Synthesis and reactivity of tungsten (II) methylene complexes

Article abstract of DOI:10.1021/om970470a

Treatment of the methyl complex Tp′(CO)(PhC₂Me)W-Me (1) or Tp(CO)(PhC₂Ph)W-Me (2) with trityl cation yields the corresponding methylene complex [Tp′(CO)(PhC₂Me)W=CH₂]-[PF₆] (3) (Tp′=hydridotris-(3,5-dimethylpyrazolyl)borate) or [Tp(CO)(PhC₂Ph)W=CH₂][PF₆] (4) (Tp = hydridotris(pyrazolyl)borate). The carbene complex (3) is unusually persistent for a methylene complex. Complexes 3 and 4 display electrophilic behavior, as evidenced both by addition of nucleophiles and by methylene transfer to electron rich olefins. When bound to either carbene 3 or 4, arylimines are activated toward nucleophilic attack by ethyl diazoacetate (EDA). The net result of the addition of excess arylimine followed by excess EDA to a solution of either 3 or 4 is catalytic aziridine formation. X-ray diffraction studies have revealed the structures of [Tp′(CO)(PhC₂Me)W-CH₂PMe₃][PF ₆] (7) and [Tp′(CO)(PhC₂-Me)W-CH₂N(Me)=C(H)(Ph)][PF ₆](15). The relative stabilities of 3 and 4 are discussed as well as the mechanism of aziridine catalysis.

