Reduction of carbodiimides by samarium(II) bis(trimethylsilyl)amides - Formation of oxalamidinates and amidinates through C-C coupling or C-H activation

Article abstract of DOI:10.1021/ic701497c

The reaction of [Sm{N(SiMe₃)₂}₂(THF) ₂] (THF = tetrahydrofuran) with carbodiimides RN=C=NR (R = Cy, C ₆H₃-2,6-ⁱPr₂) led to the formation of dinuclear Sm^III complexes via differing C-C coupling processes. For R = Cy, the product [{(Me₃Si)₂N}₂Sm(μ- C₂N₄Cy₄)Sm{N(SiMe₃) ₂}₂] (1) has an oxalamidinate [C₂N ₄Cy₄]^2- ligand resulting from coupling at the central C atoms of two CyNCNCy moieties. In contrast, for R = C ₆H₃-2,6-ⁱPr₂, H transfer and an unusual coupling of two ⁱPr methine C atoms resulted in a linked formamidinate complex, [{(Me₃Si)₂N}₂Sm{μ- (RNC(H)N(Ar-Ar)NC(H)NR)}Sm{N(SiMe₃)₂}₂] (2) (Ar-Ar = C₆H₃-2-ⁱPr-6-C(CH₃) ₂C(CH₃)₂-6′-C₆H ₃-2′-ⁱPr). Analogous reactions of RN=C=NR (R = Cy, C₆H₃-2,6-ⁱPr₂) with the Sm ^II "ate" complex [Sm{N(SiMe₂)₃Na] gave 1 for R = Cy, but a novel C-substituted amidinate complex, [(THF)Na{N(R)C(NR)CH₂Si(Me₂)N(SiMe₃)} Sm{N(SiMe₃)₂}₂] (3), for R = C ₆H₃-2,6-ⁱPr₂, via γ C-H activation of a N(SiMe₃)₂ ligand.

Full text of DOI:10.1021/ic701497c

Inorg. Chem. 2007, 46, 10022−10030
Reduction of Carbodiimides by Samarium(II)
Bis(trimethylsilyl)amides Formation of Oxalamidinates and
Amidinates through C C Coupling or C H Activation
s
−
−
Glen B. Deacon, Craig M. Forsyth, Peter C. Junk,* and Jun Wang
School of Chemistry, Monash UniVersity, P.O. Box 23, Victoria, 3800 Australia
Received July 26, 2007
The reaction of [Sm
2,6-iPr2) led to the formation of dinuclear SmIII complexes via differing C
product [ (Me3Si)2N 2Sm( -C2N4Cy4)Sm N(SiMe3)2
{
N(SiMe3)2
}
2(THF)2] (THF
)
tetrahydrofuran) with carbodiimides RN
d
C
d
NR (R
)
Cy, C6H3-
Cy, the
−C coupling processes. For R
)
-
{
}
µ
{
}
2] (1) has an oxalamidinate [C2N4Cy4]2 ligand resulting from
coupling at the central C atoms of two CyNCNCy moieties. In contrast, for R
unusual coupling of two Pr methine C atoms resulted in a linked formamidinate complex, [
)
C6H3-2,6-iPr2, H transfer and an
(Me3Si)2N 2Sm{µ
-C6H3-2
-iPr). Analogous
N(SiMe2)3Na] gave 1 for R
N(R)C(NR)CH2Si(Me2)N(SiMe3) Sm N(SiMe3)2 2] (3),
H activation of a N(SiMe3)2 ligand.
i
{
}
-
(RNC(H)N(Ar
reactions of RN
−
Ar)NC(H)NR)
}
Sm
)
{
N(SiMe3)2
}
2] (2) (Ar
−
Ar
)
C6H3-2-iPr-6-C(CH3)2C(CH3)2-6
′
′
dCdNR (R
Cy, C6H3-2,6-iPr2) with the SmII “ate” complex [Sm
{
)
Cy, but a novel C-substituted amidinate complex, [(THF)Na
{
}
{
}
for R
)
C6H3-2,6-iPr2, via
γ
C−
Scheme 1. Reactions of Carbodiimides RNdCdNR with Lanthanoid
Complexes: (a) Insertion/Guanidinate Formation; (b) Reductive
Coupling/Oxalamidinate Formation
Introduction
Carbodiimides, RNdCdNR, from the heterocumulene
family (which includes isoelectronic CO2), are important
substrates for metal-based reactivity studies. For example,
insertion reactions of carbodiimides into main-group and
early-transition-metal M-N bonds have been known for
many years.1 For lanthanoid metals, analogous insertion
reactions have been employed for the synthesis of lanthanoid-
(III) complexes with bulky guanidinate RNC(NR′)NR-
ligands (Scheme 1a),2-7 where such ligands are attractive
supports for low-coordinate, highly reactive alkyl species.8,9
2
* To whom correspondence should be addressed. E-mail: peter.junk@
sci.monash.edu.au. Fax: +61 (0)3 9905 4597.
(1) Lappert, M. F.; Prokai, B. AdV. Organomet. Chem. 1967, 5, 225-
319.
Recently, reductive coupling of carbodiimides has realized
an exciting alternative reaction leading to novel M(NCN)
metallocycles. With low-valent metallocene complexes
[(C5H5)2Ti(CO)2]10,11 or [(MeC5H4)2Sm(THF)]12 (THF )
tetrahydrofuran) or metallic lithium13 as the reducing agent,
(2) Pi, C.; Zhang, Z.; Pang, Z.; Zhang, J.; Luo, J.; Chen, Z.; Weng, L.;
Zhou, X. Organometallics 2007, 26, 1934-1946.
(3) Pi, C.; Zhang, Z.; Liu, R.; Weng, L.; Chen, Z.; Zhou, X. Organome-
tallics 2006, 25, 5165-5172.
(4) Trifonov, A. A.; Lyubov, D. M.; Fedorova, E. A.; Skvortsov, G. G.;
Fukin, G. K.; Kurskii, Yu. A.; Bochkarev, M. N. Russ. Chem. Bull.
2006, 55, 435-441.
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Eur. J. Inorg. Chem. 2004, 4396-4401.
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3303-3308.
(10) Pasquali, M.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. Inorg. Chem.
1981, 20, 349-355.
(6) Zhang, J.; Cai, R.; Weng, L.; Zhou, X. Organometallics 2003, 22,
5385-5391.
(11) Pasquali, M.; Floriani, C.; Chiesi-Villa, A.; Guastini, C. J. Am. Chem.
Soc. 1979, 101, 4740-4742.
(7) Zhang, J.; Cai, R.; Weng, L.; Zhou, X. J. Organomet. Chem. 2003,
672, 94-99.
(12) Deng, M.; Yao, Y.; Zhang, Y.; Shen, Q. Chem. Commun. 2004, 2742-
2743.
(8) Trifonov, A. A.; Lyubov, D. M.; Fedorova, E. A.; Fukin, G. K.;
Schumann, H.; Mu¨hle, S.; Hummert, M.; Bochkarev, M. N. Eur. J.
