, further
ill-defined processes compete with the metalation at
later stages of the reaction, but in the b series, meta-
lation to compounds 9b-13b is relatively clean. Because
of lowered symmetry, the 1H NMR spectra for these
compounds are complex, exhibiting seven doublets for
the isopropyl methyl groups and four multiplets for the
methines. For compounds 10b-13b, a diagnostic AB
quartet (2J HH ) 11-12 Hz) for the diastereotopic Sc-
CH2R protons of the remaining unmetalated alkyl group
appears upfield of 0 ppm (this signal is at 2.12 ppm for
11b). An X-ray structural analysis of 13b was carried
out, and while the data were not refinable to an
consistent with the notion that the ScR2 fragment
deviates from the NCCCN ligand plane in order to avoid
steric interactions with the aryl isopropyl groups (vide
supra). The anomalous values (e.g. those found for 4a
and 1b) imply that electronic factors are also playing a
role in determining the barrier to the process. Interest-
ingly, in the related complex LbSc(TeCH2SiMe3)2, where
the two scandium substituents are π-donating and
bulky tellurolate ligands, the barrier to their equilibra-
tion cannot be measured via this technique and a static
out-of-plane structure is also observed at room temper-
ature in solution.15
The NMR spectra for the mixed-ligand derivatives 7b
and 8b exhibit aryl isopropyl resonance patterns ex-
pected on the basis of the now broken top-bottom
symmetry, even in the averaged structure. These com-
pounds undergo a related dynamic process which ex-

A New Family of Organoscandium Complexes
Organometallics, Vol. 20, No. 12, 2001 2541
Ta ble 8. Ha lf-Lives a n d kobsd (Ca lcu la ted ) for
Meta la tion Rea ction s
compd
R
T (K)
t1/2 (h)
kobsd (s-1
)
4a
5a
6a
6b
2b
3b
4b
5b
6b
CH2Ph
360
360
360
360
333
333
333
333
333
7.2
0.37
3.8
0.13
0.53
0.15
11.7
0.33
1.6
2.68 × 10-5
5.32 × 10-4
5.09 × 10-5
1.47 × 10-3
3.59 × 10-4
1.34 × 10-3
1.65 × 10-5
5.86 × 10-4
1.22 × 10-4
CH2CMe3
CH2SiMe3
CH2SiMe3
CH3
CH2CH3
CH2Ph
CH2CMe3
CH2SiMe3
10-3 M), the observed half-lives are ∼3.8 h and 8 min,
respectively. Much precedence exists for the notion that
steric crowding about a metal center favors metalation
processes,27 and this observation is another manifesta-
tion of the significantly higher steric impact of the b
ligand vs that of the a donor. Given the complex
interplay of steric and electronic effects on the fluxion-
ality observed for these compounds (vide supra) and
likely on the energetics of the σ-bond metathesis transi-
tion state, meaningful conclusions regarding the trends
observed within each series are difficult to come by.
However, the almost complete lack of correlation be-
tween the observed barriers to endo/exo ligand exchange
and the rates of metalation suggest that metalation does
not occur from the in-plane C2v structure. Interestingly,
when the mixed-alkyl complex 8b is induced to undergo
metalation at 75 °C, methane elimination to produce
13b is preferred over loss of SiMe4 to give 9b by an 8:1
margin (Scheme 5). We speculate that the metalation
transition state occurs from an out-of-plane structure
and preferentially involves loss of the exo alkyl sub-
stituent. In fact, as many of the ORTEP diagrams in
Figures 2-7 show, the exo alkyl group is closely
proximal to the lower isopropyl groups, facilitating
metalation from this structure.
F igu r e 9. (A) First-order kinetic plots for the metalation
of 6b to produce 13b and SiMe4 at various temperatures.
The complete data set for the run at 30 °C is not shown in
the figure; this run took over 80 000 s to go to 5 half-lives.
(B) Eyring plot of the temperature dependence of the rate
constants.
acceptable level, analysis did confirm the connectivity
of this compound as formulated.
The metalation process for bis((trimethylsilyl)methyl)
derivative 6b was monitored quantitatively by 1H NMR
spectroscopy; these studies indicate that the process is
first order in the dialkyl species, consistent with an
intramolecular reaction. The reaction was followed at
various temperatures (Figure 9A), and an Eyring plot
(Figure 9B) allowed for extraction of the activation
parameters ∆Hq ) 19.7(6) kcal mol-1 and ∆Sq ) -17-
(2) cal mol-1 K-1. The ∆Hq value compares well to that
As the only example in the series which contains
â-hydrogen-containing alkyl groups, diethyl derivative
3b deserves special comment. Although alternate mecha-
nistic possibilities involving â-hydride elimination28 or
abstraction29 in the metalation chemistry observed for
diethyl complex 3b are feasible, it appears that meta-
lation via direct σ-bond metathesis is operative for this
derivative as well. This is indicated by the results of
the metalation of d10-3b, specifically deuterated in the
ethyl groups. When this compound was allowed to
undergo metalation, only d5-10b was observed in the
2H NMR spectrum, as indicated by two signals appear-
ing at 0.6 and -0.6 ppm (integrating in a 3:2 ratio) in
the 2H{1H} NMR spectrum. Also produced was CD3-
CD2H (identified in the 1H NMR spectrum). If this
reaction proceeded, for example, by initial â-elimination
of CD3CD3, followed by metalation of the resulting
scandacyclopropane, d4-10b would have been expected.
