Insertion of isocyanides into tantalum-methyl and tantalum-amido bonds

Article abstract of DOI:10.1021/om000194r

The imido-amido complex [TaCp*(N^tBu)Cl(NH^tBu)], 1, was isolated from the reaction of [TaCp*Cl₄] with 3 equiv of LiNH^tBu. The dimethyl [TaCp*(N^tBu)Me₂], 2, and chloro-methyl [TaCp*(N^tBu)ClMe], 3, complexes were obtained by methylation of [TaCp*(N^tBu)Cl₂] with 2 equiv of LiMe and 1 equiv of ZnMe₂, respectively. Metathetical reactions of complex 3 with alkali metal salts MX (M = Na, X = OMe; M = Li, X = O^tBu, NH^tBu) afforded the new imido-methyl compounds [TaCp*(N^tBu)MeX] (X = OMe 4, O^tBu 5, NH^tBu 6). Insertion of CNR (R = 2,6-Me₂C₆H₃) into the Ta-NH_tBu and Ta-Me bonds of the imido-pentamethylcyclopentadienyl complexes 1-6 gave the η²-iminocarbamoyl compound [TaCp*(N^tBu)Cl-{η²-C(NH^tBu)=NR}], 7, and the η²-iminoacyl compounds [TaCp*(N_tBu)X{η²-C(Me)=NR}] (X = Me 8, Cl 9, OMe 10, O^tBu 11, NH^tBu 12), which under appropriate thermal conditions react with a second equivalent of CNR (R = 2,6-Me₂C₆H₃) to give the double insertion imine-η²-iminoacyl products [TaCp*(N^tBu)X{η²-C[C(Me)=NR]=NR}] (X = Me 13, Cl 14, OMe 15, O^tBu 16, NH^tBu 17). When compound 17 was heated at 140 °C for 3 days, an intramolecular proton migration occurred to give the η²-diamidoalkene complex [TaCp*(N_tBu){η-N^tBu-C(NHR)=C(Me)-η-NR}], 18. All of the new compounds were characterized by IR, ¹H NMR, and ¹³C NMR spectroscopy, and the molecular structures of 14 and 18 were studied by X-ray diffraction methods.

Full text of DOI:10.1021/om000194r

Organometallics 2000, 19, 3161-3169
3161
In ser tion of Isocya n id es in to Ta n ta lu m -Meth yl a n d
Ta n ta lu m -Am id o Bon d s
J avier Sa´nchez-Nieves,† Pascual Royo,*,† Maria Angela Pellinghelli,‡ and
Antonio Tiripicchio‡
Departamento de Quı´mica Inorga´nica, Universidad de Alcala´, Campus Universitario, Edificio
de Farmacia, 28871 Alcala´ de Henares, Spain, and Dipartimento di Chimica Generale ed
Inorganica, Chimica Analitica, Chimica Fisica, Universita` di Parma, Centro di Studio per la
Strutturistica Diffrattometrica del CNR, Parco Area delle Scienze 17A, I-43100 Parma, Italy
Received February 29, 2000
The imido-amido complex [TaCp*(NtBu)Cl(NHtBu)], 1, was isolated from the reaction of
[TaCp*Cl4] with 3 equiv of LiNHtBu. The dimethyl [TaCp*(NtBu)Me2], 2, and chloro-methyl
[TaCp*(NtBu)ClMe], 3, complexes were obtained by methylation of [TaCp*(NtBu)Cl2] with
2 equiv of LiMe and 1 equiv of ZnMe2, respectively. Metathetical reactions of complex 3
with alkali metal salts MX (M ) Na, X ) OMe; M ) Li, X ) OtBu, NHtBu) afforded the new
imido-methyl compounds [TaCp*(NtBu)MeX] (X ) OMe 4, OtBu 5, NHtBu 6). Insertion of
CNR (R ) 2,6-Me2C6H3) into the Ta-NHtBu and Ta-Me bonds of the imido-pentameth-
ylcyclopentadienyl complexes 1-6 gave the η2-iminocarbamoyl compound [TaCp*(NtBu)Cl-
{η2-C(NHtBu)dNR}], 7, and the η2-iminoacyl compounds [TaCp*(NtBu)X{η2-C(Me)dNR}]
(X ) Me 8, Cl 9, OMe 10, OtBu 11, NHtBu 12), which under appropriate thermal conditions
react with a second equivalent of CNR (R ) 2,6-Me2C6H3) to give the double insertion imine-
η2-iminoacyl products [TaCp*(NtBu)X{η2-C[C(Me)dNR]dNR}] (X ) Me 13, Cl 14, OMe 15,
OtBu 16, NHtBu 17). When compound 17 was heated at 140 °C for 3 days, an intramolecular
proton migration occurred to give the η2-diamidoalkene complex [TaCp*(NtBu){η-NtBu-
1
C(NHR)dC(Me)-η-NR}], 18. All of the new compounds were characterized by IR, H NMR,
and 13C NMR spectroscopy, and the molecular structures of 14 and 18 were studied by X-ray
diffraction methods.
In tr od u ction
However, very few examples of this type of reaction have
been reported for tantalum. An important study5b by
Rothwell et al. describes the isolation of adducts con-
taining two coupled isocyanides to give diazametalla-
cycles with exocyclic ketene-imine or phosphine ligands
bound to the electrophilic isocyanide carbon atom.
The insertion of CO and CNR into early transition
metal-amido bonds has been less intensively studied,
although participation of the analogous η2-carbamoyl
complexes in intramolecular alkylations and inter- and
intramolecular coupling reactions, to give the amino
counterparts of the dialkyl-η2-imino and enediamido
ligands, respectively, are important and potentially
useful reactions that open new horizons in synthetic
applications based on C-N bond formation processes.1,6
We reported the insertion of isocyanides into the
tantalum-methyl bonds of various η5-pentamethylcy-
clopentadienyl chloro methyl tantalum complexes7 to
Migratory insertion of carbon monoxide or isocyanides
into M-X bonds (X ) alkyl, hydrido, silyl, amido,
phosphido) is one of the most exciting fields of research
in organometallic chemistry because of the reactivity
of the resulting products and their involvement in many
stoichiometric and catalytic applications.1 The insertion
of isocyanides into early transition metal-alkyl bonds
has been extensively studied in recent years because
the resulting η2-iminoacyl compounds are much more
accessible and less reactive than the related η2-acyl
derivatives. Moreover, while further insertion of CO into
the metal-carbon bond of η2-acyl compounds is less
known, insertion of isocyanides into metal-iminoacyl
bonds has been observed, and many examples of the
double insertion of isocyanides into the metal-carbon
bond of η2-iminoacyl ligands have been reported.1-5
* Corresponding author. Tel: 34-1-8854765. Fax: 34-1-8854683.
E-mail: proyo@inorg.alcala.es.
(5) (a) Clark, J . R.; Fanwick, P. E.; Rothwell, I. P. J . Chem. Soc.,
Chem. Commun. 1993, 1233. (b) Clark, J . R.; Fanwick, P. E.; Rothwell,
I. P. Organometallics 1996, 15, 3232. (c) Gerlach, C. P.; Arnold, J . J .
Chem. Soc., Dalton Trans. 1997, 4795.
(6) (a) Yin, X.; Moss, J . R. Coord. Chem. Rev. 1999, 181, 27. (b)
Holland, P. L.; Andresen, R. A.; Bergman, R. G. J . Am. Chem. Soc.
1996, 118, 1092.
† Universidad de Alcala´.
‡ Universita` di Parma.
(1) Durfee, L. D.; Rothwell, I. P. Chem. Rev. 1988, 88, 1059.
(2) (a) Filippou, A. C.; Gru¨nleitner, W.; Vo¨lkl, C.; Kiprof, P. J .
Organomet. Chem. 1991, 413, 181. (b) Filippou, A. C.; Vo¨lkl, C.; Kiprof,
P. J . Organomet. Chem. 1991, 415, 375.
(3) Carmona, E.; Mar´ın, J . M.; Palma, P.; Poveda, M. L. J . Orga-
nomet. Chem. 1989, 377, 157.
(4) (a) Berg, F. J .; Petersen, J . L. Organometallics 1989, 8, 2461.
(b) Berg, F. J .; Petersen, J . L. Organometallics 1991, 10, 1599. (c)
Valero, C.; Greh, M.; Wingbermu¨hle, D.; Kloppenburg, L.; Carpenetti,
D.; Erker, G.; Petersen, J . L. Organometallics 1994. 13, 415.
(7) a) Galakhov, M. V.; Go´mez, M.; J ime´nez, G.; Royo, P.; Pelling-
helli, M. A.; Tiripicchio, A. Organometallics 1994, 13, 1564. (b)
Galakhov, M. V.; Go´mez, M.; J ime´nez, G.; Royo, P.; Pellinghelli, M.
A.; Tiripicchio, A. Organometallics 1995, 14, 1901. (c) Galakhov, M.
V.; Go´mez, M.; J ime´nez, G.; Royo, P.; Pellinghelli, M. A.; Tiripicchio,
A. Organometallics 1995, 14, 2843.
10.1021/om000194r CCC: $19.00 © 2000 American Chemical Society
Publication on Web 07/11/2000

3162 Organometallics, Vol. 19, No. 16, 2000
Sa´nchez-Nieves et al.
