Studies on the insertion reactions of activated alkynes into Nb-H bonds in hydride-niobocene complexes. X-ray crystal structures of Nb(η5-C5H4SiMe3) 2(H)[η2-RO2C(H)=C(H)CO2R] (R = Me or tBu)

Article abstract of DOI:10.1021/om9605241

The hydride isocyanide complexes, Nb(η⁵-C₅H₄SiMe₃) ₂(H)(CNR), R = xylyl = 2,6-dimethylphenyl; Cy (cyclohexyl); ^tBu; as well as the hydride carbonyl complex Nb(η⁵-C₅H₄SiMe₃) ₂-(H)(CO) react with several activated alkynes to afford the corresponding alkenyl isocyanide complexes Nb(η⁵-C₅H₄SiMe₃) ₂(CNR)(C(R′)=CH(R″)), R = Xylyl, R′ = R″ = CO₂Me 1; R = Xylyl, R′ = R″ = CO₂^tBu 2; R = Xylyl, R′ = CO₂Me, R″ = H 3; R = Xylyl, R′ = CO₂Me, R″ = Me 4; R = Cy, R′ = R″ = CO₂Me 5; R = Cy, R′ = R″ = CO₂^tBu 6; R = Cy, R′ = CO₂Me, R″ = Me 7; R = ^tBu, R′ = R″ = CO₂Me 8; ^tBu, R′ = R″ = CO₂^tBu 9 and alkenyl-carbonyl complexes, Nb(η⁵-C₅H₄SiMe₃) ₂(CO)(C(R′)=CH(R″)), R′ = R″ = CO₂Me 10; R′ = R″ = CO₂^tBu 11; R′ = CO₂Me, R″ = H 12. The reaction of hydride isocyanide complexes with activated alkynes gives cis-insertion resulting in the formation of (E)-alkenyl products. However, the hydride carbonyl derivative undergoes insertion to give, under kinetic control, a mixture of (E)- and (Z)-alkenyl isomers. Finally, the trihydride niobocene complex Nb(η⁵-C₅H₄-SiMe₃) ₂(H)₃, reacts with esters RO₂CC≡CCO₂R′ or MeO₂CC≡CH to give the hydride olefin derivatives, Nb(η⁵-C₅H₄SiMe₃) ₂(H)[η²-RO₂C(H)=C(H)CO ₂R′], R = R′ = Me 13; R = R′ = ^tBu 14; and Nb(η⁵-C₅H₄SiMe₃) ₂(H)[η²-MeO₂C(H)=CH₂] 15, probably as the result of a stereospecific trans-insertion. The different complexes have been characterized by spectroscopic methods. In addition, the structure of 13 and 14 were determined by single crystal X-ray diffraction.

Full text of DOI:10.1021/om9605241

Organometallics 1996, 15, 5507-5513
5507
Stu d ies on th e In ser tion Rea ction s of Activa ted Alk yn es
in to Nb-H Bon d s in Hyd r id e-Niobocen e Com p lexes.
X-r a y Cr ysta l Str u ctu r es of
Nb(η5-C5H4SiMe3)2(H)[η2-RO2C(H)dC(H)CO2R]
t
(R ) Me or Bu )
Antonio Antin˜olo,† Fernando Carrillo-Hermosilla,† Mariano Fajardo,‡
Santiago Garc´ıa-Yuste,† Maurizio Lanfranchi,§ Antonio Otero,*,†
Maria Angela Pellinghelli,§ Sanjiv Prashar,† and Elena Villasen˜or†
Departamento de Quı´mica Inorga´nica, Orga´nica y Bioquı´mica, Facultad de Quı´micas,
Campus Universitario, Universidad de Castilla-La Mancha, 13071-Ciudad Real, Spain,
Departamento de Quı´mica Inorga´nica, Campus Universitario, Universidad de Alcala´,
28871-Alcala´ de Henares, Spain, Dipartimento di Chimica Generale ed Inorganica,
Chimica Analitica, Chimica Fisica, Universita degli Studi di Parma, Centro di Studio per la
Strutturistica Diffractometrica del CNR, Viale delle Scienze 78, I-43100 Parma, Italy
Received J uly 1, 1996X
The hydride isocyanide complexes, Nb(η5-C5H4SiMe3)2(H)(CNR), R ) xylyl ) 2,6-dimeth-
ylphenyl; Cy (cyclohexyl); tBu; as well as the hydride carbonyl complex Nb(η5-C5H4SiMe3)2-
(H)(CO) react with several activated alkynes to afford the corresponding alkenyl isocyanide
complexes Nb(η5-C5H4SiMe3)2(CNR)(C(R′)dCH(R′′)), R ) xylyl, R′ ) R′′ ) CO2Me 1; R )
t
Xylyl, R′ ) R′′ ) CO2 Bu 2; R ) Xylyl, R′ ) CO2Me, R′′ ) H 3; R ) Xylyl, R′ ) CO2Me, R′′
t
) Me 4; R ) Cy, R′ ) R′′ ) CO2Me 5; R ) Cy, R′ ) R′′ ) CO2 Bu 6; R ) Cy, R′ ) CO2Me,
t
t
t
R′′ ) Me 7; R ) Bu, R′ ) R′′ ) CO2Me 8; Bu, R′ ) R′′ ) CO2 Bu 9 and alkenyl-carbonyl
complexes, Nb(η5-C5H4SiMe3)2(CO)(C(R′)dCH(R′′)), R′ ) R′′ ) CO2Me 10; R′ ) R′′ ) CO2 Bu
t
11; R′ ) CO2Me, R′′ ) H 12. The reaction of hydride isocyanide complexes with activated
alkynes gives cis-insertion resulting in the formation of (E)-alkenyl products. However, the
hydride carbonyl derivative undergoes insertion to give, under kinetic control, a mixture of
(E)- and (Z)-alkenyl isomers. Finally, the trihydride niobocene complex Nb(η5-C5H4-
SiMe3)2(H)3, reacts with esters RO2CCtCCO2R′ or MeO2CCtCH to give the hydride olefin
derivatives, Nb(η5-C5H4SiMe3)2(H)[η2-RO2C(H)dC(H)CO2R′], R ) R′ ) Me 13; R ) R′ ) tBu
14; and Nb(η5-C5H4SiMe3)2(H)[η2-MeO2C(H)dCH2] 15, probably as the result of a stereospe-
cific trans-insertion. The different complexes have been characterized by spectroscopic
methods. In addition, the structure of 13 and 14 were determined by single crystal X-ray
diffraction.
In tr od u ction
plexes of early transition metals react readily with
activated alkynes bearing electron-withdrawing groups
to give alkenyl complexes, and thus in earlier work the
behavior of niobocene-hydrides, especially Nb(η5-C5H5)2-
(H)(CO) was extensively studied.2h,3 In connection with
our studies on the use of unsaturated molecules in the
synthesis of new families of niobium organometallics,
the insertions of CO2 and CS2 into Nb-H bonds to
produce formate and dithioformate derivatives were
Insertion of unsaturated molecules into metal-hy-
dride bonds are considerered as fundamental chemical
steps in several catalytic cycles and frequently leads to
reactive intermediates. In particular the insertion of
alkynes into transition metal-hydrogen bonds is a key
elementary step in catalytic polymerization and hydro-
genation processes.1 In the last few years, the stereo-
chemistry and mechanism involved in the insertion
process have received considerable attention.2 Insertion
results in the formation of alkenyl products show that
cis- and trans-insertions yield the (E)-alkenyl and (Z)-
alkenyl products, respectively, and that the importance
of the cis/trans stereochemistry depends on several
factors, such as the nature of the metal center, ancillary
ligands, and substituents on the alkyne. Electron-rich,
coordinatively saturated, metallocene-hydride com-
(2) Some representative examples: (a) Clark, H. C.; Tsang, W. S.
