Alkene and alkyne insertion reactions with tantalum metallacarborane complexes: The Et2C2B4H42- carborane ligand as a spectator and participant1

Article abstract of DOI:10.1021/om980242w

The tantalum carborane complex (Et₂C₂B₄H₄)CpTaMe₂ (1) is thermally stable but undergoes clean photochemical insertion with alkynes to give vinyltantalum species, in contrast to the thermal reactivity of isoelectronic group 4 metallocenes which give methylidene intermediates. Certain tantalum vinyltitanium products display NMR resonances indicative of γ-agostic Ta-H₃C interactions sufficiently strong to stabilize two different regioisomers. Decomposition of these species occurs by apparent alkyne deinsertion and ejection of the tantalum fragment to give R₂Et₂C₄B₄H₄ (R = Me, Et, Ph) carborane clusters. The analogous diphenyl complex (Et₂C₂B₄H₄)CpTaPh₂ (8) is thermally reactive, eliminating benzene and undergoing trapping reactions of the derived benzyne intermediate with alkynes. The structures of the resulting metallaindene complexes are supported by X-ray crystallography, protonolysis, and spectroscopy. Insertions occur with good regioselectivity, controlled by steric and stereoelectronic factors that differ somewhat from those observed for zirconocene and titanocene analogues. Reaction of complex 8 with excess styrene results in a novel triple-insertion process in which styrene units are added to both ortho positions of an aryl ligand and to the central boron atom of the C₂B₃ ring. The proposed mechanism (supported by the use of styrene-d₈ and alkylated metallacarborane starting materials) features two benzyne intermediates, derived from activation of both ortho-CH bonds, and one insertion into a putative Ta-B bond. An important hypothesis is that a Ta-C fragment can undergo intramolecular insertion into a carborane B-H bond, a step unknown for cyclopentadienyl C-H bonds and one that is potentially relevant to the use of metallacarborane complexes as catalysts for olefin polymerization and related processes.

Full text of DOI:10.1021/om980242w

Organometallics 1998, 17, 3865-3874
3865
Alk en e a n d Alk yn e In ser tion Rea ction s w ith Ta n ta lu m
2-
Meta lla ca r bor a n e Com p lexes: th e Et2C2B4H4
Ca r bor a n e Liga n d a s a Sp ecta tor a n d P a r ticip a n t1
Eric Boring, Michal Sabat, M. G. Finn,* and Russell N. Grimes*
Department of Chemistry, University of Virginia, Charlottesville, Virginia 22901
Received March 31, 1998
The tantalum carborane complex (Et2C2B4H4)CpTaMe2 (1) is thermally stable but
undergoes clean photochemical insertion with alkynes to give vinyltantalum species, in
contrast to the thermal reactivity of isoelectronic group 4 metallocenes which give
methylidene intermediates. Certain tantalum vinyltitanium products display NMR reso-
nances indicative of γ-agostic Ta-H3C interactions sufficiently strong to stabilize two different
regioisomers. Decomposition of these species occurs by apparent alkyne deinsertion and
ejection of the tantalum fragment to give R2Et2C4B4H4 (R ) Me, Et, Ph) carborane clusters.
The analogous diphenyl complex (Et2C2B4H4)CpTaPh2 (8) is thermally reactive, eliminating
benzene and undergoing trapping reactions of the derived benzyne intermediate with alkynes.
The structures of the resulting metallaindene complexes are supported by X-ray crystal-
lography, protonolysis, and spectroscopy. Insertions occur with good regioselectivity,
controlled by steric and stereoelectronic factors that differ somewhat from those observed
for zirconocene and titanocene analogues. Reaction of complex 8 with excess styrene results
in a novel triple-insertion process in which styrene units are added to both ortho positions
of an aryl ligand and to the central boron atom of the C2B3 ring. The proposed mechanism
(supported by the use of styrene-d8 and alkylated metallacarborane starting materials)
features two benzyne intermediates, derived from activation of both ortho-CH bonds, and
one insertion into a putative Ta-B bond. An important hypothesis is that a Ta-C fragment
can undergo intramolecular insertion into a carborane B-H bond, a step unknown for
cyclopentadienyl C-H bonds and one that is potentially relevant to the use of metallacar-
borane complexes as catalysts for olefin polymerization and related processes.
Sch em e 1
In tr od u ction
We have recently reported on our efforts to map the
organometallic reactivity of early transition metal met-
allacarborane complexes with unsaturated small mole-
cules.2-5 Photochemical and thermal insertion reactions
of isocyanides and alkynes have led to different prod-
ucts, indicative of both insertion and rearrangement
processes.4,5 Here we report the reactions of alkynes
and alkenes with Ta(V) metallacarborane compounds
demonstrating sequential C-H and B-H bond activa-
tion processes, the former through benzyne intermedi-
ates and the latter by an unknown mechanism.
diphenylacetylene or dimethylacetylene dicarboxylate.
However, photolysis in the presence of excess amounts
of 2-butyne, 3-hexyne, or diphenylacetylene gave vinyl-
tantalum species 2, 3, and 4, respectively (Scheme 1),
analogous to the facile thermal insertion chemistry of
Cp2TiMe2.6 Unlike the titanocene system,6,7 however,
the formation of metallacyclobutenes is not observed
upon subsequent heating (90 °C) or photolysis. We see
no other signs of the formation of tantalum methylidene
intermediates8 by elimination of methane from 1, in
contrast to the strong evidence for such intermediates
Resu lts a n d Discu ssion
The tantalum(V) dimethyl complex 1 was found to be
inert when heated (90 °C, 24 h) with an excess of either
(1) (a) Organotransition-Metal Metallacarboranes. 52. For part 51,
see: Curtis, M. A.; Houser, E. J .; Sabat, M.; Grimes, R. N. Inorg. Chem.
1998, 37, 102-111. (b) Based in part on the Ph.D. Thesis of E. Boring,
University of Virginia, 1998.
(2) Stockman, K. E.; Houseknecht, K. L.; Boring, E. A.; Sabat, M.;
Finn, M. G.; Grimes, R. N. Organometallics 1995, 14, 3014-3029.
(3) Houseknecht, K. L.; Stockman, K. E.; Sabat, M.; Finn, M. G.;
Grimes, R. N. J . Am. Chem. Soc. 1995, 117, 1163-1164.
(4) Boring, E.; Sabat, M.; Finn, M. G.; Grimes, R. N. Organometallics
1997, 16, 3993-4000.
(6) Doxsee, K. M.; J uliette, J . J . J .; Mouser, J . K. M.; Zientara, K.
Organometallics 1993, 12, 4682-4686.
(7) Petasis, N. A.; Fu, D.-K. Organometallics 1993, 12, 3776-3780.
(8) Complex 1 shows no ROMP activity with norbornene or a furan-
maleimide cycloadduct upon heating or photolysis nor do we observe
metallacyclobutane formation in the presence of these and other olefins.
(5) Curtis, M. A.; Finn, M. G.; Grimes, R. N. J . Organomet. Chem.
1998, 550, 469-472.
S0276-7333(98)00242-8 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 08/05/1998

3866 Organometallics, Vol. 17, No. 18, 1998
Boring et al.
Sch em e 2
Sch em e 3
complexes, which are relatively electron-rich despite
their formal 16-electron configuration. A definitive
identification of agostic Ta-H bonding in 2-4 must
await additional structural and/or spectroscopic data.
Complexes 2-4 proved to be mildly air sensitive,
decomposing to the carboranes Et2R2C4B4H4, for which
structures 5-7 are proposed (Scheme 3). A compound
corresponding to 5 was obtained by Sneddon and co-
workers from the reaction of NiCl2 and (Et2C2B4H4)Li2
in the presence of terminal alkynes21 and from the
neutral Et2C2B4H6 and 2-butyne in the presence of
ruthenium carbonyl phosphine catalysts.22 Other
R2R′2C4B4H4 carboranes have also been reported,23,24
and the nido cage structure shown in Scheme 3 has
recently been observed by X-ray crystallography for
H4C4B4Et4.25 Remarkably, the formation of these prod-
ucts in our case requires that the C-C bond formed in
the alkyne insertion process be broken, such that only
the original R2C2 alkyne fragment, rather than the vinyl
moiety, is incorporated into the new carborane cage. It
is tempting to speculate that the agostic interaction
discussed above assists in reversing the alkyne insertion
event. Exposure of 2-4 to moisture alone without O2
does not cause decomposition. The cage-expansion
process and the sensitivity of the formally Ta(V) com-
plexes to oxygen, both unusual in metallocene chemis-
try, highlight some of the ways in which early transition
metal group n complexes of the C2B4 system differ from
cyclopentadienyl complexes of group n - 1. Note that
a cage expansion event involving an isonitrile substrate
in which the CpTa center is retained has also been
reported by us,4 and a related boratabenzene ring fusion
has been observed by Ashe and co-workers.26
observed in higher-temperature thermolysis of Cp2-
TiMe27,9,10 and other systems.11 Photolysis of Cp2TiMe2
in the presence of diphenylacetylene has been shown
to produce mostly a titanacyclopentadiene (presumably
from Cp2TiII)12,13 and an unstable vinyltitanocene spe-
cies analogous to 4.14,15 Thus, as we have found previ-
ously for other processes,2-5 dimethyl complex 1 displays
reactivity analogous to its isoelectronic group 4 metal-
locene congeners but with enhanced ground-state sta-
bility. In this case, it is stimulated by irradiation not
to undergo ethane elimination to a Ta(III) intermediate,
but rather to react as Cp2TiMe2 does under gentle
heating.16
Complex 2 is isolated as a 2:1 mixture of isomers (2a
and 2b), clearly resolved in the NMR spectra. Each
isomer displays one methyl 1H (0.09 and 0.03 ppm) and
13C resonance that is significantly upfield from the
others, in addition to the expected high-field resonances
of the methyl groups bound directly to the metal.
Similar upfield CH3 signals are observed for complexes
3 and 4, but only one isomer is resolved in each case.