Interestingly, the only other LSc(CH2CH3)2 reported in
the literature6 also appeared to be immune to â-elimi-
nation pathways.
found for the σ-bond metathesis reaction between d30
-
Cp*2ScCH3 and C6H6 (∆Hq ) 18.9(2) kcal mol-1).26
However, the ∆Sq value is more negative than one would
expect for an intramolecular reaction (cf. the value of
-23(2) cal mol-1 K-1 found for ∆Sq in the intermolecular
reaction). Perhaps the fluxionality of these complexes
contributes to the more negative activation entropy
observed.
For the ligand a series of compounds, the metalation
process was not as clean as for the b series. At the
higher temperatures required to induce metalation in
the a series, other decomposition processes complicate
the situation somewhat; however, semiquantitative
estimates of the half-lives of these reactions are obtain-
able (Table 8). In general, the THF-free complexes
incorporating ligand a are more resistant to metalation
than those of the b series. For example, when solutions
of 6a and 6b are heated at 360 K (concentration 4.16 ×
(27) (a) Constable, E. C. Polyhedron 1984, 3, 1037. (b) Ibers, J . A.;
DiCosimo, R.; Whitesides, G. M. Organometallics 1982, 1, 13.
(28) Burger, B. J .; Thompson, M. E.; Cotter, W. D.; Bercaw, J . E. J .
Am. Chem. Soc. 1990, 112, 1566.
(26) Thompson. M. E.; Baxter, S. M.; Bulls, A. R.; Burger, B. J .;
Nolan, M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J . E. J . Am.
Chem. Soc. 1987, 109, 203.
(29) By analogy to the loss of butane/1-butene from Cp2Zr(nBu)2: (a)
Negishi, E.-I.; Takahashi, T. Acc. Chem. Res. 1994, 27, 124. (b)
Dioumaev, V. K.; Harrod, J . F. Organometallics 1997, 16, 1452.

2542 Organometallics, Vol. 20, No. 12, 2001
Hayes et al.
12.8 mmol) and evacuated. Toluene (300 mL) was condensed
into the vessel, which was then sealed and heated to 110 °C
for 3 days. The mixture was then cannula-transferred to a
swivel frit apparatus. A hot filtration to remove the salts was
performed, followed by removal of toluene and trituration with
hexanes to give 1b in 77% yield as a pale yellow solid (5.35 g,
8.66 mmol). Anal. Calcd for C35H53N2Cl2Sc: C, 68.06; H, 8.65;
N, 4.54. Found: C, 68.54; H, 7.98; N, 4.92.
Su m m a r y a n d Con clu sion s. Facile routes to base-
free dialkyl derivatives have been developed, opening
up opportunities to study the organoscandium chemistry
of these species in detail. Several structural determina-
tions have shown that the â-diketiminato ligand frame-
work, equipped with bulky 2,6-iPrC6H3 groups, is well-
suited tothe stabilization oflower coordinate,electronically
unsaturated ScR2 fragments. These compounds exhibit
complex solution behavior that can be understood in
terms of a dynamic process by which out-of-plane
bonding modes are equilibrated via an in-plane transi-
tion state. Although these highly electrophilic species
undergo intramolecular metalation reactions, eliminat-
ing RH, in solution, these processes are slow enough
on the chemical time scale that the organometallic
chemistry of these compounds is rich.15 In particular,
this ligand can be viewed as a monoanionic version of
the successful diamido ligand set employed by McCon-
ville in living titanium olefin polymerization catalysts,30
and we have shown that stable scandium alkyl cations
can be generated via reaction of compounds 4a ,7 2b, and
6b with the strong organometallic Lewis acid B(C6F5)3.31
We are also exploring new, more metalation resistant
â-diketiminato ligands.