J . Am. Chem. Soc. 1967, 89, 533. (b) Davidson, J . L.; Green, M.;
Gordon, F.; Stone, A.; Welch, A. J . J . Chem. Soc., Chem. Commun.
1975, 286. (c) Otsuka, S.; Nakamura, A. Adv. Organomet. Chem. 1976,
14, 245. (d) Williams, J . P.; Wojcicki, A. Inorg. Chem. 1977, 16, 3116.
(e) Pe´tillon, F. Y.; de Floch-Pe´rennou, F.; Guerchais, J . E.; Sharp, D.
W. A.; Manojlovic-Muir, L. J .; Muir, K. W. J . Organomet. Chem. 1980,
202, 23. (f) Scordia, H.; Kergoat, R.; Kubicki, M. M.; Guerchais, J . E.
J . Organomet. Chem. 1983, 249, 371. (g) Pe´tillon, F. Y.; de Que´re´,
J .-L.; de Floch-Pe´rennou, F.; Guerchais, J . E.; Gomes de Lima, M.-B.;
Manojlovic-Muir, L. J .; Muir, K. W.; Sharp, D. W. A. J . Organomet.
Chem. 1984, 255, 231. (h) Amaudrut, J .; Leblanc, J .-C.; Mo¨ıse, C.;
Sala-Pala, J . J . Organomet. Chem. 1985, 295, 167. (i) Clark, H. C.;
Ferguson, G.; Goel, A. B.; J anzen, E. G.; Ruegger, H.; Siew, P. Y.; Wong,
C. S. J . Am. Chem. Soc. 1986, 108, 6961. (j) Cariou, M.; Etienne, M.;
Guerchais, J . E.; Kergoat, R.; Kubicki, M. M. J . Organomet. Chem.
1987, 327, 393. (k) J ones, W. D.; Chandler, V. L.; Feher, E. J .
Organometallics 1990, 9, 164. (l) Herberich, G. E.; Mayer, H. Orga-
nometallics 1990, 9, 2655.
† Universidad de Castilla-La Mancha.
‡ Universidad de Alcala´.
§ Universita degli Studi di Parma.
X Abstract published in Advance ACS Abstracts, November 1, 1996.
(1) Collman, J . P.; Hegedus, L. S.; Norton, J . R.; Finke, R. E.
Principles and Applications of Organotransition Metal Chemistry;
University Science Books: Mill Valley, CA, 1987.
S0276-7333(96)00524-9 CCC: $12.00 © 1996 American Chemical Society

5508 Organometallics, Vol. 15, No. 26, 1996
Antin˜olo et al.
Sch em e 1. P r op osed Mech a n ism for th e In ser tion of Activa ted Alk yn es in to Nb-H Bon d s
recently explored.4,5 Continuing in this field, we report
here our results on the reactivity of Nb(η5-C5H4-
SiMe3)2(H)(CNR), Nb(η5-C5H4SiMe3)2(H)(CO), and Nb(η5-
C5H4SiMe3)2(H)3 with activated alkynes which has
permitted the preparation of new niobocene isocyanide
or carbon monoxide alkenyl complexes, Nb(η5-C5H4-
SiMe3)2(L)(C(R′)dCH(R′′)), L ) CNR, CO, as well as
hydride olefin complexes, Nb(η5-C5H4SiMe3)2(H)[η2-
RO2C(H)dC(H)CO2R′].
remained the alkenyl derivative, Nb(η5-C5H4SiMe3)2(L)-
(C(R′)dCH(R′′)), and therefore an alternative insertion
in the Nb-isocyanide bond or coupling in the primary
insertion reactions of alkenyl and isocyanide ligands
were not observed. However reactions of Nb(η5-C5H4-
SiMe3)2(H)(CNtBu) with esters HCtCCO2Me and
MeCtCCO2Me and Nb(η5-C5H4SiMe3)2(H)(CNCy) with
HCtCCO2Me gave a mixture of unidentifiable products.
The alkenyl niobocene complexes 1-9 behave as air-
sensitive products, and they were all isolated exclusively
as the (E)-alkenyl isomer, probably as result of a
stereoselective cis-insertion of the alkyne into the Nb-H
bond via a four-centered transition state (see route a,
Scheme 1).2c
It is noteworthy that most of the processes of hydride
metallocenes with disubstituted activated alkynes occur
via stereospecific trans-insertion reactions that give rise
to kinetic products of (Z)-configuration.7 However in
some cases of sterically more crowded metallocenes, for
example Nb(η5-C5H5)2(H)(Me3SiCtCSiMe3),21 the (E)-
isomer is exclusively formed under kinetic control
probably via the aforementioned four-centered transi-
tion state. With these precedents, we must consider
that in the reactions reported here, the presence of
bulky isocyanide ligands favors the proposed stereospe-
cific cis-insertion to give exclusively (E)-isomers.
However, in the reaction of Nb(η5-C5H4SiMe3)2(H)-
(CO) with the activated alkynes, under kinetic control,
a mixture of the (Z)- and (E)-alkenyl niobocene com-
plexes were obtained (eq 2).
Resu lts a n d Discu ssion
We have previously prepared the hydride isocyanide
complexes, Nb(η5-C5H4SiMe3)2(H)(CNR)6 and viewed it
as an ideal complex for studying its behavior with
activated alkynes bearing electron-withdrawing sub-
stituents with the principal aim of extending the
knowledge of the insertion processes of these reagents
into the Nb-H bond. This is the first time that such a
study has been carried out with niobocenes containing
isocyanides as ancillary ligands.
Nb(η5-C5H4SiMe3)2(H)(CNR) complexes react with the
corresponding activated alkynes to give, in a straight-
forward manner, the corresponding alkenyl isocyanide
complexes (eq 1).
Nb(η5-C5H4SiMe3)2(H)(CNR) + R′CtCR′′ f
Nb(η5-C5H4SiMe3)2(CNR)(C(R′)dCH(R′′)
1, R ) xylyl, R′ ) R′′ ) CO2Me
t
2, R ) xylyl, R′ ) R′′ ) CO2 Bu
As in the reactions of the isocyanide-containing
complexes, derivatives 10-12 were the only species to
be isolated. No reaction was observed with the ester
MeCtCCO2Me. We propose, in accordance with data
3, R ) xylyl, R′ ) CO2Me, R′′ ) H
4, R ) xylyl, R′ ) CO2Me, R′′ ) Me
5, R ) Cy, R′ ) R′′ ) CO2Me
t
6, R ) Cy, R′ ) R′′ ) CO2 Bu
(3) Herberich, G. E.; Mayer, H. J . Organomet. Chem. 1988, 347, 93.
(4) Antin˜olo, A.; Fajardo, M.; Garc´ıa-Yuste, S.; del Hierro, I.; Otero,
A.; Elkrami, S.; Mourad, Y.; Mugnier, Y. J . Chem. Soc., Dalton Trans.
1995, 3409.
(5) Antin˜olo, A.; Carrillo, F.; Fajardo, M.; Garc´ıa-Yuste, S.; Otero,
A. J . Organomet. Chem. 1994, 482, 93.
7, R ) Cy,R′ ) CO2Me, R′′ ) Me
8, R ) tBu, R′ ) R′′ ) CO2Me
t
9, R ) tBu, R′ ) R′′ ) CO2 Bu
(1)
(6) Garc´ıa-Yuste, S. Unpublished results.
(7) (a) Herberich, G. E.; Barlage, W. Organometallics 1987, 6, 1924.
(b) Herberich, G. E.; Barlage, W. J . Organomet. Chem. 1987, 331, 63.
