Synthesis, structure, and density functional theory analysis of a scandium dinitrogen complex, [(C5Me4H)2Sc] 2(μ-η2: η2-N2)

Article abstract of DOI:10.1021/ja102681w

Investigation of the bis(tetramethylcyclopentadienyl) metallocene chemistry of scandium has revealed that the method involving reduction of trivalent salts with alkali metals used with lanthanides can also be applied to scandium to make a dinitrogen complex of the first member of the transition metal series. ScCl₃ reacts with 2 equiv of KC₅Me₄H to form (C₅Me₄H)₂ScCl(THF), 1, which reacts with allylmagnesium chloride to make (C₅Me₄H) ₂Sc(η³-C₃H₅), 2. Complex 2 reacts with [HNEt₃][BPh₄] to yield [(C₅Me ₄H)₂Sc][(μ-Ph)BPh₃], 3, which has just one primary Sc-C(phenyl) contact connecting the tetraphenylborate anion and the metallocene cation. Treatment of 3 with KC₈ in THF under N ₂ generates [(C₅Me₄H)₂Sc] ₂(μ-η²:²-N₂), which has a coplanar arrangement of scandium and nitrogen atoms within a square planar array of tetramethylcyclopentadienyl rings. Density functional calculations explain the bonding that results in the 1.239(3) A N-N bond distance in the (N=N)^2- moiety.

Full text of DOI:10.1021/ja102681w

Published on Web 07/21/2010
Synthesis, Structure, and Density Functional Theory Analysis
of a Scandium Dinitrogen Complex, [(C5Me4H)2Sc]2(µ-η2:η2-N2)
Selvan Demir,†,‡ Sara E. Lorenz,† Ming Fang,† Filipp Furche,† Gerd Meyer,‡
Joseph W. Ziller,† and William J. Evans*,†
Department of Chemistry, UniVersity of California, IrVine, California 92697-2025, and Institut
fu¨r Anorganische Chemie, UniVersita¨t zu Ko¨ln, Greinstrasse 6, D-50939 Ko¨ln, Germany
Received March 30, 2010; E-mail: wevans@uci.edu
Abstract: Investigation of the bis(tetramethylcyclopentadienyl) metallocene chemistry of scandium has
revealed that the method involving reduction of trivalent salts with alkali metals used with lanthanides can
also be applied to scandium to make a dinitrogen complex of the first member of the transition metal series.
ScCl3 reacts with 2 equiv of KC5Me4H to form (C5Me4H)2ScCl(THF), 1, which reacts with allylmagnesium
chloride to make (C5Me4H)2Sc(η3-C3H5), 2. Complex 2 reacts with [HNEt3][BPh4] to yield [(C5Me4H)2Sc]-
[(µ-Ph)BPh3], 3, which has just one primary Sc-C(phenyl) contact connecting the tetraphenylborate anion
and the metallocene cation. Treatment of 3 with KC8 in THF under N2 generates [(C5Me4H)2Sc]2(µ-η2:η2-
N2), which has a coplanar arrangement of scandium and nitrogen atoms within a square planar array of
tetramethylcyclopentadienyl rings. Density functional calculations explain the bonding that results in the
1.239(3) Å N-N bond distance in the (NdN)2- moiety.
Introduction
shown in eq 1, where Z is defined as a monoanionic ligand that
allows these reactions to occur.4,5
Although numerous examples of dinitrogen complexes of the
early transition metals are known,1 no dinitrogen complex of
scandium has been isolated. Since scandium is the first transition
metal with the lowest atomic number, its dinitrogen complexes
would be the simplest transition metal compounds to analyze by
theoretical methods. However, the small size of scandium along
with its electropositive nature also makes it one of the more
experimentally challenging metals2,3 to use to explore dinitrogen
chemistry.
With dinitrogen as a substrate, these reactions provide
[Z2(THF)xLn]2(µ-η2:η2-N2) products with a coplanar arrange-
ment of the bridging side-on bound dinitrogen and the two
metals as shown in eq 1. These complexes have N-N bond
An attractive synthetic route to a scandium dinitrogen
complex is the method used with yttrium and lanthanide
complexes to access divalent-like “Ln2+” reactivity by com-
bining complexes of trivalent metal ions with alkali metals as
distances of 1.233(5)-1.305(6) Å and can be considered to be
4-10
complexes of (N2)2-
.
Since scandium in some complexes
is known to have oxidation states lower than 3+ (subvalent
scandium),11-13 this appeared to be a reasonable way to access
scandium dinitrogen chemistry.
† University of California, Irvine.
‡ Universita¨t zu Ko¨ln.
Tetraphenylborate salts of yttrium and lanthanide metallocene
cations of general formula [(C5Me4R)2Ln][(µ-η2:η1-Ph)2BPh2]
(1) Reviews and leading references: (a) Fryzuk, M. D. Acc. Chem. Res.
2009, 42, 127–133. (b) Special issue on dinitrogen chemistry. Can.
J. Chem. 2005, 83, 277-402. (c) Chirik, P. J. Dalton Trans. 2007,
16–25. (d) Pun, D.; Leopold, S. M.; Bradley, C. A.; Lobkovsky, E.;
Chirik, P. J. Organometallics 2009, 28, 2471–2484. (e) Nikiforov,
G. B.; Vidyaratne, I.; Gambarotta, S.; Korobkov, I. Angew. Chem.,
Int. Ed. 2009, 48, 7415–7419. (f) Hirotsu, M.; Fontaine, P. P.; Zavalij,
P. Y.; Sita, L. R. J. Am. Chem. Soc. 2007, 129, 12690–12692. (g)
Knobloch, D. J.; Benito-Garagorri, D.; Bernskoetter, W. H.; Keresztes,
I.; Lobkovsky, E.; Toomey, H.; Chirik, P. J. J. Am. Chem. Soc. 2009,
131, 14903–14912. (h) Knobloch, D. J.; Lobkovsky, E.; Chirik, P. J.
Nat. Chem. 2009, 2, 30–35. (i) Chirik, P. J. Nat. Chem. 2009, 1, 520–
522.
(4) Evans, W. J.; Lee, D. S.; Rego, D. B.; Perotti, J. M.; Kozimor, S. A.;
Moore, E. K.; Ziller, J. W. J. Am. Chem. Soc. 2004, 126, 14574–
14582.
(5) Evans, W. J.; Lee, D. S.; Johnston, M. A.; Ziller, J. W. Organometallics
2005, 24, 6393–6397.
(6) Jaroschik, F.; Momin, A.; Nief, F.; Goff, X. L.; Deacon, G. B.; Junk,
P. C. Angew. Chem., Int. Ed. 2009, 48, 1117–1121.
(7) Evans, W. J.; Lee, D. S.; Lie, C.; Ziller, J. W. Angew. Chem., Int. Ed.
2004, 43, 5517–5519.
(8) Evans, W. J.; Allen, N. T.; Ziller, J. W. J. Am. Chem. Soc. 2001, 123,
7927–7928.
(2) Piers, W. E.; Shapiro, P. J.; Bunel, E. E.; Bercaw, J. E. Synlett 1990,
74–84.
(9) Evans, W. J.; Allen, N. T.; Ziller, J. W. Angew. Chem., Int. Ed. 2002,
41, 359–361.