Inorg. Chem. 2006, 747-756.
(13) Villiers, C.; Thue´ry, P.; Ephritikhine, M. Chem. Commun. 2006, 392-
394.
10022 Inorganic Chemistry, Vol. 46, No. 23, 2007
10.1021/ic701497c CCC: $37.00
© 2007 American Chemical Society
Published on Web 10/11/2007

Reduction of Carbodiimides
Scheme 2. Synthesis of Complex 1 (L ) N(SiMe3)2, R ) Cy)
Table 1. A Summary of Crystal Data and Refinement Details for Complexes 1-3
1
2
3
formula
fw
C50H116N8Si8Sm2
1354.95
C74H140N8Si8Sm2
1667.36
C47H95N5NaOSi6Sm
1088.16
cryst sys
space group
a, Å
b, Å
c, Å
monoclinic
C2/c
monoclinic
P21/n
orthorhombic
Pbca
19.4815(7)
23.6653(8)
25.3705(9)
90
11696.7(7)
8
1.236
22.7524(2)
17.3941(2)
20.5878(2)
120.867(1)
6993.73(13)
4
1.287
2832
1.835
10.8127(2)
18.2560(3)
22.5778(4)
101.49501)
4367.39(13)
2
1.268
1752
1.483
â, deg
V, Å3
Z
F
calc, g cm-3
F(000)
4616
1.170
µ, mm-1
cryst size, mm
θ range, deg
0.25 × 0.15 × 0.04
3.47-27.50
36 345 (0.046)
8019/0/322
1.038
0.15 × 0.08 × 0.05
1.96-27.50
48 919 (0.054)
10017/0/435
1.355
0.30 × 0.15 × 0.05
1.57-27.50
68 565 (0.041)
13440/0/574
1.115
reflns (Rint
)
data/restraints/params
GOF
R1 [I > 2σ(I)]
wR2 (all data)
residual density, e Å-3
0.0274
0.0549
0.607 and -0.493
0.0578
0.0950
0.463 and -1.335
0.0379
0.0809
0.838 and -0.828
carbodiimides are reduced to oxalamidinate, [C2N4R4]2- (R
) Cy, Pr, C6H4-p-Me), ligands (Scheme 1b) via C-C
Samarium(II) bis(trimethylsilyl)amide, [Sm{N(SiMe3)2}2-
(THF)2], first introduced by Evans,19 is an attractive reducing
agent, as it can be formed conveniently from commercially
available reagents and is readily soluble in hydrocarbon
solvents.19,20 Although plausibly milder than lanthanocene
reagents (E0 values for Ln(C5R5)2 species21,22 have been
shown to be more negative than for the corresponding Ln-
{N(SiMe3)2}223), the reduction of O- and N-containing
substrates by [Sm{N(SiMe3)2}2(THF)2] has been explored,
mirroring similar reactions using [Sm(C5Me5)2(THF)2]. For
example, with fluorenone, both a ketyl radical anion complex
[Sm{N(SiMe3)2}2(OC13H8)(HMPA)] (HMPA ) hexamethyl-
phosphoric triamide) and the corresponding C-C coupled
pinacolate complex [{(Me3Si)2N}2(HMPA)Sm(µ-O2C26H16)-
Sm(HMPA){N(SiMe3)2}2] have been characterized.24 The
conversion of nitroaryls (ArNO2) to anilines (ArNH2) can
be mediated by [Sm{N(SiMe3)2}2(THF)2] and was shown
to proceed via O abstraction and the subsequent reduction
of ArNdNAr.25 Phenyl benzophenone imine (Ph2CdNPh)
i
coupling at the central C atoms of two carbodiimides. This
transformation parallels CO2 reduction by [Sm(C5Me5)2-
(THF)2] to yield an analogous oxalate complex [(C5Me5)2-
Sm(µ-O2CCO2)Sm(C5Me5)2].14 Our interest in lanthanoid
complexeswithbulkyaryl-formamidinateligands,RNC(H)NR-,
e.g., R ) C6H3-2,6-iPr2),15-17 (for reviews of amidinate
complexes, see ref 18) prompted us to investigate the redox
reactions of low-valent, non-metallocene lanthanoid com-
plexes with bulky carbodiimides as potential sources of
sterically hindered lanthanoid(III) metallocyclic (LnNCN)
frameworks.
(14) Evans, W. J.; Seibel, C. A.; Ziller, J. W. Inorg. Chem. 1998, 37, 770-
776.
(15) Cole, M. L.; Deacon, G. B.; Konstas, K.; Junk, P. C. Chem. Commun.
2005, 1581-1583.
(16) Cole, M. L.; Junk, P. C. Chem. Commun. 2005, 2695-2697.
(17) Cole, M. L.; Deacon, G. B.; Forsyth, C. M.; Junk, P. C.; Konstas, K.;
Wang, J. Chem.sEur. J. 2007, 13, 8092-8110.
(18) (a) Junk, P. C.; Cole, M. L. Chem. Commun. 2007, 1579-1590. (b)
Kempe, R. Angew. Chem., Int. Ed. 2000, 39, 468-493. (c) Roesky,
P. W. Chem. Soc. ReV. 2000, 29, 335-345. (d) Piers, W. E.; Emslie,
D. J. H. Coord. Chem. ReV. 2002, 233, 131-155. (e) Edelmann, F.
T.; Freckmann, D. M. M.; Schumann, H. Chem. ReV. 2002, 102,
1851-1896. (f) Cotton, S. In ComprehensiVe Coordination Chemistry
II, McCleverty, J. A., Meyer, T. J., Eds.; Elsevier: Oxford, 2004; Vol.
3 (Parkin, G. F. R., Ed.), Chapter 3.2, p 93-188. (g) Anwander, R.
Top. Current Chem. 1996, 179, 33-112. (h) Edelmann, F. T. Coord.
Chem. ReV. 1994, 137, 403-481. (i) Edelmann, F. T. Top. Current
Chem. 1996, 179, 113-148. (j) Edelmann, F. T. AdV. Organomet.
Chem., in press. (k) Edelmann, F. T. In ComprehensiVe Organometallic
Chemistry III; Crabtree, R. H., Mingos, D. M. P., Eds.; Elsevier:
Oxford, U.K., 2006; Vol. 4, pp 1-190.
(19) Evans, W. J.; Drummond, D. K.; Zhang, H.; Atwood, J. L. Inorg.
Chem. 1988, 27, 575-579.
(20) Deacon, G. B.; Fallon, G. D.; Forsyth, C. M.; Schumann, H.; Weimann,
R. Chem. Ber. 1997, 130, 409-415.
(21) Bond, A.; Deacon, G. B.; Newnham, R. H. Organometallics 1986, 5,
2312-2316.
(22) Watson, P. L.; Tulip, T. H.; Williams, I. Organometallics 1990, 9,
1999-2009.