With an excess of alkyne and varying the experimen-
tal conditions of the reaction the only isolable product

Insertion Reactions of Activated Alkynes into Nb-H Bonds
Nb(η5-C5H4SiMe3)2(H)(CO) + R′CtCR′′ f
Organometallics, Vol. 15, No. 26, 1996 5509
Nb(η5-C5H4SiMe3)2(CO)(C(R′)dCH(R′′)
10, R′ ) R′′ ) CO2Me
t
11, R′ ) R′′ ) CO2 Bu
12, R′ ) CO2Me, R′′ ) H
(2)
previously described,3 that a primary trans stereospe-
cific insertion occurs via a four-centered transition
state2c (see route b, Scheme 1) to give the kinetic (Z)-
isomer (10a and 11a ), and a subsequent isomerization
gives (E)-isomer (10b and 11b) resulting in the mixture
of (E)- and (Z)-isomers. In fact, the (Z)-isomer is the
major product from the reaction mixture (Z/E ratio of
ca. 4/1), but in solution at room temperature isomer-
ization takes place slowly and after 2 days the Z/E ratio
was ca. 3/2. It has previously been reported that Nb-
(η5-C5H5)2(H)(CO) reacts with dimethylacetylene dicar-
boxylate or cyanoethyne to give, under kinetic control,
a mixture of (Z)- and (E)-isomers, although exclusive
formation of the (Z)-isomer was observed with hexafluo-
robut-2-yne.2h,3 In the case of 10 the (Z)-isomer was
isolated, by means of differing solubilities, and slowly
evolved (2 days) to give a mixture of (E)- and (Z)-isomers
(Z/E ratio of ca. 3/2). As a consequence of these results
and other reported in the literature, we can establish
that in the presence of bulky ancillary ligands, such as
some alkynes and isocyanides, a primary cis stereospe-
cific insertion under kinetic control affords the (E)-
isomer probably via the four-centered transition state
shown in route a, Scheme 1, which is favored by steric
arguments.
F igu r e 1.
affording the new hydride olefin complexes Nb(η5-
C5H4SiMe3)2(H)[η2-RO2C(H)dC(H)CO2R′] and Nb(η5-
C5H4SiMe3)2(H)[η2-MeO2C(H)dCH2] (eq 3).
Nb(η5-C5H4SiMe3)2(H)3 + RCtCR′ f
Nb(η5-C5H4SiMe3)2(H)[η2-RC(H)dC(H)R′]
13, R ) R′ ) CO2Me
t
14, R ) R′ ) CO2 Bu
15, R ) CO2Me, R′ ) H
(3)
The reaction takes place virtually instantaneously in
THF with the disubstituted alkynes, giving rise to 13
and 14, but requires 6 h at room temperature for the
monosubstituted alkyne 15; nevertheless, with nonac-
tivated alkynes the corresponding alkyne hydride niob-
ocene complexes are the only products to be isolated.10
This is the first example of hydride olefin niobocene
complexes that have been prepared by the reaction of a
niobocene trihydride with alkynes, since this type of
complexes was synthesized by employing two alterna-
tive processes, namely the reaction of Nb(η5-C5R5)2Cl2
and Nb(η5-C5R5)2(H)3 with various alkylmagnesium
halides and olefins, respectively.11 A similar behavior
was reported in the reaction of a tantalocene trihydride
with activated alkynes containing electron-withdrawing
substituents where Ta(η5-C5H5)2(H)3 reacts with the
esters RO2CCtCCO2R (R ) Me, SiMe3) to give the
corresponding fumaric ester complexes Ta(η5-C5H5)2-
(H)(trans-RO2CCHdCHCO2R),12 but with simple alkynes,
as our trihydride complex, the corresponding alkyne
hydride tantalocenes were isolated. Complexes 13-15
were isolated as air-sensitive materials, and their
special inertness towards several unsaturated reagents
is noteworthy, namely CO, CNR, CS2, and activated
alkynes, thus preventing insertion processes even under
drastic conditions. This is in contrast with the behavior
that has been previously observed for other hydride
olefin niobocene complexes.13
The structural characterization of the different alk-
enyl niobocene complexes was carried out by IR and
NMR spectroscopy. The IR spectra show the charac-
teristic bands of the alkenyl and the different isocyanide
or carbonyl ancillary ligands (see Experimental Section).
In NMR spectroscopy the value of the vicinal coupling
constant of the alkenyl protons with the carbonyl carbon
atom of the R-carbon has been used as a useful tool to
establish (E)- or (Z)-stereochemistry for the alkenyl
group (Figure 1).21,7a,b
In the alkenyl isocyanide niobocene complexes (except
3
3), the coupling constant J (1H-13C) of ca. 15 Hz agrees
with a trans-disposition of the R-ester and the alkenyl
proton in the (E)-isomer. In the case of 4 and 7 a
quartet and a doublet were observed (2J (1H-1H) ca. 6.5
Hz) showing the existence of a CdCHMe moiety.
Furthermore, NMR spectra of the carbonyl alkenyl
derivatives 10 and 11 indicate, in accordance with the
coupling constants 3J (1H-13C) of ca. 9 Hz and ca. 15
Hz (see Experimental Section), that a mixture of (E)-
and (Z)-isomers were present. Finally in 1H NMR
spectra of 3 and 12, a doublet with a small coupling
constant of (2J (1H-1H)) ca. 3.5 Hz indicates that a
CdCH2 moiety is present8 as a result of a regiospecific
R-insertion.
Although we have not been able to detect any inter-
mediate species on following the reactions by variable
(8) Cullen, W. R.; Dawson, D. S.; Styan, G. E. Can. J . Chem. 1965,
43, 3392.
(9) (a) Labinger, J . A.; Schwartz, J . J . Am. Chem. Soc. 1975, 97,
159. (b) Sala-Pala, J .; Amaudrut, J .; Guerchais, J . E.; Mercier, R.;
Cerutti, M. J . Fluor. Chem. 1979, 14, 269. (c) Sala-Pala, J .; Amaudrut,
J .; Guerchais, J . E.; Mercier, R.; Douglade, J .; Theopold, J . G. J .
Organomet. Chem. 1981, 204, 347. (d) Threlkel, R. S.; Bercaw, J . E.
J . Am. Chem. Soc. 1981, 103, 2650.
(10) Antin˜olo, A.; Fajardo, M.; J alo´n, F.; Lo´pez Mardomingo, C.;
Otero, A.; Sanz-Bernabe´, C. J . Organomet. Chem. 1989, 369, 187.
(11) (a) Klazinga, A. H.; Teuben, J . H. J . Organomet. Chem. 1978,
157, 413. (b) Eichiner, M. E.; Alt, H. G.; Rausch, M. D. J . Organomet.
Chem. 1984, 264, 309. (c) Klazinga, A. H.; Teuben, J . H. J . Organomet.
Chem. 1980, 194, 309. (d) Doherty, N. M.; Bercaw, J . E. J . Am. Chem.
Soc. 1985, 107, 2670. (e) Green, M. L. H.; Sella, A.; Wong, L.-K.
Organometallics 1992, 11, 2650.
Following the study on the insertion processes of
activated alkynes into the niobium-hydride bond in
niobocenes, we have examined the behavior of the
trihydride complex Nb(η5-C5H4SiMe3)2(H)3 with some
of these activated reagents. Reactions of niobocene
trihydride with alkynes are well known and generally
give rise to alkyne hydride complexes.9 However Nb-
(η5-C5H4SiMe3)2(H)3 reacts with the activated alkynes
(12) Herberich, G. E.; Savvopoulos, I. J . Organomet. Chem. 1989,
362, 345.

5510 Organometallics, Vol. 15, No. 26, 1996
Antin˜olo et al.
Sch em e 2. P r op osed Mech a n ism for th e F or m a tion of th e Hyd r id e Olefin Com p lexes 13-15
F igu r e 2. View of complex 13 with atom-numbering
F igu r e 3. View of complex 14 with atom-numbering
scheme (30% probability ellipsoids).
scheme (30% probability ellipsoids).