(3) Thompson, M. E.; Baxter, S. M.; Bulls, A. R.; Burger, J. B.; Nolan,
M. C.; Santarsiero, B. D.; Schaefer, W. P.; Bercaw, J. E. J. Am. Chem.
Soc. 1987, 109, 203–219.
(10) Evans, W. J.; Zucchi, G.; Ziller, J. W. J. Am. Chem. Soc. 2003, 125,
10–11.
9
10.1021/ja102681w  2010 American Chemical Society
J. AM. CHEM. SOC. 2010, 132, 11151–11158 11151

A R T I C L E S
Demir et al.
Figure 1. Binding modes of (BPh4)- in (a) [(C5Me4H)2Lu][(µ-η2:η1-Ph)2BPh2]5 and (b) [(C5Me5)2Sc][(µ-η2:η1-Ph)BPh3].15
(R ) Me, H),5,14 e.g. Figure 1a, have proven to be excellent
starting materials for the formation of [(C5Me4R)2(THF)xLn]2-
(µ-η2:η2-N2) products. These complexes are molecular species
that are soluble in arene solvents and contain an easily displaced
leaving group since the tetraphenylborate is only loosely
coordinated to the metal center via agostic interactions involving
two of the phenyl groups. When the scandium example of this
class was crystallographically characterized,15 it displayed a new
type of (BPh4)- bonding mode involving dihapto coordination
from a single phenyl group, i.e. [(C5Me5)2Sc][(µ-η2:η1-Ph)BPh3],
Figure 1b. However, unlike the [(C5Me4R)2M][(µ-η2:η1-Ph)2-
BPh2] complexes (R ) Me, H) of the lanthanides and uranium,16
the [(C5Me5)2Sc][(µ-η2:η1-Ph)BPh3] complex has minimal solu-
bility in arene solvents.
molecular sieves, and degassed by three freeze-pump-thaw cycles
prior to use. Potassium bis(trimethylsilyl)amide (Aldrich) was
dissolved in toluene, and the mixture was centrifuged and decanted.
Solvent was removed from the supernatant before use as a white
solid. KC5Me4H was prepared as described for KC5Me5.18
18
[HNEt3][BPh4]19 and KC8 were prepared according to the
literature. 1H and 13C NMR spectra were recorded on Bruker GN500
or CRYO500 MHz spectrometers. 45Sc NMR spectra were recorded
on a Bruker Avance 600 spectrometer operating at 145 MHz for
45Sc. The 45Sc NMR spectra were referenced to [Sc(H2O)6]3+ in
D2O. 15N NMR spectra were recorded with an Avance 600 MHz
spectrometer operating at 61 MHz for 15N and calibrated using an
external reference, 15N-formamide in DMSO (-268 ppm with
respect to nitromethane at 0 ppm). IR samples were prepared as
KBr pellets, and the spectra were obtained on a Varian 1000 FT-
IR system. Elemental analyses were performed using a PerkinElmer
Series II 2400 CHNS elemental analyzer.
The synthesis of a [Z2Sc]2(µ-η2:η2-N2) analogue of the
complexes in eq 1 with Z ) C5Me5 appeared challenging not
only because the cationic precursor had low solubility but also
because the small size of scandium could make it sterically
difficult to form such a complex. Hence, a sterically less
crowded target was chosen with Z ) C5Me4H. This paper
reports the synthetic chemistry needed to make the previously
unknown (C5Me4H)2ScX precursors and [(C5Me4H)2Sc][(µ-
Ph)BPh3], as well as its reductive chemistry with potassium
graphite.
(C5Me4H)2ScCl(THF), 1. In
a nitrogen-filled glovebox,
KC5Me4H (2.623 g, 16 mmol) was slowly added to a stirred white
slurry of ScCl3 (1.237 g, 8 mmol) in 100 mL of THF. After the
mixture was stirred for 48 h, the suspension was centrifuged to
separate insoluble materials, presumably KCl, the supernatant was
decanted, and the solution was evaporated to dryness. The resulting
pale-orange powder was extracted with toluene to give a bright
orange solution that was evaporated to dryness to yield a pale-
orange powder (2.482 g). Washing this powder with hexanes leaves
(C5Me4H)2ScCl(THF), 1, as a pale-yellow powder (2.126 g, 66%).
Crystals suitable for X-ray diffraction were grown from a concen-
Experimental Section
1
trated THF solution at -35 °C over the course of 72 h. H NMR
The manipulations described below were performed under
nitrogen or argon with rigorous exclusion of air and water using
Schlenk, vacuum line, and glovebox techniques. Solvents were
saturated with UHP-grade argon (Airgas) and dried by passage
through Glasscontour17 drying columns before use. NMR solvents
were dried over NaK alloy, degassed, and vacuum transferred before
use. Allylmagnesium chloride (2.0 M in THF) was purchased from
Aldrich and used as received. 1,4-Dioxane was purchased from
Aldrich and used as received. 1,2,3,4-Tetramethylcyclopentadiene
(C5Me4H2) was purchased from Aldrich, distilled onto 4 Å
(500 MHz, THF-d8): δ 5.62 (s, 2H, C5Me4H), 1.98 (s, 12H,
C5Me4H), 1.85 (s, 12H, C5Me4H). 13C NMR (126 MHz, THF-d8):
δ 123.99 (C5Me4H), 117.96 (C5Me4H), 112.43 (C5Me4H), 13.92
(C5Me4H), 12.44 (C5Me4H). 45Sc NMR (145 MHz, THF-d8): δ 55
(∆ν1/2 ) 400 Hz). Anal. Calcd for C22H34ClOSc: C, 66.91; H, 8.68.
Found: C, 66.42; H, 8.83. The desolvated derivative,
(C5Me4H)2ScCl, is described in the Supporting Information.
(C5Me4H)2Sc(η3-C3H5), 2. In a nitrogen-filled glovebox, allyl-
magnesium chloride (0.53 mL, 1.06 mmol) was added to a stirred
orange slurry of 1 (0.420 g, 1.06 mmol) in 100 mL of toluene. A
yellow solution immediately formed. After the mixture was stirred
for 24 h, the solution was evaporated to dryness to yield a pale
yellow powder. This material was treated with 2% 1,4-dioxane in
hexanes (75 mL) and the mixture centrifuged to separate a white
precipitate. The yellow supernatant was decanted, and removal of
solvent under vacuum yielded (C5Me4H)2Sc(η3-C3H5), 2 (0.337 g,
96%), as a yellow powder. Crystals suitable for X-ray analysis were
grown from a concentrated toluene solution of 2 at -35 °C over
(11) Cloke, F. G. N.; Khan, K.; Perutz, R. N. J. Chem. Soc., Chem.
Commun. 1991, 1372–1373.
(12) Arnold, P. L.; Cloke, F. G. N.; Hitchcock, P. B.; Nixon, J. F. J. Am.
Chem. Soc. 1996, 118, 7630–7631.
(13) Clentsmith, G. K. B.; Cloke, F. G. N.; Green, J. C.; Hanks, J.;
Hitchcock, P. B.; Nixon, J. F. Angew. Chem., Int. Ed. 2003, 42, 1038–
1041.
