Synthesis, reactivity, and structure of mixed-ligand ytterbium complexes supported by β-diketiminate

Article abstract of DOI:10.1021/om010803a

The preparation and reaction chemistry of β-diketiminate ytterbium complexes is described. Reaction of [(DIPPh)₂nacnac]Li ((DIPPh)₂nacnac = N,N-diisopropylphenyl-2,4-pentanediimine anion) with 1 equiv of anhydrous YbCl₃ in THF, followed by crystallization from toluene, affords the monomeric complex [(DIPPh)₂nacnac]YbCl₂(THF)₂ (1) in high yield. Recrystallization of complex 1 from toluene gives an unexpected dimeric complex, {[(DIPPh)₂-nacnac]YbCl(μ-Cl)₂Yb[(DIPPh)nacnac](THF)} ·1/2MePh (2), which has a rare triple chloride bridge. Reaction of complex 1 with CH₃C₅H₄Na in 1:1 molar ratio in THF gives the mixed-ligand ytterbium chloride (CH₃C₅H₄)[(DIPPh)₂nacnac]YbCl (3). Complex 3 readily undergoes metathesis reactions with 1 equiv of LiNPh₂ or LiNPrⁱ₂ in THF to form the compounds (CH₃C₅H₄)[(DIPPh)₂nacnac]YbNPh₂ (4) and (CH₃C₅H₄)[(DIPPh)₂nacnac]YbNPrⁱ ₂ (5), respectively. The complexes 2, 3, and 4 have been characterized by an X-ray diffraction structure determination.

Full text of DOI:10.1021/om010803a

Organometallics 2002, 21, 819-824
819
Syn th esis, Rea ctivity, a n d Str u ctu r e of Mixed -Liga n d
Ytter biu m Com p lexes Su p p or ted by â-Dik etim in a te
Yingming Yao,† Yong Zhang,† Qi Shen,*,†,‡ and Kaibei Yu§
Department of Chemistry and Chemical Engineering, Suzhou University, Suzhou 215006,
People’s Republic of China, State Key Laboratory of Organometallic Chemistry, Shanghai
Institute of Organic Chemistry, Chinese Academy of Sciences, Shanghai 200032, People’s
Republic of China, and Chengdu Institute of Organic Chemistry, Chinese Academy of Sciences,
Chengdu 610041, People’s Republic of China
Received September 6, 2001
The preparation and reaction chemistry of â-diketiminate ytterbium complexes is described.
Reaction of [(DIPPh)2nacnac]Li ((DIPPh)2nacnac ) N,N-diisopropylphenyl-2,4-pentanedi-
imine anion) with 1 equiv of anhydrous YbCl3 in THF, followed by crystallization from
toluene, affords the monomeric complex [(DIPPh)2nacnac]YbCl2(THF)2 (1) in high yield.
Recrystallization of complex 1 from toluene gives an unexpected dimeric complex, {[(DIPPh)2-
nacnac]YbCl(µ-Cl)3Yb[(DIPPh)2nacnac](THF)}‚1/2MePh (2), which has a rare triple chloride
bridge. Reaction of complex 1 with CH3C5H4Na in 1:1 molar ratio in THF gives the mixed-
ligand ytterbium chloride (CH3C5H4)[(DIPPh)2nacnac]YbCl (3). Complex 3 readily undergoes
metathesis reactions with 1 equiv of LiNPh2 or LiNPri in THF to form the compounds
2
(CH3C5H4)[(DIPPh)2nacnac]YbNPh2 (4) and (CH3C5H4)[(DIPPh)2nacnac]YbNPri (5), respec-
2
tively. The complexes 2, 3, and 4 have been characterized by an X-ray diffraction structure
determination.
In tr od u ction
features; for example, their steric and electronic proper-
ties can be easily tuned,20 and they can coordinate to
the metal center in different bonding models ranging
from purely σ to a combination of σ and π donation.7 In
particular, some of these â-diketiminate complexes are
active for olefin polymerization1,7-10 and lactide “living”
polymerization.12-15 However, the utilization of â-diketim-
inates as ancillary ligands in the synthesis of lanthanide
complexes still remains relatively poorly explored. Apart
from [(Ph)2nacnac]GdBr2(THF)2, [(Ph)2nacnac]3Ln (Ln
) Sm, Gd) ((Ph)2nacnac ) N,N-phenyl-2,4-pentanedi-
imine anion),21 [(Pri)2nacnac)]2LnBr (Ln ) Sm, Gd)
((Pri)2nacnac ) N,N-isopropyl-2,4-pentanediimine an-
ion),22 and {[PhC(NSiMe3)]2CH}2Yb,23 the recently re-
ported [(DIPPh)2nacnac]ScCl2(THF) and [(DIPPh)2-
nacnac]Sc+CH2Ph[η6-PhCH2B-(C6F5)3] ((DIPPh)2nacnac
) N,N-diisopropylphenyl-2,4-pentanediimine anion)24
are the only well-characterized complexes of this type
in the literature to our knowledge.
