Mono(pentamethylcyclopentadienyl)yttrium compounds stabilized by N,N′-Bis(Trimethylsilyl)benzamidmate ligands

Article abstract of DOI:10.1021/om9508187

Reaction of YCl₃·3.5THF with Cp*K followed by [PhC(NSiMe₃)₂]Li·OEt₂ in THF gives the surprisingly stable yttrium cyclopentadienyl-benzamidinate chloride {Cp*[PhC(NSiMe₃)₂]Y-(μ-Cl)}₂ (1). Thermally induced redistribution of the various ligands leading to disproportionation of the molecule was not observed. The dimer does not split easily, e.g., it does not react with THF to give Cp*[PhC(NSiMe₃)₂]YCl·THF. Attempts to produce monomeric derivatives of 1 by substitution of the chloride by alkoxy, amide, or alkyl substituents using salt metathesis methodology were not successful. Reaction of 1 with 2 equiv of MeLi in the presence of TMEDA (TMEDA = N,N,N′, ′-tetramethylethylenediamine) afforded the structurally characterized Cp*[PhC(NSiMe₃)₂]Y(μ-Me)₂Li-TMEDA (2). Compound 2 is a useful precursor for other yttrium pentamethylcyclopentadienyl-benzamidinate derivatives by controlled protolysis: with HC≡CCMe₃ or HOAr it yields Cp*[PhC(NSiMe₃)₂]Y(μ-C≡CCMe ₃)Li-TMEDA (3) and Cp*[PhC(NSiMe₃)₂]YOAr (4), respectively.

Full text of DOI:10.1021/om9508187

1656
Organometallics 1996, 15, 1656-1661
Mon o(p en ta m eth ylcyclop en ta d ien yl)yttr iu m Com p ou n d s
Sta bilized by N,N′-Bis(Tr im eth ylsilyl)ben za m id in a te
Liga n d s
Robbert Duchateau, Auke Meetsma, and J an H. Teuben*,†
Groningen Center for Catalysis and Synthesis, Department of Chemistry,
University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
Received October 16, 1995X
Reaction of YCl3‚3.5THF with Cp*K followed by [PhC(NSiMe3)2]Li‚OEt2 in THF gives the
surprisingly stable yttrium cyclopentadienyl-benzamidinate chloride {Cp*[PhC(NSiMe3)2]Y-
(µ-Cl)}2 (1). Thermally induced redistribution of the various ligands leading to dispropor-
tionation of the molecule was not observed. The dimer does not split easily, e.g., it does not
react with THF to give Cp*[PhC(NSiMe3)2]YCl‚THF. Attempts to produce monomeric
derivatives of 1 by substitution of the chloride by alkoxy, amide, or alkyl substituents using
salt metathesis methodology were not successful. Reaction of 1 with 2 equiv of MeLi in the
presence of TMEDA (TMEDA ) N,N,N′,N′-tetramethylethylenediamine) afforded the
structurally characterized Cp*[PhC(NSiMe3)2]Y(µ-Me)2Li‚TMEDA (2). Compound 2 is a
useful precursor for other yttrium pentamethylcyclopentadienyl-benzamidinate derivatives
by controlled protolysis: with HCtCCMe3 or HOAr it yields Cp*[PhC(NSiMe3)2]Y(µ-
CtCCMe3)Li‚TMEDA (3) and Cp*[PhC(NSiMe3)2]YOAr (4), respectively.
In tr od u ction
center for C-C bond formation.3 A theoretical analysis
of these results indicated that this drop in catalyic
activity probably is due to an increased ionicity of the
metal benzamidinate bonding. Therefore it is interest-
ing to investigate mixed-ligand, Cp* benzamidinate,
yttrium compounds to see whether or not these com-
plexes would exhibit reactivity intermediate to that of
Cp*2YR and [PhC(NSiMe3)2]2YR.
The number of well-characterized mono(pentameth-
ylcyclopentadienyl)yttrium and -lanthanide derivatives
is limited.1j,2f,4 In general mono(pentamethylcyclopen-
tadienyl) compounds are sterically less crowded than
the bis(pentamethylcyclopentadienyl) derivatives and a
kinetically stable, well-defined configuration is more
difficult to achieve. The choice of the yttrium/lan-
thanide precursor complex appears to be crucial, be-
cause incorporation of salt and solvent molecules, which
block further reactivity, is even more frequently ob-
served than in the corresponding bis(pentamethylcy-
clopentadienyl) systems, Cp*2LnR.4,5
The activity of homogeneous catalysts based on lan-
thanides and group 3 metals carbyl and hydrido deriva-
tives is profoundly influenced by the ancillary ligand
system. While previous work has primarily focused on
compounds stabilized by two (substituted) cyclopenta-
dienyl ligands, Cp′2LnR,1 there has been increased
attention for other spectator ligands whether as alter-
natives for or in addition to cyclopentadienyls ligands.1j,2
Recently, we have reported the synthesis and reactivity
of bis(N,N′-bis(trimethylsilyl)benzamidinato)yttrium com-
plexes, [PhC(NSiMe3)2]2YR (R ) alkyl, alkynyl, hy-
drido).3 It was shown that replacing the bis(pentame-
thylcyclopentadienyl) ligand system by two N,N′-
bis(trimethylsilyl)benzamidinate ligands results in a
dramatic decrease of catalytic reactivity of the metal
† E-mail address: TEUBEN@rugch4.chem.rug.nl.
X Abstract published in Advance ACS Abstracts, February 15, 1996.
(1) For example see: (a) Evans, W. J .; Meadows, J . H.; Hunter, W.
E.; Atwood, J . L. J . Am. Chem. Soc. 1984, 106, 1291. (b) Evans, W. J .
Adv. Organomet. Chem. 1985, 24, 131. (c) Thompson, M. E.; Baxter,
S. M.; Bulls, A. R.; Burger, B. J .; Nolan, M. C.; Santarsiero, B. D.;
Schaefer, W. P.; Bercaw, J . E. J . Am. Chem. Soc. 1987, 109, 203. (d)
J eske, G.; Lauke, H.; Mauermann, H.; Swepston, P. N.; Schumann,
H.; Marks, T. J . J . Am. Chem. Soc. 1985, 107, 8091. (e) J eske, G.;
Schock, L. E.; Swepston, P. N.; Schumann, H.; Marks, T. J . J . Am.