(14) Evans, W. J.; Seibel, C. A.; Ziller, J. W. J. Am. Chem. Soc. 1998,
120, 6745–6752.
1
the course of 24 h. H NMR (500 MHz, benzene-d6): δ 7.10 (m,
(15) Bouwkamp, M. W.; Budzelaar, P. H. M.; Gercama, J.; Morales, I.;
Del, H.; de Wolf, J.; Meetsma, A.; Trojanov, S. I.; Teuben, J. H.;
Hessen, B. J. Am. Chem. Soc. 2005, 127, 14310–14319.
(16) Evans, W. J.; Nyce, G. W.; Forrestal, K. J.; Ziller, J. W. Organome-
tallics 2002, 21, 1050–1055.
(18) Evans, W. J.; Kozimor, S. A.; Ziller, J. W.; Kaltsoyannis, N. J. Am.
Chem. Soc. 2004, 126, 14533–14547.
(19) Evans, W. J.; Johnston, M. A.; Greci, M. A.; Gummersheimer, T. S.;
Ziller, J. W. Polyhedron 2003, 22, 119–126.
(17) http://www.glasscontoursolventsystems.com/.
9
11152 J. AM. CHEM. SOC. VOL. 132, NO. 32, 2010

Synthesis and Analysis of a Scandium Dinitrogen Complex
A R T I C L E S
Table 1. X-ray Data Collection Parameters for (C5Me4H)2ScCl(THF), 1, (C5Me4H)2Sc(η3-C3H5), 2, [(C5Me4H)2Sc][(µ-Ph)BPh3], 3,
[(C5Me4H)2Sc]2(µ-η2:η2-N2), 4, and {[(C5Me4H)2Sc]2(µ-η2:η2-N2)[(C5Me4H)2Sc]2(µ-O)}, 5
complex
1
2
3
4
5
empirical formula
fw
temp (K)
crystal system
space group
a (Å)
C22H34ClOSc
394.90
153(2)
monoclinic
P21/n
8.6644(5)
14.8610(9)
16.4746(10)
90
97.4774(7)
90
2103.3(2)
4
1.247
0.484
C21H31Sc
328.42
153(2)
monoclinic
P21/n
8.7813(8)
14.7244(13)
14.1177(13)
90
92.186(2)
90
1824.1(3)
4
1.196
0.399
0.0282
0.0798
C42H46BSc
606.56
163(2)
C36H52N2Sc2
602.72
98(2)
monoclinic
P21/n
8.4928(9)
10.1010(10)
18.4580(18)
90
90.3390(10)
90
1583.4(3)
2
1.264
0.455
[C36H52N2Sc2][C36H52OSc2]
1193.41
148(2)
monoclinic
Pn
8.8370(14)
21.042(3)
17.909(3)
90
91.485(2)
90
3329.1(9)
2
triclinic
j
P1
11.8363(13)
11.9868(13)
12.4080(13)
100.450(2)
98.128(2)
100.555(2)
1674.0(3)
2
1.203
0.248
0.0517
0.1239
b (Å)
c (Å)
R (deg)
ꢀ (deg)
γ (deg)
volume (Å3)
Z
Fcalcd (Mg/m3)
1.191
0.433
0.0675
0.1647
µ (mm-1
)
R1 [I > 2.0σ(I)]a
wR2 (all data)a
0.0333
0.0913
0.0327
0.0885
a
2
2
Definitions: wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo )2]]1/2, R1 ) ∑||Fo| - |Fc||/∑|Fo|.
1H, CH2CHCH2), 5.93 (s, ∆ν1/2 ) 9 Hz, 2H, C5Me4H), 3.81 (s,
∆ν1/2 ) 102 Hz, 2H, allyl anti CH2), 1.95 (s, 12H, C5Me4H), 1.64
(s, ∆ν1/2 ) 12 Hz, 12H, C5Me4H). 13C NMR (126 MHz, benzene-
d6): δ 157.3 (CH2CHCH2), 121.2 (C5Me4H), 116.6 (C5Me4H), 112.6
(C5Me4H), 70.6 (CH2CHCH2), 13.4 (C5Me4H), 12.3 (C5Me4H). 1H
NMR (500 MHz, toluene-d8): δ 7.0 (m, 1H, CH2CHCH2), 5.88 (s,
∆ν1/2 ) 9 Hz, 2H, C5Me4H), 3.70 (s, ∆ν1/2 ) 98 Hz, 2H, allyl anti
CH2), 1.93 (d, 12H, C5Me4H), 1.62 (s, ∆ν1/2 ) 12 Hz, 12H,
C5Me4H). 1H NMR (500 MHz, toluene-d8, 228 K): δ 7.06 (m, 1H,
CH2CHCH2), 6.07 (s, 1H, C5Me4H), 5.73 (s, 1H, C5Me4H), 3.82
(d, 2H, allyl anti CH2), 2.07 (d, 2H, allyl syn CH2), 1.96 (d, 12H,
grown from a concentrated toluene solution at -35 °C over the
course of 48 h. Isolation of the solvated analogue of 3,
[(C5Me4H)2Sc(THF)2][BPh4], is given in the Supporting Informa-
tion.
[(C5Me4H)2Sc]2(µ-η2:η2-N2), 4. In a nitrogen-filled glovebox,
KC8 (0.032 g, 0.25 mmol) was added to a stirred solution of 3
(0.150 g, 0.25 mmol) in 5 mL of THF. After the reaction mixture
was stirred for 20 min, black and white insoluble materials
(presumably graphite and KBPh4) were removed by centrifugation
and filtration. The green filtrate was stored at -35 °C for 4 d to
afford 4 as a dark red microcrystalline solid (22 mg, 30%). Red
crystals of 4 suitable for X-ray analysis were obtained in an NMR
tube from a concentrated benzene-d6 solution at 25 °C over the
1
C5Me4H), 1.79 (s, 6H, C5Me4H), 1.42 (s, 6H, C5Me4H). H NMR
(500 MHz, toluene-d8, 373 K): δ 7.01 (m, 1H, CH2CHCH2), 5.85
(s, 2H, C5Me4H), 2.84 (d, ∆ν1/2 ) 25.7 Hz, 4H, allyl CH2), 1.92
(s, 12H, C5Me4H), 1.64 (s, 12H, C5Me4H). 13C NMR (126 MHz,
toluene-d8): δ 157.1 (CH2CHCH2), 120.8 (C5Me4H), 116.2
(C5Me4H), 112.3 (C5Me4H), 70.2 (CH2CHCH2), 13.0 (C5Me4H),
11.9 (C5Me4H). 45Sc NMR (145 MHz, benzene-d6): δ 153 (∆ν1/2
) 350 Hz). IR: 3078w, 3062w, 2963m, 2909s, 2860s, 2726w,
1663w, 1555w, 1485m, 1435m, 1382m, 1329w, 1253w, 1176w,
1147w, 1028m, 974w, 834m, 794vs, 702s, 614w, 594w cm-1. Anal.
Calcd for C21H31Sc: C, 76.80; H, 9.51; Sc, 13.69. Found: C, 76.60;
H, 9.45; Sc, 14.02.
