Successive insertion of alkynes into a tantalum-alkynyl bond: Implications for the coordination polymerization of alkynes

Article abstract of DOI:10.1021/om970593v

The reaction of 2,6-[ArN(SiMe₃)CH₂]₂NC₅H₃ (1, BDPP(SiMe₃)₂, Ar = 2,6-ⁱPr₂C₆H₃) with TaCl₅ yields the complex mer-(BDPP)TaCl

Full text of DOI:10.1021/om970593v

1290
Organometallics 1998, 17, 1290-1296
Su ccessive In ser tion of Alk yn es in to a
Ta n ta lu m -Alk yn yl Bon d : Im p lica tion s for th e
Coor d in a tion P olym er iza tion of Alk yn es
Fre´de´ric Gue´rin,† David H. McConville,*,† J agadese J . Vittal,‡ and
Glen A. P. Yap§
Department of Chemistry, University of British Columbia, 2036 Main Mall,
Vancouver, British Columbia, Canada V6T 1Z1, Department of Chemistry, University of
Western Ontario, London, Ontario, Canada N6A 5B7, and Windsor Molecular Structure
Center, Department of Chemistry and Biochemistry, University of Windsor,
Windsor, Ontario, Canada, N9B 3P4
Received J uly 14, 1997
The reaction of 2,6-[ArN(SiMe3)CH2]2NC5H3 (1, BDPP(SiMe3)2, Ar ) 2,6-iPr2C6H3) with
TaCl5 yields the complex mer-(BDPP)TaCl3 (2) and 2 equiv of ClSiMe3. The reduction of
compound 2 with excess Na/Hg in the presence of alkynes yields the pseudo 5-coordinate
Ta(III) derivatives (BDPP)Ta(η2-RCtCR′)Cl (3a , R ) R′ ) Pr; 3b, R ) R′ ) Et; 3c, R ) R′
) Ph; 3d , R ) Ph, R′ ) H). An X-ray study of 3a revealed a distorted square pyramidal
geometry with the chloride occupying the apical position. Compound 3a reacts with LiCtCR
to give the acetylide octyne derivatives (BDPP)Ta(η2-PrCtCPr)(CtCR) (5a , R ) Ph; 5b, R
) Bu; 5c, R ) SiMe3; 5d , R ) o-Me3SiC6H4). Compound 5a reacts with phenylacetylene to
give the metallacyclic derivative (BDPP)Ta[(η2-PhCtC)PrCdCPrHCdCPh] (6a ). An X-ray
study of 6a again revealed a square pyramidal geometry with the alkenyl carbon occupying
the apical position. Similarly, compounds 5b,c react with HCtCBu and HCtCSiMe3 to
give the metallacycles (BDPP)Ta[(η2-BuCtC)PrCdCPrHCdCBu] (6b) and (BDPP)Ta[(η2-
Me3SiCtC)PrCdCPrHCdCSiMe3] (6b), respectively. Compound 5b reacts with HCtCPh
to give (BDPP)Ta[(η2-BuCtC)PrCdCPrHCdCPh] (7b) only, establishing that the starting
acetylide is retained in the final product.
Sch em e 1
In tr od u ction
The polymerization of alkynes is catalyzed by certain
group 5 metal complexes;1-3 however, the active species
are often ill-defined. Two mechanistic pathways have
been proposed for this transformation: the 2 + 2
cycloaddition between an alkyne and a carbene which
affords a vinyl-substituted carbene upon ring-opening;4
the coordination insertion of an alkyne into a metal-
carbon bond to give a propagating alkenyl species
(Scheme 1).5
Relevant to the latter mechanism, formally d2 metal
alkyl complexes are known to insert alkynes; however,
the alkenyl complexes are typically reluctant to engage
in further insertions. For example, the d2 η2-alkyne
complex Tp*NbCl(CH2CH3)(η2-PhCtCCH2CH3) (Tp* )
hydrotris(3,5-dimethyl-pyrazolyl)borate) readily inserts
the coordinated alkyne PhCtCCH2CH3 but stops short
of inserting additional alkyne.6 Precursor complexes of
the type LnTa(η2-RCtCR)X (A, X ) alkyl, hydride, or
halide),7 where the metal is formally in the +3 oxidation
state, are ideally suited for studying the latter mecha-
nism. The choice of ancillary ligand system (Ln) for
complexes of type A is critical since metallacyclopenta-
diene compounds can result from the coupling of alkynes,
impeding the coordination insertion process. For in-
stance, η2-alkyne complexes are obtained with bis(cy-
clopentadienyl) templates (e.g., Cp2Ta(η2-RCtCR)X)8-10
and mono(pentamethylcyclopentadienyl) ligation (e.g.,
† University of British Columbia.
‡ University of Western Ontario.
§ University of Windsor.
(1) Masuda, T.; Niki, A.; Isobe, E.; Higashimura, T. Macromolecules
1985, 18, 2109.
(2) Masuda, T.; Isobe, E.; Higashimura, T.; Takada, K. J . Am. Chem.
Soc. 1983, 105, 7473.
(6) Etienne, M.; Mathieu, R.; Donnadieu, B. J . Am. Chem. Soc. 1997,
119, 3218.
(7) Chao, Y.-W.; Wexler, P. A.; Wigley, D. E. Inorg. Chem. 1989,
28, 3860.
(3) Cotton, F. A.; Hall, W. T.; Cann, K. J .; Karol, F. J . Macromol-
ecules 1981, 14, 233.
(4) Katz, T. J .; Ho, T. H.; Shih, N.; Ying, Y.; Stuart, V. I. W. J . Am.
Chem. Soc. 1984, 106, 2659.
(8) Gibson, V. C.; Parkin, G.; Bercaw, J . Organometallics 1991, 10,
220.
(9) Green, M. L. H.; J ousseaume, B. J . Organomet. Chem. 1980, 193,
339.
(5) Taqui Kahn, M. M.; Martell, A. E. Homogeneous Catalysis by
Transition Metal Complexes; Academic Press: New York, 1974.
(10) Labinger, J . A.; Schwartz, J .; Townsend, T. M. J . Am. Chem.
Soc. 1974, 96, 4009.
