Insertion and C-H bond activation of unsaturated substrates by Bis(benzamidinato)yttrium Alkyl, [PhC(NSiMe3)2]2YR (R = CH2Ph·THF, CH(SiMe3)2), and Hydrido, {[PhC(NSiMe3)2]2Y(μ-H)}2, compounds

Article abstract of DOI:10.1021/om9508142

The reactivity of benzamidinate-stabilized yttrium complexes [PhC(NSiMe₃)₂]₂YR (R = CH₂Ph·THF, CH(SiMe₃)₂) and {[PhC(NSiMe₃)₂]₂Y(μ-H)}₂ has been investigated. The complexes are thermally stable showing no sign of decomposition, ligand or solvent metalation, or H/D exchange after hours at 100°C in cyclohexane-d₁₂ or benzene-d_t. The alkyls are also stable in ethereal solvents. However, {[PhC(NSiMe₃)₂]₂Y(μ-H)}₂ induces C-O cleavage in THF solutions. The complexes [PhC(NSiMe₃)₂]₂YCH₂Ph·THF and {[PhC-(NSiMe₃)₂]₂Y(μ-H)}₂ are modestly active in ethylene polymerization but are inactive toward propylene and 1-hexene. Terminal alkynes react stoichiometrically with [PhC(NSiMe₃)₂]₂-YCH(SiMe₃) ₂ and {[PhC(NSiMe₃)₂]₂Y(μ-H)}₂ to give μ-acetylide dimers, {[PhC(NSiMe₃)₂]₂Y-(μ-C≡CR)} ₂ (1, R = H; 2, R = Me; 3, R = n-Pr; 4, R = SiMe₃; 5, R = Ph; 6, R = CMe₃). Treatment with THF leads to cleavage of these dimers, yielding [PhC(NSiMe₃)₂]₂YC≡CR·-THF (7, R = H; 8, R = CMe₃). [PhC(NSiMe₃)₂]₂Y(μ-Me) ₂Li·TMEDA reacts with HC≡CCMe₃ to afford [PhC(NSiMe₃)₂]₂Y(μ-C≡CCMe ₃)₂Li·TMEDA. [PhC(NSiMe₃)₂]₂YCH(SiMe₃) ₂ catalyzes the regioselective dimerization of bulky 1-alkynes. With small 1-alkynes, HC≡CR (R = H, Me, n-Pr), no dimerization was observed and the reaction stops with the formation of the alkynyl dimers {PhC(NSiMe₃)₂]₂Y(μ-C≡CR)}₂ (1-3). Treatment of [PhC(NSiMe₃)₂]₂YR with acetonitrile gives either C-H bond activation or insertion. For R = CH(SiMe₃)₂, C-H bond activation occurs, yielding {[PhC(NSiMe₃)₂] ₂Y(μ-(N,N′)-N(H)C(Me)=C(H)C≡N)}₂ (10). For R = CH₂Ph·THF a mixture of C-H bond activation (10, 10%) and insertion products, {[PhC-(NSiMe₃)₂]₂Y(μ-N=C(Me)CH ₂Ph)}₂ (11a, 50%) and {[PhC(NSiMe₃)₂]₂Y(μ-N(H)C(Me)=C(H)-Ph)} ₂ (11b, 40%), was obtained. The hydride {[PhC(NSiMe₃)₂]₂Y(μ-H)}₂ exclusively gives insertion of acetonitrile, affording {[PhC(NSiMe₃)₂]₂Y(μ-N=C(H)Me)}₂ (12). With pyridine, [PhC(NSiMe₃)₂]₂YCH(SiMe₃) ₂ gives C-H bond activation, whereas [PhC(NSiMe₃)₂]₂YCH₂-Ph·THF and {[PhC(NSiMe₃)₂]₂Y(μ-H)}₂ undergo insertion yielding [PhC(NSiMe₃)₂]₂Y-(NC₅H₅R) (13, R = H; 14, R = CH₂Ph). In contrast, with α-picoline, [PhC(NSiMe₃)₂]₂YR (R = CH(SiMe₃)₂, CH₂Ph·THF) and {[PhC(NSiMe₃)₂]₂Y(μ-H)}₂ afford the α-picolyl derivative, [PhC(NSiMe₃)₂]₂Y(η ²-(C,N)-2-CH₂NC₅H₄ (15). The difference in reactivity of the bis-(benzamidinate)-stabilized complexes compared to the corresponding Cp*₂YR systems, e.g. the low tendency to catalyze C-C bond formation, the reduced or even the absence of C-H/ C-O activation properties, and the enhanced nucleophilic and Br?nsted base reactivities, is interpreted in terms of the high ionicity of the benzamidinate-stabilized yttrium complexes. The contracted yttrium orbitals are less exposed than in the dicyclopentadienyl derivatives and therefore not suited to establish the first initiating interaction with substrate molecules.

Full text of DOI:10.1021/om9508142

Organometallics 1996, 15, 2291-2302
2291
In ser tion a n d C-H Bon d Activa tion of Un sa tu r a ted
Su bstr a tes by Bis(ben za m id in a to)yttr iu m Alk yl,
[P h C(NSiMe3)2]2YR (R ) CH2P h ‚THF , CH(SiMe3)2), a n d
Hyd r id o, {[P h C(NSiMe3)2]2Y(µ-H)}2, Com p ou n d s
Robbert Duchateau, Cornelis T. van Wee, and J an H. Teuben*,†
Groningen Center for Catalysis and Synthesis, Department of Chemistry, Nijenborgh 4,
9747 AG Groningen, The Netherlands
Received October 13, 1995X
The reactivity of benzamidinate-stabilized yttrium complexes [PhC(NSiMe3)2]2YR (R )
CH2Ph‚THF, CH(SiMe3)2) and {[PhC(NSiMe3)2]2Y(µ-H)}2 has been investigated. The
complexes are thermally stable showing no sign of decomposition, ligand or solvent
metalation, or H/D exchange after hours at 100 °C in cyclohexane-d12 or benzene-d6. The
alkyls are also stable in ethereal solvents. However, {[PhC(NSiMe3)2]2Y(µ-H)}2 induces C-O
cleavage in THF solutions. The complexes [PhC(NSiMe3)2]2YCH2Ph‚THF and {[PhC-
(NSiMe3)2]2Y(µ-H)}2 are modestly active in ethylene polymerization but are inactive toward
propylene and 1-hexene. Terminal alkynes react stoichiometrically with [PhC(NSiMe3)2]2-
YCH(SiMe3)2 and {[PhC(NSiMe3)2]2Y(µ-H)}2 to give µ-acetylide dimers, {[PhC(NSiMe3)2]2Y-
(µ-CtCR)}2 (1, R ) H; 2, R ) Me; 3, R ) n-Pr; 4, R ) SiMe3; 5, R ) Ph; 6, R ) CMe3).
Treatment with THF leads to cleavage of these dimers, yielding [PhC(NSiMe3)2]2YCtCR‚-
THF (7, R ) H; 8, R ) CMe3). [PhC(NSiMe3)2]2Y(µ-Me)2Li‚TMEDA reacts with HCtCCMe3
to afford [PhC(NSiMe3)2]2Y(µ-CtCCMe3)2Li‚TMEDA. [PhC(NSiMe3)2]2YCH(SiMe3)2 catalyzes
the regioselective dimerization of bulky 1-alkynes. With small 1-alkynes, HCtCR (R ) H,
Me, n-Pr), no dimerization was observed and the reaction stops with the formation of the
alkynyl dimers {PhC(NSiMe3)2]2Y(µ-CtCR)}2 (1-3). Treatment of [PhC(NSiMe3)2]2YR with
acetonitrile gives either C-H bond activation or insertion. For R ) CH(SiMe3)2, C-H bond
activation occurs, yielding {[PhC(NSiMe3)2]2Y(µ-(N,N ′)-N(H)C(Me)dC(H)CtN)}2 (10). For
R ) CH2Ph‚THF a mixture of C-H bond activation (10, 10%) and insertion products, {[PhC-
(NSiMe3)2]2Y(µ-NdC(Me)CH2Ph)}2 (11a , 50%) and {[PhC(NSiMe3)2]2Y(µ-N(H)C(Me)dC(H)-
Ph)}2 (11b, 40%), was obtained. The hydride {[PhC(NSiMe3)2]2Y(µ-H)}2 exclusively gives
insertion of acetonitrile, affording {[PhC(NSiMe3)2]2Y(µ-NdC(H)Me)}2 (12). With pyridine,
[PhC(NSiMe3)2]2YCH(SiMe3)2 gives C-H bond activation, whereas [PhC(NSiMe3)2]2YCH2-
Ph‚THF and {[PhC(NSiMe3)2]2Y(µ-H)}2 undergo insertion yielding [PhC(NSiMe3)2]2Y-
(NC5H5R) (13, R ) H; 14, R ) CH2Ph). In contrast, with R-picoline, [PhC(NSiMe3)2]2YR (R
) CH(SiMe3)2, CH2Ph‚THF) and {[PhC(NSiMe3)2]2Y(µ-H)}2 afford the R-picolyl derivative,
[PhC(NSiMe3)2]2Y(η2-(C,N)-2-CH2NC5H4 (15). The difference in reactivity of the bis-
(benzamidinate)-stabilized complexes compared to the corresponding Cp*2YR systems, e.g.
the low tendency to catalyze C-C bond formation, the reduced or even the absence of C-H/
C-O activation properties, and the enhanced nucleophilic and Brønsted base reactivities,
is interpreted in terms of the high ionicity of the benzamidinate-stabilized yttrium complexes.
The contracted yttrium orbitals are less exposed than in the dicyclopentadienyl derivatives
and therefore not suited to establish the first initiating interaction with substrate molecules.
In tr od u ction
that benzamidinate ligands accumulate negative charge
more strongly than cyclopentadienyls and therefore the
bis(benzamidinato)yttrium complexes are more ionic.
This increased ionicity is expected to have a notable
effect on the reactivity of Y-C and Y-H (and Y-X)
bonds. To probe this, an exploratory study of the
reactivity of bis(benzamidinato)yttrium complexes, [PhC-
(NSiMe3)2]2YR (R ) CH(SiMe3)2, CH2Ph) and {[PhC-
(NSiMe3)2]2Y(µ-H)}2, was carried out. For (pentamethyl)-
cyclopentadienyl ligand-stabilized yttrium systems, the
dominant reaction pathways are insertion of unsatur-
ated substrates into Ln-X (X ) C, H, N) bonds and
X-H (X ) C, H, N, O) bond activation.2 In the latter
In a previous article1 we have reported a new class
of yttrium complexes [PhC(NSiMe3)2]2YX in which Y-H,
Y-C, and Y-X (X ) heteroatom) bonds are stabilized
by two N,N ′-bis(trimethylsilyl)benzamidinato ligands.
These new ancillary ligands may function as attractive
alternatives for pentamethylcyclopentadienyls. Molec-
ular modeling studies indicate that the steric aspects
of the two ligand systems do not differ dramatically.
Theoretical considerations on the other hand suggest
† E-mail address: TEUBEN@rugch4.chem.rug.nl.
X Abstract published in Advance ACS Abstracts, April 15, 1996.
(1) Duchateau, R.; van Wee, C. T.; Meetsma, A.; van Duijnen, P.
Th.; Teuben, J . H. Organometallics 1996, 15, 2279.
S0276-7333(95)00814-4 CCC: $12.00 © 1996 American Chemical Society