(23) Bradley, D. C.; Ahmed, M. Polyhedron 1983, 2, 87-95.
(24) Hou, Z.-M.; Fujita, A.; Zhang, Y.-G.; Miyano, T.; Yamazaki, H.;
Wakatsuki, Y. J. Am. Chem. Soc. 1998, 120, 754-766.
(25) Brady, E. D.; Clark, D. L.; Keogh, D. W.; Scott, B. L.; Watkin, J. G.
J. Am. Chem. Soc. 2002, 124, 7007-7015.
Inorganic Chemistry, Vol. 46, No. 23, 2007 10023

Deacon et al.
Figure 1. Molecular structure of 1, viewed approximately down the c axis and shown with 50% thermal ellipsoids and H atoms omitted for clarity. Atoms
1
denoted with # are generated by the symmetry operator -x, y, /2 -z.
Table 2. Selected Bond Distances (Å) and Angles (deg) for 1a
Scheme 3. Synthesis of Complex 2 (L ) N(SiMe3)2, R ) C6H3-
2,6-iPr2)
Sm(1)-N(1)
Sm(1)-N(2)
Sm(2)-N(3)
Sm(2)-N(4)
N(2)-C(7)
2.286(2)
2.417(2)
2.293(2)
2.418(2)
1.335(2)
1.332(2)
1.543(4)
N(1)-Sm(1)-N(1)a
N(1)-Sm(1)-N(2)
N(1)-Sm(1)-N(2)a
N(2)-Sm(1)-N(2)a
N(3)-Sm(2)-N(3)a
N(3)-Sm(2)-N(4)
N(3)-Sm(2)-N(4)a
N(4)-Sm(2)-N(4)a
116.75(9)
134.18(7)
103.35(6)
55.57(8)
117.17(9)
102.88(6)
134.38(6)
55.54(8)
N(4)-C(14)
C(7)-C(14)
1
a Symmetry transformation: -x, y, /2 -z.
or phenyl fluorenone imine (C12H8CdNPh) also reacts with
[Sm{N(SiMe3)2}2(THF)2] to yield SmIII complexes [Sm{η2-
(R2C-NPh)}{N(SiMe3)2}2(THF)3] (R2 ) Ph2 or C12H8),
which incorporate three-membered metallocycles (SmCN).26
We now report the reactions of [Sm{N(SiMe3)2}2(THF)2]19,20
or the “ate” complex, [Sm{N(SiMe3)2}3Na],27 with the bulky
carbodiimides RNdCdNR (R ) Cy, C6H3-2,6-iPr2) that
show formation of both the anticipated SmIII oxalamidinate
and some unusual SmIII amidinate complexes that demon-
strate the unpredictable and versatile nature of these reduction
reactions.
1
aided by H-1H COSY measurements. 29Si NMR spectra were
recorded in THF-d8 using a DRX 400 spectrometer with chemical
shifts referenced to an external SiMe4 standard. Electrospray
ionization (ESI) mass spectra were determined in positive ion mode
using a Micromass Platform II mass spectrometer. Melting points
were determined in sealed glass capillaries under nitrogen and are
uncalibrated. A magnetic susceptibility measurement for 1 was
obtained at 295 K by the Gouy method using an automatic magnetic
susceptibility balance (Sherwood Scientific, Cambridge, England).
The magnetic moment for 3 was measured at 300 K using a
Quantum Design MPMS 5 SQUID magnetometer. Microanalyses
were determined by the Campbell Microanalytical Service, Uni-
versity of Otago, New Zealand. Stock solutions of [Sm{N(SiMe3)2}2-
(THF)2]19 and [Sm{N(SiMe3)2}3Na]27 were prepared from 2:1 or
3:1 mole ratio reactions between Na{N(SiMe3)2} (0.6 M in toluene,
Aldrich) and [SmI2(THF)2].28 RNdCdNR (R ) C6H3-2,6-iPr2)29
was prepared according to the literature procedure, and CyNdCd
NCy was used as purchased from Aldrich.
Experimental Section
All manipulations were performed using conventional Schlenk
or glovebox techniques under high-purity nitrogen. THF and hexane
were dried with sodium/benzophenone while toluene, C6D6, and
THF-d8 were dried over sodium. All solvents were distilled and
stored under high-purity nitrogen. Infrared spectra (4000-650 cm-1
)
were recorded as Nujol mulls using sodium chloride plates with a
Perkin-Elmer 1600 FTIR spectrophotometer. 1H NMR spectra were
recorded using a Bruker DPX 300 or DRX 400 spectrometer at
303 K unless stated otherwise, and chemical shifts are referenced
to the residual 1H resonances of the solvent. All assignments were
Synthesis of [{(Me3Si)2N}2Sm(µ-C2N4Cy4)Sm{N(SiMe3)2}2]
(1). (a) A solution of N,N′-dicyclohexylcarbodiimide (0.41 g, 2.00
mmol) in THF (20 mL) was added at ambient temperature with
stirring to a purple solution of [Sm{N(SiMe3)2}2(THF)2] (0.10 M,
(26) Hou, Z.-M.; Yoda, C.; Koizumi, T.; Nishiura, M.; Wakatsuki, Y.;
Fukuzawa, S.; Takats, J. Organometallics 2003, 22, 3586-3592.
(27) Evans, W. J.; Johnston, M. A.; Clark, R. D.; Anwander, R.; Ziller, J.
W. Polyhedron 2001, 20, 2483-2490.
(28) Namy, J. L.; Girard, P.; Kagan, H. B.; Caro, P. E. NouV. J. Chim.
1981, 5, 479-484.
(29) Ogawa, K.; Akazawa, M. Japanese Patent Application, JP 91-
208987910517.
10024 Inorganic Chemistry, Vol. 46, No. 23, 2007

Reduction of Carbodiimides
Scheme 4. Hydrolysis of 2 Yielding 2a (R ) C6H3-2,6-iPr2)
Table 3. Selected Bond Distances (Å) and Angles (deg) for 2a
Sm(1)-N(1)
Sm(1)-N(2)
Sm(1)-N(3)
Sm(1)-N(4)
C(1)-N(1)
C(1)-N(2)
N(1)-C(2)
2.433(3)
2.482(3)
2.260(4)
2.276(4)
1.333(5)
1.319(5)
1.433(5)
N(2)-C(14)
1.432(5)
1.596(8)
C(20)-C(20)a
N(1)-Sm(1)-N(2)
N(3)-Sm(1)-N(4)
N(1)-Sm(1)-N(4)
N(2)-Sm(1)-N(3)
N(1)-C(1)-N(2)
55.69(11)
112.07(13)
118.99(12)
121.88(13)
119.9(4)
a Symmetry transformation: 1 - x, -y, -z.
N, 6.72. Crystals suitable for X-ray crystallography were obtained
by crystallization from C6D6.