S0276-7333(97)00593-1 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 03/12/1998

Insertion of Alkynes into a Tantalum-Alkynyl Bond
Organometallics, Vol. 17, No. 7, 1998 1291
Cp*Ta(η2-RCtCR)X2),11-13 while less coordinatively satu-
rating alkoxide ligands yield metallacycles (e.g.,
(DIPP)3Ta(C4Et4), DIPP ) 2,6-diisopropylphenoxide).14
Herein we describe the synthesis and alkyne insertion
chemistry of η2-alkyne complexes of tantalum bearing
a pyridine diamide ligand, including an unusual double
insertion of alkyne into a tantalum alkynyl bond. We
have previously15 shown that the pyridine diamide
ligand imparts metallocene-like structural and elec-
tronic features on group 4 complexes while providing a
variable steric environment about the metal. Some of
this work has appeared in a preliminary form.16
methylene protons (NCH2) appear as an AB quartet
centered at about 5.1 ppm indicating that there is
asymmetry about the N3-plane of the ligand. In addi-
tion, the spectra show two isopropyl methine resonances
and four isopropyl methyl resonances, which is consis-
tent with the aforementioned asymmetry coupled with
restricted arene rotation. A single low-field acetylenic
carbon resonance is observed in the 13C{1H} NMR
spectra of complexes 3a -c, suggesting that the alkyne
acts as a 4-electron donor.18 Compound 3d which bears
a terminal alkyne (η2-HCtCPh) necessarily displays
two low-field acetylenic resonances. Given the induced
asymmetry of the BDPP ligand and since both ends of
the coordinated alkynes in compound 3a -c are spec-
troscopically equivalent, a rapid rotation of the alkynes
on the NMR time scale is advanced. Compounds 3a -d
are surprisingly inert to excess amalgam which permits
the use of excess amalgam. Furthermore, we see no
evidence of metallacycle formation even under forcing
conditions (excess alkyne 110 °C); hence, an excess of
alkyne can be used in the synthesis. The coordinated
alkynes do not exchange with free alkyne; for example,
no reaction occurs between compound 3a and 50 equiv
of phenylacetylene at 80 °C.
Resu lts a n d Discu ssion
We have reported17 the synthesis of the silylated
pyridine diamine ligand 2,6-[ArN(SiMe3)CH2]2NC5H3 (1,
BDPP{SiMe3}2, Ar ) 2,6-iPr2C6H3). Compound 1 reacts
cleanly with TaCl5 at 80 °C in benzene to give 2 equiv
of ClSiMe3 (confirmed by 1H NMR spectroscopy) and the
yellow trichloride complex mer-(BDPP)TaCl3 (2) in 84%
yield (eq 1).
The solid-state structure of 3a was determined by
X-ray crystallography (Table 1). The molecular struc-
ture of complex 3a can be found in Figure 1, and
relevant bond distances and angles are in Table 2.
Overall the molecular structure is best described as a
distorted square pyramid with the chloride (Cl(1))
occupying the apical position. The 4-octyne unit is
located trans to the pyridine of the BDPP ligand and is
rotated by about 50° with respect to the Cl(1)-Ta(1)-
N(2) plane (Figure 1, bottom). The bond distances in
the Ta-alkyne moiety are comparable to other mono-
nuclear Ta(III) alkyne complexes reported.12-14,19 Each
amide is sp2-hybridized as evidenced by the sum of the
angles about each nitrogen (N(1) ) 359.5° and N(3) )
359.9°). The rigid coordination of the ligand and
enforced location of the aryl isopropyl groups creates a
“pocket” opposite the pyridine and necessarily protects
the metal above and below the N3-plane.
Compound 2 is contaminated with small amounts of
unreacted TaCl5; however, this impurity can be removed
by dissolving the crude reaction solids in THF, followed
by filtration. The proton NMR spectrum of compound
2 displays a sharp singlet at 5.84 ppm for the ligand
methylene protons (NCH2), confirming the meridional
coordination of the ligand. The isopropyl methyl groups
of the arene are diastereotopic, which is likely the result
of restricted rotation about the N-Cipso bond.
The reduction of compound 2 with excess Na/Hg
amalgam in the presence of excess alkyne affords the
pseudo 5-coordinate Ta(III) η2-alkyne derivatives (BD-
PP)Ta(η2-RCtCR′)Cl (3a , R ) R′ ) Pr; 3b, R ) R′ )
Et; 3c, R ) R′ ) Ph; 3d , R ) Ph, R′ ) H) in 51-82%
yield (eq 2).
To explore the insertion chemistry of LnTa(η2-RCtCR)-
R′ (R′ ) alkyl) type complexes, (BDPP)Ta(η2-PrCtCPr)-
Me (4) was prepared from 3a and MeMgBr (eq 3).
The 1H NMR spectra of compounds 3a -d display very
The proton NMR spectrum of compound 4 displays a
Ta-CH3 resonance at 0.44 ppm while the carbon
spectrum shows a resonance at 39.04 ppm. The coor-
dinated 4-octyne in complex 4 does not insert into the
Ta-Me bond at elevated temperatures (110 °C) even
in the presence of PMe3.
similar features for the BDPP ligand; in particular, the
(11) Hirpo, W.; Curtis, M. D. Organometallics 1994, 13, 2706.
(12) Curtis, M. D.; Real, J .; Hirpo, W.; Butler, W. D. Organometallics
1990, 9, 66.
(13) Smith, G.; Schrock, R. R.; Churchill, M. R.; Youngs, W. J . Inorg.
Chem. 1981, 20, 387.
(14) Strickler, J . R.; Wexler, P. A.; Wigley, D. E. Organometallics
1991, 10, 118.
(15) Gue´rin, F.; McConville, D. H.; Vittal, J . J . Organometallics
1996, 15, 5586.
The reaction of compound 4 with an excess of pheny-
lacetylene in toluene at 110 °C affords methane (con-
1
firmed by H NMR spectroscopy) and the spectroscopi-
(16) Gue´rin, F.; McConville, D. H.; Vittal, J . J . Organometallics
1995, 14, 3154.
(17) Gue´rin, F.; McConville, D. H.; Payne, N. C. Organometallics
1996, 15, 5085.
(18) Templeton, J . L.; Ward, B. C. J . Am. Chem. Soc. 1980, 102,
3288.
(19) Cotton, F. A.; Hall, W. T. Inorg. Chem. 1980, 19, 2352.

1292 Organometallics, Vol. 17, No. 7, 1998
Gue´rin et al.
Ta ble 1. Cr ysta l Da ta a n d Exp er im en ta l Deta ils for Com p ou n d s 3a a n d 6a
3a 6a
empirical formula
fw
temp (°C)
C
39H65ClN3Ta
C58H73N3Ta
993.14
20
729.36
23
wavelength (Å)
cryst system
space group
unit cell dimens
0.710 73
triclinic
P1h
a ) 9.936(2) Å
b ) 11.558(1) Å
c ) 17.689(2) Å
R ) 74.997(6)°
â ) 87.424(10)°
γ ) 75.372(9)°
1898.0(5)
0.710 73
monoclinic
P21/c
a ) 13.530(2) Å
b ) 18.389(2) Å
c ) 21.604(3) Å
â ) 102.98(1)°
V (Å3)
5238(1)
Z
2
4
Dcalcd (g cm-3
)
1.386
1.259
F(000) electrons
820
2060
reflcns collcd
6078
18018
indepdt reflctns
5179 [R(int) ) 0.0284]
full-matrix least-squares on F2
5179/90/408
5624 [R(int) ) 0.0902]
refinement method
data/restraints/params
goodness-of-fit (GooF)a
final R indices [I > 2σ(I)]a
R indices (all data)a
full-matrix least-squares on F2
5575/3/500
1.037
1.230
R1 ) 0.0401, wR2 ) 0.0946
R1 ) 0.0519, wR2 ) 0.1011
R1 ) 0.0794, wR2 ) 0.1458
R1 ) 0.1099, wR2 ) 0.1593
R1 ) ∑(||Fo| - |Fc||)/∑|Fo|; wR2 ) [∑w(Fo - Fc2)2/∑wFo
]
1/2; GooF ) [∑w(Fo - Fc2)2/(n - p)]1/2 (where n is the number of reflections
a
2
4
2
and p is the number of parameters refined).
