Reaction of samarium 1,4-diaza-1,3-diene complexes with ketones: Generation of a new versatile tridentate ligand via 1,3-dipolar cycloaddition

Article abstract of DOI:10.1021/om010323j

Treatment of SmI₂(THF)_n with the dilithium 1,4-diaza-1,3-diene (DAD) compound Li₂[(tBu)NCH=CHN(tBu)] (≡Li₂(tBu-DAD); 2) prepared by reduction of tBu-DAD by 2 equiv of lithium in THF surprisingly results in the formation of the samarium(III) iodide complex [(THF)₂Li(tBu-DAD)][(THF)Li(tBu-DAD)]SmI (5). The characteristic structural feature of 5 is formed by two (Z)-1,4-diaza-but-2-ene-1,4-diyl units bridging the Sm³⁺ with two Li⁺ ions. Complex 5 and the analogous chloride complex [(THF)Li(tBu-DAD)]₂Sm(μ-Cl)₂Li(THF)₂ (4b) react with 2 equiv of benzophenone to give the structurally very similar samarium complexes {[OC(Ph)₂CH{CH=N(tBu)}N(tBu)]Li}₂SmX(THF) (X = Cl (6), I (7)) in high yield. The reaction formally proceeds via a 1,3-dipolar cycloaddition of the benzophenone C=O bond across a Sm-N-C= fragment of the enediamide samarium complexes 4b and 5, including the formation of a new C-C bond, and results in the formation of the novel tripodal ligand [OC(Ph)₂CH{CH=N(tBu)}N(tBu)]^2-. X-ray structure determinations of 6 and 7 revealed that the two tripodal ligands and the halogen atom form a slightly distorted octahedral coordination geometry around the Sm³⁺ ion and that the Li⁺ ions are retained within the ligand sphere by close contacts to their N and O atoms. By controlled hydrolysis of the cycloaddition product 6, the new tripodal ligands can be separated from the samarium and isolated in the form of the lithium compound {[OC(Ph)₂CH{CH=N(tBu)}N(tBu)]Li}₂ (8). The crystal structure of 8, which is dimeric in the solid state, is reported.

Full text of DOI:10.1021/om010323j

4394
Organometallics 2001, 20, 4394-4402
Rea ction of Sa m a r iu m 1,4-Dia za -1,3-d ien e Com p lexes
w ith Keton es: Gen er a tion of a New Ver sa tile Tr id en ta te
Liga n d via 1,3-Dip ola r Cycloa d d ition
J oachim Scholz,*,† Helmar Go¨rls,‡ Herbert Schumann,§ and Roman Weimann§
Institut fu¨r Chemie, Universita¨t Koblenz-Landau, Rheinau 1, D-56075 Koblenz, Germany,
Institut fu¨r Anorganische und Analytische Chemie, Friedrich-Schiller-Universita¨t J ena,
Lessingstrasse 8, D-07743 J ena, Germany, and Institut fu¨r Anorganische und Analytische
Chemie, Technische Universita¨t Berlin, Strasse des 17. J uni 135, D-10623 Berlin, Germany
Received April 19, 2001
Treatment of SmI2(THF)n with the dilithium 1,4-diaza-1,3-diene (DAD) compound Li2-
[(tBu)NCHdCHN(tBu)] (≡Li2(tBu-DAD); 2) prepared by reduction of tBu-DAD by 2 equiv
of lithium in THF surprisingly results in the formation of the samarium(III) iodide complex
[(THF)2Li(tBu-DAD)][(THF)Li(tBu-DAD)]SmI (5). The characteristic structural feature of 5
is formed by two (Z)-1,4-diaza-but-2-ene-1,4-diyl units bridging the Sm3+ with two Li+ ions.
Complex 5 and the analogous chloride complex [(THF)Li(tBu-DAD)]2Sm(µ-Cl)2Li(THF)2 (4b)
react with 2 equiv of benzophenone to give the structurally very similar samarium complexes
{[OC(Ph)2CH{CHdN(tBu)}N(tBu)]Li}2SmX(THF) (X ) Cl (6), I (7)) in high yield. The reaction
formally proceeds via a 1,3-dipolar cycloaddition of the benzophenone CdO bond across a
Sm-N-Cd fragment of the enediamide samarium complexes 4b and 5, including the
formation of a new C-C bond, and results in the formation of the novel tripodal ligand
[OC(Ph)2CH{CHdN(tBu)}N(tBu)]2-. X-ray structure determinations of 6 and 7 revealed that
the two tripodal ligands and the halogen atom form a slightly distorted octahedral
coordination geometry around the Sm3+ ion and that the Li+ ions are retained within the
ligand sphere by close contacts to their N and O atoms. By controlled hydrolysis of the
cycloaddition product 6, the new tripodal ligands can be separated from the samarium and
isolated in the form of the lithium compound {[OC(Ph)2CH{CHdN(tBu)}N(tBu)]Li}2 (8). The
crystal structure of 8, which is dimeric in the solid state, is reported.
Sch em e 1. Rea ction of (tBu -DAD)2M (M ) Zr , Hf)
In tr od u ction
w ith Keton es
One of the most interesting and useful aspects of
transition-metal centers in organometallic chemistry is
that they can induce unusual transformations in coor-
dinated ligands. C-C bond-forming reactions have
attracted special attention in this respect and have
found application in metal-directed organic synthesis.1
Recently, we reported on the novel reaction of early-
transition-metal DAD2 complexes with ketones.3 We had
found that DAD ligands bonded to early transition
metals can be selectively functionalized by forming a
new C-C bond between one of the imine carbon atoms
and a carbon atom of the electrophilic substrate. Thus,
the reaction of ketones with (tBu-DAD)2M (M ) Zr (1a ),
Hf (1b)) leads to complexes in which the metal atom is
octahedrally coordinated by two novel tridentate ligands
(Scheme 1).
† Universita¨t Koblenz-Landau.
‡ Friedrich-Schiller-Universita¨t J ena.
§ Technische Universita¨t Berlin.
(1) (a) Braterman, P. S., Ed. Reactions of Coordinated Ligands;
Plenum Press: New York, 1986; Vol. 1. (b) Collman, J . P.; Hegedus,
L. S.; Norton, J . R.; Finke, G. R. Principles and Applications of
Organotransition Metal Chemistry; University Science Books: Mill
Valley, CA, 1987.
(2) Throughout this paper the 1,4-diaza-1,3-dienes in general are
abbreviated as DAD. 1,4-Diaza-1,3-dienes of the formula RNdCHCHd
NR are abbreviated as R-DAD; hence, (tBu)NdCHCHdN(tBu) is
abbreviated as tBu-DAD.
With respect to the metallacyclic nature of the reac-
tion product and in view of the results of Fru¨hauf et
al., this reaction may be described as a 1,3-dipolar
cycloaddition.4 In a series of papers Fru¨hauf et al.
reported that complexes such as (iPr-DAD)FeL3 (L )
(3) Scholz, J .; Go¨rls, H. Inorg. Chem. 1996, 35, 4378-4382.
(4) Fru¨hauf, H.-W. Chem. Rev. 1997, 97, 523-596.
