Effect of ligand variation on the site of protonation in the metal carbynes CpL2Mo≡CBu and TpL2Mo≡CBu [L = CO, P(OR)3]

Article abstract of DOI:10.1021/om990047x

The site of thermodynamic protonation of the Fischer carbynes CpL₂Mo≡CBu and TpL₂-Mo≡CBu [L = CO, P(OR)₃] with HBF₄ depends on the number of π-acid CO ligands. As the number of carbonyls increases from zero to t

Full text of DOI:10.1021/om990047x

2262
Organometallics 1999, 18, 2262-2266
Effect of Liga n d Va r ia tion on th e Site of P r oton a tion in
th e Meta l Ca r byn es Cp L2MotCBu a n d Tp L2MotCBu
[L ) CO, P (OR)3]
Karen E. Torraca, Ion Ghiviriga, and Lisa McElwee-White*
Department of Chemistry, University of Florida, Gainesville, Florida 32611-7200
Received J anuary 26, 1999
The site of thermodynamic protonation of the Fischer carbynes CpL2MotCBu and TpL2-
MotCBu [L ) CO, P(OR)3] with HBF4 depends on the number of π-acid CO ligands. As the
number of carbonyls increases from zero to two and the electron density at the metal center
is decreased by back-bonding, the protonation site shifts from the metal to the carbyne carbon.
Parallel behavior in the Tp and Cp series of complexes allows the change in protonation
site to be attributed to electronic effects in the ancillary ligands.
In tr od u ction
protonation can induce further reaction to produce η2-
acyl complexes8 and compounds in which the original
alkylidyne ligand has been lost via protonolysis.6c,d
In alkylidyne complexes that bear no π-acid ligands,
thermodynamic protonation occurs either on the alkyl-
idyne face or at the metal. Steric considerations have
been invoked to explain the preference.1,6a,b,9 However,
in the presence of π-acid ligands, electronic effects
appear to be the overriding factor in determining the
ultimate site of protonation. It has been suggested that
alkylidene (face-protonated) complexes that bear π-acid
ligands do not rearrange into the corresponding alkyl-
idyne hydride species because the resulting oxidation
of the metal center would interfere with back-bonding.1
A noted absence in the discussion is a closely related
series of compounds where all three protonation out-
comes (alkylidene, face-protonated alkylidyne, and alkyl-
idyne hydride) are available.
We now report that protonation of the Fischer car-
bynes CpL2MotCBu and TpL2MotCBu [L ) CO,
P(OR)3] with HBF4 results in a systematic shift of the
thermodynamic protonation product from the alkylidyne
hydride to the face-protonated alkylidyne to the nona-
gostic alkylidene as the number of carbonyl groups
increases from zero to two. These results are consistent
with determination of the final protonation site by the
electron density at the metal. As π-back-bonding to the
carbonyl ligands decreases the electron density at the
metal, the protonation site shifts from the metal toward
the carbyne carbon, consistent with earlier calculations
Protonation of carbyne (alkylidyne) complexes has
been a topic of long-standing interest due to the variety
of observed products and the difficulty of predicting
which will be obtained.1,2 In addition, complications
arise in discerning kinetic vs thermodynamic protona-
tion sites.3 On the basis of computational studies that
assigned a net negative charge to the carbyne carbon,
kinetic protonation has been assumed to involve charge-
controlled addition of the proton at that site.4 However,
the final thermodynamic outcome is variable. The
protonation product is dependent on the metal, the
ancillary ligands, and the counterion of the acid. Prod-
ucts obtained from simple protonation of alkylidyne
complexes include metal carbenes (alkylidenes) from
protonation at the carbyne carbon,5 metal hydrides from
addition to the metal center,6 and “face-protonated”
alkylidynes in which the product is an alkylidene whose
C-H bond is engaged in agostic interaction with the
metal.1,7 In the presence of coordinating anions, carbyne
(1) Bastos, C. M.; Lee, K. S.; Kjelsberg, M. A.; Mayr, A.; Van Engen,
D.; Koch, S. A.; Franolic, J . D.; Klooster, W. T.; Koetzle, T. F. Inorg.
Chim. Acta 1998, 279, 7-23.
(2) Brew, S. A.; Stone, F. G. A. Adv. Organomet. Chem. 1993, 35,
135-186.
(3) Henderson, R. A. Angew. Chem., Int. Ed. Engl. 1996, 35, 946-
967.
(4) (a) Kostic, N. M.; Fenske, R. F. J . Am. Chem. Soc. 1981, 103,
4677-4685. (b) Kostic, N. M.; Fenske, R. F. Organometallics 1982, 1,
489-496. (c) Ushio, J .; Nakatsuji, H.; Yonezawa, T. J . Am. Chem. Soc.