Chem. Soc. 1985, 107, 8103. (f) Evans, W. J .; Ulibarri, T. A.; Ziller, J .
W. Organometallics 1991, 10, 134. (g) Heeres, H. J .; Teuben, J . H.
Organometallics 1991, 10, 1980. (h) Booij, M.; Deelman, B.-J .; Ducha-
teau, R.; Postma, D. S.; Meetsma, A.; Teuben, J . H. Organometallics
1993, 12, 3531. (i) Hajela, S.; Bercaw, J . E. Organometallics 1994, 13,
1147. (j) Shapiro, P. J .; Cotter, W. D.; Schaefer, W. P.; Labinger, J . A.;
Bercaw, J . E. J . Am. Chem. Soc. 1994, 116, 4623. (k) Giardello, M. A.;
Conticello, V. P.; Brard, L.; Gagne´, M. R.; Marks, T. J . J . Am. Chem.
Soc. 1994, 116, 10241.
(2) (a) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J . Organometallics
1991, 10, 2026. (b) Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J .
Organometallics 1992, 11, 2967. (c) Schaverien, C. J . Orpen, A. G.
Inorg. Chem. 1991, 30, 4968. (d) Bazan, G. C.; Schaefer, W. P.; Bercaw,
J . E. Organometallics 1993, 12, 2126. (e) Karsch, H. H.; Ferazin, G.;
Kooijman, H.; Steigelmann, O.; Schier, A.; Bissinger, P.; Hiller, W. J .
Organomet. Chem. 1994, 482, 151. (f) Schaverien, C. J . Organometallics
1994, 13, 69.
A major problem, encountered when studying mono-
(pentamethylcyclopentadienyl)yttrium and -lanthanide
complexes, is that they often show ligand exchange
which leads to disproportionation.4b,5a,b In this respect,
organolanthanide complexes resemble main group or-
ganometallics like organomagnesium (Schlenk equilib-
(3) (a) Duchateau, R.; Wee, C. T. van; Meetsma, A.; Teuben, J . H.
J . Am. Chem. Soc. 1993, 115, 4931. (b) Duchateau, R.; Wee, C. T. v.;
Meetsma, A.; Duijnen, P. Th. v.; Teuben, J . H. Organometallics,
submitted for publication. (c) Duchateau, R.; Wee, C. T. v.; Teuben, J .
H. Organometallics, submitted for publication. (d) Bijpost, E. A.;
Duchateau, R.; Teuben, J . H. J . Mol. Catal. 1995, 95, 121.
(4) For example see: (a) Albrecht, I.; Hahn, E.; Pickardt, J .;
Schumann, H. Inorg. Chim. Acta 1985, 110, 145. (b) Booij, M.; Kiers,
N. H.; Heeres, H. J .; Teuben, J . H. J . Organomet. Chem. 1989, 364,
79. (c) Booij, M.; Kiers, N. H.; Meetsma, A.; Teuben, J . H. Organome-
tallics 1989, 8, 2454. (d) Heeres, H. J .; Teuben, J . H.; Rogers, R. D. J .
Organomet. Chem. 1989, 364, 87. (e) Heijden, H. v. d.; Schaverien, C.
J .; Orpen, A. G. Organometallics 1989, 8, 255. (f) Schaverien, C. J .
Adv. Organomet. Chem. 1994, 36, 289 and references therein.
(5) (a) Heeres, H. J .; Teuben, J . H. Recl. Trav. Chim. Pays-Bas 1990,
109, 226. (b) Heeres, H. J . Ph.D. Thesis, University Groningen, 1990.
0276-7333/96/2315-1656$12.00/0 © 1996 American Chemical Society

Mono(pentamethylcyclopentadienyl)yttrium Compounds
Organometallics, Vol. 15, No. 6, 1996 1657
6
ria with mixtures of RMgX, MgR2, and MgX2 ) and
organocalcium compounds (disproportionation of
Cp*CaI‚2THF to Cp*2Ca‚2THF and CaI2‚2THF7 ). When
the reactivity of mixed-ligand yttrium compounds is to
be studied, the complexes should be kinetically suf-
ficiently inert with respect to redistribution of the
ancillary ligands under the reaction conditions.
Here we report the synthesis and characterization of
several mono(pentamethylcyclopentadienyl)(N,N′-bis-
(trimethylsilyl)benzamidinato)yttrium complexes which
are resistant to disproportionation. The molecular
structure of Cp*[PhC(NSiMe3)2]Y(µ-Me)2Li‚TMEDA is
described, together with a study of its potential applica-
tion as a precursor for the synthesis of other Cp*-
(benzamidinato)yttrium complexes.
Resu lts a n d Discu ssion
F igu r e 1. ORTEP drawing of Cp*[C6H5C(NSiMe3)2]Y(µ-
Me)2Li‚TMEDA (2) with 50% probability ellipsoids.
Syn th esis a n d Ch a r a cter iza tion of Mon o(p en -
t a m e t h y lc y c lo p e n t a d i e n y l)(b e n z a m i d i n a t o )-
yttr iu m Com p ou n d s, Cp *[P h C(NSiMe3)2]YR. The
benzamidinate ligand can conveniently be introduced
by treatment of YCl3‚3.5THF with Cp*K followed by
[PhC(NSiMe3)2]Li‚OEt2 in THF, affording {Cp*[PhC-
(NSiMe3)2]Y(µ-Cl)}2 (1) after extraction with hot toluene
(eq 1). When YCl3‚3.5THF was first treated with [PhC-
conformation (or fast dynamic processes involving the
benzamidinate ligands).