1
course of 6 d. H NMR (500 MHz, benzene-d6): δ 6.01 (s, 4H,
C5Me4H), 2.01 (s, 24H, C5Me4H), 2.00 (s, 24H, C5Me4H). 13C NMR
(126 MHz, benzene-d6): δ 119.8 (C5Me4H), 118.4 (C5Me4H), 114.5
(C5Me4H), 12.6 (C5Me4H), 11.9 (C5Me4H). 15N NMR (61 MHz,
benzene-d6, referenced to MeNO2): δ 385. 45Sc NMR (145 MHz,
benzene-d6): δ 143 (∆ν1/2 ) 2700 Hz). IR: 2971m, 2908s, 2861s,
2724w, 1746w, 1641w, 1485w, 1444m, 1383m, 1370m, 1332w,
1149w, 1110w, 1020w, 973w, 825vs, 773m, 700w, 619m cm-1
.
UV-vis (benzene, nm (ꢀ)): 592 (60), 447 sh (200). Anal. Calcd
for C36H52N2Sc2: C, 71.74; H, 8.70; N, 4.65. Found: C, 71.33; H,
9.15; N, 4.37.
[(C5Me4H)2Sc][(µ-Ph)BPh3], 3. In an argon-filled glovebox free
of coordinating solvents, [HNEt3][BPh4] (0.185 g, 0.435 mmol) was
added to a stirred yellow solution of 2 (0.119 g, 0.362 mmol) in
20 mL of toluene. After the mixture was stirred for 3 h, the yellow
solution was filtered to remove insoluble yellow-white material.
Evaporation of the solution yielded an oily product that crystallized
after at least 2 h under vacuum (10-3 Torr). The thoroughly dried
material was washed with hexane to give a yellow crystalline solid.
The hexane washing cycle of this yellow crystalline material was
repeated until the supernatant was colorless. This yielded 3 as a
X-ray Crystallographic Data. Information on X-ray data
collection, structure determination, and refinement for 1-5 is given
in Table 1. Details are given in the Supporting Information.
Computational Details. The structure of 4 was initially opti-
mized using the TPSSH20 hybrid meta-GGA functional and split
valence basis sets with polarization functions on non-hydrogen
atoms (SV(P)).21 TPSSH was chosen due to its established
performance for transition metal22,23 and lanthanide compounds.24
Fine quadrature grids (size m4)25 were used throughout except for
the final TZVP optimization. Vibrational frequencies were computed
at the TPSSH/SV(P) level26 and scaled by a factor of 0.95 to
1
yellow crystalline powder (0.165 g, 75%). H NMR (500 MHz,
benzene-d6): δ 8.02 (m, 8H, C6H5), 7.21 (m, 8H, C6H5), 7.12 (m,
4H, C6H5), 5.17 (s, 2H, C5Me4H), 1.49 (s, 12H, C5Me4H), 1.35 (s,
12H, C5Me4H). 13C NMR (126 MHz, benzene-d6): δ 136.2 (C6H5),
134.1 (C6H5), 131.9 (C5Me4H), 128.9 (C5Me4H), 128.8 (C6H5),
127.7 (C6H5), 125.7 (C6H5), 124.2 (C6H5), 120.4 (C5Me4H), 13.5
(C5Me4H), 12.2 (C5Me4H). 45Sc NMR (145 MHz, benzene-d6): δ
190 (∆ν1/2 ) 7800 Hz). IR: 3122w, 3088w, 3051m, 3040m, 2997m,
2983m, 2911m, 2861m, 2732w, 1933w, 1873w, 1807w, 1759w,
1581m, 1568m, 1479s, 1426s, 1385s, 1376m, 1328w, 1286w,
1267w, 1240m, 1184m, 1157m, 1150m, 1066m, 1031m, 1022s,
978w, 910w, 895m, 837s, 824s, 764m, 744vs, 730vs, 705vs, 624m,
605vs cm-1. Anal. Calcd for C42H46BSc: C, 83.16; H, 7.64. Found:
C, 83.00; H, 7.79. Single crystals suitable for X-ray analysis were
(20) Staroverov, V. N.; Scuseria, G. E.; Tao, J.; Perdew, J. P. J. Chem.
Phys. 2003, 119, 12129–12137.
(21) Scha¨fer, A.; Horn, H.; Ahlrichs, R. J. Chem. Phys. 1992, 97, 2571–
2577.
(22) Furche, F.; Perdew, J. P. J. Chem. Phys. 2006, 124, 044103-27.
(23) Waller, M. P.; Braun, H.; Hojdis, N.; Bu¨hl, M. J. Chem. Theory
Comput. 2007, 3, 2234–2242.
(24) Evans, W. J.; Fang, M.; Zucchi, G.; Furche, F.; Ziller, J. W.; Hoekstra,
R. M.; Zink, J. I. J. Am. Chem. Soc. 2009, 131, 11195–11202.
(25) Treutler, O.; Ahlrichs, R. J. Chem. Phys. 1995, 102, 346–354.
(26) Deglmann, P.; Furche, F.; Ahlrichs, R. Chem. Phys. Lett. 2002, 362,
511–518.
9
J. AM. CHEM. SOC. VOL. 132, NO. 32, 2010 11153

A R T I C L E S
Demir et al.
account for anharmonicity and basis set incompleteness; this factor
was chosen to approximately fit the computed vibrational frequency
of free N2 to the gas-phase value27 of 2359 cm-1. All structures
were found to be minima. Natural population analyses28 and plots
were also obtained at the TPSSH/SV(P) level; the contour values
were 0.08 for molecular orbital plots. The structural parameters
reported in the text are the result of reoptimization using larger
triple-zeta valence basis sets with two sets of polarization functions
(def2-TZVP)29 and fine quintature grids (size m5). The differences
between the SV(P) and the TZVP structures were found to be small,
typically amounting to 0.01 Å or less in bond length. The electronic
stability of the ground state was tested by performing open-shell
calculations. No spin symmetry breaking was found. The triplet
excited state was computed to be 32 kcal/mol above the singlet
ground state. All computations were performed using the TUR-
BOMOLE program package.30
Results and Discussion
Syntheses. The synthetic sequence used to obtain
[(C5Me4H)2Sc][(µ-Ph)BPh3], 3, shown in eqs 2-4, is similar
to the route used to make [(C5Me4R)2M][(µ-Ph)2BPh2] com-
plexes (M ) Y, lanthanides; R ) Me, H)5,14 and has many
parallelsinearlierstudiesofscandiummetallocenechemistry.2,3,31,32
Individual steps in the synthetic procedure are described in the
following paragraphs.
Figure 2. Thermal ellipsoid plot of (C5Me4H)2ScCl(THF), 1, drawn at the
50% probability level. Hydrogen atoms are omitted for clarity.
Figure 3. Thermal ellipsoid plot of (C5Me4H)2Sc(η3-C3H5), 2, drawn at
the 50% probability level. Hydrogen atoms are omitted for clarity.