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 3a
Bond Distances
Ta(1)-N(1)
Ta(1)-N(3)
Ta(1)-C(32)
C(32)-C(36)
2.053(6)
2.033(6)
2.062(7)
1.287(11)
Ta(1)-N(2)
Ta(1)-Cl(1)
Ta(1)-C(36)
Aceta-Ta
2.255(6)
2.361(2)
2.085(7)
1.97
Bond Angles
N(3)-Ta(1)-N(1)
N(3)-Ta(1)-N(2)
N(2)-Ta(1)-Cl(1)
137.2(2) N(1)-Ta(1)-N(2)
71.9(2) N(1)-Ta(1)-Cl(1)
93.7(2) N(3)-Ta(1)-Cl(1)
71.4(2)
106.6(2)
96.9(2)
C(36)-C(32)-C(33) 132.6(8) C(32)-C(36)-C(37) 137.2(8)
a
Acet ) midpoint of C(32)-C(36).
Compound 6a is characterized by two low-field acety-
lenic resonances in the carbon NMR spectrum. In
addition, the proton NMR spectrum displays resonances
for two inequivalent propyl groups and two different
phenyl moieties. The proton and carbon NMR reso-
nances for the BDPP ligand indicate overall Cs sym-
metry in solution.
The solid-state structure of 6a was determined by
X-ray crystallography (Table 1). The molecular struc-
ture of complex 6a can be found in Figure 2, and
relevant bond distances and angles are in Table 3. The
molecular structure of compound 6a is very similar to
3a ; for example, the alkenyl carbon (C(6)) occupies the
apical position of a distorted square pyramid (Cl(1)
occupies the apical position in 3a ), while the acetylenic
group (C(1)-C(2)) resides in the basal plane (the octyne
unit resides in this position in compound 3a ). In
comparison to complex 3a , the acetylenic unit in com-
pound 6a is only rotated about 12° relative to the C(6)-
Ta-N(16) plane which is likely a result of the restraints
of the metallacycle. Alternating short and long bonds
are observed in the metallacyclic unit (C(6) through to
C(1)), consistent with the coupling of the alkynes and
the acetylide.
F igu r e 1. Top: Chem 3D representation of compound 3a .
Bottom: Chem 3D representation of the core of compound
3a showing the orientation of the octyne unit. (The 2,6-
diisopropylphenyl groups have been removed for clarity.)
cally and structurally characterized metallacycle 6a in
1
quantitative yield by H NMR spectroscopy (eq 4).
Compound 6a appears to result from the insertion of
coordinated octyne into a Ta-CCPh bond, followed by
a 2,1-insertion of phenylacetylene into the newly formed
alkenyl unit. The 2,1-insertion of phenyl acetylene

Insertion of Alkynes into a Tantalum-Alkynyl Bond
Organometallics, Vol. 17, No. 7, 1998 1293
1
The H NMR spectra of compounds 5a -d display an
AB quartet at 5.08-5.12 ppm for the ligand methylene
protons (NCH2) again indicating asymmetry about the
N3-plane of the ligand. The low-field acetylenic carbon
resonances observed in the 13C{1H} NMR spectra of
complexes 5a -d are consistent with the octyne acting
as a 4-electron donor.18
As expected, the reaction of the phenylacetylide
derivative 5a with phenylacetylene in toluene at 110
°C affords the metallacycle 6a in quantitative yield by
proton NMR spectroscopy. Compound 5a does not react
with internal alkynes (4-octyne, 3-hexyne) at 110 °C.
In a similar way, the reaction of the acetylides 5b and
5c with 1-hexyne and (trimethylsilyl)acetylene gives the
new metallacyclic products 6b,c, respectively.
F igu r e 2. Top: Chem 3D representation of compound 6a
showing the orientation of the pyridine diamide ligand
relative to the metallacycle. (The metallacycle substituents
have been removed for clarity.) Bottom: Chem 3D repre-
sentation of compound 6a showing the substituents on the
metallacycle. (The 2,6-diisopropylphenyl groups have been
removed for clarity.)
The proton NMR resonances for the BDPP ligand in
complex 6b are very similar to those observed for the
phenyl-substituted derivative 6a ; hence, the compounds
are likely isostructural. In contrast, the 1H NMR
spectrum of compound 6c is quite different, displaying
resonances for a single species with C1-symmetry (6a ,b
display Cs-symmetry in solution). For example, two AB
quartets are observed for the ligand methylene protons
(NCH2), along with four isopropyl methine and eight
isopropyl methyl resonances. Regioisomers of the met-
allacycle, that is, those arising from both a 1,2- and a
2,1-insertion of (trimethylsilyl)acetylene, can be dis-
counted since there are only two silylmethyl resonances
in the proton and carbon spectra of compound 6c.
Assuming compound 6c has the same basic features as
complexes 6a ,b, we conclude that the two trimethylsilyl
groups in the metallacycle cause the aryl groups of the
ligand to twist relative to one another about the N-Cipso
bond, thus avoiding interaction with these bulky groups.
The primary interaction that may be responsible for this
observation is the one between the trimethylsilyl group
bound to the η2-alkyne unit and the isopropyl groups
adjacent to it (vide infra). No change in the spectral
features of compound 6c are observed to 80 °C.
Ta ble 3. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for Com p ou n d 6a
Bond Distances
Ta-N(1)
Ta-N(16)
Ta-C(2)
C(1)-C(2)
C(3)-C(4)
C(5)-C(6)
2.006(11)
2.225(6)
2.030(12)
1.30(2)
1.33(2)
1.37(2)
Ta-N(2)
Ta-C(1)
Ta-C(6)
C(2)-C(3)
C(4)-C(5)
2.005(10)
2.075(14)
2.19(2)
1.45(2)
1.51(2)
Bond Angles
N(1)-Ta-N(2)
N(2)-Ta-N(16)
N(2)-Ta-C(6)
Ta-C(6)-C(5)
C(5)-C(4)-C(3)
C(3)-C(2)-C(1)
137.9(2)
72.6(4)
100.2(5)
127.2(10)
122.1(13)
140.0(13)
N(1)-Ta-N(16)
N(1)-Ta-C(6)
N(16)-Ta-C(6)
C(6)-C(5)-C(4)
C(4)-C(3)-C(2)
71.4(4)
102.8(5)
93.0(4)
129.9(13)
116.4(12)
likely minimizes the interaction between the phenyl
group and the propyl chains of the octyne unit. To
demonstrate that an acetylide octyne complex is the
intermediate in this reaction, a series of such com-
pounds were prepared. Compound 3a reacts cleanly
with LiCtCR in ether at -78 °C to give the acetylide
derivatives 5a -d (eq 5).