Initial attempts to substitute the chloride ligand in 1
with Li-O-2,6-(CMe3)C6H3, MN(SiMe3)2 (M ) Li, Na),
or alkylating reagents such as MCH(SiMe3)2 (M ) Li,
K), Li-CH2-2-NC5H3-6-Me, or LiCH2XMe3 (X ) Si, C)
were unsuccessful. Although reaction occurred with
KCH2Ph, it led to a complex product mixture. Only
treatment of 1 with 2 equiv of MeLi in the presence of
TMEDA (N,N,N′,N′-tetramethylethylenediamine) gave
a well-defined product, Cp*[PhC(NSiMe3)2]Y(µ-Me)2Li‚-
TMEDA (2, eq 2). The reason for the observed low
(NSiMe3)2]Li‚OEt2 followed by Cp*K, a mixture of
products was obtained. From this mixture, [PhC-
(NSiMe3)2]2YCl‚THF rather than the mixed-ligand chlo-
ride 1 was isolated, indicating that the order of intro-
duction of the ligands is crucial. Complex 1 is moderately
soluble in hot toluene and THF. Remarkably, it does
not retain salt or solvent molecules, as commonly
observed in group 3 metal and lanthanide chemistry.
The compound is thermally stable in toluene and THF
(both solvents: 12 h, reflux), showing no sign of inter-
molecular ligand exchange. Apparently, the chloro
bridge in 1 is very stable and prevents ligand redistri-
bution and solvation. Unlike {Cp*2Y(µ-Cl)}2, 1 does not
react with THF to form the monochloro THF adduct.
Spectroscopic data (NMR) show that 1 equiv of toluene
is present in the crystal lattice. While slowly released
in the solid state at room temperature, the toluene can
be quantitatively removed by gently warming (50 °C)
reactivity of 1 is assumed to be the (kinetic) stability of
the bridging chloride unit. Apparently, only the smaller
MeLi approaches the chloride bridge closely enough to
react. Furthermore, TMEDA seems to be essential to
stabilize the alkyl complex since reaction of 1 with MeLi
(1, 2 equiv, pentane, ether, toluene, THF) in the absence
of TMEDA invariably resulted in complex product
mixtures. As observed for 1, the 1H and 13C NMR
spectra of 2 show single resonances for both the C5Me5
(1H, δ ) 2.42 ppm; 13C, δ ) 12.1 ppm) and benzamidi-
nate-SiMe3 (1H, δ ) 0.11 ppm; 13C, δ ) 3.7 ppm) groups.
In contrast to the analogous Cp*2Y(µ-Me)2Li‚2OEt2 (δ
) -1.80 ppm)1a and [PhC(NSiMe3)2]2Y(µ-Me)2Li‚TMEDA
(1H, δ -0.48 ppm; 13C, δ ) 10.1 ppm),3b the µ-CH3
resonance (1H, δ ) -0.91 ppm; 13C, δ ) 13.5 ppm)
appears as a broad singlet.
1
in vacuo. The H and 13C NMR spectra of 1 show one
signal for the C5Me5 (1H, δ ) 2.28 ppm; 13C, δ ) 12.0
ppm) and benzamidinate-SiMe3 (1H, δ ) 0.10 ppm; 13C,
δ ) 3.1 ppm) groups, suggesting a highly symmetric
A low-temperature X-ray diffraction determination of
the molecular structure of 2 was carried out. An
ORTEP drawing of 2 is shown in Figure 1, and impor-
tant bond lengths and angles are listed in Table 1. The
yttrium is coordinated by one pentamethylcyclopenta-
(6) Wilkinson, G.; Stone, F. G. A.; Abel, E. W. Comprehensive
Organometallic Chemistry; Pergamon Press: Oxford, U.K., 1982.
(7) McCormick, M. J .; Sockwell, S. C.; Davies, C. E. H.; Hanusa, T.
P.; Huffman, J . C. Organometallics 1989, 8, 2044.

1658 Organometallics, Vol. 15, No. 6, 1996
Duchateau et al.
Ta ble 1. Selected Dista n ces a n d An gles for Cp *[C6H5C(NSiMe3)2]Y(µ-Me)2Li‚TMEDA (2)
Distances (Å)
Angles (deg)
Y(1)-C(ring)av
Y(1)-Cent
Y(1)-N(1)
2.678(3)
2.392(3)
2.423(3)
2.414(2)
2.480(3)
Y(1)-C(25)
N(1)-C(11)
N(2)-C(11)
C(24)-Li(1)
C(25)-Li(1)
2.493(3)
1.338(4)
1.329(4)
2.175(6)
2.191(6)
Y(1)-N(2)
Y(1)-C(24)
C(11)-Y(1)-C(24)
C(11)-Y(1)-C(25)
Cent-Y(1)-C(24)
Cent-Y(1)-C(25)
Cent-Y(1)-C(11)
Cent-Y(1)-N(1)
106.85(10)
Y(1)-C(24)-Li(1)
Y(1)-C(25)-Li(1)
N(1)-Y(1)-C(24)
N(2)-Y(1)-C(25)
C(24)-Y(1)-C25)
N(1)-Y(1)-N(2)
N(1)-C(11)-N(2)
81.61(18)
81.02(18)
86.88(10)
89.15(10)
89.67(11)
56.75(8)
109.28(10)
108.91(10)
107.46(10)
127.97(10)
120.09(10)
120.74(10)
87.0(4)
Cent-Y(1)-N(2)
119.1(3)
N(1)-C(11)-C(12)-C(13)
dienyl, one chelating benzamidinate, and two methyl
ligands. The latter bridge yttrium and lithium. The
complex can be described as a four-legged piano stool,
with yttrium in the center (Cent-Y(1)-N(1) ) 120.09-
(10)°, Cent-Y(1)-N(2) ) 120.74(10)°, Cent-Y(1)-C(24)
) 108.91(10)°, Cent-Y(1)-C(25) ) 107.46(10)°). The
structure is similar to that of the previously described
Cp[PhC(NSiMe3)2]ZrCl2 and Cp[PhC(NSiMe3)2]TiMe2.8
It exhibits pseudo-Cs symmetry where the two methyl
groups are related by an imaginary plane of symmetry
bisecting the Me-Y-Me angle. As expected, the ben-
zamidinate group forms an almost planar four-mem-
bered ring with yttrium (torsion angle N(2)-Y(1)-N(1)-
C(11) ) -5.94(19)°), with the benzamidinate phenyl ring
almost perpendicular to it (the acute dihedral angle
between the N(1)-C(11)-N(2) and C(11)-C(12)-C(13)
planes being 87.0(4)°). Compared to [p-MeOC6H4C-
(NSiMe3)2]2YCH(SiMe3)2 (Y-Nav ) 2.338(4) Å)3b and
{[PhC(NSiMe3)2]2Y(µ-R)}2 (R ) H, Y-Nav ) 2.356(3) Å;
R ) CtCH, Y-Nav ) 2.366(4) Å),3a,b the Y-N distances
are notably longer (Y(1)-N(1) ) 2.423(3) Å, Y(1)-N(2)
) 2.414(2) Å), which may be a result of the lower
electrophilicity of the metal center in the systems.3 The
N(1)-C(11) (1.338(4) Å) and N(2)-C(11) (1.329(4) Å)
bonds are identical to those in bis(benzamidinato)-
yttrium derivatives and indicate effective charge delo-
calization in the N-C-N fragment.9 The distance
between the Cp*(cent)-Y(1) (2.392(3) Å) is normal and
is comparable to values observed for other mono- and
bis-Cp*Y derivatives (2.363(3)-2.420(6) Å).10 The
Y-C(Me) bond distances of 2.480(3) and 2.493(3) Å are
comparable to the Y-C bond in Cp*2YCH(SiMe3)2
(2.468(7) Å)10a and are considerably shorter than in
{Cp2Y(µ-Me)}2 (2.553(10), 2.537(9) Å).10c where presum-
ably steric congestion of the metal center is the reason
for the long Y-C bond.