Use of (Et2C2B4H4)CpTa(CD3)2 with 2-butyne and diphen-
ylacetylene provides the deuterium-substituted ana-
logues of 2 and 4 in similar yields, for which the upfield
NMR signals are missing. These data suggest that an
agostic interaction17-19 may inhibit rotation about the
Ta-vinyl bond, giving rise to “H-in” vs “H-out” isomers
(analogous to N-in vs N-out of iminoacyl complexes)4 as
shown in Scheme 2.20 Complexes 3 and 4 exist as single
isomers, presumably because of a steric preference.
Agostic interactions are somewhat unexpected in these
(9) Petasis, N. A.; Fu, D.-K. J . Am. Chem. Soc. 1993, 115, 7208-
7214.
In contrast to the thermal stability of 1, the tantalum
diphenyl complex 8 is reactive upon heating, being
converted to a stable benzyne adduct in the presence of
trimethylphosphine.3 In the absence of phosphine and
the presence of alkynes, five-membered metallacycles
9-13 are produced in generally excellent yields, pre-
sumably resulting from the addition of alkyne to a
reactive benzyne intermediate (Scheme 4). The analo-
gous zirconocene compounds are well-known;27-29 the
(10) Hughes, D. L.; Payack, J . F.; Cai, D. W.; Verhoeven, T. R.;
Reider, P. J . Organometallics 1996, 15, 663-667.
(11) Mashima, K.; Kaidzu, M.; Nakayama, Y.; Nakamura, A. Or-
ganometallics 1997, 16, 1345-1348.
(12) Alt, H.; Rausch, M. D. J . Am. Chem. Soc. 1974, 96, 5936-5937.
(13) Atwood, J . L.; Hunter, W. E.; Alt, H.; Rausch, M. D. J . Am.
Chem. Soc. 1976, 98, 2454-2459.
(14) Boon, W. H.; Rausch, M. D. J . Chem. Soc., Chem. Commun.
1977, 397-398.
(15) Rausch, M. D.; Boon, W. H.; Alt, H. J . Organomet. Chem. 1977,
141, 299-312.
(16) Interestingly, the analogous complex (Et2C2B4Br3H)(Cp)TaMe2,
in which the three “ring” borons bear bromine substituents instead of
hydrogen, does not undergo the same chemistry. Photolysis in the
presence of 3-hexyne produces a product tentatively identified as the
metallacyclopentadiene expected from the combination of two alkynes
and a (carborane)(Cp)TaIII fragment. This and other reactions of
metallacarborane complexes of varying electronic and steric properties
will be reported in due course.
(17) Brookhart, M.; Green, M. L. H. J . Organomet. Chem. 1983, 250,
395-408.
(18) Brookhart, M.; Green, M. L. H.; Wong, L. L. Prog. Inorg. Chem.
1988, 36, 1-124.
(21) Mirabelli, M. G. L.; Sneddon, L. G. Organometallics 1986, 5,
1510-1511.
(22) Mirabelli, M. G. L.; Carroll, P. J .; Sneddon, L. G. J . Am. Chem.
Soc. 1989, 111, 592-597.
(23) Fehlner, T. P. J . Am. Chem. Soc. 1977, 99, 8355-8356.
(24) Siebert, W.; El-Essawi, M. E. M. Chem. Ber. 1979, 112, 2.
(25) Wrackmeyer, B.; Schanz, H.-J .; Hofmann, M.; Schleyer, P. v.
R.; Boese, R. Submitted for publication. We thank these authors for
permission to quote their results prior to publication.
(26) Ashe, A. J . I.; Al-Ahmad, S.; Kampf, J . W.; Young, V. G. J .
Angew. Chem., Int. Ed. Engl. 1997, 36, 2014-2016.
(27) Erker, G.; Kropp, K. J . Organomet. Chem. 1980, 194, 45-60.
(28) Broene, R. D.; Buchwald, S. L. Science 1993, 261, 1696-1701.
(29) Buchwald, S. L.; Nielsen, R. B. Chem. Rev. 1988, 88, 1047-
1058.
(19) Grubbs, R. H.; Coates, G. W. Acc. Chem. Res. 1996, 29, 85-93.
(20) For an example of γ-agostic interactions, see: den Haan, K.
H.; de Boer, J . L.; Teuben, J . H.; Spek, A. L.; Kojic-Prodic, B.; Hays,
G. R.; Huis, R. Organometallics 1986, 5, 1726-1733.

Alkene and Alkyne Insertion Reactions
Organometallics, Vol. 17, No. 18, 1998 3867
Sch em e 4
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 10b
Sch em e 5
Ta-C4
2.20(1)
2.18(1)
2.35(1)
2.47(1)
2.41(1)
2.40(1)
2.43(1)
Ta-C1R3
C4-C5
2.43(1)
1.33(2)
1.50(2)
1.41(2)
1.51(2)
1.52(2)
Ta-C7
Ta-C2
C5-C6
Ta-C3
C6-C7
C4-C12
C5-C13
Ta-B6
Ta-C1R1
Ta-C1R2
Ta-C4-C5
C4-C5-C6
C5-C6-C7
C6-C7-Ta
C4-Ta-C7
108.7(9)
122(1)
118(1)
108.5(8)
82.0(4)
Ta-C4-C12
C5-C4-C12
C4-C5-C13
C6-C5-C13
125.9(8)
125(1)
121(1)
117(1)
first example of related tantalum metallacycles was the
(C5H5)(CH3)2M(C6H4)CH2CH2 system of Schrock and co-
workers (M ) Ta, Nb).30 Befitting the enhanced stabil-
ity afforded by the carborane fragment, the insertion
reactions shown in Scheme 4 were all performed in air
with unpurified reagent-grade solvents. No further
reactions occur upon additional heating in the presence
of excess alkyne. The metallaindene products are stable
to the following conditions: room-temperature storage
in air for weeks, ultraviolet irradiation (Hanovia lamp)
in benzene solution for 12 h, and thermal or photo-
chemical reaction with alkynes, alkenes, or nitriles.
The metallacycle carbon fragments can be released
by treatment with acid. Thus, protonation of diphenyl-
acetylene adduct 11 at room temperature gave triphen-
ylethylene, and reaction with 2,6-dimethylphenyl iso-
cyanide afforded 2,6-dimethylphenylimino-2,3-diphen-
ylindenone (Scheme 5).31 However, complexes 10b and
11 are inert toward prolonged reaction with PhPCl2 at
85 °C, which afforded phosphole derivatives from analo-
gous titanocene metallacycles under much milder condi-
tions.32
That terminal alkynes undergo insertion to give
metallacyclopentadienes, rather than deprotonation to
acetylide species of the type (carborane)CpTa(Ph)(Ct
CR), is demonstrated by the absence of acetylenic 13C
NMR resonances, the appearance of a vinylic signal at
7.48 ppm for complex 13 (the corresponding peaks for
9a and 9b are obscured by aromatic resonances), and
the isolation of the corresponding alkenes upon treat-
ment with HCl. Unsymmetrical alkynes are incorpo-
F igu r e 1. ORTEP drawing of the solid-state structure of
10b showing 30% probability ellipsoids with atom-number-
ing scheme. H atoms are omitted for clarity.
rated with substantial regioselectivity, as shown by the
isolated yields listed in Scheme 4. The molecular
structure of the major isomer 10b from 1-phenyl-1-
propyne insertion was determined by X-ray crystal-
lography and is shown in Figure 1 (Table 1). The
structure shows the expected flat metallaindenyl moiety
bisecting the carborane-Ta-Cp angle, with the pendant
phenyl group found away from the tantalum center and
oriented roughly perpendicular to the Ta-C4-C5-C6-
C7 plane. The same regiochemical preference was
demonstrated for phenylacetylene insertion by proto-
nolysis of the major isomer 9b to give exclusively 1,1-
diphenylethylene.
(30) Schrock, R. R. J . Am. Chem. Soc. 1979, 101, 263-264.
(31) Exposure of metallacycle 11 to PhPCl2 in refluxing THF
afforded predominantly the vinyl complex (Et2C2B4H4)(Cp)Ta(C2Ph3)-
Cl but also 15% of the monophenyl chloride complex (Et2C2B4H4)(Cp)-
TaPhCl (products characterized by NMR, mass spectrometry, elemen-
tal analysis, and reaction with HCl to liberate triphenylethylene in
the first case). While the first product may arise from reaction of 11
with trace HCl contaminating the chlorophosphine reagent, the
formation of the monophenyl adduct suggests a novel reaction of the
P-Ph bond. No phosphole formation was observed, in contrast to the
reported reactivities of titanocene and zirconocene metallacycles with
PhPCl2.
(32) Fagan, P. J .; Nugent, W. A. J . Am. Chem. Soc. 1988, 110, 2310-
2312.

3868 Organometallics, Vol. 17, No. 18, 1998
Boring et al.
Sch em e 6
These results contrast somewhat with the chemistry
of zirconocene and titanocene benzyne and alkyne
complexes, which insert unsymmetrical alkynes with
little selectivity or with preference for the isomer having
the larger substituent adjacent to the metal center.33-35
Thus, the (carborane)CpTa center appears to be more
congested than Cp2Zr or Cp2Ti, giving rise to the
observed regioselectivity by virtue of a steric effect. The
structure of the {trimethylsilyl}acetylene insertion prod-
uct 13, isolated as a single isomer, is assigned on the
basis of NOE enhancements in the vinylic (10.4%) and
Cp (4.1%) resonances observed upon irradiation of the
SiMe3 signal, with no enhancement found for any
aromatic resonance. This regiochemical outcome, with
the SiMe3 group next to the metal, is consistent with
the strong electronic stabilization provided by the silyl
group to the incipient negative charge at the R-carbon,
as is consistently observed in insertion reactions of
metallocene-alkyne complexes.33-35
Reaction of 2 equiv of 8 with 1,4-diphenylbutadiyne
under standard conditions gave 14 in approximately
50% yield plus approximately 4% of a bis-insertion
product tentatively identified as structure 15 (Scheme
6). Treatment of 14 with 10 equiv of 8 in a separate
step results in the conversion of only 8% of 14 to 15
before all of the diphenyl complex is consumed (moni-
tored by NMR), consistent with the steric crowding
expected for the highly substituted bridging diene unit
of 15.