1984, 106, 5892-5901. (d) Poblet, J . M.; Strich, A.; Wiest, R.; Be´nard,
M. Chem. Phys. Lett. 1986, 126, 169-175.
(5) (a) Howard, J . A. K.; J effery, J . C.; Laurie, J . C. V.; Moore, I.;
Stone, F. G. A.; Stringer, A. Inorg. Chim. Acta 1985, 100, 23-32. (b)
J effery, J . C.; Stone, F. G. A.; Williams, G. K. Polyhedron 1991, 10,
215-219. (c) J effery, J . C.; Li, S.; Stone, F. G. A. J . Chem. Soc., Dalton
Trans. 1992, 635-640. (d) Howard, J . A. K.; J effery, J . C.; Li, S.; Stone,
F. G. A. J . Chem. Soc., Dalton Trans. 1992, 627-634. (e) Bruce, G. C.;
Stone, F. G. A. Polyhedron 1992, 11, 1607-1613. (f) Kim, H. P.; Kim,
S.; J acobson, R. A.; Angelici, R. A. Organometallics 1984, 3, 1124-
1126. (g) Doyle, R. A.; Angelici, R. A. Organometallics 1989, 8, 2207-
2214.
(6) (a) Holmes, S. J .; Schrock, R. R. J . Am. Chem. Soc. 1981, 103,
4599-4600. (b) Holmes, S. J .; Clark, D. N.; Turner, H. W.; Schrock, R.
R. J . Am. Chem. Soc. 1982, 104, 6322-6329. (c) Green, M.; Orpen, A.
G.; Williams, I. D. J . Chem. Soc., Chem. Commun. 1982, 493-495. (d)
Bottrill, M.; Green, M.; Orpen, A. G.; Saunders: D. R.; Williams, I. D.
J . Chem. Soc., Dalton Trans. 1989, 511-518. (e) Kingsbury, K. B.;
Carter, J . D.; McElwee-White, L.; Ostrander, R. L.; Rheingold, A. L.
Organometallics 1994, 13, 1635-1640.
(7) (a) Holmes, S. J .; Schrock, R. R.; Churchill, M. R.; Wasserman,
H. J . Organometallics 1984, 3, 476-484. (b) Etienne, M.; White, P. S.;
Templeton, J . L. J . Am. Chem. Soc. 1991, 113, 2324-2325. (c) J effery,
J . C.; Weller, A. S. J . Organomet. Chem. 1997, 548, 195-203.
(8) (a) Kreissl, F. R.; Sieber, W. J .; Wolfgruber, M.; Riede, J . Angew.
Chem., Int. Ed. Engl. 1984, 23, 640. (b) Kreissl, F. R.; Sieber, W. J .;
Keller, H.; Riede, J .; Wolfgruber, M. J . Organomet. Chem. 1987, 320,
83-90. (c) Kreissl, F. R.; Keller, H.; Schu¨tt, W. J . Organomet. Chem.
1992, 441, 75-80. (d) Kingsbury, K. B.; Carter, J . D.; Wilde, A.; Park,
H.; Takusagawa, F.; McElwee-White, L., J . Am. Chem. Soc. 1993, 115,
10056-10065. (e) Schoch, T. K.; Orth, S. D.; Zerner, M. C.; J ørgensen,
K. A.; McElwee-White, L. J . Am. Chem. Soc. 1995, 117, 6475-6482.
(9) (a) Wengrovius, J . H.; Schrock, R. R.; Churchill, M. R.; Wasser-
man, H. J . J . Am. Chem. Soc. 1982, 104, 1739-1740. (b) Churchill, M.
R.; Wasserman, H. J .; Turner, H. W.; Schrock, R. R. J . Am. Chem.
Soc. 1982, 104, 1710-1716.
10.1021/om990047x CCC: $18.00 © 1999 American Chemical Society
Publication on Web 05/06/1999

Site of Protonation in Metal Carbynes
Organometallics, Vol. 18, No. 11, 1999 2263
which assign negative charge to the alkylidyne carbon
in cationic complexes.4
Resu lts a n d Discu ssion
We previously reported that oxidation of the butyl
carbyne Cp{P(OPh)3}(CO)MotCBu (1) with acetyl fer-
rocenium results in the formation of 1-pentene.10 In the
proposed mechanism, electron transfer generates a 17-
electron complex that undergoes H atom abstraction to
yield the electrophilic carbene [Cp{P(OPh)3}(CO)Mod
CHBu]+ (2). Carbene 2 then undergoes a facile 1,2-
hydride shift followed by decomplexation to yield the
free alkene.8e Although carbene 2 has never been
directly observed in these studies, its presence is implied
by the formation of 1-pentene. Subsequent observation
that the formation of 1-pentene is suppressed upon
oxidation of 1 in the presence of alkynes10 raised the
question of whether the alkyne had reacted with car-
bene 2 or with the 17-electron cationic carbyne prior to
hydrogen abstraction. In conjunction with mechanistic
studies on oxidation of 1 in the presence of alkynes, we
began to explore ways to generate carbene 2 indepen-
dently.