under mild conditions, 2 is potentially a useful precursor
for a range of derivatives. Specifically, the reaction of
2 with 2 equiv of 3,3-dimethyl-but-1-yne, HCtCCMe3,
selectively yields Cp*[PhC(NSiMe3)2]Y(µ-CtCCMe3)2-
Li‚TMEDA (3, eq 3). During the reaction, the interme-
diate Cp*[PhC(NSiMe3)2]Y(µ-Me)(µ-CtCCMe3)Li‚-
TMEDA (3a ) could be identified by two inequivalent
benzamidinate-Si(CH3)3 resonances (δ ) 0.18, 0.10 ppm)
in the 1H NMR spectrum. The observation of 3a
supports stepwise substitution of the methyl groups of
2. The structure of complex 3 is comparable to [PhC-
(NSiMe3)2]2Y(µ-CtCCMe3)2Li‚TMEDA,3c Cp*2Y(µ-Ct
CCMe3)2Li‚THF,11a and Cp*2Sm(µ-CtCPh)K.11b Analo-
1
gous to 1 and 2, in the H and 13C NMR spectra of 3,
single resonances are observed for C5(CH3)5 (1H, δ )
2.53 ppm; 13C, δ ) 13.0 ppm) and PhC(NSi(CH3)3)2 (1H,
δ ) 0.16 ppm; 13C, δ ) 4.0 ppm), suggesting a symmetric
structure in solution. The CtCC(CH3)3 groups appear
as singlets (1H, δ ) 1.29 ppm; 13C, δ ) 32.5 ppm),
whereas the doublet resonance of the acetylide R-carbon
1
(δ ) 120.5 ppm, J Y-C ) 8 Hz) indicates a monomeric
P r otolysis Rea ction s of Cp *[P h C(NSiMe3)2]Y(µ-
Me)2Li‚TMEDA (2). Because the alkyl ligands of
compound 2 are susceptible to controlled protolysis
structure for 3. The yttrium coupling at the alkynyl
R-carbon is small compared to the corresponding one
in [PhC(NSiMe3)2]2Y(µ-CtCCMe3)2Li‚TMEDA (1J Y-C
)
15 Hz) and in the dimeric acetylides {[PhC(NSiMe3)2]2Y-
(µ-CtCR)}2 (R ) H, alkyl, Ph, SiMe3: 20-21 Hz).3c
Whereas with HCtCCMe3 the anionic structure is
preserved, reaction of 2 with 2 equiv of 2,6-di-tert-
butylphenol yielded the neutral Cp*[PhC(NSiMe3)2]-
YOAr (4, OAr ) 2,6-OC6H3(CMe3)2, eq 4). Competitive
protolysis of the Cp* or benzamidinate ligand is not
observed, indicating the high kinetic stability of these
(8) (a) Go´mez, R.; Duchateau, R.; Chernega, A. N.; Edelmann, F.
T.; Teuben, J . H.; Green, M. L. H. J . Organomet. Chem. 1995, 491,
153. (b) Go´mez, R.; Duchateau, R.; Chernega, A. N.; Meetsma, A.;
Edelmann, F. T.; Teuben, J . H.; Green, M. L. H. J . Chem. Soc., Dalton
Trans. 1995, 217.
(9) For the nondelocalized N,N,N′-tris(trimethylsilyl)benzamidine
the CsN and CdN bond distances are 1.410(3) and 1.266(3) Å,
respectively: Ergezinger, C.; Weller, F.; Dehnicke, K. Z. Naturforsch.
1988, 43b, 1119.
(10) For instance see: (a) Haan, K. H. den; Boer, J . L. de; Teuben,
J . H.; Spek, A. L.; Kojic-Prodic, B.; Hays, G. R. Organometallics 1986,
5, 1726. (b) Evans, W. J .; Foster, S. E. J . Organomet. Chem. 1992,
433, 79. (c) Holton, J .; Lappert, M. F.; Ballard, D. G. H.; Pearce, R.;
Atwood, J . L.; Hunter, W. E. J . Chem. Soc. Dalton Trans. 1979, 54.
(11) (a) Evans, W. J .; Drummond, D. K.; Hanusa, T. P.; Olofson, J .
M. J . Organomet. Chem. 1989, 376, 311. (b) Evans, W. J .; Keyer, R.
A.; Ziller, J . W. Organometallics 1993, 12, 2618.

Mono(pentamethylcyclopentadienyl)yttrium Compounds
Organometallics, Vol. 15, No. 6, 1996 1659
12
continuous extraction of anhydrous YCl3 with THF.
5
13
Cp*Y[OAr]2 and [PhC(NSiMe3)2]Li‚OEt2 were pre-
pared according to literature procedures. NMR spectra
were recorded on a Varian VXR 300 (1H NMR at 300
MHz, 13C NMR at 75.4 MHz) spectrometer at 30 °C. 1H
and 13C NMR spectra were referenced internally using
the residual solvent resonances. IR spectra were re-
corded on a Mattson-4020 Galaxy FT-IR spectropho-
tometer.
ligands. Compound 4 is extremely soluble in hexane.