Styrene was used as a probe for olefin reactivity with
the putative benzyne intermediate derived from 8.
Reaction with 10 equiv of styrene in refluxing benzene
for 16 h afforded the product of a single insertion 16,
isolated in 63% yield and characterized by 1H NMR, 13
C
NMR, and mass spectrometry (Scheme 7). Complex 16
was purified by column chromatography in air but
decomposed to a complex mixture of materials upon
extended exposure to the atmosphere at room temper-
ature. When 16 and excess styrene were heated for 60
h, a new complex 17 was formed in high yield and was
found to contain the elements of three styrene units
(Scheme 7). The X-ray crystal structure of 17 is shown
in Figure 3 (Table 2), revealing styrene fragments on
both sides of the Ta-aryl bond (one as a phenethyl
group and one incorporated into a metallacycle) as well
as a phenethyl unit on the central ring boron, B(5). NMR
and crystallographic parameters show that each con-
tains a saturated ethyl unit; thus, three insertion
reactions have occurred using two aryl-H bonds and
one B-H bond. Direct insertion of styrene into the
B(5)-H bond is unlikely because no such insertion
occurs with (carborane)(Cp)TaCl2 or (carborane)(Cp)-
TaMe2 complexes.
Use of styrene-d8 gives 16-d8 with no proton reso-
nances visible in the sp3 region other than those of the
carborane ethyl groups, as expected for the trapping of
the putative intermediate benzyne with alkene (verified
by mass spectrometry). Further reaction with styrene-
d8 gave 17-d24 by mass spectrometry, displaying a new
broad singlet at 1.61 ppm (2H) as the only non-
carborane aliphatic resonance. This signal is assigned
to H1 and H2 shown in Scheme 7, which derive from
the B-H and C-H bonds that are apparently conserved
in the second and third insertion steps.
The alkyne insertion products are chiral, with the
metal atom as the stereogenic center, in contrast to the
axial chirality that characterizes the highly useful ansa-
metallocene complexes first developed by Brintzinger
and co-workers. The expected configurational stability
of our structures was demonstrated by the complete
resolution of 9b by high-performance liquid chromatog-
raphy using a Chiralcel OD-H column. The enanti-
omers isolated on a small scale in this manner are
characterized by [R]20 ) -565 ( 20° (c ) 0.50 g/100
D
mL of cyclohexane) for the faster-eluting isomer and
[R]20 ) +555 ( 20° (c ) 0.60 g/100 mL of cyclohexane)
D
for the slower-eluting isomer.36 The mirror-image
circular dichroism spectra of the two enantiomers along
with their UV-vis spectrum are shown in Figure 2. The
sinusoidal quality of the CD spectra allows some of the
component bands of the electronic spectrum to be clearly
identified.
(33) Buchwald, S. L.; Nielsen, R. B. Chem. Rev. 1988, 88, 1047-
1058 and references therein.
(34) Ca´mpora, J .; Buchwald, S. L. Organometallics 1993, 12, 4182-
F igu r e 2. Electronic spectrum of racemic 9b (0.088 mM),
and circular dichroism of the resolved enantiomers (2.7
mM), both in cyclohexane.
4187.
(35) Buchwald, S. L.; Nielsen, R. B. J . Am. Chem. Soc. 1989, 111,
2870-2874.

Alkene and Alkyne Insertion Reactions
Organometallics, Vol. 17, No. 18, 1998 3869
Sch em e 7
Ta ble 2. Selected Bon d Len gth s (Å) a n d An gles
(d eg) for Com p lex 17
Sch em e 8
Ta-C4
2.24(1)
2.176(7)
2.47(1)
2.472(9)
2.45(1)
2.427(9)
2.41(1)
Ta-C1R1
B5-C26
2.37(1)
1.63(1)
1.54(1)
1.54(1)
1.53(1)
1.48(1)
Ta-C17
Ta-C2
C4-C11
Ta-C3
Ta-B4
Ta-C1R4
Ta-C1R5
C11-C12
C18-C19
C26-C27
Ta-C4-C11
Ta-C4-C5
C4-C11-C12
C11-C12-C17
Ta-C17-C12
99.4(5)
122.2(6)
115.8(8)
120.1(7)
105.3(5)
Ta-B5-C26
133.8(7)
112.4(8)
119.1(9)
111.5(9)
113.6(9)
B5-C26-C27
C26-C27-C28
C16-C18-C19
C18-C19-C20
the bis(o-tolyl) complex 20 from (Et2C2B4H4)CpTaCl2
and (o-tolyl)MgBr, employing forcing conditions to
overcome the steric hindrance of the system. Two
compounds of the desired composition were isolated,
which are tentatively assigned as the syn and anti
o-tolyl isomers shown in Scheme 8. These isomers were
separated by column chromatography and do not inter-
convert at room temperature.38 Exposure of each isomer
to an excess of styrene in refluxing benzene leads to
consumption of the starting diaryl species, but no
identifiable organometallic products could be isolated
from the resulting complex mixture. The reaction of
trans-stilbene with 8 was similarly unrewarded with
identifiable products.
The sequence of steps shown in Scheme 9 is consistent
with the above observations. Metallacycle intermediate
16 results from trapping of benzyne complex 21. Note
that the regioselectivity of insertion is opposite to that
observed for alkynes: the bulkier alkene substituent is
found adjacent to the metal center. It is not clear
whether this difference is the result of stereoelectronic
F igu r e 3. ORTEP drawing of the solid-state structure of
17 showing 30% probability ellipsoids with atom-number-
ing scheme. H atoms are omitted for clarity.
To further probe the sequence of events, these active
hydrogen atoms were replaced by carbon fragments.
Thus, the triphenyl complex 18, prepared from a B(5)-
brominated37 tantalum dichloride precursor, reacts with
styrene to give only the monoinserted complex 19; no
further reaction is observed, even upon extended heat-
ing (Scheme 7). In addition, we attempted to prepare
(38) An attempted synthesis of the analogous zirconocene complex,
Cp2Zr(o-C6H4Me)2, was reported to give a thermally unstable mixture
lacking a substantial amount of the desired compound (Erker, G. J .
Organomet. Chem. 1977, 134, 189-202), although a successful syn-
thesis was later claimed (Chen, S.-S.; Wang, C.-T. K’o Hsueh T’ung
Pao 1980, 25, 270-271; Chem. Abstr. 94: 208952). Zirconocene and
titanocene bis(o-tolyl) complexes are assumed to undergo rapid elimi-
nation to the analogous benzyne (Rausch, M. D.; Mintz, E. A. J .
Organomet. Chem. 1980, 190, 65-72 and references therein). Since
neither isomer of 20 provides insertion products analogous to those of
the diphenyl complex 8, as one would expect for a meta-substituted
aryl complex, we do not believe that m-tolyl groups are formed here.
However, the characterization data presently in hand do not rule out
this possibility.
(36) For comparison, the optical rotation of (S,S)-ethylenebis(4,5,6,7-
25
tetrahydro-1-indenyl)titanium dichloride is [R]435 ) -3300° (Wild,
F. R. W. P.; Zsolnai, L.; Huttner, G.; Brintzinger, H. H. J . Organomet.
Chem. 1982, 232, 233-247).
(37) Stockman, K. E.; Garrett, D. L.; Grimes, R. N. Organometallics
1995, 14, 4661-4667.

3870 Organometallics, Vol. 17, No. 18, 1998
Boring et al.
Sch em e 9
array spectrophotometer. Unit resolution mass spectra were
obtained on a Finnegan MAT 4600 spectrometer using per-
fluorotributylamine (FC43) as the calibration standard and
chemical ionization using CH4; both positive- and negative-
ion spectra were recorded. The values reported are for the
technique that provides the molecular ion as the base peak.
In all cases, strong parent ion envelopes were observed.
Elemental analyses were obtained in this department on a
Perkin-Elmer 2400 CHN analyzer using 2,4-dinitrophenylhy-
drazone as the calibration standard. Infrared spectra were
recorded as thin films on a Nicolet Impact-400 spectrometer.
Photolyses were performed in Pyrex flasks using a water-
cooled 450-W Hanovia mercury arc lamp at a distance of
approximately 15 cm. All solvents were distilled under a dry
nitrogen atmosphere from Na/benzophenone. (Et2C2B4H4)-
(C5H5)Ta(CH3)2 (1) and (Et2C2B4H4)(C5H5)Ta(C6H5)2 (8) were
prepared as previously described.2 (Et2C2B4H4)(Cp)Ta(CD3)2
was prepared by an analogous procedure, starting from 150
mg of (Et2C2B4H4)(Cp)TaCl2 and 3 equiv of CD3MgBr in 5 mL
of THF for 2 h at room temperature. The complex was purified
by filtration through silica gel (CH2Cl2 eluant) and isolated in
98% yield. 1H NMR (δ, CDCl3): 6.03 (s, 5H), 2.81 (m, 4H),
1.30 (t, 6H). MS: m/z 412. All other reagents were purchased
and used as received. Unless otherwise indicated, reactions
and purifications were performed in air.
factors or the differing steric demand in the approach
of alkyne vs alkene to the benzyne intermediate. The
first novel step in the reaction mechanism is the
proposed cleavage of the newly formed Ta-C bond. We
envision an addition of B(5)-H across this bond, giving
an intermediate 22 that is stabilized by enhanced
interaction of B(5) with the metal center; it is this step
that is blocked by the placement of a phenyl group on
B(5). Insertion of styrene gives a new proposed metal-
lacycle (23), which undergoes a second benzyne-generat-
ing C-H activation to give 24. Note of course that the
organic fragment that accepts the H atom is not released
but rather remains attached to B(5) as a phenethyl
group. Blocking this step with the o-tolyl complex 20
would leave the system at the point of intermediate 23,
which can be expected to undergo other types of
decomposition reactions. Capture of benzyne 24 with
a third equivalent of styrene completes the suggested
sequence, giving 17.