2292 Organometallics, Vol. 15, No. 9, 1996
Duchateau et al.
case, the activation of saturated hydrocarbons like
methane is among the most intriguing.2a,d,f Although
some modifications of the ligand system have been
introduced,3,4 the most extensively studied system is
Cp*2LnR (Ln ) Sc, Y, lanthanides; R ) alkyl, hydride).2
This contribution reports the results of an extensive
study on the potential of bis(benzamidinato)-stabilized
Y-C and Y-H bonds in (catalytic) insertion and activa-
tion chemistry (e.g. with alkenes, alkynes, nitriles, C-O,
and aromatic C-H bonds). In order to make a realistic
comparison, the substrates and reactions selected to be
investigated were those studied earlier for the well-
known yttrocene and analogous systems.2,3 Parts of this
work have been published in communication form.5
(R ) alkyl, H; Ln ) Sc, Y, lanthanides) which undergo
metalation of the Cp* ligands upon thermolysis, yielding
fulvene species.2,6 Another interesting feature of the
bis(N,N ′-bis(trimethylsilyl)benzamidinato)yttrium alkyls
and hydride is their complete lack of C-H bond activa-
tion of solvent molecules, i.e. H/D scrambling and
metalation of deuterated aromatic solvents, which is a
prominent and well-investigated feature of Cp*2LnR
systems.2
(b) Eth er Solven ts. The alkyls [PhC(NSiMe3)2]2YR
(R ) CH2Ph‚THF, CH(SiMe3)2) are stable in ethers
(Et2O, THF; reflux, days). Whereas {Cp*2Y(µ-H)}2
reacts instantaneously with Et2O at room temperature,
the hydride {[PhC(NSiMe3)2]2Y(µ-H)}2 is stable (2 weeks,
25 °C) in ether.2f In benzene, {[PhC(NSiMe3)2]2Y(µ-H)}2
does not react with THF (2 equiv, room temperature,
days), but in neat THF (hours, room temperature),
ethane and minor amounts ((15%) of ethylene (To¨pler
pump determination, GC-MS) are formed. Olefinic
resonances in the 1H NMR spectrum of the product
mixture suggest the formation of yttrium enolate species
as a result of C-O bond activation.
Resu lts a n d Discu ssion
Th er m olysis an d Beh avior of [P h C(NSiMe3)2]2YR
(R ) CH 2P h ‚TH F , CH (SiMe3)2) a n d {[P h C(NSi-
Me3)2]2Y((µ-H)}2 in Com m on Solven ts. Before the
reactivity of these compounds toward unsaturated
substrates was tested, their thermolysis in, and behav-
ior toward, common solvents was investigated.
Group 3 metal and lanthanide complexes can cleave
THF in a variety of ways. Which route is followed
seems to depend on many variables like metal, ancillary
ligand system, and the nature of the carbyl or hydrido
ligand. For [C5H4Me]2YR‚THF (R ) Me, CH2SiMe3),7
ortho-metalation followed by extrusion of ethylene has
been proposed (Scheme 1A). The hydrides {Cp*2Ln(µ-
H)}2 (Ln ) Y, Sm) activate the C-O bond yielding
n-butoxo derivatives Cp*2LnO-n-Bu2o,8 In an analogous
reaction, [Cp*2Sm‚2THF]+[BPh4]- reacts with Cp*K to
form Cp*2SmO(CH2)4C5Me5‚THF (Scheme 1B).9 In
contrast, the closely related {Cp*2Ce(µ-H)}2 yields a
µ-oxo species with elimination of ethane (0.5 mol/mol
Ce; Scheme 1C).8 The almost quantitative formation
(a ) Ar om a tic a n d Alip h a tic Solven ts. The alkyl
and hydrido complexes are stable in aromatic (benzene-
d6) and aliphatic solvents (cyclohexane-d12) for pro-
longed periods of time at 100 °C. This stability is quite
surprising when compared with the Cp*2LnR analogues
(2) (a) Watson, P. L. J . Am. Chem. Soc. 1983, 105, 6491. (b) Watson,
P. L. J . Chem. Soc., Chem. Commun. 1983, 276. (c) Evans, W. J .;
Meadows, J . H.; Hunter, W. E.; Atwood, J . L. J . Am. Chem. Soc. 1984,
106, 1291. (d) J eske, G.; Lauke, H.; Mauermann, H.; Swepston, P. N.;
Schumann, H.; Marks, T. J . J . Am. Chem. Soc. 1985, 107, 8091. (e)
Den Haan, K. H.; Wielstra, Y.; Teuben, J . H. Organometallics 1987,
6, 2053. (f) 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. (g) Bunel, E.; Burger, B. J .; Bercaw, J . E.
J . Am. Chem. Soc. 1988, 110, 976. (h) Evans, W. J .; Chamberlain, L.
R.; Ulibarri, T. A.; Ziller, J . W. J . Am. Chem. Soc. 1988, 110, 6423. (i)
Burger, B. J .; Thompson, M. E.; Cotter, W. D.; Bercaw, J . E. J . Am.
Chem. Soc. 1990, 112, 1566. (j) Heeres, H. J .; Meetsma, A.; Teuben, J .
H. Angew. Chem., Int. Ed. Engl. 1990, 29, 420. (k) Heeres, H. J .;
Heeres, A.; Teuben, J . H. Organometallics 1990, 9, 1508. (l) Heeres,
H. J .; Teuben, J . H. Organometallics 1991, 10, 1980. (m) Sakakura,
T.; Lautenschlager, H.-J .; Tanaka, M. J . Chem. Soc., Chem. Commun.
1991, 40. (n) Forsyth, G. M.; Nolan, S. P.; Marks, T. J . Organometallics
1991, 10, 2543. (o) Evans, W. J .; Ulibarri, T. A.; Ziller, J . W.
Organometallics 1991, 10, 134. (p) Gagne´, M. R.; Stern, C. L.; Marks,
T. J . J . Am. Chem. Soc. 1992, 114, 275. (q) Harrison, K. N.; Marks, T.
J . J . Am. Chem. Soc. 1992, 114, 9220. (r) Yasuda, H.; Yamamoto, H.;
Yokota, K.; Miyake, S.; Nakamura, A. J . Am. Chem. Soc. 1992, 114,
4908. (s) Booij, M.; Deelman, B.-J .; Duchateau, R.; Postma, D. S.;
Meetsma, A.; Teuben, J . H. Organometallics 1993, 12, 3531. (t) Li, Y.;
Fu, P.-F.; Marks, T. J . Organometallics 1994, 13, 439. (u) Hajela, S.;
Bercaw, J . E. Organometallics 1994, 13, 1147.
(3) (a) J eske, G.; Schock, L. E.; Swepston, P. N.; Schumann, H.;
Marks, T. J . J . Am. Chem. Soc. 1985, 107, 8103. (b) J eske, G.; Lauke,
H.; Mauermann, H.; Schumann, H.; Marks, T. J . J . Am. Chem. Soc.
1985, 107, 8111. (c) Coughlin, E. B.; Bercaw, J . E. J . Am. Chem. Soc.
1992, 114, 7606. (d) Giardello, M. A.; Conticello, V. P.; Brard, L.; Gagne´,
M. R.; Marks, T. J . J . Am. Chem. Soc. 1994, 116, 10241. Decreasing
the steric bulk of the ancillary ligand system does not always lead to
an increase in reactivity: (e) Stern, D.; Sabat, M.; Marks, T. J . J . Am.
Chem. Soc. 1990, 112, 9558.
(4) (a) Piers, W. E.; Shapiro, P. J .; Bunel, E. E.; Bercaw, J . E. Synlett
1990, 74. (b) Shapiro, P. J .; Cotter, W. D.; Schaefer, W. P.; Labinger,
J . A.; Bercaw, J . E. J . Am. Chem. Soc. 1994, 116, 4623. (c) Schaverien,
C. J .; Orpen, G. Inorg. Chem. 1991, 30, 4968 and references cited
therein. (d) Schaverien, C. J . Organometallics 1994, 13, 69. (e) Fryzuk,
M. D.; Haddad, T. S.; Rettig, S. J . Organometallics 1991, 10, 2026. (f)
Fryzuk, M. D.; Haddad, T. S.; Rettig, S. J . Organometallics 1992, 11,
2967. (g) Bazan, G. C.; Schaefer, W. P.; Bercaw, J . E. Organometallics
1993, 12, 2126. (h) J ubb, J .; Gambarotta, S.; Duchateau, R.; Teuben,
J . H. J . Chem. Soc., Chem. Commun. 1994, 2641.
1
of ethane in combination with the H NMR spectrum
of the product mixture, which indicates that an enolate
fragment, [Y]-OCHdCH2, has been formed, suggests
that the reaction of {[PhC(NSiMe3)2]2Y(µ-H)}2 with THF
proceeds by the same mechanism as proposed for {Cp*2-
Ce(µ-H)}2. The presence of minor amounts of ethylene,
also formed during the reaction of {[PhC(NSiMe3)2]2Y-
(µ-H)}2 with THF, suggests that subsequent C-O bond
activation of the enolate, yielding a µ-oxo species, also
occurs (Scheme 1C).
Rea ctivity tow a r d Alk en es. (a ) Olefin P olym er -
iza tion . When heated to 65 °C, in benzene-d6, {[PhC-
(NSiMe3)2]2Y(µ-H)}2 polymerizes ethylene (4 atm). 1H
NMR spectra collected during the reaction showed the
gradual consumption of ethylene and, more importantly,
no other yttrium compounds other than {[PhC(NSi-
Me3)2]2Y(µ-H)}2. Resonances attributable to ethylene
oligomers and mixed hydrido-alkyl species, [Y](µ-H)-
(µ-R)[Y] ([Y] ) [PhC(NSiMe3)2]2Y), as observed by Marks
et al. for [Y] ) [µ,η5,η5-(C5Me4)SiR2(C5H4)]2Y3e and by
Schaverien for [Y] ) Cp*[ArO]Y,4d were absent. Under
more drastic conditions (55 °C, 70 atm of ethylene) a
(6) Den Haan, K. H.; Teuben, J . H. J . Chem. Soc., Chem. Commun.
1986, 682.
(7) Evans, W. J .; Dominguez, R.; Hanusa, T. Organometallics 1986,
5, 1291.
(5) The reaction of [PhC(NSiMe3)2]2YCH(SiMe3)2 with ethyne, lead-
ing to the ethynyl-bridged dimer {[PhC(NSiMe3)2]2Y(µ-CtCH)}2 and
the molecular structure of this acetylide complex have been pub-
lished: Duchateau, R.; van Wee, C. T.; Meetsma, A.; Teuben, J . H. J .
Am. Chem. Soc. 1993, 115, 4931.
(8) (a) Booij, Ph.D. Thesis, University of Groningen, 1989. (b)
Deelman, B.-J .; Booij, M.; Meetsma, A.; Teuben, J . H.; Kooijman, H.;
Spek, A. L. Organometallics 1995, 14, 2306.
(9) Evans, W. J .; Ulibarri, T. A.; Chamberlain, L. R.; Ziller, J . W.;
Alvarez, D., J r. Organometallics 1990, 9, 2124.