In recent years, the use of â-diketiminate as support-
ing ligand systems in both main and transition metal
coordination chemistry has attracted considerable
attention.1-19 These ligands have several attractive
† Suzhou University.
‡ Shanghai Institute of Organic Chemistry.
§ Chengdu Institute of Organic Chemistry.
(1) Feldman, J .; McLain, S. J .; Parthasarathy, A.; Marshall, W. J .;
Clabrese, J . C.; Arthur, S. D. Organometallics 1997, 16, 1514.
(2) Radzewich, C. E.; Coles, M. P.; J ordan, R. F. J . Am. Chem. Soc.
1998, 120, 9384.
(3) Radzewich, C. E.; Guzei, I. A.; J ordan, R. F. J . Am. Chem. Soc.
1999, 121, 8673.
(4) Qian, B.; Ward, D. L.; Smith, M. R., III. Organometallics 1998,
17, 3070.
(5) Qian, B.; Scanlon, W. J ., IV.; Smith, M. R., III; Motry, D. H.
Organometallics 1999, 18, 1693.
(6) Kakaliou, L.; Scanlon, W. J ., IV.; Qian, B.; Baek, S. W.; Smith,
M. R., III; Motry, D. H. Inorg. Chem. 1999, 38, 5964.
(7) Rahim, M.; Taylor, N. J .; Xin, S.; Collins, S. Organometallics
1998, 17, 1315.
(8) Vollmerhaus, R.; Rahim, M.; Tomaszewski, R.; Xin, S.; Taylor,
N. J .; Collins, S. Organometallics 2000, 19, 2161.
(9) Gibson, V. C.; Maddox, P. J .; Newton, C.; Redshaw, C.; Solan,
G. A.; White, A. J . P.; Williams, D. J . J . Chem. Soc., Chem. Commun.
1998, 1651.
(10) Kim, W. K.; Fevola, M. J .; Liable-Sands, L. M.; Rheingold, A.
L.; Theopold, K. H. Organometallics 1998, 17, 4541.
(11) Gibson, V. C.; Segal, J . A.; White, A. J . P.; Williams, D. J . J .
Am. Chem. Soc. 2000, 122, 7120.
(12) Dove, A. P.; Gibson, V. C.; Marshall, E. L.; White, A. J . P.;
Williams, D. J . J . Chem. Soc., Chem. Commun. 2001, 283.
(13) Chamberlain, B. M.; Cheng, M.; Moore, D. R.; Ovitt, T. M.;
Lobkovsky, E. B.; Coates, G. W. J . Am. Chem. Soc. 2001, 123, 3229.
(14) Cheng, M.; Attygalle, A. B.; Lobkovsky, E. B.; Coates, G. W. J .
Am. Chem. Soc. 1999, 121, 11583.
Now, we are interested in the synthesis and reactivity
of â-diketiminate lanthanide complexes and find that
the (DIPPh)2nacnac anion is an ideal ligand for the
synthesis of mixed-ligand lanthanide complexes. In this
paper, we report the synthesis and characterization of
several mono(methylcyclopentadienyl)-â-diketiminate
ytterbium complexes. The molecular structures of
(18) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H. G.; Power,
P. P. Organometallics 2001, 20, 1190.
(19) Ayers, A. E.; Klapotke, T. M.; Dias, H. V. R. Inorg. Chem. 2001,
40, 1000.
(15) Cheng, M.; Lobkovsky, E. B.; Coates, G. W. J . Am. Chem. Soc.
1998, 120, 11018.
(16) Budzelaar, P. H. M.; Gelder, R.; Gal, A. W. Organometallics
1998, 17, 4121.
(17) Bailey, P. J .; Coxall, R. A.; Dick, C. M.; Fabre, S.; Parsons, S.
Organometallics 2001, 20, 798.
(20) Parks, J . E.; Holm, R. H. Inorg. Chem. 1968, 7, 1408.
(21) Drees, D.; Magull, J . Z. Anorg. Allg. Chem. 1994, 620, 814.
(22) Drees, D.; Magull, J . Z. Anorg. Allg. Chem. 1995, 621, 948.
(23) Lappert, M. F.; Liu, D. S. J . Organomet. Chem. 1995, 500, 203.
(24) Lee, L. W. M.; Piers, W. E.; Elsegood, M. J .; Clegg, W.; Parvez,
M. Organometallics 1999, 18, 2947.
10.1021/om010803a CCC: $22.00 © 2002 American Chemical Society
Publication on Web 01/30/2002

820 Organometallics, Vol. 21, No. 5, 2002
Yao et al.