Sch em e 1a
a
Legend: (i) 3 LiNHtBu, Et2O, 12 h; (ii) LiNHtBu, Et2O; (iii) 2 LiMe, Et2O, 4 h; (iv) ZnMe2, toluene, 12 h; (v) MX (M ) Li, X
) OtBu, NHtBu; M ) Na, X ) OMe), Et2O.
Sch em e 2
give azatantalacyclopropane derivatives, which were
then converted into their imido and vinylamido com-
pounds by further reactions with isocyanide. More
recently we also reported the reactivity of related imido
methyl-tantalum8 and benzyl-niobium9 compounds in
similar carbon monoxide and isocyanide insertion reac-
tions.
In this paper we report the synthesis of new methyl-
and amido-tantalum complexes containing the imido
η5-pentamethylcyclopentadienyl tantalum moiety and
the insertion of 2,6-dimethylphenylisocyanide into their
tantalum-alkyl and tantalum-amido bonds to give new
products resulting from single and double insertion
reactions.
Resu lts a n d Discu ssion
The reactivity of a metal-alkyl bond to migratory
insertion of CO or isocyanides and the stability of the
resulting η2-acyl and η2-iminoacyl products are greatly
influenced by the nature of the other substituents on
the metal. We reported8 that insertion of CO into the
Ta-Me bond of complexes of the type [Ta]MeX, where
[Ta] ) [TaCp*{N(2,6-Me2C6H3)}], gave enediolate de-
rivatives when X ) Me, whereas it resulted in exchange
of the imido group by the oxo group with formation of
the oxo-η2-iminoacyl derivative when X ) Cl. This
moved us to study related reactions with isocyanide
using different X substituents in order to compare their
behavior. The migratory insertion in all of these for-
mally 16-electron compounds proceeds by coordination
of the isocyanide and further migration of methyl to the
electrophilic isocyanide carbon atom to give the imino-
acyl derivative, which is then η2-coordinated to complete
the 18-electron configuration. The reactivity should thus
be influenced by the acidity of the metal center, which
can be modified by the electron-releasing and π-bond-
donating capacity of the X substituent as well as by its
steric demand. To study the influence of different X
substituents, we isolated some new [TaCp*(NtBu)MeX]
complexes to complete a series together with the already
reported10 dimethyl complex [TaCp*(NtBu)Me2].
starting material. Methylation10 of the dichloro com-
pound [TaCp*(NtBu)Cl2] with 2 equiv of LiMe gave the
dimethyl derivative [TaCp*(NtBu)Me2], 2, whereas se-
lective monoalkylation to give [TaCp*(NtBu)ClMe], 3,
resulted when 1 equiv of ZnMe2 was used as the
alkylating agent (Scheme 1). Metathetical replacement
of the chloro group by different substituents was achieved
by reaction of complex 3 with 1 equiv of lithium (OtBu,
NHtBu) or sodium (OMe) MX salts to give the new
compounds [TaCp*(NtBu)MeX] (X ) OMe 4, OtBu 5,
NHtBu 6).
The amido compound 1 and all of the new methyl
complexes 3-6 were isolated as air-sensitive yellow-
brown oils, thermally stable for long periods under a
dry inert atmosphere (N2, Ar) at room temperature.
1
They were identified as pure compounds by H and 13C
The new imido-amido derivative [TaCp*(NtBu)Cl-
(NHtBu)], 1, obtained from the reaction of [TaCp*Cl4]
with 3 equiv of LiNHtBu in ethyl ether was used as a
NMR spectroscopy, although not entirely satisfactory
analytical data were obtained for compounds 1 and 4-6
(see Experimental Section).
Reaction of the amido complex 1 with 1 equiv of the
isocyanide CNR (R ) 2,6-Me2C6H3) in hexane afforded
the η2-iminocarbamoyl compound [TaCp*(NtBu)Cl{η2-
C(NHtBu)dNR}], 7, and similar reactions of the methyl
derivatives gave the η2-iminoacyl compounds [TaCp*-
(8) Go´mez, M.; Go´mez-Sal, P.; J ime´nez, G.; Mart´ın, A.; Royo, P.;
Sa´nchez-Nieves, J . Organometallics 1996, 15, 3579.
(9) Alcalde, M. I.;. Go´mez-Sal, P.; Mart´ın, A.; Royo, P. Organome-
tallics 1998, 17, 1144.
(10) Schmidt, S.; Sundermeyer, J . J . Organomet. Chem. 1994, 472,
127.

Insertion of Isocyanides
Organometallics, Vol. 19, No. 16, 2000 3163
(NtBu)X{η2-C(Me)dNR}] (X ) Me 8, Cl 9, OMe 10, Ot-
Bu 11, NHtBu 12) (see Scheme 2).
Sch em e 3
Insertion into the Ta-Me bond is almost immediate
at room temperature for methyl 2, chloro 3, and methoxo
4 derivatives, although complex 10 could not be obtained
free of a small amount of 4 and 15 (see below). Clearly,
the presence of potential π-donor ligands such as Cl or
OMe, which have the capacity to block the empty metal
orbital required to allow the isocyanide to coordinate,
does not significantly influence the insertion reaction.
However, the insertion reaction using the tert-butyloxo
complex 5 was significantly slower and 11 was obtained
after stirring for 7 h at room temperature. Heating the
amido complex 6 with 1 equiv of CNR for 3 days at 75
°C in C6D6 resulted in only partial formation of 12,
which could not be isolated, as evidenced by 1H and 13C
NMR. This behavior indicates that the higher steric
demand of the more bulky tBu substituent in the alkoxo
5 and amido 6 ligands hinders coordination of the
isocyanide and slows down the insertion process. Inser-
tion into the Ta-NHtBu bond of 1 was slower than
insertion into the Ta-Me bond of 3, and the quantita-
tive transformation required 7 h stirring at room
temperature. Furthermore, in complex 6, which has
both Ta-Me and Ta-NHtBu bonds, the insertion reac-
tion occurred preferentially at the Ta-Me bond, indicat-
ing a higher activation energy for insertion into the
Ta-N bond.
identical conditions, giving white to yellow solids identi-
fied as the double insertion imine-η2-iminoacyl prod-
ucts [TaCp*(NtBu)X{η2-C[C(Me)dNR]dNR}] (X ) Me
13, Cl 14, OMe 15, OtBu 16, NHtBu 17) by elemental
1
analyses, H and 13C NMR spectroscopy, and a molec-
ular structure determination of 14. This reaction is
rapid for complex 10, which was easily and completely
converted into 15 at room temperature. This rapid
transformation explains how small amounts of 15 are
formed even when a 1:1 molar ratio of the isocyanide
was used. However the same reaction is much slower
and was not observed at room temperature for any of
the other complexes, their solutions required heating
in sealed tubes under various conditions to effect the
transformation. Compound 8 was the most reactive
species and was quantitatively transformed into 13 after
14 h at 120 °C, whereas 9 and 11 required 3 days at
150 °C and 2 days at 120 °C, respectively. 17 was
obtained after heating 6 with 2 equiv of CNR for 3 days
at 75 °C.
NMR evidence suggests that the iminoacyl ligand in
all of these compounds is coordinated in an η2 fashion,
probably with the nitrogen atom occupying the central
position in the equatorial plane.11 The 13C resonance
observed between δ 243 and δ 253 is consistent with
1
an iminoacyl sp2 carbon atom, while the H resonance
of the inserted methyl group observed between δ 2.40
and δ 2.56 is displaced to low field. The 13C resonance
of the η2-iminocarbamoyl sp2 carbon atom in complex 7
at δ 203.1 indicated an even more significant effect
attributable to the presence of the more nucleophilic
amino substituent. The ν(CN) IR stretching vibration
is lower for the η2-iminocarbamoyl complex 7 (1540
cm-1) than for the η2-iminoacyl compounds (1616-1597
cm-1), indicating that the different electron distribution
in 7 modifies the CdN bond order.
The η2-iminoacyl compounds 8-11 are air stable,
whereas the η2-iminocarbamoyl derivative 7 is air
sensitive and must be manipulated under an inert
atmosphere. Complexes 7-11 are all very soluble in the
usual organic solvents and most are thermally stable,
with the exception of 7, which decomposes when heated
above 120 °C. Complex 12 also decomposes by heating
at 90 °C. We reported that when the related methyl-
iminoacyl complexes were heated, a double migration
of the methyl group occurred to give η2-imino deriva-
tives;7 a similar transformation did not occur when 8
was heated. However a further double insertion into the
Ta-iminoacyl bond was observed (see Scheme 2) when
complexes 8-11 were treated with an additional 1 equiv
of the isocyanide CNR (R ) 2,6-Me2C6H3) or when 2
equiv of CNR was added to compounds 2-6 under
These results cannot be explained by the coordination
of the isocyanide at the electrophilic carbon of the η2-
iminoacyl ligand observed by Rothwell et al.,5b which
would lead to an amido keteneimine compound. The
alternative pathway proposed for this reaction is shown
in Scheme 3.
