Reduction of ketimines by samarium(II) complexes. Isolation and structural characterization of samarium(III) η1-amine/η 1-ketimido and η2-ketimine complexes

Article abstract of DOI:10.1021/om030366v

The reaction of (C₅Me₅)₂Sm(THF) ₂ with 2 equiv of benzophenone imine (Ph₂C=NH) in THF at room temperature gave the samarocene(III) amine/ketimido complex (C ₅Me₅)₂Sm-(N=CPh₂)(NH ₂CHPh₂) (1) in 58% isolated yield. The use of 1 equiv of Ph₂C=NH also afforded 1 as the only isolable product, albeit in a lower yield (ca. 20%). Deuterium-labeling experiments suggest that 1 is formed via hydrogen abstraction by the in-situ-generated imine radical anion species, followed by acid-base reaction between the resulting amido species and another molecule of Ph₂C=NH. The reactions of 2 equiv of Sm(OAr) ₂(THF)₃ (Ar = C₆H₂- ^tBu₂-2,6-Me-4) with N-phenyl benzophenone imine (Ph ₂C=NPh) and N-phenyl fluorenone imine (C₁₂H ₈C=NPh) yielded the Sm(III) η²-imine-diamon/aryloxide complexes Sm(η²-Ph₂-CNPh)(OAr)(THF)₃ (3, 65%) and Sm(η²-C₁₂H₈CNPh)(OAr)(THF) ₃ (4, 77%), respectively, together with the byproduct Sm(OAr) ₃. The reaction of 1 equiv of Sm(OAr)₂(THF)₃ with Ph₂C=NPh also gave the imine-dianion complex 3, whereas an imine radical anion species was not observed. Similarly, the reactions of 2 equiv of Sm{N(SiMe₃)₂}₂(THF)₂ with Ph₂-C=NPh and C₁₂H₈C==NPh yielded the η²-imine-dianion/silylamido complexes Sm(η ²-Ph₂-CNPh){N(SiMe₃)₂}(THF) ₃ (5, 87%) and Sm(η²-C₁₂H ₈CNPh){N(SiMe₃)₂}(THF)₃ (6, 71%), respectively. Complexes 3-6 represent the first examples of structurally characterized trivalent lanthanide η²-imine complexes.

Full text of DOI:10.1021/om030366v

3586
Organometallics 2003, 22, 3586-3592
Red u ction of Ketim in es by Sa m a r iu m (II) Com p lexes.
Isola tion a n d Str u ctu r a l Ch a r a cter iza tion of
Sa m a r iu m (III) η1-Am in e/η1-Ketim id o a n d η2-Ketim in e
Com p lexes
Zhaomin Hou,*,† Chikako Yoda,†,‡ Take-aki Koizumi,† Masayoshi Nishiura,†
Yasuo Wakatsuki,† Shin-ichi Fukuzawa,‡ and J osef Takats§
Organometallic Chemistry Laboratory, RIKEN Institute, Hirosawa 2-1,
Wako, Saitama 351-0198, J apan, Department of Applied Chemistry, Chuo University,
Kasuga 1-13-27, Bunkyo, Tokyo 112-0003, J apan, and Department of Chemistry,
University of Alberta, Edmonton, Alberta, Canada T6G 2G2
Received May 16, 2003
The reaction of (C5Me5)2Sm(THF)2 with 2 equiv of benzophenone imine (Ph2CdNH) in
THF at room temperature gave the samarocene(III) amine/ketimido complex (C5Me5)2Sm-
(NdCPh2)(NH2CHPh2) (1) in 58% isolated yield. The use of 1 equiv of Ph2CdNH also afforded
1 as the only isolable product, albeit in a lower yield (ca. 20%). Deuterium-labeling
experiments suggest that 1 is formed via hydrogen abstraction by the in-situ-generated imine
radical anion species, followed by acid-base reaction between the resulting amido species
and another molecule of Ph2CdNH. The reactions of 2 equiv of Sm(OAr)2(THF)3 (Ar ) C6H2-
tBu2-2,6-Me-4) with N-phenyl benzophenone imine (Ph2CdNPh) and N-phenyl fluorenone
imine (C12H8CdNPh) yielded the Sm(III) η2-imine-dianion/aryloxide complexes Sm(η2-Ph2-
CNPh)(OAr)(THF)3 (3, 65%) and Sm(η2-C12H8CNPh)(OAr)(THF)3 (4, 77%), respectively,
together with the byproduct Sm(OAr)3. The reaction of 1 equiv of Sm(OAr)2(THF)3 with
Ph2CdNPh also gave the imine-dianion complex 3, whereas an imine radical anion species
was not observed. Similarly, the reactions of 2 equiv of Sm{N(SiMe3)2}2(THF)2 with Ph2-
CdNPh and C12H8CdNPh yielded the η2-imine-dianion/silylamido complexes Sm(η2-Ph2-
CNPh){N(SiMe3)2}(THF)3 (5, 87%) and Sm(η2-C12H8CNPh){N(SiMe3)2}(THF)3 (6, 71%),
respectively. Complexes 3-6 represent the first examples of structurally characterized
trivalent lanthanide η2-imine complexes.
In tr od u ction
these reactions, the isolation and structural character-
ization of such an intermediate species from the reduc-
tion of imines remains very rare.2b,3a,b,e For the lan-
thanides only one example of a structurally characterized
Yb(II) imine-dianion complex, Yb(η2-Ph2CNPh)(HMPA)3,
has been reported previously, which was isolated from
the reaction of metallic Yb with Ph2CdNPh in the
presence of hexamethylphosphoric triamide (HMPA).2b
The isolation and structural characterization of an imine
radical anion species, which is isoelectronic with ket-
yls,4,5 remains a challenge for any metal.