Compounds 5b,c react with excess phenylacetylene
to give only the mixed metallacycles 7b,c, respectively.
The absence of compound 6a suggests that the starting
acetylide unit is retained in the final product. Com-
pound 7c which bears one trimethylsilyl group on the
η2-alkyne unit also displays C1-symmetry in solution.

1294 Organometallics, Vol. 17, No. 7, 1998
Gue´rin et al.
to C6D6 (δ ) 128.0 ppm). Elemental analyses were performed
using sealed tin cups on a Fisons Instruments model 1108
elemental analyzer by Mr. Peter Borda of this department or
by Oneida Research Services Inc., Whitesboro, NY. BDPP )
[2,6-(ArNCH2)2NC5H3]2- (Ar ) 2,6-iPr2C6H3).
As noted above, the interaction of this group with the
isopropyl groups of the arene may cause the aryl groups
to distort.
In an attempt to discourage the coordination of the
alkyne unit once the metallacycle is formed, possibly
leading to the polymerization of alkynes, the bulky (o-
(trimethylsilyl)phenyl)acetylide derivative 5d was re-
acted with HCtCPh, HCtCBu, and HCtCSiMe3 in
toluene at 110 °C. Surprisingly, compound 5d does not
react with these alkynes over several days. It is not
clear why this particular acetylide derivative is reluc-
tant to engage in what appears to be a general reaction.
We have attempted to trap the proposed intermediate
alkenyl species “(BDPP)Ta(PrCdCPrCtCPh)” formed
via the insertion of the octyne into the phenylacetylide
bond; however, no reaction occurs between compound
5a and a variety of Lewis bases (PMe3, py, NEt3) at 110
°C in toluene. Alternatively, the initial reaction be-
tween compound 5a and HCtCPh could involve the
formation of the metallacyclopentadiene acetylide in-
termediate “(BDPP)Ta(PhCdCHPrCdCPr)(CtCPh)”,
followed by coupling of the metallacycle and the acetyl-
ide. This seems unlikely since we see no evidence of
metallacyclopentadiene formation between compound
3a and HCtCPh at elevated temperatures (110 °C).
m er -(BDP P )Ta Cl3 (2). Solid TaCl5 (2.670 g, 7.454 mmol)
was added in small portions to a benzene (150 mL) solution of
17
BDPP(SiMe3)2 (4.087 g, 6.768 mmol) at 23 °C. The turbid
solution immediately turned bright yellow and was heated to
80 °C for 12 h. The volatile compounds were removed under
vacuum, and the resulting solid was dissolved in THF (50 mL).
The solution was filtered through Celite and the solvent
removed in vacuo. The resulting solid was washed with
hexanes (3 × 50 mL) to yield a bright yellow crystalline solid
2 (4.204 g, 5.658 mmol, 84%). 1H NMR: δ 7.14 (m, 6H, Ar),
6.84 (t, 1H, py), 6.38 (d, 2H, py), 5.84 (s, 4H, NCH2), 3.80 (sept,
4H, CHMe2), 1.52 (d, 12H, CHMe2), 1.12 (d, 12H, CHMe2). 13C-
{1H} NMR: δ 161.64, 148.84, 146.56, 139.66, 125.35, 122.28,
117.51, 71.78, 28.89, 27.57, 23.64. Anal. Calcd for
C
31H41N3TaCl3: C, 50.11; H, 5.56; N, 5.66. Found: C, 50.25;
H, 5.68; N, 5.11.
(BDP P )Ta (η2-P r CtCP r )Cl (3a ). A toluene (30 mL) solu-
tion of compound 2 (0.500 g, 0.673 mmol) and 4-octyne (0.297
g, 2.70 mmol) was added to an excess of Na/Hg amalgam (0.460
g of Na, 20.0 mmol; 46.0 g of Hg). The mixture was stirred
for 12 h. The solution was decanted from the amalgam and
filtered through Celite. The solvent was removed in vacuo to
yield an orange-brown solid. The solid was dissolved in a
minimum amount of diethyl ether and cooled to -30 °C for 12
h. Yellow crystalline 3a was isolated by filtration and dried
under vacuum (0.401 g, 0.513 mmol, 75%). 1H NMR: δ 7.19
(t, 2H, Ar), 7.13 (d, 4H, Ar), 6.85 (t, 1H, py), 6.39 (d, 2H, py),
Con clu sion
The pyridine diamide ligand BDPP affords a steric
and electronic mimic of a metallocene environment for
alkyne derivatives of tantalum. In contrast to com-
plexes of the type Cp2Ta(η2-RCtCR)R′ (R ) alkyl, aryl;
R′ ) alkyl), the acetylide derivatives (BDPP)Ta(η2-
PrCtCPr)(CtCR) (R ) Ph, Bu, SiMe3) readily engage
in alkyne insertion chemistry. What appears to prevent
this system from undergoing multiple insertions of
alkyne is the relatively strong interaction between the
alkyne unit of the metallacycle and tantalum. We are
currently examining complexes of the type (BDPP)Ta-
(η2-PrCtCPr)X (X ) vinyl and -CtN) in the hope that
these moieties will be reluctant to participate in bonding
with tantalum once incorporated into the proposed
alkenyl intermediate.
2
5.12 (AB quartet, J HH ) 20.1 Hz, 4H, NCH2), 3.79 (sept, 2H,
CHMe2), 3.15 (sept, 2H, CHMe2), 2.51 (m, 4H, tCCH2), 1.46
(d, 6H, CHMe2), 1.34 (m, 4H, CH2CH3), 1.32 (d, 6H, CHMe2),
1.24 (d, 6H, CHMe2), 1.01 (d, 6H, CHMe2), 0.84 (t, 6H,
CH2CH3). 13C{1H} NMR: δ 237.01 (CtC), 160.77, 154.41,
145.19, 142.96, 138.41, 125.49, 124.32, 123.57, 116.99, 70.95,
40.02, 28.60, 27.95, 26.66, 25.76, 24.61, 23.80, 21.94, 15.45.
Anal. Calcd for C39H55N3TaCl: C, 59.88; H, 7.09; N, 5.37.
Found: C, 59.62; H, 7.19; N, 5.16.