The initial transformation of the η2-iminoacyl complex
into the 16-electron η1-iminoacyl species with coordina-
tion of the isocyanide to the metal center, followed by
migration of the η1-iminoacyl ligand, would give an
imine-η1-iminoacyl derivative. The results observed
indicate that this reaction is favored by the presence of
π-donor ligands such as OMe, which enhance the
transformation of η2- into η1-iminoacyl and favor coor-
dination of the isocyanide. However the steric demands
of bulky substituents also have an important influence
and would justify the lower reactivity observed for the
OtBu derivative. Further η2-coordination of the imine-
η1-iminoacyl ligand takes place through the â-nitrogen
to give the imine-η2-iminoacyl compound. Under our
experimental conditions we have never observed the
incorporation of a third isocyanide when excess isocya-
nide was used, as evidenced by the elemental analyses
of the isolated compounds. This can probably be at-
tributed to both the steric demands of the ligand and
the fact that the temperatures the reaction would
require would cause decomposition, which occurs at 130
°C for 13, 160 °C for 14, 130 °C for 15, 170 °C for 16,
and 90 °C for 17. We did not study reactions with less
(11) (a) J ordan, R. F.; Chodosh, D. F. Inorg. Chem. 1978, 17, 41. (b)
Erker, G. Acc. Chem. Res. 1984, 17, 103. (c) Chamberlain, L. R.; Durfee,
L. D.; Fanwick, P. E.; Kobriger, L.; Latesky, S. L.; McMullen, A. K.;
Rothwell, I. P.; Folting, K.; Huffman, J . C.; Streib, W. E.; Wang, R. J .
Am. Chem. Soc. 1987, 109, 390.

3164 Organometallics, Vol. 19, No. 16, 2000
Sa´nchez-Nieves et al.
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) w ith Esd ’s in P a r en th eses for Com p ou n d 14a
Ta-Cl
2.405(5)
1.790(15)
2.161(14)
2.14(2)
2.15(2)
2.060(14)
2.44(2)
Ta-C(4)
2.52(2)
2.53(2)
1.43(3)
1.25(2)
1.44(2)
1.47(2)
1.24(2)
1.41(2)
1.51(3)
Ta-N(3)
Ta-N(1)
Ta-C(19)
Ta-CE(1)
Ta-M(1)
Ta-C(1)
Ta-C(2)
Ta-C(3)
Ta-C(5)
N(3)-C(30)
N(1)-C(19)
N(1)-C(11)
C(19)-C(20)
N(2)-C(20)
N(2)-C(21)
C(20)-C(29)
2.38(2)
2.41(2)
CE(1)-Ta-Cl
CE(1)-Ta-N(3)
CE(1)-Ta-M(1)
Cl-Ta-N(3)
107.2(5) N(3)-Ta-C(19)
122.2(8) Ta-N(1)-C(19)
118.6(7) Ta-N(1)-C(11)
100.2(6) C(11)-N(1)-C(19)
100.8(5) Ta-C(19)-N(1)
104.3(7) Ta-C(19)-C(20)
124.6(6) N(1)-C(19)-C(20)
99.5(7)
72.4(11)
156.4(12)
130.2(15)
73.9(10)
159.6(15)
126.5(17)
120.1(16)
Cl-Ta-M(1)
N(3)-Ta-M(1)
CE(1)-Ta-N(1)
CE(1)-Ta-C(19) 110.4(7) C(19)-C(20)-N(2)
N(1)-Ta-C(19)
Cl-Ta-N(1)
Cl-Ta-C(19)
N(3)-Ta-N(1)
F igu r e 1. ORTEP view of the molecular structure of the
complex 14 with the atom-numbering scheme. The thermal
ellipsoids are drawn at the 30% probability level.
33.6(6) C(19)-C(20)-C(29) 113.6(16)
84.1(4) N(2)-C(20)-C(29)
117.7(5) C(20)-N(2)-C(21)
107.8(7) Ta-N(3)-C(30)
126.3(17)
123.4(16)
174.7(17)
bulky or more electrophilic isocyanides, which could lead
to further insertions,4 coupling,5,12 or polymerization13
processes.
a
CE(1) is the centroid of the C(1)‚‚‚C(5) cyclopentadienyl ring
and M(1) the midpoint of the N(1)-C(19) double bond.
The 13C NMR spectra observed for compounds 13-
17 are consistent with their formulation as compounds
containing the imine-η2-iminoacyl ligand. They showed
one resonance between δ 238.2 and δ 247.2 due to the
metal-coordinated iminoacyl carbon, which is sensitive
to the nature of the other metal substituents, and one
resonance between δ 168.6 and δ 173.2 due to the
noncoordinated imino carbon, which is much less sensi-
tive to the metal substituents. Higher field resonances
with less diverse chemical shifts would be expected for
cyclic imino-η-alkyl-η-imine compounds,2,3 and very
different chemical shifts should be observed if the second
isocyanide were not inserted but simply coordinated to
the metal.14
No second migration of the remaining methyl group
of 13 or the amido group of 17 was observed under these
conditions. This proposal was confirmed by an X-ray
study of complex 14.
A view of the molecular structure of complex 14 is
shown in Figure 1 together with the atomic labeling
system. Selected bond distances and angles are given
in Table 1.
The tantalum atom is bound to a pentamethylcyclo-
pentadienyl ring [Ta-CE(1) ) 2.15(2) Å, CE(1) being
the centroid of the ring], to a chlorine atom [Ta-Cl )
2.405(5) Å], to an imido ligand [Ta-N(3) ) 1.790(15)
Å], and to the carbon and nitrogen atoms from the
imine-η2-C,N-iminoacyl ligand [Ta-C(l9) ) 2.14(2) and
Ta-N(1) ) 2.161(14) Å]. The coordination geometry
around the Ta atom can be described as pseudo-
tetrahedral if the centroid of the Cp* ring and the
midpoint M(1) of the imine C(19)-N(1) double bond
[Ta-M(1) ) 2.060(14) Å] are considered as coordination
sites. The complex is chiral, and both enantiomers are
present in the crystals (in Figure 1 the T-4(R) enanti-
omer is shown). The inside coordination of the iminoacyl
N(1) located between C(19) and Cl is similar to that
found8 for the related iminoacyl derivative [TaCp*Me-
(NR)(η2-CMedNR)] (R ) 2,6-Me2C6H3). The Cp* ring
is not coordinated in a symmetric η5-fashion; a slight
trend toward the η3-coordination is observed, as indi-
cated by three short and two long Ta-to-CCp* ring carbon
distances [Ta-C(l) ) 2.44(2), Ta-C(2) ) 2.38(2), Ta-
C(3) ) 2.41(2), Ta-C(4) ) 2.52(2), and Ta-C(5) ) 2.53-
(2) Å] involving the two carbon atoms trans to the imido
ligand. In the complex the imido N(3) atom eclipses the
C(2) atom of the Cp* (τ[C(2)-CE(1)-Ta-N(3)]) -5(2)°),
and this conformation leads to a greater bending of the
eclipsed ring substituent away from the imido group,
as observed in the half-sandwhich imido complexes of
niobium and tantalum [M(η5-C5R5)(NR′)Cl2] (M ) Nb,
t
Ta; R ) H, Me; R′ ) Me, Bu, C6H3Pri -2,6).15 In fact
2
the maximum deviation of the methyl carbon atoms
from the cyclopentadienyl ring is observed for the C(7)
atom [0.28(2) Å]. The value of the Ta-N(3) bond length,
1.790(15) Å, consistent with a triple bond character, and
the nearly linear Ta-N(3)-C(3) angle of 174.7(17)° are
those expected for an imido ligand and are strictly
comparable with those found for the same ligand in
complex 18 (see below). The 1,4-diaza-1,3-butadiene
fragment exibits the η2-C,N-imine mode D16 as found
in [Cp*Ta(tBu2-dad)(StBu)2] (dad ) 1,4-diaza-1,3-buta-
diene).17 The Ta-C(19) bond distance, 2.14(2) Å, is
comparable to that found, 2.188(9) Å, in the imido
iminoacyl complex [TaCp*Me(NAr)(η2-NArdCCMe2-
CMedNAr)]7c (Ar ) 2,6-Me2C6H3) and in the azatanta-
lacyclopropane ligand in [TaCp*Me2(η2-Me2CNAr)], 2.209-
(6) Å.7b The value of the Ta-N(1) bond length, 2.161(14)
(12) (a) Campion, B. K.; Falk, J .; Tilley, T. D. J . Am. Chem. Soc.
1987, 109, 2049. (b) Mart´ın, A.; Mena, M.; Pellinghelli, M. A.; Royo,
P.; Serrano, R.; Tiripicchio, A. J . Chem. Soc., Dalton Trans. 1993, 2117.
(c) Ru´ız, J .; Vivanco, M.; Floriani, C.; Chiesi-Villa, A.; Rizzoli, C.
Organometallics 1993, 12, 1811.