The proposed step of the greatest mechanistic signifi-
cance in Scheme 9 is the suggested intramolecular
insertion of a Ta-C bond into the B(5)-H bond in going
from 16 to 22. Thus, while the carborane fragment
usually gives rise to extra stability, it may also provide
for additional reactivity by making available alternative
reaction pathways. These contrasting themes have
emerged in our studies of the olefin polymerization
activity of related group 4 metallacarborane systems,
as will be reported in due course.
Rea ction s of Alk yn es w ith 1. (Et2C2B4H4)(Cp )Ta (CH3)-
[(CH3)CdC(CH3)2] (2). Under an argon atmosphere, a solu-
tion of complex 1 (100 mg, 0.247 mmol) in 5 mL of benzene
was treated with dry, degassed 2-butyne (133 mg, 2.5 mmol)
via syringe. With constant stirring, the reaction flask was
irradiated for 6 h, causing a color change to dark red-brown.
The volatiles were removed in vacuo, and the solid residue
was dissolved in hexane (in air atmosphere) and immediately
filtered through a Celite plug. Evaporation of the solvent gave
2 as a reddish oil (43 mg, 38% yield). A dark yellow solid
remaining on the frit could not be characterized. NMR
analysis of 2 revealed the presence of two stereoisomers. For
the major isomer: 1H NMR (δ, C6D6) 5.11 (s, C5H5), 2.53, 2.26
(m, m, 2H, 2H, carborane ethyl CH2), 1.82 (s, 3H, vinylic
C-Me), 1.74 (s, 3H, vinylic C-Me), 1.18 and 0.90 (t, t, 3H,
3H, carborane ethyl CH3), 0.03 (s, 3H, vinylic C-Me (agostic)),
Exp er im en ta l Section
1H (300 MHz), 11B (115.8 MHz), and 13C (75.5 and 125.3
MHz) NMR spectra were acquired on Nicolet NT-360 and GE
QE-300 instruments. Unless otherwise noted, the 1H NMR
spectra of all new carborane complexes display ethyl CH2
signals as doublets of quartets with coupling constants of 15
and 7.5 Hz, and ethyl CH3 as triplets with J ) 7.5 Hz. UV-
vis spectra were recorded on a Hewlett-Packard 8452A diode

Alkene and Alkyne Insertion Reactions
Organometallics, Vol. 17, No. 18, 1998 3871
-0.22 (s, 3H, Ta-Me); 13C NMR (δ, C6D6) 129.3 (vinyl), 125.6
(vinyl), 106.1 (Cp), 29.4 (vinylic C-Me), 25.5 (vinylic C-Me),
24.8, 24.1 (carborane ethyl CH2), 19.7 (vinylic C-Me (agostic)),
17.0, 15.9 (carborane ethyl CH3), 10.4 (1J CH ) 146 Hz, Ta-
Me). For the minor isomer: 1H NMR (δ, CDCl3) 5.11 (s, 5H,
C5H5), 2.47, 2.01 (m, m, 2H, 2H, carborane ethyl CH2), 2.22
(s, 3H, vinylic C-Me), 1.97 (s, 3H, vinylic C-Me), 1.004 and
0.997 (t, t, 3H, 3H, carborane ethyl CH3), 0.09 (s, 3H, vinylic
C-Me (agostic)), -0.24 (s, 3H, Ta-Me); 13C NMR (δ, CDCl3)
129.0 (vinyl), 127.3 (vinyl), 108.7 (Cp), 30.3 (vinylic C-Me),
27.5 (vinylic C-Me), 25.4, 23.6 (carborane ethyl CH2), 20.3
(vinylic C-Me (agostic)), 19.2, 16.8 (carborane ethyl CH3), 10.9
(Ta-Me). For the mixture of isomers: 11B NMR (δ, CDCl3)
3.5 (1B, d, J ) 146 Hz), -1.1 (1B, d, J ) 146 Hz), -13.5 (1B,
d, J ) 132 Hz), -16.8 (1B, d, J ) 161 Hz); IR (CH2Cl2, cm-1):
2961 (w), 2917 (w), 2875 (w), 2525 (w, B(H)), 2324 (w), 1517
(w), 1362 (w), 817 (w); UV-vis (CH2Cl2, nm) 406 (25%), 348
(44%), 300 (100%); MS (negative ion), m/z 458. Anal. Calcd
for TaC17B4H31: C, 44.42; H, 6.80. Found: C, 44.13; H, 6.92.
(Et2C2B4H4)(Cp )Ta (CD3)[(CH3)CdC(CD3)(CH3)] (2-d 6).
Reaction of (Et2C2B4H4)(Cp)Ta(CD3)2 (100 mg) and 5 equiv of
2-butyne by the above procedure provided 2-d6 in 37% yield.
For the major isomer: 1H NMR (δ, C6D6) 5.11 (s, 5H), 2.53,
2.26 (m, m, 2H, 2H), 1.82 (s, 3H), 1.74 (s, 3H), 1.18 and 0.90
(t, t, 3H, 3H). For the minor isomer: 1H NMR (δ, C6D6) 5.11
(s, 5H), 2.47, 2.01 (m, m, 2H, 2H), 2.22 (s, 3H), 1.97 (s, 3H),
1.004 and 0.997 (t, t, 3H, 3H). For the mixture of isomers:
MS (negative ion), m/z 464.
(Et2C2B4H4)(Cp )Ta (CH3)[(Et)CdC(Et)(CH3)] (3). The
above procedure with 10 equiv of 3-hexyne (202 mg) provided
3 as a red oil in 43% yield (52 mg). Filtration of a hexane
solution of this material through a 1 cm alumina plug and
removal of the solvent gave 50 mg of a dark orange solid. 1H
NMR (δ, CDCl3): 5.49 (s, 5H, C5H5), 2.46 (m, 2H), 2.32 (q, J )
6.6 Hz, 4H), 2.16 (m, 2H), 1.22, 1.14, 1.04, 0.99 (each t, J )
7.8 Hz, each 3H), -0.23 (s, 3H, Ta-CdCMe), -0.53 (s, 3H,
Ta-Me). 13C NMR (δ, CDCl3): 127.0, 126.9, 105.9 (Cp), 27.6,
25.9, 25.6, 25.0, 24.3, 17.0, 16.8, 16.0, 15.9, 10.8. 11B NMR (δ,
CDCl3): 2.9 (1B, d, J ) 147 Hz), -0.8 (1B, d, J ) 147 Hz),
-13.7 (1B, d, J ) 132 Hz), -18.1 (1B, d, J ) 160 Hz). IR (CH2-
Cl2, cm-1): 2959 (s), 2930 (s), 2875 (s), 2576 (s, B(H)), 2344
(w), 1497 (w), 1378 (w), 821 (w). UV-vis (CH2Cl2, nm): 404
(100%), 346 (33%), 302 (83%). MS: m/z 487. Anal. Calcd for
TaC19H35B4: C, 46.80; H, 7.23. Found: C, 46.25; H, 7.48.
(Et2C2B4H4)(Cp )Ta (CH3)[(P h )CdC(P h )(CH3)] (4). The
above procedure with 5 equiv of diphenylacetylene (220 mg)
provided 4 as a dark red oil in 34% yield (40 mg), following
elution through a 25-cm column of neutral alumina using 4:1
pentane:CH2Cl2. The reaction was also conducted with 1 equiv
of diphenylacetylene in a minimum volume of benzene solution
(approximately 1 mL). Photolysis for 10 h was followed by
removal of the volatiles in vacuo and purification of the residue
by passage through a short alumina plug in hexane solution
to give a 41% yield (49 mg) of 4. 1H NMR (δ, C6D6): 7.33 (d,
J ) 3.9 Hz, 2H), 7.22 (t, J ) 2.1 Hz, 1H), 7.13 (t, J ) 3.9 Hz,
2H), 7.10 (t, J ) 3.9 Hz, 2H), 6.95 (d, J ) 3.9 Hz, 2H), 6.85 (t,
J ) 2.1 Hz, 1H), 5.47 (s, 5H), 2.55 (m, 2H), 2.32 (m, 2H), 1.22
(t, 3H), 0.96 (t, 3H), 0.14 (s, 3H, Ta-CdCMe), -0.10 (s, 3H,
Ta-Me). 13C NMR (δ, C6D6): 143.2, 141.5, 132.2, 128.8, 126.6,
126.3, 108.0 (Cp), 30.2 (Ta-Me), 24.7, 24.4, 16.9, 15.9, 14.0
(Ta-CdCMe). 11B NMR (δ, CDCl3): 4.2 (1B, d, J ) 146 Hz),
-1.3 (1B, d, J ) 146 Hz), -11.4 (1B, d, J ) 131 Hz), -15.1
(1B, d, J ) 160 Hz). IR (cm-1, CH2Cl2): 3075 (s), 2943 (s),
2800 (m), 2543 (B(H), s), 2312 (w), 1610 (w), 1436 (w), 875
(w). UV-vis (nm, CH2Cl2): 425 (100%), 330 (45%), 290 (11%).
MS (negative ion), m/z 583. Anal. Calcd for TaC27H35B4: C,
55.55; H 6.04. Found: C, 54.33; H, 6.23.
2H), 7.22 (t, J ) 2.1 Hz, 1H), 7.13 (t, J ) 3.9 Hz, 2H), 7.10 (t,
J ) 3.9 Hz, 2H), 6.95 (d, J ) 3.9 Hz, 2H), 6.85 (t, J ) 2.1 Hz,
1H), 5.47 (s, Cp), 2.55 (m, 2H), 2.32 (m, 2H), 1.22 (t, 3H), 0.96
(t, 3H). MS (negative ion) m/z 590.