Bis(benzamidinato)yttrium Compounds
Organometallics, Vol. 15, No. 9, 1996 2293
Sch em e 1. Exa m p les of C-O Bon d Activa tion a n d Meta la tion of THF by Gr ou p 3 Meta l a n d La n th a n id e
Alk yls a n d Hyd r id esa
a
Key: (A) M ) [C5H4Me]2Y, R ) CH3‚THF, CH2SiMe3‚THF; (B) M ) Cp*2Ln (Ln ) Y, Sm), R ) µ-H; (C) M ) Cp*2Ce,
[C6H5C(NSiMe3)2]2Y, R ) µ-H.
somewhat higher activity was found (4 g of PE/mmol of
[Y]‚h), but the total yield of polyethylene remained low.
The benzyl THF adduct, [PhC(NSiMe3)2]2YCH2Ph‚THF,
also polymerizes ethylene (65 °C, 4 atm of ethylene),
but the rate appears to be even lower than for {[PhC-
(NSiMe3)2]2Y(µ-H)}2 under the same conditions. Again,
the 1H NMR spectra collected during and after the
reaction showed the gradual consumption of ethylene
and [PhC(NSiMe3)2]2YCH2Ph‚THF as the only detect-
able organoyttrium derivative present. With propylene
(4 atm) and 1-hexene (neat), the precursors
{[PhC(NSiMe3)2]2Y(µ-H)}2 and [PhC(NSiMe3)2]2YCH2-
Ph‚THF were found unreacted. Neither oligo/poly-
merization nor indication for the formation of an η3-allyl
species, as found for {Cp*2Ln(µ-H)}2 (Ln ) Y, lan-
thanides),2dg,10 could be observed under the conditions
employed (days, 80 °C).
in view of the low catalytic activity of the system studied
this aspect has not been analyzed further.
(b) Olefin Hyd r obor a tion . As part of a more
general study on the hydroboration of alkenes catalyzed
by group 3 and 4 metals and lanthanides, the catalytic
activity of the bis(benzamidinato)yttrium alkyl, [PhC-
(NSiMe3)2]2YR (R ) CH2Ph, CH(SiMe3)2), and hydrido,
{[PhC(NSiMe3)2]2Y(µ-H)}2, compounds in the hydrobo-
ration of 1-hexene with catecholborane was investigated.
Although published elsewhere,12 a short account of the
results for the compounds under discussion here seems
appropriate. The bis(benzamidinato)yttrium complexes
proved to be catalytically active, but the activity is about
5-10% of that of the lanthanum complex, Cp*2LaCH-
(SiMe3)2, for which the highest activity has been
reported.2q In all cases, fast catalyst deactivation
occurs, probably due to the reaction of catecholborane
with the benzamidinato ligands. Nevertheless, [PhC-
(NSiMe3)2]2YCH(SiMe3)2 and {[PhC(NSiMe3)2]2Y(µ-H)}2
showed catalytic activities substantially higher than
that for Cp*2YCH(SiMe3)2.12 This is surprising, be-
cause, in the absence of catecholborane, {[PhC(NSi-
Me3)2]2Y(µ-H)}2 does not react at all with 1-hexene.
Possibly, catecholborane activates the yttrium catalyst
by forming intermediates such as [PhC(NSiMe3)2]2Y(µ-
H)2B(O2C6H4). It could also be that activation is due
to partial transfer of benzamidinate ligands from yt-
trium to boron, comparable to the observed ligand
exchange reaction of [PhC(NSiMe3)2]2YCl‚THF with
LiAlH4 yielding [PhC(NSiMe3)2]2AlH.1 Probably, reac-
tion of the precursors with catecholborane yields ini-
tially an active, though unstable, catalyst which rapidly
decomposes.
Clearly, activation of the precatalysts by dissociation
and/or precomplexation of ethylene is unfavorable in
these complexes. This can be explained as a conse-
quence of the high ionic character of these bis(benza-
midinato)yttrium compounds, which causes the yttrium
orbitals to contract strongly, making them less available
to interact with an incoming olefin. The fact that the
precursors are the only organoyttrium complexes present
in detectable amounts during NMR tube polymerization
experiments indicates that dissociation of {[PhC-
(NSiMe3)2]2Y(µ-H)}2 into the corresponding monomeric
hydride, and dissociation of THF from [PhC(NSiMe3)2]2-
YCH2Ph‚THF, is slow which will also reduce the activ-
ity. The polyethylene obtained (Mw ) 239 900, Mn
)
46 300) has a broad molecular weight distribution (Mw/
Mn ) 5.2). In this it strongly resembles the polyethylene
obtained by Schaverien et al.,4d who used a cyclopen-
tadienyl aryloxy stabilized yttrium hydride, {Cp*[2,6-
(CMe3)2C6H3O]Y(µ-H)}2, as a catalyst. Several possi-
bilities were discussed (slow initiation and rapid
propagation, heterogenization, â-H elimination, chain
transfer) to explain the observed broad dispersity.4d,11
For the system reported here, these explanations may
hold too but there may be another reason as well, e.g.
the generation of several active species by ligand loss
or redistribution. The GPC chromatogram indicates a
multimodality of the polyethylene obtained. However,
R ea ct ivit y t ow a r d 1-Alk yn es. Both [PhC(NSi-
Me3)2]2YCH(SiMe3)2 and {[PhC(NSiMe3)2]2Y(µ-H)}2 re-
act quickly (1 h, room temperature) with 1-alkynes
(stoichiometric amounts or excess) affording dimeric
alkynyl complexes, {[PhC(NSiMe3)2]2Y(µ-CtCR)}2. With
respect to the formation of these alkynyls, the catalytic
dimerization of 1-alkynes is very slow and the rate
strongly depends on the steric bulk of the alkyne
substituents. Whereas bulky alkynes are dimerized,
sterically unhindered 1-alkynes are not and the reaction
stops with the formation of the dimeric alkynyl com-
(10) (a) Watson, P. L.; Roe, D. C. J . Am. Chem. Soc. 1982, 104, 6471.
(b) Eshuis, J . J . W. Ph.D. Thesis, University of Groningen, 1991.
(11) Gold, L. J . Chem. Phys. 1958, 28, 91.
(12) Bijpost, E. A.; Duchateau, R.; Teuben, J . H. J . Mol. Catal. 1995,
95, 121.

2294 Organometallics, Vol. 15, No. 9, 1996
Duchateau et al.
plexes. Clearly, the dimeric alkynyls play a decisive
role, stabilizing the catalytically active monomeric alky-
nyl species. First the synthesis and characterization of
some well-defined alkynyl derivatives will be described.
A study concerning the dimerization of 1-alkynes cata-
lyzed by bis(benzamidinato)yttrium complexes will be
discussed further on.
by a Lewis base. Addition of THF to solutions of 1 or 6
resulted in instantaneous formation of the correspond-
ing monomeric THF adducts, [PhC(NSiMe3)2]2YCtCR‚
THF (R ) H (7); R ) CMe3 (8), eq 3). This corresponds
(a ) Syn th esis of Bis(N,N-bis(tr im eth ylsilyl)ben -
zam idin ato)yttr iu m Alkyn yls. [PhC(NSiMe3)2]2YCH-
(SiMe3)2 reacts with 1 equiv of 1-alkyne, HCtCR, to
form the corresponding dimeric alkynyls, {[PhC(NSi-
Me3)2]2Y(µ-CtCR)}2 (R ) H (1), Me (2), n-Pr (3), SiMe3
(4), Ph (5), CMe3 (6); eq 1).5 With the hydride {[PhC-
with the reaction of {Cp*2Ce(µ-CtCCMe3)}n with THF,
affording Cp*2CeCtCCMe3‚THF.2l,17b In contrast, the
compounds [C5H4R]2Y(µ-CtCCMe3)}2 (R ) H, Me) do
not react with THF.2d
When [PhC(NSiMe3)2]2Y(µ-Me)2Li‚TMEDA was treated
with HCtCCMe3, the corresponding [PhC(NSiMe3)2]2Y(µ-
CtCCMe3)2Li‚TMEDA (9, eq 4) could be isolated. This
(NSiMe3)2]2Y(µ-H)}2 as starting material for 6, minor
amounts of the intermediate [{[PhC(NSiMe3)2]2Y}2(µ-
H)(µ-CtCCMe3)] (1H NMR: δ 8.0, t, µ-H, 1J YH ) 28 Hz)
and traces of H2 and H2CdC(H)CMe3 could be identified
compound is analogous with Cp*[PhC(NSiMe3)2]Y(µ-
CtCCMe3)2Li‚TMEDA13 and Cp*2Y(µ-CtCCMe3)2Li‚
THF and [Cp*2Sm(µ-CtCPh)K]n, prepared by Evans et
al.14
1
by H NMR spectroscopy. The presence of the inter-
mediate suggests a stepwise reaction with HCtCCMe3
(eq 2), similar to the reaction of {Cp*[ArO]Y(µ-H)}2 with
HCtCSiMe3.4d
(b) Ch a r a cter iza tion . The IR spectra of the acetyl-
ides (1-9) show ν(CtC) frequencies ranging from 1914
to 2060 cm-1, comparable to those of other dimeric group
3 and lanthanide acetylide compounds2e,f,l,4d,14,15 and
notably lower than for the corresponding free acetyl-
enes.16 The 1H NMR spectra (25 °C) of 1-9 show sharp
singlets for the benzamidinato trimethylsilyl groups,
indicating fast fluxional behavior in solution. The 13C
NMR spectra of 1-6 display a triplet (1J Y-C ) 20-21
Hz) for the R-carbon of the acetylide. The splitting is
due to 89Y-13C coupling and indicates that each alkynyl
ligand interacts with two (time-averaged) identical
yttrium centers. It is remarkable that the R-C reso-
1
nance of 4 (δ ) 172.3 ppm, J Y-C ) 19 Hz) is consider-
ably shifted to low field compared to 1-3 and 5 and 6
(these range from 136.0 to 146.6 ppm); why this should
be so is, as yet, unclear. The 13C NMR spectra of 7-9
The traces of H2CdC(H)CMe3 indicate insertion of the
alkyne into the Y-H bond and subsequent protonation
by another alkyne. This could even take place in the
dimeric hydride and form the first step to the mixed
hydride-alkynyl intermediate. It is not due to straight-
forward hydrogenation of the alkyne by {[PhC(NSi-
Me3)2]2Y(µ-H)}2 since in a reaction with excess H2 and
HCtCCMe3 no H2CdC(H)CMe3 was formed. Clear-
ly, the insertion of an alkyne into an Y-H bond cannot
compete with protonolysis by the acidic hydrogen of the
alkyne and formation of the alkynyls. The insertion/
protonation competition is very similar to the reaction
of [PhC(NSiMe3)2]2AlH with HCtCCMe3, but here the
insertion is much easier and considerable amounts of
the olefin are formed.13
1
show a doublet (7, δ ) 111.6 ppm, J Y-C ) 11 Hz; 8, δ
1
1
) 89.3 ppm, J Y-C ) 12 Hz; 9, δ ) 121.1, J Y-C ) 15
Hz) for the R-carbon of the acetylide, in agreement with
a monomeric structure. Worth mentioning is that, due
to the coupling with yttrium, the â-H of the ethynyl
(13) Duchateau, R.; Meetsma, A.; Teuben, J . H. J . Chem. Soc., Chem.
Commun., submitted for publication.
(14) (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.
(15) For example see: (a) Evans, W. J .; Wayda, A. L. J . Organomet.
Chem. 1980, 202, C6. (b) Evans, W. J .; Engerer, W. J .; Coleson, K. M.
J . Am. Chem. Soc. 1981, 103, 6672. (c) Atwood, J . L.; Hunter, W. E.;
Wayda, A. L.; Evans, W. J . Inorg. Chem. 1981, 20, 4115. (d) Boncella,
J . M.; Tilley, T. D.; Andersen, R. A. J . Chem. Soc., Chem. Commun.
1984, 710. (e) Evans, W. J .; Bloom, I.; Hunter, W. E.; Atwood, J . L.
Organometallics 1983, 2, 709. (f) Shen, Q.; Zheng, D.; Lin, L.; Lin, Y.
J . Organomet. Chem. 1990, 391, 307.
The 13C NMR spectra (benzene-d6) of the yttrium
acetylides (1-6) at elevated temperatures (70-80 °C)
did not show any sign of dissociation, suggesting stable
dimeric structures. However, the dimers can be cleaved
(16) HCtCH, ν(CtC)(Raman) ) 1947 cm-1; HCtCMe, ν(CtC) )
2140 cm-1; HCtCPh, ν(CtC) ) 2110 cm-1; HCtCCMe3, ν(CtC) )
2110 cm-1; HCtCSiMe3, ν(CtC) ) 2037 cm-1
.