(C5Me4H)2ScCl(THF), 1. Two equivalents of KC5Me4H
reacted with ScCl3 in THF to form (C5Me4H)2ScCl(THF), 1,
demonstrated by the lithium ansa complex, {Me2Si[C5H2-2,4-
(CHMe2)2]2}Sc(µ-Cl)2Li(THF)2,31 but this is not observed with
1, which has a larger (ring centroid)-Sc-(ring centroid) angle
and larger alkali metal. Single crystals of 1 can be obtained
from THF, Figure 2, and the structural details are described
below. Unsolvated (C5Me4H)2ScCl can be obtained from 1 by
sublimation in a procedure analogous to the synthesis of
(C5Me5)2ScCl.3
eq 2, in
a reaction similar to the preparation of
(C5Me5)2ScCl(THF) from ScCl3(THF)3 with LiC5Me5 in xylene
at reflux.3 These complexes can be obtained without any
observed complications of forming an “ate” salt, i.e.
(C5Me4H)2ScCl2K(THF)x, as is typical for yttrium and the
lanthanides.33,34 Scandium metallocene ate salts can form as
(C5Me4H)2Sc(η3-C3H5), 2. As shown in eq 3, complex 1
reacted with allylmagnesium chloride to form (C5Me4H)2Sc(η3-
(27) Huber, K. P.; Herzberg, G. Constants of Diatomic Molecules (data
prepared by Gallagher, J. W., Johnson, R. D., III). In NIST Chemistry
WebBook, NIST Standard Reference Database No. 69; Linstrom, P. J.,
Mallard, W. G., Eds.; National Institute of Standards and Technology:
Gaithersburg MD, 2009; http://webbook.nist.gov, (retrieved December
6, 2009).
1
C3H5), 2, which was characterized by H, 13C, and 45Sc NMR
spectroscopy as well as by X-ray diffraction, Figure 3. An
analogous reaction was used to make {Me2Si[C5H2-2,4-
(CHMe2)2]2}Sc(η3-C3H5),31 whereas (C5Me5)2Sc(C3H5)3 and
{Me2Si(C5H3-3-CMe3)2}Sc(η3-C3H5)32 were made from an
allene and the corresponding metallocene hydrides. Like other
scandium,yttrium,andlanthanidemetalloceneallylcomplexes,32,35
2 displays fluxional behavior in solution. A single set of
(28) Reed, A. E.; Weinstock, R. B.; Weinhold, F. J. Chem. Phys. 1985,
83, 735–746.
(29) Weigend, F.; Ahlrichs, R. Phys. Chem. Chem. Phys. 2005, 18, 3297–
3305.
(30) TURBOMOLE, V6.0; TURBOMOLE GmbH: Karlsruhe, 2008; http://
www.turbomole.com.
(31) Yoder, J. C.; Day, M. W.; Bercaw, J. E. Organometallics 1998, 17,
4946–4958.
(34) Evans, W. J.; Keyer, R. A.; Ziller, J. W. Organometallics 1993, 12,
2618–2633.
(32) Abrams, M. B.; Yoder, J. C.; Loeber, C.; Day, M. W.; Bercaw, J. E.
Organometallics 1999, 18, 1389–1401.
(35) Evans, W. J.; Kozimor, S. A.; Brady, J. C.; Davis, B. L.; Nyce, G. W.;
Seibel, C. A.; Ziller, J. W.; Doedens, R. J. Organometallics 2005, 24,
2269–2278.
(33) Evans, W. J.; Boyle, T. J.; Ziller, J. W. Inorg. Chem. 1992, 31, 1120–
1122.
9
11154 J. AM. CHEM. SOC. VOL. 132, NO. 32, 2010

Synthesis and Analysis of a Scandium Dinitrogen Complex
A R T I C L E S
Figure 5. Thermal ellipsoid plot of [(C5Me4H)2Sc]2(µ-η2:η2-N2), 4, drawn
at the 50% probability level. Hydrogen atoms are omitted for clarity.
Figure 4. Thermal ellipsoid plot of [(C5Me4H)2Sc][(µ-Ph)BPh3], 3, drawn
at the 50% probability level. Hydrogen atoms are omitted for clarity.
Table 2. 45Sc NMR Chemical Shifts and Line Widths at Half-Height
in Scandium Metallocenes
cyclopentadienyl resonances is observed for 2 at room temper-
ature in toluene-d8, but these split at low temperature. The
coalescence temperature for the methyl resonances, 268 K,
fits well with the 318, 283, and 257 K analogues for
(C5Me5)2Y(C3H5),35 (C5Me5)2Lu(C3H5),35 and (C5Me5)2-
Sc(C3H5),3 respectively. This series shows a good correlation
with steric crowding based on the size of the metal and the
cyclopentadienyl ligand.
complex
chemical shift (ppm) line width at half-height (Hz)
(C5H5)2ScCl
-9.5
13.5
55
85
280
400
(C5H5)3Sc
(C5Me4H)2ScCl(THF)
(C5H5)2ScBH4
67.5
143
153
190
250
2700
350
[(C5Me4H)2Sc]2(µ-η2:η2-N2)
(C5Me4H)2Sc(η3-C3H5)
[(C5Me4H)2Sc][(µ-Ph)BPh3]
7800
[(C5Me4H)2Sc][(µ-Ph)BPh3], 3. Complex 2 reacted with
[HNEt3][BPh4] to form the tetraphenylborate salt, [(C5Me4H)2Sc]-
[(µ-Ph)BPh3], 3, eq 4. This synthesis is similar to that of
[(C5Me5)2Sc][(µ-η2:η1-Ph)BPh3] from the reaction of
(C5Me5)2ScMe with [PhNMe2H][BPh4] in toluene (67% yield).15
Both complex 3 and the (C5Me5)- analogue have very limited
solubility in arene solvents. Single crystals of 3 suitable for
X-ray diffraction were obtained from toluene and gave the
structure shown in Figure 4. Complex 3 is not thermally stable:
yellow solutions of 3 in toluene, as well as the isolated solid,
readily go colorless at room temperature. Hence, samples were
routinely stored at -35 °C. In THF, complex 3 converts to the
solvated complex [(C5Me4H)2Sc(THF)2][BPh4], which was
identified by X-ray crystallography in THF (see Supporting
Information).
complexes,36-40 relatively few data are available on scandium
metallocenes. Hence, reported shifts function mainly as finger-
print spectra that show purity. McGlinchey showed as early as
1985 that there was considerable variation in 45Sc NMR shifts
for simple cyclopentadienyl metallocenes as a function of
composition.36 Table 2 shows those data as well as similar
results for the tetramethylcyclopentadienyl complexes in this
study.
The 15N NMR shift of 4 is lower than those observed for the
[(C5Me4H)2Ln]2(µ-η2:η2-N2) complexes (ppm): Ln ) Lu, 521;5
La, 495;7 Y, 468;41 Sc, 385 (complex 4). The Sc-Y-La values
show an increase in shift as the principal quantum number
increases, but the difference between Sc and Y is much larger
than that between Y and La. The shifts do not correlate with
metal size since Lu is slightly smaller than Y. There are also
no correlations in this series of complexes with the experimen-
tally determined N-N bond distances, which are indistinguish-
able (Å): Ln ) Lu, 1.243(12);5 La, 1.233(5) Å;7 Y, 1.252(5)
Å;41 Sc, 1.239(3) (see below).