Sch em e 1
{[(DIPPh)2nacnac]YbCl(µ-Cl)3Yb[(DIPPh)2nacnac](THF)}‚
1/2MePh (2), (CH3C5H4)[(DIPPh)2nacnac]YbCl (3), and
(CH3C5H4)[(DIPPh)2nacnac]YbNPh2 (4) are described.
crystals in high yield. The reaction of complex 1 with
other anionic ligands, such as aryloxo, indenyl, and
amido, is currently being studied.
We notice that the mixed-ligand pentamethylcyclo-
pentadienyl-benzamidinate yttrium chloride {Cp*[PhC-
(NSiMe3)2]YCl}2 is inert for substitution of the chloride
with aryloxides, amides, or some alkyls.25 We wonder
whether this is a special case. Therefore, the reaction
chemistry of complex 3 with selected nucleophiles has
been further studied. Treatment of complex 3 with 1
Resu lts a n d Discu ssion
Syn th esis of Ytter biu m â-Dik etim in a te Com -
p lexes. [(DIPPh)2nacnac]Li reacted with 1 equiv of
anhydrous YbCl3 in THF to afford the â-diketiminate
ytterbium dichloride which was identified by elemental
analysis as [(DIPPh)2nacnac]YbCl2(THF)2 (1) in 72%
yield as red microcrystals after crystallization from
toluene (Scheme 1). To obtain crystals suitable for X-ray
analysis, complex 1 was recrystallized from toluene. The
unexpected complex 2, which was characterized to be
part of coordinated THF lost, was obtained as violet
crystals. Structural analysis of complex 2 reveals that
it has a rare triple chloride bridge, {[(DIPPh)2nacnac]-
YbCl(µ-Cl)3Yb[(DIPPh)2nacnac](THF)}‚1/2MePh (vide
infra). Attempts to prepare bis(â-diketiminate) ytter-
bium complex [(DIPPh)2nacnac]2YbCl by the metathesis
reaction of complex 1 with additional [(DIPPh)2nacnac]-
Li or YbCl3 with 2 equiv of [(DIPPh)2nacnac]Li in THF
were unsuccessful; even under more drastic conditions,
the isolated products were complex 1 and [(DIPPh)2-
nacnac]Li, respectively. Therefore, the (DIPPh)2nacnac
anion seems to be an ideal ligand for synthesis of the
mixed-ligand lanthanide derivatives.
equiv of LiNPh2 or LiNPri in THF smoothly allowed
2
for the replacement of chloride and the production of
the complexes (CH3C5H4)[(DIPPh)2nacnac]YbNPh2 (4)
and (CH3C5H4)[(DIPPh)2nacnac]YbNPri (5) in good
2
yields (65-77%) after crystallization from toluene,
respectively. These results show complex 3 is a useful
precursor for the synthesis of mono(methylcyclopenta-
dienyl) lanthanide derivatives. Comparison of the re-
activity between complex 3 and complex {Cp*[PhC-
(NSiMe3)2]YCl}2 indicates that the effect of a π ancillary
ligand on the reactivity of the complex should be crucial.
Complexes 1-5 were characterized by elemental
analyses, IR spectra, and X-ray structural analysis
(complexes 2-4). These complexes have good thermal
stability. Complexes 1-3 are moderately sensitive to air
and moisture and are well soluble in THF and DME,
moderately in aromatic solvents, and insoluble in ali-
When complex 1 was treated with 1 equiv of CH3C5H4-
Na in THF, the desired mixed-ligand ytterbium chloride
(CH3C5H4)[(DIPPh)2nacnac]YbCl (3) was isolated as red
(25) Duchateau, R.; Meetsma, A.; Teuben, J . H. Organometallics
1996, 15, 1656.