10.1021/om010323j CCC: $20.00 © 2001 American Chemical Society
Publication on Web 09/11/2001

Reaction of Samarium Complexes with Ketones
Organometallics, Vol. 20, No. 21, 2001 4395
Sch em e 2. Rea ction Step s in th e Cycloa d d ition of
Alk yn es to th e F e-NdC F r a gm en t in th e
Com p lexes (DAD)F e(L)3
Ch a r t 1. Str u ctu r es of Com p lexes w ith
N,N′-Ch ela tin g DAD Liga n d s: (a ) σ2 (4e Don or ); (b)
σ2 (Ra d ica l An ion ); (c) σ2,π (En ed ia m id e); (d ) µ-σ2,π
(Br id gin g En ed ia m id e)
Sch em e 3. Sch em a tic Rep r esen ta tion of th e
1,3-Dip ola r Cycloa d d ition (a ) of (DAD)F e(L)3 to
Alk yn es a n d (b) of (DAD)Zr L2 to Keton es
CO, RNC), containing a σ2-N,N′-chelating DAD ligand,
react with organic substrates, e.g. alkynes, to give
different C-C coupling products (Scheme 2).5 In the
initial step the dipolarophilic alkyne adds across the
Fe-NdC fragment of the DAD complex, resulting in the
formation of a [2.2.1] bicyclic intermediate. On the basis
of the isolobal analogy6 between the Fe-NdC fragment
and the azomethine ylide, a classical organic 1,3-dipole,
the initial step was described as an oxidative 1,3-dipolar
[3 + 2] cycloaddition reaction. Moreover, Fru¨hauf et al.
have demonstrated that the Fe-NdC fragment is
comparable with an electron-rich nucleophilic dipole
that reacts preferentially with electron-deficient dipo-
larophiles such as the alkyne dimethyl acetylenedicar-
boxylate (Scheme 2).5 In the next step this [2.2.1]
intermediate can further react with a second dipolaro-
phile, forming a double cycloaddition product.
However, although the products of the reaction of 1a
and 1b with ketones and that of the reaction of (iPr-
DAD)Fe(CNR)3 with alkynes show similar structural
features, there are some facts which suggest that the
mechanism of their formation must be different: In
contrast to the low-valent iron complexes (iPr-DAD)-
FeL3 (L ) CO, RNC), where a neutral DAD ligand is
bonded to the central metal, forming a planar five-
membered metallacycle (Chart 1, a ),7 for DAD com-
plexes of the early transition metals the “folded envelope
geometry” is well-established. Thus, the DAD bonding
situation in 1a and 1b is best described by a σ2,π-
enediamide structure with extensive dianionic character
of the heterodiene, as shown by c in Chart 1.8
(5) 1,3-Dipolar cycloaddition reactions of Fe-, Ru-, and Mn(DAD)
complexes were reported in the following publications. (a) Part 1:
Fru¨hauf, H.-W.; Seils, F.; Romao, M. J .; Goddard, R. J . Angew. Chem.
1983, 95, 1014-1015. (b) Part 2: Fru¨hauf, H.-W.; Seils, F.; Goddard,
R. J .; Romao, M. J . Organometallics 1985, 4, 948-949. (c) Part 3:
Fru¨hauf, H.-W.; Seils, F. J . Organomet. Chem. 1986, 302, 59-64. (d)
Part 4: Fru¨hauf, H.-W.; Seils, F. J . Organomet. Chem. 1987, 323, 67-
76. (e) Part 5: Fru¨hauf, H.-W.; Seils, F.; Stam, C. H. Organometallics
1989, 8, 2338-2343. (f) Part 6: De Lange, P. P. M.; Fru¨hauf, H.-W.;
van Wijnkoop, M.; Vrieze, K.; Wang, Y.; Heijdenrijk, D.; Stam, C. H.
Organometallics 1990, 9, 1691-1694. (g) Part 7: Van Wijnkoop, M.;
de Lange, P. P. M.; Fru¨hauf, H.-W.; Vrieze, K.; Wang, Y.; Goubitz, K.;
Stam, C. H. Organometallics 1992, 11, 3607-3617. (h) Part 8: De
Lange, P. P. M.; Fru¨hauf, H.-W.; Kraakman, M. J . A.; van Wijnkoop,
M.; Kranenburg, M.; Groot, A. H. J . P.; Vrieze, K.; Fraanje, J .; Wang,
Y.; Numan, M. Organometallics 1993, 12, 417-427. (i) Part 9: Van
Wijnkoop, M.; Siebenlist, R.; de Lange, P. P. M.; Fru¨hauf, H.-W.;
Smeets, W. J . J .; Spek, A. L. Organometallics 1993, 12, 4172-4181.
(j) Part 10: De Lange, P. P. M.; van Wijnkoop, M.; Fru¨hauf, H.-W.;
Vrieze, K.; Goubitz, K. Organometallics 1993, 12, 428-439. (k) Part
11: De Lange, P. P. M.; de Boer, R. P.; van Wijnkoop, M.; Fru¨hauf,
H.-W.; Vrieze, K.; Smeets, W. J . J .; Spek, A. L.; Goubitz, K. Organo-
metallics 1993, 12, 440-453. (l) Part 12: De Lange, P. P. M.; Alberts,
E.; van Wijnkoop, M.; Fru¨hauf, H.-W.; Vrieze, K. J . Organomet. Chem.
1994, 465, 241-249. (m) Part 13: Van Wijnkoop, M.; Siebenlist, R.;
Ernsting, J . M.; de Lange, P. P. M.; Fru¨hauf, H.-W.; Horn, E.; Spek,
A. L. J . Organomet. Chem. 1994, 482, 99-109. (n) Part 14: Feiken,
N.; Fru¨hauf, H.-W.; Vrieze, K.; Fraanje, J .; Goubitz, K. Organometallics
1994, 13, 2825-2832. (o) Part 15: Van Wijnkoop, M.; De Lange, P. P.
M.; Fru¨hauf, H.-W.; Vrieze, K.; Smeets, W. J . J .; Spek, A. L. Organo-
metallics 1995, 14, 4781-4791. (p) Part 16: Feiken, N.; Fru¨hauf, H.-
W.; Vrieze, K.; Veldman, N.; Spek, A. L. J . Organomet. Chem. 1996,
511, 281-291. (q) Part 17: Feiken, N.; Schreuder, P.; Siebenlist, R.;
Fru¨hauf, H.-W.; Vrieze, K.; Kooijman, H.; Veldman, N.; Spek, A. L.;
Fraanje, J .; Goubitz, K. Organometallics 1996, 15, 2148-2169. (r) Part
18: Siebenlist, R.; de Beurs, M.; Feiken, N.; Fru¨hauf, H.-W.; Vrieze,
K.; Kooijman, H.; Veldman, N.; Lakin, M. T.; Spek, A. L. Organome-
tallics 2000, 19, 3032-3053.
Furthermore, since the high valent d0 metal centers
of the formally unsaturated eight-electron complexes 1a
and 1b exhibit an appreciable Lewis acidity, the M-N-
Cd fragment prefers to react with dipolarophiles con-
taining a strongly nucleophilic part such as ketones.
Finally, the cycloaddition reaction of (iPr-DAD)FeL3
results in the oxidation of Fe0 to Fe2+, whereas for 1a
and 1b the oxidation state of the transition metal (+4)
does not change (Scheme 3).
Thus, to provide additional insight regarding the
mechanism of the cycloaddition reaction and the factors
that might be used to influence this process, a study of
the reaction of the DAD complexes of lanthanides with
ketones was undertaken.
In contrast to the DAD complexes of early and late
transition metals, relatively little is known about DAD
(7) (a) van Koten, G.; Vrieze, K. Adv. Organomet. Chem. 1982, 21,
151-239. (b) Vrieze, K. J . Organomet. Chem. 1986, 300, 307-326.
(8) (a) Chamberlain, L. R.; Durfee, L. D.; Fanwick, P. E.; Kobriger,
L. M.; Latesky, St. L.; McMullen, A. K.; Steffey, B. D.; Rothwell, I. P.;
Folting, K.; Huffman, J . C. J . Am. Chem. Soc. 1987, 109, 6068-6076.
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Chem., Int. Ed. Engl. 1982, 21, 711-723.

4396 Organometallics, Vol. 20, No. 21, 2001
Scholz et al.