Bis(benzamidinato)yttrium Compounds
Organometallics, Vol. 15, No. 9, 1996 2295
Ta ble 1. P r od u ct Distr ibu tion of th e Oligom er iza tion of Ter m in a l Alk yn es, HCtCR, Ca ta lyzed by Gr ou p 3-
a n d La n th a n id e-Ba sed Com p lexes
2,4-
1,4-
higher
oligomers
compd
Ra
Me
CMe3
Ph
dimerb,d
dimerc,d
ref
[C6H5C(NSiMe3)2]2YR′
(R′ ) CH(SiMe3)2, µ-H)
100
100
100
this work
SiMe3
H
Me
CMe3
Ph
SiMe3
Me
CMe3
Ph
SiMe3
Me
100
Cp*2ScMe
100
21
1e
1k
100
100
89
20
78
Cp*2YCH(SiMe3)2
11
80
Cp*2LaCH(SiMe3)2
Cp*2CeCH(SiMe3)2
1k
1k
100
86
45
14
51
25
4
74
CMe3
Ph
SiMe3
CMe3
SiMe3
100
82
61
18
32
7
100
Cp*2Ce[CH(SiMe3)2]2
Cp*[ArO]YCH(SiMe3)2
22
4d
100
a
b
d
Alkyne substituent. 2,4-Disubstituted 1-buten-3-yne. c 1,4-Disubstituted 1-buten-3-yne. Structures:
ligand of 7 appears as a doublet in the 1H NMR
spectrum (δ ) 1.99 ppm, 3J Y-H ) 1.3 Hz). This suggests
a stronger interaction of yttrium with the ethynyl
fragment in the monomeric 7 than in the dimeric 1, for
which no yttrium coupling is observed. However, the
yttrium-carbon coupling constants in these compounds
Sc,2f,18a Y,2e,l La,2l,17b Ce,2l,17b Sm;14b R ) alkyl, alkynyl,
H), Cp*Ce[CH(SiMe3)2]2,19 and Cp*[ArO]YR (R ) alkyl,
alkynyl)4d systems.
(d .1) Scop e of th e Dim er iza tion . The dimerization
of 1-alkynes catalyzed by [PhC(NSiMe3)2]2YR (R ) CH-
(SiMe3)2, CH2Ph‚THF) and {[PhC(NSiMe3)2]2Y(µ-H)}2
strongly depends on the alkyne substituent. For small
1-alkynes, HCtCR (R ) H, Me, n-Pr), no dimerization
is observed (days, 80 °C) and the reaction stops with
the formation of the dimeric acetylides (1-3). It is only
for acetylenes HCtCR with bulky substituents (R ) Ph,
SiMe3, CMe3) that catalytic dimerization takes place at
all (vide infra). This observation strongly contrasts with
the Cp*2LnR-catalyzed dimerization of 1-alkynes, for
which high activity was observed for all alkynes regard-
less the size of the substituent. The assumption that
the first step in the dimerization is formation of the
acetylide is supported by the fact that the reaction rate
is independent from whether [PhC(NSiMe3)2]2YCH-
(SiMe3)2, {[PhC(NSiMe3)2]2Y(µ-H)}2, or the acetylides
4-6 are used as precursor.
Compared to the Cp*2LnCH(SiMe3)2 (Ln ) La, Ce)
catalyzed dimerization of 1-alkynes (Nt(25 °C) g 1900
mol of substrate‚mol of catalyst-1‚h-1),2l,17b the observed
catalytic activity of [PhC(NSiMe3)2]2YCH(SiMe3)2 or
{[PhC(NSiMe3)2]2Y(µ-H)}2 is much lower (Nt(80 °C) )
20-40 mol‚mol-1‚h-1). Although the coordinated THF
retards the reaction considerably, the THF adduct 8 still
does catalyze the dimerization of HCtCCMe3 (Nt(50 °C)
≈ 1 mol‚mol-1‚h-1), which implies that coordinated THF
can be replaced by an incoming acetylene.
1
1
(7, J Y-C ) 11 Hz; 1, J Y-C ) 20 Hz) suggest the
opposite.
(c) Th er m olysis of {[P h C(NSiMe3)2]2Y(µ-CtCR)}2.
Thermolysis (24-72 h, 100 °C) of the dimeric alkynyls
(1-6) resulted in the formation of several unidentified
products. The rate of the thermolysis strongly depends
on the alkynyl substituent. Complex 1 decomposes
within hours at 100 °C, while for 4 the characteristic
triplet signal for the alkynyl R-carbon is still present
after 2 days at 100 °C. Unequivocal assignment of
resonances in the NMR spectra arising from C-C-
coupled µ-trienediyl compounds, as formed upon ther-
molysis of {Cp*2LnCtCR}n (Ln ) La, Ce, Sm),17 was
1
not possible. Although the â-H signal in the H NMR
of 1 disappeared upon thermolysis (100 °C, 24h), forma-
tion of an acetylenediyl species, similar to Cp*2-
LnCtCLnCp*2 (Ln ) Sc,18a Sm18b), could not be estab-
lished for our system. Since a complicated mixture of
very soluble thermolysis products was formed, isolation
and characterization of the individual products proved
to be not possible.
(d ) Ca ta lytic Dim er iza tion of Ter m in a l Alk yn es.
To probe the catalytic activity of bis(benzamidinato)-
yttrium compounds in 1-alkyne dimerization, a variety
of different 1-alkynes were examined and the results
compared with those obtained from Cp*2LnR (Ln )
The regio- and stereoselectivity of the reaction de-
pends strongly on the acetylene substituent and catalyst
applied. For Cp*2LnCH(SiMe3)2, the only other group
3 metal and lanthanide complexes for which the dimer-
ization of a variety of 1-alkynes has been investigated,
(17) (a) Evans, W. J .; Keyer, R. A.; Ziller, J . W. Organometallics
1990, 9, 2628. (b) Heeres, H. J .; Nijhof, J .; Teuben, J . H. Organome-
tallics 1993, 12, 2609. (c) Forsyth, C. M.; Nolan, S. P.; Stern, C. L.;
Marks, T. J .; Reingold, A. L. Organometallics 1993, 12, 3618.
(18) (a) St. Clair, M.; Schaefer, W. P.; Bercaw, J . E. Organometallics
1991, 10, 525. (b) Evans, W. J .; Rabe, G. W.; Ziller, J . W. J . Organomet.
Chem. 1994, 483, 21.
(19) Heeres, H. J . Ph.D. Thesis, University of Groningen, 1990.

2296 Organometallics, Vol. 15, No. 9, 1996
Duchateau et al.
Sch em e 2
HCtCCMe3 is selectively coupled to the head-to-tail
H2CdC(CMe3)CtCCMe3. For all other 1-alkynes tested,
HCtCR (R ) Me, Ph, SiMe3), the selectivity was lower,
yielding either mixtures of head-to-tail and head-to-head
isomers (Ln ) Y, La, Ce) or the additional formation of
higher oligomers (Ln ) La, Ce; Table 1).
In our system, HCtCPh and HCtCCMe3 are selec-
tively coupled to head-to-tail dimers: 2,4-disubstituted
1-buten-3-ynes (Table 1). However, for HCtCSiMe3 the
regioselectivity is reversed, exclusively yielding the
head-to-head coupled product: trans-Me3SiC(H)dC-
(H)CtCSiMe3 (Table 1). This remarkable change in
regioselectivity was also observed by Schaverien and
Heeres, who found that Cp*[ArO]YCH(SiMe3)2 and
Cp*2YCH(SiMe3)2 preferentially couple HCtCSiMe3 to
trans-Me3SiC(H)dC(H)CtCSiMe3 (Table 1).2l,4b,17b The
origin of this change in regioselectivity is proposed to
be of an electronic nature (vide infra).2l,4b,20 That other
factors may also play a decisive role is clearly illustrated
by the [Cp*2ZrMe(B(4-C6H4F)4)]-catalyzed coupling of
HCtCSiMe3, which exclusively yields head-to-tail
coupled dimers and trimers.21
(d.2) Mech an istic Con sider ation s. The same mech-
anism as generally accepted for the dimerization of
1-alkynes by group 3 metals and lanthanides can also
be applied to the system discussed here (Scheme
2).2e,f,l,4b,14b,17b Reactions of the precursors [PhC(NSi-
Me3)2]2YR (R ) CH(SiMe3)2, CH2Ph‚THF) give the
dimers (4-6) or THF adducts (7, 8) in the presence of
1-alkyne. The essential step, however, is formation of
monomeric alkynyl compounds either by dissociation of
dimers (4-6) or by dissociation of THF from adducts
like 8. The monomeric alkynyls [PhC(NSiMe3)2]2-
YCtCR then complex a molecule of 1-alkyne followed
by migratory insertion in a selectivity determining step
to give enynyl complexes [PhC(NSiMe3)2]2YC(H)dC-
(R)CtCR (R ) CMe3, Ph) or [PhC(NSiMe3)2]2YC(R)dC-
(H)CtCR (R ) SiMe3), depending on R. The catalytic
cycle is closed by hydrogen transfer from an alkyne with
formation of the 1-buten-3-ynes, H2CdC(R)CtCR (R )
CMe3, Ph) or RC(H)dC(H)CtCR (R ) SiMe3) and the
alkynyl complex [PhC(NSiMe3)2]2YCtCR. 1H NMR
studies of the alkyne dimerization show that the only
(benzamidinato)yttrium complexes present in suffi-
ciently high concentrations are the dimers, {[PhC-
(20) Stockis and Hoffmann have performed calculations on the
polarization of the π* orbitals of HCtCMe and HCtCSiMe3. The
acetylene substituent appears to have a pronounced influence on the
electron density of the alkyne sp-carbon atoms, and distinct differences
in polarization were found for both alkynes. These electronic effects
are believed to be responsible for the difference in regioselectivity of
the catalytic dimerization of 1-alkynes: Stockis, A.; Hoffmann, R. J .
Am. Chem. Soc. 1980, 102, 2952.
(21) Horton, A. D. J . Chem. Soc., Chem. Commun. 1992, 185.

Bis(benzamidinato)yttrium Compounds
Organometallics, Vol. 15, No. 9, 1996 2297
determining. The absence of the expected build up of
monomeric [PhC(NSiMe3)2]2YCtCR can be explained by
fast dimerization of this monomer into the dimeric
precursor (or THF adduct).
Rea ctivity tow a r d Heter oa tom -Con ta in in g Su b-
str a tes: In ser tion ver su s C-H Bon d Activa tion .
With heteroatom-containing unsaturated substrates
such as acetonitrile,2d,j,22 R,â-unsaturated ketones,23 or
pyridines,2b,d-f,24 group 3 metal and lanthanide alkyl or
hydrido complexes either give insertion or C-H bond
activation. Whether insertion or C-H bond activation
occurs, strongly depends on the M-C/M-H bond.
Therefore, a study of the reactions of [PhC(NSiMe3)2]2-
YR (R ) CH(SiMe3)2, CH2Ph‚THF, µ-H) with such
substrates will give information about the character of
the Y-C and Y-H bond in this system.
(a ) Aceton itr ile. With acetonitrile, [PhC(NSiMe3)2]2-
YCH(SiMe3)2 gives C-H bond activation rather than
insertion, yielding H2C(SiMe3)2 and the novel dimeric
crotonitrileamido complex, {[PhC(NSiMe3)2]2Y(µ-(N,N ′)-
N(H)C(Me)dC(H)CtN)}2 (10, eq 5). This contrasts with
F igu r e 1. Normalized ratio of substrate to yttrium
concentration as a function of time and temperature for
the dimerization of HCtCCMe3 using [C6H5C(NSiMe3)2]2-
YCH(SiMe3)2 as precatalyst.
(NSiMe3)2]2Y(µ-CtCR)}2, or the THF adducts, [PhC-
(NSiMe3)2]2YCtCR‚THF. This suggests that a very
small fraction (<3%) of yttrium is actually involved in
the catalytic process as such. An estimate of the
catalytic activity based on this 3% participation as-
sumption leads to a turnover frequency Nt ) 1300
mol‚mol-1‚h-1 at 80 °C. Although clearly higher than
the observed activity, this intrinsic catalytic activity of
the bis(benzamidinato)yttrium complexes is still lower
than that of the corresponding Cp*2LnR system (Ln )
Y, La, Ce; R ) CMe3, at 25 °C; Nt ) 1900 mol‚mol-1‚h-1).
The selectivity of the bis(benzamidinato)yttrium system,
however, is higher than observed for the corresponding
Cp*2LnR complexes. It is clear that the decrease of
catalytic activity going from Cp*2LnR to [PhC(NSiMe3)2]2-
YR has two reasons. First, presumably very low
monomer concentrations refer to low equilibrium con-
centrations of a monomeric complex (ligated or base
free) rather than low substrate (i.e. alkyne) concentra-
tions. The second reason arises from the monomer itself
which seems less eager to complex and insert an
incoming alkyne. Again this can be explained by the
strongly contracted orbitals of the highly positively
charged yttrium atom, which reduces the capacity of
these orbitals to interact with substrates.1 This fits the
general reactivity pattern observed so far for the highly
ionic bis(benzamidinato)yttrium complexes. Why the
dimers are so stable is not easy to explain. Steric
reasons seem to be important since the smaller the
substituent on the alkyne (HCtCR) is, the more stable
the dimer appears to be. The stability increase even
results in complete catalytic inactivity for R ) H, Me,
and n-Pr.
the reactions of {[C5H4R]2Y(µ-H)‚THF}2 (R ) H, Me)
and Cp*2ScR (R ) p-Me-C6H4, Me) with acetonitrile:
both giving clean insertion.2d,22 Metalation was also
observed for Cp*2LnCH(SiMe3)2 (Ln ) La, Ce) with
acetonitrile, resulting in dimeric cyanomethyl com-
plexes, {Cp*2Ln(µ-CH2CtN)}2.2 For our system, this
compound could not be detected. However, it is likely
that it is formed as an intermediate which reacts further
by insertion of another 1 equiv of acetonitrile, followed
by a 1,3-H shift, to give 10 (eq 5).25
The reaction is strongly reminiscent of the alkali
metal catalyzed dimerization of acetonitrile to crotoni-
trileamides,26,27 emphasizing the ionic character of the
Y-C bond in the bis(benzamidinato)yttrium system.
The IR and NMR data for 10 are in good agreement with
those of Na[N(H)C(Me)dC(H)CtN].26,27 The lowfield
shift of the C(Me)dC (δ ) 131.3 ppm) and the highfield
shifts of the C(H)dC (δ ) 48.1 ppm) and C(H)dC (δ )
1
3.50 ppm) resonances in the 13C and H NMR spectra
Although no build up of intermediates like [PhC-
(NSiMe3)2]2YCtCR (R ) CMe3, Ph, SiMe3), [PhC(NSi-
Me3)2]2YC(H)dC(R)CtCR (R ) CMe3, Ph), or [PhC-
(NSiMe3)2]2YC(R)dC(H)CtCR (R ) SiMe3,) could be
observed, the first-order dependence on 1-alkyne (Figure
1) suggests that the rate-determining step is within the
catalytic cycle. If C-H bond activation would be rate-
determining, buildup of the yttrium-1-buten-3-ynyl
should occur. Since this is not the case, probably
insertion of an alkyne into the YsCtCR bond is rate-
of 10 clearly demonstrate the extensive charge delocal-
ization within the crotonitrileamido fragment.
(22) Bercaw, J . E.; Davies, D.; Wolczanski, P. T. Organometallics
1986, 5, 443.
(23) (a) Yasuda, H.; Yamamoto, H.; Yokota, K.; Miyake, S.; Naka-
mura, A. J . Am. Chem. Soc. 1992, 114, 4908. (b) Deelman, B.-J .;
Bijpost, E. A.; Teuben, J . H. J . Chem. Soc., Chem. Commun. 1995,
1741.
(24) (a) Deelman, B.-J .; Stevels, W. M.; Lakin, M. T.; Spek, A. L.;
Teuben, J . H. Organometallics 1994, 13, 3881. (b) Deelman, B.-J . Ph.D.
Thesis, University of Groningen, 1994.