(BDP P )Ta (η2-EtCtCEt)Cl (3b). The preparation of com-
pound 3b is identical to that for 3a . Compound 2 (0.500 g,
0.673 mmol), 3-hexyne (0.200 g, 2.43 mmol), and excess Na/
Hg amalgam (0.186 g Na, 8.09 mmol; 18.6 g Hg) gave yellow
crystalline 3b (0.417 g, 0.553 mmol, 82%). 1H NMR: δ 7.19,
(t, 2H, Ar), 7.11 (d, 4H, Ar), 6.84 (t, 1H, py), 6.39 (d, 2H, py),
2
5.11 (AB quartet, J HH ) 20.1 Hz, 4H, NCH2), 3.79 (sept, 2H,
CHMe2), 3.13 (sept, 2H, CHMe2), 2.59 (q, 4H, tCCH2), 1.46
(d, 6H, CHMe2), 1.32 (d, 6H, CHMe2), 1.21 (d, 6H, CHMe2),
1.02 (d, 6H, CHMe2), 0.94 (t, 6H, CH2CH3). 13C{1H} NMR: δ
237.81 (CtC), 160.76, 154.34, 145.17, 142.88, 138.41, 125.57,
124.35, 123.59, 117.01, 70.94, 30.56, 28.53, 27.94, 26.69, 25.76,
24.61, 23.77, 13.03. Anal. Calcd for C37H51N3TaCl: C, 58.92;
H, 6.82; N, 5.57. Found: C, 58.97; H, 6.70; N, 5.38.
Exp er im en ta l Deta ils
Gen er a l Deta ils. All experiments were performed under
a dry dinitrogen atmosphere using standard Schlenk tech-
niques or in an Innovative Technology Inc. glovebox. Solvents
were distilled from sodium/benzophenone ketyl (DME, THF,
hexanes, diethyl ether, and benzene) or molten sodium (tolu-
ene) under argon and stored over activated 4 Å molecular
sieves. Tantalum(V) chloride was purchased from Alfa and
used as received. Diphenylacetylene, phenylacetylene, 3-hex-
yne, 1-hexyne, 4-octyne, and MeMgBr were purchased from
Aldrich and used as received. The (o-(trimethylsilyl)phenyl)-
acetylene was prepared using a previously reported synthe-
sis.20 The acetylides LiCtCR (R ) Ph, Bu, SiMe3, o-Me3-
SiC6H4) were prepared from BuLi and the appropriate acetylene
in hexanes at 25 °C. Unless otherwise specified, proton (300
MHz) and carbon (75.46 MHz) NMR spectra were recorded in
C6D6 at approximately 22 °C on a Varian Gemini-300 or 300-
XL spectrometer. The proton chemical shifts were referenced
to internal C6D5H (δ ) 7.15 ppm), and the carbon resonances,
(BDP P )Ta (η2-P h CtCP h )Cl (3c). The preparation of com-
pound 3c is identical to that for 3a . Compound 2 (1.001 g,
1.346 mmol), diphenylacetylene (0.288 g, 1.62 mmol), and
excess Na/Hg amalgam (0.619 g Na, 26.9 mmol; 61.9 g Hg)
gave yellow crystalline 3c (0.567 g, 0.667 mmol, 51%). 1H
NMR: δ 7.15-6.95 (m, 17H, Ar and Ph), 6.48 (d, 2H, py), 5.14
2
(AB quartet, J HH ) 19.5 Hz, 4H, NCH2), 4.02 (sept, 2H,
CHMe2), 3.30 (sept, 2H, CHMe2), 1.30 (d, 6H, CHMe2), 1.08
(d, 12H, CHMe2), 1.04 (d, 6H, CHMe2). 13C{1H} NMR:
δ
228.20 (CtC), 159.94, 152.52, 147.23, 145.25, 144.13, 138.67,
126.96, 126.17, 124.55, 124.03, 117.37, 70.90, 28.85, 28.59,
27.56, 25.93, 24.33, 23.95. Anal. Calcd for C45H51N3TaCl: C,
63.56; H, 6.05; N, 4.94. Found: C, 63.21; H, 6.07; N, 4.42.
(BDP P )Ta (η2-P h CtCH)Cl (3d ). The preparation of com-
pound 3d is identical to that for 3a . Compound 2 (0.250 g,
0.336 mmol), phenylacetylene (0.103 g, 1.01 mmol), and excess
(20) Masuda, T.; Hamano, T.; Tsuchihara, K.; Higashimura, T.
Macromolecules 1990, 23, 1374.

Insertion of Alkynes into a Tantalum-Alkynyl Bond
Organometallics, Vol. 17, No. 7, 1998 1295
Na/Hg amalgam (0.230 g of Na, 10.0 mmol; 23.0 g of Hg) gave
ivory crystalline 3d (0.207 g, 0.267 mmol, 79%). 1H NMR: δ
11.91 (s, 1H, CtCH) 7.20-6.90 (m, Ar and Ph), 6.83 (t, 1H,
NMR: δ 7.19 (t, 2H, Ar), 7.15 (d, 4H, Ar), 6.77 (t, 1H, py),
6.34 (d, 2H, py), 5.00 (AB quartet, 2J HH ) 20.2 Hz, 4H, NCH2),
4.01 (sept, 2H, CHMe2), 3.35 (sept, 2H, CHMe2), 2.77 (m, 4H,
CH2CH2Me), 1.51 (d, 6H, CHMe2), 1.43 (d, 6H, CHMe2), 1.32
(d, 6H, CHMe2), 1.19 (m, 4H, CH2CH2Me), 1.06 (d, 6H, CHMe2),
0.85 (t, 6H, CH2CH2Me), 0.26 (s, 9H, SiMe3). 13C {1H} NMR:
δ 232.68 (PrCtCPr), 169.14, 161.22, 153.05, 145.02, 143.08,
138.15, 130.89, 125.32, 124.33, 123.31, 117.04, 70.91, 40.89,
28.85, 27.52, 27.10, 25.88, 25.07, 24.11, 21.86, 15.47, 1.21.
(BDP P )Ta (η2-P r CtCP r )(CtC-o-Me3SiC6H4) (5d ). The
preparation of complex 5d is identical to that of complex 5a .
Complex 3a (0.100 g, 0.128 mmol) and LiCtC-o-Me3SiC6H4
(0.023 g, 0.128 mmol) yielded orange crystalline 5d (0.087 g,
0.095 mmol, 74%). 1H NMR: δ 7.83 (d, 1H, Ph), 7.40 (d, 1H,
Ph), 7.20-6.90 (m, 9H, Ar, py and Ph), 6.54 (d, 2H, py), 5.12
2
py), 6.36 (d, 2H, py), 5.08 (AB quartet, J HH ) 20.3 Hz, 4H,
NCH2), 3.82 (sept, 2H, CHMe2), 3.43 (sept, 2H, CHMe2), 1.31
(d, 6H, CHMe2), 1.26 (d, 6H, CHMe2), 1.20 (d, 6H, CHMe2),
1.08 (d, 6H, CHMe2). 13C{1H} NMR: δ 236.45 (PhCtC),
225.81(CtCH), 160.65, 152.78, 146.77, 145.38, 142.25, 138.68,
126.86, 125.94, 124.35, 123.69, 117.30, 70.60, 28.54, 27.96,
26.47, 26.27, 24.70, 23.99.
(BDP P )Ta (η2-P r CtCP r )Me (4). To a diethyl ether (25
mL) solution of compound 3a (0.600 g, 0.767 mmol) was added
1.2 equiv of MeMgBr (0.38 mL, 2.4 M, 0.91 mmol) at -78 °C.
The yellow solution was warmed to 25 °C and stirred for 12 h.