Decom p osition of Alk yn e Ad d u cts 2-4. Et2Me2C4B4H4
(5). Complex 2 (100 mg, 0.22 mmol) was dissolved in 5 mL of
methylene chloride and allowed to stir in air for 72 h. The
solution was filtered through a 3-cm plug of silica, and the
volatiles were removed in vacuo to give 5 as a clear oil (12
mg, 30% yield), showing NMR data that match the reported
values21 and an appropriate mass spectrum. 1H NMR (δ,
C6D6): 2.30 (m, 4H), 1.88 (s, 6H), 1.02 (t, 6H). 11B NMR (δ,
C6D6): -11.1 (d, 2B), -12.5 (d, 1B), -12.9 (d, 1B). MS: m/z
184.
Et4C4B4H4 (6). The above procedure was applied to 100
mg of complex 3, (36 h reaction time), providing 6 as a clear
oil (14 mg, 32%), with the expected21 NMR spectrum. 1H NMR
(δ, CDCl3): 2.52, 2.35 (m, 8H), 1.10 (t, 12H). MS: m/z 212.
Et2P h 2C4B4H4 (7). The above procedure was applied to 100
mg of complex 4, (24 h reaction time). The reaction mixture
was filtered through a 3-cm plug of Celite and then purified
by preparative TLC (silica; 4:1 hexane:CH2Cl2). The second
(major) band proved to be 7, isolated as a clear oil in 36% yield
(19 mg). 1H NMR (δ, CDCl3): 7.20 (m, 4H), 7.08 (m, 2H), 7.05
(m, 3H), 7.06 (d, J ) 7.8 Hz, 1H), 2.63 (m, 2H), 2.52 (m, 2H),
1.19 (t, 6H). 13C NMR (δ, CDCl3): 139.1, 131.5, 128.3, 128.2,
128.1, 128.0, 127.7, 127.1, 25.2, 13.6. MS: m/z 307.
Rea ction s of Alk yn es w ith 8 (See Sch em e 4 for Yield s
of Isola ted P r od u cts). (Et2C2B4H4)(Cp )Ta (C6H4(HCC-
(C6H5)) (9a a n d 9b). A mixture of 8 (100 mg, 0.189 mmol)
and phenylacetylene (96 mg, 0.94 mmol, 5 equiv) was heated
at reflux in 2 mL of benzene for 12 h, causing a slow color
change to dark brown. After removal of the solvent, the
residue was freed of phenylacetylene by hexane elution
through a 3-cm plug of silica. When all the phenylacetylene
was eluted (TLC), the plug was washed with CH2Cl2 until free
of colored material. Removal of the solvent affords a clean
mixture of 9a and 9b. The two isomers can be separated on
a 25-cm silica column eluting with 8:1 hexane:CH2Cl2. For
9a : 1H NMR (δ, CDCl3) 7.38 (m, 6H), 7.20 (t, J ) 7.8 Hz, 2H),
7.02 (d, J ) 6.8 Hz, 2H), 6.19 (s, 5H), 3.18 (m, 1H), 2.86 (m,
2H), 2.62 (m, 1H), 1.24 (t, 3H), 1.13 (t, 3H); 13C NMR (δ, CDCl3)
144.5, 136.2, 133.4, 132.3, 131.2, 129.3, 129.1, 128.8, 128.7,
124.7, 122.7, 111.6, 109.8 (Cp), 24.8, 24.2, 14.8, 14.3; 11B NMR
(δ, CDCl3) 40.2 (1B, d, J ) 122 Hz), 28.7 (1B, d, J ) 104 Hz),
25.5 (1B, d, J ) 133 Hz), 0.4 (1B, d, J ) 118 Hz); IR (CH2Cl2,
cm-1) 3087 (w), 2968 (m), 2924 (m), 2885 (w), 2563 (B(H), s),
1565 (w), 1472 (m), 1380 (w), 1257 (w), 1033 (m), 834 (s), 750
(s), 721 (s); UV-vis (CH2Cl2, nm) 240 (100%), 272 (77%), 333
(43%), 414 (5%); MS m/z 554. Anal. Calcd for TaC25H29B4:
C, 54.23; H, 5.28. Found: C, 54.62; H, 5.76. For 9b: 1H NMR
(δ, CDCl3) 7.37 (m, 1H), 7.33 (d, J ) 6.8 Hz, 2H), 7.28 (m, 1H),
7.19 (t, J ) 7.8 Hz, 1H), 7.12 (t, J ) 7.8 Hz, 1H), 7.01 (t, J )
7.8 Hz, 1H), 6.86 (d, J ) 7.8 Hz, 1H), 6.84 (t, J ) 7.8 Hz, 2H),
6.13 (s, 5H), 2.47 (m, 1H), 2.34 (m, 1H), 2.02 (m, 1H), 1.85 (m,
1H), 1.22 (t, 3H), 1.06 (t, 3H); 13C NMR (δ, CDCl3) 145.3, 136.5,
128.1, 127.9, 127.6, 127.5, 127.2, 126.9, 126.8, 126.5, 124.6,
115.6, 109.3 (Cp), 24.3, 24.1, 14.6, 14.1; 11B NMR (δ, CDCl3)
39.6 (1B, d, J ) 124 Hz), 29.8 (1B, d, J ) 100 Hz), 23.4 (1B, d,
J ) 124 Hz), -0.2 (1B, d, J ) 124 Hz); IR (CH2Cl2, cm-1) 3043
(w), 2968 (m), 2924 (m), 2874 (w), 2571 (B(H), s), 1596 (w),
1489 (m), 1445 (m), 1382 (w), 1262 (w), 1011 (w), 834 (s), 765
(s), 721 (s), 696 (m); UV-vis (CH2Cl2, nm) 242 (100%), 276
(82%), 328 (42%), 348 (36%), 404 (7%); MS m/z 554. Anal.
Calcd for TaC25H29B4: C, 54.23; H, 5.28. Found: C, 54.21; H,
5.70.
Enantiomeric resolution of 9b was accomplished in 0.5-
1.0 mg aliquots on a Chiralcel OD-H analytical HPLC column
(Chiral Technologies, Inc.), elution with 2% 2-propanol in
hexane at 1.0 mL/min (retention times, isomer 1 ) 7.0 min;
isomer 2 ) 8.6 min). Approximately 6 mg of each pure
(Et2C2B4H4)(Cp)Ta(CD3)[(P h )CdC(P h )(CD3)] (4-d6). The
standard procedure, using (Et2C2B4H4)(Cp)Ta(CD3)2 (100 mg)
and 5 equiv of diphenylacetylene, afforded 4-d6 in 41% yield
(59 mg) as a red oil. 1H NMR (δ, C6D6): 7.33 (d, J ) 3.9 Hz,

3872 Organometallics, Vol. 17, No. 18, 1998
Boring et al.
enantiomer was isolated; the enantiomeric purity of each was
verified by HPLC analysis on the same column. Circular
dichroism measurements (Figure 2; J asco J -720 spectropola-
rimeter) were performed on 2.7 mM solutions of each enanti-
omer in cyclohexane at 24 °C, in a cell of 1 mm path length.
(Et2C2B4H4)(Cp )Ta (C6H4(C6H5)CC(CH3)) (10a a n d 10b).
The above procedure was performed with 8 (100 mg) and
1-phenyl-1-propyne (109 mg, 0.95 mmol, 5 equiv). Direct
column chromatography of the crude product residue (25-cm
silica; 4:1 hexane:CH2Cl2) provided 10b (the major product)
as a brown-red solid and 10a (the minor product) as a dark
green solid. X-ray quality crystals of 10b were obtained by
slow diffusion of hexane into a diethyl ether solution at -20
°C. For 10a : 1H NMR (δ, CDCl3) 7.36 (m, 1H), 7.33 (m, 1H),
7.28 (d, J ) 6.8 Hz, 2H), 7.21 (t, J ) 6.8 Hz, 2H), 7.06 (m,
2H), 6.51 (m, 1H), 6.05 (s, 5H), 2.30 (m, 2H), 1.97 (m, 2H),
1.99 (s, 3H), 1.19 (t, 3H), 1.13 (t, 3H); 13C NMR (δ, CDCl3)
146.1, 135.3, 134.7, 130.4, 129.4, 128.1, 127.5, 126.2, 126.1,
125.2, 121.0, 110.6 (Cp), 24.5, 23.9, 18.9, 14.5, 14.1; 11B NMR
(δ, CDCl3) 41.2 (1B, d, 130 Hz), 31.9 (1B, d, 133 Hz), 23.6 (1B,
d, 165 Hz), 1.9 (1B, d, 104 Hz); IR (CH2Cl2, cm-1) 3238 (s),
2968 (s), 2930 (s), 2880 (w), 2565 (B(H), s), 2263 (w), 1678 (s),
1602 (m), 1464 (s), 1268 (s), 1199 (w), 1092 (s), 1023 (s), 841
(s), 740 (s); UV-vis (CH2Cl2, nm) 234 (100%), 250 (88%), 316
(25%), 410 (5%); MS m/z 568. Anal. Calcd for TaC26H31B4:
C, 55.00; H, 5.59. Found: C, 54.57; H, 5.78. For 10b: 1H NMR
(δ, CDCl3) 7.44 (t, J ) 7.8 Hz, 1H), 7.36 (t, J ) 7.8 Hz, 1H),
7.31 (d, J ) 10.7 Hz, 1H), 6.94 (t, J ) 6.8 Hz, 2H), 6.81 (t, J
) 6.8 Hz, 1H), 6.58 (d, J ) 7.8 Hz, 1H), 6.52 (d, J ) 6.8 Hz,
2H), 6.27 (s, 5H), 2.41 (m, 1H), 2.36 (m, 2H), 2.01 (m, 1H),
1.81 (s, 3H), 1.22 (t, 3H), 1.20 (t, 3H); 13C NMR (δ, CDCl3)
141.1, 135.4, 130.0, 129.4, 128.4, 128.1, 128.0, 127.5, 126.3,
137.8, 137.3, 128.1, 127.9, 124.5, 122.7, 108.7 (Cp), 24.1, 23.7,
23.5, 23.1, 14.9, 14.3, 15.3, 15.1. 11B NMR (δ, CDCl3): 42.4
(1B, d, J ) 118 Hz), 27.6 (1B, d, J ) 108 Hz). UV-vis (CDCl3,
nm): 234 (96%), 254 (100%), 314 (24%). MS: m/z 535. Anal.