Sch em e 4. Syn th eses of th e La n th a n id e DAD
complexes of the lanthanides. It has been shown that a
variety of lanthanide metal vapors react with tBu-DAD
to yield the homoleptic complexes Ln(tBu-DAD)3 (Ln )
Y, Nd, Sm, Eu, Gd, Ho, Yb).9 The room-temperature
X-ray crystallographic results and the magnetic sus-
ceptibility of Yb(tBu-DAD)3 at higher temperature are
consistent with the formulation of an Yb3+ center and
three N,N′-coordinated radical anions (tBu-DAD)- (Chart
1, b).9c Similar bonding situations have been observed
Com p lexes
[(THF )2Li(tBu -DAD)][(THF )Li(tBu -DAD)]Ln Cl (Ln
) Y (3a ), Lu (3b)) a n d
[(THF )Li(tBu -DAD)]2Ln (µ-X)2Li(THF )2 (Ln ) La , X
) I (4a ); Ln ) Sm , X ) Cl (4b))
for the DAD complexes Cp*2M(DAD) (M ) Sm,10a Y10b
)
and (COT)Sm(DAD)(THF).10c More recently we have
found that [(tBu-DAD)Li]- units may act as cyclopen-
tadienyl-like ligands in organolanthanide complexes.11
For example, reaction of the THF adducts of the
lanthanide halogenides LnX3 (Ln ) La, Sm, Lu, Y) with
the dilithium DAD compound Li2(tBu-DAD) (2)12 in a
molecular ratio of 1:2 yields the complexes [[(THF)2Li-
(tBu-DAD)][(THF)Li(tBu-DAD)]LnCl (Ln ) Y (3a ), Lu
(3b)) and [(THF)Li(tBu-DAD)]2Ln(µ-X)2Li(THF)2 (Ln )
La, X ) I (4a ); Ln ) Sm, X ) Cl (4b), Scheme 4), whose
structure is featured by the two heterodienes which are
coordinated in their enediamide form bridging the
lanthanide with two lithium ions (Chart 1, d ).
Certainly, owing to their structural relationship with
the cyclopentadienyl lanthanide halides Cp*2LnCl and
Cp*2Ln(µ-Cl)2Li(THF)2 (Cp* ≡ C5Me5),13 respectively,
these new lanthanide DAD complexes 3a ,b and 4a ,b are
of interest as starting materials in organolanthanide
chemistry. In this paper we present our initial results
on the reaction of these lanthanide DAD complexes with
benzophenone. Altogether, the studies reported here
focus on gaining a better insight into the overall
mechanism of 1,3-dipolar reactivity.
Resu lts a n d Discu ssion
Syn th esis of [[(THF )2Li(tBu -DAD)][(THF )Li(tBu -
DAD)]Sm I (5). As the structural features of the lan-
thanide(III) complexes with [(tBu-DAD)Li]- ligands are
very similar to those of the cyclopentadienyl complexes,
it should also be possible to prepare the analogue of the
divalent samarium complex Cp*2Sm(THF)x (x ) 0,14a
1,14b 214c). The original cause for this investigation was
to produce the samarium(II) complex [[(THF)2Li(tBu-
DAD)]2Sm, which was expected to provide access to a
wide range of unusual reactions, as has been done by
the metallocene complex Cp*2Sm.15
Slow addition of 2 equiv of Li2(tBu-DAD) (2) (gener-
ated in situ from tBu-DAD and lithium at room tem-
perature in THF)11a,12 to a suspension of SmI2 in THF
gives a red-violet product which is obtained in 64% yield.
However, the reaction of SmI2 with Li2(tBu-DAD) is
unusual: the red-violet color of the isolated product
suggested that the samarium(II) metal center was
oxidized to the trivalent state and a qualitative halogen
test indicated the presence of iodine. Moreover, the
results of the combustion analysis data and an X-ray
crystal structure (vide infra) revealed that instead of
the expected samarium(II) complex the new complex
[(THF)2Li(tBu-DAD)][(THF)Li(tBu-DAD)]SmI (5) had
been formed (Scheme 5).
(9) (a) Cloke, F. G. N.; de Lemos, H. C.; Sameh, A. A. J . Chem.
Soc., Chem. Commun. 1986, 1344-1345. (b) Cloke, F. G. N. Chem.
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G. N.; Dalby, C. I.; Matsunaga, P. T.; Andersen, R. A.; Schumann, H.;
Loebel, J .; Hemling, H. J . Organomet. Chem. 1995, 486, 177-182.
(10) (a) Recknagel, A.; Noltemeyer, M.; Edelmann, F. T. J . Orga-
nomet. Chem. 1991, 410, 53-61. (b) Scholz, A.; Thiele, K.-H.; Scholz,
J .; Weimann, R. J . Organomet. Chem. 1995, 501, 195-200. (c)
Poremba, P.; Edelmann, F. T.; J . Organomet. Chem. 1997, 549, 101-
104.
(11) (a) Go¨rls, H.; Neumu¨ller, B.; Scholz, A.; Scholz, J . Angew. Chem.
1995, 107, 732-735; Angew. Chem., Int. Ed. Engl. 1995, 34, 673-676.
(b) Trifonov, A. A.; Zakharov, L. N.; Bochkarev, M. N.; Struchkov, Y.
T. Izv. Akad. Nauk, Ser. Khim. 1994, 148-151.
(12) Haaf, M.; Schmiedl, A.; Schmedake, T. A.; Powell, D. R.;
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Rev. 1995, 95, 865-986. (b) Evans, W. J .; Foster, S. E. J . Organomet.
Chem. 1992, 433, 79-94.
(14) (a) Evans, W. J .; Hughes, L. A.; Hanusa, T. P. Organometallics
1986, 5, 1285-1291. (b) Evans, W. J .; Kociok-Ko¨hn, G.; Foster, S. E.;
Ziller, J . W.; Doedens, R. J . J . Organomet. Chem. 1993, 444, 61-66.
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Evans, W. J . Polyhedron 1987, 6, 803-835. (b) Evans, W. J .; Ulibarri,
T. A.; Ziller, J . W. J . Am. Chem. Soc. 1988, 110, 6877-6879. (c) Evans,
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Chem. 1998, 37, 770-776.

Reaction of Samarium Complexes with Ketones
Organometallics, Vol. 20, No. 21, 2001 4397
Sch em e 5. Syn th esis of
[(THF )2Li(tBu -DAD)][(THF )Li(tBu -DAD)]Sm I (5)
Complex 5 has a simple 1H NMR spectrum consisting
of broad single lines for the tert-butyl (δ 0.30) and imine
protons (δ 8.58) and signals caused by the coordinated
THF (δ 3.63, 1.77). Equivalence of the tBu-DAD ligands
in the 13C NMR spectrum, as exemplified by single
resonances at δ 59.65 and 28.09 (CMe3) and at δ 127.30
(HCdCH), also indicates that 5 has C2v molecular
symmetry in solution. As expected, although the signals
of the 1H and the 13C NMR spectra are observed at
chemical shifts similar to those of 4b,11a the paramag-
netic nature of this complex hindered full interpretation
of the spectra. Definitive formulation of the bonding
situation of the heterodiene ligands was provided by a
single-crystal X-ray structure analysis.
Consistent with the other known lanthanide com-
plexes with [Li(tBu-DAD)]- ligands,11 the structural
analysis of 5 (Figure 1, Table 2) revealed a monomeric
complex with a coordination sphere of the Sm(III) center
composed of four nitrogen atoms of two chelating
enediamide dianions and the iodide. The four nitrogen
atoms bridge the samarium with two lithium ions. The
bonding parameters within the two heterodiene ligands
are not different from those of the analogous samarium
chloride complex 4b11a and show a pronounced “long-
short-long” sequence of the N-CdC-N bond length
(N11-C16 ) 1.399(12) Å, C15-C16 ) 1.350(14) Å,
N12-C15 ) 1.401(13) Å, N21-C25 ) 1.401(12) Å, C25-
C26 ) 1.371(14) Å, N22-C26 ) 1.406(12) Å), which is
typical for an enediamide structure. Moreover, the short
distances between the olefinic carbon atoms C15 and
C16 and the metal centers Li1 and Sm as well as the
close contacts of Li2 to C25 and C26 (2.23(2) and 2.24(2)
Å) lie in the range of usual Li-C16 and Sm-C17 bonds
and indicate an intensive π interaction: thus, one
heterodiene dianion is formally η4 coordinated to Sm
and Li1 and the other η4 coordinated to Li2, respectively.