The solvent was removed in vacuo. The resulting solid was
extracted with toluene (3 × 10 mL) and filtered through Celite
to give a bright yellow solution. The solvent was removed in
vacuo, the solid esd dissolved in a minimum amount of diethyl
ether, and the solution was cooled to -30 °C for 12 h. Yellow
crystalline 4 was isolated by filtration and dried under vacuum
(0.531 g, 0.697 mmol, 91%). 1H NMR: δ 7.22-7.10 (m, 6H,
2
(AB quartet, J HH ) 20.4 Hz, 4H, NCH2), 3.99 (sept, 2H,
CHMe2), 3.43 (sept, 2H, CHMe2), 2.87 (m, 4H, CH2CH2Me),
1.43 (d, 6H, CHMe2), 1.37 (d, 6H, CHMe2), 1.35 (m, 4H,
CH2CH2Me), 1.30 (d, 6H, CHMe2), 1.10 (d, 6H, CHMe2), 0.91
(t, 6H, CH2CH2Me), 0.21 (s, 9H, SiMe3). 13C {1H} NMR: δ
233.304 (PrCtCPr), 161.67, 153.07, 152.80, 145.27, 142.98,
138.25, 133.99, 133.54, 132.40, 129.22, 128.88, 126.26, 125.30,
124.29, 123.29, 117.20, 70.89, 40.83, 28.85, 27.78, 26.95, 25.96,
24.77, 24.06, 21.95, 15.50, -1.00. Anal. Calcd for C50H68N3-
SiTa: C, 65.27; H, 7.45; N, 4.57. Found: C, 65.48; H, 7.59; N,
4.80.
Ar), 6.88 (t, 1H, py), 6.45 (d, 2H, py), 5.05 (AB quartet, 2J HH
)
20.5 Hz, 4H, NCH2), 3.60 (sept, 2H, CHMe2), 3.15 (sept, 2H,
CHMe2), 2.46 (m, 4H, tCCH2), 1.42 (d, 6H, CHMe2), 1.34 (m,
4H, CH2CH3), 1.33 (d, 6H, CHMe2), 1.21 (d, 6H, CHMe2), 1.05
(d, 6H, CHMe2), 0.86 (t, 6H, CH2CH3), 0.44 (s, 3H, Me). 13C-
{1H} NMR: δ 237.45 (CtC), 161.93, 155.12, 144.61, 143.12,
138.05, 124.84, 124.02, 123.61, 116.98, 70.69, 39.06 (Ta-CH3),
37.94, 28.78, 27.75, 26.49, 25.80, 24.56, 23.84, 22.10, 16.63.
Anal. Calcd for C40H58N3Ta: C, 63.06; H, 7.67; N, 5.52.
Found: C, 63.02; H, 7.79; N, 6.38.
(BDP P )Ta (η2-P r CtCP r )(CtCP h ) (5a ). To a diethyl
ether (25 mL) solution of compound 3a (0.500 g, 0.634 mmol)
was added 1.1 equiv of PhCtCLi (0.076 g, 0.703 mmol) at -78
°C. The yellow solution was warmed to 25 °C and stirred for
12 h. The solvent was removed in vacuo. The resulting solid
was extracted with toluene (3 × 10 mL) and filtered through
Celite to give a bright yellow solution. The solvent was
removed in vacuo, the solid was dissolved in a minimum
amount of pentane, and the solution was cooled to -30 °C for
12 h. Yellow crystalline 5a was isolated by filtration and dried
under vacuum (0.406 g, 0.479 mmol, 76%). 1H NMR: δ 7.59
(m, 2H, Ph), 7.22-7.10 (m, 7H, Ar and Ph), 7.01 (m, 2H, Ph),
6.80 (t, 1H, py), 6.38 (d, 2H, py), 5.08 (AB quartet, 2J HH ) 20.2
Hz, 4H, NCH2), 4.10 (sept, 2H, CHMe2), 3.39 (sept, 2H,
CHMe2), 2.81 (m, 4H, tCCH2), 1.53 (d, 6H, CHMe2), 1.39 (d,
6H, CHMe2), 1.36 (d, 6H, CHMe2), 1.22 (m, 4H, CH2CH3), 1.10
(d, 6H, CHMe2), 0.87 (t, 6H, CH2CH3). 13C{1H} NMR δ 233.64
(PrCtCPr), 161.41, 153.22, 149.40, 145.21, 143.08, 138.16,
130.97, 127.12, 126.48, 126.23, 125.33, 124.32, 123.35, 117.05,
70.99, 40.96, 28.86, 27.84, 27.09, 25.93, 24.94, 24.10, 21.95,
15.52.
(BDP P )Ta (η2-P r CtCP r )(CtCBu ) (5b). The preparation
of compound 5b is identical to that of complex 5a . Complex
3a (0.100 g, 0.128 mmol) and LiCtCBu (0.012 g, 0.128 mmol)
yielded orange crystalline 5b (0.077 g, 0.093 mmol, 73%). 1H
NMR: δ 7.24 (t, 2H, Ar), 7.14 (d, 4H, Ar), 6.85 (t, 1H, py),
6.41 (d, 2H, py), 5.09 (AB quartet, 2J HH ) 20.1 Hz, 4H, NCH2),
4.05 (sept, 2H, CHMe2), 3.32 (sept, 2H, CHMe2), 2.67 (m, 4H,
CH2CH2Me), 2.22 (t, 2H, TaCtCCH2), 1.52 (d, 6H, CHMe2),
1.44 (d, 6H, CHMe2), 1.40 (m, 8H, CH2 of octyne and buty-
lacetylide), 1.31 (d, 6H, CHMe2), 1.08 (d, 6H, CHMe2), 0.88 (t,
6H, CH2CH2Me), 0.87 (t, 3H, CH2CH2CH2Me). 13C{1H}
NMR: δ 235.46 (PrCtCPr), 161.46, 153.90, 145.11, 143.04,
139.10, 137.98, 125.50, 125.08, 124.16, 123.33, 116.88, 70.78,
40.50, 32.09, 28.70, 27.64, 27.02, 25.79, 24.88, 23.95, 22.19,
22.04, 21.36, 15.53, 13.91.
(BDP P )Ta [(η2-P h CtC)P r CdCP r HCdCP h ] (6a ). To a
toluene solution (5 mL) of compound 5a (0.100 g, 0.118 mmol)
in a glass pressure vessel was added 1.5 equiv of phenylacety-
lene (0.018 g, 0.177 mmol) at 25 °C. The yellow solution was
stirred at 110 °C for 12 h. The solvent was removed in vacuo.