Evaporation of the solvent leaves a colorless, sticky oil,
which did not solidify on standing at room temperature.
Attempts to purify 4 by sublimation or vacuum distil-
lation failed due to thermal decomposition. Compound
4 can also be prepared directly by treatment of Cp*Y-
[OAr]2 with [PhC(NSiMe3)2]Li‚OEt2 in toluene (eq 5).
P r ep a r a tion of {Cp *[P h C(NSiMe3)2]Y(µ-Cl)}2‚2-
(tolu en e) (1). YCl3‚3.5THF (1.8 g, 40.2 mmol) was
added to a suspension of Cp*K (6.2 g, 35.5 mmol) in THF
(250 mL) at room temperature. The reaction mixture
was stirred overnight, after which [PhC(NSiMe3)2]Li‚-
OEt2 (13.5 g, 39.2 mmol) was added. After the solution
was stirred for an additional 1 h, the solvent was
removed in vacuo and the residue extracted with hot
toluene (200 mL). Concentration and cooling to -30 °C
yielded 1 (4.0 g, 6.5 mmol, 18%) as colorless crystals.
Concentration and cooling to -30 °C of the mother
liquor yielded another crop of 1 (4.2 g, 6.8 mmol, 19%)
1
as a white microcrystalline material. The H and 13C
NMR spectra of 1 showed the presence of toluene,
apparently in the crystal lattice. IR (KBr/Nujol, cm-1):
2953 (vs), 2924 (vs), 2855 (vs), 1460 (s), 1398 (s), 1377
(s), 1258 (m), 1246 (m), 1005 (m), 995 (m), 837 (s), 781
(w), 760 (m), 733 (w), 712 (w), 704 (w), 490 (w). 1H NMR
(benzene-d6, δ): 7.10 (m, 10H, Ar), 2.28 (s, 15 H, C5-
(CH3)5), 2.11 (s, 3H, PhCH3), 0.10 (s, 18H, PhC(NSi-
(CH3)3)2). 13C{1H} NMR (benzene-d6, δ): 184.1 (s,
PhC(NSiMe3)2), 141.4 (s, Ar), 129.1 (s, Ar), 128.3 (s, Ar),
126.5 (s, Ar), 125.5 (s, Ar), 120.2 (s, C5Me5), 21.2 (s,
PhCH3), 12.0 (s, C5(CH3)5), 3.1 (s, PhC(NSi(CH3)3)2). The
product slowly lost toluene from the crystal lattice. To
obtain a satisfactory elemental analysis, it was gently
warmed (50 °C) in vacuo to remove all the toluene.
Anal. Calcd (found) for (C23H38ClN2Si2Y)2: C, 52.81
(52.34); H, 7.32 (7.26); Y, 17.00 (16.71).
Again, purification is hindered due to the extremely
high solubility of 4. Because (neutral) yttrium alkyl
complexes are normally more soluble than their aryl-
oxide congeners, no attempts to alkylate 4 were under-
taken.
Con clu sion s
This study shows that mixed-ligand compounds Cp*-
[PhC(NSiMe3)2]YX are accessible through stepwise ligand
introduction, starting from YCl3‚3.5THF , although the
order of introduction of ancillary ligands appears to be
crucial. The reaction of Cp*Y[OAr]2 (OAr ) 2,6-OC6H3-
(CMe3)2) with the lithium benzamidinate salt [PhC-
(NSiMe3)2]Li‚OEt2 offers an alternative strategy for the
preparation of mixed-ligand yttrium complexes such as
Cp*[PhC(NSiMe3)2]YOAr. The chloride {Cp*[PhC-
(NSiMe3)2]YCl}2 (1) is sufficiently inert with respect to
redistribution of the various ligands. It also resists
reaction with Lewis bases such as THF. Substitution
of the chloride ligands in 1 is difficult: even powerful
alkylation reagents such as MCH(SiMe3)2 (M ) Li, K)
do not seem to react with 1. The kinetic stability of this
dimeric chloro derivative considerably hampers the
development of this chemistry by chloride metathesis
of 1. So far, only the methyl complex, Cp*[PhC-
(NSiMe3)2]Y(µ-Me)2Li‚TMEDA (2), has been shown to
be accessible. Nevertheless, compound 2 provides a
useful a useful starting material for further reactivity
studies, since the methyl substituents are susceptible
to controlled protolysis by HCtCR and H-OR under
mild conditions.
P r ep a r a tion of Cp *[P h C(NSiMe3)2]Y(µ-Me)2Li‚-
TMEDA (2). An ethereal solution (50 mL) of 1 (1.6 g,
2.6 mmol) and TMEDA (0.8 mL, 5.2 mmol) was cooled
to -80 °C and treated with MeLi (3.8 mL, 5.2 mmol).
During warming to room temperature, salt precipitated.
After the mixture was stirred for an additional 1 h, the
volatiles were removed in vacuo and the residue was
extracted with ether (40 mL). Cooling to -30 °C yielded
2 (1.1 g, 1.7 mmol, 66%) as large cube-shaped crystals.