[(C5Me4H)2Sc]2(µ-η2:η2-N2), 4. Following the reductive method
shown in eq 1,4,5 complex 3 was treated with KC8 in THF under
dinitrogen to generate the scandium dinitrogen complex
[(C5Me4H)2Sc]2(µ-η2:η2-N2), 4, eq 5, Figure 5.
{[(C5Me4H)2Sc]2(µ-η2:η2-N2)[(C5Me4H)2Sc]2(µ-O)}, 5. During
one attempt to make the 15N analogue of 4, golden crystals of
a decomposition product were isolated. X-ray crystallography
revealed this to be {[(C5Me4H)2Sc]2(µ-η2:η2-N2)[(C5Me4H)2Sc]2-
(36) Bougeard, P.; Mancini, M.; Sayer, B. G.; McGlinchey, M. J. Inorg.
Chem. 1985, 24, 93–95.
Short, 20 min reaction times are favored for this procedure, as
other byproducts begin to appear if the reaction mixture is in
solution for longer time periods. Crystallization from THF was
also found to be preferable to isolation from toluene, since 4 is
not very soluble in toluene. Solutions of 4 in THF are green,
and benzene solutions are yellow-green, but the complex is red
in the solid state.
(37) Kirakosyan, G. A.; Tarasov, V. P.; Buslaev, Y. A. Magn. Reson. Chem.
1989, 27, 103–111.
(38) Neculai, A. M.; Roesky, H. W.; Neculai, D.; Magull, J. Organome-
tallics 2001, 20, 5501–5503.
(39) Neculai, A. M.; Neculai, D.; Roesky, H. W.; Magull, J.; Baldus, M.;
Andronesi, O.; Jansen, M. Organometallics 2002, 21, 2590–2592.
(40) Neculai, A. M.; Cummins, C. C.; Neculai, D.; Roesky, H. W.;
Bunkoczi, G.; Walfort, B.; Stalke, D. Inorg. Chem. 2003, 42, 8803–
8810.
Both 45Sc NMR and 15N NMR data were obtainable on 4.
Although 45Sc NMR data have been reported for a variety of
(41) Lorenz, S. E.; Schmiege, B. M.; Lee, D. S.; Ziller, J. W.; Evans, W. J.
Inorg. Chem. 2010, 49, 6655–6663.
9
J. AM. CHEM. SOC. VOL. 132, NO. 32, 2010 11155

A R T I C L E S
Demir et al.
Sc3+ metal center is 0.107 Å smaller than the Lu3+ metal center
according to eight-coordinate Shannon ionic radii.46 The smaller
size of the (C5Me4H)- ligands in 3 compared to the (C5Me5)-
ligands in 11 apparently allows a single phenyl carbon to get
in closer to the metal cation and make a Sc-C connection 0.1
Å shorter than that in 11. However, these structures may also
be influenced by crystal packing effects, as was found with the
tris-ring complexes, (C5Me5)Ln[(η6-Ph)2BPh2] (Ln ) Eu, Sm,
Yb), where the pyramidal Eu and Sm complexes differed from
the trigonal planar Yb analogue.47
[(C5Me4H)2Sc]2(µ-η2:η2-N2), 4. The scandium dinitrogen
complex 4 differs from most of the [Z2(THF)xLn]2(µ-η2:η2-N2)
lanthanide and yttrium complexes previously characterized by
t
X-ray crystallography (Z ) N(SiMe3)2, OC6H3 Bu2, C5Me5,
C5Me4H, x ) 0-2)4,5,7,10,24,48,49 in that it is unsolvated. The
only other unsolvated examples are [(C5Me5)2Sm]2(µ-η2:η2-
N2),50 which had an unusually short 1.088(12) Å N-N distance,
[(C5Me5)2Tm]2(µ-η2:η2-N2)8 and {[C5H3(SiMe3)2]2Dy}2(µ-η2:η2-
N2),9 for which good crystallographic data were not obtained,
and [(C5H2tBu3)2Nd]2(µ-η2:η2-N2)6 and {[C5H3(SiMe3)2]2Tm}2(µ-
η2:η2-N2),8 which had 1.23 and 1.259(4) Å N-N distances,
respectively. The structure of 4 is also unusual in that the four
(C5Me4H)- ring centroids define a square plane rather than a
tetrahedron. Hence, the dihedral angle between the planes
defined by the two ring centroids and Sc for each metallocene
is 0° rather than the 90° common for bimetallic metallocene
complexes with small bridging ligands such as [(C5Me5)2Sm]2(µ-
η2:η2-N2),50 [(C5Me5)2Sm]2(µ-H)2,51 and [(C5Me5)2Sm]2(µ-O).42
The C-H components of the (C5Me4H)- rings are arranged such
that they are staggered within a metallocene, with one C-H
over the (N2)2- ligand in the open part of the wedge and the
other where the two rings have their closest approach. The
dihedral angle between the two planes defined by the ring carbon
attached to H, the ring centroid, and Sc is 177.2°.
Despite this unconventional arrangement of ancillary ligands,
theSc2(µ-η2:η2-N2)unitin4isplanar,asitisinthe[Z2(THF)xLn]2(µ-
η2:η2-N2) complexes. The 1.239(3) Å N-N distance is in the
broad 1.233(5)-1.305(6) Å range found for the lanthanide and
yttrium examples and is indistinguishable from those of the
[(C5Me4H)2Ln(THF)]2(µ-η2:η2-N2) complexes (Ln ) Lu,
1.243(12) Å;5 La, 1.233(5) Å;7 Y, 1.252(5) Å41). The 2.216(1)
and 2.220(1) Å Sc-N(N2) distances are about 0.1 Å shorter
than those in {[(Me3Si)2N]2(THF)Y}2(µ-η2:η2-N2), 12,24 and
[(C5Me4H)2Lu(THF)]2(µ-η2:η2-N2), 13.5 This is consistent with
the smaller size of scandium. Comparisons of the metrical
parameters of 4, 12, and 13 are presented in Table 6.
Figure 6. Thermal ellipsoid plot of {[(C5Me4H)2Sc]2(µ-η2:η2-N2)-
[(C5Me4H)2Sc]2(µ-O)}, 5, drawn at the 50% probability level. Hydrogen
atoms are omitted for clarity.
(µ-O)}, 5, Figure 6. Evidently, the oxide, [(C5Me4H)2Sc]2(µ-
O), a common type of decomposition product with f element
metallocenes,42,43 formed and co-crystallized with 4 into a single
crystal of 5. This co-crystallization may be facilitated by the
fact that 4 and the oxide both have compact dianionic ligands
coordinated to the two metallocenes. Although 5 was isolated
in only a single case, it was included here to show that oxides
and reduced dinitrogen complexes can co-crystallize.
Structural Studies. (C5Me4H)2ScCl(THF), 1, and (C5Me4H)2-
Sc(η3-C3H5), 2. The structures of 1 and 2 are not unusual compared
to analogues when the differences in ligands and metals are taken
into account. This is shown for 1 in Table 3, where its data are
compared to those of (C5Me4H)(C5H4CH2CH2NMe2)ScCl, 6,44 and
(C5Me5)2YCl(THF), 7.45 The structure of 2 is compared with the
scandium ansa complex, rac-Me2Si[η5-C5H2-2,4-(CHMe2)2]2Sc(η3-
C3H5), 8,32 and the yttrium analogue, (C5Me4H)2Y(η3-C3H5), 9,41
in Table 4.