1
temperature H NMR studies, the formation of 13-15
In complex 13 only the (S,S) enantiomer is present
while in 14 the enantiomers (S,S) and (R,R) are
found. Selected bond distances and angles are given
in Table 1.
may be explained by a similar rationale to that previ-
ously described for the tantalocene trihydride (see
Scheme 2).12
A stereospecific trans-insertion to give a dihydride
alkenyl intermediate is suggested in the first step,
followed by an intramolecular rearrangement which
leads to the final hydride olefin complexes, although
alternative plausible pathways cannot be excluded.
The structural characterization of 13-15 was carried
out by spectroscopic and X-ray diffraction studies. 1H
and 13C NMR spectra exhibit eight and ten resonances
for the proton and carbon atoms, respectively, for the
two cyclopentadienyl ligands, indicating that they are
nonequivalent, and this behavior is in agreement with
the structural disposition (vide infra) observed for these
complexes where the olefinic carbon atoms are coplanar
with the niobium and hydride atoms in such a way that
their substituents (in a trans-disposition) are situated
in a plane orthogonal to that containing the aforemen-
tioned atoms. This structural confirmation leads to the
presence of two resonances for the inequivalent SiMe3
The Cp′ ligands (Cp′ ) C5H4SiMe3), nearly staggered
with the two SiMe3 groups trans to each other, are
coordinated to the Nb atom in the conventional η5-
fashion (range of the Nb-C distances: 2.391(6)-2.422-
(5), 2.384(6)-2.433(5) Å for 13, and 2.370(4)-2.427(5)
and 2.386(4)-2.411(4) Å for 14), the distances between
the Nb atom and the centroids CE(1) and CE(2) of the
rings being 2.091(5) and 2.086(5) Å for 13 and 2.084(4)
and 2.081(4) Å for 14. The angles between the weighted
least-squares planes of the Cp′ ring carbon atoms are
not significantly different in the two complexes (47.3-
(2)° for 13 and 46.8(2)° for 14). The niobium atom is
also bound to the C(18) and C(19) carbon atoms of the
dihapto coordinated alkene. The metal coordination
description obviously requires positioning of the light
hydride atom which was clearly in evidence, for both
compounds, in the final ∆F map. (The Nb-H bond
lengths are 1.54(6) Å for 13 and 1.84(6) Å for 14, the
distance for 13 being somewhat shorter than expected).
The resultant coordination around the metal atom may
be described as an irregular flattened tetrahedron with
the centroids CE(1), CE(2), M(1) (the midpoint of the
olefinic C(18)dC(19) bond), and the hydride at the
vertices of the polyhedron. The NbM(1)H plane is
essentially perpendicular to the NbCE(1)CE(2) plane
(96.5(20)° for 13 and 93.1(9)° 14). The four atoms Nb,
C(18), C(19), and the hydride are practically coplanar
(the hydride ligand is out of the NbC(18)C(19) plane by
0.17(6) Å in 13 and 0.06(4) Å in 14), and the Nb-H bond
is parallel to the C(18)dC(19) bond. In fact the angles
subtended by the two weighted least-squares lines NbH
1
groups. Finally, the presence in the H NMR spectra
of AB spin systems for the olefinic protons must also
be emphasized (see Experimental Section).
In addition the X-ray crystal structures were deter-
mined for 13 and 14. Views, of the two similar
complexes, which adopt the typical bent-metallocene
structure are shown in Figures 2 and 3 together with
the atom-numbering schemes.
The chirality of the two complexes is due to the
configuration of the coordinated C(18) and C(19) atoms.
(13) (a) Antin˜olo, A.; Carrillo, F.; Garc´ıa-Yuste, S.; Otero, A. Orga-
nometallics 1994, 13, 2761. (b) Antin˜olo, A.; del Hierro, I.; Fajardo,
M.; Garc´ıa-Yuste, S.; Otero, A.; Blacque, O.; Kubicki, M. M.; Amaudrut,
J . Organometallics 1996, 15, 1966.

Insertion Reactions of Activated Alkynes into Nb-H Bonds
Organometallics, Vol. 15, No. 26, 1996 5511
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for 13 a n d 14 w ith ESDs in P a r en th esesa
in the ethylene complex (2.277(9), 2.320(9) Å) are similar
to those found in 13 (2.316(5), 2.299(5) Å) and in 14
(2.308(4), 2.294(4) Å).
13
14
The most remarkable differences between the π-bond-
ed alkene ligands in the two parent complexes are the
bond angles C(17)-O(2)-C(21) [116.3(4)° for 13 and
121.7(3)° for 14] and C(20)-O(4)-C(22) [115.4(5)° for
13 and 120.9(4)° for 14] due to the steric hindrance of
Nb-CE(1)
Nb-CE(2)
Nb-M(1)
2.091(5)
2.086(5)
2.194(5)
1.54(6)
2.084(4)
2.081(4)
2.184(4)
1.84(6)
Nb-H
Nb-C(18)
Nb-C(19)
C(18)-C(19)
C(18)-C(17)
C(19)-C(20)
C(17)-O(1)
C(17)-O(2)
O(2)-C(21)
C(20)-O(3)
C(20)-O(4)
O(4)-C(22)
2.316(5)
2.299(5)
1.429(7)
1.468(7)
1.451(8)
1.224(7)
1.352(7)
1.431(8)
1.205(8)
1.373(8)
1.432(8)
2.308(4)
2.294(4)
1.448(6)
1.462(6)
1.470(6)
1.207(5)
1.355(6)
1.478(6)
1.204(5)
1.366(6)
1.462(7)
t
the bulky Bu groups in 14. Some π delocalization
occurs which involves the O(1)C(17)C(18)C(19) and the
O(3)C(20)C(19)C(18) fragments although the torsion
angles τ[C(17)-C(18)-C(19)-C(20)] ) -134.3(5)° 13,
(127.9(4)° 14 reveal a deformation from planarity of
the C(17)C(18)C(19)C(20) moiety due to the “σ-π”-
interaction with the metal.
CE(1)-Nb-CE(2)
CE(1)-Nb-M(1)
CE(2)-Nb-M(1)
CE(1)-Nb-H
134.4(2)
111.5(2)
111.7(2)
102.0(22)
89.4(22)
93.2(21)
121.1(4)
121.0(5)
126.3(5)
111.9(4)
121.8(5)
116.3(4)
127.4(6)
111.3(5)
121.3(6)
115.4(5)
134.5(2)
112.1(2)
112.1(2)
97.9(14)
92.0(14)
90.3(14)
119.6(3)
120.4(4)
126.3(4)
110.2(3)
123.4(4)
121.7(3)
127.4(4)
108.9(4)
123.7(4)
120.9(4)
Exp er im en ta l Section
Gen er a l P r oced u r es. All reactions were performed using
standard Schlenk-tube techniques in an atmosphere of dry
nitrogen. Solvents were distilled from appropriate drying
agents and degassed before use.
CE(2)-Nb-H
M(1)-Nb-H
C(17)-C(18)-C(19)
C(18)-C(19)-C(20)
C(18)-C(17)-O(1)
C(18)-C(17)-O(2)
O(1)-C(17)-O(2)
C(17)-O(2)-C(21)
C(19)-C(20)-O(3)
C(19)-C(20)-O(4)
O(3)-C(20)-O(4)
C(20)-O(4)-C(22)
The complexes Nb(η5-C5H4SiMe3)2(H)(CN(2,6-Me2-C6H3),
Nb(η5-C5H4SiMe3)2(H)(CNC6H11), Nb(η5-C5H4SiMe3)2(H)(CNtBu),
Nb(η5-C5H4SiMe3)2(H)(CO), and Nb(η5-C5H4SiMe3)2(H)3 were
prepared as described earlier.6,10,17 IR spectra were recorded
on a Perkin-Elmer PE 883 IR spectrophotometer. 1H and 13C
spectra were recorded on Varian FT-300 and Varian Gemini
FT-200 spectrometers and referenced to the residual deuteri-
ated solvent. Microanalyses were carried out with a Perkin-
Elmer 2400 microanalyzer.
a
Nb(η5-C5H4SiMe3)2(CNR)(C(R′)dCH(R′′) [R ) xylyl, R′ )
CE(1) and CE(2) are the centroids of the C(1)‚‚‚C(5) and
C(9)‚‚‚C(13) Cp′ rings, respectively, M(1) the midpoint of the
C(18)dC(19) bond.
t
R′′ ) CO2Me 1; R ) xylyl, R′ ) R′′ ) CO2 Bu 2; R ) xylyl, R′
) CO2Me, R′′ ) H 3; R ) xylyl, R′ ) CO2Me, R′′ ) Me 4; R )
t
Cy, R′ ) R′′ ) CO2Me 5; R ) Cy, R′ ) R′′ ) CO2 Bu 6; R ) Cy,
t
and C(18)C(19) are 6.7(21)° for 13 and 1.8(14)° for 14.