The resulting orange solid was dissolved in a minimum
amount of diethyl ether, and the solution was cooled to -30
°C for 12 h. Orange crystalline 6a was isolated by filtration
and dried under vacuum (0.108 g, 0.114 mmol, 97%). 1H
NMR: δ 7.19-7.10 (m, 6H, Ar), 7.05 (s, 1H, PhCdCH), 7.04-
6.98 (m, 4H, Ph), 6.90 (t, 2H, Ph), 6.82 (tt, 1H, Ph), 6.76 (t,
1H, py), 6.74 (tt, 1H, Ph), 6.25 (d, 2H, py), 5.60 (dd, 2H, Ph),
2
4.87 (AB quartet, J HH ) 20.1 Hz, 4H, NCH2), 4.10 (sept, 2H,
CHMe2), 3.36 (sept, 2H, CHMe2), 2.24 (m, 4H, tCH2), 1.62 (m,
2H, tCH2), 1.43 (d, 6H, CHMe2), 1.35 (d, 6H, CHMe2), 1.22
(m, 2H, CH2CH3), 1.08 (d, 6H, CHMe2), 1.01 (d, 6H, CHMe2),
0.93 (t, 3H, CH2CH3), 0.51 (t, 3H, CH2CH3). 13C{1H} NMR: δ
220.26 (PhCtCH), 189.90 (PhCtCH), 160.83, 158.63, 154.09,
151.86, 147.39, 145.14, 144.72, 142.08, 137.95, 128.89, 127.16,
126.73, 125.69, 125.47, 124.08, 123.98, 123.87, 123.34, 116.85,
71.21, 37.31, 34.30, 29.03, 27.95, 27.83, 25.92, 24.88, 24.58,
23.52, 23.30, 15.24, 14.68. Anal. Calcd for C55H66N3Ta: C,
69.53; H, 7.00; N, 4.42. Found: C, 69.95; H, 7.41; N, 4.71.
(BDP P )Ta [(η2-Bu CtC)P r CdCP r HCdCBu ] (6b). The
preparation of compound 6b is identical to that of compound
6a . Complex 5b (0.100 g, 0.098 mmol) and HCtCBu (0.010
g, 0.122 mmol) yielded red crystalline 6b (0.086 g, 0.078 mmol,
80%). 1H NMR: δ 7.17-7.05 (m, 6H, Ar), 6.91 (t, 1H, py), 6.85
2
(s, 1H, BuCdCH), 6.46 (d, 2H, py), 4.98 (AB quartet, J HH
)
21.0 Hz, NCH2), 3.66 (sept, 2H, CHMe2), 3.59 (sept, 2H,
CHMe2), 2.77 (m, 2H, CH2CH2Me), 2.48 (m, 2H, CH2CH2Me),
2.34 (t, 2H, CH2CH2CH2Me), 2.23 (br m, 2H, CH2CH2CH2Me),
1.63 (m, 4H, CH2CH2CH2Me), 1.42 (d, 6H, CHMe2), 1.33 (d,
6H, CHMe2), 1.26 (d, 6H, CHMe2), 1.12 (d, 6H, CHMe2), 1.30
(buried, 8H, CH2 Pr and Bu), 1.00, 0.86, 0.82, and 0.71 (t, 3H
each, CH2Me Pr and Bu). 13C{1H} NMR: δ 237.52, 236.28,
195.53, 162.11, 153.35, 145.00, 144.20, 141.34, 140.95, 138.11,
137.01, 128.09, 124.27, 123.25, 116.19, 71.52, 43.49, 39.59,
37.17, 35.27, 34.96, 31.15, 28.84, 27.29, 26.99, 25.99, 25.33,
24.50, 24.42, 23.76, 23.65, 21.99, 15.23, 14.81, 14.58, 14.10.
(BDP P )Ta [(η2-Me3SiCtC)P r CdCP r HCdCSiMe3] (6c).
The synthesis of compound 6c is identical to that of 6a .
Complex 5c (0.100 g, 0.096 mmol) and HCtCSiMe3 (0.015 g,
0.153 mmol) yielded red crystalline 6c (0.113 g, 0.088 mmol,
92%). 1H NMR: δ 7.10-6.90 (m, 7H, Ar and py), 6.54 (d, 1H,
(BDP P )Ta (η2-P r CtCP r )(CtCSiMe3) (5c). The prepara-
tion of compound 5c is identical to that of 5a . Complex 3a
(0.100 g, 0.128 mmol) and LiCtCSiMe3 (0.013 g, 0.128 mmol)
yielded yellow crystalline 5c (0.102 g, 0.121 mmol, 95%). 1H

1296 Organometallics, Vol. 17, No. 7, 1998
Gue´rin et al.
2
py), 6.49 (d, 1H, py), 5.17 (AB quartet, J HH ) 19.4 Hz, 2H,
-11 e k e 12, -19 e l e 19) in ω mode at variable scan speeds
(2-20 deg/min). Four standard reflections monitored at the
end of every 297 reflections collected showed no decay of the
crystal. The data processing, solution, and refinement were
done using SHELXTL-PC programs.22 The final refinements
were performed using SHELXL-93 software programs.23 An
empirical absorption correction was applied to the data using
the routine “XEMP” on the basis of the ψ scans of 11 reflections
with 2θ ranging from 8.5 to 25.9° (µ ) 2.995 mm-1). The
methyl carbon atoms attached to C(29) were found to be
disordered. Three orientation (0.33/0.33/0.33) of C(30) and
C(31) were located in the final difference Fourier methods.
Isotropic thermal parameters were refined for these disordered
carbon atoms. Anisotropic thermal parameters were refined
for all non-hydrogen atoms. No attempt was made to locate
the hydrogen atoms; however, they were placed in calculated
positions. The C-C distances in the isopropyl groups were
restrained to be equal using the option SADI. In the final
difference Fourier synthesis the electron density fluctuates in
2
NCH2), 4.93 (AB quartet, J HH ) 20.4 Hz, 2H, NCH2), 4.08
(sept, 1H, CHMe2), 3.58 (sept, 1H, CHMe2), 3.08 (sept, 1H,
CHMe2), 2.96 (m, 1H, CH2CH2Me), 2.90 (s, 1H, CHtCSiMe3),
2.67 (m, 2H, CHMe2 and CH2CH2Me), 2.36 (m, 1H, CH2CH2-
Me), 2.24 (m, 1H, CH2CH2Me), 1.84 (m, 1H, CH2CH2Me), 1.64
(m, 1H, CH2CH2Me), 1.57 (d, 3H, CHMe2), 1.51 (d, 3H, CHMe2),
1.27 (d, 3H, CHMe2), 1.26 (d, 3H, CHMe2), 1.20 (m, 2H,
CH2CH2Me), 1.10 (d, 3H, CHMe2), 1.08 (d, 3H, CHMe2), 1.08
(buried, 3H, CH2CH2Me), 1.06 (d, 3H, CHMe2), 0.92 (d, 3H,
CHMe2), 0.74 (t, 3H, CH2CH2Me), 0.28 (s, 9H, SiMe3), -0.19
(s, 9H, SiMe3). 13C{1H} NMR: δ 233.53, 190.05, 169.56,
167.86, 163.49, 162.93, 155.43, 154.54, 145.76, 144.21, 143.31,
142.58, 138.57, 132.39, 124.51, 123.93, 123.84, 123.51, 123.37,
122.32, 117.11, 116.88, 68.81, 68.59, 55.34, 33.06, 29.98, 29.03,
27.48, 27.36, 27.28, 26.10, 25.84, 25.12, 24.86, 24.25, 24.17,
24.00, 22.57, 14.83, 14.69, 3.95, -0.51.