Calcd for TaC23H33B4: C, 51.76; H, 6.23. Found: C, 52.54; H,
6.01. Although the microanalytical data is not satisfactory,
as occasionally happens for oils of this type, the identity of
the compound is not in doubt and the NMR spectra show no
impurities.
(Et2C2B4H4)(Cp)Ta(C6H4(HCdCSi(CH3)3)) (13). The above
procedure was performed with 30 mg 8 and 8 equiv of
(trimethylsilyl)acetylene, heating for 16 h. A color change to
red-orange occurred over the first several hours. Purification
of the crude product by filtration through a 3-cm plug of
alumina provided 13 as an orange-yellow solid. 1H NMR (δ,
C6D6): 7.48 (s, 1H, CdCH), 6.98 (t, J ) 7.8 Hz, 1H), 6.90 (t, J
) 7.8 Hz, 1H), 6.59 (d, J ) 7.8 Hz, 1H), 6.53 (d, J ) 7.8 Hz,
1H), 5.70 (s, 5H), 2.28 (m, 2H), 2.14 (m, 2H), 1.23 (t, 3H), 1.12
(t, 3H), 0.28 (s, 9H). 1H NMR (δ, CDCl3): 7.36 (s, 1H, Cd
CH), 7.03 (t, J ) 7.8 Hz, 1H), 6.96 (t, J ) 7.8 Hz, 1H), 6.72 (d,
J ) 7.8 Hz, 1H), 6.62 (d, J ) 7.8 Hz, 1H), 6.14 (s, 5H), 2.36
(m, 1H), 2.24 (m, 1H), 2.21 (m, 1H), 1.88 (m, 1H), 1.184 (t,
3H), 1.176 (t, 3H), 0.18 (s, 9H). 13C NMR (δ, CDCl3): 136.6,
128.1, 127.7, 127.6, 126.7, 126.5, 126.4, 126.0, 109.1 (Cp), 24.2,
24.0, 14.5, 13.9, 1.51. IR (cm-1, CH2Cl2): 3128 (w), 3052 (w),
2962 (m), 2933 (m), 2895 (m), 2871 (w), 25557 (B(H), s), 1494
(w), 1456 (w), 1437 (w), 1243 (m), 1017 (w), 891 (s), 822 (s),
752 (m), 721 (m). UV-vis (nm, CH2Cl2): 247 (100%), 272
(79%), 322 (51%), 350 (33%), 406 (6%). MS: m/z 549. Anal.
Calcd for TaC22H33B4Si: C, 48.06; H, 6.05. Found: C, 47.68;
H, 6.12.
(Et2C2B4H4)(Cp )Ta (C6H4)((C6H5)CCCC(C6H5)) (14) a n d
[(Et2C2B4H4)(Cp )Ta (C6H4)]2((C6H5)CCCC(C6H5)) (15). The
standard procedure with 100 mg of 8 and 18 mg of 1,4-
diphenylbutadiyne (0.5 equiv) was performed under a nitrogen
atmosphere in degassed benzene. Evaporation of volatiles and
chromatography as for 10 provided 14 as the major product
(46% yield; 52% based on recovered starting material) and 6
mg of 15. Complex 14 (20 mg, 0.018 mmol) was treated with
10 equiv of complex 8 in C6D6 solution and heated to 80 °C for
22 h, until all of 8 was consumed. NMR analysis showed the
appearance of approximately 8% of 15 relative to the amount
of 14 used, measured against the residual benzene signal as
an internal standard. For 14: 1H NMR (δ, CDCl3) 7.92 (m,
2H), 7.55 (d, J ) 7.8 Hz, 2H), 7.34 (t, J ) 6.8 Hz, 2H), 7.28 (t,
J ) 7.8 Hz, 2H), 7.13 (m, 4H), 6.13 (s, 5H), 2.39 (m, 2H), 2.04
(m, 1H), 1.92 (m, 1H), 1.18 (t, 3H), 1.14 (t, 3H); 13C NMR (δ,
CDCl3) 144.5, 139.8, 132.9, 131.8, 130.7, 128.8, 128.6, 128.2,
124.2, 122.3, 24.8, 24.2, 14.8, 14.3. For 15: 1H NMR (δ, CDCl3)
8.02 (d, J ) 7.8 Hz, 4H), 7.92 (d, J ) 8.8 Hz, 2H), 7.73 (d, J )
6.8 Hz, 2H), 7.55 (t, J ) 6.8 Hz, 2H), 7.50 (t, J ) 6.8 Hz, 4H),
7.42 (t, J ) 6.8 Hz, 4H), 7.24 (t, J ) 5.8 Hz, 2H), 5.41 (s, 10H),
1.58 (m, 4H), 1.39 (m, 4H), 0.78 (t, 6H), 0.69 (t, 6H); 13C NMR
(δ, CDCl3) 146.4, 1141.8, 139.9, 138.3, 133.6, 129.1, 128.7,
128.6, 128.5, 126.0, 125.8, 123.7, 102.8 (Cp), 24.3, 21.0, 15.2,
14.4. Anal. Calcd for Ta2C50H56B8: C, 54.32; H, 5.11.
Found: C, 54.43; H, 5.49.
Rea ction s of Alk yn e In ser tion P r od u cts w ith Electr o-
p h iles. P r oton olysis of 11. Complex 11 (100 mg, 0.16
mmol) in diethyl ether was treated under a nitrogen atmo-
sphere with HBF4 (85% solution in ether, 64 mg, 2.1 equiv)
by syringe with stirring at room temperature. After 12 h, the
volatiles were removed and the oily residue was dissolved in
CH2Cl2 and allowed to stir for 15 min before being flushed
through a 3-cm plug of silica gel. The resulting material was
purified by preparative TLC (4:1 hexane: CH2Cl2); the least
polar band gave triphenylethylene as a white solid in 73%
yield, with 1H and 13C NMR data matching the published
spectra (Aldrich). 1H NMR (δ, CDCl3): 7.32 (m, 8H), 7.21 (m,
2H), 7.12 (m, 3H), 7.04 (m, 2H), 6.97 (s, 1H). 13C NMR (δ,
CDCl3): 143.3, 142.5, 140.2, 137.3, 130.3, 129.5, 128.11, 127.9,
125.9, 125.1, 122.3, 109.9 (Cp), 24.8, 24.2, 24.0, 14.5, 14.4; 11
B
NMR (δ, CDCl3) 39.9 (1B, d, J ) 122 Hz), 31.8 (1B, d, J ) 100
Hz), 24.1 (1B, d, J ) 111 Hz), -1.3 (1B, d, J ) 151 Hz); UV-
vis (CH2Cl2, nm) 234 (100%), 250 (95%), 312 (24%), 394 (7%);
IR (CH2Cl2, cm-1) 3232 (m), 2968 (m), 2930 (m), 2880 (w), 2559
(B(H), s), 1376 (s), 1073 (w), 1017 (w), 841 (s), 734 (s), 702 (s);
MS m/z 568. Anal. Calcd for TaC26H31B4: C, 55.00; H, 5.59.
Found: C, 54.65; H, 5.27.
(Et2C2B4H4)(Cp )Ta (C6H4(C6H5)CC(C6H5) (11). The above
procedure was performed with 8 (100 mg) and diphenylacety-
lene (168 mg, 0.95 mmol, 5 equiv), the color of the reaction
mixture changing from deep yellow to dark green. Workup
as for 9a /b provided 11 as a dark green oil. 1H NMR (δ,
CDCl3): 7.20 (m, 1H), 7.14 (m, 1H), 7.10 (t, J ) 6.8 Hz, 1H),
7.06 (t, J ) 5.8 Hz, 1H), 7.00 (d, J ) 6.8 Hz, 2H), 6.97 (d, J )
7.8 Hz, 2H), 6.92 (t, J ) 7.8 Hz, 2H), 6.86 (t, J ) 7.8 Hz, 2H),
6.83 (t, J ) 6.8 Hz, 1H), 6.60 (d, J ) 7.8 Hz, 1H), 6.13 (s, 5H),
2.41 (m, 1H), 2.36 (m, 1H), 2.02 (M, 1H), 1.91 (M, 1H), 1.23 (t,
3H), 1.18 (t, 3H). 13C NMR (δ, CDCl3): 145.8, 141.2, 135.7,
135.0, 134.99, 131.4, 131.2, 131.1, 129.9, 128.3, 127.6, 127.0,
126.2, 125.9, 124.8, 123.6, 110.7 (Cp), 24.3, 24.0, 14.6, 14.3.
11B NMR (δ, CDCl3): 42.6 (1B, d, J ) 95 Hz), 32.6 (1B, d, J )
107 Hz), 24.3 (1B, d, J ) 132 Hz), -0.6 Hz (1B, d, J ) 112
Hz). IR (CH2Cl2, cm-1): 3062 (w), 2968 (m), 2924 (m), 2867
(w), 2565 (s, B(H)), 1596 (w), 1439 (m), 1375 (w), 1262 (w),
734 (s), 834 (s), 708 (s). UV-vis (CH2Cl2, nm): 234 (100%),
252 (91%), 324 (38%). MS: m/z 629. Anal. Calcd for
TaC31H33B4: C, 59.11; H, 5.28. Found: C, 59.03; H, 5.44.
(Et2C2B4H4)(Cp)Ta(C6H4(C2H5)CC(C2H5)) (12). The above
procedure was performed with 50 mg of 8 and 10 equiv of
3-hexyne, heating for 24 h. The reaction solution changed to
a dark green color after several hours. The green-brown oily
residue remaining after removal of the solvent was purfied
by column chromatography (silica, 25 cm, CH2Cl2 eluent) to
give 12 as a brown-green oil. 1H NMR (δ, CDCl3): 7.22 (d, J
) 7.8 Hz, 1H), 6.94 (m, J ) 7.8 Hz, 2H), 6.44 (d, J ) 7.8 Hz,
1H), 6.24 (s, 5H), 2.92 (m, 1H), 2.28 (m, 1H), 2.14 (m, 1H),
1.84 (m, 1H), 2.39 (q, J ) 7.8 Hz, 4H), 1.17 (t, 3H), 1.16 (t,
3H), 1.12 (m, 3H), 1.08 (m, 3H). 13C NMR (δ, CDCl3): 143.7,

Alkene and Alkyne Insertion Reactions
Organometallics, Vol. 17, No. 18, 1998 3873
127.5, 127.4, 127.3, 126.6. MS: m/z 256. Analogous treatment
of a THF solution of 11 in air with concentrated HCl (5 equiv)
caused a color change from dark green to orange over several
hours. Basic workup and ether extraction afforded several
organometallic species, the dominant one identified as
(Et2C2B4H4)(Cp)TaCl2 by comparison with an authentic sample.