Mixed-Ligand Ytterbium Complexes
Organometallics, Vol. 21, No. 5, 2002 821
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 2
Yb(1)-N(1)
Yb(1)-N(2)
Yb(1)-Cl(1)
Yb(1)-Cl(2)
Yb(1)-Cl(3)
Yb(1)-Cl(4)
Yb(1)-C(13)
Yb(1)-C(15)
N(1)-C(13)
C(13)-C(14)
C(14)-C(15)
C(15)-N(2)
2.253(5)
2.282(5)
2.505(2)
2.710(2)
2.663(2)
2.752(2)
3.105(7)
3.144(6)
1.335(7)
1.410(8)
1.403(8)
1.325(7)
Yb(2)-N(3)
Yb(2)-N(4)
Yb(2)-O(1)
Yb(2)-Cl(2)
Yb(2)-Cl(3)
Yb(2)-Cl(4)
Yb(1)-Yb(2)
N(3)-C(42)
C(42)-C(43)
C(43)-C(44)
C(44)-N(4)
2.295(5)
2.298(5)
2.299(4)
2.612(2)
2.593(2)
2.610(2)
3.692(6)
1.339(8)
1.382(8)
1.379(8)
1.350(7)
N(1)-Yb(1)-N(2)
84.19(18) N(3)-Yb(2)-N(4)
81.92(18)
N(1)-Yb(1)-Cl(2) 153.03(14) N(3)-Yb(2)-Cl(2) 177.85(14)
N(2)-Yb(1)-Cl(2)
N(1)-Yb(1)-Cl(3) 114.65(14) N(3)-Yb(2)-Cl(3)
N(2)-Yb(1)-Cl(3) 160.83(14) N(4)-Yb(2)-Cl(3) 176.59(14)
N(1)-Yb(1)-Cl(4) 86.13(14) N(3)-Yb(2)-Cl(4) 102.22(14)
87.25(13) N(4)-Yb(2)-Cl(2) 100.23(13)
97.60(14)
erally, the central metals in dimeric lanthanide halides
are connected by one or two halogen bridge(s). Only a
few examples of crystallographically characterized mul-
tiple halogen bridges between two lanthanide atoms are
those found in lanthanide clusters.31 Moreover, the
coordination environment around the two ytterbium
centers in complex 2 is inequivalent, although the
coordination geometry around two ytterbium centers is
similar (six-coordinate distorted octahedral). The Yb(1)
atom is coordinated by two nitrogen atoms of the
â-diketiminate ligand and one terminal chlorine atom
and three bridged chlorine atoms; the Yb(2) center is
coordinated by two nitrogen atoms and three bridged
chlorine atoms and one oxygen atom of THF molecule.
The reason for the formation of a triple chloride bridge
and the coordination of only one THF molecule may be
attributed to the increased steric demand of the bulky
â-diketiminate ligands.
Two â-diketiminate ligands are symmetrically coor-
dinated to Yb(1) and Yb(2), respectively, but the Yb-
(1)-N(1,2) bond lengths (2.253(5), 2.282(5) Å) are
slightly shorter than those of Yb(2)-N(3,4) (2.295(5),
2.298(5) Å). The bond distances of C(13)-C(14), C(14)-
C(15), N(1)-C(13), and N(2)-C(15) (see Table 1) suggest
significant delocalization within the π-system of the
â-diketiminate ligand. The Yb-C(13,14,15) distances
are quite long, suggesting a negligible π contribution
to the â-deketiminate-Yb bonding in this compound.
Molecu la r Str u ctu r es of (CH3C5H4)[(DIP P h )2-
n a cn a c]YbR (3, R ) Cl; 4, R ) NP h 2). A drawing of
complex 3 is shown in Figure 2, and selected bond
distances and angles are listed in Table 2. The structure
analysis reveals complex 3 to be a solvent-free mono-
meric species formed by ytterbium, methylcyclopenta-
dienyl, (DIPPh)2nacnac, and chlorine. The unsolvated
monomeric structure is rare in lanthanide monochloride
derivatives. Normally, they have solvated monomeric
structures or solvent-free bridging structures in the solid
state.31-33 The coordination geometry about the ytter-
F igu r e 1. Molecular structure of complex 2 (hydrogen
atoms omitted for clarity).
phatic hydrocarbons, and complexes 4 and 5 have good
solubility even in aromatic solvents.
Our previous work has shown that bis(methylcyclo-
pentadienyl) lanthanide amides are highly active initia-
tors in the syndiotactic polymerization of methyl meth-
acrylate (MMA).26-29 To understand the effect of the
ancillary ligand on the activity of amide complexes, we
tested the catalytic activity of complexes 4 and 5 in
MMA polymerization. Preliminary studies show that
both complexes have no catalytic activity at all. It is
really unexpected that replacing one methylcyclopen-
tadienyl group by a â-diketiminate ligand results in
such a dramatic decrease of its activity, although a
decrease of catalytic reactivity has been observed by
replacing the bis(pentamethylcyclopentadienyl) ligand
system with two N,N′-bis(trimethylsilyl)benzamidinate
ligands.30 Considering the great difference in activity
between (CH3C5H4)2YbNPh2 and sterically crowded
complex (C5Me5)2YbNPh2 in MMA polymerization (the
former very high, the latter no activity at all),28 we
ascribe this failure mainly to the steric congestion
around the metal center brought about by the bulky
(DIPPh)2nacnac ligand, although this difference in
activity could also be ascribed to electronic changes
caused by the nitrogen ligation of the ytterbium ion. We
are currently investigating the activity of these com-
plexes with other monomers.
Molecu la r Str u ctu r e of {[(DIP P h )2n a cn a c]YbCl-
(µ-Cl)3Yb[(DIP P h )2n a cn a c](THF )}‚1/2MeP h (2). The
molecular structure of complex 2 is shown in Figure 1,
and the selected bond lengths and angles are listed in
Table 1. The molecule is dinuclear in the solid state.
The most interesting feature of the structure is that the
two ytterbium centers are triply chloride-bridged. Gen-
(26) Mao, L. S.; Shen, Q. J . Polym. Sci., Part A: Polym. Chem. 1998,
36, 1593.