However, the structure of 5 significantly differs from
that of 4b in that complex 5 has not added an extra LiI
molecule and therefore the central samarium atom does
not achieve the coordination number 6. Nevertheless,
an intramolecular contact between Li2 and the iodide
(2.887(16) Å) which is only slightly longer than the Li-I
distance of [LiI(pmedien)] (2.75(3) and 2.67(3) Å)18a or
[LiI(NC5H3-3,5-Me2)3] (2.80(1) Å)18b strongly affects the
Sm-I distance: this bond length of 3.362(1) Å is not
only significantly longer than the terminal Sm-I dis-
F igu r e 1. ORTEP representation of the molecular struc-
ture of 5. Thermal ellipsoids are shown at the 40%
probability level, and hydrogen atoms are omitted for
clarity.
Ta ble 1. Selected Str u ctu r a l P a r a m eter s for
[(THF )2Li(tBu -DAD)][(THF )Li(tBu -DAD)]Sm I (5)
Bond Distances (Å)
Sm-N11 2.399(8) Sm-N12 2.361(7) Sm-N21 2.315(8)
Sm-N22 2.339(8) Sm-C15 2.654(10) Sm-C16 2.688(10)
Sm-I
3.362(1) Li2-I
2.887(16) Li1-N11 2.102(18)
Li1-N12 2.141(18) Li1-C15 2.485(19) Li1-C16 2.478(20)
Li2-N21 2.163(20) Li2-N22 2.195(19) Li2-C25 2.230(20)
Li2-C26 2.244(20) Li1-O4
Li2-O3
C15-C16 1.350(14) N21-C25 1.401(12) N22-C26 1.406(12)
C25-C26 1.371(14)
1.960(18) Li1-O5
2.000(19)
1.909(18) N11-C16 1.399(12) N12-C15 1.401(13)
Bond Angles (deg)
N21-Sm-N22
Li1-Sm-Li2
72.73(28)
159.81(48)
N11-Sm-N12
72.78(25)
Interplanar Angles (deg)
(N11, Sm, N12)(N21, Sm, N22)
87.3(3)
tances of Cp*2SmI(THF) (3.043(2) Å)19a and Cp*2SmI-
(C6H10N4) (3.100(2) Å)19b as is typical for bridging vs
terminal ligands but also longer than those of the iodide-
bridged diiminophosphinate samarium(III) complex
[Ph2P(NSiMe3)2]2Sm(µ-I)2Li(THF)2 (3.161(1) and 3.162(1)
Å).20 The fact that the reaction of SmI2(THF)5 with Li2-
(tBu-DAD) is accompanied by an oxidation of the sa-
(18) (a) [LiI(pmedien)] (pmedien ≡ [Me2N(CH2CH2)]2NMe), 2.75(3),
2.67(3) Å: Raston, C. L.; Skelton, B. W.; Whitaker, C. R.; White, A. H.
J . Chem. Soc., Dalton Trans. 1988, 987-990. (b) [LiI(NC5H3-3,5-Me2)3],
2.80(1) Å: Raston, C. L.; Whitaker, C. R.; White, A. H. J . Chem. Soc.,
Dalton Trans. 1988, 991-995.
(19) (a) 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. (b) Evans, W. J .; Drummond, D. K.; Hughes, L. A.; Zhang,
H.; Atwood, J . L. Polyhedron 1988, 7, 1693-1703.
(20) Recknagel, A.; Steiner, A.; Noltemeyer, M.; Brooker, S.; Stalke,
D.; Edelmann, F. T. J . Organomet. Chem. 1991, 414, 327-335.
(16) A distance of 2.50 Å has been discussed as an upper limit for
a Li-C interaction: Zarges, W.; Marsch, M.; Harms, K.; Koch, W.;
Frenking, G.; Boche, G. Chem. Ber. 1991, 124, 543-549.
(17) The Sm-(CdC) distances in 5 are comparable with the average
Sm-CCp* distances of 2.68(1)-2.80(1) Å of Cp*2SmIII complexes.13

4398 Organometallics, Vol. 20, No. 21, 2001
Scholz et al.
Sch em e 6. Rea ction of
marium(II) center has not been fully understand to this
day, but it has been observed in other reactions of
divalent samarium also: for instance, reaction of SmI2-
(THF)5 with the lithium diiminophosphinate compound
Li(THF)2[Ph2P(NSiMe3)2]20 or with the lithium salt of
2-(phenylamino)-4-(phenylimino)-2-pentene, Li[PhNd
CMeCHdCMeNPh],21 always leads to samarium(III)
complexes, irrespective of the stoichiometric ratio of the
reagents.
[[(THF )Li(tBu -DAD)]2Sm (µ-Cl)2Li(THF )2 (4b) a n d
[(THF )2Li(tBu -DAD)][(THF )Li(tBu -DAD)]Sm I (5)
w ith Ben zop h en on e
R ea ct ion of [(TH F )Li(tBu -DAD)]2Sm (µ-Cl)2Li-
(THF)2 (4b) an d [(THF)2Li(tBu -DAD)][(THF)Li(tBu -
DAD)]Sm I (5) w ith Ben zop h en on e. The reaction of
the samarium DAD complex 4b with 2 equiv of ben-
zophenone was carried out in diethyl ether at room
temperature. As the reaction proceeds, the solution
initially acquires a dark green color which changes to
pale yellow. Furthermore, the concomitant formation of
a precipitate (LiCl) was observed. The reaction produced
a single new product (6) isolated as colorless prisms
from diethyl ether. Preliminary qualitative analysis
tests indicated the presence of both chlorine and lithium
in this product, and the combustion analysis was
consistent with the formula {[OC(Ph)2CH{CHdN(tBu)}-
N(tBu)]Li}2SmCl(THF) (6) (Scheme 6).
Complex 6 is air- and moisture-sensitive and soluble
in aromatic solvents and ethers. Unfortunately, at room
temperature it shows a very complicated 1H NMR
spectrum, which is uninformative due to numerous
resonances combined with partial line broadening and
strong paramagnetic shifts. However, these NMR data
suggest that 6 exhibits a high asymmetry even in
solution.
The reaction of the samarium iodide complex 5 with
benzophenone carried out under identical conditions as
reported above at first resulted also in a transient color
change of the reaction mixture from red-violet to dark
green. Unfortunately, as in the case of the reaction of
4b, we were not successful in characterizing the dark
green intermediate, which is perhaps a simple coordina-
tion adduct of the samarium DAD complex. Finally,
complex 7 was isolated as an analytically pure colorless
solid by crystallization from diethyl ether in 68% yield.
The large number of resonances in the 1H NMR
spectrum of 7 is consistent with a complete lack of
symmetry of 7 on the NMR time scale. Moreover, the
spectrum shows the same signal pattern and chemical
shifts nearly identical with those observed for 6. Close
1
examination of the number of signals in the H NMR
spectra of 6 and 7 suggests that a second isomer must
be present in nearly equal amount in the solution of 6
as well as of 7. In view of the solid-state structures of 6
and 7 (vide infra), we speculate that the second isomer
may be another diastereomer.
To understand the molecular geometries and the
structural parameters of the new tripodal ligand, the
X-ray crystal structures of 6 and 7 were determined.
Single crystals of both compounds were obtained from
diethyl ether solutions at -20 °C. Selected bond lengths
and angles are given in Table 2, experimental crystal-
lographic data are summarized in Table 4, and perspec-
tive views are presented in Figures 2 and 3. Further
data are available in the Supporting Information.