Syn th esis of [Ar NC(CH3)CHC(CH3)NAr ]Sc(CH3)2‚THF
(2a ). Hexanes (10 mL) and THF (10 mL) were condensed into
an evacuated flask containing 1a (0.390 g, 0.640 mmol) and
solid methyllithium (0.028 g, 1.28 mmol) at -78 °C. The yellow
mixture was warmed gradually to room temperature and
stirred for 1 h before removal of the solvent mixture under
reduced pressure. The residue was suspended in toluene and
filtered. The filtrate was concentrated, and hexanes were
added to induce crystallization of the product. Cold filtration
(-30 °C) gave 2a (0.120 g, 0.198 mmol, 31%). Anal. Calcd for
C
35H55N2OSc: C, 74.43; H, 9.82; N, 4.96. Found: C, 72.52; H,
9.70; N, 4.98. Repeated attempts consistently gave low carbon
analyses for this compound.
Syn th esis of [Ar NC(Bu t)CHC(Bu t)NAr ]Sc(CH3)2 (2b).
Toluene (30 mL) was condensed into an evacuated flask
containing 1b (1.00 g, 1.62 mmol) and solid methyllithium
(0.132 g, 6.00 mmol) at -78 °C. The resultant mixture was
warmed slowly to room temperature and stirred for 1 h. The
reaction mixture was filtered and the toluene removed in
vacuo. The residue was recrystallized from hexanes, affording
yellow crystals of 2b (0.480 g, 0.832 mmol, 51%). Anal. Calcd
for C37H59N2Sc: C, 77.04; H, 10.31; N, 4.86. Found: C, 76.55;
H, 9.53; N, 4.98.
Syn t h esis of [Ar NC(Bu t)CH C(Bu t)NAr ]Sc(CH2CH 3)2
(3b). Toluene (25 mL) was condensed into an evacuated flask
charged with LiCH2CH3 (0.058 mg, 1.62 mmol) and 1b (0.500
g, 0.809 mmol) at -78 °C. The reaction mixture was stirred
for 30 min after the vessel was slowly warmed to room
temperature. Hot filtration followed by removal of the solvent
in vacuo and trituration with hexanes afforded an orange solid
(168 mg, 0.283 mmol, 35%). Anal. Calcd for C35H53N2Cl2Sc: C,
77.44; H, 10.50; N, 4.63. Found: C, 77.28; H, 10.63; N, 4.74.
Exp er im en ta l Section
Gen er a l P r oced u r es. All operations were performed under
a purified argon atmosphere using glovebox or vacuum-line
techniques. Toluene, hexane, and THF solvents were dried and
purified by passing through activated alumina and Q5 col-
umns.32 NMR spectra were recorded in dry, oxygen-free C6D6,
unless otherwise noted. 1H, 2H, 13C{1H}, HMQC, ROESY, and
COSY NMR experiments were performed on Bruker AC-200,
AMX-300, and WH-400 or Varian 200 MHz spectrometers.
Data are given in ppm relative to solvent signals for 1H and
13C spectra. UV spectra were obtained on a Hewlett-Packard
Model 8452A diode array spectrophotometer interfaced to a
PC computer in hexanes solutions with concentrations between
1 × 10-5 and 1 × 10-4 M. Elemental analyses were performed
by Mrs. Dorothy Fox of this department. The ligands HL10b (L
) ArNC(R)CHC(R)NAr, where Ar ) 2,6-iPr-C6H3 and R )
CH3, But), and benzylpotassium33 were prepared by literature
procedures. The protio ligands were converted to their lithium
salts by treatment with n-BuLi in hexanes. All other materials
were obtained from Sigma-Aldrich and purified according to
standard procedures.
Syn th esis of [Ar NC(CH3)CHC(CH3)NAr ]ScCl2‚THF (1a).
Toluene (20 mL) was condensed into an evacuated flask
containing LiL (3.50 g, 8.26 mmol) and ScCl3‚3THF (3.03 g,
8.26 mmol) at -78 °C. The mixture was heated with stirring
at 85 °C for 16 h. The reaction mixture was hot-filtered to
remove LiCl and the toluene removed in vacuo. Trituration of
the residue with hexanes followed by filtration led to isolation
of pure 1a as a pale yellow solid (3.23 g, 5.34 mmol, 65%). Anal.
Calcd for C33H49N2Cl2OSc: C, 65.44; H, 8.15; N, 4.63. Found:
C, 65.35; H, 8.71; N, 4.61.
Syn th esis of [Ar NC(Bu t)CHC(Bu t)NAr ]Sc(CD2CD3)2 (d10
-
3b). This compound was prepared in a manner identical with
that previously described for 3b, with the exception that LiCD2-
CD3 was used. The 1H NMR spectrum matched 3b, with the
exception that no resonances were observed for the ethyl
groups.