The NbC(18)C(19) plane bisects the two Cp′ rings (the
angles between the weighted least-squares plane NbC-
(18)C(19) and the C(1)‚‚‚C(5) Cp′ ring and the C(9)‚‚‚
C(13) Cp′ ring are 23.6(2)° and 23.6(2)° for 13 and
25.8(2) and 21.9(2)° for 14, respectively).
R′ ) CO2Me, R′′ ) Me 7; R ) Bu, R′ ) R′′ ) CO2Me 8; R )
t
tBu, R′ ) R′′ ) CO2 Bu 9]. The activated alkyne, MeO2-
CCtCCO2Me (0.062 mL, 0.50 mmol), was added to a solution
of Nb(η5-C5H4SiMe3)2(H)(CN(2,6-Me2-C6H3)) (0.25 g, 0.50 mmol)
in THF (ca. 30 mL). The resulting mixture was stirred for 15
min at room temperature, and the solvent was removed, in
vacuo, to give a red oily solid which was washed with cold
hexane (20 mL at -30 °C) to yield the red solid 1 (0.26 g, 81%).
2, 5, 6, 8, and 9 were prepared in a similar manner to 1; for 3,
4, and 7, the reaction mixture was stirred for 5 h at 50 °C.
Yields of 60-80% were recorded for 2-9.
With the exception of 13 and 14, only one structurally
characterized hydride alkene complex with the position-
ing of the hydride ligand, Nb(η5-C5Me5)2(H)[η2-C(H)Hd
C(H)C6H5], has been reported.14 In the case of [Nb(η-
C4H6)2(H)(dmpe)2] the hydride was not located.15 In the
styrene complex Nb(η5-C5Me5)2(H)[(η2-C(H)HdC(H)-
C6H5] the Nb-CCp*, Nb-CE distances and the CE(1)-
Nb-CE(2) angle (Nb-C range: 2.415(4)-2.506(4), 2.439-
(4)-2.484(4) Å; Nb-CE: 2.140, 2.143 Å; CE(1)-Nb-
CE(2) ) 141.4°) are obviously larger than in the present
complexes although the olefinic carbon-carbon bond
length (1.431(6) Å) is very similar to those found in 13
(1.429(7) Å) and in 14 (1.448(6) Å). These values are
larger than that of a free olefin and may be indicative
of substantial back donation from the metal to the olefin,
introducing some metallacyclopropane-Nb(V) character
into the formally Nb(III) olefin adduct. The CdC bond
distances do not seem to be significantly different to that
found in the ethylene complex Nb(η5-C5H5)2((C2H5))[(η2-
C(H)HdC(H)H] (1.406(13) Å).16 The Nb-C olefin bond
lengths in the styrene complex (2.289(4), 2.309(4) Å) and
1: IR (Nujol) νCN 2037 cm-1, νCdC 1624 cm-1
.
1H NMR (200
MHz, C6D6): δ 0.01 (s, 18H, SiMe3), 4.79 (2H), 5.10 (2H), 5.15
(2H), 5.55 (2H) (m, C5H4), 2.21 (s, 6H, MeCNR), 6.67 (m, 3H,
C6H3CNR), 3.36 (3H), 3.46 (3H) (s, CO2Me), 6.24 (s, 1H,
CdCH). 13C{1H} NMR (300 MHz, C6D6): δ 0.18 (SiMe3), 90.80,
94.61 (C1), 98.43, 100.95, 105.15 (C5H4), 18.96 (MeCNR), 230.00
(CNR), 187.00 (CdCH), 129.74 (CdCH), 162.02, 179.93 (CO2-
Me), 50.18, 50.37 (CO2Me). 13C NMR (300 MHz, C6D6):
3J (13C1-1Hâ) 15.96 Hz. Anal. Calcd for C31H42NNbO4Si2: C,
58.02; H, 6.60; N, 2.18. Found: C, 57.83; H, 6.54; N, 2.16.
2: IR (Nujol) νCN 2038 cm-1, νCdC 1575 cm-1 1H NMR (200
.
MHz, C6D6): δ 0.04 (s, 18H, SiMe3), 4.87 (2H), 5.14 (2H), 5.20
(2H), 5.57 (2H) (m, C5H4), 2.29 (s, 6H, MeCNR), 6.71 (m,
t
3H, C6H3CNR), 1.40 (9H), 1.55 (9H) (s, CO2 Bu), 6.62 (s,
1H, CdCH). 13C{1H} NMR (300 MHz, C6D6): δ 0.17 (SiMe3),
90.69, 94.21 (C1) 98.24, 101.36, 104.88 (C5H4), 19.00 (MeCNR),
228.63 (CNR), 183.50 (CdCH), 131.56 (CdCH), 161.19,
t
t
179.21 (CO2 Bu), 28.46, 29.01, 77.76, 78.03 (CO2 Bu). 13C NMR
(300 MHz, C6D6): 3J (13C1-1Hâ) 15.10 Hz. Anal. Calcd for
C
37H54NNbO4Si2: C, 61.22; H, 7.50; N, 1.93. Found: C, 61.15;
(14) Burger, B. J .; Santarsiero, B. D.; Trimmer, M. S.; Bercaw, J .
E. J . Am. Chem. Soc. 1988, 110, 3134.
H, 7.51; N, 1.88.
(15) Brown, P. R.; Green, M. L. H.; Hare, P. M.; Bandy, J . A.
Polyhedron 1988, 7, 1819.
(16) Guggenberger, L. J .; Meakin, P.; Tebbe, F. N. J . Am. Chem.
Soc. 1974, 96, 5420.
(17) Antin˜olo, A.; Chaudret, B.; Commenges, G.; Fajardo, M.; J alo´n,
F.; Morris, R. H.; Otero, A.; Schweltzer, C. T. J . Chem. Soc., Chem.
Commun. 1988, 1210.

5512 Organometallics, Vol. 15, No. 26, 1996
3: IR (Nujol) νCN 2045 cm-1, νCdC 1591 cm-1 1H NMR (200
Antin˜olo et al.
.
1Hâ) 14.61 Hz. Anal. Calcd for C33H54NNbO4Si2: C, 58.47;
H, 8.03; N, 2.07. Found: C, 58.15; H, 7.87; N, 2.11.
Nb(η5-C5H4SiMe3)2(CO)(C(R′)dCH(R′′) [R′ ) R′′ ) CO2-
MHz, C6D6): δ 0.07 (s, 18H, SiMe3), 4.85 (2H), 5.19 (2H), 5.23
(2H), 6.71 (2H) (m, C5H4), 2.22 (s, 6H, MeCNR), 6.71 (m, 3H,
C6H3CNR), 3.33 (s, 3H, CO2Me), 5.53 (1H), (d, CdCH), 2J (1H-
1H) 4.34 Hz. 13C{1H} NMR (300 MHz, C6D6): δ 0.27 (SiMe3),
90.83, 94.30 (C1), 97.63, 101.31, 104.68 (C5H4), 19.02 (MeCNR),
225.72 (CNR), 166.17 (CdCH), 135.20 (CdCH), 181.31 (CO2-
Me), 49.95 (CO2Me). Anal. Calcd for C29H40NNbO2Si2: C,
59.67; H, 6.91; N, 2.40. Found: C, 59.40; H, 6.80; N, 2.35.
t
Me 10; R′ ) R′′ ) CO2 Bu 11; R′ ) CO2Me, R′′ ) H 12]. 10,
11, and 12 were prepared in a similar manner to 1 in yields
of 60-80%.