2298 Organometallics, Vol. 15, No. 9, 1996
Duchateau et al.
It appears that the bulky carbyl group in [PhC-
(NSiMe3)2]2YCH(SiMe3)2 acts as a classic Brønsted base,
while the sterically less hindered NtCCH2 fragment of
the intermediate cyanomethyl complex is a better nu-
cleophile which leads to insertion of another acetonitrile.
When the reaction of [PhC(NSiMe3)2]2YCH(SiMe3)2 with
exactly 1 equiv of acetonitrile was carried out, a 1:1
mixture of [PhC(NSiMe3)2]2YCH(SiMe3)2 and 10 was
obtained. Hence, the insertion of the second 1 equiv of
NtCMe is faster than the preceding metalation. In
contrast, for Cp*2LnCH(SiMe3)2 (Ln ) La, Ce), C-H
bond activation is faster as is illustrated by the selective
formation of the dimeric cyanomethyl complex.2j
The reaction of [PhC(NSiMe3)2]2YCH2Ph‚THF with
acetonitrile yields a mixture of compounds. Besides
insertion products {[PhC(NSiMe3)2]2Y(µ-NdC(Me)CH2-
Ph)}2 (11a, 50%) and {[PhC(NSiMe3)2]2Y(µ-NHC(Me)dC-
(H)Ph)}2 (11b, 40%),25 competitive deprotonation of
acetonitrile is observed yielding the crotonitrileamido
complex (10, 10%, eq 6). The enamine complex 11b is
formed as a result of imine-enamine tautomerism,
similar to that observed for 10.
tra of 12 are consistent with those of the corresponding
{[C5H4R]2Y(µ-NdC(H)Me)}2 (R ) H, Me) species, pre-
pared in a similar fashion by Evans et al.2c In contrast
to its yttrocene analogues, complex 12 is unstable and
decomposes rapidly at room temperature, forming an
mixture of unidentified products.
These results show that the competition between
nucleophilicity and Brønsted basicity of the R group in
[PhC(NSiMe3)2]2YR (R ) CH(SiMe3)2, CH2Ph, µ-H) has
a strong influence on the reaction of these compounds
with R-hydrogen-containing nitriles. The bulky bis-
(trimethylsilyl)methyl substituent tends to react as a
classic Brønsted base like M2-naphthalene (M ) Li, Na,
K, MgCl)26 and NaN(SiMe3)2,27 deprotonating acetoni-
trile. With only 10% deprotonation of acetonitrile, the
benzyl group in [PhC(NSiMe3)2]2YCH2Ph‚THF clearly
shows a reduced Brønsted base character and resembles
Cp*2ScR (R ) p-Me-C6H4, Me),22 [Cp′2MR]+ (Cp′ ) C5H5,
C5H4Me; M ) Ti, Zr; R ) alkyl),28a-c and Al(NEt2)Et2.29
As a result of its highly nucleophilic character, the
hydride, {[PhC(NSiMe3)2]2Y(µ-H)}2, only shows inser-
tion of acetonitrile, analogous to Cp*2ScH,22 Cp*2-
ZrH2,22a and [Cp′2ZrH]+ (Cp′ ) C5H5, C5H4Me).28c,d
(b) P yr id in es. When [PhC(NSiMe3)2]2YCH(SiMe3)2
was treated with excess pyridine, a complicated reaction
occurred. Quantitative formation of the alkane, H2C-
(SiMe3)2, indicated metalation of pyridine. However, the
expected pyridyl species could not be detected by 1H
NMR spectroscopy. Vinylic C-H resonances (δ ) 4-6
ppm) suggest partial reduction of pyridine. It is prob-
able that insertion of another 1 equiv of pyridine into
the Y-C bond of the initially formed pyridyl derivative
occurred, similar to that proposed for the reaction of
Cp*2Y(η2-(C,N)-2-NC5H4) with pyridine (eq 8).24
Finally, the hydride {[PhC(NSiMe3)2]2Y(µ-H)}2 reacts
instantaneously at room temperature with NtCMe (eq
7), exclusively yielding the insertion product {[PhC-
While {Cp*2Y(µ-H)}2 is known to give C-H bond
activation with pyridine yielding the pyridyl, Cp*2Y(η2-
(C,N)-2-NC5H4),2e,24 reaction of {[PhC(NSiMe3)2]2Y(µ-
H)}2 resulted in insertion rather than C-H bond
activation, as the 1,2-inserted product [PhC(NSiMe3)2]2-
YNC5H6 (13, eq 9) was obtained. Hence, the reactivity
1
(NSiMe3)2]2Y(µ-NdC(H)Me)}2 (12). The H NMR spec-
(25) The products (10, 11a ,b) in these reactions and the intermedi-
ates proposed in eq 5 all are suggested to be dimeric. The justification
for this is the close analogy with strongly related (structurally
characterized) complexes, e.g. 10, [Me2Si(CMe3)(OCMe3)]2Y(µ-(N,N ′)-
N(H)C(Me)dC(H)CtN)}2 (Duchateau, R.; Tuinstra, T.; Brussee, E. A.;
Meetsma, A.; van Duijnen, P. Th.; Teuben, J . H. Manuscript in
preparation), and 11a ,b, {Cp2Y(µ-NdC(H)Me)}2 (ref 2c).
(26) (a) Binev, I. G.; Todorova-Momcheva, R. I.; J uchnovski, I. N.
Dokl. Bolgarskoj Acad. Nauk. 1976, 29, 1301. (b) J uchnovski, I. N.;
Binev, I. G. J . Organomet. Chem. 1975, 99, 1.
of {[PhC(NSiMe3)2]2Y(µ-H)}2 toward pyridine resembles
(28) (a) Guram, A. S.; J ordan, R. F.; Taylor, D. F. J . Am. Chem.
Soc. 1991, 113, 1833. (b) Borkowsky, S. L.; Baenziger, N. C.; J ordan,
R. F. Organometallics 1993, 12, 486. (c) Alelyunas, Y. W.; Guo, Z.;
LaPointe, R. E.; J ordan, R. F. Organometallics 1993, 12, 544. (d)
J ordan, R. F.; Taylor, D. F.; Baenziger, N. C. Organometallics 1990,
9, 1546.
(29) Hirabayashi, T.; Itoh, K.; Sakai, S.; Ishii, Y. J . Organomet.
Chem. 1970, 21, 273.
(27) Kru¨ger, C. J . Organomet. Chem. 1967, 9, 125.

Bis(benzamidinato)yttrium Compounds
Organometallics, Vol. 15, No. 9, 1996 2299
that of {[C5H4R]2Y(µ-H)‚THF}2 (R ) H, Me).2c Subse-
quent thermal isomerization into the 1,4-addition prod-
uct, as observed for the latter, did not occur in our
system (days, 100 °C), however. Since the reactivity of
the benzyl derivative, [PhC(NSiMe3)2]2YCH2Ph‚THF
toward acetonitrile was found to be intermediate be-
tween that of the bulky alkyl, [PhC(NSiMe3)2]2YCH-
(SiMe3)2 (C-H bond activation), and the hydride, [PhC-
(NSiMe3)2]2Y(µ-H)}2 (insertion), we were interested to
see how it would react with excess pyridine. Compound
[PhC(NSiMe3)2]2YCH2Ph‚THF reacts instantaneously
with pyridine (2.5 equiv) by insertion to form exclusively
the 1,2-insertion product, [PhC(NSiMe3)2]2YNC5H5-2-
CH2Ph (14, eq 9). Unfortunately, its extremely high
solubility precluded purification, although it could
conclusively be identified (1H, 13C NMR). Hence, the
reactivity of [PhC(NSiMe3)2]2YCH2Ph‚THF toward py-
ridine is very similar to that of {[PhC(NSiMe3)2]2Y(µ-
H)}2 and alkyllithium reagents. The Ziegler alkylation
of pyridines by alkyllithium reagents involves interme-
diate 1,2-insertion products which subsequently un-
dergo elimination of LiH.30 However, analogous forma-
tion of the yttrium hydride {[PhC(NSiMe3)2]2Y(µ-H)}2
and release of 2-benzylpyridine, or formation of [PhC-
(NSiMe3)2]2Y(η2-(C,N)-2-C(H)PhNC5H4) (vide infra), was
not observed in this system.
to induce C-O activation with ethers and their complete
inactivity in aromatic/aliphatic C-H bond activation
upon thermolysis. Furthermore, the bis(benzamidina-
to)yttrium complexes are clearly less suited to catalyze
C-C bond formation, e.g. with unsaturated hydrocar-
bons like olefins and 1-alkynes. Although this may be
due to several factors like the high stability of the
(dimeric) precursors, the low ability of the potential
catalytic site to complex substrates is thought to be the
main reason. During ethylene polymerization, 1-hexene
hydroboration, and 1-alkyne dimerization, activation of
the (dimeric or ether complexed) precursors appears to
be difficult as the dimeric complexes, {[PhC(NSiMe3)2]2Y-
(µ-R)}2 (R ) H, CtCR), are very stable. The absence
of notable amounts of monomeric bis(benzamidinato)-
yttrium complexes (with or without substrates com-
plexed to them) during these reactions clearly empha-
sizes the relative difference in stability between the
dimeric precursors and the monomeric active catalysts.
The highly ionic character of the bis(benzamidinato)-
yttrium complexes is indicated by their strong nucleo-
philic and Brønsted base behavior which is observed in
the reactions with acetonitrile and pyridines and which
is very similar to that of alkali-metal compounds.
Treatment of [PhC(NSiMe3)2]2YR with acetonitrile gives,
dependent on R, either C-H bond activation or insertion
and reflects the different character of the R (R ) CH-
(SiMe3)2, CH2Ph‚THF, µ-H) group. Replacing the bulky
alkyl group by a benzyl or an hydrido group results in
an increased tendency of the compounds, [PhC(NSi-
Me3)2]2YR (R ) CH2Ph‚THF, µ-H), to undergo insertion
rather than C-H bond activation. These observations
are as expected for strongly ionic complexes in which
the contracted metal orbitals are too small and unsuited
to start initial complexation and activation of the
substrate prior to reaction. The view of too high ionicity
is supported by theoretical calculations.1
Since its methyl protons are rather acidic, metalation
at the methyl position of picoline was expected to
compete with insertion. NMR tube reactions of [PhC-
(NSiMe3)2]2YR (R ) CH(SiMe3)2, CH2Ph‚THF) and
{[PhC(NSiMe3)2]2Y(µ-H)}2 with R-picoline indeed showed
the formation of H2C(SiMe3)2, toluene, and H2, respec-
tively, together with the R-picolyl derivative, [PhC-
(NSiMe3)2]2Y(η2-(C,N)-CH2-2-NC5H4) (15, eq 10).31 While
Exp er im en ta l Section
Gen er a l Com m en ts. All compounds are extremely oxy-
gen- and moisture-sensitive. Manipulations were therefore
carried out under nitrogen by using glovebox (Braun MB-200)
and Schlenk techniques. Hydrogen (Hoek-Loos 99.9995%),
ethylene, propylene (DSM Research B.V.), acetylene (Ucar,
C.P.), and propyne (Matheson, C.P.) were used as purchased.
1-Hexene, alkynes, nitriles, pyridine, and picoline (J anssen)
were dried over 4 Å molecular sieves and distilled prior to use.
Benzene-d6 and cyclohexane-d12 were degassed and dried over
Na/K alloy. All solvents were distilled from Na (toluene), K
(THF), or Na/K alloy (ether, pentane) and stored under
nitrogen. [PhC(NSiMe3)2]2YR (R ) (µ-Me)2‚TMEDA, CH2-
Ph‚THF, CH(SiMe3)2) and {[PhC(NSiMe3)2]2Y(µ-H)}2 were
prepared according to literature procedures.1 NMR spectra
were recorded on a Varian VXR 300 (1H NMR at 300 MHz,
13C NMR at 75.4 MHz) spectrometer. 1H and 13C NMR spectra
were referenced internally using the residual solvent reso-
nances. IR spectra were recorded on a Mattson-4020 Galaxy
FT-IR spectrophotometer. Elemental analyses were carried
out at the Analytical Department of this laboratory; quoted
data are the average of at least two independent determina-
tions.
this reaction is strictly analogous to that of [Me2Si-
31
(NCMe3)(OCMe3)]2YCH(SiMe3)2 and alkyllithium re-
agents with R-picoline,32 it fully contrasts that of the
corresponding Cp*2YR (R ) Me‚THF, CH(SiMe3)2)
systems, which metalated the pyridyl ring to give
Cp*2Y(η2-(C,N)-2-NC5H3-6-Me).2e
Con clu sion s
It is clear that the chemistry of bis(N,N ′-bis(trimeth-
ylsilyl)benzamidinato)yttrium alkyl and hydrido com-
pounds is significantly different from that of the corre-
sponding Cp*2YR complexes. Most outstanding is the
low tendency of bis(benzamidinato)yttrium complexes
(30) (a) March, J . Advanced Organic Chemistry, Reactions, Mechan-
sims and Structure, 3rd ed.; J ohn Wiley and Sons: New York, 1985.
(b) J oule, J . A.; Smith, G. F. Heterocyclic Chemistry; Van Nostrand
Reinhold Co.: London, 1972.
(31) Complex 15 is formulated as a monomer on the basis of the
close spectroscopic analogy with the structurally characterized
[Me2Si(NCMe3)(OCMe3)]2Y(η2-(C,N)-CH2-2-NC5H4): Duchateau, R.;
Brussee, E. A.; Meetsma, A.; Teuben, J . H. Manuscript in preparation.
(32) Colgan, D.; Papasergio, R. I.; Raston, C. L.; White, A. H. J .
Chem. Soc., Chem. Commun. 1984, 1708.
NMR Tu be Rea ction of [P h C(NSiMe3)2]2YCH2P h ‚THF
a n d {[P h C(NSiMe3)2]2Y(µ-H)}2 w ith Eth ylen e. NMR tubes
containing benzene-d6 (0.5 mL) solutions of [PhC(NSiMe3)2]2-
YCH2Ph‚THF or {[PhC(NSiMe3)2]2Y(µ-H)}2 (0.01-0.02 mmol)
were charged with ethylene (4 atm) and monitored at fixed
time intervals. Heating was required for the reaction to
proceed. At 65 °C the ethylene was gradually consumed with