(13) (a) Kramer, J . C. P.; Clej, M. C.; Nolte, R. J . M.; Harada, T.;
Hezemans, M. F.; Drenth, W. J . Am. Chem. Soc. 1988, 110, 1581. (b)
Deming, T. J .; Novak, B. M. J . Am. Chem. Soc. 1992, 114, 7926. (c)
Takei, F.; Tung, S.; Yanai, K.; Onitsuka, K.; Takahashi, S. J . Orga-
nomet. Chem. 1998, 559, 91.
(15) Williams, D. N.; Mitchell, J . P.; Poole, A. D.; Siemeling, U.;
Clegg, W.; Hockless, D. C. R.; O’Neil, P. A.; Gibson, V. C. J . Chem.
Soc., Dalton Trans. 1992, 739.
(14) (a) Alcalde, M. I. de la Mata, J .; Go´mez, M.; Royo, P.; Pelling-
helli, M. A.; Tiripicchio, A. Organometallics 1994, 13, 465. (b) Alcalde,
M. I.; de la Mata, J .; Go´mez, M.; Royo, P.; Sa´nchez, F. J . Organomet.
Chem. 1995, 492, 151.
(16) Mashima, K.; Matsuo, Y.; Tani, K. Organometallics 1999, 18,
1471.
(17) Kawaguchi, H.; Yamamoto, Y.; Asaoka, K., Tatsumi, K. Orga-
nometallics 1998, 17, 4380.

Insertion of Isocyanides
Sch em e 4
Organometallics, Vol. 19, No. 16, 2000 3165
F igu r e 2. ORTEP view of the molecular structure of the
complex 18 with the atom-numbering scheme. The thermal
ellipsoids are drawn at the 30% probability level.
Å, is in agreement with that found in the above-
mentioned imido imino iminoacyl tantalum complex,
2.148(7) Å.7c The values of the N(1)-C(19) and N(2)-
C(20) bond lengths, 1.25(2) and 1.24(2) Å, respectively,
are consistent with a double bond character, and the
two double bonds are not conjugated (τ[N(1)-C(19)-
C(20)-N(2)] ) 65(3)°). The C(11)N(1)C(19)C(20) moiety
forms dihedral angles of 4.7(8)° and 86.1(6)° with the
TaN(1)C(19) and the aryl groups, respectively, and the
C(29)C(19)C(20)N(2)C(21) fragment forms an angle of
87.1(8)° with the phenyl ring C(21)‚‚‚C(26). The phenyl
rings C(11)‚‚‚C(16) and C(21)‚‚‚C(26) are almost per-
pendicular one to another (dihedral angle 81.3(6)°).
When compound 17 was heated at 140 °C for 3 days,
the iminoacyl ligand rearranged to give a new cyclic
alkenediamido product [TaCp*(NtBu){η-NtBu-C(NHR)d
C(Me)-η-NR}] (R ) 2,6-Me2C6H3), 18, isolated as yellow
crystals, which were characterized by elemental analy-
sis, IR and NMR spectroscopy, and X-ray diffraction
methods (see Scheme 4). The most significant features
of this diazabutadiene derivative are the 13C resonance
due to the amino-substituted carbon, which was greatly
displaced to high field (δ 104.9), and the IR absorption
band observed at 1594 cm-1 due to the ν(CdC) stretch-
ing vibration.
This rearrangement could be explained by assuming
the intermediate formation of a diimido amino-carbene
species whose formation would result from proton
transfer from the amido to the imino group, followed
by attack of the imido ligand at the electrophilic carbene
carbon, as shown in Scheme 4. However we have no
experimental data for this proposal because no inter-
mediate was observed when the reaction was monitored
by NMR spectroscopy.
The molecular structure of complex 18 is shown in
Figure 2 together with the atomic labeling system.
Selected bond distances and angles are given in Table
2.
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) w ith Esd ’s in P a r en th eses for Com p ou n d 18a
Ta-N(1)
Ta-N(2)
Ta-N(4)
Ta-CE(1)
Ta-C(1)
Ta-C(2)
Ta-C(3)
Ta-C(4)
Ta-C(5)
1.997(4)
2.072(4)
1.772(5)
2.222(6)
2.490(6)
2.488(6)
2.486(6)
2.586(6)
2.571(6)
N(4)-C(34)
N(1)-C(19)
C(19)-C(20)
N(2)-C(20)
N(3)-C(20)
N(1)-C(11)
N(2)-C(22)
N(3)-C(26)
C(19)-C(21)
1.463(7)
1.386(7)
1.397(7)
1.374(6)
1.429(7)
1.442(7)
1.510(7)
1.423(7)
1.535(7)
CE(1)-Ta-N(1)
CE(1)-Ta-N(2)
CE(1)-Ta-N(4)
N(1)-Ta-N(2)
N(1)-Ta-N(4)
N(2)-Ta-N(4)
Ta-N(1)-C(19)
Ta-N(1)-C11)
123.5(2) Ta-N(2)-C(22)
115.9(2) C(20)-N(2)-C(22)
118.8(2) N(1)-C(19)-C(20)
82.5(2) N(1)-C(19)-C(21)
136.2(3)
124.4(4)
116.9(5)
120.3(5)
101.4(2) C(20)-C(19)-C(21) 122.7(6)
108.6(2) N(2)-C(20)-C(19)
100.0(3) N(2)-C(20)-N(3)
139.4(4) C(19)-C(20)-N(3)
118.6(5)
118.1(5)
122.9(5)
133.0(5)
173.3(5)
C(11)-N(1)-C(19) 120.2(4) C(20)-N(3)-C(26)
Ta-N(2)-C(20) 99.4(4) Ta-N(4)-C(34)
the centroid of the ring] and to three nitrogen atoms:
N(4) from the imido ligand and N(1) and N(2) from the
enediamido ligand. The complex can be described as
pseudo-tetrahedral if the centroid of the Cp* ring CE-
(1) is considered as occupying a coordination site and is
chiral. In the crystals both enantiomers are present (in
Figure 2 the T-4(R) enantiomer is shown) due to the
centrosymmetric space group. The Cp* ring is again not
coordinated in an ideal η5-fashion; a slight trend toward
the η3-coordination is still observed, leading to three
short and two long Ta-CCp* ring carbon distances [Ta-
C(l) ) 2.490(6), Ta-C(2) ) 2.488(6), Ta-C(3) ) 2.486-
(6), Ta-C(4) ) 2.586(6), and Ta-C(5) ) 2.571(6) Å]. In
the complex the imido N(4) atom again eclipses the C(2)
atom of the Cp* (τ[C(2)-CE(1)-Ta-N(4)] ) 6.3(5)°), and
a greater bending of the eclipsed ring substituent away
from the imido group is observed. In fact the largest
deviations of the methyl carbon atoms from the cyclo-
The tantalum atom is bound to a pentamethylcyclo-
pentadienyl ring [Ta-CE(1) ) 2.222(6) Å, CE(1) being

3166 Organometallics, Vol. 19, No. 16, 2000
Sa´nchez-Nieves et al.
pentadienyl ring are 0.236(6) Å for C(7) and 0.237(6) Å
for C(9). This last bending is due to the nearly eclipsed
conformation of C(4) (from Cp*) and the amido N(1)
atoms (τ[C(4)-CE(1)-Ta-N(1)] ) -8.5(5)°). The longest
Ta-CCp* bonds involve again the two carbon atoms
trans to the imido ligand. The Ta-N(4) bond length,
1.772(5) Å, lies within the range expected for a triple
bond and is comparable with the values of the Ta-imido
nitrogen values found in 14, 1.790(15) Å, in [TaCp*(N-
tion, and this trigonal planar geometry is preferred to
make the pπ-dπ interaction with the metal center.
Con clu sion s
Insertion of 2,6-dimethylphenylisocyanide into the
Ta-Me bond of complexes [TaCp*(NtBu)MeX] is de-
pendent on the nature of the substituent X and yields
η2-iminoacyl [TaCp*(NtBu)X{η2-[C(Me)dNR]}] deriva-
tives.
C6H3 Pr2)-2,6)Cl2],15 1.780(5) Å, in [TaCp*Cl2(NAr)],7a
i
1.774(5) Å, in [TaCp*Me(NAr){N(Ar)C(Me)dCMe2}],7c
1.784(4) Å, in [TaCp*Me(NAr)(η2-NArdCCMe2CMe)
NAr)],7c 1.812(8) Å, and in [TaCp*(NAr)(CH2dCH2)-
(PMe3)],18 1.833(4) Å (Ar ) 2,6-Me2C6H3). The Ta-
N(4)-C(34) angle is almost linear, 173.3(5)°.
The slightly asymmetric Ta-N(1) and Ta-N(2) bond
lengths, 1.997(4) and 2.072(4) Å, present a certain
degree of double bond character and are comparable to
those found in other tantalum amido derivatives such
as [TaCp*Me2(η2-Me2CNAr)],7b 1.930(4) Å, [TaCp*Cl3-
{η2-N(Ar)(CMe2CNHAr)}],7c 2.029(3) Å, and [TaCp*Me-
(NAr){N(Ar)(CMedCMe2)}],7c 2.050(5) Å. The tantalum-
amido nitrogen bond lengths agree well with those found
in the substituted 1,4-diaza-1,3-butadiene (dad) chloro,
methyl, alkynyl, and benzyl CpTa and Cp*Ta com-
plexes, in the range 2.000(4)-2.046(3) Å17 and 2.004(5)-
2.064(4) Å,16 respectively.