10: IR (Nujol) νCO 1904 cm-1, νCdC 1566 cm-1 1H NMR (200
.
MHz, C6D6): 10a δ 0.05 (s, 18H, SiMe3), 4.80 (2H), 4.92 (2H),
5.20 (2H), 5.55 (2H) (m, C5H4), 3.35 (3H), 3.70 (3H) (s, CO2Me),
6.80 (s, 1H, CdCH); 10b δ 0.15 (s, 18H, SiMe3), 4.85 (2H), 4.89
(2H), 5.20 (2H), 5.39 (2H) (m, C5H4), 3.39 (3H), 3.60 (3H) (s,
CO2Me), 6.28 (s, 1H, CdCH). 13C{1H} NMR (300 MHz,
C6D6): 10a δ 0.32 (SiMe3), 95.72 (C1), 99.53, 100.51, 101.94,
105.01 (C5H4), 260.06 (CO), 181.64 (CdCH), 131.55 (CdCH),
169.07, 180.19 (CO2Me), 50.16, 50.46 (CO2Me); 10b δ 0.23
(SiMe3), 90.55, 92.53 (C1), 94.06, 96.07, 98.57 (C5H4), 258.32
(CO), 184.32 (CdCH), 128.53 (CdCH), 162.11, 181.64 (CO2-
Me), 51.53, 52.52 (CO2Me). 13C NMR (300 MHz, C6D6): 10a
4: IR (Nujol) νCN 2032 cm-1, νCdC 1604 cm-1 1H NMR (200
.
MHz, C6D6): δ 0.09 (s, 18H, SiMe3), 4.88 (2H), 5.13 (2H), 5.26
(2H), 5.65 (2H) (m, C5H4), 2.31 (s, 6H, MeCNR), 6.75 (m, 3H,
C6H3CNR), 3.27 (s, 3H, CO2Me), 1.67 (d, 3H, CdCMe), 6.58
2
(q, 1H, CdCH), J 1H-1H) 6.30 Hz. 13C{1H} NMR (300 MHz,
C6D6): δ 0.43 (SiMe3), 90.74, 93.20 (C1), 97.29, 101.63, 105.42
(C5H4), 19.11 (MeCNR), 220.45 (CNR), 170.87 (CdCH), 135.40
(CdCH), 21.67 (CdCMe), 180.87 (CO2Me), 49.76 (CO2Me). 13
C
NMR (300 MHz, C6D6): 3J (13C1-1Hâ) 15.35 Hz. Anal. Calcd
for C30H42NNbO2Si2: C, 60.28; H, 7.08; N, 2.34. Found: C,
59.98; H, 6.97; N, 2.25.
3J (13C1-1Hâ) 8.62 Hz; 10b J (13C1-1Hâ) 13.50 Hz. Anal. Calcd
for C23H33NbO5Si2: C, 51.29; H, 6.18. Found: C, 51.62; H,
6.24.
11: IR (Nujol) νCO 1920 cm-1, νCdC 1558 cm-1 1H NMR (200
.
3
5: IR (Nujol) νCN 2100 cm-1, νCdC 1616 cm-1 1H NMR (200
.
MHz, C6D6): δ 0.09 (s, 18H, SiMe3), 4.68 (2H), 5.00 (2H), 5.08
(2H), 6.40 (2H) (m, C5H4), 0.94-1.60, 3.53 (m, 11H, CNC6H11),
3.42 (3H), 3.76 (3H) (s, CO2Me), 6.40 (s, 1H, CdCH). 13C{1H}
NMR (300 MHz, C6D6): δ 0.36 (SiMe3), 89.75, 93.93 (C1), 99.50,
99.97, 102.87 (C5H4), 23.85, 25.22, 25.83, 33.67, 56.69 (C1),
67.79 (CNC6H11), 208.68 (CNC6H11), 188.65 (CdCH), 131.41
(CdCH), 161.85, 181.26 (CO2Me), 50.50, 56.69 (CO2Me). 13C
NMR (300 MHz, C6D6): 3J (13C1-1Hâ) 13.70 Hz. Anal. Calcd
for C29H44NNbO4Si2: C, 56.20; H, 7.16; N, 2.26. Found: C,
56.22; H, 7.16; N, 2.29.
MHz, C6D6): 11a δ 0.13 (s, 18H, SiMe3), 4.84 (2H), 5.06 (2H),
t
5.16 (2H), 5.51 (2H) (m, C5H4), 1.37 (9H), 1.48 (9H) (s, CO2 -
Bu), 6.72 (s, 1H, CdCH); 11b δ 0.22 (s, 18H, SiMe3), 4.82 (2H),
5.10 (2H), 5.20 (2H), 5.31 (2H) (m, C5H4), 1.40 (9H), 1.62 (9H)
t
(s, CO2 Bu), 6.21 (s, 1H, CdCH). 13C{1H} NMR (300 MHz,
C6D6): 11a δ 0.08 (SiMe3), 90.79, 95.39, 95.89 (C1), 100.21,
105.54 (C5H4), 259.81 (CO), 161.50 (CdCH), 133.46 (CdCH),
t
t
168.79, 180.10 (CO2 Bu), 28.39, 28.80, 78.22, 78.93 (CO2 Bu);
11b δ 0.16 (SiMe3), 90.83, 92.34 (C1), 94.26, 98.41, 102.32
(C5H4), 256.52 (CO), 141.84 (CdCH), 132.15 (CdCH), 161.76,
6: IR (Nujol) νCN 2091 cm-1, νCdC 1605 cm-1 1H NMR (200
.
t
t
178.81 (CO2 Bu), 28.40, 29.00, 78.31, 79.11 (CO2 Bu). 13C NMR
(300 MHz, C6D6): 11a 3J (13C1-1Hâ) 9.50 Hz; 11b 3J (13C1-1Hâ)
14.83 Hz. Anal. Calcd for C29H45NbO5Si2: C, 55.93; H, 7.28.
Found: C, 56.25; H, 7.36.
MHz, C6D6): δ 0.14 (s, 18H, SiMe3), 4.82 (2H), 5.02 (2H), 5.59
(2H), 6.09 (2H) (m, C5H4), 0.91-1.62, 3.53 (m, 11H, CNC6H11),
t
1.42 (9H), 1.69 (9H) (s, CO2 Bu), 6.45 (s, 1H, CdCH). 13C{1H}
NMR (300 MHz, C6D6): δ 0.45 (SiMe3), 88.82 (C1), 89.89,
100.66, 104.83, 112.06 (C5H4), 24.05, 25.53, 26.18, 33.84, 57.07
(C1), 67.79 (CNC6H11), 215.73 (CNC6H11), 180.53 (CdCH),
12: IR (Nujol) νCO 1912 cm-1, νCdC 1570 cm-1 1H NMR (200
.
MHz, C6D6): δ 0.04 (s, 18H, SiMe3), 4.68 (2H), 4.86 (2H), 4.89
(2H), 5.44 (2H) (m, C5H4), 3.29 (3H), (s, CO2Me), 6.29 (1H),
6.31 (1H) (d, CdCH2) 2J (1H-1H) 3.84 Hz. 13C{1H} NMR
(300 MHz, C6D6): δ 0.00 (SiMe3), 74.89 (C1), 90.80, 98.57,
99.17, 101.92 (C5H4), 260.76 (CO), 152.95 (CdCH), 133.84
(CdCH), 180.79, (CO2Me), 50.24 (CO2Me). Anal. Calcd for
t
132.86 (CdCH), 165.78, 179.91 (CO2 Bu), 29.21, 29.63, 77.53,
t
78.13 (CO2 Bu). 13C NMR (300 MHz, C6D6): 3J (13C1-1Hâ) 15.72
Hz. Anal. Calcd for C35H56NNbO4Si2: C, 59.72; H, 8.02; N,
1.99. Found: C, 59.54; H, 7.91; N, 1.95.
.