The samarium atom is surrounded by two dianionic
tripodal ligands [OC(Ph)2CH{CHdN(tBu)}N(tBu)]2- aris-
ing from the cycloaddition reaction of benzophenone to
the Sm-N-Cd moiety of the enediamide ligands of 4b
and 5. However, only one of these ligands is coordinated
by the three donor functions O1, N1, and N2, resulting
in a [2.2.1] bicyclic structure motive. The bridgehead
positions are occupied by the samarium atom and the
C-C-coupled former imine carbon atom C2. As a
consequence of the cycloaddition reaction N2 and C2
have changed their hybridization into sp3 (sum of angles
at N2: 6 at 338.8(2)°; 7 at 337.2(5)°; sum of angles at
C2: 6 at 329.9(3)°; 7 at 330.8(5)°) and now display
regular tetrahedral geometry. Furthermore, the atoms
of the starting enediamide skeleton N1-C1dC2-N2 are
(21) Drees, D.; Magull, J . Z. Anorg. Allg. Chem. 1994, 620, 814-
818.

Reaction of Samarium Complexes with Ketones
Organometallics, Vol. 20, No. 21, 2001 4399
Ta ble 2. Selected Str u ctu r a l P a r a m eter s for {[OC(P h )2CH{CHdN(tBu )}N(tBu )]Li}2Sm Cl(THF ) (6) a n d
{[OC(P h )2CH{CHdN(tBu )}N(tBu )]Li}2Sm I(THF ) (7)
6
7
6
7
6
7
Bond Distances (Å)
2.406(3)
Sm-N1
Sm-O1
N1-C1
C2-C11
C24-C25
O2-C34
Li2-N2
Li2-O2
2.679(3)
2.323(2)
1.266(4)
1.572(4)
1.527(5)
1.396(4)
2.071(7)
1.891(6)
2.709(6)
2.304(5)
1.272(9)
1.585(9)
1.537(10)
1.413(8)
2.108(13)
1.943(12)
Sm-N2
Sm-O2
N2-C2
O1-C11
N4-C25
Li1-N3
Li1-O1
Li2-O3
2.438(5)
2.457(4)
1.490(9)
1.397(8)
1.267(10)
2.271(14)
1.844(15)
1.978(13)
Sm-N3
Sm-Cl(I)
C1-C2
N3-C24
C24-C34
Li1-N4
Li1-O2
2.406(3)
2.692(1)
1.519(4)
1.459(4)
1.609(4)
1.992(7)
2.350(6)
3.137(1)
1.503(10)
1.467(8)
1.587(10)
2.009(15)
2.047(14)
2.282(2)
1.470(4)
1.400(4)
1.264(4)
2.036(7)
1.784(6)
1.972(7)
Bond Angles (deg)
N1-Sm-N2
N2-Sm-N3
N2-Sm-O2
70.58(8)
136.66(9)
78.63(8)
71.05(18)
142.14(18)
79.71(17)
N1-Sm-O1
N1-Sm-O2
N3-Sm-O1
74.19(8)
147.12(8)
78.83(8)
74.80(17)
142.06(16)
85.12(18)
N2-Sm-O1
N1-Sm-O2
70.13(8)
147.12(8)
71.20(17)
142.06(16)
Ta ble 3. Selected Str u ctu r a l P a r a m eter s for
{[OC(P h )2CH{CHdN(tBu )}N(tBu )]Li}2 (8)
Bond Distances (Å)
Li-N1
Li-OA
C1-C2
2.120(4)
1.792(4)
1.487(3)
Li-N2
N1-C1
C2-C3
2.109(5)
1.268(3)
1.593(3)
Li-O
N2-C2
O-C3
1.988(4)
1.466(3)
1.368(3)
Bond Angles (deg)
N1-Li-N2
N2-Li-O
O-Li-OA
Li-N2-C2
LiA-O-C3
N1-C1-C2
C1-C2-C3
83.6(2)
79.8(2)
100.8(2)
90.5(2)
158.4(2)
122.2(2)
108.2(2)
N1-Li-O
98.4(2)
79.2(2)
Li-O-LiA
Li-N1-C1
Li-O-C3
O-C3-C2
C1-C2-N2
C3-C2-N2
100.0(2)
110.5(2)
107.7(2)
111.8(2)
106.4(2)
no longer in the same plane and the observed N-C
distances are longer in the amide fragments (N2-C2:
6, 1.470(4) Å; 7, 1.490(9) Å) than in the imine groups
(N1-C1: 6, 1.266(4) Å; 7, 1.272(9) Å). The second
tripodal ligand chelates the samarium center only by
the amidato nitrogen atom N3 (Sm-N3: 6, 2.406(3) Å;
7, 2.350(6) Å) and the oxygen atom O2 (Sm-O2: 6,
2.282(2) Å; 7, 2.457(4) Å) to form a puckered five-
membered ring with a “bite” angle N3-Sm-O2 of
68.99(9)° (6) and 65.08(16)° (7), respectively, whereas
the imine function N4 is coordinated to one of the
lithium ions Li1 (Li1-N4: 6, 1.992(7) Å; 7, 2.009(15)
Å).
F igu r e 2. ORTEP representation of the molecular struc-
ture of 6. Thermal ellipsoids are shown at the 40%
probability level. For clarity, no hydrogen atoms and only
the ipso carbon atoms of the phenyl groups are shown.
An interesting structural feature of the cycloaddition
products 6 and 7 is the bridging linkage of the lithium
ions Li1 and Li2 with the ligand framework. Small
differences between the molecular structures of 6 and
7 in this respect primarily may be ascribed to the steric
effects of the halogen atoms. In both complexes the
amidato nitrogen atom N2 of the tridentate ligand and
the oxygen atom O2 of the bidentate ligand are bridged
by the Li2(THF) moiety. In complex 7 the oxygen atom
O2 is also bonded to the lithium ion Li1 (Li1-O2 )
2.047(14) Å), which in turn is attached in both com-
plexes to the nitrogen atoms N3 and N4 of the bidentate
ligand (Li1-N3: 6 at 2.036(7) Å, 7 at 2.271(14) Å; Li1-
N4: 6 at 1.992(7) Å, 7 at 2.009(15) Å) and the oxygen
atom O1 of the tridentate ligand (Li1-O1: 6 at 1.784(6)
Å, 7 at 1.844(15) Å). Altogether, this close network of
bridging interactions between the two tripodal ligands
generates a hemispherical shield around the samarium
center which perhaps is a prerequisite for the stability
of the complexes. The Sm-halogenide distances (6, Sm-
Cl ) 2.692(1) Å; 7, Sm-I ) 3.137(1) Å) are not unusual
and compare well with those observed in nonmetal-
locene samarium(III) complexes with terminally bonded
F igu r e 3. ORTEP representation of the molecular struc-
ture of 7. Thermal ellipsoids are shown at the 40%
probability level. For clarity, no hydrogen atoms and only
the ipso carbon atoms of the phenyl groups are shown.
chloride ({O(SiPh2O)2Li(dme)}2SmCl(dme), 2.717(1) Å;22a
SmCl3(THF)4, 2.635(3)-2.679(3) Å22b) or iodide ligands
((ArO)2SmI(THF)2, 3.024(2) Å (Ar ≡ 2,6-(tBu)2-4-
Me-C6H2);23a {(Me3Si)NC(tBu)CH(SiMe3)}2SmI(THF),
3.092(1) Å23b).

4400 Organometallics, Vol. 20, No. 21, 2001
Ta ble 4. Su m m a r y of X-r a y Diffr a ction Da ta a n d Over a ll Refin em en t P a r a m eter s for
Scholz et al.