IR (KBr/Nujol, cm-1): 2949 (vs), 2918 (vs), 2724 (sh),
1460 (vs), 1377 (s), 1354 (s), 1312 (w), 1287 (w), 1242
(m), 1159 (w), 1125 (w), 1063 (w), 1034 (w), 1020 (w),
1003 (m), 990 (m), 949 (w), 918 (w), 835 (s), 785 (m),
756 (s), 735 (s), 725 (s), 704 (m), 679 (w), 486 (w), 438
(w). 1H NMR (benzene-d6, δ): 7.10 (m, 5H, Ar), 2.42
(s, 15H, C5(CH3)5), 1.94 (s, 12H, TMEDA-CH3), 1.62 (s,
4H, TMEDA-CH2), 0.11 (s, 18H, PhC(NSi(CH3)3)2),
-0.91 (br-s, 6H, µ-CH3). 13C NMR (benzene-d6, δ):
183.0 (s, PhC(NSiMe3)2), 143.4 (s, Ar), 128.2 (d, Ar,
1
1J C-H ) 158 Hz), 127.4 (d, Ar, J C-H ) 160 Hz), 126.1
Exp er im en ta l Section
1
(d, Ar, J C-H ) 165 Hz), 115.7 (s, C5Me5), 56.4 (t,
1
Gen er a l Com m en ts. All compounds are extremely
oxygen- and moisture-sensitive. Manipulations were
therefore carried out under nitrogen using glovebox
(Braun MB-200) and Schlenk-line techniques. Solvents
were distilled from Na (toluene), K (THF), or Na/K alloy
(pentane, hexane, benzene, benzene-d6, THF-d8) and
stored under nitrogen. YCl3‚3.5THF was prepared by
TMEDA-CH2, J C-H ) 130 Hz), 46.1 (q, TMEDA-CH3,
1J C-H ) 135 Hz), 13.5 (br-s, µ-CH3), 12.1 (q, C5(CH3)5,
1
1J C-H ) 125 Hz), 3.7 (q, PhC(NSi(CH3)3)2, J C-H ) 118
(12) Freeman, J . H.; Smith, M. L. J . Inorg. Nucl. Chem. 1958, 7,
224.
(13) (a) Sanger, A. R. Inorg. Nucl. Chem. Lett. 1973, 9, 351. (b) Boere´,
R. T.; Oakley, R. T.; Reed, R. W. J . Organomet. Chem. 1987, 331, 161.

1660 Organometallics, Vol. 15, No. 6, 1996
Duchateau et al.
Hz). Anal. Calcd (found) for C31H60LiN4Si2Y: C, 58.10
(58.14); H, 9.44 (9.36); Y, 13.87 (13.82).
Me5), 35.0 (s, CMe3), 32.1 (s, C(CH3)3), 11.7 (s, C5(CH3)5),
4.5 (s, PhC(NSi(CH3)3)2).
NMR Tu be Rea ction of 2 w ith HCtCCMe3. An
NMR tube charged with 2 (10 mg, 0.016 mmol) in
benzene-d6 (1 mL) was treated with 3,3-dimethyl-but-
X-r a y Cr ysta llogr a p h ic An a lysis of Cp *[P h C-
(NSiMe3)2]Y(µ-Me)2Li‚TMEDA (2). A suitable color-
less polyfacial crystal was glued on top of a glass fiber
in a drybox and transferred into the cold nitrogen
stream of the low-temperature unit14 mounted on an
Enraf-Nonius CAD-4F diffractometer interfaced to a
MicroVAX-2000 computer. Unit cell parameters and
orientation matrix were determined from a least-
squares treatment of the SET4 setting angles15 of 22
reflections in the range 15.23o < θ < 20.63o. The unit
cell was identified as triclinic, space group P1h. Reduced
cell calculations did not indicate any higher metric
lattice symmetry,16 and examination of the final atomic
coordinates of the structure did not yield extra metric
symmetry elements.17 The intensity of three standard
reference reflections, monitored every 3 h of X-ray
exposure time, showed no significant fluctuations during
data collection. A 360° Ψ-scan for a reflection close to
axial (2h2h2) showed a variation in intensity of less than
13% about the mean value. Intensity data were cor-
rected for Lorentz and polarization effects and scale
variation but not for absorption. Standard deviation σ-
(I) in the intensities were increased according to an
analysis of the excess variance of the reference reflec-
tion: Variance was calculated on the basis of counting
statistics and the term (P2I2) where P ()0.023) is the
instability constant18 as derived from the excess vari-
ance in the reference reflections. Equivalent reflections
were averaged and stated observed if satisfying the I g
2.5σ(I) criterion of observability. The structure was
solved by Patterson methods, and extension of the model
was accomplished by direct methods applied to differ-
ence structure factors using the program DIRDIF.19 The
positional and anisotropic thermal displacement pa-
rameters for the non-hydrogen atoms refined with block-
diagonal least-squares procedures (CRYLSQ)20 mini-
1
1-yne (5 µL, 0.04 mmol). Following the reaction by H
NMR spectroscopy showed the gradual decrease of
resonances of 2 and increase of resonances which can
be attributed to the intermediate Cp*[PhC(NSiMe3)2]Y-
(µ-Me)(µ-CtCCMe3)Li‚TMEDA (3a ) and the final prod-
uct Cp*[PhC(NSiMe3)2]Y(µ-CtCCMe3)2Li‚TMEDA (3).
1
After several hours at room temperature, the H NMR
spectrum showed only resonances of 3 and unreacted
HC≡CCMe3. Cp*[PhC(NSiMe3)2]Y(µ-Me)(µ-CtCCMe3)-
Li‚TMEDA (3a ): 1H NMR (benzene-d6, δ) 7.08 (m, 5H,
Ar), 2.48 (s, 15H, C5(CH3)5), 2.06 (s, 12H, TMEDA-CH3),
2
1.84 (d, 2H, TMEDA-CH2, J H-H ) 11 Hz), 1.62 (d, 2H,
2
TMEDA-CH2, J H-H ) 11 Hz), 1.28 (s, 9H, CtCC-
(CH3)3), 0.18 (s, 9H, PhC(NSi(CH3)3)2), 0.10 (s, 9H, PhC-
(NSi(CH3)3)2), -0.93 (br s, 3H, CH3).