The reduction of imines by low-valent lanthanides
(e.g., SmI2 and Yb2) and other reducing metals3 has
1
attracted considerable current interest. The reductive
homocoupling of imines offers a convenient route to
vicinal diamines, while the cross-coupling of imines with
ketones or aldehydes affords R-amino alcohols,1-3 both
of which are valuable subunits found in medicinally
important compounds or biologically active natural
products. Although imine radical anion or imine-dianion
species are thought to be important intermediates in
* Corresponding author. E-mail: houz@postman.riken.go.jp
† RIKEN.
(3) For examples, see: (a) Cameron, T. M.; Ortiz, C. G.; Abboud, K.
A.; Boncella, J . M.; Baker, R. T.; Scott, B. L. Chem. Commun. 2000,
573. (b) Takai, K., Ishiyama, T.; Yasue, H.; Nobunaga, T.; Itoh, M.;
Oshiki, T.; Mashima, K.; Tani, K. Organometallics 1998, 17, 5128. (c)
Rieke, R. D.; Kim, S.-H. J . Org. Chem. 1998, 63, 5235, and references
therein. (d) Talukdar, S.; Banerji, A. J . Org. Chem. 1998, 63, 3468. (e)
Lefeber, C.; Arndt, P.; Tillack, A.; Baumann, W.; Kempe, R.; Burlakov,
V. V. Rosenthal, U. Organometallics 1995, 14, 3090. (f) Tanaka, H.;
Dhimane, H.; Fujita, H.; Ikemoto, Y. Tetrahedron Lett. 1992, 33, 4469.
(g) Ito, H.; Taguchi, T.; Hanazawa, Y. Tetrahedron Lett. 1988, 29, 3811.
(h) Mangeney, P.; Tejero, A.; Alexakis, A.; Grosjean, F.; Normant, J .
Synthesis 1988, 255. (i) Roskamp, E. J .; Pedersen, S. F. J . Am. Chem.
Soc. 1987, 109, 6551.
‡ Chuo University.
§ University of Alberta.
(1) (a) Tanaka, Y.; Taniguchi, N.; Uemura, M. Org. Lett. 2002, 4,
835. (b) Taniguchi, N.; Uemura, M. J . Am. Chem. Soc. 2000, 122, 8301.
(c) Machrouhi, F.; Namy, J .-L. Tetrahedron Lett. 1999, 40, 1315. (d)
Annunziata, R.; Benaglia, M.; Cinquini, M.; Cozzi, F.; Raimondi, L.
Tetrahedron Lett. 1998, 39, 3333. (e) Taniguchi, N.; Uemura, M.
Synlett. 1997, 51. (f) Lebrun, A.; Rantze, E.; Namy, J .-L.; Kagan, H.
B. New J . Chem. 1995, 19, 699. (g) Imamoto, T.; Nishimura, S. Chem.
Lett. 1990, 1141. (h) Enholm, E. J .; Forbes, D. C.; Holub, D. P. Synth.
Commun. 1990, 20, 981.
(2) (a) J in, W.-S.; Makioka, Y.; Taniguchi, Y.; Kitamura, T.; Fuji-
wara, Y. Chem. Commun. 1998, 1101. (b) Makioka, Y.; Taniguchi, Y.;
Fujiwara, Y.; Takaki, K.; Hou, Z.; Wakatsuki, Y. Organometallics 1996,
15, 5476. (c) Takaki, K.; Tanaka, S.; Fujiwara, Y. Chem. Lett. 1991,
493. (d) Takaki, K.; Tsubaki, Y.; Tanaka, S.; Beppu, F.; Fujiwara, Y.
Chem. Lett. 1990, 203.
(4) For examples of structurally characterized ketyl complexes
formed by one-electron reduction of ketones, see: (a) Hou, Z.; Koizumi,
T.; Nishiura, M.; Wakatsuki, Y. Organometallics 2001, 20, 3323. (b)
Hou, Z.; J ia, X.; Fujita, A.; Tezuka, H.; Yamazaki, H.; Wakatsuki, Y.
Chem. Eur. J . 2000, 6, 2994. (c) Hou, Z.; Fujita. A.; Koizumi, T.;
Yamazaki, H.; Wakatsuki, Y. Organometallics 1999, 18, 1979. (d) Hou,
10.1021/om030366v CCC: $25.00 © 2003 American Chemical Society
Publication on Web 07/25/2003

Reduction of Ketimines by Sm(II) Complexes
Organometallics, Vol. 22, No. 17, 2003 3587
Sch em e 1
In attempts to isolate a lanthanide imine radical
anion species, we examined the reactions of several
sterically demanding Sm(II) complexes with aromatic
ketimines, as we did in the isolation of ketyl com-
plexes.4,5 In this paper, we report on the reactions of
benzophenone imine, N-phenyl benzophenone imine,
and N-phenyl fluorenone imine with the Sm(II) com-
F igu r e 1. ORTEP drawing of 1 with 30% thermal el-
lipsoids. Hydrogen atoms are omitted for clarity.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) of 1
Sm1-N1
Sm1-C27
Sm1-C29
Sm1-C31
Sm1-C38
Sm1-C40
N1-C1
2.24(1)
2.76(1)
2.74(1)
2.75(1)
2.72(1)
2.779(9)
1.23(1)
Sm1-N2
Sm1-C28
Sm1-C30
Sm1-C37
Sm1-C39
Sm1-C41
N2-C14
2.62(1)
2.71(1)
2.73(1)
2.79(1)
2.73(1)
2.78(1)
1.37(1)
t
plexes (C5Me5)2Sm(THF)2, Sm(OC6H2 Bu2-2,6-Me-4)2-
(THF)3, and Sm{N(SiMe3)2}2(THF)2, which afforded
structurally characterizable Sm(III) η1-amine/η1-ket-
imido and η2-ketimine complexes, depending on the
structures of the imines and the reducing agents.6 Some
mechanistic aspects of these reactions are also de-
scribed.