[(THF )2Li(tBu -DAD)][(THF )Li(tBu -DAD)]Sm I (5), {[OC(P h )2CH{CHdN(tBu )}N(tBu )]Li}2Sm Cl(THF ) (6),
{[OC(P h )2CH{CHdN(tBu )}N(tBu )]Li}2Sm I(THF ) (7), a n d {[OC(P h )2CH-{CHdN(tBu )}N(tBu )]Li}2 (8)
5
6
7
8
chem formula
mol wt
C
32H64N4O3ILi2Sm
C50H68N4O3ClLi2Sm
972.79
C50H68N4O3ILi2Sm
1064.24
C46H62N4O2Li2
716.89
844.02
cryst dimens (mm3)
cryst color, shape
cryst syst
0.15 × 0.40 × 0.20
red-violet prism
monoclinic
P21/c (No. 14)
-88
0.40 × 0.38 × 0.36
colorless prism
orthorhombic
Pbca (No. 61)
-90
0.22 × 0.18 × 0.12
colorless prism
orthorhombic
P212121 (No. 19)
-90
0.32 × 0.30 × 0.28
colorless prism
orthorhombic
Pbca (No. 61)
-90
space group
temp (°C)
cell params
a (Å)
b (Å)
c (Å)
11.472(4)
14.608(3)
23.844(6)
99.64(3)
3939.3(18)
4
1.423
22.41
æ-scan
0.743/0.995
1708
18.618(3)
20.007(2)
26.098(5)
11.0244(3)
20.0222(6)
22.9007(9)
17.268(2)
12.748(2)
19.842(2)
â (deg)
V (Å3)
9721(2)
8
1.329
5054.9(3)
4
1.398
18.14
æ-scan
0.691/0.811
2164
4367(1)
4
1.090
0.66
no. of formula units Z
calcd density Dc (g cm-3
)
abs coeff µ(Mo KR) (cm-1
scan type
)
13.06
æ-scan
0.218/0.278
4040
min/max transmissn
F(000)
1552
hkl range
0-12, 0-15,
-25 to +25
1.28-44.84
5665
4646
0.045
0-24, 0-25,
-33 to 0
4.82-54.84
11 065
11 065
0.067
-14 to +11, -23 to +26,
-24 to +29
6.36-55.02
23 095
11 289
0.034
0-24, -17 to 0,
0-27
2θ range (deg)
no. of unique total data
no. of indep data
Rint
4.48-59.98
6353
6352
no. of obsd data with Fo > 4σ(Fo)
3868
385
0
0.055
0.137
0.0958
0.1178
1.112
6717
550
0
0.033
0.076
0.0958
0.1178
1.072
8128
556
18
0.057
0.104
0.095
0.117
1.010
2391
368
0
0.062
0.140
0.0958
0.1178
1.144
0.243/-0.223
no. of params
restraints
R1obsd
wR2obsd
a
R1all
b
wR2all
goodness of fit
largest diff peak and hole (e Å-3
)
1.569/-0.895
0.594/-0.637
0.610/-0.938
R1 ) (∑||Fo| - |Fc||)/∑Fo. wR2 ) [∑[w(Fo - Fc2)2]/∑[w(Fo2)2]]1/2
.
a
b
2
Sch em e 7. Hyd r olysis of
{[OC(P h )2CH{CHdN(tBu )}N(tBu )]Li}2Sm Cl(THF )
Hyd r olysis of {[OC(P h )2CH{CHdN(tBu )}N(tBu )]-
Li}2Sm Cl(THF ) (6). As mentioned above, solutions of
6 and 7 are sensitive to air and moisture. To further
explore the reactivity of these species and to learn more
about the robustness of the newly generated tripodal
ligand in view of its further application in organome-
tallic and coordination chemistry, controlled hydrolysis
of 6 was performed: after addition of 2 equiv of H2O to
a stirred solution of 6 in diethyl ether the reaction
mixture became cloudy and a white solid precipitated.
Colorless crystals of the new compound 8 were isolated
in reasonable yield after careful filtration of the reaction
mixture and concentration of the filtrate with subse-
quent cooling to -30 °C.
(6)
The room temperature 1H and 13C NMR spectra of
the air- and moisture-sensitive compound 8 recorded in
THF-d8 are in agreement with the structure consisting
of a 2-(tert-butylamino)-3-(tert-butylimino)-1,1-diphen-
ylpropanolate anion, which is coordinated by the three
donor atoms to the lithium ion (Scheme 7).
1
In the H NMR spectrum the methine protons of the
ligand backbone give rise to two doublets at very
different positions: One doublet appears at δ 7.30,
(22) (a) Lorenz, V.; Fischer, A.; J acob, K.; Bru¨ser, W.; Edelmann,
F. T. Chem. Eur. J . 2001, 7, 848-857. (b) Anfang, S.; Karl, M.; Faza,
N.; Massa, W.; Magull, J .; Dehnicke, K. Z. Anorg. Allg. Chem. 1997,
623, 1425-1432.
(23) (a) Hou, Z.; Fujita, A.; Yoshimura, T.; J esorka, A.; Zhang, Y.;
Yamazaki, H.; Wakatsuki, Y. Inorg. Chem. 1996, 35, 7190-7195. (b)
Hitchcock, P. B.; Lappert, M. F.; Tian, S. J . Organomet. Chem. 1997,
549, 1-12.
which is in the typical range of imine protons. The other
proton resonates at δ 4.75, which reflects a change in
hybridization from sp2 to sp3, resulting from the cy-
cloaddition reaction. The J H-H coupling between these
methine protons is rather small (2.0 Hz), indicating a
3
larger dihedral angle between the C-H bonds as a

Reaction of Samarium Complexes with Ketones
Organometallics, Vol. 20, No. 21, 2001 4401
Furthermore, the bond distance of the reduced imine
function N2-C2 (1.466(3) Å) is as expected for a C-N
single bond,26 while the N1-C1 bond of the intact imine
function is somewhat shorter and is consistent with the
presence of some degree of C-N double-bond character
(1.268(3) Å).26 Altogether, in the case of {[OC(Ph)2CH-
{CHdN(tBu)}-N(tBu)]Li}2 (8) we succeeded in the isola-
tion and structural characterization of a stable imine-
amine-functionalized lithium alcoholate dimer which
can be further used in the syntheses of other complexes
with this new multidentate ligand system.
The reaction reported in this paper demonstrates for
the first time that the coordination of dianionic 1,4-
diaza-1,3-dienes to an electrophilic lanthanide ion re-
sults in the specific activation of the diimine skeleton
itself and affords an opportunity for a subsequent C-C
coupling reaction with ketones. In other words, the
results presented here constitute the transformation of
a dianionically bonded 1,4-diaza-1,3-diene to a triden-
tate N,O,N-bound ligand by addition of benzophenone,
a strategy reported recently for zirconium and hafnium
DAD complexes.3
F igu r e 4. ORTEP representation of the molecular struc-
ture of 8. Thermal ellipsoids are shown at the 40%
probability level. For clarity, only the hydrogen atoms
bound to C1, C2, and N2 and only the ipso carbon atoms
of the phenyl groups are shown.
Furthermore, it has been shown that the C-C cou-
pling product can be easily displaced from the lan-
thanide complex as a lithium adduct of a 2-amine-3-
imine-functionalized alcohol. Certainly, the synthesis of
organic products such as 2-amine- or 3-imine-function-
alized alcohols has been previously achieved by a variety
of known methods.27 However, the reaction of the
samarium DAD complexes demonstrates their capabil-
ity in organic synthesis and completes the series of
C-H, C-C, and C-N coupling reactions which have
been observed in DAD complexes.5,28 Further studies on
the chemistry of DAD complexes of samarium and other
lanthanides are in progress.
consequence of the distorted [2.2.1] bicyclic geometry.
Interestingly, the N-H proton signal appears as a
rather sharp singlet at δ 1.42.