Syn th esis of [Ar NC(CH3)CHC(CH3)NAr ]Sc(CH2C6H5)2
(4a ). A two-necked flask was charged with 1a (0.400 g, 0.660
mmol) and attached to a swivel frit apparatus. A solid addition
tube was loaded with benzylpotassium (0.172 g, 1.32 mmol)
and attached to the second port on the flask. The entire
assemblage was evacuated, and benzene (50 mL) was vacuum-
distilled into the flask. After it was warmed to room temper-
ature, benzylpotassium was gradually added to the solution
over 30 min. Stirring was continued for another 4 h. The
reaction mixture was filtered and the benzene removed under
vacuum to give crude 4a . Recrystallization from hexanes
afforded pure 4a (0.230 g, 0.389 mmol, 59%). Anal. Calcd for
C
49H67N2Sc: C, 80.09; H, 8.60; N, 4.34. Found: C, 80.46; H,
Syn th esis of [Ar NC(Bu t)CHC(Bu t)NAr ]ScCl2 (1b). A
thick-walled reactor bomb equipped with a Kontes valve was
charged with LiL (5.70 g, 11.2 mmol) and ScCl3‚3THF (4.70 g,
8.04; N, 4.46.
Syn t h esis of [Ar NC(Bu t)CH C(Bu t)NAr ]Sc(CH2C6H 5)2
(4b). A 100 mL flask was charged with 1b (0.750 g, 1.21 mmol)
and BnMgCl (0.366 g, 2.43 mmol). Toluene (65 mL) was
condensed into the evacuated flask at -78 °C. The mixture
was slowly warmed to room temperature, whereby stirring was
continued for another 17 h. The toluene was removed in vacuo
to afford an orange solid. Benzene (55 mL) was condensed into
the flask, and the assemblage was sonicated for 10 min. The
reaction mixture was filtered and benzene removed under
vacuum to afford 4b as an orange solid (0.605 g, 0.829 mmol,
(30) Scollard, J . D.; McConville, D. H.; Payne, N. C.; Vittal, J . J .
Macromolecules 1996, 29, 5241.
(31) Piers, W. E.; Hayes, P. G.; Clegg, W. Abstracts of OCOP 2000,
Organometallic Catalysts and Olefin Polymerization, J une 18-22,
2000, Oslo, Norway.
(32) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J . Organometallics 1996, 15, 1518.
(33) Schlosser, M.; Hartmann, J . Angew. Chem., Int. Ed. Engl. 1973,
12, 508.

A New Family of Organoscandium Complexes
Organometallics, Vol. 20, No. 12, 2001 2543
69%). Anal. Calcd for C49H67N2Sc: C, 80.73; H, 9.26; N, 3.84.
Found: C, 79.57; H, 8.91; N, 3.89.
yellow powder. This material was further recrystallized from
hexanes (0.125 g, 0.193 mmol, 38%).
Syn t h esis of [η3-Ar NC(Bu t)CH C(Bu t)NC6H 3C3H 6]Sc-
CH2SiMe3 (13b). In an evacuated flask at -78 °C containing
6b (0.150 g, 0.208 mmol) was condensed toluene (25 mL). The
solution was heated to 65 °C for 3 h and solvent removed under
vacuum, yielding a red oil. Recrystallization from hexanes at
-35 °C afforded small yellow crystals of 13b (0.032 g, 0.0505
mmol, 24%). 1H NMR: δ 7.20-6.94 (m, 6H; C6H3), 5.57 (s, 1H;
CH), 3.43 (sp, 1H; CH(CH3)2, J H-H ) 6.8 Hz), 3.10 (m, 2H;
CH(CH3)2, CH2CH(CH3), J H-H ) 6.8 Hz), 2.84 (sp, 1H;
CH(CH3)2, J H-H ) 6.8 Hz), 1.48 (d, 3H; CH(CH3)2, J H-H ) 6.8
Hz), 1.39 (d, 3H; CH(CH3)2, J H-H ) 6.8 Hz), 1.31 (d, 3H; CH-
(CH3)2, J H-H ) 6.8 Hz), 1.26 (d, 3H; CH(CH3)2, J H-H ) 6.8 Hz),
1.21 (d, 3H; CH(CH3)2, J H-H ) 6.8 Hz), 1.18 (d, 3H; CH(CH3)2,
J H-H ) 6.8 Hz), 1.18 (s, 18H; NCC(CH3)3), 1.02 (d, 3H; CH-
(CH3)2, J H-H ) 6.8 Hz), 0.95, 0.93 (dd, 1H; CH2CH(CH3), J H-H
) 11.8 Hz), 0.09, 0.06 (dd, 1H; CH2CH(CH3), J H-H ) 11.8 Hz),
0.00 (s, 2H; CH2Si(CH3)3), -0.25 (s, 9H; CH2Si(CH3)3), -1.08,
-1.16 (dd, 2H; CH2Si(CH3)3, J H-H ) 11.2 Hz). 13C{1H} NMR:
δ 174.2, 173.9 (NCC(CH3)3), 147.6 (Cipso), 144.9, 144.7, 142.2,
138.2, 127.7, 125.7, 125.6, 124.9, 123.9, 121.5 (C6H3), 99.0 (CH),
45.0 (CH2Si(CH3)3), 43.4, 43.2 (C(CH3)3), 39.7 (CH2CH(CH3),
32.9, 32.2 (C(CH3)3), 28.9, 28.7, 28.4 (CH(CH3)2, one peak not
observed), 26.8, 26.0, 25.7, 25.0, 24.5, 23.1 (CH(CH3)2, one peak
not observed), 4.1 (CH2Si(CH3)3). Anal. Calcd for C38H56N2ClSc:
C, 74.00; H, 10.03; N, 4.43. Found: C, 74.42; H, 10.05; N, 4.47.