Sm1-N1-C1
N1-C1-C2
C2-C1-C8
177.0(7)
123.9(10)
114.8(9)
117(1)
Sm1-N2-C14
N1-C1-C8
N2-C14-C15
C15-C14-C21
137.6(8)
121.2(9)
117(1)
N2-C13-C21
110(1)
Resu lts a n d Discu ssion
suggested the presence of two benzophenone imine-
derived units per two C5Me5 groups. A triplet at δ 5.15
(J ) 7 Hz, 1 H) and a broad singlet at δ 1.74 (2 H, NH2)
with an integration of 1:2 were evident for the presence
of a diphenylmethylamine unit (NH2CHPh2). The IR
spectrum of 1 in Nujol showed a strong absorption at
1600 cm-1 for the CdN double bond of the ketimido unit,
which is slightly low-frequency shifted from that of free
benzophenone imine (1605 cm-1).
In agreement with the spectral data, an X-ray crys-
tallographic study showed that 1 bears two C5Me5
ligands and two significantly different benzophenone
imine-derived ligands (Figure 1 and Table 1). The Sm-
C(Cp*) bond distances, ranging from 2.71(1) to 2.79(1)
Å, are typical for a trivalent decamethylsamarocene
complex. The Sm1-N1 bond distance (2.239(9) Å) is
comparable with that of the Sm-N(ketimido) bond
found in (C5Me5)2Sm[NdCPh(C5Me5)](NCPh) (2.225(8)
Å),7 but much shorter than that of the Sm1-N2 bond
(2.62(1) Å). The C1-N1 bond distance (1.23(1) Å) in 1
is also comparable with that of the CdN double bond
in (C5Me5)2Sm[NdCPh(C5Me5)](NCPh) (1.26(1) Å),7 but
significantly shorter than that of the C14-N2 bond
(1.37(1) Å). The sum of the angles around C1 is 360(1)°
(sp2-hybrid), which is in contrast with that around C14
(344(1)°). These data strongly suggest that the N1
moiety in 1 is a ketimido ligand, while N2 belongs to a
neutral amine ligand.
Redu ction of Ben zoph en on e Im in e with (C5Me5)2-
Sm (THF )2. Because of its similarity with a ketone, an
N-H ketimine was first chosen as an imine substrate.
The reaction of benzophenone imine (Ph2CdNH) with
1 equiv of (C5Me5)2Sm(THF)2 in THF at room temper-
ature gave an orange-red complex, 1, as the only isolable
product (ca. 20% yield based on Sm). When 2 equiv of
Ph2CdNH was used, 1 was obtained in 58% isolated
yield as orange-red blocks (Scheme 1). The well-resolved
1H NMR spectrum in THF-d8 showed that 1 is a
samarocene(III) diphenylketimido/diphenylmethylamine
complex, (C5Me5)2Sm(NdCPh2)(NH2CHPh2), rather than
a radical species. A 30:20 integration of the C5Me5 signal
at δ 1.44 (s) and the Ph peaks at 7.12-7.70 (m)
Z.; Fujita. A.; Zhang, Y.; Miyano, T.; Yamazaki, H.; Wakatsuki, Y. J .
Am. Chem. Soc. 1998, 120, 754. (e) Hou, Z.; J ia, X.; Wakatsuki, Y.
Angew. Chem., Int. Ed. Engl. 1997, 36, 1292. (f) Takats, J . J .
Alloys Compd. 1997, 249, 51. (g) Clegg, W.; Eaborn, C.; Izod, K.;
O’Shaughnessy, P.; Smith, J . D. Angew. Chem., Int. Ed. Engl. 1997,
36, 2815. (h) Hou, Z.; Fujita. A.; Yamazaki, H.; Wakatsuki, Y. J . Am.
Chem. Soc. 1996, 118, 7843. (i) Hou, Z.; Fujita, A.; Yamazaki, H.;
Wakatsuki, Y. J . Am. Chem. Soc. 1996, 118, 2503. (j) Hou, Z.; Miyano,
T.; Yamazaki, H.; Wakatsuki, Y. J . Am. Chem. Soc. 1995, 117, 4421.
(k) Bock, H.; Herrmann, H.-F.; Fenske, D.; Goesmann, H. Angew.
Chem., Int. Ed. Engl. 1988, 27, 1067.
(5) For examples of structurally characterized ketone-dianion com-
plexes formed by two-electron reduction of ketones, see: (a) Tardif,
O.; Hou, Z.; Nishiura, M.; Koizumi, T.; Wakatsuki, Y. Organometallics
2001, 20, 4565. (b) Hou, Z.; Fujita, A.; Yamazaki, H.; Wakatsuki, Y.
Chem. Commun. 1998, 669. (c) Yoshimura, T.; Hou, Z.; Wakatsuki, Y.
Organometallics 1995, 14, 5382. (d) Hou, Z.; Yamazaki, H.; Kobayashi,
K.; Fujiwara, Y.; Taniguchi, H. J . Chem. Soc., Chem. Commun. 1992,
722. (e) Hou, Z.; Yamazaki, H.; Fujiwara, Y.; Taniguchi, H. Organo-
metallics 1992, 11, 2711. (f) Bogdanovic, B.; Kruger, C.; Wermeckes,
B. Angew. Chem., Int. Ed. Engl. 1980, 19, 817.
Addition of 1 equiv of Ph2CdNH to a THF solution of
1 yielded quantitatively the imine-coordinated complex
(6) No reaction occurred between the insoluble Sm(TpMe2
)
(TpMe2
(7) Evans, W. J .; Forrestal, K. J .; Ziller, J . W. J . J . Am. Chem. Soc.