7: IR (Nujol) νCN 2032 cm-1, νCdC 1609 cm-1 1H NMR (200
C
21H31NbO3Si2: C, 52.49; H, 6.50. Found: C, 52.63; H, 6.56.
Nb(η5-C5H4SiMe3)2(H)[η2-RO2C(H)dC(H)CO2R′] [R ) R′
MHz, C6D6): δ 0.07 (s, 18H, SiMe3), 4.67 (2H), 4.92 (2H), 5.05
(2H), 5.51 (2H) (m, C5H4), 0.75-1.41, 3.47 (m, 11H, CNC6H11),
3.47 (s, 3H, CO2Me), 1.68 (d, 3H, CdCMe), 5.65 (q, 1H, CdCH),
2J (1H-1H) 6.4 Hz. 13C{1H} NMR (300 MHz, C6D6): δ 0.42
(SiMe3), 89.95, 92.71 (C1), 98.92, 101.13, 102.75 (C5H4), 23.98,
25.37, 25.80, 33.89, 57.40 (C1), 67.73 (CNC6H11), 224.53
(CNC6H11), 149.63 (CdCH), 136.81 (CdCH), 20.08 (CdCMe),
181.65 (CO2Me), 49.49 (CO2Me). 13C NMR (300 MHz, C6D6):
3J (13C1-1Hâ) 15.80 Hz. Anal. Calcd for C28H44NNbO2Si2: C,
58.41; H, 7.70; N, 2.43. Found: C, 58.13; H, 7.68; N, 2.45.
) Me 13: R ) R′ ) Bu 14] a n d Nb(η5-C5H4SiMe3)2(H)[η2-
MeO2C(H)dCH2] 15. Nb(C5H4SiMe3)2(H)3 (0.30 g, 0.80 mmol)
was dissolved in 40 mL of THF to give a light brown solution.
To this solution was added 0.80 mmol of the corresponding
activated alkyne. The mixture was stirred at room tempera-
ture for 15 min for 13 and 14, and for 24 h for 15. The
resulting yellow-brown solution was filtered, and solvent was
removed, from the filtrate, in vacuo. After washing the solid
with 30 mL of hexane and recrystallization from diethyl ether,
13 and 14 were isolated as yellow (13, yield: 80%) or light
blue crystals (14, yield: 75%). 15 was isolated as a yellow-
brown oily material (yield: 90%).
t
8: IR (Nujol) νCN 2085, 1825 cm-1, νCdC 1630 cm-1 1H NMR
.
(200 MHz, C6D6): δ 0.06 (s, 18H, SiMe3), 4.64 (2H), 5.00 (2H),
5.11 (2H), 5.52 (2H) (m, C5H4), 1.08 (s, 9H, CNtBu), 3.41 (3H),
3.78 (3H) (s, CO2Me), 6.40 (s, 1H, CdCH). 13C{1H} NMR (300
MHz, C6D6): δ 0.35 (SiMe3), 89.52, 93.96 (C1), 99.16, 99.76,
103.43 (C5H4), 30.74, 58.32 (CNtBu), 278.39 (CNtBu), 189.20
(CdCH), 161.78, 181.17 (CO2Me), 52.58, 67.77 (CO2Me). 13C
NMR (300 MHz, C6D6): 3J (13C1-1Hâ) 15.70 Hz. Anal. Calcd
for C27H42NNbO4Si2: C, 54.62; H, 7.13; N, 2.36. Found: C,
54.80; H, 7.22; N, 2.42.
13: IR (Nujol) νCO 1700 cm-1
.
1H NMR (200 MHz, C6D6): δ
-1.65 (s, 1H, NbH), 0.23 (9H), 0.28 (9H) (s, SiMe3), 2.68,
1
2.72 (dd, AB system, 2H, CO2Me(H)CdC(H)CO2Me) J AB
)
13.23 Hz, 3.46 (s, 3H, CO2Me), 3.51 (s, 3H, CO2Me), 3.95,
4.01, 4.29, 4.36, 4.52, 5.12, 5.15, 5.30 (s, 8H, C5H4). 13C{1H}
NMR (300 MHz, C6D6): δ 0.10, 0.14, (SiMe3), 29.92, 30.23
(MeO2C(H)CdC(H)CO2Me), 50.24, 50.50, (CO2Me), 91.98, 95.79,
98.21, 100.07, 102.26, 102.86, 103.12(C1), 106.50, 107.79,
107.99(C1) (C5H4), 180.29, 178.0 (CO2Me). Anal. Calcd for
22H35NbO4Si2: C, 51.50; H, 6.83. Found: C, 51.55; H, 6.83.
14: IR (Nujol) νCO 1665 cm-1 1H NMR (200 MHz, C6D6): δ
-1.80 (s, 1H, NbH), 0.25 (9H), 0.26 (9H) (s, SiMe3), 1.41 (s,
9: IR (Nujol) νCN 2093, 1836 cm-1, νCdC 1598 cm-1 1H NMR
.
(200 MHz, C6D6): δ 0.13 (s, 18H, SiMe3), 4.72 (2H), 5.00 (2H),
5.02 (2H), 5.55 (2H) (m, C5H4), 1.13 (s, 9H, CNtBu), 1.40 (9H),
C
t
1.67 (9H) (s, CO2 Bu), 6.44 (s, 1H, CdCH). 13C{1H} NMR (300
.
MHz, C6D6): δ 0.49 (SiMe3), 84.57, 89.62, 90.56 (C1), 101.4,
102.5 (C5H4), 28.50, 58.36 (CNtBu), 265.4 (CNtBu), 187.15 (C]-
t
t
9H, CO2 Bu), 1.44 (s, 9H, CO2 Bu), 2.54, 2.72 (dd, AB system,
2H, CO2 Bu(H)CdC(H)CO2 Bu) J AB ) 11.21 Hz, 3.83, 4.30,
t
t
t
1
dbdCH), 132.61 (CdCH), 179.95, 160.94 (CO2 Bu), 28.70, 28.86,
t
77.33, 78.17 (CO2 Bu). 13C NMR (300 MHz, C6D6): 3J (13C1-
4.40, 4.65, 4.85, 5.10, 5.35, 5.45 (s, 8H, C5H4). 13C{1H} NMR

Insertion Reactions of Activated Alkynes into Nb-H Bonds
Organometallics, Vol. 15, No. 26, 1996 5513
Ta ble 2. Su m m a r y of Cr ysta llogr a p h ic Da ta for
Com p lexes 13 a n d 14
rameters for all the non-hydrogen atoms. The hydride anions,
the hydrogen atoms of the Cp′ rings and of the C(18), C(19)
atoms of the η2 coordinated ligands were clearly located in the
∆F map and refined isotropically, all the others were placed
at their geometrically calculated positions (C-H ) 0.96 Å) and
refined “riding” on the corresponding carbon atoms (with
isotropic thermal parameters). The final cycles of refinement
were carried out on the basis of 310 for 13 and 364 for 14
variables; after the last cycles no parameters shifted by more
than 0.48 for 13 and 0.51 for 14 esd. The highest remaining
peak in the final difference map was equivalent to about 0.47
13
14
mol formula
mol wt
C22H35O4Si2Nb
512.594
C28H47O4Si2Nb
596.755
crystal system
space group
radiation (Mo KR)
a, Å
b, Å
c, Å
orthorhombic
P212121
λ ) 0.71073 Å graphite monochromated
12.227(2)
14.183(2)
14.903(4)
monoclinic
P21/n
14.171(4)
19.725(3)
12.390(3)
110.43(2)
3245.4(14)
4
for 13 and 0.78 for 14 e/Å3. In the final cycles of refinement
â, deg
V, Å3
2584.4(9)
4
1.317
2
a weighting scheme, w ) k[σ(Fo) + gFo
]
-1, was used; at
Z
D
convergence the k and g values were 0.3961 and 0.00138 for
13, 1.3373 and 0.00029 for 14, respectively. Since the space
group P212121 for 13 leads to a chiral configuration in the
structure, a refinement of the non-hydrogen atoms with
anisotropic thermal parameters was carried out using the
coordinates -x, -y, -z; an increase of the R and Rw values
was obtained [R(x,y,z)] ) 0.0445, Rw(x,y,z) ) 0.0598; R(-x,-
y,-z) ) 0.0457, Rw(-x,-y,-z) ) 0.0617]. The former model
was selected. Also the final refinement with the hydrogen
atoms was performed and confirmed the selected model [R(-
x,-y,-z) ) 0.0352, Rw(-x,-y,-z) ) 0.0393]. Although the
Nb-hydride distance results somewhat short in 13 after the
refinement, the direction of the Nb-H bond seems to be
correct; in fact the positional parameters were tested by means
of a “potential energy” technique using the HYDEX program.19
The analytical scattering factors, corrected for the real and
imaginary parts of anomalous dispersions, were taken from
ref 20. All calculations were carried out on the GOULD
POWERNODE 6040 and ENCORE 91 of the Centro di Studio
per la Strutturistica Diffrattometrica del CNR, Parma. The
system of computer programs SIR92,21 SHELXS-86 and
SHELX-76,22 Parst,23 and ORTEP24 were used. The final
atomic coordinates for the non-hydrogen atoms are given in
Table 3 for 13 and Table 4 for 14 in the supporting information.