Kin etic Exp er im en ts. In a typical experiment, the com-
pound of interest (0.0208 mmol) was dissolved in 0.5 mL of
toluene-d8 (4.15 × 10-3 M) and kept at -78 °C until inserted
into the NMR probe, at which time it was given 10 min to
equilibrate to the specified temperature. The progress of
reaction was monitored by integration of the ligand backbone
Syn th esis of [Ar NC(CH3)CHC(CH3)NAr ]Sc(CH2C-
(CH3)3)2 (5a ). Toluene (20 mL) was condensed into an evacu-
ated flask containing LiCH2C(CH3)3 (0.139 g, 1.78 mmol) and
1a (0.474 g, 0.890 mmol) at -78 °C. The reaction vessel was
slowly warmed to room temperature, after which stirring was
continued for another 90 min. The solvent was removed under
reduced pressure, and hexanes (20 mL) was vacuum-distilled
into the flask. The mixture was filtered to remove LiCl. The
solvent was removed in vacuo and the residue triturated with
hexanes to afford 5a as a white crystalline solid (0.340 g, 0.562
mmol, 64%). Anal. Calcd for C39H63N2Sc: C, 77.44; H, 10.50;
N, 4.63. Found: C, 77.56; H, 9.80; N, 4.73.
Syn th esis of [Ar NC(Bu t)CHC(Bu t)NAr ]Sc(CH2C(CH3)3)2
(5b). Toluene (20 mL) was condensed into an evacuated flask
containing LiCH2C(CH3)3 (0.088 g, 1.13 mmol) and 1b (0.350
g, 0.566 mmol) at -78 °C. The yellow mixture was warmed to
room temperature and stirred for 1 h. Removal of solvent
followed by trituration with cold hexanes permitted isolation
of crude 5b as a pale yellow solid. Recrystallization from
hexanes at -35 °C afforded 5b in 42% yield (0.165 g, 0.239
mmol). Anal. Calcd for C45H75N2Sc: C, 78.43; H, 10.97; N, 4.07.
Found: C, 77.50; H, 10.59; N, 4.80.
Syn th esis of [Ar NC(CH3)CHC(CH3)NAr ]Sc(CH2SiMe3)2
(6a ). A 50 mL flask was charged with LiCH2Si(CH3)3 (0.128
g, 1.36 mmol) and 1a (0.410 g, 0.680 mmol) and evacuated.
Toluene (25 mL) was condensed into the vessel at -78 °C. The
solution was gradually warmed to room temperature, where-
upon it was stirred for 2 h. The mixture was hot-filtered to
remove LiCl. The solvent was removed in vacuo, and the
residue was triturated with hexanes to give 250 mg (0.392
mmol, 58%) of 6a as a white powder. Anal. Calcd for C37H63N2
Si2Sc: C, 69.76; H, 9.97; N, 4.40. Found: C, 69.11; H, 9.34; N,
4.58.
Syn th esis of [Ar NC(Bu t)CHC(Bu t)NAr ]Sc(CH2SiMe3)2
(6b). In an evacuated flask at -78 °C containing LiCH2Si-
(CH3)3 (0.058 g, 0.616 mmol) and 1b (0.190 g, 0.308 mmol) was
condensed toluene (15 mL). The reaction mixture was warmed
to room temperature and then stirred for 90 min. The mixture
was filtered, and the solvent was removed in vacuo to afford
a yellow residue which was triturated with hexanes to give
6b as a yellow crystalline solid (0.109 g, 0.151 mmol, 49%).
Anal. Calcd for C43H75N2Si2Sc: C, 71.61; H, 10.48; N, 3.88.
Found: C, 70.76; H, 10.41; N, 4.00.
Syn th esis of [Ar NC(Bu t)CHC(Bu t)NAr ]Sc(CH3)Cl (7b).
A 50 mL flask was charged with 1b (0.085 g, 0.144 mmol) and
2b (0.089 g, 0.144 mmol), and 30 mL of toluene was condensed
into it at -78 °C. The reaction mixture was gradually warmed
to room temperature and solvent removed under vacuum to
afford a light yellow powder. Hexanes (25 mL) were added,
and the mixture was filtered to give a clear yellow solution.