[(C5Me4H)2Sc][(µ-Ph)BPh3], 3. The structure of 3 differs from
lanthanide and actinide analogues14,16 exemplified by
[(C5Me4H)2Lu][(µ-η2:η1-Ph)2BPh2], 10, Figure 1a, in that the
anion in 3 interacts with the cation through one, not two phenyl
groups. This [(µ-Ph)BPh3]- type of attachment had previously
been observed in the (C5Me5)- scandium analogue,
[(C5Me5)2Sc][(µ-η2:η1-Ph)BPh3], 11, which had Sc-C(phenyl)
distances of 2.679(2) and 2.864(2) Å. In 3, the disparity in Sc-C
distances of the two closest carbons of the single phenyl bridge
is even greater: 2.568(2) and 2.889(2) Å, such that this structure
is approaching an [(µ-η1:η1-Ph)BPh3]- orientation. Comparisons
of the metrical parameters of 3, 10, and 11 are presented in
Table 5.
Detailed comparisons of the structure of 4 with the analogous
component in {[(C5Me4H)2Sc]2(µ-η2:η2-N2)[(C5Me4H)2Sc]2(µ-
O)}, 5, are not possible since the crystal quality of 5 provided
connectivity only. The structure of the [(C5Me4H)2Sc]2(µ-η2:
η2-N2) component of 5 is similar to that of 4 in that the dihedral
angle between the planes defined by the two ring centroids and
Sc for each metallocene is 5.2°. The [(C5Me4H)2Sc]2(µ-O)
The fact that only one phenyl substituent is oriented toward
the metal center in 3 is reasonable compared to 10 since the
(46) Shannon, R. D. Acta Crystallogr. 1976, A32, 751–767.
(47) Evans, W. J.; Walensky, J. R.; Furche, F.; DiPasquale, A. G.;
Rheingold, A. L. Organometallics 2009, 28, 6073–6078.
(48) Evans, W. J.; Lee, D. S.; Ziller, J. W. J. Am. Chem. Soc. 2004, 126,
454–455.
(42) Evans, W. J.; Grate, J. W.; Bloom, I.; Hunter, W. E.; Atwood, J. L.
J. Am. Chem. Soc. 1985, 107, 405–409.
(43) Evans, W. J.; Davis, B. L.; Nyce, G. W.; Perotti, J. M.; Ziller, J. W.
J. Organomet. Chem. 2003, 677, 89–95.
(49) Evans, W. J.; Rego, D. B.; Ziller, J. W. Inorg. Chem. 2006, 45, 10790–
10798.
(44) Schumann, H.; Erbstein, F.; Herrmann, K.; Demtschuk, J.; Weimann,
R. J. J. Organomet. Chem. 1998, 562, 255–262.
(50) Evans, W. J.; Ulibarri, T. A.; Ziller, J. W. J. Am. Chem. Soc. 1988,
110, 6877.
(45) Evans, W. J.; Grate, J. W.; Levan, K. R.; Bloom, I.; Peterson, T. T.;
Doedens, R. J.; Zhang, H.; Atwood, J. L. Inorg. Chem. 1986, 25, 3614–
3619.
(51) Evans, W. J.; Bloom, I.; Hunter, W. E.; Atwood, J. L. J. Am. Chem.
Soc. 1983, 105, 1401–1403.
9
11156 J. AM. CHEM. SOC. VOL. 132, NO. 32, 2010

Synthesis and Analysis of a Scandium Dinitrogen Complex
A R T I C L E S
Table 3. Selected Bond Distances (Å) and Angles (deg) for (C5Me4H)2ScCl(THF), 1, (C5Me4H)(C5H4CH2CH2NMe2)ScCl, 6,44 and
(C5Me5)2YCl(THF), 7 45
1
6
7
M
Sc
133.0
108.4, 106.4
2.222, 2.219
2.4332(4)
Sc
132.43(7)
108.12(6), 107.30(6)
2.193(2), 2.199(2)
2.4574(12)
Y
(Cnt)-M-(Cnt)a
(Cnt)-M-Cl
M-(Cnt)
M-Cl
136.2(4), 136.6(4)
106.0(3), 106.0(3), 105.4(3), 105.5(3)
2.382(1), 2.379(1), 2.373(1), 2.388(1)
2.579(3), 2.577(3)
M-O
M-N
2.2557(10)
2.410(7), 2.410(7)
2.396(3)
a Cnt ) centroid of the cyclopentadienyl ring.
Table 4. Selected Bond Distances (Å) and Angles (deg) for
(C5Me4H)2Sc(η3-C3H5), 2, rac-Me2Si[η5-C5H2-2,4-(CHMe2)2]2-
Sc(η3-C3H5), 8,32 and (C5Me4H)2Y(η3-C3H5), 9 41
Table 6. Selected Bond Distances (Å) and Angles (deg) for
[(C5Me4H)2Sc]2(µ-η2:η2-N2), 4, {[(Me3Si)2N]2(THF)Y}2(µ-η2:η2-N2),
12,24 and [(C5Me4H)2Lu(THF)]2(µ-η2:η2-N2), 13 5
2
8
9
4
12
13
M
Sc
Sc
Y
M
Sc
131.0
2.195
2.196
2.216(1)
2.220(1)
1.239(3)
Y
Lu
129.9
2.369
2.385
2.290(6)
2.311(6)
1.243(12)
(Cnt)-M-(Cnt)
M-(Cnt(1))
M-(Cnt(2))
134.6
2.204
2.190
128.5(2)
2.188(1)
2.189(1)
134.5, 134.7
2.347, 2.348
2.334, 2.341
2.585(3), 2.590(3)
2.592(3), 2.594(3)
2.603(3), 2.603(3)
Cnt1-M(1)-Cnt2
M(1)-Cnt1
M(1)-Cnt2
M(1)-N(1)
M(1)-N(1′)
N(1)-N(1′)
117.44(6)
2.2443(15)
2.2640(15)
2.2958(17)
2.3170(16)
1.268(3)
M-C(terminal allyl) 2.4702(11) 2.487(3)
M-C(terminal allyl) 2.4774(11) 2.469(3)
2.465(5), 2.436(7)b
a
M-C(internal allyl) 2.4618(11)
a Sc-centroid3A
b Sc-centroid3B (C13-C14B-C15, minor rotamer).
(C13-C14A-C15,
major
rotamer).
was calculated for [(C5Me4H)2Sc]2(µ-η2:η2-O2) that is clearly
different from the distances observed in 4 and similar to the
component of 5 differs in that the dihedral angle between the
planes defined by the two ring centroids and Sc for each
metallocene is 83.3° rather than 0°. This gives a tetrahedral
arrangement of rings more common for bimetallic metallocenes.
The possibility that bimetallic (N2)2- and (O)2- complexes could
be structurally similar and co-crystallize to give unusual metrical
parameters a` la bond stretch isomerism52,53 is generally a
concern in these complexes. In the case of 5, the two units have
very different dihedral angles between the planes defined by
the two ring centroids and Sc for each metallocene and do not
disorder.