(27) Mao, L. S.; Shen, Q.; Sun, J . J . Organomet. Chem. 1998, 566,
(31) Schumann, H.; Meese-Marktschffel, J . A.; Esser, L. Chem. Rev.
1995, 95, 865.
9.
(28) Wang, Y. R.; Shen, Q.; Xue, F.; Yu, K. B. J . Organomet. Chem.
2000, 598, 359.
(29) Wang, Y. R.; Shen, Q.; Ma, J . L.; Zhao, Q. Chin. J . Chem. 2000,
18, 428.
(30) Duchateau, R.; van Wee, C. T.; Teuben, J . H. Organometallics
1996, 15, 2291.
(32) Edelmann, F. T. In Comprehensive Organometallic Chemistry
II, Vol. 4; Abel, E. W., Stone, F. G. S., Wilkinson, G., Eds.; Pergamon:
Oxford, 1995; pp 11-212.
(33) Marks, T. J .; Ernst, R. D. In Comprehensive Organometallic
Chemistry, Vol. 3; Wilkinson, G., Stone, F. G. S., Abel, E. W., Eds.;
Pergamon: Oxford, 1982; pp 173-270.

822 Organometallics, Vol. 21, No. 5, 2002
Yao et al.
Ta ble 3. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 4
4a
4b
Yb(1)-N(1)
Yb(1)-N(2)
Yb(1)-N(3)
Yb(1)-C(13)
Yb(1)-C(15)
Yb(1)-C(42)
Yb(1)-C(43)
Yb(1)-C(44)
Yb(1)-C(45)
Yb(1)-C(46)
N(1)-C(13)
N(2)-C(15)
C(13)-C(14)
C(14)-C(15)
2.298(6) Yb(2)-N(4)
2.257(5) Yb(2)-N(5)
2.259(6) Yb(2)-N(6)
3.184(7) Yb(2)-C(60)
3.156(7) Yb(2)-C(62)
2.592(7) Yb(2)-C(89)
2.570(8) Yb(2)-C(90)
2.554(8) Yb(2)-C(91)
2.590(7) Yb(2)-C(92)
2.607(7) Yb(2)-C(93)
1.346(8) N(4)-C(60)
1.341(8) N(5)-C(62)
1.385(9) C(60)-C(61)
1.387(9) C(61)-C(62)
2.281(5)
2.310(6)
2.214(6)
3.192(6)
3.221(7)
2.583(14)
2.584(14)
2.596(17)
2.602(18)
2.594(10)
1.339(8)
1.313(9)
1.393(9)
1.414(10)
F igu r e 2. Molecular structure of complex 3 (hydrogen
atoms omitted for clarity).
N(1)-Yb(1)-N(2)
82.9(2)
N(4)-Yb(2)-N(5)
82.2(2)
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 3
N(1)-Yb(1)-N(3) 113.9(2)
N(2)-Yb(1)-N(3) 110.9(2)
N(4)-Yb(2)-N(6) 114.9(2)
N(5)-Yb(2)-N(6) 113.5(2)
Yb-N(1)
Yb-N(2)
Yb-Cl
Yb-C(30)
Yb-C(31)
Yb-C(32)
Yb-C(33)
2.247(3)
2.239(3)
2.4704(14)
2.584(6)
2.554(7)
2.557(8)
2.588(6)
Yb-C(34)
2.610(5)
3.086(4)
3.049(5)
1.330(5)
1.322(5)
1.409(6)
1.396(6)
Yb-C(13)
Yb-C(15)
N(1)-C(13)
N(2)-C(15)
C(13)-C(14)
C(14)-C(15)
N(1)-Yb-N(2)
N(1)-Yb-Cl
N(2)-Yb-Cl
85.43(13)
105.07(10)
107.48(10)
C(13)-N(1)-Yb
C(15)-N(2)-Yb
C(13)-C(14)-C(15)
116.9(3)
115.4(3)
132.3(5)
bium center approximates a three-legged piano stool
with the two nitrogen atoms of the chelating â-diketimi-
nate anion and a chlorine atom constituting the “legs”
of the molecule, and the formal coordination number of
the central metal is six.
Interestingly, the Yb-C(13) and Yb-C(15) distances
are 3.086(4) and 3.049(5) Å, respectively, which are
comparable with those of 2.986(6) and 3.180(9) Å for
bridging η2-C5H5 bonding in (C5Me5)2Sm(µ-C5H5)Sm(C5-
34
Me5)2 and 2.814(4)-3.148(6) Å for chelating η6-, η1-
F igu r e 3. Molecular structure of complex 4 (hydrogen
atoms omitted for clarity). Only one of the two independent
molecules is presented.