2300 Organometallics, Vol. 15, No. 9, 1996
Duchateau et al.
formation of polyethylene. For [PhC(NSiMe3)2]2YCH2Ph‚THF,
the ethylene was consumed after several hours. For {[PhC-
(NSiMe3)2]2Y(µ-H)}2 the reaction is complete within 30 min (1H
NMR). The contents of the NMR tubes were quenched with
methanol. The polyethylene was filtered off, dried, and
characterized by IR.
Eth ylen e P olym er iza tion Exp er im en t. A 200 mL au-
toclave was charged with 100 mg (0.16 mmol) of {[PhC-
(NSiMe3)2]2Y(µ-H)}2 dissolved in 75 mL of toluene. The
autoclave was closed, pressurized with ethylene (70 atm), and
heated to 50 °C. After 1.5 h, the autoclave was cooled to room
temperature and the pressure released. After quenching of
the reaction mixture (methanol), the polyethylene was filtered
off and washed with methanol and pentane. After drying, 1.0
g of polyethylene was obtained. The product was characterized
by IR spectroscopy and high temperature GPC: Mn ) 46 300,
Mw ) 239 900, Mw/Mn ) 5.2.
NMR Tu be P r ep a r a tion of {[P h C(NSiMe3)2]2Y(µ-CtC-
n -P r )}2 (3). To an NMR tube charged with a benzene-d6 (0.7
mL) of {[PhC(NSiMe3)2]2Y(µ-H)}2 (32 mg, 0.052 mmol), 1-pen-
tyne (5.5 µL, 0.056 mmol) was added. After 24 h at room
temperature, all 1-pentyne had been consumed to give {(PhC-
(NSiMe3)2)2Y(µ-CtC-n-Pr}2 (3) as the only product. 1H NMR
(benzene-d6, δ): 7.40 (m, 4H, Ar), 7.07 (m, 6H, Ar), 2.60 (t,
2H, CtCCH2), 1.91 (dt, 2H, CH2CH2CH3), 1.03 (t, 3H, CH2CH3),
0.26 (s, 36H, Ph(NSi(CH3)3)2). 13C NMR (benzene-d6, δ): 185.1
(s, PhC(NSiMe3)2), 143.3 (s, Ar), 136.5 (t, Y-C(tC(CH2)2CH3)Y,
1
1J Y-C ) 21 Hz), 132.4 (s, Y-CtC), 128.4 (d, Ar, J C-H ) 155
1
1
Hz), 127.7 (d, Ar, J C-H ) 159 Hz), 126.5 (d, Ar, J C-H ) 173
Hz), 25.1 (t, CtCCH2CH2, 1J C-H ) 129 Hz), 22.8 (m, CH2CH2-
CH3), 14.4 (q, CH2CH3, J C-H ) 117 Hz), 4.1 (q, PhC(NSi-
(CH3)3)2, J C-H ) 117 Hz).
1
1
P r ep a r a tion of {[P h C(NSiMe3)2]2Y(µ-CtCR)}2 (4, R )
SiMe3; 5, R ) P h ; 6, R ) CMe3). 4. At room temperature,
HCtCSiMe3 (0.34 mL, 2.47 mmol) was made to diffuse slowly
into a pentane (5 mL) solution of [PhC(NSiMe3)2]2YCH(SiMe3)2
(1.65 g, 2.13 mmol). After 24 h, the colorless microcrystalline
material formed was washed with pentane (5 mL) and dried
in vacuo, yielding 4 (1.00 g, 1.4 mmol, 66%) as colorless
crystals. IR (KBr/Nujol, cm-1): 2957 (vs), 2926 (vs), 2855 (s),
1983 (w), 1952 (w), 1904 (w), 1447 (vs), 1435 (vs), 1389 (vs),
1246 (s), 1005 (m), 986 (s), 922 (w), 843 (vs), 783 (w), 760 (s),
729 (w), 702 (w), 677 (w), 650 (w), 567 (w), 480 (w), 438 (w).
1H NMR (benzene-d6, δ): 7.49 (m, 4H, Ar), 7.10 (m, 6H, Ar),
0.54 (s, 9H, CtCSi(CH3)3), 0.28 (s, 36H, PhC(NSi(CH3)3)2). 13C-
{1H} NMR (benzene-d6, δ): 185.6 (s, PhC(NSiMe3)2), 172.3 (t,
NMR Tu be Rea ction of [P h C(NSiMe3)2]2YCH2P h ‚THF
an d {[P h C(NSiMe3)2]2Y(µ-H)}2 with P r opylen e an d 1-Hex-
en e. P r op ylen e. NMR tubes containing benzene-d6 (0.5 mL)
solutions of [PhC(NSiMe3)2]2YCH2Ph‚THF or {[PhC(NSi-
Me3)2]2Y(µ-H)}2 (0.01-0.02 mmol) were charged with propylene
(4 atm) and monitored at fixed time intervals. Heating at 80
°C for several days only resulted in partial thermolysis of
{[PhC(NSiMe3)2]2Y(µ-H)}2. No propylene polymers/oligomers
1
were formed. The H NMR spectrum of the reaction mixture
showed no evidence for the presence of η3-allyl species.
1-Hexen e. In the drybox, a 5 mL vessel was charged with
1-hexene (2 mL) solutions of [PhC(NSiMe3)2]2YCH2Ph‚THF or
{[PhC(NSiMe3)2]2Y(µ-H)}2 (0.02-0.04 mmol). The vessel was
then heated to 80 °C for several days. The volatiles were
removed in vacuo and checked by GC and 1H NMR: Exclu-
sively 1-hexene was detected. The 1H NMR spectrum of the
remaining powder exclusively showed resonances attributable
to {[PhC(NSiMe3)2]2Y(µ-H)}2 and traces of thermolysis prod-
ucts but no 1-hexene oligomers.
1
Y-C(tCSiMe3)-Y, J Y-C ) 20 Hz), 143.1 (s, Ar), 140.3 (s,
CtCSiMe3), 128.3 (s, Ar), 127.9 (s, Ar), 125.6 (s, Ar), 4.8 (s,
PhC(NSi(CH3)3)2), 2.8 (s, CtCSi(CH3)3). Anal. Calcd (found)
for C62H110N8Si10Y2: C, 52.21 (52.35); H, 7.77 (7.81); Y, 12.47
(12.57). Compounds 5 and 6 were prepared by a similar
procedure (1-2 g scale) and isolated as colorless crystals in
70% (5) and 77% (6) yield.
5. NMR data and elemental analysis showed that
5
P r ep a r a tion of {[P h C(NSiMe3)2]2Y(µ-CtCR)}2 (1, R )
H; 2, R ) Me). 1. Meth od a . A 100 mL Schlenk flask
charged with a solution of {[PhC(NSiMe3)2]2Y(µ-H)}2 (1.4 g,
1.1 mmol) in benzene (10 mL) was treated with acetylene (1.5
mmol) and allowed to stand for 3 days at room temperature,
upon which large colorless crystals of 1 were formed (1.1 g,
0.86 mmol, 78%).
contained 0.25 equiv of pentane/dimer in the crystal lattice.
IR (KBr/Nujol, cm-1): 3040 (w), 2912 (vs), 2857 (vs), 2049 (m),
1883 (w), 1769 (w), 1597 (w), 1576 (w), 1441 (vs), 1414 (vs),
1381 (vs), 1072 (m), 982 (m), 843 (vs), 785 (s), 756 (vs), 721
(vs), 702 (s), 689 (s), 544 (m), 482 (s), 438 (m). 1H NMR
(benzene-d6, δ): 7.92 (d, 2H, Ar), 7.48 (m, 4H, Ar), 7.07 (m,
9H, Ar), 1.23 (m, 1.5H, pentane), 0.88 (m, 1.5H, pentane), 0.16
(s, 36H, PhC(NSi(CH3)3)2). 13C NMR (benzene-d6, δ): 184.8
(s, PhC(NSiMe3)2, 143.0 (s, Ar), 141.8 (t, Y-C(tCPh)-Y, 1J Y-C
Meth od b. A 100 mL Schlenk flask charged with a solution
of [PhC(NSiMe3)2]2YCH(SiMe3)2 (1.95 g, 2.52 mmol) in benzene
(10 mL) was treated with acetylene (2.6 mmol). The flask was
allowed to stand for 3 days at room temperature, upon which
large colorless crystals of 1 were formed (1.3 g, 1.0 mmol, 80%).
IR (KBr/Nujol, cm-1): 3262 (w), 2926 (vs), 2855 (s), 1914 (w),
1445 (vs), 1387 (vs), 1242 (s), 1003 (m), 982 (s), 841 (vs), 785
(w), 760 (s), 725 (w), 700 (w), 679 (w), 482 (w). 1H NMR
(benzene-d6, δ): 7.33 (m, 4H, Ar), 7.10 (m, 6H, Ar), 3.22 (s,
1H, CtCH), 0.19 (s, 36H, PhC(NSi(CH3)3)2). 13C NMR (benzene-
d6, δ): 184.5 (s, PhC(NSiMe3)2), 146.7 (dt, Y-C(tCH)-Y, 1J Y-C
1
2
) 21 Hz), 133.7 (dt, Ar, J C-H ) 162 Hz, J C-H ) 7 Hz), 131.1
(s, CtCPh), 129.3 (dt, Ar, 1J C-H ) 158 Hz, 2J C-H ) 7 Hz), 124.6
(t, Ar, J C-H ) 9 Hz), 22.7 (t, pentane, J C-H ) 124 Hz), 14.2
(q, pentane, J C-H ) 124 Hz), 4.0 (q, PhC(NSi(CH3)3)2, J C-H
) 119 Hz). Anal. Calcd (found) for C68H112N8Si8Y2(C5H12
C, 57.60 (57.44); H, 7.40 (43); Y, 12.09 (12.25).
2
1
1
1
)
0.25
:
6. IR (KBr/Nujol, cm-1): 3057 (w), 2957 (vs), 2926 (vs), 2870
(s), 2855 (s), 2037 (m), 1443 (s), 1429 (vs), 1414 (vs), 1397 (vs),
1248 (vs), 1003 (w), 980 (s), 839 (vs), 785 (m), 758 (s), 748 (s),
721 (s), 704 (s), 480 (s), 438 (m), 415 (m). 1H NMR (benzene-
d6, δ): 7.39 (4H, Ar), 7.04 (m, 6H, Ar), 1.52 (s, 9H, C(CH3)3),
0.19 (s, 36H, PhC(NSi(CH3)3)2). 13C NMR (benzene-d6, δ):
185.7 (s, PhC(NSiMe3)2), 143.1 (s, Ar), 141.8 (t, Y-C(tC-
2
1
) 20 Hz, J C-H ) 27 Hz), 143.2 (s, Ar), 128.1 (d, Ar, J C-H
)
218 Hz), 126.5 (d, Ar, 1J C-H ) 160 Hz), 115.4 (d, CtCH, 1J C-H
) 218 Hz), 3.19 (q, PhC(NSi(CH3)3)2, J C-H ) 118 Hz). Anal.
1
Calcd (found) for C56H94N8Si8Y2: C, 52.47 (52.83); H, 7.39
(7.52); Y, 13.87 (13.91).
1
(CMe3))-Y, J Y-C ) 22 Hz), 140.2 (s, CtC(CMe3)), 128.2 (dt,
2. Compound 2 was prepared by a similar procedure from
[PhC(NSiMe3)2]2YCH(SiMe3)2 (1.00 g, 1.29 mmol) and propyne;
it was isolated as microcrystalline material (0.60 g, 0.46 mmol,
71%). IR (KBr/Nujol, cm-1): 2924 (vs), 2855 (s), 2060 (w), 1445
(vs), 1429 (vs), 1402 (vs), 1246 (s), 1005 (m), 982 (s), 843 (vs),
785 (w), 760 (s), 727 (w), 702 (w), 480 (w). 1H NMR (benzene-
d6, δ): 7.37 (m, 4H, Ar), 7.10 (m, 6H, Ar), 2.01 (s, 3H,
CtCCH3), 0.21 (s, 36H, PhC(NSi(CH3)3)2). 13C{1H} NMR
(benzene-d6, δ): 184.8 (s, PhC(NSiMe3)2), 143.3 (s, Ar), 136.0
(t, Y-C(tCMe)-Y, 1J Y-C ) 21 Hz), 128.1 (s, Ar), 126.8 (s, Ar),
8.0 (s, CtCCH3), 3.9 (s, PhC(NSi(CH3)3)2). Anal. Calcd (found)
for C58H98N8Si8Y2: C, 53.18 (53.85); H, 7.54 (7.56); Y, 13.57
(13.48).
1
1
1
Ar, J C-H ) 160 Hz, J C-H ) 7 Hz), 127.4 (dd, Ar, J C-H ) 117
1
1
Hz, J C-H ) 7 Hz), 31.8 (q, C(CH3)3, J C-H ) 126 Hz), 4.8 (q,
1
PhC(NSi(CH3)3)2, J C-H ) 119 Hz). Anal. Calcd (found) for
C
64H110N8Si8Y2: C, 55.14 (55.23); H, 7.95 (8.01); Y, 12.75
(12.82).
NMR Tu b e P r ep a r a t ion of [P h C(NSiMe3)2]2YCtCH‚
THF (7). THF (9 µL, 0.1 mmol) was added to an NMR tube
charged with 1 (15 mg, 0.023 mmol) in benzene-d6 (0.5 mL).
The 1H NMR spectrum taken after 5 min at room temperature
showed the quantitative formation of 7 and the presence of
free THF. 1H NMR (benzene-d6, δ): 7.25 (m, 4H, Ar), 7.07
(m, 6H, Ar), 3.70 (m, 17.2 H, THF-R-CH2), 1.99 (d, 1H, CtCH,