1998, 120, 9273.
2
) HB(3,5-Me2-pyrazolyl)3) and the imines under similar conditions.

3588 Organometallics, Vol. 22, No. 17, 2003
Hou et al.
Sch em e 2
Sch em e 3
(C5Me5)2Sm(NdCPh2)(NHdCPh2) (2) with release of
NH2CHPh2 (Scheme 1), indicating that Ph2CdNH is a
stronger ligand for Sm(III) than Ph2CHNH2. Alterna-
tively, the reaction of 3 equiv of Ph2CdNH with (C5-
Me5)2Sm(THF)2 also afforded 2 in 60% isolated yield
(Scheme 1). The IR absorption of the CdN double bond
of the ketimido unit shifted to 1625 cm-1 in 2 from 1600
cm-1 in 1, suggesting that the CdN double bond of the
ketimido unit in 2 is stronger than that in 1. This is
probably due to the influence of the stronger coordina-
tion of the imine ligand to the metal center in 2, which
weakens the Sm-ketimido bond and thus strengthens
the ketimido CdN bond. The absorption of the CdN
bond of the coordinated imine ligand Ph2CdNH in 2
appeared at 1595 cm-1, 10 cm-1 lower than that of free
Ph2CdNH (1605 cm-1).
The formation of 1 apparently requires the reduction
(hydrogenation) of the CdN bond of one Ph2CdNH
molecule and the cleavage of the N-H bond of another
Ph2CdNH molecule. To gain more information about
the hydrogen transfer processes, deuterium-labeling
experiments were carried out as shown in Scheme 2.
The reaction of Ph2CdND with (C5Me5)2Sm(THF)2 in
THF-d8 led to complete deuteration at both the methine
carbon and the amino group of the diphenylmethyl-
amine unit to give 1-d ′′. However, the reaction of
Ph2CdNH with (C5Me5)2Sm(THF)2 in THF-d8 or that
of Ph2CdND with (C5Me5)2Sm(THF)2 in normal THF
resulted in only partial deuteration at the methine
carbon and the amino group of the diphenylmethyl-
amine unit.8 These results suggest that an intra-
molecular hydrogen atom transfer from the N atom to
the methine C atom, as well as hydrogen (or deuterium)
abstraction from the solvent by both the N atom and
the methine C atom, took place. On the basis of these
results, a possible mechanism for the formation of 1, as
shown in Scheme 3, can be proposed. One-electron
transfer from (C5Me5)2Sm(THF)2 to Ph2CdNH would
generate the radical species A. Intramolecular hydrogen
radical (H•) transfer from the N atom to the radical
carbon atom in A could generate the nitrogen radical
species B, which upon abstraction of H• from THF
solvent gives C. The H• abstraction from the solvent by
A could also occur to yield C. Hydrogen abstraction from
another molecule of Ph2CdNH by the amido species C
ultimately affords 1.
The isolation of the amine/ketimido complex 1 instead
of a amido complex such as C as the final product even
when only 1 equiv of Ph2CdNH was used shows that
benzophenone imine (Ph2CdNH) is much more acidic
than diphenylmethylamine (Ph2CHNH2) and the acid-
base reaction between C and Ph2CdNH is much faster
than the electron transfer from (C5Me5)2Sm(THF)2 to
Ph2CdNH. These results are in contrast with what was
observed previously in the reactions of titanocene and
zirconocene reducing agents with Ph2CdNH, in which
the corresponding amido/ketimido complexes Cp2M-
(NHCHPh2)(NdCPh2) (M ) Ti, Zr) were obtained.3e The
easy formation of the amine/ketimido complex 1 in the
present reactions also suggests that the acid-base
reaction between a lanthanide amido species and an
N-H ketimine compound could constitute a convenient
method for the synthesis of the corresponding lan-
thanide ketimido complexes.9,10
Red u ction of N-P h en yl Ben zop h en on e Im in e
a n d N-P h en yl F lu or en on e Im in e by Sm (OAr )2-
(THF )3 a n d Sm {N(SiMe3)2}2(THF )2. To prevent the
intramolecular H transfer reaction observed above and
generate a more stable radical species, N-phenyl ben-
zophenone imine (Ph2CdNPh) and N-phenyl fluorenone
imine (C12H8CdNPh) were then examined. The reaction
of (C5Me5)2Sm(THF)2 with 1 equiv of Ph2CdNPh, how-
(9) For examples of the formation of group 3 (Sc, Y) metal ketimido
or aldimido complexes, see: (a) Evans, W. J .; Meadows, J . H.; Hunter,
W. E.; Atwood, J . L. J . Am. Chem. Soc. 1984, 106, 1291. (b) Bercaw, J .
E.; Davies, D. L.; Wolczanski, P. T. Organometallics 1986, 5, 443. (c)
den Haan, K. H.; Luinstra, G. A.; Meetsma, A. Teuben, J . H.
Organometallics 1987, 6, 1509. (d) Duchateau, R.; van Wee, C. T.;
Teuben, J . H. Organometallics 1996, 15, 2291. See also ref 7.
(10) For the synthesis and structural characterization of an actinide
ketimido complex, see: Kiplinger, J . L.; Morris, D. E.; Scott, B. L.;
Burns, C. J . Organometallics 2002, 21, 3073.
(8) The D/H contents in 1-d and 1-d ′ seemed different. An accurate
determination of the D/H-incorporation percentages was, however,
difficult, because the corresponding NMR signals (1H and 2H) were
too weak to give an accurate integration ratio. It was roughly estimated
that 1-d bears ca. 0.3-0.4 H (0.6-0.7 D) at the methine carbon and
ca. 1.6-1.7 H (0.3-0.4 D) at the amino group of the diphenylmethyl-
amine unit, while 1-d ′ possesses ca. 0.1-0.2 H (0.8-0.9 D) at the
methine carbon and ca. 0.8-0.9 H (1.1-1.2 D) at the amino group.