Generation of the agostic alkylidene species 3 upon
protonation of 1 was intriguing. Complex 3 was clearly
not the species generated in the previously reported
oxidative chemistry of 1 because it did not produce
1-pentene upon decomposition. Face-protonation was
also a different outcome from what we had obtained by
protonation of the related complex Cp{P(OMe)3}2Mot
C(c-C3H5) (4) with HBF4.6e The protonation of 4 occurred
at the metal center to yield the hydrido carbyne species
[Cp{P(OMe)3}2(H)MotC(c-C3H5)]+[BF4]- (5). The 1H
NMR spectrum of complex 5 had also exhibited an
upfield resonance at -2.42 ppm, but the much larger
J PH ) 64.7 Hz clearly identified the complex as a metal
hydride. In addition, the carbyne carbon of 5 was shifted
downfield to 344 ppm, as compared to 299.5 ppm for
the neutral carbyne 4 and 276.8 ppm for the face-
protonated alkylidyne 3.
In a formal sense, carbene 2 results from addition of
H+ to carbyne 1. Although the protonation chemistry
of metal carbynes is complex, it seemed possible that
employing an acid with a noncoordinating anion could
provide an independent generation of 2. However,
protonation of butyl carbyne 1 with HBF4 at low
Cyclopropyl carbyne 4 and butyl carbyne 1 differ both
in the alkyl substituent and the ancillary ligand set (two
phosphites for 4 vs one phosphite and one carbonyl for
1). To differentiate the effects on the site of protonation,
the bis(phosphite) butyl carbyne complex Cp{P(OMe)3}2-
MotCBu (6) was synthesized. Reaction of 6 with HBF4
at -78 °C (eq 2) results in protonation at the metal
center to yield the hydrido carbyne species
1
temperature resulted in an unstable species whose H
NMR spectra were not consistent with the expected
carbene. While the protons on electrophilic carbenes are
known to exhibit 1H NMR signals between 10 and 18
ppm,11 the newly generated species showed a new
resonance at -2.96, with J PH ) 10 Hz.
1
Although the H NMR spectrum appeared to rule out
a carbene product, the 13C NMR spectrum of the product
contained two deshielded carbons at 276.8 and 226.8
ppm, consistent with carbene and carbonyl carbons.
Elucidation of the structure was carried out by 2D NMR.
Of the two deshielded carbons at 226.8 and 276.8 ppm,
the latter is CR of the original alkylidyne ligand, as
indicated by its long-range coupling to the protons on
Câ and Cγ (1.44, 1.52, 2.07, and 2.33 ppm) observed in
the HMBC12 spectrum. The carbon at 276.8 ppm is
coupled to the proton at -2.96 ppm, as indicated by the
HMQC13 spectrum. The value of the coupling constant
was then measured more accurately in a 1D HMQC
spectrum optimized for the J value observed in the 2D
[Cp{P(OMe)3}2(H)MotCBu]+[BF4]- (7), as character-
1
ized by the H NMR resonance at -2.6 ppm with J PH
)
64 Hz. Carbyne 7 exhibits a downfield shift of the
1
HMQC. The value J CH ) 73.4 ( 0.7 Hz indicates that
the proton is centered neither on the metal nor on the
carbon. Instead, the complex is face-protonated carbyne
3, in which the hydrogen participates in an agostic
interaction with the metal center (eq 1). Similar J CH
values in the range of 45-84 Hz have been reported for
other face-protonated alkylidynes.7,9
carbyne carbon to 347 ppm in the 13C NMR, similar to
what is observed for the related hydrido carbyne com-
plex 4. As further evidence that the proton resides at
the metal center, J CH between the carbyne carbon and
the added proton was determined to be less than 6 Hz.
As discussed above, kinetic protonation of alkylidyne
complexes has been postulated to be charge-controlled,
which should result in protonation at the carbyne
carbon. Consistent with this interpretation, a different
species was observed upon reaction of carbyne 6 with
HBF4 at low temperature. 1H NMR spectra recorded at
-50 °C exhibited a resonance at -5 ppm, with the small
(10) Torraca, K. E.; Abboud, K. A.; McElwee-White, L. Organome-
tallics 1998, 17, 4413-4416.
(11) (a) Main, A. D.; McElwee-White, L. J . Am. Chem. Soc. 1997,
119, 4551-4552. (b) Casey, C. P.; Miles, W. H.; Tukada, H. J . J . Am.
Chem. Soc. 1985, 107, 2924-2931.
(12) Bax, A.; Summers, M. F. J . Am. Chem. Soc. 1986, 108, 2093-
2094.
(13) Bax, A.; Griffey, R. H.; Hawkins, B. I. J . Magn. Reson. 1985,
55, 301-315

2264 Organometallics, Vol. 18, No. 11, 1999
Torraca et al.
J PH indicative of a face-protonated carbyne. Upon
warming, this species converted irreversibly to hydrido
carbyne 7.