The influence of π-donor ligands on the insertion
process is less significant than their steric requirement,
which hinders the coordination of the isocyanide to the
metal center. Under appropriate thermal conditions a
second insertion into the Ta-iminoacyl bond also takes
place through the coordination of the isocyanide to the
metal after a preliminary transformation of the η2- into
η1-iminoacyl ligand. This step is also dominated by the
steric demands of the remaining ligand.
The presence of the imido ligand is also significant
because the double insertion does not take place for the
weaker π-donor [N(2,6-Me2C6H3)] ligand,8 probably due
to a stronger interaction of the η2-iminoacyl ligand in
the resulting product.
Exp er im en ta l Section
Gen er a l Com m en ts. All operations were carried out under
a dry argon atmosphere either in a Vacuum Atmosphere Dri-
lab or by standard Schlenck techniques. Hydrocarbon solvents
were dried and freshly distilled: n-hexane from sodium
potassium alloy and toluene from sodium. Reagent grade CN-
(2,6-Me2C6H3) (Fluka) and NaOMe (Fluka) were purchased
form commercial sources and used without further purification.
The starting complexes [TaCp*Cl4],19 [TaCp*(NtBu)Cl2],20 and
[TaCp*(NtBu)Me2]10 were synthesized by reported methods
and LiX (X ) OtBu, NHtBu) were obtained by deprotonating
the alcohol or amine with LiBu in n-hexane. Infrared spectra
were recorded on a Perkin-Elmer 583 spectrophotometer
These Ta-N amido distances are shorter than those
found in the dad butadiene tantalum complexes [Ta-
Cp*(η2-N,N′-p-MeOC6H4-dad)(η4-s-cis-1,3-butadiene)],16
2.128(4) and 2.128(4) Å, and in [TaCp*(η2-N,N′-Cy-dad)-
(η4-s-cis-1,3-butadiene)],16 2.118(8) and 2.116(9) Å. The
three N(1)-C(19), C(19)-C(20), and N(2)-C(20) bond
distances, 1.386(7), 1.397(7), and 1.374(6) Å, are shorter,
longer, and shorter than those expected for a single
C-N, double C-C, and single C-N bond, respectively.
The TaN(1)C(19)C(20)N(2) five-membered ring adopts
an envelope conformation and is folded by 136.0(2)°
along the N-N vector, with the Ta atom displaced by
1.062(1) Å from the mean plane through NCCN. This
fold θ angle is larger than those found in the η4-supine
(in the range 118.4-121.1°) and η4-prone (in the range
121.2-127.3°) conformations in the dad Ta complexes16,17
and narrower than those found in the η2-N,N′-enedia-
mido dad Ta complexes,16 in the range 154.9(3)-155.9-
(3)°. The distances Ta-C(19) and Ta-C(20), 2.621(5)
and 2.667(5) Å, are longer than those found in the η4-
dad complexes, in the range 2.430(5)-2.555(6) Å. The
N-C-C-N fragment assumes a slightly prone confor-
mation (τ[CE(1)-Ta-N(1)-C(19)] ) 76.0(4)°, (τ[CE(1)-
Ta-N(2)-C(20] ) -86.7(4)°).
1
(4000-200 cm-1). H and 13C NMR spectra were recorded on
a Varian Unity VXR 300 MHz instrument, and chemical shifts
1
were measured relative to residual H and 13C resonances in
the deuterated solvents C6D6 (δ 7.15), CDCl3 (δ 7.24) and C6D6
(δ 128), CDCl3 (δ 77). C, H, and N analyses were carried out
with a Perkin-Elmer 240C microanalyzer.
[Ta Cp *(NtBu )Cl(NHtBu )] (1). A solution of [TaCp*Cl4]
(1.00 g, 2.18 mmol) and 3 equiv of LiNHtBu (0.51 g, 6.55 mmol)
in Et2O (20 mL) was stirred for 12 h at room temperature.
The solvent was removed in vacuo, and the oily residue was
extracted into pentane (20 mL). Removal of the solvent gave
1 as a yellow oil (yield: 0.78 g, 72%).
1
Data for 1: IR (KBr, ν, cm-1): 3330 (w), 1356 (s). H NMR
(CDCl3; δ, ppm): 5.64 (s, 1H, NH), 2.07 (s, 15H, C5Me5), 1.29
(s, 9H, CMe3), 1.22 (s, 9H, CMe3). 13C{1H} NMR (CDCl3; δ,
ppm): 116.8 (C5Me5), 65.0 (TadNCMe3), 55.7 (TadNHCMe3),
The dihedral angle between the planes TaC(19)C(20)
and N(1)C(19)C(20)N(2)C(21)N(3) is only 27.0(2)°. All
these structural features prevent some π-donation of the
CdC bond, which was found weaker in the prone than
in the supine conformation. All the above-mentioned
arguments indicate that the new η2-enediamido ligand
exibits a coordination mode A,16 with some contribution
of the structure C.16 The sums of the three angles
around the N(1) and N(2) atoms are 359.6° and 360.0°,
indicating a planar geometry as in the prone conforma-
34.3 (CMe3), 33.3 (CMe3), 11.6 (C5Me5). Anal. Calcd for C18H34
ClN2Ta: C, 43.68; H, 6.94; N, 5.66. Found: C, 42.40; H, 6.11;
N, 5.23.
[Ta Cp *(NtBu )ClMe] (3). A 2.0 M toluene solution of ZnMe2
(2.50 mL, 5.00 mmol) was added to a solution of [TaCp*(Nt-
Bu)Cl2] (2.00 g, 4.36 mmol) in toluene (15 mL). The solution,
which turned immediately cloudy, was stirred overnight at
room temperature. The volatiles were removed in vacuo, and
n-hexane (15 mL) was added to give a solution, which after
-
(19) de la Mata, J .; Fandos, R.; Go´mez-Sal, P.; Mart´ınez-Carrera,
S.; Royo, P. Organometallics 1990, 9, 2846.
(20) Royo, P.; Sa´nchez-Nieves, J . J . Organomet. Chem. 2000, 597,
61.
(18) Royo, P.; Sanchez-Nieves, J .; Pellinghelli, M. A.; Tiripichio, A.
J . Organomet. Chem. 1998, 563, 15.

Insertion of Isocyanides
Organometallics, Vol. 19, No. 16, 2000 3167
filtration and removal of solvent in vacuo rendered compound
Data for 8: IR (CsI, ν, cm-1): 1612 (s), 1268 (s). 1H NMR
(CDCl3; δ, ppm): 6.97 (m, 3H, 2,6-Me2C6H3), 2.46 (s, 3H, C(Me)-
NR), 2.03 (s, 15H, C5Me5), 1.99 (s, 3H, 2,6-Me2C6H3), 1.80 (s,
3H, 2,6-Me2C6H3), 0.99 (s, 9H, CMe3), -0.07 (s, 3H, Ta-Me).
13C{1H} NMR (CDCl3; δ, ppm): 244.5 (C(Me)NR), 142.2, 130.3,
129.5, 128.1, 127.6, 125.2 (2,6-Me2C6H3), 112.5 (C5Me5), 64.1
(CMe3), 33.6 (CMe3), 21.8 (C(Me)NR), 18.9 (2,6-Me2C6H3), 18.7
(2,6-Me2C6H3), 13.2 (Ta-Me), 11.6 (C5Me5). Anal. Calcd for
3 as a yellow oil (yield: 1.43 g, 75%).
1
Data for 3: IR (CsI, ν, cm-1): 1275 (s). H NMR (CDCl3; δ,
ppm): 2.07 (s, 15H, C5Me5), 1.19 (s, 9H, CMe3), 0.40 (s, 3H,
Ta-Me). 13C{1H} NMR (CDCl3; δ, ppm): 117.2 (C5Me5), 64.8
(CMe3), 37.6 (Ta-Me), 33.0 (CMe3), 11.5 (C5Me5). Anal. Calcd
for C15H27ClNTa: C, 41.15; H, 6.23; N, 3.20. Found: C, 41.19;
H, 6.11; N, 3.53.
[Ta Cp *(NtBu )Me(OMe)] (4). A mixture of 3 (2.00 g, 4.57
mmol) and NaOMe (0.24 g, 4.57 mmol) was stirred in Et2O
(40 mL) for 16 h at room temperature. The solvent was
removed in vacuo, and the residue was extracted into n-hexane
(20 mL) to give a solution, which gave 4 as a dark oil after
removal of the solvent in vacuo (yield: 1.76 g, 89%).
C
25H39N2Ta: C, 54.73; H, 7.18; N, 5.11. Found: C, 54.12; H,
7.15; N, 5.17.
[Ta Cp *(NtBu )Cl{η2-C(Me)dNR}] (R ) 2,6-Me2C6H3) (9).
n-Hexane (15 mL) was added to a mixture of [TaCp*(NtBu)-
ClMe], 3 (1.00 g, 2.28 mmol), and CNR (0.32 g, 2.44 mmol),
and the solution was stirred for 1 h at room temperature.