Bis(benzamidinato)yttrium Compounds
Organometallics, Vol. 15, No. 9, 1996 2301
3J Y-H ) 1.3 Hz), 1.45 (m, 17.2H, THF-â-CH2), 0.16 (s, 36H,
PhC(NSi(CH3)3)2). 13C{1H} NMR (benzene-d6, δ): 183.5 (s,
PhC(NSiMe3)2), 143.4 (s, Ar), 128.2 (s, Ar), 128.0 (s, Ar), 126.2
(s, Ar), 89.2 (d, CtCH, J Y-C ) 12 Hz), 68.4 (s, THF-R-CH2),
25.6 (s, THF-â-CH2), 2.5 (s, PhC(NSi(CH3)3)2.
constant temperature ((0.2 °C) and 1H NMR spectra were
recorded at regular time intervals until the reaction was
complete. The kinetics were monitored by following the
difference in integral of the vinylic protons of the 1-butene-3-
ynes formed and the 1-alkyne acetylenic proton. The mea-
surements were repeated at different temperatures ranging
53.0-84.0 °C. For both the dimerization of HCtCCMe3 and
HCtCSiMe3, clean first-order dependence on 1-alkyne was
observed.
1
P r ep a r a tion of [P h C(NSiMe3)2]2YCtCCMe3‚THF (8).
At room temperature, THF (50 µL, 0.62 mmol) was added to
a pentane (20 mL) solution of 6 (0.8 g, 0.57 mmol). After 10
min, the solution was concentrated until crystallization started.
Cooling to -30 °C yielded 8 (0.63 g, 0.82 mmol, 72%) as a white
microcrystalline solid. IR (KBr/Nujol, cm-1): 3061 (w), 2955
(vs), 2922 (vs), 2854 (s), 2043 (w), 2022 (w), 1446 (vs), 1431
(vs), 1410 (vs), 1366 (s), 1244 (s), 1005 (m), 984 (s), 916 (w),
841 (vs), 787 (m), 758 (s), 723 (m), 700 (m), 480 (m), 457 (w).
1H NMR (benzene-d6, δ): 7.17 (4H, Ar), 7.02 (m, 6H, Ar), 4.14
(m, 4H, THF-R-CH2), 1.44 (m, 4H, THF-â-CH2) 1.41 (s, 9H,
C(CH3)3), 0.13 (s, 36H, PhC(NSi(CH3)3)2). 13C NMR (benzene-
d6, δ): 182.8 (s, PhC(NSiMe3)2), 143.7 (s, Ar), 143.1 (s,
Y-C(tCCMe3)), 127.9 (dt, Ar, 1J C-H ) 160 Hz, 2J C-H ) 7 Hz),
P r ep a r a tion of {[P h C(NSiMe3)2]2Y2(µ-(N,N ′)-N(H)C-
(Me)dC(H)CtN)}2 (10). To a solution of [PhC(NSiMe3)2]2-
YCH(SiMe3)2 (1.5 g, 1.9 mmol) in pentane (15 mL) was added
acetonitrile (200 µL, 3.8 mmol) at room temperature. After
being stirred for 16 h at room temperature, the formed yellow
solution was concentrated until crystallization started and
cooled to -30 °C. After isolation (1.0 g), the crude product
was recrystallized from pentane (10 mL). Cooling to -30 °C
yielded 10 (0.8 g, 1.1 mmol, 60%) as large colorless crystals.
IR (KBr/Nujol, cm-1): 2953 (s), 2924 (vs), 2854 (s), 2152 (s),
1523 (s), 1429 (vs), 1313 (m), 1246 (s), 1180 (m), 1074 (w), 1030
(w), 1004 (m), 986 (s), 920 (m), 839 (vs), 785 (m), 760 (s), 731
(m), 702 (s), 684 (m), 638 (w), 569 (w), 482 (m), 414 (w). 1H
NMR (benzene-d6, δ): 7.22 (m, 4H, Ar), 7.03 (m, 6H, Ar), 6.84
(s, 1H, NH), 3.50 (s, 1H, CH), 2.16 (s, 3H, CH3), 0.16 (s, 36H,
PhC(NSi(CH3)3)2. 13C NMR (benzene-d6, δ): 183.6 (s, PhC(N-
SiMe3)2), 179.1 (s, CtN), 143.2 (s, Ar), 131.3 (d, C(CH3)dC,
2J Y-C ) 5 Hz), 128.1 (d, Ar, 1J C-H ) 161 Hz), 126.3 (d, Ar, 1J C-H
1
2
127.8 (dd, Ar, J C-H ) 160 Hz, J C-H ) 7 Hz), 126.2 (dt, Ar,
1J C-H ) 160 Hz; 2J C-H ) 7 Hz), 111.1 (d, Y-C(tCCMe3), 1J Y-C
1
) 11 Hz), 71.1 (t, THF-R-CH2, J C-H ) 150 Hz), 32.7 (q,
1
C(CH3)3, J C-H ) 126 Hz), 28.1 (s, CMe3), 25.3 (t, THF-â-CH2,
1J C-H ) 133 Hz), 2.56 (q, PhC(NSi(CH3)3)2, J C-H ) 118 Hz).
1
Anal. Calcd (found) for C36H63N4OSi4Y: C, 56.22 (56.31); H,
8.26 (8.34); Y, 11.56 (11.65).
P r epar ation of [P h C(NSiMe3)2]2Y(µ-CtCCMe3)2Li‚TME-
DA‚h exa n e (9). To a solution of [PhC(NSiMe3)2]2Y(µ-Me)2-
Li‚TMEDA (1.4 g, 1.8 mmol) in ether (40 mL) was added 3,3-
dimethyl-1-butyne (0.45 mL, 3.7 mmol). After 16 h at room
temperature, the solution was concentrated until crystalliza-
tion started and cooled to -30 °C. Yield: 1.4 g (1.4 mmol,
75%) of 9 as large colorless crystals. NMR data showed that
9 contains 1 equiv of hexane in the crystal lattice. IR (KBr/
Nujol, cm-1): 2956 (vs), 2934 (vs), 2826 (vs), 2047 (m), 1460
(vs), 1454 (vs), 1379 (s), 1290 (m), 1242 (s), 1036 (w), 1022 (w),
1005 (m), 984 (s), 949 (m), 847 (s, br), 785 (s), 756 (s), 735 (s),
702 (s), 683 (m), 602 (m), 478 (m), 421 (m). 1H NMR (benzene-
d6, δ): 7.42 (m, 4H, Ar), 7.14 (m, 6H, Ar), 2.33 (s, 12H,
TMEDA-CH3), 2.02 (s, 4H, TMEDA-CH2), 1.40 (s, 18H, C(CH3)3),
0.87 (m broad, 14H, hexane), 0.26 (s, 36H, PhC(NSi(CH3)3)2.
13C NMR (benzene-d6, δ): 182.3 (s, PhC(NSiMe3)2), 144.2 (s,
1
1
) 159 Hz), 48.1 (d, CH, J C-H ) 175 Hz), 25.1 (qd, CH3, J C-H
3
1
) 127 Hz, J Y-C ) 10 Hz), 2.5 (q, PhC(NSi(CH3)3)2, J C-H
)
118 Hz). Anal. Calcd (found) for C60H102N12Si8Y2: C, 51.70
(51.64); H, 7.38 (7.44); Y, 12.75 (12.78).
NMR Tu be Rea ction of [P h C(NSiMe3)2]2YCH2P h ‚THF
w ith NtCMe. To an NMR tube containing a solution of [PhC-
(NSiMe3)2]2YCH2Ph‚THF (21 mg, 0.027 mmol) in benzene-d6
(0.5 mL) was added acetonitrile (3 µL, 0.05 mmol) at room
temperature. The 1H NMR spectrum taken after 10 min at
room temperature showed that all [PhC(NSiMe3)2]2YCH2Ph‚
THF had reacted, yielding a mixture of compounds: 10 (10%),
{[PhC(NSiMe3)2]2Y(µ-NdC(Me)CH2Ph)}2 (11a , 50%), {[PhC-
(NSiMe3)2]2Y(µ-NHC(Me)dC(H)Ph)}2 (11b, 40%), and uncoor-
1
2
Ar), 127.8 (dd, Ar, J C-H ) 162 Hz, J C-H ) 6 Hz), 127.4 (d,
1
dinated THF. A H NMR spectrum recorded after 2 days at
1
1
Ar, J C-H ) 160 Hz), 126.6 (d, Ar, J C-H ) 166 Hz), 121.1 (d,
room temperature showed no changes. 1H NMR (benzene-d6)
for 11a : 3.47 (s, 2H, CH2), 1.86 (s, 3H, CH3), 0.07 (s, 36H,
PhC(NSi(CH3)3)2). 1H NMR (benzene-d6, δ) for 11b: 6.60 (s,
1H, NH), 4.78 (s, 1H, CH), 2.16 (s, 3H, CH3), 0.16 (s, 36H, PhC-
(NSi(CH3)3)2).
1
1
Y-C, J Y-C ) 15 Hz), 57.1 (t, TMEDA-CH2, J C-H ) 134 Hz),
46.9 (q, TMEDA-CH3, 1J C-H ) 134 Hz), 32.4 (q, C(CH3)3, 1J C-H
1
) 126 Hz), 3.3 (q, PhC(NSi(CH3)3)2, J C-H ) 118 Hz). The
hexane from the crystal lattice could be removed by heating
the compound in vacuo at 50 °C, leaving an amorphous white
solid. Anal. Calcd (found) for C44H85LiN6Si4Y: C, 58.31
(58.39); H, 9.45 (9.51); Y, 9.81 (9.92).
NMR Tu be P r ep a r a tion of {[P h C(NSiMe3)2]2Y(µ-NdC-
(H)Me)}2 (12). To an NMR tube containing a benzene-d6 (0.5
mL) solution of {[PhC(NSiMe3)2]2Y(µ-H)}2 (20 mg, 0.032 mmol)
was added NtCMe (1.8 µL, 0.03 mmol). The 1H NMR
spectrum monitored directly after the NMR tube was filled
showed resonances characteristic for {[PhC(NSiMe3)2]2Y(µ-
NdC(H)Me)}2 (12), δ 9.3 (m, 1H, NdC(H)Me), 7.28 (m, 4H,
Ca ta lytic Dim er iza tion of Alk yn es HCtCR (R ) P h ,
CMe3, SiMe3). Alkynes (100 µL, 0.9-0.7 mmol) were added
to NMR tubes charged with benzene-d6 solutions (0.5 mL) of
[PhC(NSiMe3)2]2YCH(SiMe3)2 or {[PhC(NSiMe3)2]2Y(µ-R)}2 (R
) H, CtCR′; R′ ) Ph, CMe3, SiMe3) (0.015-0.025 mmol). The
1H NMR spectra collected after 1.5 h at 80 °C indicated the
nearly quantitative formation of the 1-buten-3-ynes, the pres-
ence of some traces of unreacted 1-alkyne and characteristic
resonances of {[PhC(NSiMe3)2]2Y(µ-CtCR)}2 (4-6). Nt(80 °C)
) 20-40 mol‚mol-1‚ h-1. For the dimerization of HCtCMe3,
catalyzed by 8 (0.02 mmol of 8, 100 µL of HCtCCMe3, 0.5 mL
of benzene-d6), the 1H NMR spectra collected after 1 h at 80
°C showed the presence of H2CdC(CMe3)CtCCMe3, reso-
nances attributable to 8, and considerable amounts of unre-
acted HCtCCMe3 (Nt(80 °C) ≈ 1 mol‚mol-1‚h-1).
3
Ar), 7.08 (m, 6H, Ar), 2.40 (d, NdC(H)CH3, J H-H ) 3.4 Hz),
and 0.11 (s, 36H, PhC(NSi(CH3)3)2, and uncoordinated THF.
Compound 12 is unstable and decomposes within 1 h at room
temperature to form a mixture of unidentified products.
NMR Tu be Rea ction of [P h C(NSiMe3)2]2YCH(SiMe3)2
w ith P yr id in e. Pyridine (6.6 µL, 0.08 mmol) was added to
an NMR tube charged with 25 mg (0.032 mmol) of [PhC-
(NSiMe3)2]2YCH(SiMe3)2 in benzene-d6 (0.5 mL). The reaction
1
was followed by H NMR. At room temperature, no reaction
occurred. The NMR tube was warmed to 50 °C, upon which
the solution changed from colorless to red. After 1 week at
50 °C, the 1H NMR spectrum showed that all [PhC(NSiMe3)2]2-
YCH(SiMe3)2 had reacted. Besides resonances of H2C(SiMe3)2,
several resonances in the vinyllic (4-6 ppm) and aromatic
(7-9 ppm) regions were present.
NMR Kin etic Exp er im en ts for th e Ca ta lytic Dim er -
iza tion of HCtCCMe3 a n d HCtCSiMe3. In a typical
kinetics experiment, an NMR tube was charged with
a
standard solution of [PhC(NSiMe3)2]2YCH(SiMe3)2 (0.17 mM)
in benzene-d6 (0.7 mL) and 1-alkyne (100 µL, 0.7-0.8 mmol).
After the NMR tube was filled and sealed, it was kept at