The difference in protonation behavior between butyl
carbynes 1 and 6 can be attributed to the change in
ancillary ligands. The carbyne with two phosphite
ligands (6) was protonated at the metal. In the related
complex with one carbonyl and one phosphite (1), the
site of thermodynamic protonation was shifted toward
the carbyne carbon to yield the face-protonated alkyl-
idyne. This change is consistent with withdrawal of
electron density from the metal by the π-acid carbonyl,
rendering the metal less basic with respect to the
carbyne carbon. If this were the case, a second carbonyl
ligand might be expected to decrease the electron
density at the metal to the point where the protonation
site would shift completely to the carbon. As a test of
this hypothesis, we prepared the dicarbonyl carbyne Cp-
(CO)2MotCBu (8) by reaction of the bis(pyridine)
complex Cl(C5H5N)2(CO)2MotCBu with NaCp.
the same protonation trend held for the Tp carbynes as
for the Cp derivatives. As predicted, protonation of the
Tp carbyne 12 results in face-protonation to yield
complex 13 (eq 5) just as protonation of its Cp analogue
1 yields 3 (eq 1). Assignment of 13 as the face-
Reaction of carbyne 8 with HBF4 at low temperature
resulted in the dinuclear species [Mo2(µ-H){µ-C2(Bu)2}-
(CO)4Cp2][BF4] (9) (eq 3). Complex 9 is structurally
1
protonated species was possible via its H and 13C NMR
spectra, which exhibited a proton resonance at 0.45 ppm
equivalent to a product previously prepared by proto-
5a
that is coupled to the carbon at 253 ppm with J CH
)
nation of Cp(CO)2WtCTol with HBF4 and could be
1
91.0 ( 0.4 Hz. Hence, despite the electronic difference
between Tp and Cp ligands, the protonation site once
again shifted from the carbon to the alkylidyne face
upon replacement of a strong π-acid carbonyl with a
phosphite.
identified by the characteristic H NMR resonance at
-15.7 ppm for the bridging hydride. In the original
report on the tungsten analogue of 9, Stone proposed
that protonation of the carbyne carbon produced the
corresponding cationic carbene. Reaction of the carbene
with starting material then yielded the binuclear alkyne
complex. However, the carbene intermediate was not
directly observed. To verify that the dicarbonyl com-
plexes did indeed undergo protonation at the carbon,
we prepared the analogous but more sterically encum-
bered complex Tp(CO)2MotCBu (10) in which dimer-
ization would be inhibited.
Su m m a r y. We have demonstrated that the site of
protonation in metal carbynes can be shifted from the
carbon to the metal by manipulation of the ancillary
ligand set. In the absence of π-acid ligands, the metal
is sufficiently basic for the thermodynamic protonation
product to be the alkylidyne hydride complex. Replacing
one phosphite with a π-acid carbonyl results in a loss
of electron density at the metal and a shift to face-
protonation of the carbyne. Carbynes bearing two car-
bonyl ligands selectively react with HBF4 at the carbyne
carbon to produce cationic carbenes. These carbenes
undergo secondary reactions unless the remaining
ligands are sufficiently sterically encumbered to prevent
dimerization.
Protonation of 10 with HBF4 at -78 °C resulted in a
species that was difficult to characterize spectroscopi-
cally due to poor solubility at low temperatures. How-
ever, the structure could be assigned as carbene 11 (eq
1
4) on the basis of certain resonances in its H and 13C
spectra. A proton signal at 12.6 ppm and a carbon
resonance at 260 ppm are in agreement with similar
Tp carbene complexes, one of which was characterized
by X-ray crystallography.5b
Exp er im en ta l Section
Although protonation of the Tp carbyne 10 at the
carbon was as expected on the basis of its two carbonyl
ligands, concerns about the electronic differences be-
tween the Tp and Cp ligands led us to prepare Tp-
{P(OMe)3}(CO)MotCBu (12) in order to confirm that
Gen er a l P r oced u r es. Standard inert atmosphere tech-
niques were used throughout. Hexane, petroleum ether,
chloroform, and methylene chloride were distilled from CaH2.
Diethyl ether and THF were distilled from Na/Ph2CO. All
NMR solvents were degassed by three freeze-pump-thaw

Site of Protonation in Metal Carbynes
Organometallics, Vol. 18, No. 11, 1999 2265
cycles. Benzene-d6 was vacuum transferred from Na/Ph2CO.
CDCl3 and CD2Cl2 were stored over 3 Å molecular sieves.
Triphenyl phosphite was purified by rinsing an ethereal
solution with 10% KOH and then brine. After drying over Na2-
SO4 and removal of solvent, pure triphenyl phosphite was
obtained by vacuum distillation. All other starting materials
were purchased in reagent grade and used without further
purification. Cl{P(OMe)3}3(CO)MotCBu (14)8e and [Cp(CO)-
{P(OPh)3}HMotCBu](BF4) (3)10 were synthesized as reported
previously.
1H, 31P, and 13C NMR spectra were recorded on Gemini-300,
VXR-300, and UNITY 500 NMR spectrometers. IR spectra
were recorded on a Perkin-Elmer 1600 spectrometer. High-
resolution mass spectrometry was performed by the University
of Florida analytical service.