Hydrolysis of 2 and Synthesis of RN(H)C(H)N(Ar-Ar)NC-
(H)N(H)R (2a) (R ) C6H3-2,6-iPr2; Ar-Ar ) C6H3-2-iPr-6-
C(CH3)2C(CH3)2-6′-C6H3-2′-iPr). Absolute methanol (0.5 mL) was
added to a test tube containing 2 (0.33 g, 0.20 mmol) under nitrogen.
The mixture was stirred continuously for 0.5 h. The volatile
components were removed under vacuum, the residue was extracted
with ether (3.0 mL × 2), and the ethereal solution was dried over
anhydrous MgSO4. The solvent was removed under vacuum to leave
a colorless crystalline compound 2a (0.13 g, 90%). Mp: 228-
232 °C. IR (Nujol): ν 3190 w, 3137 w, 1934 w, 1916 w, 1862 w,
1800 w, 1658 s, 1582 m, 1362 m, 1329 m, 1289 s, 1198 w, 1183
m, 1164 w, 1138 w, 1088 m, 1013 m, 923 w, 822 m, 805 m, 753
s, 717 w cm-1. 1H NMR (C6D6, 300 MHz): δ 9.73 (br s, 2H, NC-
(H)dN), 7.08 (s, 12H, C6H3), 4.25 (br s, 2H, NH), 3.43 (m, 6H,
20 mL, 2.00 mmol) in hexane. The color gradually turned light
yellow, and the mixture was stirred continuously for 0.5 h. The
volume of solvent was reduced to 20 mL and stored at -30 °C for
1 week, after which time light-yellow crystals of 1 were collected
(1.00 g, 74%). Mp: 340-344 °C. IR (Nujol): ν 1364 m, 1346 w,
1245 m, 1175 w, 1121 w, 1075 w, 1012 s, 860 w, 829 m, 759 w,
1
674 w, 656 w cm-1. H NMR (THF-d8, 300 MHz): δ 8.09 (br s,
4H, CyNCNCy), 3.99 (br s, 8H, CyNCNCy), 1.75 (br s, 8H,
CyNCNCy), 1.46 (br d, 3J ) 12.4 Hz, 8H, CyNCNCy), 1.37 (br d,
3J ) 12.8 Hz, 4H, CyNCNCy), 0.40 (m, 4H, CyNCNCy), -0.53
(br s, 8H, CyNCNCy), -2.50 (br s, 72H, SiCH3). µeff (295 K):
1.35 µB. Found: C, 44.45; H, 8.72; N, 8.07. Anal. Calcd for
C50H116N8Si8Sm2: 44.32; H, 8.63; N, 8.27. Crystallization from
THF provided crystals suitable for X-ray crystallography. (b) Using
a similar procedure to that above, N,N′-dicyclohexylcarbodiimide
(0.41 g, 2.00 mmol) in THF (20 mL) was treated with a solution
of [Sm{N(SiMe3)2}3Na] (0.10 M, 20 mL, 2.00 mmol) in hexane.
After workup, 1 was obtained as light-yellow crystals (0.93 g, 68%).
The product had IR and 1H NMR spectra in agreement with those
obtained for the product of (a) above.
CH, Pr), 1.20-1.70 (m, 48H, CH3, Pr). MS-ESI: 727 ([MH]+,
100%). Found: C, 82.49; H, 9.85; N, 7.85. Anal. Calcd for
C50H70N4: C, 82.59; H, 9.70; N, 7.71. Crystals suitable for X-ray
crystallography were obtained from toluene (see the Supporting
Information for the X-ray structure of 2a).
i
i
Synthesis of [(THF)Na{N(R)C(NR)CH2Si(Me2)N(SiMe3)}Sm-
{N(SiMe3)2}2] (3) (R ) C6H3-2,6-iPr2). A solution of N,N′-bis-
(2,6-diisopropylphenyl)carbodiimide (0.73 g, 2.00 mmol) in hexane
(20 mL) was added at ambient temperature with stirring to a purple
solution of [Sm{N(SiMe3)3}3Na] (0.10 M, 20 mL, 2.00 mmol) in
hexane. The solution turned colorless within 5 min. The mixture
was heated to 60 °C and stirred continuously at this temperature
for 1 h. The volume of solvent was reduced to 20 mL and stored
at -30 °C overnight, after which time colorless crystals of 3 were
collected (0.75 g, 35%). Mp: 213 °C (dec). IR (Nujol): ν 1428 m,
1342 m, 1308 m, 1246 s, 1191 m, 1159 w, 1112 w, 1091 w, 1042
m, 969 s, 955 s, 886 w, 860 w, 830 s, 775 w, 754 m, 743 m, 666
m, 630 s, cm-1. 1H NMR (THF-d8, 400 MHz): δ 12.71 (br s, 1H,
Synthesis of [{(Me3Si)2N}2Sm{µ-(RNC(H)N(Ar-Ar)NC(H)-
NR)}Sm{N(SiMe3)2}2] (2) (R ) C6H3-2,6-iPr2; Ar-Ar ) C6H3-
2-iPr-6-C(CH3)2C(CH3)2-6′-C6H3-2′-iPr). A solution of N,N′-bis(2,6-
diisopropylphenyl)carbodiimide (0.73 g, 2.00 mmol) in hexane (20
mL) was added at ambient temperature with stirring to a purple
solution of [Sm{N(SiMe3)2}2(THF)2] (0.10 M, 20 mL, 2.00 mmol)
in hexane. The color gradually turned light-green/yellow, and the
mixture was stirred continuously for 1 h. The volume of solvent
was reduced to 20 mL and stored at ambient temperature for 2
weeks, after which time light-yellow crystals of 2 were collected
(0.77 g, 46%). Mp: 224-228 °C. IR (Nujol): ν 1511 s, 1422 m,
1334 w, 1308 w, 1283 s, 1247 s, 1200 w, 1178 w, 1098 w, 1076
w, 1052 w, 1022 w, 955 s, 878 w, 832 s, 768 m, 756 m, 661 m,
i
3
CH, Pr), 7.39-7.00 (m, 3H, C6H3), 5.67 (d, J ) 7.41 Hz, 1H,
3
i
C6H3), 5.34 (t, J ) 7.59 Hz, 1H, C6H3), 5.23 (m, 1H, CH, Pr),
i
3
5.00 (m, 1H, CH, Pr), 4.79 (d, J ) 7.53 Hz, 1H, C6H3), 3.45 (s,
2H, CH2), 2.54 (d, 3J ) 5.82 Hz, 3H, CH3, iPr), 1.89 (d, 3J ) 7.14
Hz, 3H, CH3, iPr), 1.86 (d, 3J ) 6.84 Hz, 3H, CH3, iPr), 1.45 (d, 3J
1
608 m, cm-1. H NMR (THF-d8, 400 MHz, 323 K): δ 18.13 (s,
1H, NC(H)N), 17.78 (s, 1H, NC(H)N), 9.93 (s, 1H, CH, iPr), 8.20-
i
3
i
) 4.74 Hz, 3H, CH3, Pr), 1.39 (d, J ) 6.45 Hz, 3H, CH3, Pr),
i
1.09 (s, 9H, SiCH3), 0.92 (m, 1H, CH, iPr), 0.72 (d, 3J ) 6.54 Hz,
5.70 (m, 15H, C6H3 + CH, Pr), 3.16 (s, 6H, CH3), 2.84 (s, 6H,
i
3
i
CH3), 2.22 (s, 6H, CH3), 1.92 (s, 6H, CH3), 1.23 (s, 6H, CH3),
0.66 (s, 6H, CH3), -0.73 (s, 6H, CH3), -1.28 (s, 6H, CH3), -2.20
(s, 36 H, SiCH3), -2.46 (s, 36H, SiCH3), -3.47 (br s, 1H, CH,
3H, CH3, Pr), 0.68 (d, J ) 6.03 Hz, 3H, CH3, Pr), 0.30 (s, 18H,
3
i
SiCH3), -0.81 (d, J ) 6.27 Hz, 3H, CH3, Pr), -1.48 (s, 6H,
SiCH3), -3.27 (s, 18H, SiCH3). Resonances of THF were observed
at 3.54 and 1.67 ppm, partially overlapping residual solvent THF
signals, and could not be reliably integrated. 29Si NMR (THF-d8,
79.495 MHz): δ 0.23, -1.43, -10.68, -11.96. µeff (300 K): 1.69
µB. Found: C, 51.63; H, 8.59; N, 6.38. Anal. Calcd for C47H95N5-
NaOSi6Sm: C, 51.88; H, 8.80; N, 6.44. Crystallization from toluene
provided crystals of 3 suitable for X-ray crystallography.