Removal of solvent in vacuo gave crude 7b as a pale yellow
powder, which was then recrystallized from hexanes at -35
°C (0.150 g, 0.255 mmol, 89%). Anal. Calcd for C38H56N2ClSc:
C, 72.40; H, 9.45; N, 4.61. Found: C, 72.21; H, 9.32; N, 4.61.
(Note: the sample contained 5% of both 1b and 2b.)
1
peak in the H spectrum. The reaction was followed until 95%
completion. Although compounds 9b, 10b, 11b, and 12b were
produced via the kinetic experiments, they were not isolated
and as a result only the 1H and 13C NMR spectra are reported.
Unfortunately, further decomposition of 11a , 12a , and 13a
occurred before completion of the kinetic experiments, making
it impossible to obtain clean spectra. The kinetic data obtained
for these species were limited to the first 65% of the metalation
process and are therefore considered only semiquantitative.
3
In the spectroscopic data presented below, the J H-H coupling
constant between methyl and methine protons in the aryl Pri
groups was invariably 6.6-7.0 Hz.
9b: 1H NMR δ 7.27-6.98 (m, 6H; C6H3), 5.58 (s, 1H; CH),
3.48 (sp, 1H; CH(CH3)2), 3.12 (m, 2H; CH(CH3)2, CH2CH(CH3)),
2.89 (sp, 1H; CH(CH3)2), 1.43 (d, 3H; CH(CH3)2), 1.33 (d, 3H;
CH(CH3)2), 1.32 (d, 3H; CH(CH3)2), 1.31 (d, 3H; CH(CH3)2),
1.27 (d, 3H; CH(CH3)2), 1.20 (d, 3H; CH(CH3)2), 1.19 (s, 18H;
NCC(CH3)3), 1.00 (d, 3H; CH(CH3)2), 0.81, 0.80 (dd, 1H; CH2-
CH(CH3), J H-H ) 11.8 Hz), -0.02, -0.05 (dd, 1H; CH2CH(CH3),
J H-H ) 11.8 Hz), -1.10 (s, 3H; CH3); 13C{1H} NMR δ 174.2,
173.9 (NCC(CH3)3), 147.7, 145.2 (Cipso), 144.9, 141.8, 141.4,
138.1, 127.5, 126.5, 125.9, 124.6, 124.5, 123.3 (C6H3), 98.8 (CH),
43.4, 43.2 (C(CH3)3), 39.7 (CH2CH(CH3), 32.9, 32.2 (C(CH3)3),
29.6, 29.1, 28.9, 28.5 (CH(CH3)2), 26.8 (CH3), 26.3, 26.1, 26.0,
25.9, 25.2, 24.4, 22.7 (CH(CH3)2).
Syn t h esis of [Ar NC(Bu t)CH C(Bu t)NAr ]Sc(CH3)(CH2-
SiMe3) (8b). A 100 mL flask was charged with 7b (0.300 g,
0.511 mmol) and LiCH2Si(CH3)3 (0.053 g, 0.563 mmol) and
attached to a swivel frit apparatus. The entire assemblage was
evacuated, and toluene (50 mL) was vacuum-distilled into the
flask. After it was warmed to room temperature, the reaction
mixture was stirred for another 45 min, whereby the solvent
was removed under vacuum to afford a thick yellow oil.
Hexanes (40 mL) were added, and the reaction mixture was
filtered. The volume was reduced to 25 mL and the mixture
cooled to -78 °C for 30 min; during this time a small quantity
of fine yellow powder precipitated. The mixture was back-
filtered and solvent removed in vacuo to afford 8b as a light
10b: 1H NMR δ 7.35-6.86 (m, 6H; C6H3), 5.55 (s, 1H; CH),
3.45 (sp, 1H; CH(CH3)2), 3.14 (m, 2H; CH(CH3)2, CH2CH(CH3)),
2.91 (sp, 1H; CH(CH3)2), 1.46 (d, 3H; CH(CH3)2), 1.45 (d, 3H;
CH(CH3)2), 1.32 (d, 3H; CH(CH3)2), 1.31 (d, 3H; CH(CH3)2),
1.26 (d, 3H; CH(CH3)2), 1.19 (d, 3H; CH(CH3)2), 1.18 (s, 18H;
NCC(CH3)3), 1.03 (d, 3H; CH(CH3)2), 0.88, 0.87 (dd, 1H; CH2-
CH(CH3), J H-H ) 11.8 Hz), 0.63 (t, 3H; CH2CH3, J H-H ) 8.2
Hz), 0.22 (dd, 1H; CH2CH(CH3), J H-H ) 11.8 Hz), -0.63 (q,
1H; CH2CH3, J H-H ) 8.2 Hz), -0.62 (q, 1H; CH2CH3, J H-H
)
8.2 Hz); 13C{1H} NMR: δ 174.1, 173.8 (NCC(CH3)3), 147.8,
145.2 (Cipso), 144.7, 142.2, 141.7, 139.7, 127.5, 126.3, 125.6,
124.7, 123.3, 122.1 (C6H3), 98.7 (CH), 43.4, 43.2 (C(CH3)3), 40.0
(CH2CH3), 39.7 (CH2CH(CH3), 32.9, 32.3 (C(CH3)3), 29.0, 28.9,

2544 Organometallics, Vol. 20, No. 12, 2001
Hayes et al.