The atomic coordinates of the hydrogen atoms and thermal
parameters are also given in the supporting information.
calcd, g cm-3
1.221
F(000)
1072
1264
cryst dimens, mm
µ(Mo KR), cm-1
diffractometer
2θ range, deg
reflns measd
unique total data
unique obsd data
[I g 2σ(I)]
0.25 × 0.30 × 0.35
0.27 × 0.32 × 0.40
5.81
4.72
Philips PW 1100
Siemens AED
6-60
h,k,l
4196
2580
h,k,(l
9456
3966
goodness of fit
1.02
0.0335, 0.0372
0.47
1.20
0.0430, 0.0450
0.78
RaRw
b
∆Fmax, e Å-3
a
b
R ) ∑||Fo| - |Fc||/∑|Fo|. Rw ) [∑w(|Fo| - |Fc|)2/∑w(Fo)2]1/2
.
(300 MHz, C6D6): δ -0.86, -0.55 (SiMe3), 27.68, 27.83
t
t
(CO2 Bu), 29.50, 34.56 (tBuO2C(H)CdC(H)CO2 Bu), 89.42,
90.29, 96.35, 99.20 (C1), 100.10, 101.52, 104.39, 105.44 (C1),
107.63, 113.81 (C5H4), 178.00, 180.29 (CO2 Bu). Anal. Calcd
t
for C28H47NbO4Si2: C, 56.31; H, 6.87. Found: C, 56.45; H,
6.90.
.
15: IR (Nujol) νCO 1650 cm-1 1H NMR (200 MHz, C6D6): δ
-2.15 (s, 1H, NbH), 0.32 (s, 9H, SiMe3), 0.36 (s, 9H, SiMe3),
0.80-1.20 (m, ABC system, 2H, CO2Me(H)CdCH2), 1.91 (dd,
2
2
ABC system, 1H, CO2Me(H)CdCH2) J AC ) 13.53 Hz, J BC
)
12.13 Hz, 3.88 (s, 3H, CO2Me), 3.51 (s, 3H, CO2Me), 4.10, 4.36,
4.49, 4.53, 5.42, 5.53, 5.63, 5.70 (s, 8H, C5H4). 13C{1H} NMR
(300 MHz, C6D6): δ 0.19, 0.21 (SiMe3), 18.40 (MeO2C-
(H)CdCH2), 23.84 (MeO2C(H)CdCH2), 52.86 (CO2Me), 95.34,
96.89, 97.22, 97.26, 97.32, 101.77 (C1), 102.77, 103.87, 104.85-
(C1), 105.35 (C5H4), 177.00 (CO2Me).
Ack n ow led gm en t. The authors gratefully acknowl-
edge financial support from the Ministero dell’Universita´
e della Ricerca Scientifica e Tecnologica (MURST) and
Consiglio Nazionale delle Ricerche (CNR) (Rome, Italy),
the Direccio´n General de Investigacio´n Cient´ıfica y
Te´cnica (Grant. No. PB-92-0715), and the European
Union for a postdoctoral grant to S.P. under the Human
Capital and Mobility Program (Contract No. ERB-
CHRXCT930281).
X-r a y Da ta Collection , Str u ctu r e Deter m in a tion , a n d
Refin em en t for Nb(η5-C5H4SiMe3)2(H)[η2-MeO2C(H)dC(H)-
CO2Me] 13 a n d Nb (η5-C5H 4SiMe3)2(H )[η2-tBu O2C(H )d
t
C(H)CO2 Bu ] 14. A crystal of each compound was sealed in
Lindemann capillary under dry nitrogen and used for data
collection. The crystallographic data are summarized in Table
2. Accurate unit-cell parameters were determined by least-
squares treatment of the setting angles of 30 carefully centered
reflections in the θ range 9.2-17.3° for 13 and 10.2-18.0° for
14. Data (3 < θ < 30°) were collected at 22 °C on a Philips
PW 1100 for 13 and on a Siemens AED for 14 single-crystal
diffractometer, using the graphite-monochromated Mo KR
radiation (λ ) 0.71073 Å) and the θ/2θ scan method. The
reflections were collected with a variable scan speed of 3-9°
min-1 and a scan width of 1.20 + 0.34 tan θ. One standard
reflection was monitored every 50 measurements; no signifi-
cant decay was noticed over the time of data collections. The
individual profiles have been analyzed following the method
of Lehmann and Larsen.18 Intensities were corrected for
Lorentz and polarization effects. Only the observed reflections
were used in the structure refinements.
Su p p or tin g In for m a tion Ava ila ble: Tables of hydrogen
atom coordinates (Tables SI, SII), anisotropic thermal param-
eters (Tables SIII, SIV), complete bond distances and angles
(Tables SV, SVI), complete crystallographic data (Tables SVII,
SVIII), and non-hydrogen atom coordinates (12 pages). Order-
ing information is given on any current masthead page.
A
list of structure factors is available upon request from the
authors.
OM9605241
(19) Orpen, A. G. J . Chem. Soc., Dalton Trans. 1980, 2509.
(20) International Tables for X-Ray Crystallography; Kynoch
Press: Birmingham, England, 1974; Vol. IV.
(21) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Gualiardi, A. J .
Appl. Crystallogr. 1993, 26, 343.
(22) Sheldrick, G. M. SHELXS-86 Program for the Solution of
Crystal Structures. University of Go¨ttingen, Go¨ttingen, Germany,
1986; Sheldrick, G. M. SHELX-76 Program for Crystal Structure
Determination. University of Cambridge, Cambridge, England, 1976.
(23) Nardelli, M. Comput. Chem. 1983, 7, 95.
(24) J ohnson, C. K. ORTEP. Report ORNL-3794, revised; Oak Ridge
National Laboratory: Oak Ridge, TN, 1965.
The structures were solved by direct and Fourier methods
and refined by full-matrix least-squares, first with isotropic
thermal parameters and then with anisotropic thermal pa-
(18) Lehmann, M. S.; Larsen, F. K. Acta Crystallogr., Sect. A 1974,
30, 580.