Synthesis of [(THF)2NaN(R)C(NR)CH2Si(Me2)N(SiMe3)Sm-
{N(SiMe3)2}2]‚1/2(C7H8) (3a) (R ) C6H3-2,6-iPr2). Crystallization
of 3 (0.22 g, 0.20 mmol) from a minimum amount of THF/toluene
(v/v 1:1) gave colorless crystals of 3a (0.21 g, 87%). Mp: 207 °C
i
iPr), -4.01 (br s, 1H, CH, Pr); at 233 K, 18.69 (s, 1H, NC(H)N),
i
17.81 (s, 1H, NC(H)N), 11.08 (s, 1H, CH, Pr), 8.79 (s, 1H, CH,
iPr), 7.87-5.54 (m, 14H, C6H3 + CH, iPr), 3.77 (s, 3H, CH3), 3.15
(s, 3H, CH3), 3.07 (s, 3H, CH3), 2.87 (s, 3H, CH3), 2.58 (s, 3H,
CH3), 2.47 (s, 3H, CH3), 2.27 (s, 3H, CH3), 2.06 (s, 3H, CH3),
1.81 (s, 3H, CH3), 1.42 (s, 3H, CH3), 1.36 (s, 3H, CH3), 0.67 (s,
3H, CH3), 0.40 (s, 3H, CH3), -0.66 (s, 3H, CH3), -0.96 (s, 3H,
CH3), -1.44 (s, 3H, CH3), -2.46 (s, br, 72H, SiCH3), -4.04 (s,
i
i
br, 1H, CH, Pr), -5.13 (s, br, 1H, CH, Pr). Found: C, 53.49; H,
8.43; N, 6.43. Anal. Calcd for C74H140N8Si8Sm2: 53.31; H, 8.46;
Inorganic Chemistry, Vol. 46, No. 23, 2007 10025

Deacon et al.
Figure 2. Molecular structure of 2, viewed approximately down the a axis and shown with 50% thermal ellipsoids and H atoms omitted for clarity. Atoms
denoted with # are generated by the symmetry operator 1 - x, -y, -z.
(dec). IR (Nujol): ν 1621 w, 1585 w, 1523 w, 1342 m, 1308 m,
squares on all F2 data using SHELX 97.32 Crystallographic data
(excluding structure factors) for the structure(s) reported in this
paper have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication nos. CCDC 655689-
655693. Copies of the data can be obtained free of charge on appli-
cation to the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K.
(fax, int. code + 44(1223)336-033; e-mail, deposit@ccdc.cam.ac.uk).
1247 s, 1191 w, 1159 w, 1113 w, 1091 w, 1042 w, 970 m, 955 s,
1
868 w, 840 m, 831 m, 767 w, 754 w, 723 w, 666 w cm-1. H
i
NMR (THF-d8, 300 MHz): δ 12.68 (br s, 1H, CH, Pr), 7.36-
6.94 (m, 5.5H, C6H3 and PhMe), 5.64 (d, 3J ) 7.11 Hz, 1H, C6H3),
3
i
5.31 (t, J ) 7.56 Hz, 1H, C6H3), 5.19 (m, 1H, CH, Pr), 4.97 (m,
1H, CH, iPr), 4.76 (d, 3J ) 8.07 Hz, 1H, C6H3), 3.41 (s, 2H, CH2),
3
i
2.51 (d, J ) 5.40 Hz, 3H, CH3, Pr), 2.27 (s, 1.5H, PhMe), 1.86
3
i
3
Results and Discussion
(d, J ) 7.14 Hz, 3H, CH3, Pr), 1.83 (d, J ) 6.60 Hz, 3H, CH3,
iPr), 1.42 (d, J ) 4.74 Hz, 3H, CH3, Pr), 1.36 (d, J ) 6.48 Hz,
3H, CH3, iPr), 1.09 (s, 9H, SiCH3), 0.89 (m, 1H, CH, iPr), 0.69 (d,
3J ) 6.42 Hz, 3H, CH3, iPr), 0.65 (d, 3J ) 6.45 Hz, 3H, CH3, iPr),
0.26 (s, 18H, SiCH3), -0.84 (d, 3J ) 6.00 Hz, 3H, CH3, iPr), -1.51
(s, 6H, SiCH3), -3.31 (s, 18H, SiCH3). Resonances of THF were
observed at 3.60 and 1.74 ppm, overlapping residual solvent THF
signals, and could not be integrated reliably. Found: C, 54.00; H,
8.74; N, 5.77. Anal. Calcd for C54.5H107N5NaO2Si6Sm: C, 54.26;
H, 8.94; N, 5.81. Crystallization of 3a (0.24 g) from toluene gave
3 (0.18 g, 85%) as colorless prismatic crystals (as identified by
unit cell measurements).
3
i
3
The reaction of a deep-purple solution of [Sm{N(SiMe3)2}2-
(THF)2] in hexane with an equivalent amount of N,N′-
dicyclohexylcarbodiimide in THF resulted in a rapid color
change to light yellow, indicative of the oxidation of SmII.
From the resulting solution, crystals of the yellow SmIII
oxalamidinate complex 1 could be isolated in good yield.
The same product was also obtained, in a similar yield,
from the carbodiimide and the SmII “ate” complex [Sm-
{N(SiMe3)2}3Na] (Scheme 2).