Ta ble 9. Su m m a r y of Da ta Collection a n d Str u ctu r e Refin em en t Deta ils for 1b, 2a , 2b-4b, a n d 6a ,b
1b
2a
2b
3b
4b
6a
6b
formula
fw
C
35H53N2Cl2Sc
C35H55N2OSc
564.79
C37H59N2Sc
576.82
C39H63N2Sc
604.90
C49H67N2Sc
729.04
C37H63N2ScSi2
637.03
C43H75N2ScSi2
721.21
617.68
cryst syst
a, Å
b, Å
monoclinic
11.916(2)
16.243(3)
19.108(4)
tetragonal
27.692(3)
monoclinic
12.9021(10)
11.0349(9)
25.341(2)
monoclinic
18.759(5)
10.427(6)
19.608(5)
monoclinic
12.653(4)
12.096(3)
28.069(4)
triclinic
10.4634(6)
11.1017(6)
18.0333(10)
80.055(2)
79.994(2)
72.406(2)
1950.23(19)
P1h
monoclinic
13.469(6)
17.939(6)
19.132(5)
c, Å
17.954(4)
R, deg
â, deg
γ, deg
V, Å3
101.353(15)
98.147(2)
107.32(2)
90.77(2)
90.93(3)
3626.0(11)
P21/n
4
1.131
0.373
0.056
0.054
13768(4)
I1/a
16
1.090
0.238
0.053
0.048
3571.5(5)
P21/n
4
1.073
0.231
3661.4(28)
P21/n
4
1.097
0.225
0.052
0.054
4296(2)
P21/c
4
1.127
0.205
0.063
0.136
4622(3)
P21/c
4
1.036
0.236
0.060
0.059
space group
Z
2
d
calcd, Mg m-3
1.085
0.275
µ, mm-1
R
Rw
R1
wR2
GOF
0.0364
0.1022
1.090
0.0351
0.0915
1.051
2.02
1.76
1.89
1.02
2.18
28.6, 28.5 (CH(CH3)2), 26.3, 26.2, 26.0, 25.9, 25.2, 24.4, 22.8
(CH(CH3)2), 12.2 (CH2CH3).
-113 °C with a θ range from 1.62 to 28.42°. The structure
was solved by Patterson synthesis and refined on F2 values
by full-matrix least squares for all unique data. Programs used
were standard Bruker SMART (control) and SAINT (integra-
tion), SHELXTL for structure solution, refinement and mo-
lecular graphics, and local programs.
11b: 1H NMR δ 7.27-6.84 (m, 11H; C6H3, C6H5), 5.58 (s,
1H; CH), 3.13 (sp, 1H; CH(CH3)2), 3.11 (m, 2H; CH(CH3)2,
CH2CH(CH3)), 2.92 (sp, 1H; CH(CH3)2), 2.12 (s, 2H; CH2C6H5)
1.39 (d, 3H; CH(CH3)2), 1.37 (d, 3H; CH(CH3)2), 1.31 (d, 3H;
CH(CH3)2), 1.25 (d, 3H; CH(CH3)2), 1.24 (d, 3H; CH(CH3)2),
1.22 (d, 3H; CH(CH3)2), 1.21 (d, 3H; CH(CH3)2), 1.07 (s, 18H;
NCC(CH3)3), 0.90, 0.89 (dd, 1H; CH2CH(CH3), J H-H ) 11.8 Hz),
0.09, 0.05 (dd, 1H; CH2CH(CH3), J H-H ) 11.8 Hz); 13C{1H}
NMR δ 175.4, 173.8 (NCC(CH3)3), 149.1, 146.6, 145.4 (Cipso),
143.7, 142.2, 141.7, 140.8, 129.7, 129.1, 128.9, 128.7, 127.0,
126.2, 125.6, 125.0, 123.7, 120.0, 119.5 (C6H3, CH2C6H5), 99.4
(CH), 43.4, 43.2 (C(CH3)3), 39.7 (CH2CH(CH3), 32.9, 32.3
(C(CH3)3), 29.0, 28.9, 28.7, 28.6, (CH(CH3)2), 26.8, 26.2, 26.0,
25.7, 25.2, 24.5, 23.6 (CH(CH3)2), CH2C6H5 not observed.