Formation of a dark precipitate was observed. The solution
was filtered off, and the solid residue was recrystallized from
n-hexane (50 mL) by cooling at -30 °C to give 9 as a yellow
solid (yield: 1.17 g, 90%).
1
Data for 4: IR (CsI, ν, cm-1): 1279 (s). H NMR (CDCl3; δ,
ppm): 4.34 (s, 3H, OMe), 1.99 (s, 15H, C5Me5), 1.22 (s, 9H,
CMe3), 0.10 (s, 3H, Ta-Me). 13C{1H} NMR (CDCl3; δ, ppm):
115.5 (C5Me5), 65.6 (OMe), 63.8 (CMe3), 33.8 (CMe3), 22.5 (Ta-
Me), 11.0 (C5Me5). Anal. Calcd for C16H30NOTa: C, 44.34; H,
6.98; N, 3.23. Found: C, 43.79; H, 6.71; N, 3.00.
1
Data for 9: IR (KBr, ν, cm-1): 1616 (s), 1256 (s). H NMR
(CDCl3; δ, ppm): 6.95 (m, 3H, 2,6-Me2C6H3), 2.56 (s, 3H, C(Me)-
NR), 2.12 (s, 15H, C5Me5), 2.08 (s, 3H, 2,6-Me2C6H3), 1.92 (s,
3H, 2,6-Me2C6H3), 1.06 (s, 9H, CMe3). 13C{1H} NMR (CDCl3;
δ, ppm): 243.7 (C(Me)NR), 140.4, 130.4, 130.0, 128.4, 127.8,
125.9 (2,6-Me2C6H3), 115.4 (C5Me5), 65.4 (CMe3), 33.8 (CMe3),
22.4 (C(Me)NR), 19.1 (2,6-Me2C6H3), 19.0 (2,6-Me2C6H3), 11.9
(C5Me5). Anal. Calcd for C24H36N2ClTa: C, 50.65; H, 6.39; N,
4.92. Found: C, 50.44; H, 6.26; N, 4.78.
[Ta Cp *(NtBu )Me(OtBu )] (5). A mixture of 3 (2.00 g, 4.57
mmol) and LiOtBu (0.37 g, 4.57 mmol) was stirred in Et2O (40
mL) for 4 h at room temperature. The solvent was removed in
vacuo, and the residue was extracted into n-hexane (20 mL).
Compound 5 was isolated as a brown oil after removal of the
solvent in vacuo (yield: 1.87 g, 86%).
1
Data for 5: IR (CsI, ν, cm-1): 1350 (s). H NMR (CDCl3; δ,
ppm): 1.99 (s, 15H, C5Me5), 1.24 (s, 9H, CMe3), 1.12 (s, 9H,
CMe3), 0.04 (s, 3H, Ta-Me). 13C{1H} NMR (CDCl3; δ, ppm):
115.3 (C5Me5), 77.0 (OCMe3), 63.5 (NCMe3), 33.7 (CMe3), 32.6
[Ta Cp *(NtBu )(OMe){η2-C(Me)dNR}] (R ) 2,6-Me2C6H3)
(10). n-Hexane (10 mL) was added to a mixture of [TaCp*(Nt-
Bu)Me(OMe)], 4 (1.00 g, 2.31 mmol), and CNR (0.30 g, 2.31
mmol), and the solution was stirred for 1 h at room temper-
ature. The solution was filtered and the volatiles were removed
in vacuo to yield a residue that could not be purified by
recrystallization. This residue contained 10 as the major
(CMe3), 21.1 (Ta-Me), 11.2 (C5Me5). Anal. Calcd for C19H36
-
NOTa: C, 47.99; H, 7.65; N, 2.94. Found: C, 47.00; H, 7.43;
N, 2.71.
[Ta Cp *(NtBu )Me(NHtBu )] (6). A mixture of 2 (2.00 g, 4.57
mmol) and LiNHtBu (0.36 g, 4.57 mmol) was stirred in Et2O
(40 mL) for 4 h at room temperature. The solvent was removed
in vacuo, and the residue was extracted into n-hexane (20 mL)
to give 6 as a brown oil after removal of the solvent in vacuo
(yield: 1.80 g, 84%).
1
component (>90% by H NMR).
Data for 10: 1H NMR (CDCl3; δ, ppm): 6.97 (m, 3H, 2,6-
Me2C6H3), 3.98 (s, 3H, OMe), 2.43 (s, 3H, C(Me)NR), 2.13 (s,
3H, 2,6-Me2C6H3), 2.09 (s, 15H, C5Me5), 1.98 (s, 3H, 2,6-
Me2C6H3), 1.08 (s, 9H, CMe3). 13C{1H} NMR (CDCl3; δ, ppm):
252.6 (C(Me)NR), 143.6, 130.1, 129.3, 128.2, 127.7, 125.1 (2,6-
Me2C6H3), 114.8 (C5Me5), 65.5 (NCMe3), 62.1 (OMe), 34.3
(CMe3), 23.1 (C(Me)NR), 19.0 (2,6-Me2C6H3), 18.8 (2,6-Me2C6H3),
11.5 (C5Me5).
1
Data for 6: IR (CsI, ν, cm-1): 3250 (w), 1280 (s). H NMR
(CDCl3; δ, ppm): 5.06 (s, 1H, NH), 1.98 (s, 15H, C5Me5), 1.22
(s, 9H, CMe3), 1.16 (s, 9H, CMe3), -0.21 (s, 3H, Ta-Me). 13C-
{1H} NMR (CDCl3; δ, ppm): 113.9 (C5Me5), 64.0 (TadNCMe3),
54.6 (NHCMe3), 34.6 (CMe3), 33.6 (CMe3), 19.2 (Ta-Me), 11.3
(C5Me5). Anal. Calcd for C19H37NOTa: C, 48.09; H, 7.88; N,
5.90. Found: C, 47.29; H, 7.71; N, 5.78.
[Ta Cp *(NtBu )Cl{η2-C(NHtBu )dNR}] (R ) 2,6-Me2C6H3)
(7). A solution of [TaCp*(NtBu)Cl(NHtBu)] 1 (1.00 g, 2.02
mmol) in n-hexane (20 mL) was treated with CNR (0.28 g, 2.13
mmol), and the mixture was stirred for 7 h at room temper-
ature. Formation of a dark precipitate was observed. The
solution was filtered off, and the solid residue was extracted
into n-hexane (2 × 25 mL). The solution was concentrated to
ca. 10 mL and cooled to -30 °C to give 7 as white crystals
(yield: 1.09 g, 86%).
Data for 7: IR (KBr pellets, ν, cm-1): 3200 (w), 1540 (s),
1260 (s). 1H NMR (CDCl3; δ, ppm): 6.99 (m, 3H, 2,6-Me2C6H3),
5.75 (s, 1H, NH), 2.19 (s, 15H, C5Me5), 2.15 (s, 3H, 2,6-
Me2C6H3), 2.00 (s, 3H, 2,6-Me2C6H3), 1.46 (s, 9H, CMe3), 1.13
(s, 9H, CMe3). 13C{1H} NMR (CDCl3; δ, ppm): 203.1 (C[NHt-
Bu]NR), 139.8, 133.4, 132.4, 128.6, 127.8, 125.4 (2,6-Me2C6H3),
116.6 (C5Me5), 65.7 (NCMe3), 52.8 (NHCMe3), 32.9 (CMe3), 31.3
(CMe3), 19.7 (2,6-Me2C6H3), 19.0 (2,6-Me2C6H3), 12.4 (C5Me5).
Anal. Calcd for C27H43ClN3Ta: C, 51.79; H, 6.94; N, 6.71.
Found: C, 51.57; H, 6.91; N, 6.64.
[Ta Cp *(NtBu )Me{η2-C(Me)dNR}] (R ) 2,6-Me2C6H3) (8).
n-Hexane (15 mL) was added to a mixture of [TaCp*(NtBu)-
Me2], 2 (1.00 g, 2.40 mmol), and CNR (0.31 g, 2.40 mmol), and
the solution was stirred for 1 h at room temperature. The
solution was filtered, and the solvent was removed in vacuo
to yield 8 as a pale orange oil (yield: 1.21 g, 92%).
[Ta Cp *(NtBu )(OtBu ){η2-C(Me)dNR}] (R ) 2,6-Me2C6H3)
(11). n-Hexane (10 mL) was added to a mixture of [TaCp*(Nt-
Bu)Me(OtBu)], 5 (1.00 g, 2.10 mmol), and CNR (0.29 g, 2.21
mmol), and the solution was stirred for 7 h at room temper-
ature. Formation of a white precipitate was observed. The
solvent was filtered off, and the solid residue was washed with
n-pentane (15 mL) to yield 11 as yellow solid (yield: 1.06 g,
83%).