(BDP P )Ta [(η2-Bu CtC)P r CdCP r HCdCP h ] (7b). The
synthesis of compound 7b is identical to that of 6a . Complex
5b (0.100 g, 0.098 mmol) and HCtCPh (0.015 g, 0.147 mmol)
yielded red crystalline 7b (0.076 g, 0.068 mmol, 69%). 1H
NMR: δ 7.30-7.10 and 6.90-6.70 (m, 12H, Ar, Ph and py),
6.14 (d, 2H, Ph), 5.38 (AB quartet, 2J HH ) 19.9 Hz, 4H, NCH2),
4.16 (sept, 2H, CHMe2), 3.39 (m, 2H, CH2CH2CH2Me), 3.11
(s, 1H, PhCdCH), 3.05 (sept, 2H, CHMe2), 2.30 (m, 2H, CH2-
CH2Me), 1.65 (m, 4H, CH2 Pr or Bu), 1.60 (m, 4H, CH2 Pr or
Bu), 1.49 (d, 6H, CHMe2), 1.43 (d, 6H, CHMe2), 1.35 (d, 6H,
CHMe2), 1.22 (m, 5H, CH2 and CH3, Pr or Bu), 1.02 (d, 6H,
CHMe2), 0.97 (t, 3H, CH3 Pr or Bu), 0.81 (t, 3H, CH3 Pr or
Bu). 13C{1H} NMR: δ 221.17, 204.45, 163.86, 162.56, 156.19,
149.68, 148.58, 148.10, 143.55, 138.81, 127.03, 126.20, 125.16,
123.46, 123.27, 117.30, 70.91, 48.59, 34.79, 28.77, 28.65, 28.25,
27.55, 24.31, 23.44, 23.13, 22.84, 15.88, 15.40.
the range 0.788 to -0.677 e Å-3
.
X-r a y Cr ysta llogr a p h ic An a lysis of 6a . A suitable
crystal of 6a (dimension 0.10 × 0.1 × 0.1 mm) was grown from
a saturated ether solution at -30 °C. Data were collected on
a Siemens Smart system CCD diffractometer. The data were
collected in the range of θ ) 1.47-21° (-17 e h e 17, -11 e
k e 23, -28 e l e 27). Unit-cell parameters were calculated
from reflections obtained from 60 data frames collected at
different sections of the Ewald sphere. The systematic ab-
sences in the diffraction data and the determined unit-cell
parameters were uniquely consistent for the reported space
group. A trial application of a semiempirical absorption
correction based on redundant data at varying effective
azimuthal angles yielded Tmax/Tmin at unity and was ignored.
A molecule of cocrystallized n-hexane solvent was located at
the inversion center. All C-C distances in the solvent
molecule were constrained to be equal. All non-hydrogen
atoms were refined with anisotropic displacement coefficients.
All hydrogen atoms were treated as idealized contributions.
The structure was solved by direct methods, completed by
subsequent Fourier syntheses, and refined with full-matrix
least-squares methods. All scattering factors and anomalous
dispersion coefficients are contained in the SHELXTL 5.03
program library.24 In the final difference Fourier synthesis
the electron density fluctuates in the range 0.667 to -0.634 e
(BDP P )Ta [(η2-Me3SiCtC)P r CdCP r HCdCP h ] (7c). The
synthesis of compound 7c is identical to that of 6a . Complex
5c (0.100 g, 0.096 mmol) and HCtCPh (0.015 g, 0.147 mmol)
yielded red crystalline 7c (0.097 g, 0.076 mmol, 79%). 1H
NMR: δ 7.50-6.50 (m, 10H, Ar, Ph and py), 6.37 (d, 1H, py),
2
6.35 (d, 1H, py), 6.21 (d, 2H, Ph), 5.01 (AB quartet, J HH
)
2
20.1 Hz, 2H, NCH2), 4.97 (AB quartet, J HH ) 20.1 Hz, 2H,
NCH2), 4.10 (sept, 1H, CHMe2), 3.77 (br m, 4H, CHMe2 and
PhCdCH), 2.55 (m, 1H, CH2CH2Me), 2.41 (m, 3H, CH2CH2-
Me), 1.78 (m, 4H, CH2CH2Me), 1.60 (d, 3H, CHMe2), 1.53 (d,
3H, CHMe2), 1.38 (d, 3H, CHMe2), 1.31 (d, 3H, CHMe2), 1.24
(d, 3H, CHMe2), 1.00-0.84 (m, 15H, CH2CH2Me and CHMe2),
-0.29 (s, 9H, SiMe3). 13C{1H} NMR: δ 240.72, 234.10, 192.94,
161.07, 160.43, 156.69, 156.16, 154.01, 153.35, 153.02, 146.04,
144.64, 144.21, 144.05, 143.59, 140.09, 139.37, 138.96, 138.00,
136.14, 131.14, 127.11, 126.80, 126.72, 126.14, 125.86, 125.43,
124.84, 124.46, 124.64, 124.11, 123.90, 123.88, 116.70, 116.65,
71.76, 71.44, 38.95, 31.13, 30.33, 29.93, 28.05, 27.20, 26.94,
26.45, 26.29, 25.77, 25.39, 24.60, 24.23, 24.14, 22.86, 22.78,
15.34, 15.10, 0.54.
Å-3
.
Ack n ow led gm en t. Funding from the Natural Sci-
ences and Engineering Research Council (Canada) in
the form of a Research Grant to D.H.M. is gratefully
acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables listing final
crystallographic atomic coordinates, equivalent isotropic ther-
mal parameters, hydrogen atom parameters, anisotropic ther-
mal parameters, and complete bond lengths and angles and
ORTEP’s for 3a and 6a (19 pages). Ordering information is
given on any current masthead page.
X-r a y Cr ysta llogr a p h ic An a lysis of 3a . A suitable
crystal of 3a (dimension 0.45 × 0.23 × 0.20 mm) was grown
from a saturated ether solution at -30 °C. Data were collected
on a Siemens P4 diffractometer with the XSCANS software
package.21 The cell constants were obtained by centering 25
reflections (18.0 ) 2θ ) 24.7°). The Laue symmetry 1h was
determined by merging symmetry equivalent positions. The
data were collected in the range of θ ) 1.9-23° (-1 e h e 10,
OM970593V
(22) Sheldrick, G. M. SHELXTL.-PC Software; Siemans Analytical
X-ray Instruments Inc.: Madison WI, 1990.
(23) Sheldrick, G. M. SHELXL-93; Institute fuer Anorg. Chemie:
Goettingen, Germany, 1993.
(21) XSCANS; Siemans Analytical X-ray Instruments Inc.: Madi-
son, WI, 1990.
(24) SHELXTL Version 5; Siemans Analytical X-ray Instruments
Inc.: Madison, WI, 1994.