P r ep a r a t ion of Cp *[P h C(NSiMe3)2]Y(µ-CtCC-
Me3)2Li‚TMEDA (3). A solution of 2 (1.4 g, 2.2 mmol)
in ether (40 mL) was treated with 0.6 mL (4.8 mmol) of
3,3-dimethyl-but-1-yne at room temperature. After 16
h, the volatiles were removed in vacuo and the residue
was dissolved in ether (30 mL). Concentration and
cooling to -30 °C gave 3 (1.1 g, 1.4 mmol, 71%) as
colorless crystals. IR (KBr/Nujol, cm-1): 2955 (vs), 2922
(vs), 2359 (w), 2029 (w), 1460 (s), 1400 (m), 1377 (s),
1360 (m), 1310 (w), 1290 (m), 1238 (s), 1200 (w), 1159
(w), 1003 (m), 991 (m), 991 (m), 951 (w), 839 (s), 783
(w), 758 (m), 731 (m), 700 (w), 482 (w), 426 (w). 1H NMR
(benzene-d6, δ): 7.07 (m, 5H, Ar), 2.53 (s, 15H, C5-
(CH3)5), 2.22 (s, 12H, TMEDA-CH3), 1.96 (s, 4H, TMEDA-
CH2), 1.29 (s, 18H, CtCC(CH3)3), 0.16 (s, 18H, PhC-
(NSi(CH3)3)2). 13C NMR (benzene-d6, δ): 182.1 (s,
1
PhC(NSiMe3)2), 143.3 (s, Ar), 128.2 (d, Ar, J C-H ) 159
1
1
Hz), 127.7 (d, Ar, J C-H ) 163 Hz), 127.4 (d, Ar, J C-H
1
) 160 Hz), 120.5 (d, YsC(tCCMe3), J Y-C ) 8 Hz),
mizing the function Q ) ∑h [w(|Fo| - k|Fc|)2].
A
117.6 (s, C5Me5), 57.0 (t, TMEDA-CH2, 1J C-H ) 133 Hz),
47.6 (q, TMEDA-CH3, 1J C-H ) 134 Hz), 32.5 (q, CtCC-
subsequent difference Fourier synthesis resulted in the
location of all the hydrogen atoms which coordinates
were included in the refinement. Final refinement on
Fo by full-matrix least-squares techniques with aniso-
tropic thermal displacement parameters for the nonhy-
drogen atoms and isotropic thermal displacement pa-
1
(CH3)3, J C-H ) 126 Hz), 28.5 (s, CtCCMe3), 13.0 (q,
1
C5(CH3)5, J C-H ) 125 Hz), 4.0 (q, PhC(NSi(CH3)3)2,
1J C-H ) 118 Hz). Anal. Calcd (found) for C41H72LiN4-
Si2Y: C, 63.70 (63.80); H, 9.39 (9.46); Y, 11.50 (11.55).
rameters for the hydrogen atoms converged at RF
)
P r ep a r a tion of Cp *[P h C(NSiMe3)2]YOAr (OAr )
2,6-OC6H3(CMe3)2) (4). Meth od a . A solution of 2 (0.7
g, 1.1 mmol) in ether (40 mL) was treated with 2,6-di-
tert-butyl-phenol (0.45 g, 2.2 mmol). The reaction
mixture was stirred for 1 h, after which the solvent was
removed in vacuo. The residue was extracted with
pentane (40 mL). Evaporation of the solvent yielded 4
(0.4 g, 0.6 mmol, 52%) as a colorless oil.
0.040 (wR ) 0.045). Unit weights were used throughout
the refinement. A final difference Fourier map did not
show any significant residual features. Crystal data
and experimental details of the structure determination
are compiled in Table 2. The final fractional atomic
coordinates and equivalent isotropic thermal displace-
ment parameters for the non-hydrogen atoms are given
Meth od b. A hexane (40 mL) solution of Cp*Y(OAr)2
(1.7 g, 2.7 mmol) was treated with [PhC(NSiMe3)2]Li‚-
OEt2 (0.9 g, 2.6 mmol). The reaction mixture was
heated to reflux, upon which salt precipitated. The
mixture was then stirred overnight at room tempera-
ture. After filtration, the solvent was removed in vacuo
leaving 4 as a colorless oil. Isolated yield: 0.6 g (0.9
mmol, 32%). 1H NMR (benzene-d6, δ): 7.25 (m, 2H, Ar),
7.0 (m, 6H, Ar), 2.12 (s, 15H, C5(CH3)5), 1.60 (s, 18H,
C(CH3)3), 0.01 (s, 18H, PhC(NSi(CH3)3)2). 13C{1H} NMR
(benzene-d6, δ): 136.9 (s, Ar), 132.2 (s, Ar), 128.6 (s, Ar),
126.4 (s, Ar), 125.2 (s, Ar), 125.0 (s, Ar), 117.2 (s, C5-
(14) Bolhuis, F. v. J . Appl. Crystallogr. 1971, 4, 263.
(15) Boer, J . L. d.; Duisenberg, A. J . M. Acta Crystallogr.1984, A40,
C410.
(16) Spek, A. L. J . Appl. Crystallogr. 1988, 21, 578.
(17) (a) Le Page, Y. J . Appl. Crystallogr. 1987, 20, 264. (b) Le Page,
Y. J . Appl. Crystallogr. 1988, 21, 983.
(18) McCandlish, L. E.; Stout, G. H.; Andrews, L. C. Acta Crystallogr.
1975, A31, 245.
(19) Beurskens, P. T.; Admiraal, G.; Beurskens, G.; Bosman, W. P.;
Garc´ıa-Granda, S.; Gould, R. O.; Smits, J . M. M.; Smykalla, C. The
DIRDIF program system, Technical Report of the Crystallography
Laboratory; University of Nijmegen: Nijmegen, The Netherlands, 1992.
(20) Olthof-Hazekamp, R. QRYLSQ, Xtal3.0 Reference Manual; Hall,
S. R., Stewart, J . M., Eds.; University of Western Australia and
Maryland; Lamb: Perth, Australia, 1992.

Mono(pentamethylcyclopentadienyl)yttrium Compounds
Organometallics, Vol. 15, No. 6, 1996 1661
Ta ble 2. Deta ils of th e X-r a y Str u ctu r e
Deter m in a tion of
Cp *[C6H5C(NSiMe3)2]Y(µ-Me)2Li‚TMEDA (2)
Ta ble 3. F in a l F r a ction a l Atom ic Coor d in a tes a n d
Equ iva len t Isotr op ic Th er m a l Disp la cem en t
P a r a m eter s for Non -h yd r ogen Atom s for
Cp *[C6H5C(NSiMe3)2]Y(µ-Me)2Li‚TMEDA (2).