Cp {P (OMe)3}2MotCBu (6). Cl{P(OMe)3}4(CO)MotCBu
(2.135 g, 3.065 mmol) was dissolved in 25 mL of THF. After
addition of solid NaCp (0.404 g, 4.60 mmol), the mixture was
heated to 55 °C for 15 h. The solvent was removed in vacuo,
and the resulting residue was filtered through alumina eluting
with Et2O at -78 °C. After removal of the solvent, the golden-
brown oil was chromatographed on alumina at -78 °C with
hexane as the eluent. Increasing amounts of Et2O were added
to obtain a bright yellow fraction. Removal of the solvent in
vacuo yielded 6 as a bright yellow oil (619 mg, 42.2% yield):
1H NMR (C6D6) δ 5.29 (s, 5H), 3.52 (virtual t, 18 H), 2.30 (m,
2H), 1.60 (pentet, 2H), 1.41 (sextet, 2H), 0.89 (t, 3H) ppm; 13C-
{1H} NMR (C6D6) δ 310.4 (t, J PC ) 29 Hz, MotC), 89.0 (Cp),
50.8 (P(OMe)3), 49.1, 31.6, 22.6, 14.1 ppm; 31P{1H} NMR
(CDCl3) δ 214.3 ppm; HRMS (FAB) m/z calcd for M+ (C16H32
-
98MoP2O6) 480.0733, found 480.0725.
Cl{P (OP h )3}2(CO)2MotCBu (15). Mo(CO)6 (2.408 g, 9.122
mmol) was dissolved in 30 mL of Et2O and cooled to 0 °C. A
solution of n-butyllithium (2.0 M in hexane, 4.56 mL, 9.12
mmol) was added dropwise. After 1 h, the solution volume was
reduced to 5 mL in vacuo. The solution was filtered through
Celite and the solvent removed in vacuo to leave a golden-tan
powdery solid. This solid was dissolved in 30 mL of CH2Cl2.
After cooling to -95 °C, oxalyl chloride (0.637 mL, 7.30 mmol)
was added dropwise, ensuring the temperature remained
below -90 °C. After the addition was complete, the bath was
removed and the solution warmed to -30 °C. During this time
effervescence was observed. After cooling the solution below
-50 °C, excess P(OPh)3 (9.56 mL, 36.5 mmol) was added. The
solution was allowed to stir at room temperature for 2 h. The
solvent was removed in vacuo to leave a golden-brown oil, and
excess P(OPh)3 was extracted with pentane (4 × 10 mL). The
resulting residue was dissolved in Et2O and filtered through
Celite. The remaining solvent was removed in vacuo to leave
a golden-brown oil (6.010 g, 75.1% yield) which was a mixture
of 15, the tris(triphenyl phosphite) carbyne Cl{P(OPh)3}3(CO)-
MotCBu (16), and free P(OPh)3 (50% by 31P NMR). The crude
solid was used in the preparation of 1 without further
purification. For 15: 31P{1H} NMR (CDCl3) δ 148.4. For 16:
[Cp {P (OMe)3}2HMotCBu ][BF 4] (7). Butyl carbyne 6 (245
mg, 0.512 mmol) was dissolved in 8 mL of CH2Cl2 at -78 °C
and mixed with a 54% solution of HBF4 in ether (70.6 µL, 0.512
mmol). After 25 min, 30 mL of pentane at -78 °C was added
and a red-orange oil formed. The solution was removed by filter
cannulation to yield a solid, which was rinsed with pentane
at -78 °C. Some of the remaining solvent was removed in
vacuo at -78 °C. Keeping the temperature below -78 °C, 1
mL of CD2Cl2 was added. The resulting solution was cannu-
lated into an NMR tube for spectral characterization at -50
°C. For 7: 1H NMR (CD2Cl2) δ 5.67 (s, 5H), 3.67 (d, J PH ) 12
Hz, 18 H), 2.47 (m, 2H), 1.47 (pentet, 2H), 1.27 (sextet, 2H),
0.82 (t, 3H), -2.60 (t, J PH ) 64 Hz, 1H) ppm; 13C{1H} NMR
(CD2Cl2) δ 347.0 (t, J PC ) 33 Hz, MotC), 96.2 (Cp), 53.5
(P(OMe)3), 51.4, 29.5, 22.2, 13.5 ppm.