Complex 1 is thermally stable up to its melting point
(340-344 °C) and gave satisfactory elemental analyses,
while the IR and NMR spectra were consistent with the
X-ray Crystallography. A summary of crystal data and refine-
ment parameters is given in Table 1. Crystalline samples of
compounds 1-3 were mounted on glass fibers in viscous paraffin
oil at -150 °C (123 K). Reflection data were obtained using an
Enraf-Nonius Kappa CCD or Bruker X8 APEX CCD diffracto-
meter (Mo KR radiation, λ ) 0.71073 Å). Each data set was
empirically corrected for absorption (SORTAV;30 SADABS31), then
merged (Rint as quoted) to N unique reflections. The structures were
solved by conventional methods and refined by full-matrix least
1
proposed formulation. The H NMR spectrum was shifted
from the normal diamagnetic region due to the paramagnetic
SmIII center (µeff ) 1.7 µB),33 but a broad singlet for the SiMe3
protons was clearly evident at -2.50 ppm, (cf. [Sm-
{N(SiMe3)2}2(THF)(µ-PhNNPh)Sm{N(SiMe3)2}2], δ ) -1.97
ppm25). The cyclohexyl protons appear as seven individual
(30) Blessing, R. H. J. Appl. Crystallogr. 1997, 30, 421-426.
(31) Sheldrick, G. M. SADABS; Universita¨t Go¨ttingen: Go¨ttingen, Ger-
many, 1996 (as part of the Bruker Apex2, version 2.0, program system;
Bruker AXS: Madison, WI, 2005).
(32) Sheldrick, G. M. SHELX-97; Universita¨t Go¨ttingen: Go¨ttingen,
Germany, 1997.
(33) Evans, W. J.; Hozbor, M. A. J. Organomet. Chem. 1987, 326, 299-
306.
10026 Inorganic Chemistry, Vol. 46, No. 23, 2007

Reduction of Carbodiimides
Scheme 5. Proposed Reaction Pathway Leading to the Formation of Oxalamidinate and Formamidinate Complexes from the Reduction of
Carbodiimides by [Sm{N(SiMe3)2}2(THF)2] (L ) N(SiMe3)2)
Scheme 6. Synthesis of Complex 3 (L ) N(SiMe3)2, R ) C6H3-
central carbon atoms. Both trigonal planes are approximately
orthogonal (dihedral angle 82.46(8)°) as are also the two
amidinate Sm(NCN) planes (dihedral angle 83.3(1)°), which
results in a favorable staggered arrangement of the two
N(SiMe3)2 ligands and the Cy rings, as well as the two pairs
of Cy groups attached to the oxalamidinate ligand. The Sm-
N(SiMe3)2 distances (Table 2) are comparable with those in
related complexes (e.g., five-coordinate [Sm{N(SiMe3)2}2-
(THF)(µ-PhNNPh)Sm{N(SiMe3)2}2] average ) 2.28(2) Å),25
while the bond distances to the µ-C2N4Cy4 ligand (Table 2)
are shorter than those (2.560(5) and 2.447(5) Å) in nine-
coordinate [{Sm(MeC5H4)2(HMPA)}2(µ-C2N4Cy4)],12 con-
sistent with the difference in ionic radii (ca. 0.18 Å)34 due
to the change in coordination number. The central C-C
distance (Table 2) is typical of a single bond, whereas the
C-N distances (Table 2) in the C2N4 unit are shorter and
equal, indicating a typically delocalized amidinate fragment.
Replacement of the N,N′-dicyclohexylcarbodiimide with
the bulkier N,N′-bis(2,6-diisopropylphenyl)carbodiimide (RNd
CdNR, R ) C6H3-2,6-iPr2), in the reaction with [Sm-
{N(SiMe3)2}2(THF)2] also gave a color change from purple
to yellow, signifying oxidation of the samarium center to
SmIII. However, crystallization of the product from solution
did not give the corresponding oxalamidinate complex but
instead a binuclear SmIII C-C coupled formamidinate
2,6-iPr2)
resonances over a range from 8.09 to -0.53 ppm. The
identity of compound 1 was unequivocally established by
an X-ray structure determination. The molecular diagram is
shown in Figure 1, with selected bond distances and angles
listed in Table 2. The complex crystallizes in monoclinic
C2/c with the two Sm atoms and the two central amidinate
C atoms, C(7) and C(14), lying on a crystallographic two-
fold axis (thus, only half the molecule is unique). Each Sm
atom is bound in an amidinate fashion (rather than as a
diamide, e.g., in [{Li(py)2}2(µ-C2N4R4)] (R ) p-tolyl)13) to
either side of a tetracyclohexyloxalamidinate(2-) ligand with
two N(SiMe3)2- ligands completing each coordination sphere.
Both samarium centers are four-coordinate, and each adopts
a pseudo-trigonal-planar geometry if the oxalamidinate
ligands are considered to be point donors located at the
(34) Shannon, R. D. Acta Crystallogr., Sect. A 1976, 32, 751-767.
Inorganic Chemistry, Vol. 46, No. 23, 2007 10027

Deacon et al.
Figure 3. Molecular structure of 3, shown with 50% thermal ellipsoids and H atoms omitted for clarity.
Table 4. Selected Bond Distances (Å) and Angles (deg) for 3
nyl)formamidinate complexes of SmIII, e.g., [Sm(RNC(H)-
NR)3] and [Sm(RNC(H)NR)2F(THF)] (R ) C6H3-2,6-iPr2),
show only one broad singlet each for the isopropyl CH3
groups at δ 1.45 and 0.89, respectively.16 Thus, the current
data are consistent with the observed structure, apart from
observation of two NC(H)N resonances at 323 K, suggesting
a less symmetrical structure in solution than in the solid state,
though this is not evident from the number of methyl
resonances (eight). However, a spectrum at 233 K reveals
greater separation of the NC(H)N resonances and 16 equal-
intensity methyl resonances consistent with a lower symmetry
structure in solution. Further evidence of the presence of the
coupled ligand was obtained on hydrolysis of bulk 2 which
gave 2a as the sole nonvolatile organic product in high yield
(Scheme 4).