Reduction of Ketimines by Sm(II) Complexes
Organometallics, Vol. 22, No. 17, 2003 3589
Sch em e 4
Sch em e 5
F igu r e 2. ORTEP drawing of 3 with 30% thermal el-
lipsoids. Hydrogen atoms are omitted for clarity.
ever, did not afford a structurally characterizable
product. Under similar conditions, the reaction of
Sm(OAr)2(THF)3 (Ar ) C6H2-tBu2-2,6-Me-4) with 1 equiv
of Ph2CdNPh in THF at room temperature gave the
Sm(III) monoaryloxide/imine-dianion complex Sm(η2-
Ph2CNPh)(OAr)(THF)3 (3, ca. 20%) together with the
tris(aryloxide) complex Sm(OAr)3 and unreacted Ph2-
CdNPh. A radical species was not observed. When 2
equiv of Sm(OAr)2(THF)3 was used in this reaction, the
η2-imine-dianion complex 3 was isolated in 65% yield
(based on imine) as green crystals (Scheme 4). The
similar reaction of N-phenyl fluorenone imine (C12H8-
CdNPh) with Sm(OAr)2(THF)3 afforded Sm(η2-C12H8-
CNPh)(OAr)(THF)3 (4). Analogously, the reactions of
Sm{N(SiMe3)2}2(THF)2 with Ph2CdNPh and N-phenyl
fluorenone imine yielded the corresponding η2-imine-
dianion/silylamido complexes 5 and 6, respectively, as
shown in Scheme 5.
F igu r e 3. ORTEP drawing of 4 with 30% thermal el-
lipsoids. Hydrogen atoms are omitted for clarity.
Complexes 3-6 adopt a similar overall structure (see
Figures 2-5 and Tables 2 and 3). The Sm-N1(imine)
bond distances in 3-6 (2.203(6)-2.270(4) Å) are some-
what shorter than those of the Sm-N2(silylamido)
bonds in 5 (2.351(5) Å) and 6 (2.34(2) Å), but comparable
with that of the Sm-N1(ketimido) bond in 1 (2.24(1)
Å). The Sm-C7(imine) bond distances in 3-6
(2.564(4)-2.64(2) Å) are longer than the Sm-C(benzyl)
distance in (C5Me5)2SmCH2Ph(THF) (2.498(5) Å)11 and
the Sm-C(phenyl) distance in (C5Me5)2SmPh(THF)
(2.511(5) Å),12 but shorter than a typical Sm(III)-C(Cp*)
distance (2.7-2.8 Å). The N1-C7 bond distances in 3-6
(1.43(3)-1.45(3) Å) are comparable with those in Yb-
(η2-Ph2CNPh)(HMPA)3 (1.43(3) Å),2b (PhN)Mo{1,2-(Me3-
SiN)2C6H3}(η2-Ph(Me)CNPh) (1.414(3) Å),3a and TaCl3-
F igu r e 4. ORTEP drawing of 5 with 30% thermal el-
lipsoids. Hydrogen atoms are omitted for clarity.
(η2-Ph(H)CNCH2Ph)(MeOCH2CH2OMe) (1.401(6) Å)3b
and can be considered as C-N single bonds. The sums
of the angles formed by N1, C8, and C14 around C7 in
3-6 (357.3(7)°, 359.1(4)°, 356.9(5)°, and 360(2)°, respec-
tively) are comparable with that in Yb(η2-Ph2CNPh)-
(HMPA)3 (359(1)°)2b and those reported for ketone-
dianion complexes (358-360°),5 suggesting that the C7
carbon atoms in 3-6 are still sp2-hybridized. As far as
we are aware, complexes 3-6 represent the first ex-
(11) Evans, W. J .; Chamberlain, L. R.; Ulibarri, T. A.; Ziller, J . W.
J . Am. Chem. Soc. 1988, 110, 6423.
(12) Evans, W. J .; Bloom, I.; Hunter, W. E.; Atwood, J . L. Organo-
metallics 1985, 4, 112.

3590 Organometallics, Vol. 22, No. 17, 2003
Hou et al.
Sch em e 6
from SmX2 (X ) N(SiMe3)2, OC6H2-tBu2-2,6-Me-4) to a
ketimine should give the radical species D, which upon
reduction by another equivalent of SmX2 would afford
the disamarium imine-dianion species E. Ligand redis-
tribution in E could give SmX3 and 3-6. The isolation
of the imine-dianion complexes 3-6 rather than an
imine radical anion species such as D, even when only
1 equiv of SmX2 was used, suggests that an N-Ph
ketimine radical species is more easily reduced than its
neutral imine precursor. The easier formation of an
imine-dianion species than that of an imine radical
anion was also observed previously in the reduction of
N-phenyl ketimines by SmI2.1g These results are in
contrast with what was observed in ketone reductions,
in which both ketyl radical and ketone-dianion species
could be isolated by control of the reducing agent/
substrate ratio.4,5
F igu r e 5. ORTEP drawing of 6 with 30% thermal el-
lipsoids. Hydrogen atoms are omitted for clarity.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) of 3 a n d 4
3
4
Sm1-N1
Sm1-C7
Sm1-O1
Sm1-O2
Sm1-O3
Sm1-O4
N1-C1
2.255(6)
2.557(7)
2.187(6)
2.571(6)
2.523(5)
2.513(5)
1.372(9)
1.450(10)
2.270(4)
2.564(4)
2.168(3)
2.504(4)
2.543(3)
2.486(6)
1.386(5)
1.441(6)
N1-C7
Sm1-N1-C1
Sm1-N1-C7
Sm1-C7-N1
Sm1-C7-C8
Sm1-C7-C14
N1-Sm1-O1
O1-Sm1-C7
Sm1-O1-C20
N1-C7-C8
150.4(5)
84.3(4)
61.3(4)
127.6(5)
91.9(5)
111.4(2)
136.4(2)
158.7(5)
116.0(7)
115.8(7)
125.5(7)
153.4(3)
84.2(2)
61.8(2)
127.1(4)
94.9(3)
133.3(1)
138.4(1)
164.5(3)
127.1(4)
124.8(4)
107.2(4)
Con clu sion
We have demonstrated that the reaction of a Sm(II)
complex such as (C5Me5)2Sm(THF)2 with an N-H
ketimine compound easily gives an η1-amine/η1-ketimido
complex such as 1 through hydrogen abstraction of the
in-situ-generated imine radical anion species and the
subsequent acid-base reaction between the resulting
amido species and another molecule of the N-H ketimine.