Cl(C5H5N)2(CO)2MotCBu (17). Mo(CO)6 (2.248 g, 8.515
mmol) was dissolved in 30 mL of Et2O and cooled to 0 °C. A
solution of n-butyllithium (2.3 M in hexane, 3.70 mL, 8.51
mmol) was added dropwise. After 1.5 h, the solution volume
was reduced to 5 mL in vacuo. The solution was filtered
through Celite and the solvent removed in vacuo to leave a
golden-tan powdery solid. This solid was dissolved in 30 mL
of CH2Cl2. After cooling to -95 °C, oxalyl chloride (0.669 mL,
7.66 mmol) was added dropwise, ensuring the temperature
remained below -90 °C. After the addition was complete, the
bath was removed and the solution was allowed to warm to
-30 °C. During this time effervescence was observed. After
cooling the solution to -78 °C, excess pyridine (2.15 mL, 25.5
mmol) was added. After 5 min the bath was removed and the
solution was allowed to stir 25 min before the solvent was
removed in vacuo. The residue was dissolved in 5 mL of CH2-
Cl2 and filtered through Celite. The solvent was removed in
vacuo to leave a sticky brown solid which was dissolved in 5
mL of CH2Cl2. After addition of 5 mL of Et2O and 10 mL of
hexanes, the solution was concentrated until a golden precipi-
tate formed. The solid was isolated by filtration and rinsed
with hexanes (2 × 15 mL). Evaporation of the remaining
solvent in vacuo yielded 17 as a golden brown powder (3.200
g, 90.6% yield). This crude solid was used in the preparation
of 8 and 10 without further purification. For 17: 1H NMR
(C6D6) δ 9.05 (d, J HH ) 4.8 Hz, 4H), 6.68 (t, J HH ) 6.6 Hz, 2H),
6.35 (t, J HH ) 6.6 Hz, 4H), 2.39 (t, 2H), 1.54 (pentet, 2H), 1.27
(sextet, 2H), 0.78 (t, 3H) ppm; IR (CH2Cl2) 1998 (s), 1912 (s)
cm-1 (νCO).
31P{1H} NMR (CDCl3) δ 146.6 (d, J PP ) 56 Hz), 140.2 (t, J PP
)
56 Hz) ppm. For the mixture: IR (CH2Cl2) 1997 (s), 1924 (w)
cm-1 (νCO).
Cp {P (OP h )3}(CO)MotCBu (1). The golden-brown oil from
above was dissolved in 40 mL of THF, and solid CpNa (1.206
g, 13.70 mmol) was added. The mixture was stirred at ambient
temperature for 3 h. The solvent was removed in vacuo to leave
a dark brown oil, which was chromatographed on alumina
using Et2O as eluent at -78 °C. A bright orange-yellow fraction
was collected, and the solvent was removed in vacuo to leave
a bright orange oil. After three successive columns eluting with
hexane/Et2O (4:1) at -78 °C, 1 was obtained as a bright yellow
powder (0.964 g, 18.6% yield overall from Mo(CO)6): 1H NMR
(C6D6) δ 7.36 (d, J CH ) 7.8 Hz, 6H), 7.06 (t, J CH ) 7.8 Hz, 6H),
6.87 (t, J CH ) 7.2 Hz, 3H), 4.81 (s, 5H, Cp), 2.12 (m, 2H), 1.52
(pentet, 2H), 1.32 (sextet, 2H), 0.81 (t, 3H) ppm; 13C{1H} NMR
(CD2Cl2) δ 323.8 (d, J PC ) 31 Hz, MotC), 238.9 (d, J PC ) 19
Hz, CO), 152.7 (d, J PC ) 4 Hz), 130.0, 125.1, 122.9 (d, J PC ) 4
Hz), 91.3 (Cp), 50.0, 30.4, 22.43, 13.8 ppm; 31P{1H} NMR
(CDCl3) δ 192.3 ppm; IR (CH2Cl2) 1917 cm-1 (νCO); HRMS
(FAB) m/z calcd for M+ (C29H2998MoPO4) 570.0865, found
570.0863.
Cp (CO)2MotCBu (8). Cl(C5H5N)2(CO)2MotCBu (17) (417
mg, 1.00 mmol) was dissolved in 20 mL of THF. After addition
of solid NaCp (133 mg, 1.51 mmol) the mixture was stirred
for 1.5 h at ambient temperature. The solvent was removed
in vacuo, and the resulting residue was filtered through
alumina eluting with Et2O at -78 °C. After removal of solvent,
the golden oil was chromatographed on alumina at -78 °C
with hexane as the eluent. A bright yellow fraction was
collected. Removal of solvent in vacuo yielded 8 as a bright
yellow oil (170 mg, 59.0% yield): 1H NMR (C6D6) δ 5.05 (s,
5H), 2.19 (t, 2H), 1.42 (pentet, 2H), 1.25 (sextet, 2H), 0.75 (t,
Cl{P (OMe)3}4MotCBu (18). Cl{P(OMe)3}3(CO)MotCBu
(2.897 g, 4.824 mmol) was dissolved in trimethyl phosphite
(5.69 mL, 48.2 mmol). The mixture was refluxed 12 h and some
of the excess phosphite removed in vacuo. Impurities were
extracted into a minimal amount of hexanes (3 × 5 mL), and
the remaining solvent was removed to yield 18 as a gray-tan
oil (2.135 g, 63.5% yield), which was used in the preparation
of 6 without further purification: 1H NMR (C6D6) δ 3.79
(virtual t, 36H), 2.28 (m, 2H), 1.65 (pentet, 2H), 1.22 (sextet,
2H), 0.87 (t, 3H) ppm.