In the 13C NMR spectrum the signal of the C-C-
coupled bridgehead methine carbon atom is observed
at δ 62.83, which is a normal value for an sp3-hybridized
carbon nucleus substituted by an amine function. The
signals of the adjacent carbon atoms of the ligand
backbone appear at δ 165.40, consistent with an intact
imine function, and at δ 82.92, indicating the striking
change of the former benzophenone carbonyl carbon
atom.
Complex 8 crystallizes as prismatic crystals in the
orthorhombic space group Pbca with four dimers in the
unit cell. The complex is best described as an intramo-
lecularly coordinated imine-amine adduct of a lithium
alcoholate dimer containing a central four-membered
Li2O2 ring core (Figure 4). The O-lithiated 2-(tert-
butylamino)-3-(tert-butylimino)-1,1-diphenylpronano-
late anion acts as a tridentate ligand, chelating the
lithium ion and bridging the other lithium ion through
the oxygen atom, achieving 4-fold coordination of the
alkaline metal. Selected geometrical parameters are
given in Table 3. The Li-O distances vary considerably,
the Li-O distance to the oxygen in the chelate ring of
1.988(4) Å being longer than the distance to the other
oxygen atom of the Li2O2 ring core (1.792(4) Å).24
Nevertheless, the Li2O2 unit is exactly planar, as
required by the crystallographic symmetry. The Li-N1-
(imine) distance of 2.120(4) Å is comparable to the dative
Li-N2(amine) bond distance of 2.109(5) Å and corre-
sponds to that of other examples having a four-
coordinate lithium atom.25 The C2-C3 bond (1.593(3)
Å) joining the benzophenone molecule with the amide
carbon atom of the former DAD unit N1dC1-C2(H)-
N2(H) is comparable with a regular C-C bond.26
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All experiments were performed
under an atmosphere of dry argon using standard Schlenk
techniques. Solvents were distilled from sodium/benzophenone
ketyl (THF, diethyl ether) or LiAlH4 (pentane) under argon
and stored over activated 4 Å molecular sieves. All glassware
was thoroughly oven-dried or flame-dried under vacuum prior
to use. Benzophenone was purchased from Aldrich Chemicals
(25) (a) [Li(tBu-DAD)3Nb], Li-N(imine) ) 2.07(2), 1.98(2) Å:
Richter, B.; Scholz, J .; Sieler, J .; Thiele, K.-H. Angew. Chem. 1995,
107, 2865-2867; Angew. Chem., Int. Ed. Engl. 1995, 34, 2865-2867.
(b) [(tBu-DAD)2Li], Li-N(imine) ) 2.134(7), 2.148(6) Å: Gardiner, M.
G.; Hanson, G. R.; Henderson, M. J .; Lee, F. C.; Raston, C. L. Inorg.
Chem. 1994, 33, 2456-2461. (c) [Li{N(tBu)CHCH2N(tBu)}2AlH2], Li-
N(imine) ) 2.11(1), 2.12(1) Å: Gardiner, M. G.; Lawrence, S. M.;
Raston, C. L. Inorg. Chem. 1999, 38, 4467-4472.
(26) C-C ) 1.530 Å, C-N ) 1.469 Å, CdN ) 1.279 Å: Allen, F. H.;
Kennard, O.; Watson, D. G.; Brammer, L.; Orpen, A. G.; Taylor, R. J .
Chem. Soc., Perkin Trans. 2 1987, S1-S19. (b) tBu-DAD, CdN )
1.267(2) Å, C-C ) 1.467(2) Å: Huige, C. J . M.; Spek, A. L.; de Boer,
J . L. Acta Crystallogr. 1985, C41, 113-116.
(27) (a) Synthesis of 2-amine- and 3-imine-functionalized alcohols
using C-C bond forming reactions via organosamarium(III) intermedi-
ates: Murakami, M.; Ito, Y. J . Organomet. Chem. 1994, 473, 93-99.
(b) A highly versatile and selective method for the intermolecular
coupling of imines with aldehydes or ketones uses niobium(III) and
tantalum(III) reagents, providing a diastereoselective route to R-amino
alcohols: Roskamp, E. J .; Pedersen, S. F. J . Am. Chem. Soc. 1987,
109, 6551-6553. Takai, K.; Ishiyama, T.; Yasue, H.; Nobunaka, T.;
Itoh, M.; Oshiki, T.; Mashima, K.; Tani, K. Organometallics 1998, 17,
5128-5132.
(24) Li-O bond distances of dimeric lithium complexes containing
a Li2O2 ring core are as follows. (a) [MeCHdC(OtBu)OLi(Me2NCH2-
CH2NMe2)]2, Li-O ) 1.945 and 1.906 Å: Seebach, D.; Amstutz, R.;
Laube, T.; Schweizer, W. B.; Dunitz, J . D. J . Am. Chem. Soc. 1985,
107, 5403-5409. (b) [CH2dC(tBu)OLi(Me2NCH2CH2N(H)Me)]2, Li-O
) 1.872 and 1.898 Å: Laube, T.; Dunitz, J . D.; Seebach, D. Helv. Chim.
Acta 1985, 68, 1373-1393.
(28) tom Dieck, H.; Munz, C.; Ehlers, J . In Organometallics in
Organic Synthesis 2; Springer-Verlag: Berlin, Heidelberg, New York,
1989; pp 21-43.

4402 Organometallics, Vol. 20, No. 21, 2001
Scholz et al.
and used as received. SmI2(THF)5,29 SmCl3(THF)4,30 and tBu-
DAD31 were prepared according to literature procedures. NMR
spectra were recorded in THF-d8 on a Varian 300 BB (1H NMR
at 300.075 MHz, 13C NMR at 75.462 MHz) or a Varian UNITY
500 spectrometer (1H NMR at 499.843 MHz, 13C NMR at
2.23 (s), 2.07 (s), 1.94 (s), 1.77 (m, OCH2CH2, THF), 1.20 (br s,
CMe3), 0.33 (s), 0.06 (s), -0.19 (s), -1.78 (s), -2.72 (s), -7.49
(br, s). Mp: 136 °C dec. Anal. Calcd for C50H68N4O3ILi2Sm:
C, 56.43; H, 6.44; N, 5.26. Found: C, 56.12; H, 6.50; N, 5.35.
{[OC(P h )2CH{CHdN(tBu )}N(tBu )]Li}2 (8). To a solution
of 6 (2.00 g, 2.0 mmol) in THF (50 mL) were added via syringe
72 µL of degassed water (4.0 mmol) at 20 °C. The solution was
stirred for 2 h. The solvent was removed in vacuo and the
resulting white solid extracted with diethyl ether. The extract
was concentrated and cooled to -30 °C to yield colorless
crystalline 8 (1.08 g, 75%). 1H NMR (THF-d8, 300 MHz, 25
°C): δ 7.87 (d, 2H, o-C6H5), 7.79 (d, 2H, o-C6H5), 7.30 (d, 3J H-H
) 2.0 Hz, 1H, NdCHCH), 7.20-6.85 (m, 12H, m-/p-C6H5), 4.75
1
125.639 MHz) at 20 or 25 °C, unless indicated otherwise. H
and 13C NMR spectra were referenced internally using the
1
residual solvent resonances (THF-d8: δH 1.73, δC 25.2). J C-H
values were obtained from gated 13C{1H} NMR spectra.
Elemental analyses were carried out by the analysis laboratory
at the Martin-Luther-University of Halle-Wittenberg. Melting
points are uncorrected.
[Li(THF )2]2[(tBu )NCHdCHN(tBu )] (2). To a solution of
tBu-DAD (3.37 g, 20 mmol) in THF (50 mL) was added lithium
metal (0.28 g, 40 mmol) at room temperature. The colorless
solution rapidly took on the deep red color of the product and
was stirred until the metal pieces had dissolved completely
and the starting 1,4-diaza-1,3-diene tBu-DAD had been con-
verted quantitatively to 2 (ca. 10 h). The resulting solution
was filtered and then used without further purification in the
synthesis of 5.