1
Data for 11: IR (KBr, ν, cm-1): 1597 (s), 1263 (s). H NMR
(CDCl3; δ, ppm): 6.97 (m, 3H, 2,6-Me2C6H3), 2.40 (s, 3H, C(Me)-
NR), 2.06 (s, 15H, C5Me5), 1.98 (s, 3H, 2,6-Me2C6H3), 1.97 (s,
3H, 2,6-Me2C6H3), 1.11 (s, 9H, CMe3), 1.02 (s, 9H, CMe3). 13C-
{1H} NMR (CDCl3; δ, ppm): 252.2 (C(Me)NR), 143.9, 130.7,
129.2, 127.6, 124.8 (2,6-Me2C6H3), 114.5 (C5Me5), 73.1 (OCMe3),
64.2 (NCMe3), 34.4 (CMe3), 32.8 (CMe3), 23.8 (C(Me)NR), 19.1
(2,6-Me2C6H3), 18.7 (2,6-Me2C6H3), 11.7 (C5Me5). Anal. Calcd
for C28H45N2OTa: C, 55.43; H, 7.49; N, 4.62. Found: C, 55.35;
H, 7.49; N, 4.48.
[Ta Cp *(Nt Bu )(NHt Bu ){η2-C(Me)dNR }] (R ) 2,6-Me2-
C6H3) (12). A C6D6 solution of [TaCp*(NtBu)Me(NHtBu)], 6
(0.20 g, 0.04 mmol), and CNR (0.005 g, 0.04 mmol) was
prepared into a sealed NMR tube, and the reaction was
1
monitored by H NMR. After 3 days at 75 °C the CNR signals
disappeared, leaving a solution that contained 6, 12, and 17
(see below) in a 1:3:2 molar ratio.
Data for 12: 1H NMR (C6D6; δ, ppm): 4.15 (s, 1H, NH), 1.99
(s, 15H, C5Me5), 1.87 (s, 18H, CMe3). 13C{1H} NMR (C6D6; δ,

3168 Organometallics, Vol. 19, No. 16, 2000
Sa´nchez-Nieves et al.
Ta ble 3. Su m m a r y of Cr ysta llogr a p h ic Da ta for
th e Com p ou n d s 14 a n d 18
ppm): 240.9 (C(Me)NR), 115.0 (C5Me5), 64.9 (NCMe3), 55.2
(NHCMe3), 35.1 (CMe3), 34.3 (CMe3), 19.8 (Me), 19.5 (Me), 11.9
(C5Me5).
14
18
[Ta Cp *(Nt Bu )Me{η2-C[C(Me)dNR ]dNR }] (R ) 2,6-
Me2C6H3) (13). Toluene (15 mL) was added to a mixture of
[TaCp*(NtBu)Me{η2-C(Me)dNR}], 8 (1.00 g, 1.82 mmol), and
CNR (0.25 g, 1.88 mmol) in an ampule with a Teflon cap, and
the solution was heated at 120 °C for 14 h. After cooling at
room temperature the solvent was removed in vacuo and the
dark oily residue was recrystallized from n-hexane by cooling
the solution at -30 °C to yield 13 as dark yellow crystals (0.90
g, 73%).
Data for 13: IR (KBr, ν, cm-1): 1636 (s), 1580 (s), 1262 (s).
1H NMR (CDCl3; δ, ppm): 6.94 (m, 6H, 2,6-Me2C6H3), 2.16 (s,
18H, C5Me5 and 2,6-Me2C6H3), 2.12, 1.97, 1.86 (s, 3H, 2,6-
Me2C6H3), 1.18 (s, 3H, C(Me)NR), 1.09 (s, 9H, CMe3), 0.08 (s,
3H, Ta-Me). 13C{1H} NMR (CDCl3; δ, ppm): 239.6 (C[C(Me)-
NR]NR}), 170.0 (C(Me)NR), 148.0, 145.2, 130.5, 128.6, 128.0,
127.9, 127.4, 126.2, 125.4, 125.1, 123.1 (2,6-Me2C6H3), 113.4
(C5Me5), 64.6 (CMe3), 33.7 (CMe3), 19.4, 19.1, 18.6, 17.6, 16.8
(2,6-Me2C6H3 and C(Me)NR), 14.0 (Ta-Me), 11.8 (C5Me5). Anal.
Calcd for C34H48N3Ta: C, 60.07; H, 7.13; N, 6.18. Found: C,
59.76; H, 7.07; N, 6.13.
[Ta Cp *(NtBu )Cl{η2-C[C(Me)dNR]dNR}] (R ) 2,6-Me2-
C6H3) (14). Toluene (15 mL) was added to a mixture of [TaCp*-
(NtBu)Cl{η2-C(Me)dNR}], 9 (1.00 g, 1.75 mmol), and CNR
(0.27 g, 2.06 mmol) in a Carius tube, which was then sealed
under vacuum. The Carius tube was heated in an autoclave
at 145 °C for 3 days. After cooling at room temperature the
solvent was removed in vacuo and the dark oily residue was
recrystallized from n-hexane by cooling at -30 °C to yield 14
as yellow crystals (yield: 0.95 g, 77%).
Data for 14: IR (KBr, ν, cm-1): 1638 (s), 1580 (s), 1256 (s).
1H NMR (CDCl3; δ, ppm): 6.80-7.00 (m, 6H, 2,6-Me2C6H3),
2.22 (s, 15H, C5Me5), 2.17, 2.16, 2.04, 1.84 (s, 3H, 2,6-Me2C6H3),
1.25 (s, 3H, C(Me)NR), 1.15 (s, 9H, CMe3). 13C{1H} NMR
(CDCl3; δ, ppm): 238.2 (C[C(Me)NR]NR}), 168.6 (C(Me)NR),
147.6, 142.2, 130.5, 128.9, 128.2, 128.0, 127.9, 127.7, 126.1,
125.0, 124.9, 123.4 (2,6-Me2C6H3), 116.4 (C5Me5), 65.7 (CMe3),
33.4 (CMe3), 19.6, 19.5, 18.7, 18.0 (2,6-Me2C6H3), 16.8 (C(Me)-
NR), 12.1 (C5Me5). Anal. Calcd for C33H45ClN3Ta: C, 56.60;
H, 6.49; N, 6.00. Found: C, 56.56; H, 6.43; N, 6.18.
formula
mol wt
cryst syst
space group
radiation (λ, Å)
a, Å
C
33H45ClN3Ta
C37H55N4Ta
736.80
monoclinic
P21/a
Mo KR (0.71073)
10.317(4)
32.891(9)
10.561(6)
700.12
triclinic
P1h
Mo KR (0.71073)
8.767(4)
10.956(5)
17.316(6)
98.15(2)
95.94(2)
97.70(2)
1619(1)
2
b, Å
c, Å
R, deg
â, deg
92.45(2)
γ, deg
V, Å3
3580(3)
4
1.367
1512
Z
D
calcd, Mg m-3
1.436
708
F(000)
cryst size, mm
µ(Mo KR), mm-1
diffractometer
scan type
θ range, deg
no. of reflectns measd
0.25 × 0.28 × 0.30 0.24 × 0.26 × 0.28
3.502
3.099
Philips PW 1100
θ/2θ
3-24
5918
5597
3553 [I > 2σ(I)]
0.0291
0.0476
0.0795
Siemens AED
θ/2θ
3-22
3966
no. of unique total data 3966
no. of unique obsd data 2682 [I > 2σ(I)]
R1a [I > 2σ(I)]
wR2b [I > 2σ(I)]
R1 (all data)
0.0695
0.1763
0.1185
0.2027
wR2 (all data)
0.0590
R1 ) ∑|Fo - Fc|/|∑(Fo). wR2 ) [∑[w(Fo2 - Fc2)2]/∑[w(Fo2)2]]1/2
.
a
b
2,6-Me2C6H3), 1.21 (s, 9H, CMe3), 1.13 (s, 3H, C(Me)NR), 1.04
(s, 9H, CMe3). 13C{1H} NMR (CDCl3; δ, ppm): 247.3 (C[C(Me)-
NR]NR}), 170.4 (C(Me)NR), 147.9, 145.4, 131.2, 128.1, 127.9,
127.8, 127.6, 127.2, 126.6, 125.3, 125.0, 123.0 (2,6-Me2C6H3),
115.3 (C5Me5), 73.6 (OCMe3), 64.6 (NCMe3), 34.5 (CMe3), 32.9
(CMe3), 19.3, 19.1, 18.9, 18.1 (2,6-Me2C6H3), 16.8 (C(Me)NR),
12.1 (C5Me5). Anal. Calcd for C37H54N3OTa: C, 60.22; H, 7.39;
N, 5.70. Found: C, 60.48; H, 7.23; N, 5.83.
[TaCp*(NtBu )(NHtBu ){η2-C[C(Me)dNR]dNR}] (R ) 2,6-
Me2C6H3) (17). Toluene (30 mL) was added to a mixture of
[TaCp*(NtBu)(NHtBu)Me], 6 (2.00 g, 4.22 mmol), and CNR
(1.33 g, 10.12 mmol) in an ampule with Teflon cap, and the
solution was heated at 80 °C for 4 d. After cooling at room
temperature the solution was filtered and concentrated to ca.
10 mL in vacuo. Cooling at -30 °C afforded 17 as yellow
crystals (yield: 2.45 g, 79%).