Sm(1)-N(1)
Sm(1)-N(3)
Sm(1)-N(4)
Sm(1)-N(5)
Na(1)-N(2)
Na(1)-C(2)
Na(1)-C(3)
Na(1)-C(4)
Na(1)-C(5)
Na(1)-C(6)
Na(1)-C(7)
2.501(2)
2.330(2)
2.324(2)
2.320(2)
2.396(2)
2.678(3)
2.858(3)
3.087(3)
3.121(3)
2.918(3)
2.703(3)
Na(1)-O(1)
2.265(2)
2.967(3)
1.363(3)
1.320(3)
1.510(3)
124.82(7)
91.57(7)
108.41(7)
114.85(7)
105.52(8)
111.05(8)
Na(1)-C(24)
N(1)-C(1)
N(2)-C(1)
C(1)-C(37)
N(1)-Sm(1)-N(3)
N(1)-Sm(1)-N(4)
N(1)-Sm(1)-N(5)
N(3)-Sm(1)-N(4)
N(3)-Sm(1)-N(5)
N(4)-Sm(1)-N(5)
complex 2. This unusual product results from H transfer to
the central C atom of the carbodiimide and coupling at the
methine C atoms on one of the Pr groups (Scheme 3).
i
The identity of complex 2 was confirmed by an X-ray
structure determination (see below), while the bulk product
gave satisfactory elemental analyses. However, the 1H NMR
spectrum of paramagnetic 2 in THF-d8 was extremely
complex. Two singlet resonances at 18.13 and 17.78 ppm,
each integrating as 1H, were assigned to formamidinate
backbone CH while two SiCH3 resonances at -2.20 and
-2.46 ppm, each integrating as 36H, are clearly identified
by comparison with 1 above. At first sight, these data
may indicate the presence of more than one product in the
bulk material, and indeed, the putative complexes (Sm-
{N(SiMe3)2}2)2(µ-C2N4R4R) (2L) or Sm{N(SiMe3)2}2(RNC-
(H)NR) (2M) (R ) C6H3-2,6-iPr2) would both give virtually
indistinguishable elemental analyses (and are plausible
products of a common intermediate radical species; see
The solid-state structure of 2 is shown in Figure 2, with
selected bond distances and angles listed in Table 3. The
complexes crystallizes in monoclinic P21/n with a crystal-
lographic inversion center located at the midpoint of the
(ArMe2)C-C(Me2Ar) bond, relating the two halves of the
molecule. The Sm center is four-coordinate and bound to
-
two N(SiMe3)2 ligands and two N atoms of the chelating
formamidinate fragment. The coordination geometry is
pseudo-pyramidal (assuming the formamidinate to occupy
a single coordination site at the central C atom, C(1), of the
NCN fragment) rather than planar, as in 1 above. The Sm
atom resides out of the C(1)N(3)N(4) plane by 0.292(2) Å.
The Sm-N(SiMe3)2 bond lengths (Table 3) are slightly
shorter than those in 1 (Table 2) whereas the Sm-
N(formamidinate) bond lengths (Table 3) are marginally
longer (Table 2), reflecting the bulkier C6H3-2,6-iPr2 substitu-
tion on the amidinate nitrogen donors in the present complex.
These bond lengths match those of related complexes, e.g.,
six-coordinate [Sm(RNC(H)NR)3] (2.448(6)-2.467(6) Å),16
and are shorter than those (2.529(3) and 2.617(3) Å) of the
six-coordinate SmII complex [Sm(RNC(H)NR)2(THF)2] (R
1
below). However, in the H NMR spectrum of 2, there are
eight distinct isopropyl CH3 resonances, each integrating as
6H, in the range of 3.16 to -1.28 ppm. This observation
argues against the possibility that the bulk material is a
mixture of 2 and either 2L or 2M. The last two complexes
would each be expected to show a single CH3 resonance for
all eight isopropyl CH3 groups (24H in total). Indeed,
reported spectra of highly crowded bis(2,6-diisopropylphe-
10028 Inorganic Chemistry, Vol. 46, No. 23, 2007

Reduction of Carbodiimides
elemental analyses. As with 2 above, the 1H NMR spectrum
of paramagnetic 3 was extremely complex. The N-SiMe3
protons appear as four singlets ranging from 1.09 to -3.27
ppm in a ratio of 9:18:6:18. Consistent with this observation,
there are four distinct 29Si NMR resonances in the range of
0.23 to -11.96 ppm (relative to SiMe4). Two different
aromatic environments are observed with two sets of CH
resonances at 7.39-7.00 ppm, and at 5.67-4.79 ppm,
consistent with the unsymmetrical binding of the amidinate
to both Sm and Na (see below). Furthermore, each isopropyl
group shows distinct CH and CH3 resonances, over a wide
chemical shift range.
Figure 4. Schematic representation of the molecular structure of 3a.
) C6H3-2,6-iPr2),16 consistent with the relative sizes of
The solid-state structure of 3 is shown in Figure 3, with
selected bond distances and angles listed in Table 4. The
structure features a binuclear species containing a four-
Sm2+/3+ 34
. The C(20)-C(20)′ bond length formed by C-C
coupling is 1.596(8) Å, which is slightly longer than the
corresponding C-C bond in 1 (Table 2), plausibly attribut-
able to the bulk of the C6H3-2,6-iPr2 substituents.
-
coordinate Sm atom bound to two N(SiMe3)2 ligands and
two N atoms, one from the amidinate moiety and one from
the N(SiMe3)(SiMe2CH2) lariat attached to the amidinate
backbone. The Na atom is bound to the remaining N atom
of the amidinate ligand and is supported by an η6-arene
interaction with one of the C6H3-2,6-iPr2 substituents. The
coordination environment of the Na atom is completed by a
THF molecule and an agostic Na‚‚‚Me interaction (see
below) giving overall six-coordination. The Sm-N(SiMe3)2
bond distances (Table 4) fall in a narrow range and are
marginally longer than those of 1 and 2 above. Similarly,
the Sm(1)-N(1) (amidinate) distance (Table 4) is longer than
those in 2 (Table 3) despite both complexes being four-
coordinate. The coordination geometry around Sm(1) is
distorted by the six-membered metallocycle, which has an
internal N-Sm-N angle narrower than that of the others
(Table 4). The Na atom has a short Na(1)-N(2) distance
(Table 4) by comparison with those of analogous forma-
midinate complexes (e.g., [Na(RNC(H)NR)(THF)3], Na-N
) 2.406(2) and 2.457(2) Å or [Na(RNC(H)NR)(DME)2],
Na-N ) 2.411(3) Å, R ) C6H3-2,6-iPr2),36 which have
chelating, bidentate formamidinate ligands rather than uni-
dentate ligands (to Na) as in 3. The η6-aryl-Na interaction
is characterized by Na-C distances in the range of 2.678-
(3)-3.121(3) Å with the longest distance to the C atom para
to the amidinate N atom. The Na-CH3 interaction involves
The formation of both complexes 1 and 2 is considered
to proceed via radical intermediates (Scheme 5). Thus, the
one-electron reduction of a carbodiimide RNdCdNR by a
SmII center presumably generates radical anions bound to
SmIII (e.g., A in Scheme 5). The subsequent fate of species
A then appears to depend upon the substituents at the
carbodiimide N atoms, although other factors such as solvent
or the ancilliary ligands on the Sm may also be significant.
Thus, direct coupling of A will give the oxalamidinate
complex as in 1 and [{(MeC5H4)2(HMPA)Sm}2(µ-C2N4R4)]
i
(R ) Cy, Pr).12 For the more bulky, C6H3-2,6-iPr2 substit-
uents, this process may be kinetically hindered, allowing
intervention of other events. The formation of 2 could be
i
envisaged to occur by H abstraction from a proximal Pr
group, forming the formamidinate radical fragment B
(Scheme 5), which subsequently C-C couples at the methine
C atoms. Proton abstraction, typically thought to be derived
from solvents such as THF by radical species, has been
proposed previously in lanthanoid systems,35 and thus, the
formation of C by this route is plausible, but is not formed
as a major product. The coupling in 2 is unusual, as in
reported lanthanoid systems (e.g., ref 24), C-C coupling
usually occurs on C atoms proximal to a (coordinated) N or
O atom (as is the case for 1). However, species B should
have significant stability as a bulky tertiary radical.