In the case of N-Ph ketimines, two-electron reduction
is preferred to yield the corresponding η2-imine-dianion
complexes. The isolation of a structurally characteriz-
able imine radical anion species remains a challenge.
N1-C7-C14
C8-C7-C14
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) of 5 a n d 6
5
6
Sm1-N1
Sm1-C7
Sm1-N2
Sm1-O1
Sm1-O2
Sm1-O3
N1-C1
2.203(6)
2.588(7)
2.351(5)
2.525(4)
2.562(4)
2.522(4)
1.390(8)
1.450(7)
2.22(2)
2.64(2)
2.34(2)
2.46(1)
2.46(1)
2.53(2)
1.39(3)
1.43(3)
N1-C7
Exp er im en ta l Section
Sm1-N1-C1
Sm1-N1-C7
Sm1-C7-N1
Sm1-C7-C8
Sm1-C7-C14
N1-Sm1-N2
N2-Sm1-C7
N1-C7-C8
146.4(4)
87.7(4)
58.3(3)
116.4(4)
107.5(4)
105.6(4)
130.4(2)
115.2(5)
119.9(5)
121.8(5)
151(1)
89(1)
57(1)
106(1)
115(1)
118.4(7)
139.0(8)
125(2)
128(2)
107(2)
Gen er a l Meth od s. All reactions were carried out under a
dry and oxygen-free argon atmosphere by using Schlenk
techniques or under a nitrogen atmosphere in an MBraun
glovebox. Argon was purified by being passed through a
Dryclean column (4 Å molecular sieves, Nikka Seiko Co.) and
a Gasclean GC-XR column (Nikka Seiko Co.). The nitrogen in
the glovebox was constantly circulated through a copper/
molecular sieves (4 Å) catalyst unit. The oxygen and moisture
level in the glovebox was monitored by an O2/H2O Combi-
Analyzer (MBraun) to ensure that both were always below 1
ppm. Samples of the lanthanide complexes for NMR spectro-
scopic measurements were prepared in the glovebox by use of
J . Young valve NMR tubes (Wilmad 528-J Y). 1H NMR spectra
were recorded on a J NM-EX 270 (FT, 270 MHz) spectrometer.
Elemental analyses were carried out by the Chemical Analysis
Team, Advanced D&S Center, RIKEN. Solvents were distilled
from sodium/benzophenone ketyl, degassed by the freeze-
N1-C7-C14
C8-C7-C14
amples of structurally characterized trivalent lan-
thanide η2-imine complexes.13
The formation of 3-6 could be explained by the
mechanism shown in Scheme 6. One-electron transfer
(13) For an example of a divalent lanthanide η2-imine complex, see
ref 2b.

Reduction of Ketimines by Sm(II) Complexes
Organometallics, Vol. 22, No. 17, 2003 3591
Ta ble 4. Su m m a r y of Cr ysta llogr a p h ic Da ta
1
3
4
5
6
formula
mol wt
cryst syst
space group
a (Å)
C
46H53N2Sm
C46H62NO4Sm
843.40
C46H60NO4Sm
841.38
triclinic
P1h (No. 2)
14.033(6)
14.487(8)
10.565(1)
98.01(2)
94.08(1)
97.82(4)
2098(1)
2
14.44
874.00
1.332
9291
8327
C37H57N2O3Si2Sm
784.44
monoclinic
P21/c (No. 14)
19.345(2)
C37H55N2O3Si2Sm
782.42
monoclinic
C2/c (No. 15)
40.520(10)
10.915(6)
784.34
monoclinic
P21/c (No. 14)
16.653(5)
12.028(2)
20.108(5)
triclinic
P1h (No. 2)
11.773(1)
18.527(3)
10.551(4)
105.978(6)
100.84(2)
72.68(1)
2098.0(9)
2
14.44
878.00
1.335
8748
8389
469
b (Å)
c (Å)
9.905(2)
20.905(3)
17.896(3)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
94.260(8)
103.772(9)
96.796(10)
4017(1)
4
3890.8(10)
4
16.09
1628.00
1.339
7869
7858(5)
8
µ (cm-1
F(000)
)
14.97
1620.00
1.297
9536
6903
442
15.93
3244.00
1.322
7007
3408
406
Dcalcd (g cm-1
)
no. of unique reflns
no. of reflns with I > 3σ(I)
no. of variables
6201
406
469
R
Rw
0.078
0.078
0.068
0.079
0.043
0.063
0.044
0.067
0.092
0.115
pump-thaw method (three times), and dried over fresh Na
chips in the glovebox. Ph2CdNH was purchased from Aldrich.