[Ta Cp *(NtBu )(OMe){η2-C[C(Me)dNR]dNR}] (R ) 2,6-
Me2C6H3) (15). n-Hexane (30 mL) was added to a mixture of
[TaCp*(NtBu)Me(OMe)], 4 (1.00 g, 2.31 mmol), and CNR (0.60
g, 4.62 mmol), and the solution was stirred for 16 h at room
temperature. The solution was filtered and concentrated in
vacuo to ca. 10 mL to render 15 as yellow crystals by cooling
the solution at -30 °C (yield: 1.37 g, 85%).
Data for 17: IR (KBr, ν, cm-1): 3298 (w), 1635 (s), 1590 (s),
1250 (s). 1H NMR (CDCl3; δ, ppm): 6.90 (m, 6H, 2,6-Me2C6H3),
3.62 (s, 1H, NH), 2.19 (s, 15H, C5Me5), 2.17, 2.09, 2.04, 1.78
(s, 3H, 2,6-Me2C6H3), 1.25 (s, 9H, CMe3), 1.19 (s, 3H, C(Me)-
NR), 1.18 (s, 9H, CMe3). 13C{1H} NMR (CDCl3; δ, ppm): 240.5
(C[C(Me)NR]NR}), 173.2 (C(Me)NR), 149.0, 148.4, 128.9,
127.9, 127.7, 127.6, 126.7, 126.1, 123.6, 122.6 (2,6-Me2C6H3),
115.4 (C5Me5), 64.6 (NCMe3), 54.8 (NHCMe3), 35.1 (CMe3), 34.3
(CMe3), 20.2, 20.1, 18.8, 18.1, 17.1 (2,6-Me2C6H3 and C(Me)-
NR), 12.6 (C5Me5). Anal. Calcd for C37H55N4Ta: C, 60.30; H,
7.54; N, 7.60. Found: C, 60.10; H, 7.25; N, 7.51.
Data for 15: IR (KBr, ν, cm-1): 1631 (m), 1588 (m), 1263
(s). 1H NMR (CDCl3; δ, ppm): 6.92 (m, 6H, 2,6-Me2C6H3), 4.08
(s, 3H, OMe), 2.21 (s, 3H, 2,6-Me2C6H3), 2.18 (s, 15H, C5Me5),
2.16, 2.13, 1.79 (s, 3H, 2,6-Me2C6H3), 1.23 (s, 3H, C(Me)NR),
1.18 (s, 9H, CMe3). 13C{1H} NMR (CDCl3; δ, ppm): 247.4
(C[C(Me)NR]NR}), 169.9 (C(Me)NR), 147.9, 145.0, 130.5,
128.2, 128.0, 127.9, 127.8, 127.7, 126.2, 125.2, 123.1 (2,6-
Me2C6H3), 115.7 (C5Me5), 64.9 (NCMe3), 63.2 (OMe), 34.5
(CMe3), 19.7, 19.0, 18.7, 17.8 (2,6-Me2C6H3), 16.9 (C(Me)NR),
11.7 (C5Me5). Anal. Calcd for C34H48N3OTa: C, 58.70; H, 6.95;
N, 6.04. Found: C, 58.23; H, 6.99; N, 5.87.
[Ta Cp *(NtBu )(OtBu ){η2-C[C(Me)dNR]dNR}] (R ) 2,6-
Me2C6H3) (16). Toluene (30 mL) was added to a mixture of
[TaCp*(NtBu)(OtBu){η2-C(Me)dNR}], 11 (1.50 g, 2.47 mmol),
and CNR (0.42 g, 3.20 mmol) in an ampule with Teflon cap,
and the solution was heated at 130 °C for 48 h. After cooling
at room temperature the solution was filtered and concen-
trated to ca. 10 mL in vacuo. Cooling the solution at -30 °C
rendered 16 as white crystals (yield: 1.48 g, 81%).
[TaCp*(NtBu ){η-N(tBu )C(NHR)dC(Me)-η-NR}] (R ) 2,6-
Me2C6H3) (18). Toluene (30 mL) was added to [TaCp*(NtBu)-
(NHtBu){η2-C[C(Me)dNR]dNR}], 17 (1.20 g, 1.63 mmol), in
an ampule with a Teflon cap, and the solution was heated at
140 °C for 3 days. After cooling at room temperature the
solution was filtered and concentrated to ca. 10 mL. Cooling
at -30 °C afforded 18 as yellow crystals (yield 0.95 g, 79%).
Data for 18: IR (KBr, ν, cm-1): 3450 (w), 1554 (m), 1256
(s). 1H NMR (CDCl3; δ, ppm): 6.90 (m, 6H, 2,6-Me2C6H3), 4.74
(s, 1H, NH), 2.49 (s, 3H, 2,6-Me2C6H3), 2.33 (s, 6H, 2,6-
Me2C6H3), 2.15 (s, 15H, C5Me5), 1.98 (s, 3H, 2,6-Me2C6H3), 1.50
(s, 9H, CMe3), 1.28 (s, 3H, C(Me)dC(NHR)), 0.87 (s, 9H, CMe3).
13C{1H} NMR (CDCl3; δ, ppm): 151.9, 141.1, 135.7, 133.1,
130.6, 128.4, 128.1, 127.5, 126.9, 126.1, 125.6, 123.9, 119.9 (2,6-
Data for 16: IR (KBr, ν, cm-1): 1627 (s), 1588 (s), 1255 (s).
1H NMR (CDCl3; δ, ppm): 6.86 (m, 6H, 2,6-Me2C6H3), 2.18 (s,
3H, 2,6-Me2C6H3), 2.15 (s, 15H, C5Me5), 2.06, 2.03, 1.90 (s, 3H,

Insertion of Isocyanides
Organometallics, Vol. 19, No. 16, 2000 3169
Me2C6H3 and C(Me)dC(NHR)), 113.4 (C5Me5), 104.9 (C(Me)d
C(NHR), 64.2 (TadNCMe3), 55.3 (CMe3), 34.6 (CMe3), 33.5
(CMe3), 21.3, 20.4, 20.1 (2,6-Me2C6H3), 16.6 (C(Me)dC(NHR)),
12.5 (C5Me5). Anal. Calcd for C37H55N4Ta: C, 60.30; H, 7.54;
N, 7.60. Found: C, 60.12; H, 7.58; N, 7.40.
the hydrogen atoms were introduced from geometrical calcula-
tions and refined using a riding model with fixed thermal
parameters, excepting that bound to N(3), which was found
in the final ∆F map and refined isotropically. The final cycles
of refinement were carried out on the basis of 338 variables
for 14 and 393 for 18. The biggest remaining peak in the final
difference map was equivalent to about 1.70 e/Å3 for 14 and
Cr ysta l Str u ctu r e Deter m in a tion s. All crystals of com-
pound 14, obtained by crystallization from n-hexane, were of
very poor quality, and a suitably sized crystal in a Lindemann
tube was mounted on an Siemens AED diffractometer with
graphite-monochromated Mo KR radiation (λ ) 0.71073 Å).
Crystals of 18 were obtained by crystallization from n-hexane,
and a suitably sized crystal in a Lindemann tube was mounted
in a Philips PW 1100 diffractometer with graphite-monochro-
mated Mo KR radiation (λ ) 0.71073 Å). Crystallographic and
experimental details for both structures are summarized in
Table 3. An empirical correction for absorption was applied to
both compounds [maximum and minimum values for the
transmission coefficient was 1.000 and 0.440 for 14 and 1.000
and 0.765 for 18].21 Both structures were solved by direct
1.06 e/Å3 for 18. A weighting scheme w ) 1/ [σ2(Fo)2
+
(0.1224P)2] where P ) (Fo2 + 2Fc )/3 was used in the last cycles
of refinement for 14 and w ) 1/[σ2(Fo)2 + (0.0149P)2] where P
) (Fo2 + 2Fc2)/3. All calculations were carried out on DIGITAL
AlphaStation 255 of the “Centro di Studio per la Strutturistica
Diffrattometrica” del C.N.R., Parma.
2
Ack n ow led gm en t. The authors acknowledge DGI-
CYT (project PB97-0776) and CNR (Rome) for financial
supports. J .S.-N. acknowledges Ministerio de Educacio´n
y Ciencia for a fellowship.
2
methods and refined by least squares against Fo (SHELXL-
Su p p or tin g In for m a tion Ava ila ble: The details of the
crystal structure investigations are deposited in the Cambridge
Crystallographic Data Center as supplementary publications
no. CCDC-140106 (14) and CCDC-140107 (18). This material
is also available free of charge via the Internet at http://pubs.
acs.org.
97).22 All non hydrogen atoms were refined anisotropically
excepting the C(31), C(32), and C(33) carbon atoms of 14. All
(21) Walker, N.; Stuart, D. Acta Crystallogr., Sect. A 1983, 39 158.
Ugozzoli, F. Comput. Chem. 1987, 11, 109.
(22) Sheldrick, G. M. SHELXL-97, Program for the Solution and
the refinement of Crystal Structures; Universita¨t Go¨ttingen, Germany,
1997.
OM000194R