The reaction of the SmII “ate” complex [Sm{N(SiMe3)2}3-
Na] with RNdCdNR (R ) C6H3-2,6-iPr2) also gives an
unusual product. In this reaction, the purple color of the
divalent Sm complex rapidly changes to colorless, indicative
of oxidation to SmIII, but different from the formation of
yellow 1 and 2 above. After workup and crystallization from
toluene, colorless crystals of the substituted acetamidinate
complex 3 were isolated (Scheme 6).
i
one of the Pr2 groups attached to the remaining (non-η6-
bound) C6H3-2,6-iPr2 substituent and has a Na-C distance
near the middle of the above range (Table 4). Alkali metal
cation-arene coordination has been increasingly observed,
and the current Na-C bond lengths are typical (e.g., Na/
C6H3-2-6-iPr2, 2.881(2)-3.084(2) Å;37,38 see also ref 39 for
non-chelation supported Na-arene complexes, e.g., [Ln-
(L)4Na(PhMe)], L ) C3HN2-3,5-tBu2). A unidentate N/η6-
The THF coordinated to the Na atom presumably origi-
nates from the [SmI2(THF)2] starting material used for the
in situ preparation of [Sm{N(SiMe3)2}3Na]. The identity of
complex 3 was confirmed by an X-ray structure determina-
tion (see below), and the bulk material gave satisfactory
(36) Cole, M. L.; Davies, A. J.; Jones, C.; Junk, P. C. J. Organomet. Chem.
2004, 689, 3093-3107.
(37) Wright, R. J.; Brynda, M.; Power, P. P. Angew. Chem., Int. Ed. 2006,
45, 5953-5956.
(38) Zhu, Z.; Wright, R. J.; Olmstead, M. M.; Rivard, E.; Brynda, M.;
Power, P. P. Angew. Chem., Int. Ed. 2006, 45, 5807-5810.
(39) Deacon, G. B.; Delbridge, E. E.; Evans, D. J.; Harika, R.; Junk, P.
C.; Skelton, B. W.; White, A. H. Chem.sEur. J. 2004, 10, 1193-
1204.
(35) Deacon, G. B.; Koplick, A. J.; Raverty, W. D.; Vince, D. G. J.
Organomet. Chem. 1979, 182, 121-141.
Inorganic Chemistry, Vol. 46, No. 23, 2007 10029

Deacon et al.
treated with NaN(SiMe3)2.41 A similar deprotonated N(SiMe3)2
ligand has also been observed in [Sm(L){N(SiMe3)(SiMe2-
CH2}Na(C7H8)}] (H2L ) trans-N,N′-dimethyl-meso-octa-
ethyl-porphyrinogen)42 while [Yb{N(SiMe3)SiMe2CH2BPh3}-
(THF)2], having a chelating amidosilylmethylborate ligand,
was isolated as a side product in the synthesis of [YbN-
(SiMe3)2(thf)BPh4].43 Although insertion of the carbodiimide
into a putative metallocyclic Ln-CH2SiMe2(SiMe3)N moiety
(Scheme 7a) would generate the functionalized amidinate
ligand observed in 3, this process does not require an
oxidation state change for the Sm center (a magnetic moment
measurement confirms the oxidation state of 3); hence, a
radical pathway is likely. It is plausible that the radical
intermediate D (Scheme 7b, analogous to A above) is initially
formed from the carbodiimide and [Sm{N(SiMe3)2}3Na]. For
R ) Cy, C-C coupling and elimination of NaN(SiMe3)2
giving 1 occurs, whereas for R ) C6H3-2,6-iPr2, the larger
R group may induce unidentate binding of the amidinate
radical which possibly undergoes intramolecular attack on
a proximal CH3-Si group (e.g., E, Scheme 7b), ultimately
yielding 3. Steric modulation of reduction reactions of R,R′-
diimines, RNdC(H)C(H)dNR, by ytterbocenes, leading to
unusual insertion of CdN moieties into Yb-L bonds (L )
fluorenyl), has been observed with the bulky C6H3-2,6-iPr2
substituent on the substrate.44
Scheme 7. Possible Reaction Pathways Leading to the Formation of
Complex 3 (L ) N(SiMe3)2): (a) Insertion of a Carbodiimide into a
Metallocyclic Sm-C Bond and (b) Reductive C-C Coupling Involving
the Formation of a Radical Intermediate Having a Unidentate
RN(C•)NR- unit
Conclusions
These studies demonstrate that SmIII oxalamidinate com-
plexes, such as 1, can be prepared by the reduction of
carbodiimides using “non-metallocene” lanthanoid reagents,
e.g., [Sm{N(SiMe3)2}2(THF)2]. Furthermore, there was no
evidence of competitive Ln-N insertion reactions. However,
the reductive coupling to oxalamidinates is not exclusive,
as a different carbodiimide yielded a linked formamidinate
complex 2. Both products are considered to be derived from
a common radical intermediate, and the differing outcomes
are believed to be a consequence of the size of the R group
on the carbodiimide substrate. The larger R group also
resulted in the formation of an unusual functionalized
amidinate ligand when the “ate” complex [Sm{N(SiMe3)2}3-
Na] was the reducing agent.
aryl-M arrangement similar to that evident in 3 has been
observed in [K(RNC(H)NR)2K(THF)2]n (R ) C6H3-2,6-i-
Pr2).40
The Na environment in 3 was modified on crystallization
from THF/toluene (1:1), which gave the daughter complex
3a. X-ray crystallography of crystals of 3a confirmed the
atom connectivity (Figure 4) and showed coordination of a
second THF molecule to Na replacing the agostic Na‚‚‚Me
interaction, but the poor data quality precluded a detailed
structural comparison with 3. Complex 3a reverts to 3 when
recrystallized from toluene.
The observation of the metallocyclic SmN(SiMe3)SiMe2-
CH2C(NR)2 fragment in 3 was unexpected, although γ-CH3
deprotonation of Ln-N(SiMe3)2 systems has been observed
previously. For example, metallocyclic [Ln{N(SiMe3)2}2-
{N(SiMe3)SiMe2CH2}Na(THF)3] has been isolated from
homoleptic [Ln{N(SiMe3)2}3] (Ln ) Sc, Yb, Lu) when
Acknowledgment. This work was supported by the
Australian Research Council.
Supporting Information Available: Selected X-ray crystal data
information. This material is available free of charge via the Internet
at http://pubs.acs.org.
IC701497C
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10030 Inorganic Chemistry, Vol. 46, No. 23, 2007