Ph2CdND was prepared by reaction of CD3OD with Ph2-
CdNLi, which was generated by reaction of BuLi with 1 equiv
(C5Me5)2Sm (NdCP h 2)(NHdCP h 2) (2). To Sm(C5Me5)2-
(THF)2 (180 mg, 0.32 mmol) in THF (20 mL) was added Ph2-
CdNH (190 mg, 1.1 mmol) at room temperature. The reaction
mixture soon turned from deep purple to dark brown and then
to reddish orange. After the mixture was stirred for 2 h at
room temperature, the solvent was removed under reduced
pressure. The red solid was recrystallized from THF/hexane
to give 2 as fine red crystals (150 mg, 60%). Reaction of 1 with
1 equiv of Ph2CdNH also afforded 2 almost quantitatively.
1H NMR (THF-d8, 25 °C): δ 10.10 (br s, 1 H, NH), 7.10-7.29
(m, 20 H, Ph), 1.43 (s, 30 H, C5Me5). IR (Nujol): 3265 (νN-H),
3220 (νN-H), 1625 (νCdN), 1595 (νCdN) cm-1. Anal. Calcd for
of Ph2CdNH in THF at -78 °C. Ph2CdNPh,14
C12H8CdNPh
(N-phenyl fluorenone imine),14 (C5Me5)2Sm(THF)2,15 Sm(OC6H2-
tBu2-2,6-Me-4)2(THF)3,16 Sm{N(SiMe3)2}2(THF)2,17 and Sm-
(TpMe2
)
(TpMe2 ) HB(3,5-Me2-pyrazolyl)3)6,18 were prepared
2
according to literature methods.
(C5Me5)2Sm (NdCP h 2)(NH2CH P h 2) (1). To (C5Me5)2Sm-
(THF)2 (200 mg, 0.35 mmol) in THF (20 mL) was added Ph2-
CdNH (130 mg, 0.72 mmol) at room temperature. The mixture
soon turned from purple to dark brown and then to reddish
orange. After the reaction mixture was stirred for 2 h, THF
was removed under reduced pressure. The orange-red solid
residue was washed with hexane and recrystallized from THF/
hexane to give orange-red blocks of 1 (160 mg, 58%). The
reaction of (C5Me5)2Sm(THF)2 with 1 equiv of Ph2CdNH also
C
46H51N2Sm: C, 70.63; H, 6.57; N, 3.58. Found: C, 70.55; H,
6.50; N, 3.53.
t
Sm (η2-P h 2CNP h )(OC6H2 Bu 2-2,6-Me-4)(THF)3 (3). To Sm-
(OC6H2-tBu2-2,6-Me-4)2(THF)3 (700 mg, 0.80 mmol) in THF (20
mL) was added Ph2CdNPh (102 mg, 0.40 mmol) at room
temperature. The reaction mixture soon turned from reddish
brown to greenish brown. After the reaction mixture was
stirred for 3 days, THF was removed under reduced pressure.
The residue was washed with hexane, and the resulting green
solid was collected by filtration to give 3 (220 mg, 65%) after
drying in vacuo. The hexane filtrate was concentrated under
1
afforded 1 in ca. 20% yield (based on Sm). H NMR (THF-d8,
25 °C): δ 7.12-7.70 (m, 20 H, Ph), 5.15 (t, 1 H, J ) 7 Hz,
CHPh2), 1.74 (br s, 2 H, NH2), 1.44 (s, 30 H, C5Me5). IR
(Nujol): 3265 (νN-H), 3220 (νN-H), 1600 (νCdN) cm-1. Anal. Calcd
for C46H53N2Sm: C, 70.44; H, 6.81; N, 3.57. Found: C, 70.01;
H, 6.76; N, 3.55.
t
reduced pressure to give yellow crystals of Sm(OC6H2 Bu2-2,6-
(C5Me5)2Sm (NdCP h 2){N(H/D)2C(H/D)P h 2} (1-d ). This
complex was prepared by reaction of Sm(C5Me5)2(THF)2 with
Ph2CdNH in THF-d8 analogously to the synthesis of 1. 1H
NMR (THF-d8, 25 °C):8 δ 7.12-7.70 (m, 20 H, Ph), 5.15 (br s,
ca. 0.3-0.4 H, C(H/ D)Ph2), 1.73 (br s, ca. 1.6-1.7 H,
N(H/D)2), 1.44 (s, 30 H, C5Me5).
Me-4)3 (270 mg, 83%). Single crystals of 3 could be obtained
by recrystallization of the green solid from THF/hexane. 1H
NMR for 3 (THF-d8, 25 °C): δ 11.85 (d, 2 H, J ) 7 Hz, N-Ph-
o), 9.51 (br s, 4 H, Ph-o), 7.79 (t, 1 H, J ) 7 Hz, N-Ph-p), 7.62
(br s, 2 H, N-Ph-m), 7.25-7.45 (m, 4 H, Ph-o, C6H2), 5.51 (br
t
s, 4 H, Ph-m), 2.28 (s, 3 H, Me), 1.75 (br s, 18 H, Bu). Anal.
(C5Me5)2Sm (NdCP h 2){N(D/H)2C(D/H)P h 2} (1-d ′). This
complex was prepared by reaction of Sm(C5Me5)2(THF)2 with
Calcd for C46H62NO4Sm: C, 64.50; H, 7.62; N, 1.70. Found: C,
64.70; H, 7.42; N, 1.49.
1
Sm (η2-C12H8CNP h )(OC6H2 Bu 2-2,6-Me-4)(THF)3 (4). Com-
t
Ph2CdND in THF analogously to the synthesis of 1. H NMR
(THF-d8, 25 °C):8 δ 7.12-7.70 (m, 20 H, Ph), 5.15 (br s, ca.