12b: 1H NMR δ 7.34-6.96 (m, 6H; C6H3), 5.56 (s, 1H; CH),
3.50 (sp, 1H; CH(CH3)2), 3.20 (m, 2H; CH(CH3)2, CH2CH(CH3)),
2.89 (sp, 1H; CH(CH3)2), 1.56 (d, 3H; CH(CH3)2), 1.48 (d, 3H;
CH(CH3)2), 1.34 (d, 3H; CH(CH3)2), 1.33 (d, 3H; CH(CH3)2),
1.27 (d, 3H; CH(CH3)2), 1.18 (d, 3H; CH(CH3)2), 1.17 (s, 18H;
NCC(CH3)3), 1.11 (d, 3H; CH(CH3)2), 0.77 (s, 9H; CH2C(CH3)3),
0.21, 0.17 (dd, 1H; CH2CH(CH3), J H-H ) 11.8 Hz), -0.43, -0.55
(dd, 2H; CH2C(CH3)3, J H-H ) 12.6 Hz), 1H of CH2CH(CH3) not
observed; 13C{1H} NMR δ 174.0, 173.8 (NCC(CH3)3), 147.7,
144.8 (Cipso), 144.7, 142.3, 141.3, 138.7, 128.2, 127.6, 125.6,
123.8, 123.7, 122.1 (C6H3), 98.8 (CH), 70.8 (CH2C(CH3)3) 43.4,
43.2 (C(CH3)3), 39.8 (CH2CH(CH3), 35.7 (CH2C(CH3)3), 32.6
(C(CH3)3), 28.9, 28.8, 28.5, 26.5, (CH(CH3)2); 26.1, 26.0, 25.8,
25.7, 25.2, 24.6, 21.9 (CH(CH3)2).
3b. Crystals of 3b were grown from a hexanes solution at
-35 °C. Measurements were made at -103 °C with the ω-2θ
scan technique to a maximum 2θ value of 50.1°. The structure
was solved by direct methods and expanded using Fourier
techniques. The non-hydrogen atoms were refined anisotro-
pically; hydrogen atoms were included at geometrically ideal-
ized positions with C-H ) 0.95 Å and were not refined.
4b. Crystals of 4b were grown from a hexanes solution at
-35 °C. Measurements were made at -103 °C with the ω-2θ
scan technique to a maximum 2θ value of 50.1°. The structure
was solved by direct methods and expanded using Fourier
techniques. The non-hydrogen atoms were refined anisotro-
pically; hydrogen atoms were included at geometrically ideal-
ized positions with C-H ) 0.95 Å and were not refined.
6a . Crystals of 6a were grown from a hexanes solution at
-35 °C. Measurements were made using a Bruker AXS
SMART CCD area-detector diffractometer at -113 °C with a
θ range from 2.42 to 28.89°. The structure was solved by direct
methods and refined on F2 values by full-matrix least squares
for all unique data.
6b. Crystals of 6b were grown from a hexanes solution at
-30 °C. Measurements were made at -103 °C with the ω-2θ
scan technique to a maximum 2θ value of 55.1°. The structure
was solved by direct methods and expanded using Fourier
techniques. The non-hydrogen atoms were refined anisotro-
pically; hydrogen atoms were included at geometrically ideal-
ized positions with C-H ) 0.95 Å and were not refined.
X-r a y Cr ysta llogr a p h y. A summary of crystal data and
refinement details for all structures is given in Table 9.
Suitable crystals were covered in Paratone oil, mounted on a
glass fiber, and immediately placed in a cold stream on the
diffractometer employed.
1b. Crystals of 1b were grown from a hexanes solution at
-35 °C. Measurements were made using a Rigaku AFC6S
diffractometer with a graphite-monochromated Mo KR radia-
tion (λ ) 0.710 69 Å) source at -103 °C with the ω-2θ scan
technique to a maximum 2θ value of 55.1°. The structure was
solved by direct methods and expanded using Fourier tech-
niques. The non-hydrogen atoms were refined anisotropically;
hydrogen atoms were included at geometrically idealized
positions with C-H ) 0.95 Å and were not refined. All
calculations were performed using the teXsan crystallographic
software package of Molecular Structure Corp.
Ack n ow led gm en t. This work was generously sup-
ported by the NOVA Research & Technology Corpora-
tion of Calgary, Alberta, Canada, the NSERC of Cana-
da’s Research Partnerships office (CRD program), and
the EPSRC of the U.K.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, anisotropic displacement parameters, and all bond
distances and angles for 2a , 1b-4b, and 6a ,b. This material
is available free of charge via the Internet at http://pubs.acs.org.
2b. Crystals of 2b were grown from a hexanes solution at
-35 °C. Measurements were made using a Bruker AXS
SMART CCD area-detector diffractometer using a graphite-
monochromated Mo KR radiation (λ ) 0.710 73 Å) source at
OM010131O