Ph-Yb bonding in [Yb(Odpp)3]2 (Odpp ) 2,6-diphenyl-
phenolate),35 respectively. This indicates that the complex
may be considered to involve π coordination of the
â-diketiminate ligand to the ytterbium atom. Therefore,
the â-diketiminate ligand appears to be relatively more
π bound in complex 3 than in complex 2. There is the
expected pattern of delocalization within the â-diketimi-
nate ligand. The backbone of the ligand (NC3N) and
ytterbium atom form a stable six-membered ring which
adopts a boat conformation with C(14) and Yb lying 0.13
and 1.03 Å out of the N(1), C(13), C(15), N(2) plane,
respectively. The â-diketiminate ligand is symmetrically
coordinated to the ytterbium atom with variation in
Yb-N bond lengths of 0.008 Å (2.247(3) and 2.239(3)
Å, respectively). The Yb-C(ring) distances range from
2.554(7) to 2.610(5) Å, giving the average Yb-C(ring)
distance of 2.579(6) Å. The N(1)-Yb-N(2) angle is
85.43(13)°, which is comparable with that in complex
2.
thermal motion. An ORTEP of molecule 4a is depicted
in Figure 3. The coordination geometry around the
ytterbium atom resembles that in complex 3, and the
six-membered chelating ring also adopts a boat confor-
mation, with C(14) and Yb lying 0.11 and 0.91 Å out of
the NC2N plane, respectively. The Yb-C(13), Yb-C(14),
and Yb-C(15) distances are quite long (3.184(7), 3.419-
(7), and 3.156(7) Å, respectively), which indicates that
there is only purely σ bonding.
The N(1)-Yb(1)-N(2) angle is 82.9(2)°, which is more
acute than the corresponding angle in complex 3, and
the Yb(1)-N(1) and Yb(1)-N(2) bond lengths of 2.257-
(5) and 2.298(6) Å are slightly longer than those in
complex 3, respectively. Considering the elongated Yb-
(1)-C(13), -C(14), and -C(15) distances in complex 4,
it is reasonable to ascribe the difference in bond
parameters of complexes 3 and 4 to the increased steric
congestion in the latter due to the replacement of
chlorine by a diphenylamido group.
Complex 4 crystallizes with two crystallographically
independent but chemically similar molecules (4a and
4b) in the unit cell; the selected bond lengths and angles
are provided in Table 3 for both molecules. The methyl-
cyclopentadienyl ring of 4b is disordered due to strong
Con clu sion s
(34) Evans, W. J .; Ulibarri, T. A. J . Am. Chem. Soc. 1987, 109, 4292.
(35) Deacon, G. B.; Nickle, S.; Mackinnon, P. I.; Tiekink, E. R. T.
Aust. J . Chem. 1990, 43, 1245.
We have shown that the (DIPPh)2nacnac anion should
be a useful ancillary ligand for preparing soluble, well-

Mixed-Ligand Ytterbium Complexes
Organometallics, Vol. 21, No. 5, 2002 823
Ta ble 4. Cr ysta llogr a p h ic Da ta for Com p lexes 2, 3, a n d 4
2
3
4
formula
fw
T (K)
C
65.5H94Cl4N4OYb2
C35H48ClN2Yb
705.24
297(2)
C47H58N3Yb
838.00
290(2)
1441.33
299(2)
cryst syst
space group
unit cell
a (Å)
b (Å)
c (Å)
monoclinic
P2(1)/c
monoclinic
P2(1)/n
monoclinic
P2(1)/n
19.951(4)
13.918(2)
24.257(5)
98.710(10)
6658(2)
4
1.438
2.994
2924
10.422(2)
26.247(5)
12.653(2)
106.050(10)
3326.3(10)
4
1.408
2.916
1436
12.420(2)
16.469(3)
40.264(7)
93.530(10)
8220(2)
8
1.354
2.310
3448
â (deg)
V (Å3)
Z
Dcalcd (g cm-3
)
µ (mm-1
F(000)
)
cryst size (mm)
θmax (deg)
no. of collected reflns
no. of unique reflns
no. of obsd reflns [I > 2.0σ(I)]
no. of variables
0.40 × 0.32 × 0.20
0.52 × 0.34 × 0.34
0.52 × 0.42 × 0.22
25.0
25.0
25.0
13 060
11 734
6754
6579
5846
3902
353
16 305
14 493
7451
715
937
GOF
R
Rw
0.790
0.0405
0.0561
0.841
0.0316
0.0571
0.816
0.0478
0.0703
overnight at room temperature. Solvent was completely re-
moved under vacuum, and the red residue was extracted with
toluene. The dissolved portion was removed by centrifugation.