3
(d, J H-H ) 2.0 Hz, 1H, NdCHCH), 1.42 (s, 1H, NH), 1.12 (s,
9H, CMe3), 0.83 (s, 9H, CMe3). 13C NMR (THF-d8, 75 MHz, 25
1
2
°C): δ 165.40 (dd, J C-H ) 160.4 Hz, J C-H ) 6.8 Hz,
NdCHCH), 154.69, 153.38 (s, ipso-C6H5), 128.31, 127.93,
127.68, 127.63 (d, o-/m-C6H5), 126.22 (d, p-C6H5), 82.92 (s,
1
2
LiOC), 62.83 (dd, J C-H ) 136.2 Hz, J C-H ) 12.9 Hz, Nd
1
CHCH), 57.59, 51.47 (s, CMe3), 30.57 (q, J C-H ) 124.4 Hz,
CMe3), 29.52 (q, 1J C-H ) 125.1 Hz, CMe3). Mp: 98-99 °C. Anal.
Calcd for C23H31N2OLi: C, 77.07; H, 8.72; N, 7.82. Found: C,
76.91; H, 8.84; N, 7.91.
[(THF )2Li(tBu -DAD)][(THF )Li(tBu -DAD)]Sm I (5). To a
suspension of SmI2(THF)5 (7.65 g, 10 mmol) in THF (100 mL)
was added dropwise a THF solution (50 mL) of 2 (20 mmol) at
-30 °C. The solution was warmed to room temperature and
stirred for 12 h, during which time the solution gradually
became red-violet. The solvent was removed in vacuo and the
resulting solid extracted with diethyl ether. The resulting red-
violet solution was concentrated and cooled to -30 °C to yield
red-violet crystalline 5 (5.32 g, 63%). 1H NMR (THF-d8, 300
MHz, 25 °C): δ 8.58 (br s, 4H, HCdCH), 3.63 (m, 12H, OCH2-
CH2, THF), 1.77 (m, 12H, OCH2CH2, THF), 0.30 (br s, 36H,
CMe3). 13C{1H} NMR (THF-d8, 75 MHz, 25 °C): δ 127.30 (d,
X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d
Refin em en t. The intensity data for the compounds 5, 6, and
8 were collected on a Nonius CAD4 diffractometer and those
for the compound 7 on a Nonius Kappa CCD diffractometer,
using graphite-monochromated Mo KR radiation. Data were
corrected for Lorentz, polarization, and absorption effects. No
absorption correction was made for 8.32,33 The structures were
solved by direct methods (SHELXS)34 and refined by full-
2
matrix least-squares techniques against Fo (SHELXL-97).35
Only for the compound 8 were the hydrogen atoms located by
difference Fourier synthesis and refined isotropically. The
hydrogen atoms of the other structures were included at
calculated positions with fixed thermal parameters. All non-
hydrogen atoms were refined anisotropically.35 XP (SIEMENS
Analytical X-ray Instruments, Inc.) was used for structure
representations.
1
1J C-H ) 159 Hz, HCdCH), 68.15 (t, J C-H ) 146 Hz, OCH2-
1
CH2, THF), 59.65 (s, CMe3), 28.09 (q, J C-H ) 124 Hz, CMe3),
1
26.27 (t, J C-H ) 131 Hz, OCH2CH2, THF). Mp: 165 °C dec.
Anal. Calcd for C32H64N4O3ILi2Sm: C, 45.54; H, 7.64; N, 6.64.
Found: C, 45.30; H, 7.51; N, 6.75.
{[OC(P h )2CH{CHdN(tBu )}N(tBu )]Li}2Sm Cl(THF ) (6).
A sample of [(THF)Li(tBu-DAD)]2Sm(µ-Cl)2Li(THF)2 (4b; 2.46
g, 3.0 mmol) was dissolved in diethyl ether (100 mL). Two
equivalents of benzophenone (1.09 g, 6.0 mmol) was added at
room temperature, and the mixture was stirred for 3 h. The
precipitate (LiCl) was filtered off and the solution was con-
centrated under vacuum to about 50 mL. A colorless crystalline
solid was obtained upon cooling the solution to -20 °C for
several days. The product 6 (2.36 g, 81%) can be purified by
recrystallization from diethyl ether. 1H NMR (THF-d8, 300
MHz, 25 °C): δ 9.00-4.20 (br, m, Ph), 3.58 (m, OCH2CH2,
THF), 2.20 (s), 2.02 (s), 1.89 (s), 1.74 (m, OCH2CH2, THF), 1.17
(br s, CMe3), 0.03 (s), -0.23 (s), -1.81 (s), -2.73 (s), -7.80 (br,
s). Mp: 120 °C dec. Anal. Calcd for C50H68N4O3ClLi2Sm: C,
61.73; H, 7.45; N, 5.76. Found: C, 61.60; H, 7.40; N, 5.83.
{[OC(P h )2CH{CHdN(tBu )}N(tBu )]Li}2Sm I(THF) (7). Fol-
lowing the procedure described for 6, 2.53 g (3.0 mmol) of
[(THF)2Li(tBu-DAD)][(THF)Li(tBu-DAD)]SmI (5) was reacted
with 1.09 g (6.0 mmol) of benzophenone. The reaction mixture
was filtered, concentrated, and cooled to -20 °C to provide 2.75
g (86%) of colorless crystalline 7. 1H NMR (THF-d8, 300 MHz,
25 °C): δ 9.10-4.15 (br, m, Ph), 3.61 (m, OCH2CH2, THF),
Further details of the crystal structure investigations are
available on request from the director of the Cambridge
Crystallographic Data Center, 12 Union Road, GB-Cambridge
CB2 1 EZ, U.K., on quoting the depository numbers CCSD-
150838 (5), CCSD-150836 (6), CCSD-150835 (7), and CCSD-
150837 (8), the names of the authors, and the journal citation.
Ack n ow led gm en t. Financial support for this re-
search was provided by the Deutsche Forschungsge-
meinschaft and Bayer AG, Leverkusen, Germany. We
are also grateful to Prof. Dr. D. Steinborn (Martin-
Luther-Universita¨t Halle-Wittenberg) for providing labo-
ratory facilities. We thank Dr. F. Girgsdies (Technische
Universita¨t Berlin) for help with the X-ray diffraction
analyses.
Su p p or tin g In for m a tion Ava ila ble: Listings of atomic
coordinates, thermal parameters, and bond distances and
angles for complexes 5-8. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM010323J
(29) (a) Girad, P.; Namy, J . L.; Kagan, H. B. J . Am. Chem. Soc.
1980, 102, 2693-2698. (b) Evans, W. J .; Gummersheimer, T. S.; Ziller,
J . W. J . Am. Chem. Soc. 1995, 117, 8999-9002.
(32) MOLEN, An Interactive Structure Solution Procedure; Enraf-
Nonius, Delft, The Netherlands, 1990.
(33) Otwinowski, Z.; Minor, W. Processing of X-ray Diffraction Data
Collected in Oscillation Mode. In Methods in Enzymology; Carter, C.
W., Sweet, R. M., Eds.; Academic Press: New York, 1997; Vol. 276
(Macromolecular Crystallography, Part A), pp 307-326.
(34) Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467-473.
(35) Sheldrick, G. M. SHELXL-97; University of Go¨ttingen, Go¨t-
tingen, Germany, 1993.
(30) Anhydrous SmCl3 was prepared following a standard procedure
and then transformed into the corresponding THF adduct: (a) Free-
man, J . H.; Smith, M. L. J . Inorg. Nucl. Chem. 1958, 7, 224-227. (b)
Manzer, L. E. Inorg. Synth. 1982, 21, 135-140.
(31) Kliegman, J . M.; Barnes, R. K. Tetrahedron, 1970, 26, 2555-
2560.