Chromatography provided triphenylethylene in 63% yield.
P r oton olysis of 9b. Complex 9b (75 mg, 0.135 mmol) in
5 mL of diethyl ether was treated with 5 equiv of concentrated
HCl dropwise with stirring, causing an immediate color change
to yellow-orange. Basic workup (5% NaHCO3), ether extrac-
tion, drying (MgSO4), and evaporation provided a clear oil. The
oil was purified by vacuum transfer at ambient temperature
(10-5 Torr) into a trap at -30 °C, giving 16 mg (64%) of 1,1-
diphenylethylene, identified by comparison to an authentic
sample (Aldrich). 1H NMR (δ, CDCl3): 7.30 (m, 10H), 5.44 (s,
2H). 13C NMR (δ, CDCl3): 150.1, 141.7, 128.0, 127.9, 127.6,
114.3. The remaining nonvolatile residue was flushed through
a silica plug with methylene chloride to give (Et2C2B4H4)-
(C5H5)TaCl2 in a 38% yield.
Rea ction of 11 w ith 2,6-Dim eth ylp h en yl Isocya n id e.
Complex 11 (100 mg, 0.16 mmol) in 2 mL of toluene was
treated with 2,6-dimethylphenylisocyanide (21 mg, 0.16 mmol)
in air. Over the course of 12 h at room temperature, the color
changed from dark green to dark brown. The volatiles were
removed in vacuo and the resulting residue was purified by
preparative TLC (alumina, 3:1 hexane:CH2Cl2). The dominant
fraction was the third one, which provided 2,6-dimethylphen-
limino-2,3-diphenylindenone as an orange crystalline powder
in 72% yield, identified by the following data and by reaction
with aqueous HCl (below). A similar yield and faster reaction
time (3 h) was observed when 10 equiv of isocyanide was used.
1H NMR (δ, CDCl3): 7.36 (m, 1H), 7.28 (m, 1H), 7.22 (m, 1H),
7.20 (t, J ) 7.8 Hz, 1H), 7.09 (d, J ) 6.8 Hz, 2H), 7.02 (d, J )
6.8 Hz, 2H), 7.01 (t, J ) 6.8 Hz, 2H), 6.92 (t, J ) 6.8 Hz, 2H),
6.42 (d, J ) 7.8 Hz, 1H), 2.07 (s, 6H). 13C NMR (δ, CDCl3):
166.3 (CdN), 149.5, 148.2, 144.6, 136.3, 133.5, 132.7, 130.9,
130.8, 129.1, 128.9, 128.4, 128.2, 128.0, 127.8, 127.7, 127.5,
127.2, 124.3, 123.3, 120.6, 18.4. IR (CH2Cl2, cm-1): 3064 (m),
2921 (s), 2652 (m), 2561 (w), 1637 (s), 1591 (s), 1457 (s), 1359
(s), 1208 (s), 1091 (s), 755 (s), 699 (s). MS: m/z 385. Mp: 198-
199 °C. Anal. Calcd for C29H23N: C, 90.35; H, 6.02; N, 3.64.
Found: C, 90.62; H, 6.00; N, 4.42. A solution of the imino-
indenone (50 mg) in 1 mL of methanol was treated with 5 equiv
of concentrated HCl with stirring, causing an immediate color
change from yellow-orange to dark red-orange. The residue
remaining after evaporation of the solvent was extracted with
ether and dried (MgSO4) to yield a dark red solid identified as
2,3-diphenyl-1-indenone (93% yield) by the observation of
identical 1H NMR, mass spectrometry, and melting point data
to reported values (Aldrich).
(91 mg, 0.119 mmol, 66%) as a red-orange solid. X-ray quality
crystals were obtained by slow evaporation of a saturated
toluene solution at room temperature. 1H NMR (δ, CDCl3):
7.23 (m, 5H), 7.13 (m, 3H), 7.03 (m, 3H), 6.72 (m, 4H), 5.72 (s,
5H), 3.95 (m, 2H), 3.56 (m, 2H), 2.93 (m, 2H), 2.86 (m, 1H),
2.60 (m, 2H), 2.33 (m, 1H), 2.08 (m, 2H), 1.64 (m, 4H), 1.30 (t,
3H), 0.95 (t, 3H). MS: m/z 764. Anal. Calcd for C41H47B4Ta:
C, 64.46; H, 6.20. Found: C, 64.12; H, 6.71.
(E t 2C2B4H 4)(Cp )Ta (C(C6D5)DCD2C6H 4) (16-d 8) a n d
(Et2C2B4H3CD2CHDC6D5)(Cp)Ta[C(C6D5)(D)CD2C6H3(CD2-
CHDP h )] (17-d 24). Complex 8 (50 mg, 0.95 mmol) and 8 equiv
of styrene-d8 were sealed in a C6D6 solution in an NMR tube.
After 16 h of heating at 85 °C, NMR analysis revealed almost
total conversion of 8 to 16-d8. 1H NMR (δ, C6D6): 7.02 (t, J )
7.3 Hz, 1H), 6.91 (t, J ) 7.3 Hz, 1H), 6.71 (d, J ) 7.4 Hz, 1H),
6.54 (d, J ) 7.3 Hz, 1H), 5.43 (s, 5H), 2.31 (m, 2H), 2.18 (m,
2H), 1.33 (t, 3H), 1.11 (t, 3H). 1H NMR (δ, CDCl3): 7.08 (t, J
) 7.3 Hz, 1H), 6.96 (t, J ) 7.3 Hz, 1H), 6.82 (d, J ) 7.4 Hz,
1H), 6.66 (d, J ) 7.3 Hz, 1H), 5.86 (s, 5H), 2.42 (m, 2H), 2.30
(m, 2H), 1.34 (t, 3H), 1.16 (t, 3H). 11B NMR (δ, C6D6): 39.4
(1B, s), 31.7 (1B, bs), 25.3 (1B, bs), 3.4 (1B, bs). MS: m/z 563.
Additional heating results in partial conversion in 16 h and
complete conversion in 36 h to 17-d24. After 48 h, the latter
compound was purified by preparative TLC (4:1 hexane:CH2-
Cl2). 1H NMR (δ, CDCl3): 7.26 (d, J ) 7.2 Hz, 1H), 7.04 (t, J
) 7.5 Hz, 1H), 6.70 (d, J ) 7.3 Hz, 1H), 5.72 (s, 5H), 2.86 (m,
1H), 2.60 (m, 2H), 2.33 (m, 1H), 1.64 (bs, 2H, CDH-CH2), 1.30
(t, 3H), 0.95 (t, 3H). 11B NMR (δ, C6D6): 47.6 (1B, s), 24.5
(1B, bs), 2.4 (1B, bs), -3.4 (1B, bs). MS: m/z 788.
(Et2C2B4H3P h )(Cp )Ta P h 2 (18). (Et2C2B4H3Br)(Cp)TaCl2
was prepared by treatment of a CH2Cl2 solution of (Et2C2B4H4)-
(Cp)TaCl2 with 3 equiv of N-bromosuccinimide at room tem-
perature for 1 h.37 Removal of volatiles and filtration of a
hexane suspension of the residue provides the B(5)-brominated
product in quantitative yield. A toluene solution of (Et2C2B4H3-
Br)(Cp)TaCl2 (100 mg, 0.19 mmol) was treated under argon
atmosphere with 15 equiv of 3.0 M PhMgBr, causing an
immediate color change to dark red. Over the course of several
hours at room temperature, the color changed to dark green.
The volatiles were removed by evaporation, and the residue
was stirred in CH2Cl2 for several minutes. The solution was
filtered through a plug of silica gel, and the volatiles were
removed to give a yellow oil. The crude product was freed of
biphenyl by flash chromatography through a 5-cm column of
silica gel, followed by elution of complex 18 with CH2Cl2.
Evaporation of solvent yields 18 as a yellow solid in 95% yield.
A repeat silica filtration to remove biphenyl was occasionally
required for reactions performed on larger scale. 1H NMR (δ,
CDCl3): 7.75 (d, J ) 6.8 Hz, 1H), 7.41 (t, J ) 6.8 Hz, 1H),
7.29 (m, 1H) 7.28 (m, 2H), 7.08 (m, 1H), 5.83 (s, 5H), 2.07 (m,
2H), 2.01 (m, 2H), 1.07 (t, 6H). 13C NMR (δ, CDCl3): 202.2,
195.0 (note that these ipso Ta-Ph resonances are not equiva-
lent), 136.3, 133.7, 127.7, 127.6, 126.5, 125.2, 111.1, 24.1, 14.3.
11B NMR (δ, CDCl3): 41.8 (s, 1B), 25.3 (d, 2B, J ) 105 Hz),
4.8 (d, J ) 83 Hz). MS: m/z 606. Anal. Calcd For C29H33B4-
Ta: C, 57.40; H, 5.49. Found: C, 57.55; H, 5.21.
R ea ct ion of
8 w it h St yr en e. (E t 2C2B4H 4)(Cp )Ta -
(C(C6H5)HCH2C6H4) (16). A mixture of 8 (100 mg, 0.19
mmol) and styrene (197 mg, 1.9 mmol) in 5 mL of benzene
was heated to reflux for 16 h in air. Evaporation of solvent
and chromatography of the resulting residue (silica, 4:1
hexane:CH2Cl2) provides 16 as a dark red solid in 68% yield.