0.1-0.2 H, C(D/ H)Ph2), 1.73 (br s, 0.8-0.9 H, N(D/H)2), 1.44
(s, 30 H, C5Me5).
plex 4 was prepared in 77% yield analogously to the synthesis
t
of 3 by reaction of 2 equiv of Sm(OC6H2 Bu2-2,6-Me-4)3 with
N-phenyl fluorenone imine. 1H NMR (THF-d8, 25 °C): δ 11.17
(d, 2 H, J ) 7 Hz, Ph-o), 8.69 (d, 2 H, J ) 7 Hz, C13H8), 7.61
(br s, 3 H, C13H8, N-Ph-p), 7.49 (t, 2 H, J ) 7 Hz, C13H8), 7.22
(s, 2 H, C6H2), 5.66 (t, 2 H, J ) 7 Hz, C13H8), 4.94 (d, 2 H, J )
(C5Me5)2Sm (NdCP h 2)(ND2CDP h 2) (1-d ′′). This complex
was prepared by reaction of Sm(C5Me5)2(THF)2 with Ph2Cd
ND in THF-d8 analogously to the synthesis of 1. 1H NMR
(THF-d8, 25 °C): δ 7.12-7.70 (m, 20 H, Ph), 1.44 (s, 30 H,
C5Me5).
t
7 Hz, C13H8), 2.21 (s, 3 H, Me), 1.26 (br s, 18 H, Bu). Anal.
Calcd for C46H60NO4Sm: C, 64.66; H, 7.39; N, 1.71. Found:
C, 64.80; H, 7.01; N, 1.76.
Sm (η2-P h 2CNP h ){N(SiMe3)2}(TH F )3 (5). To Sm{N(Si-
Me3)2}2(THF)2 (1.50 g, 2.44 mmol) in THF (20 mL) was added
Ph2CdNPh (311 mg, 1.22 mmol) at room temperature. The
reaction mixture soon turned from purple to greenish brown.
After the solution was stirred for 3 days, THF was removed
under reduced pressure. The residue was washed with hexane,
and the resulting green solid was collected by filtration to give
5 (835 mg, 87%) after drying in vacuo. The hexane filtrate was
(14) Reddelein, G. Chem. Ber. 1913, 46, 2172.
(15) (a) Evans, W. J .; Grate, J . W.; Choi, H. W.; Bloom, I.; Hunter;
W. E.; Atwood, J . L. J . Am. Chem. Soc. 1985, 107, 941. (b) Watson, P.
L.; Tulip, T. H.; Williams, I. Organometallics 1990, 9, 1999.
(16) Hou, Z.; Fujita. A.; Yoshimura, T.; J esorka, A.; Zhang, Y.;
Yamazaki, H.; Wakatsuki, Y. Inorg. Chem. 1996, 35, 7190.
(17) Evans, W. J .; Drummond, D. K.; Zhang, H.; Atwood, J . L. Inorg.
Chem. 1988, 27, 575.
(18) Takats, J .; Zhang, X. W.; Day, V. W.; Eberspacher, T. A.
Organometallics 1993, 12, 4286.

3592 Organometallics, Vol. 22, No. 17, 2003
Hou et al.
concentrated under reduced pressure to give pale yellow
needles of Sm{N(SiMe3)2}3 (690 mg, 90%). Single crystals of 5
could be obtained by recrystallization of the green solid from
were performed at 20 °C on a Rigaku RAXIS CS imaging plate
diffractometer with graphite-monochromated Mo KR radiation
(λ ) 0.71070 Å). The structures were solved by using the
teXsan software package. Refinements were performed on F
anisotropically for all non-hydrogen atoms by the full-matrix
least-squares method. Hydrogen atoms were placed at the
calculated positions and were included in the structure
calculation without further refinement of the parameters. The
residual electron densities were of no chemical significance.
Crystal data and processing parameters are summarized in
Table 4.
1
THF/hexane. H NMR for 5 (THF-d8, 25 °C): δ 11.50 (br s, 2
H, N-Ph-o), 9.27 (d, 4 H, J ) 8 Hz, Ph-o), 7.58 (t, 2 H, J ) 8
Hz, Ph-p), 7.30-7.50 (m, 3 H, N-Ph-m,p), 5.78 (t, 4 H, J ) 7
Hz, Ph-m), 0.15 (s, 18 H, SiMe3). Anal. Calcd for C37H57N2O3-
Si2Sm: C, 56.65; H, 7.32; N, 3.57. Found: C, 56.33; H, 6.90;
N, 3.40.
Sm (η2-C12H8CNP h ){N(SiMe3)2}(THF )3 (6). Complex 6
was prepared in 71% yield analogously to the synthesis of 5
by reaction of 2 equiv of Sm{N(SiMe3)2}2(THF)2 with N-phenyl
1
fluorenone imine. H NMR (THF-d8, 25 °C): δ 10.76 (d, 2 H,
Ack n ow led gm en t. This work was partly supported
by a grant-in-aid from the Ministry of Education,
Culture, Sports, Science, and Technology, J apan. J .T.
thanks RIKEN for a visiting professorship.
J ) 7 Hz, Ph-o), 8.58 (d, 2 H, J ) 7 Hz, C13H8), 7.30-7.60 (m,
5 H, C13H8, Ph), 5.88 (t, 2 H, J ) 7 Hz, C13H8), 5.20 (d, 2 H, J
) 7 Hz, C13H8), -0.42 (s, 18 H, SiMe3). Anal. Calcd for
C
37H55N2O3Si2Sm: C, 56.80; H, 7.08; N, 3.58. Found: C, 56.33;
H, 6.90; N, 3.40.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, thermal parameters, and bond distances and
angles for complexes 1 and 3-6. This material is available
free of charge via the Internet at http://pubs.acs.org.
X-r a y Cr ysta llogr a p h ic Stu d ies. Crystals for X-ray analy-
ses were obtained as described in the preparations. The
crystals were manipulated in the glovebox under a microscope
mounted on the glovebox window and were sealed in thin-
walled glass capillaries under N2 atmosphere. Data collections
OM030366V