The filtrate was concentrated to 30 mL and cooled at -20 °C,
and red microcrystals were collected in two crops by filtration
defined ytterbium(III) complexes. The mixed-ligand
complexes (CH3C5H4)[(DIPPh)2nacnac]YbX are acces-
sible through stepwise ligand introduction, starting from
anhydrous YbCl3 by first introducing a â-diketiminate
ligand to the metal’s coordinate sphere. In these com-
plexes, â-diketiminates show different coordination
modes depending on the steric environment. The chlo-
ride (CH3C5H4)[(DIPPh)2nacnac]YbCl shows a similar
reactivity with its bis(methylcyclopentadienyl)ytterbium
analogues, it readily undergoes metathesis reactions
(4.29 g, 72.1%), mp 132-133 °C (dec). Anal. Calcd for C37H57
-
Cl2N2O2Yb: C, 55.15; H, 7.13; N, 3.48; Yb, 21.47. Found: C,
55.62; H, 7.38; N, 3.35; Yb, 21.58. IR (KBr, cm-1): 3060(w),
2960(vs), 2926(s), 2867(s), 1621(vs), 1550(vs), 1483(m), 1462-
(s), 1439(s), 1387(m), 1362(s), 1325(s), 1276(s), 1254(m), 1174-
(m), 1108(w), 1075(m), 1034(m), 930(w), 789(s), 758(s), 728(w).
with LiNPh2 or LiNPri in THF to form the correspond-
2
[(DIP P h )2n acn ac]YbCl(µ-Cl)3Yb[(DIP P h )2n acn ac(THF)]‚
1/2MeP h (2). Complex 1 (0.98 g, 1.22 mmol) was recrystallized
from toluene, and violet crystals suitable for X-ray analysis
were obtained at room temperature. The products were col-
lected by filtration (0.71 g, 81.3%), mp 140 °C (dec). Anal. Calcd
for C65.5H94Cl4N4OYb2: C, 54.58; H, 6.57; N, 3.88; Yb, 24.01.
Found: C, 53.85; H, 6.35; N, 3.68; Yb, 24.32. IR (KBr, cm-1):
3160(w), 2961(vs), 2927(s), 2867(s), 1622(vs), 1593(s), 1552-
(vs), 1481(s), 1462(s), 1439(s), 1383(s), 1361(s), 1326(s), 1275-
(vs), 1175(m), 1102(w), 1075(m), 1024(m), 933(w), 798(s),
758(s), 729(m), 700(m).
ing ytterbium amides. However, these ytterbium amides
show notably different reactivity compared to those seen
in related (CH3C5H4)2YbNPri2 and (CH3C5H4)2YbNPh2,
and they cannot efficiently initiate MMA polymeriza-
tion.
Exp er im en ta l Section
The chemistry described below was performed under pure
argon with exclusion of air and moisture by Schlenk tech-
niques. Solvents were dried and freed of oxygen by refluxing
over Na or sodium benzophenone ketyl and distilled under
(CH3C5H4)[(DIP P h )2n a cn a c]YbCl (3). Meth od a . To a
THF solution (30 mL) of compound 1 (3.29 g, 4.57 mmol) was
slowly added a solution of CH3C5H4Na (7.2 mL, 4.57 mmol) in
THF at room temperature. After being stirred for 24 h, the
precipitate was separated by centrifugation and the solvent
was evaporated completely under reduced pressure. Then
toluene was added to extract the product, and the dissolved
portion was separated by centrifugation. The red crystals were
obtained from concentrated toluene solution at -10 °C for 3
36
argon prior to use. Anhydrous YbCl3 and [(DIPPh)2nacnac]-
Li1 were prepared according to the literature methods. CH3C5H4-
Na was prepared by the reaction of CH3C5H5 with sodium in
THF. LiNPh2 and LiNPri were obtained by the reaction of
2
HNPh2 or HNPri with n-BuLi in a solution of toluene and
2
hexane.
Melting points were determined in sealed argon-filled
capillaries and are uncorrected. Metal analyses were carried
out using complexometric titration. Carbon, hydrogen, and
nitrogen analyses were performed by direct combustion; quoted
data are the average of at least two independent determina-
tions. The IR spectra were recorded on a Nicolet-550 FTIR
spectrometer as KBr pellets.
[(DIP P h )2n acn ac]YbCl2(THF)2 (1). A solution of [(DIPPh)2-
nacnac]Li (25 mL, 7.73 mmol) in toluene/hexane was slowly
added to a suspension of YbCl3 (2.16 g, 7.73 mmol) in 40 mL
of THF at room temperature. The color of the solution
gradually changed to red. The reaction mixture was stirred
days (2.73 g, 84.1%), mp 222-224 °C. Anal. Calcd for C35H48
-
ClN2Yb: C, 59.61; H, 6.86; N, 3.97; Yb, 24.54. Found: C, 59.31;
H, 6.68; N, 3.92; Yb, 24.47. IR (KBr, cm-1): 3058(w), 2963-
(vs), 2927(s), 2867(s), 1622(vs), 1552(vs), 1519(vs), 1462(s),
1435(s), 1386(s), 1363(s), 1317(s), 1263(s), 1173(m), 1101(m),
1072(w), 1022(m), 927(m), 853(w), 834(m), 789(s), 782(s), 757-
(s), 688(w). Crystals suitable for single-crystal structure stud-
ies were obtained by recrystallization from toluene solution
at -10 °C for a week.