16 is somewhat air-sensitive in the solid form and decomposes
into many products upon standing for 12 h; in solution, the
material is somewhat more stable. 1H NMR (δ, CDCl3): 7.28
(m, 2H), 7.08 (t, J ) 7.8 Hz, 2H), 6.99 (m, 3H), 6.82 (d, J ) 7.8
Hz, 1H), 6.66 (d, J ) 7.8 Hz, 1H), 5.87 (s, 5H), 5.38 (m, 1H),
4.05 (m, 1H), 3.14 (m, 1H), 2.35 (m, 2H), 1.36 (t, 3H), 1.17 (t,
3H). 13C NMR (δ, CDCl3): 150.3, 145.9, 136.8, 130.1, 130.0,
127.9, 127.6, 126.5, 126.2, 123.8, 110.6 (Cp), 67.2, 32.7, 24.4,
23.9, 14.4. MS: m/z ) 555.
Rea ction of 18 w ith Styr en e-d 8. For convenience in NMR
monitoring, this reaction was performed with deuterated
styrene. A solution of complex 18 (28 mg, 0.046 mmol) and 8
equiv of styrene-d8 in 1 mL of degassed C6D6 was added, and
the solution was heated at 85 °C for 36 h under nitrogen in a
sealed NMR tube. The resulting metallacycle 19 was analyzed
directly. 1H NMR (δ, C6D6): 7.84 (d, J ) 7.8 Hz, 2H), 7.40 (t,
J ) 7.8 Hz, 2H), 7.21 (t, J ) 7.8 Hz, 1H), 7.05 (t, J ) 7.8 Hz,
1H), 6.92 (t, J ) 7.8 Hz, 1H), 6.75 (d, J ) 7.8 Hz, 1H), 6.62 (d,
J ) 7.8 Hz, 1H), 5.37 (s, 5H), 2.40 (m, 1H), 2.35 (m, 1H), 2.27
(m, 1H), 2.13 (m, 1H), 1.32 (t, 3H), 1.11 (t, 3H). 1H NMR (δ,
CDCl3): 7.56 (d, J ) 7.8 Hz, 2H), 7.34 (t, J ) 7.8 Hz, 2H),
7.19 (t, J ) 7.8 Hz, 1H), 7.11 (t, J ) 7.8 Hz, 1H), 6.98 (t, J )
7.8 Hz, 1H), 6.86 (d, J ) 7.8 Hz, 1H), 6.76 (d, J ) 7.8 Hz, 1H)
(Et2C2B4H3CH2CH2P h )(Cp )Ta [C(P h )(H)CH 2C6H3(CH2-
CH2P h )] (17). A solution of 16 (100 mg, 0.18 mmol) in 2 mL
of benzene was heated at 85 °C for 62 h, causing a slow color
change to dark red-brown. Purification by preparative TLC
(silica, 8:1 hexane:CH2Cl2) provided 17 as the main product

3874 Organometallics, Vol. 17, No. 18, 1998
Boring et al.
composed of different isomers of 20. For fraction 2: 1H NMR
(δ, CDCl3) 7.58 (m, 1H), 7.20 (m, 1H), 7.14 (d, J ) 7.5 Hz, 1H),
7.09 (m, 3H), 6.84 (t, J ) 7.3 Hz, 1H), 6.48 (d, J ) 8.1 Hz,
1H), 6.12 (s, 5H), 2.67 (m, 1H), 2.55 (m, 2H), 2.45 (m, 1H),
2.20 (s, 6H), 1.21 (t, 3H), 0.94 (t, 3H); 13C NMR (δ, CDCl3)
148.3, 135.8, 135.7, 131.6, 131.5, 126.8, 126.6, 125.5, 121.5,
121.3, 117.9, 117.7, 109.7 (Cp), 26.0, 23.2, 22.8, 18.5, 14.1, 14.0;
11B NMR (δ, CDCl3) 32.0 (d, 1B, 124 Hz), 22.7 (bs, 1B), 15.7
(bs, 1B), -3.2 (d, 1B, 116 Hz); MS m/z 557. For fraction 3:
1H NMR (δ, CDCl3) 7.22 (s, 1H), 7.14 (m, 3H), 7.07 (t, 1H),
6.92 (s, 1H), 6.85 (t, J ) 7.6 Hz, 1H), 6.44 (d, J ) 8.1 Hz, 1H),
6.10 (s, 5H), 2.60 (m, 2H), 2.44 (m, 2H), 2.26 (s, 3H), 2.14 (s,
3H), 1.19 (t, 3H), 1.02 (t, 3H); 13C NMR (δ, CDCl3) 140.1, 137.0,
131.4, 128.1, 126.9, 125.3, 121.5, 117.1, 110.5 (Cp), 22.93,
22.86, 21.6, 18.1, 14.4, 14.1; 11B NMR (δ, CDCl3) 34.2 (d, 1B,
136 Hz), 22.7 (bs, 1B), 13.1 (bs, 1B), -3.5 (d, 1B, 116 Hz); MS
m/z 557.
X-r a y Cr ysta llogr a p h y. X-ray measurements were car-
ried out on a Rigaku AFC6S diffractometer using Mo KR
radiation (λ ) 0.710 69 Å) at -100 °C for complex 10b and 23
°C for 17. Calculations were performed on a VAXstation 3520
computer using the TEXSAN 5.0 software39 and in the later
stages on a Silicon Graphics Indigo 2 Extreme computer with
the teXsan 1.7 package. Relevant crystallographic data are
listed in Table 3. Unit cell dimensions were determined by
applying the setting angles of 25 high-angle reflections. Three
standard reflections were monitored during the data collection,
showing no significant variance. The intensities were cor-
rected for absorption by applying Ψ scans of several reflections
with transmission factors in the range 0.10-1.00 for 10b and
0.80-1.00 for 17. Both structures were solved by direct
methods in SIR88.40 Full-matrix least-squares refinement was
carried out with anisotropic thermal displacement parameters
for all non-hydrogen atoms. The hydrogen atoms were found
in difference Fourier maps and were subsequently included
in the calculations without further refinement. The final
difference map for 10b showed a peak of 1.5 e/Å3 close to the
Ta atom; the final difference map for 17 was essentially
featureless with the highest peak of 0.52 e/Å3. The results of
the refinements are presented in Table 3.
Ta ble 3. Cr ysta llogr a p h ic Da ta for Com p lexes
10b a n d 17
10b
17
empirical formula
fw
C
26H31B4Ta
C41H46B4Ta
763.00
567.72
cryst color and habit
cryst dimens
red plate
0.34 × 0.18 ×
0.42 mm
monoclinic
9.940(4)
13.226(5)
17.865(6)
93.62(3)
red needle
0.24 × 0.28 ×
0.44 mm
orthorhombic
11.862(3)
20.961(5)
15.003(3)
105.50(3)
3594(1)
cryst syst
a, Å
b, Å
c, Å
â, deg
V, Å3
2344(1)
space group
Z
D
P21/n (No. 14)
4
1.61
P21/n (No. 14)
16
1.41
calc, g cm-3
radiation
Mo KR (λ )
0.710 69 Å)
46.94
-100 °C
46°
total: 3211
unique: 2967
(Rint ) 0.033)
total: 3647
unique: 3422
(Rint ) 0.032)
2348
Mo KR (λ )
0.710 69 Å)
30.81
23 °C
46°
µ (Mo KR), cm-1
temp
2θmax
no. of reflns
measd
total: 1934
no. of reflns
measd
total: 5167
unique: 4382
(Rint ) 0.042)
3147
no. of reflns
I > 3σ(I)
no. of variables
residuals R; Rw
goodness of fit
max peak in final
diff map
279
410
0.045; 0.068
1.22
0.031; 0.038
1.30
1.50 e/Å3
0.52 e/Å3
5.83 (s, 5H), 2.41 (m, 3H), 2.31 (m, 1H), 1.38 (t, 3H), 1.20 (t,
3H). MS: m/z 639.
E t 2C2B4H 4)(Cp )Ta (o-C6H 4Me)2 (20).
A solution of
(Et2C2B4H4)(Cp)TaCl2 (75 mg, 0.168 mmol) in 3 mL of degassed
toluene was treated with o-tolylmagnesium bromide (1.68 mL
of 2 M solution in ether, 20 equiv) and allowed to stir at room
temperature for 12 h. After evaporation of the solvent, the
residue was dissolved in CH2Cl2 and filtered through a 3-cm
silica plug. The mixture containing several products was
purified by preparative TLC (4:1 hexane:CH2Cl2) to give three
fractions. The first was identified as (Et2C2B4H4)(Cp)Ta(o-
C6H4Me)Cl. 1H NMR (δ, CDCl3): 7.15 (m, 2H), 7.01 (m, 2H),
6.22 (s, 5H), 3.06 (m, 1H), 2.76 (m, 2H), 2.51 (m, 1H), 2.17 (s,
3H), 1.18 (t, 3H), 1.02 (t, 3H). 13C NMR (δ, CDCl3): 148.3,
131.8, 131.7, 126.1, 125.9, 125.6, 111.0 (Cp), 25.8, 23.0, 22.9,
14.0, 13.8. The second and third fractions were found to be
Ack n ow led gm en t. Funding from the National Sci-
ence Foundation (Grant No. CHE 9322490 to R.N.G.
and Grant No. CHE 9313746 to M.G.F.) for partial
support of this work is gratefully acknowledged.
Su p p or tin g In for m a tion Ava ila ble: Tables of atomic
coordinates, anisotropic displacement parameters, complete
bond distances and angles, and least-squares planes for all
crystal structures (14 pages). Ordering information is given
on any current masthead page.
(39) TEXSAN 5.0, Single-Crystal Structure Analysis Software; Mo-
lecular Structure Corp.: The Woodlands, TX, 1989.
(40) Burla, M. C.; Camalli, M.; Gascarano, G.; Giacovazzo, C.;
Polidori, G.; Spagna, R.; Viterbo, D. J . Appl. Crystallogr. 1989, 22, 389.
OM980242W