2266 Organometallics, Vol. 18, No. 11, 1999
Torraca et al.
(d, J PC ) 3 Hz), 50.9 (d, J PC ) 4 Hz, P(OMe)3), 49.5 (d, J PC
3H) ppm; 13C{1H} NMR (C6D6) δ 332.7 (MotC), 229.9 (CO),
92.1 (Cp), 50.5, 29.7, 21.9, 13.3 ppm; IR (CH2Cl2) 1992 (s), 1913
(s) cm-1 (νCO); HRMS (FAB) m/z calcd for M+ (C12H1498MoO2)
288.0051, found 288.0074.
)
3 Hz), 30.2 (d, J PC ) 4 Hz), 22.9, 14.0 ppm; 31P{1H} NMR (C6D6)
δ 185.9 ppm; IR (CH2Cl2) 1889 cm-1 (νCO); HRMS (FAB) m/z
calcd for M+ (C18H28B98MoN6O4P) 532.1065, found 532.1061.
[Tp (CO){P (OMe)3}HMotCBu ][BF 4] (13). Butyl carbyne
12 (218 mg, 0.411 mmol) was dissolved in 8 mL of CH2Cl2 at
-78 °C and mixed with a 54% solution of HBF4 in ether (56.7
µL, 0.411 mmol). After 30 min, 40 mL of pentane at -78 °C
was added and a red-orange oil formed. The solution was
removed by filter cannulation to yield a red-orange oil, which
was rinsed with pentane at -78 °C. Some of the remaining
solvent was removed in vacuo at -78 °C. Keeping the tem-
perature below -78 °C, 1 mL of CD2Cl2 was added. The
resulting solution was cannulated into an NMR tube for
spectral characterization at -50 °C. For 13: 1H NMR (CD2-
Cl2) δ 8.01 (m, 1H), 7.88 (m, 1H), 7.83 (m, 3H), 7.63 (m, 1H),
6.40 (m, 3H), 3.31 (d, J PH ) 11 Hz, 9H), 2.96 (m, 2H), 1.71
(pentet, 2H), 1.43 (sextet, 2H), 0.93 (t, 3H), 0.45 (m, 1H) ppm;
13C{1H} NMR (CD2Cl2) δ 253.6 (d, J PC ) 45 Hz, MotC), 225.1
(d, J PC ) 14 Hz, CO), 145.7 (d, J PC ) 2 Hz), 144.4, 143.7, 138.1,
137.8, 137.1 (d, J PC ) 2 Hz), 107.5, 106.9, 106.8, 52.6 (d, J PC
) 6 Hz, P(OMe)3), 44.9 (d, J PC ) 5 Hz), 30.0 (d, J PC ) 3 Hz),
22.1, 13.5 ppm; 31P{1H} NMR (CD2Cl2) δ 152.4 ppm; IR (CH2-
Cl2) 1997 cm-1 (νCO).
[Mo2(µ-H){µ-C2(Bu )2}(CO)4Cp 2][BF 4] (9). Butyl carbyne
8 (210 mg, 0.735 mmol) was dissolved in 8 mL of CH2Cl2 at
-78 °C and mixed with a 54% solution of HBF4 in ether (101
µL, 0.735 mmol). After 25 min, 30 mL of pentane at -78 °C
was added, and a red crystalline solid precipitated from
solution. The solution was removed by filter cannulation to
yield a solid, which was rinsed with pentane at -78 °C. Some
of the remaining solvent was removed in vacuo at -78 °C.
Keeping the temperature below -60 °C, 2 mL of CDCl3 was
added. The resulting solution was cannulated into an NMR
tube for spectral characterization at -50 °C. For 9: 1H NMR
(CDCl3) δ 5.54 (s, 10H, C5H5), 2.92 (m, 2H), 2.70 (m, 2H), 1.40
(m, 8H), 0.83 (m, 6H), -15.67 (s, 1H) ppm; 13C{1H} NMR
(CDCl3) δ 220.6, 219.6, 91.4 (Cp), 77.2, 69.8, 37.9, 22.4, 13.2
ppm.
Tp (CO)2MotCBu (10). Cl(C5H5N)2(CO)2MotCBu (17) (823
mg, 1.98 mmol) was dissolved in 25 mL of THF. After addition
of solid KTp (750 mg, 2.97 mmol) the mixture was stirred for
30 min at ambient temperature. The solvent was removed in
vacuo, and the resulting residue was filtered through alumina
eluting with Et2O at -78 °C. After removal of solvent, the
golden-brown oil was chromatographed on alumina at -78 °C
with hexane as the eluent. Increasing amounts of Et2O were
added to elute a bright yellow fraction. Removal of solvent in
vacuo yielded 10 as a yellow powder (566 mg, 65.8% yield):
1H NMR (C6D6) δ 7.75 (d, J HH ) 1.2 Hz, 2H), 7.30 (m, 4H),
5.80 (t, J HH ) 1.8 Hz, 2H), 5.68 (t, J HH ) 1.8 Hz, 1H), 2.43 (t,
2H), 1.58 (pentet, 2H), 1.33 (sextet, 2H), 0.78 (t, 3H) ppm; 13C-
{1H} NMR (CD2Cl2) δ 315.9 (MotC), 225.9 (CO), 144.6, 143.3,
135.9, 105.6, 50.2, 29.6, 22.9, 13.9 ppm; IR (CH2Cl2) 1992 (s),
1902 (s) cm-1 (νCO); HRMS (FAB) m/z calcd for M+ (C16H19B-
98MoN6O2) 436.0723, found 436.0717.