Met h od b . To a slurry of anhydrous YbCl3 (1.75 g, 6.26
mmol) in about 40 mL of THF was slowly added a solution of
[(DIPPh)2nacnac]Li (20 mL, 6.26 mmol) in toluene/hexane at
room temperature. After YbCl3 disappeared completely, the
THF solution of CH3C5H4Na (9.8 mL, 6.26 mmol) was added
(36) Taylor, M. D.; Carter, C. P. J . Inorg. Nucl. Chem. 1962, 24,
387.

824 Organometallics, Vol. 21, No. 5, 2002
Yao et al.
slowly. The mixture was stirred at room temperature for
another 48 h, then the precipitate was removed from the
reaction mixture by centrifugation. THF was completely
removed in a vacuum, and toluene was added to extract the
product. The precipitate was removed again by centrifugation.
The red microcrystals were obtained from the concentrated
toluene solution at -10 °C (3.35 g, 75.8%).
(s), 1363(s), 1312(s), 1255(s), 1174(m), 1112(m), 1073(w), 1030-
(m), 932(m), 853(w), 786(s), 749(vs), 692(s), 615(m), 507(m).
X-r a y Str u ctu r e Deter m in a tion . Suitable single crystals
of complexes 2, 3, and 4 were sealed in a thin-walled glass
capillary for single-crystal structure determination. Intensity
data were collected on a Siemens P4 diffractometer in ω scan
mode using Mo KR radiation (λ ) 0.71073 Å). The diffracted
intensities were corrected for Lorentz polarization effects and
empirical absorption corrections. Details of the intensity data
collection and crystal data are given in Table 4.
(CH3C5H4)[(DIP P h )2n a cn a c]YbNP h 2 (4). A toluene/hex-
ane solution of LiNPh2 (15 mL, 2.17 mmol) was slowly added
to the THF solution (30 mL) of compound 3 (1.53 g, 2.17 mmol)
at 0 °C. The mixture was stirred for 2 h at 0 °C, and then for
another 48 h at room temperature. The solvent was evaporated
completely under reduced pressure. Then toluene was added
to extract the product, and the dissolved portion was separated
by centrifugation. Black crystals suitable for single-crystal
structure studies were obtained from concentrated toluene
solution at -20 °C for 2 days (1.41 g, 77.3%), mp 161-162 °C.
Anal. Calcd for C47H58N3Yb: C, 67.36; H, 6.98; N, 5.01; Yb,
20.65. Found: C, 67.45; H, 6.83; N, 4.92; Yb, 20.54. IR (KBr,
cm-1): 3059(w), 2961(vs), 2927(s), 2867(s), 1659(m), 1622(vs),
1592(vs), 1551(vs), 1494(vs), 1460(s), 1432(s), 1385(s), 1363-
(s), 1312(s), 1255(s), 1174(m), 1112(m), 1073(w), 1030(m), 932-
(m), 853(w), 786(s), 749(vs), 692(s), 615(m), 507(m).
The crystal structures of these complexes were solved by
direct methods using the SHELXS-97 program and expanded
by Fourier techniques. All the non-hydrogen atoms were
refined anisotropically. Hydrogen atoms were all generated
geometrically (C-H bond lengths fixed at 0.95 Å), assigned
appropriate isotropic thermal parameters, and allowed to ride
on their parent carbon atoms. All the H atoms were held
stationary and included in the structure factor calculation in
the final stage of full-matrix least-squares refinement.
Ack n ow led gm en t. Financial support from the Chi-
nese National Natural Science Foundation, the Key
Laboratory of Organic Synthesis of J iangsu Province,
and Suzhou University is gratefully acknowledged.
(CH3C5H4)[(DIP P h )2n a cn a c]YbNP r i (5). The synthesis
2
of compound 5 was carried out as described for 4, but LiNPri
2
(1.56 mmol) was used in place of LiNPh2. Black microcrystals
were obtained from toluene solution (0.78 g, 65.2%), mp 156-
158 °C. Anal. Calcd for C41H62N3Yb: C, 63.95; H, 8.11; N, 5.46;
Yb, 22.47. Found: C, 63.67; H, 7.93; N, 5.52; Yb, 22.58. IR
(KBr, cm-1): 3059(w), 2961(vs), 2927(s), 2867(s), 1659(m),
1622(vs), 1592(vs), 1551(vs), 1494(vs), 1460(s), 1432(s), 1385-
Su p p or tin g In for m a tion Ava ila ble: Tables of X-ray
diffraction data for complexes 2, 3, and 4. This material is
available free of charge via the Internet at http://pubs.acs.org.
OM010803A