formula
Mr
C31H60N4Si2Y
640.86
atom
x
y
z
Ueq (Å2)a
cryst system
space group
a, Å
b, Å
c, Å
triclinic
P1h
10.415(1)
12.010(1)
15.937(1)
88.150(6)
86.041(9)
69.01(1)
1856.7(3)
1.146
2
688
16.65
Y(1)
0.19948(3)
0.26814(10)
0.24517(10)
0.2250(3)
0.2195(3)
0.5784(3)
0.6636(3)
-0.0556(3)
-0.0711(3)
-0.0111(3)
0.0441(3)
0.0156(3)
-0.1195(4)
-0.1507(4)
-0.0198(4)
0.1164(4)
0.0426(5)
0.2435(3)
0.2921(3)
0.4325(4)
0.4786(5)
0.3854(6)
0.2453(5)
0.1981(4)
0.2187(5)
0.4566(4)
0.1736(5)
0.4336(5)
0.1708(8)
0.1619(4)
0.3553(3)
0.3422(3)
0.5298(5)
0.5747(5)
0.7209(4)
0.7557(4)
0.7034(4)
0.6722(4)
0.4711(6)
0.17528(2) 0.24427(2)
0.25689(8) 0.46732(5)
0.46401(8) 0.15249(6)
0.0155(1)
0.0249(3)
0.0254(3)
Si(1)
Si(2)
N(1)
N(2)
N(3)
N(4)
C(1)
C(2)
C(3)
C(4)
C(5)
C(6)
C(7)
C(8)
C(9)
C(10)
C(11)
C(12)
C(13)
C(14)
C(15)
C(16)
C(17)
C(18)
C(19)
C(20)
C(21)
C(22)
C(23)
C(24)
C(25)
C(26)
C(27)
C(28)
C(29)
C(30)
C(31)
Li(1)
0.2850(2)
0.3693(2)
-0.2070(2)
-0.0011(3)
0.1912(3)
0.2581(3)
0.1781(3)
0.0613(3)
0.0696(3)
0.2395(5)
0.3903(3)
0.2088(4)
-0.0509(3)
-0.0353(4)
0.3693(3)
0.4618(3)
0.4392(3)
0.5222(4)
0.6292(4)
0.6537(3)
0.5702(3)
0.3910(3)
0.1718(3)
0.1628(4)
0.4267(6)
0.6261(4)
0.4414(3)
-0.0066(3)
0.1164(3)
-0.2511(4)
-0.2830(3)
-0.2097(4)
-0.1271(4)
0.0460(4)
0.0741(4)
-0.0221(5)
0.36306(16) 0.0216(8)
0.23115(16) 0.0204(7)
0.16489(18) 0.0292(8)
0.18847(19) 0.0306(9)
0.2962(2)
0.2202(2)
R, deg
â, deg
γ, deg
V, Å3
0.0252(9)
0.0235(9)
D
Z
calc, g‚mol-3
0.15357(19) 0.0208(8)
0.1884(2)
0.2760(2)
0.3810(3)
0.2132(3)
0.0616(2)
0.1387(3)
0.3362(3)
0.0219(8)
0.0256(9)
0.0438(14)
0.0398(13)
0.0329(11)
0.0358(13)
0.0427(14)
F(000)
µ(Mo, KRj), cm-1
cryst size, mm
wavelength (Mo KRj), Å
0.25 × 0.32 × 0.38
0.710 73 (graphite
monochromator)
130
1.28, 27.5
∆ω ) 0.80 + 0.34 tan θ
h, -13 f 13; k, -15 f 15;
l, 0 f 20
8802
8494
6738
592
T, K
θ range: min, max, deg
ω/2θ scan, deg
data set
0.31198(19) 0.0188(8)
0.34550(18) 0.0210(8)
0.3489(2)
0.3813(2)
0.4108(2)
0.4074(2)
0.3753(2)
0.5357(2)
0.4732(2)
0.5162(3)
0.1228(3)
0.1759(3)
0.0590(2)
0.3129(2)
0.1097(2)
0.0937(3)
0.2389(3)
0.1451(3)
0.2009(3)
0.1084(3)
0.2567(3)
0.1922(3)
0.0282(10)
0.0414(16)
0.0478(16)
0.0425(13)
0.0321(10)
0.0337(11)
0.0323(11)
0.0383(13)
0.0511(18)
0.065(2)
0.0317(11)
0.0241(9)
0.0237(9)
0.0395(12)
0.0455(13)
0.0387(11)
0.0404(11)
0.0409(11)
0.0435(16)
0.0267(17)
tot. data
unique data
obsd data (I g 2.5σ(I))
no. of refined params
final agreement factors
RF ) ∑(||Fo| - |Fc||)/∑|Fo|
wR ) [∑(w(|Fo| - |Fc|)2)/
0.040
0.045
2
∑w|Fo| ]1/2
weighting scheme
1
S ) [∑w(|Fo| - |Fc|)2/(m - n)]1/2 a
resid electron density in final diff
Fourier map, e/Å3
1.372(12)
-1.14, 1.12
max(shift/σ) final cycle
av(shift/σ) final cycle
0.1934
0.6749 × 10-2
a
m ) no. of observations; n ) no. of variables
in Table 3. Scattering factors were taken from Cromer
and Mann.21 Anomalous dispersion factors taken from
Cromer and Liberman.22 All calculations were carried
out on the HP9000/735 computer at the University of
Groningen with the program packages Xtal,23 PLA-
TON,24 and ORTEP.25
a
Ueq
)
1/3∑i∑jUijai*aj*a i‚a j.
Ack n ow led gm en t. This work was financially sup-
ported by Shell Research BV Amsterdam, which is
gratefully acknowledged.
(21) Cromer, D. T.; Mann, J . B. Acta Crystallogr. 1968, A24, 321.
(22) Cromer, D. T.; Libermann, D. J . Chem. Phys. 1970, 53, 1891.
(23) Hall, S. R.; Flack, H. D.; Stewart, J . M. Xtal3.2 Reference
Manual; Universities of Western Australia Maryland; Lamb: Perth,
Australia, 1992.
(24) Spek, A. L. Acta Crystallogr. 1990, A46, C34.
(25) J ohnson, C. K. ORTEP; Report ORNL-3794; Oak Ridge Na-
tional Laboratory: Oak Ridge, TN, 1965.
Su p p or tin g In for m a tion Ava ila ble: Tables of anisotro-
pic thermal displacement parameters, hydrogen coordinates
and thermal parameters, bond lengths, bond angles, and
torsion angles (11 pages). Ordering information is given on
any current masthead page.
OM9508187