[Tp (CO)2MotC(H)Bu ][BF 4] (11). Butyl carbyne 10 (201
mg, 0.463 mmol) was dissolved in 10 mL of CH2Cl2 at -78 °C
and mixed with a 54% solution of HBF4 in ether (63.9 µL, 0.463
mmol). After 15 min, 30 mL of pentane at -78 °C was added
and an orange solid formed. The solution was removed by filter
cannulation to yield an orange solid, which was rinsed with
pentane at -78 °C. Some of the remaining solvent was
removed in vacuo at -78 °C. Keeping the temperature below
-78 °C, 1 mL of CD2Cl2 was added. The resulting solution was
cannulated into an NMR tube for spectral characterization at
-50 °C. For 11: 1H NMR (CD2Cl2) δ 12.56 (s, 1H) ppm; 13C-
{1H} NMR (CD2Cl2) δ 260.0 (ModC), 212.9 (CO) ppm.
Tp {P (OMe)3}(CO)MotCBu (12). Cl{P(OMe)3}3(CO)Mot
CBu (2.732 g, 4.549 mmol) was dissolved in 30 mL of THF.
After addition of solid KTp (1.720 g, 6.824 mmol) the mixture
was stirred for 12 h at ambient temperature. The solvent was
removed in vacuo, and the resulting residue was filtered
through alumina eluting with Et2O at -78 °C. After removal
of solvent, the golden oil was chromatographed on alumina at
-78 °C with hexane/Et2O (1:1) as the eluent. A bright yellow-
orange fraction was collected. Removal of solvent in vacuo
yielded 12 as a yellow-orange powder (1.803 g, 74.7% yield):
1H NMR (C6D6) δ 8.24 (s, 1H), 8.05 (s, 1H), 7.70 (s, 1H), 7.42
(m, 3H), 5.90 (m, 3H), 3.27 (d, J PH ) 11 Hz, 9H), 2.62 (m, 2H),
1.73 (pentet, 2H), 1.43 (sextet, 2H), 0.85 (t, 3H) ppm; 13C{1H}
NMR (CD2Cl2) δ 304.2 (d, J PC ) 31 Hz, MotC), 240.7 (d, J PC
) 15 Hz, CO), 144.8, 143.6, 135.9, 135.5, 135.3, 105.3, 105.1
HMQC a n d HMBC Sp ectr a . HMQC and HMBC spectra
were recorded at -50 °C on a Varian UNITY 500 spectrometer
equipped with a 5 mm indirect detection probe. The HMQC
1
spectra were optimized for a J CH ) 71 Hz (measured in a
scouting run) and run in phase-sensitive mode. BIRD nulling
(null ) 0.5 s), a relaxation delay of 0.2 s, and no 13C decoupling
during acquisition were used. For the 2D spectrum, the full
proton region (6525 Hz covering the region from -4.2 to 8.6
ppm) was taken in f 2 and a spectral width of 12583 Hz,
covering the region from 200 to 300 ppm, in f 1. The 2D FID
had 2K points in f 2 and 64 increments in f 1 and were
acquired with 64 scans per increment. A Gaussian function
with a time constant of 0.09 s was used for weighting in f 2.
Zero-filling to 256 points followed by a shifted Gaussian with
a time constant of 0.001 s and a shift of 0.001 s was applied in
f 1 prior to the Fourier transform. The 1D HMQC spectrum
was recorded with 256 points over a spectral width of 363 Hz
centered about the signal at -2.98 ppm, in 1024 transients.
Zero-filling twice and a shifted Gaussian window function with
a time constant of 0.126 s and a shift of 0.084 s were applied
prior to the Fourier transform, affording a precision of 0.7 Hz
for the coupling constant. The HMBC spectrum was optimized
n
for a J CH of 8 Hz. The spectral width, number of points,
relaxation delay, and apodization in f 2 were the same as for
the 2D HMQC experiment. In f 1, 64 increments (128 tran-
sients each) were collected for a spectral width of 39 024 Hz,
covering the region -20-300 ppm. Zero-filling twice and
multiplication with a Gaussian with a time constant of 0.001
s were applied prior to the Fourier transform.
Ack n ow led gm en t. We thank the National Science
Foundation (Grant CHE-9424134) for support of this
work.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra of
compounds 1 and 6-13. This material is available free of
charge via the Internet at http://pubs.acs.org.
OM990047X