2302 Organometallics, Vol. 15, No. 9, 1996
Duchateau et al.
1
1
NMR Tu b e P r ep a r a t ion of [P h C(NSiMe3)2]2YNC5H 6
(13). Pyridine (2.6 µL, 0.032 mmol) was added at room
temperature to a solution of {[PhC(NSiMe3)2]2Y(µ-H)}2 (10 mg,
0.016 mmol) in benzene-d6 (0.5 mL). Upon addition, the
solution changed from colorless to yellow. The reaction
mixture was transferred into an NMR tube, and a 1H NMR
spectrum was recorded. This showed that all {[PhC(NSi-
Me3)2]2Y(µ-H)}2 had reacted under formation of exclusively the
1,2-insertion product [PhC(NSiMe3)2]2YNC5H6 (13). 1H NMR
(benzene-d6, δ): 6.54 (dd, 1H, H4 NC5H6, 3J H-H ) 9.0 Hz, 3J H-H
(d, CH NC5H4, J C-H ) 160 Hz), 94.9 (dd, CH NC5H4, J C-H
)
167 Hz, 3J C-H ) 6 Hz), 55.4 (dt, C(H)CH2Ph, 1J C-H ) 34.7 Hz,
3J C-H ) 6 Hz), 41.6 d, CH2, J C-H ) 29 Hz), 2.5 (q, PhC(NS-
1
1
(CH3)3)2, J C-H ) 119 Hz).
P r epar ation of [P h C(NSiMe3)2]2Y(η2-(C,N)-CH2-2-NC5H4)
(15). To a solution of [PhC(NSiMe3)2]2YCH2Ph‚THF (1.4 g,
1.8 mmol) in toluene (20 mL) was added R-picoline (180 µL,
1.8 mmol) at room temperature. After 4 h, the volatiles were
removed in vacuo and the remaining orange oil was stripped
with pentane (3 × 5 mL), but the product did not solidify. The
1H and 13C NMR spectra of the crude product (1.2 g, 1.5 mmol,
84%) showed traces of [PhC(NSiMe3)2]2YCH2Ph‚THF and
R-picoline among the contaminations. Since crystallization,
sublimation, and vacuum distillation failed, the product could
not be isolated analytically pure. 1H (benzene-d6, δ): 7.92 (d,
3
3
) 8.6 Hz), 5.44 (ddd, 1H, H5 NC5H6, J H-H ) 5.6 Hz, J H-H
)
4
3
6.0 Hz, J H-H ) 2.4 Hz), 5.22 (dt, 1H, H3 NC5H6, J H-H ) 9.4
Hz, 3J H-H ) 4.3 Hz), 4.52 (d, 2H, H2, H2′, NC5H6, 2J H-H ) 4.3
Hz), 0.04 (s, 36H, PhC(NSi(CH3)3)2).
P r ep a r a tion of [P h C(NSiMe3)2]2YNC5H5-2-CH2P h (14).
Pyridine (0.15 mL, 1.8 mmol) was added at room temperature
to a solution of [PhC(NSiMe3)2]2YCH2Ph‚THF (1.3 g, 1.7 mmol)
in toluene (10 mL). The yellow reaction mixtrure formed was
stirred for 5 h, after which the solvent was evaporated. The
remaining oil was stripped (3 × 5 mL) with pentane. Removal
3
1H, Ar, J H-H ) 5.6 Hz), 7.30 (m, 4H, Ar), 7.02 (m, 6H, Ar),
3
3
6.87 (ddd, 1H, H4 NC5H4, J H-H ) 8.6 Hz, J H-H ) 7.1 Hz,
4J H-H ) 1.2 Hz), 6.68 (d, 1H, H3 NC5H4, 3J H-H ) 8.3 Hz), 6.07
3
3
(dd, 1H, H5 NC5H4, J H-H ) 6.8 Hz, J H-H ) 5.6 Hz), 2.71 (d,
2
2H, YCH2, J Y-H ) 0.9 Hz), 0.05 (s, 36H, PhC(NSi(CH3)3)2).
1
13C NMR (benzene-d6, δ): 183.8 (s, PhC(NSiMe3)2), 166.3 (s,
of all volatiles in vacuo resulted in a sticky oil. The H NMR
1
spectrum of the oil showed that 14 had been formed in 90%
yield. Purification by sublimation or vacuum distillation failed
and exclusively resulted in decomposition of the product. 1H
NMR (benzene-d6, δ): 7.02 (m, 1H, H6), 6.44 (dd, 1H, H4, 3J H-H
NC5H4), 146.3 (d, NC5H4, J C-H ) 172 Hz), 135.6 (dd, NC5H4,
1J C-H ) 158 Hz, J C-H ) 7 Hz), 127.7 (d, Ar, J C-H ) 161 Hz),
3
1
1
1
126.3 (d, Ar, J C-H ) 157 Hz), 120.4 (d, Ar, J C-H ) 163 Hz),
106.9 (d, Ar, 1J C-H ) 163 Hz), 52.4 (dt, YCH2, 1J C-H ) 143 Hz,
3
3
1J Y-H ) 6 Hz), 2.6 (q, PhC(NSi(CH3)3)2, J C-H ) 118 Hz).
1
) 9.0 Hz, J H-H ) 8.6 Hz), 5.27 (dd, 1H, H5, J H-H ) 6.0 Hz,
3J H-H ) 4.7 Hz), 5.20 (dt, 1H, H3, 3J H-H ) 6.0 Hz, 4J H-H ) 2.6
Hz), 4.93 (dt, 1H, H2, J H-H ) 6.0 Hz, J H-H ) 5.1 Hz), 3.91
(d, 1H, C(H)H, J H-H ) 11.5 Hz, J H-H ) 11.0 Hz), 2.74 (dd,
1H C(H)H, J H-H ) 12.0 Hz, J H-H ) 8.1 Hz), 0.07 (s, 36H,
PhC(NSi(CH3)3)2). 13C NMR (benzene-d6, δ): 183.9 (s, PhC(N-
SiMe3)2), 143.1 (s, ipso-C), 140.4 (d, Ar, 1J C-H ) 161 Hz), 107.2
3
3
Ack n ow led gm en t. This work was financially sup-
ported by Shell Research B.V. Amsterdam, which is
gratefully acknowledged.
2
3
1
3
OM9508142