Theoretical Studies. The experimentally determined structure
of 4 was evaluated with density functional theory calculations
using the Tao-Perdew-Staroverov-Scuseria hybrid (TPSSH)
functional.20 The calculations were similar to those done on
{[(Me3Si)2N]2(THF)Y}2(µ-η2:η2-N2), 12.24 The optimized cal-
culated N-N bond distance of 1.226 Å for 4 agrees well with
the crystallographic value of 1.239(3) Å, as does the calculated
2.223 Å Sc-N bond (vs 2.216(1) and 2.220(1) Å). The DFT
results are consistent with an N-N bond order of 2 in 4.
To check against the possibility that 4 was the peroxide
complex [(C5Me4H)2Sc]2(µ-η2:η2-O2), calculations on this spe-
cies were also carried out. An O-O bond distance of 1.51 Å
experimental values of 1.543(4) Å in Yb2[N(SiMe3)2]4(µ-η2:η2-
54
O2)(THF)2
and 1.517(7)-1.603(8) Å
in [Yb2(µ-η2:η2-
O2)L2Cl2](ClO4)2, where L ) 2,14-dimethyl-3,6,10,13,19-
pentaazabicyclo[13.3.1]nonadeca-1(19),2,13,15,17-pentaene.55
Inspection of the computed Kohn-Sham molecular orbitals
explains the observed bond lengths. The dinitrogen-Sc bonding
in 4 results from a strong interaction between a scandium 3d
orbital and the antibonding π* orbital of N2 in the ScN2Sc plane,
Figure 7. The computed natural population analysis (NPA) for
N2 gives a charge of -0.75 and a scandium 3d population of
1.57, along with the fairly short observed Sc-N bond distance
of 2.223 Å. This indicates the presence of a polar covalent
interaction corresponding to a two-electron, four-center bond
between two (C5Me4H)2Sc fragments and N2, each with a nearly
neutral actual charge. The initial reduction of the Nt N triple
bond to a formal NdN double bond in 4 is possible because
the occupied 3d orbital of scandium is high enough in energy
and large enough to form a dπ-π* back-bond. This is the main
basis of the bonding since the occupied bonding σ and π orbitals
of N2 are too low in energy to interact with the metal atoms.
The lowest unoccupied molecular orbital of 4 is the essentially
unperturbed π* orbital of N2 perpendicular to the ScN2Sc plane,
Figure 7.
Table 5. Selected Bond Distances (Å) and Angles (deg) for [(C5Me4H)2Sc][(µ-Ph)BPh3], 3, [(C5Me4H)2Lu][(µ-η2:η1-Ph)2BPh2], 10,5 and
[(C5Me5)2Sc][(µ-η2:η1-Ph)BPh3], 1115
3
10
11
M
Sc
Lu
Sc
M-(Cnt(1))
2.122
2.137
3.895(2), 4.263(2)
2.889(2), 3.382(3)
2.568(2)
2.302
2.301
2.668(2), 2.800(2)
2.947(2), 3.237(2)
3.952(2), 4.379(2)
133.4
102.9, 114.9
100.6, 102.3
86.4, 111.9
103.6, 113.7
99.4, 100.6
2.1516(10)
2.1587(9)
4.048(2), 4.740
2.864(2), 3.788(2)
2.679(2)
M-(Cnt(2))
M-C(o-phenyl)
M-C(m-phenyl)
M-C(p-phenyl)
Cnt(1)-M-Cnt(2)
Cnt(1)-M-C(o-phenyl)
Cnt(1)-M-C(m-phenyl)
Cnt(1)-M-C(p-phenyl)
Cnt(2)-M-C(o-phenyl)
Cnt(2)-M-C(m-phenyl)
Cnt(2)-M-C(p-phenyl)
139.4
140.94
84.8, 91.0
96.6, 107.5
114.3
134.9, 126.0
120.9, 110.2
105.9
125.0, 120.3
115.5, 108.4
105.0
93.4, 96.2
100.8, 108.7
113.3
89.6, 113.1
9
J. AM. CHEM. SOC. VOL. 132, NO. 32, 2010 11157

A R T I C L E S
Demir et al.
appears that unfavorable interactions between the rings prevent
the model from moving them completely to square planar and
the global minimum. In support of this, a calculation with
(C5H5)- rings starting in a tetrahedral conformation ended with
the rings square planar in the lowest energy structure. In
summary, the calculations support the square planar arrangement
of rings found in 4 and 5 to be the lowest in energy.
Conclusion
A reduced dinitrogen complex of the smallest transition metal,
scandium, can be obtained by using the tetramethylcyclopen-
tadienyl group as the ancillary ligand. The necessary scandium
metallocene precursors (C5Me4H)2ScCl(THF), 1, (C5Me4H)2Sc-
(η3-C3H5), 2, and [(C5Me4H)2Sc][(µ-Ph)BPh3], 3, can be syn-
thesized in a manner similar to those of the larger lanthanides.
The reductive method, in which a trivalent salt is combined
with an alkali metal that was successful with yttrium and the
lanthanides in reducing dinitrogen, also applies to scandium and
provides [(C5Me4H)2Sc]2(µ-η2:η2-N2), 4, from 3. Complex 4 has
the M2(µ-η2:η2-N2) coordination mode observed with larger
metals and in solvated complexes and has an N-N bond
distance consistent with (NdN)2-. Density functional theory
shows how this moiety is stabilized by scandium via polar
covalent bonding.
Figure 7. Simplified molecular orbital scheme of [(C5Me4H)2Sc]2(µ-η2:
η2-N2), 4.
The orientation of the four cyclopentadienyl rings in 4 was
also probed by DFT. The initial calculations gave a structure
with a square planar arrangement of the four ring centroids, as
was found experimentally. Since it was possible that this was a
local minimum obtained because the starting point was the
experimental coordinates for 4, a calculation starting with
the rings in a tetrahedral arrangement was also carried out. As
the energy in this calculation was minimized, the rings began
to rotate from tetrahedral to square planar. However, a minimum
was reached when the dihedral angle between the planes defined
by the two C5Me4H ring centroid planes and Sc for each
metallocene unit was 54°. Since the energy of this structure is
2.7 kcal/mol higher than that with the square planar rings, it
Acknowledgment. We thank the National Science Foundation
for support of this research and the University of Cologne and the
Fonds der Chemischen Industrie for support for (S.D.). We also
thank Dr. Philip R. Dennison for help with the 45Sc and 15N NMR
experiments.
Supporting Information Available: X-ray data collection,
structure solution, and refinement (PDF); X-ray diffraction
details for compounds 1-5 (CIF; also deposited as CCDC Nos.
778246, 778247, 778248, 778250, and 778251). This material
is available free of charge via the Internet at http://pubs.acs.org.
(52) Parkin, G. Acc. Chem. Res. 1992, 25, 455–460.
(53) Labinger, J. A. C. R. Chim. 2002, 5, 235–244.
(54) Niemeyer, M. Z. Anorg. Allg. Chem. 2002, 628, 647–657.
(55) Patroniak, V.; Kubicki, M.; Mondry, A.; Lisowski, J.; Radecka-
Paryzek, W. Dalton Trans. 2004, 3295–3304.
JA102681W
9
11158 J. AM. CHEM. SOC. VOL. 132, NO. 32, 2010