Full text of DOI:10.1021/om970470a

Organometallics 1997, 16, 4865-4874
4865
Syn th esis a n d Rea ctivity of Tu n gsten (II) Meth ylen e
Com p lexes
T. Brent Gunnoe, Matthew Surgan, P. S. White, J . L. Templeton,* and
Luis Casarrubios
W. R. Kenan, J r., Laboratory, Department of Chemistry, The University of North Carolina,
Chapel Hill, North Carolina 27599-3290
Received J une 5, 1997X
Treatment of the methyl complex Tp′(CO)(PhC2Me)W-Me (1) or Tp(CO)(PhC2Ph)W-Me
(2) with trityl cation yields the corresponding methylene complex [Tp′(CO)(PhC2Me)WdCH2]-
[PF6] (3) (Tp′ ) hydridotris-(3,5-dimethylpyrazolyl)borate) or [Tp(CO)(PhC2Ph)WdCH2][PF6]
(4) (Tp ) hydridotris(pyrazolyl)borate). The carbene complex (3) is unusually persistent
for a methylene complex. Complexes 3 and 4 display electrophilic behavior, as evidenced
both by addition of nucleophiles and by methylene transfer to electron rich olefins. When
bound to either carbene 3 or 4, arylimines are activated toward nucleophilic attack by ethyl
diazoacetate (EDA). The net result of the addition of excess arylimine followed by excess
EDA to a solution of either 3 or 4 is catalytic aziridine formation. X-ray diffraction studies
have revealed the structures of [Tp′(CO)(PhC2Me)W-CH2PMe3][PF6] (7) and [Tp′(CO)(PhC2-
Me)W-CH2N(Me)dC(H)(Ph)][PF6] (15). The relative stabilities of 3 and 4 are discussed as
well as the mechanism of aziridine catalysis.
Sch em e 1. Bon d in g in F isch er Ca r ben e Com p lexes
In tr od u ction
Since Fischer’s formulation of a metal-carbon double
bond in (CO)5WdC(OMe)(Me), transition metal carbene
complexes have been utilized in a wide variety of
synthetic chemistry.1,2 In particular, carbene complexes
have been utilized as carbene transfer mediators2 and
as ROMP3 and olefin metathesis catalysts.4
Pettit and J olly observed that treatment of Cp(CO)2-
Fe(CH2OMe) with acid in the presence of cyclohexene
produced norcarane.6 The methylene complex [Cp(CO)2-
FedCH2]+ was postulated as a reactive intermediate,
although no direct observation of this complex was
made. Additional speculation of methylene carbene
intermediates in cyclopropanation reactions has been
reported.7
Schrock’s seminal report of the synthesis of the
persistent tantalum methylene Cp2(Me)TadCH2 focused
attention on methylene complexes.8 This group V
carbene, synthesized by deprotonation of the precursor
dimethyl complex, decomposes only slowly in solution.
Since Schrock’s discovery, both nucleophilic9,10 and
electrophilic11-13 MdCH2 moieties have been gener-
Early reports of transition metal carbenes focused on
complexes in which the carbene moiety was stabilized
via π-bonding to both the metal center and a heteroatom
substituent (Scheme 1). The presence of a heteroatom
substituent proved vital to the stability of electrophilic
carbene complexes, as evidenced by Casey’s early work
with non-heteroatom carbene complexes.5
X Abstract published in Advance ACS Abstracts, October 1, 1997.
(1) Fischer, E. O.; Maasbo¨l, A. Angew. Chem., Int. Ed. Engl. 1964,
3, 580.
(2) For metallocarbene reviews, see: (a) Hegedus, L. S. Transition
Metals in the Synthesis of Complex Organic Molecules; University
Science Books: Mill Valley, CA, 1994; p 151. (b) Brookhart, M.;
Studabaker, W. B. Chem. Rev. 1987, 87, 411. (c) Gallop, M. A.; Roper,
W. R. Adv. Organomet. Chem. 1986, 25, 121. (d) Doyle, M. P. Chem.
Rev. 1986, 86, 919. (e) Do¨tz, K. H. Angew. Chem., Int. Ed. Engl. 1984,
23, 587. (f) Do¨tz, K. H.; Fischer, H.; Hoffman, P.; Kreissl, F.; Schubert,
U.; Weiss, K. Transition Metal Carbene Complexes; Verlag Chemie:
Deerfield, FL, 1983. (g) Schrock, R. R. Science 1983, 219, 13. (h) Brown-
Wensley, K. A.; Buchwald, S. L.; Cannizzo, L.; Clawson, L.; Ho, S.;
Meinhardt, D.; Stille, J . R.; Straus, D.; Grubbs, R. H. Pure Appl. Chem.
1983, 55, 1733. (i) Schrock, R. R. Acc. Chem. Res. 1979, 12, 98. (j)
Cardin, D. J .; Cetinkaya, B.; Lappert, M. F. Chem. Rev. 1972, 72, 545.
(k) Cotton, F. A.; Lukehart, C. M. Prog. Inorg. Chem. 1972, 16, 487.
(3) For reviews of ROMP, see: refs 3-5 in Schwab, P.; France, M.
B.; Ziller, J . W.; Grubbs, R. H. Angew. Chem., Int. Ed. Engl. 1995, 34,
2039.
(4) For reviews of olefin metathesis, see: (a) Ivin, J . J . Olefin
Metathesis; Academic Press: New York, 1983. (b) Calderon, N.;
Lawrence, J . P.; Ofstead, E. A. Adv. Organomet. Chem. 1979, 17, 449.
(c) Grubbs, R. H. Comprehensive Organometallic Chemistry; Wilkinson,
G. W., Stone, A., Abel, E. W., Eds.; Pergamon Press: Oxford, 1982;
Vol. 8, p 499. (d) Schwab, P.; Grubbs, R. H.; Ziller, J . W. J . Am. Chem.
Soc. 1996, 118, 100 and references therein.
(6) J olly, P. W.; Pettit, R. J . Am. Chem. Soc. 1966, 88, 5044.
(7) See, for example: (a) Mango, F. D.; Dvoretzky, I. J . Am. Chem.
Soc. 1966, 88, 1654. (b) Green, M. L. H.; Ishaq, M.; Whiteley, R. N. J .
Chem. Soc. A 1967, 1508. (c) Collier, M. R.; Kingston, B. M.; Lappert,
M. F. J . Chem. Soc. D (Chem. Commun.) 1970, 1498.
(8) (a) Schrock, R. R. J . Am. Chem. Soc. 1975, 97, 6577. (b)
Guggenberger, L. J .; Schrock, R. R. J . Am. Chem. Soc. 1975, 97, 6578.
(c) Schrock, R. R.; Sharp, P. R. J . Am. Chem. Soc. 1978, 100, 2389.
(9) For representative examples of other nucleophilic methylene
carbenes, see: (a) Tour, J . M.; Bedworth, P. V.; Wu, R. Tetrahedron
Lett. 1989, 30, 3927. (b) Cannizzo, L. F.; Grubbs, R. H. J . Org. Chem.
1985, 50, 2316. (c) Cannizzo, L. F.; Grubbs, R. H. J . Org. Chem. 1985,
50, 2386. (d) Schwartz, J .; Gell, K. I. J . Organomet. Chem. 1980, 184,
C1. (e) Petasis, N. A.; Bzowej, E. I. J . Am. Chem. Soc. 1990, 112, 6392.
(f) Tebbe, F. N.; Parshall, G. W.; Reddy, G. S. J . Am. Chem. Soc. 1978,
100, 3611. (g) Pine, S. H.; Zahler, R.; Evans, D. A.; Grubbs, R. H. J .
Am. Chem. Soc. 1980, 102, 3270. (h) Hartner, F. W., J r.; Schwartz, J .;
Clift, S. M. J . Am. Chem. Soc. 1983, 105, 640.
(10) Numerous papers have been published concerning group VIII
and group IX d8 and d6 carbenes that display nucleophilic behavior,
see: Roper, W. R. Advances in Metal Carbene Chemistry; Schubert,
U., Ed.; Kluwer Academic Publishers: Norwell, MA, 1989, p 27 and
references therein.
(5) See, for example: (a) Casey, C. P.; Burkhardt, T. J . J . Am. Chem.
Soc. 1973, 95, 5833. (b) Casey, C. P.; Tuinstra, H. E.; Saeman, M. C.
J . Am. Chem. Soc. 1976, 98, 608. (c) Casey, C. P.; Polichnowski, S. W.
J . Am. Chem. Soc. 1977, 99, 6097.
S0276-7333(97)00470-6 CCC: $14.00 © 1997 American Chemical Society

4866 Organometallics, Vol. 16, No. 22, 1997
Gunnoe et al.
Sch em e 2. Qu a lita tive Molecu la r Or bita l Dia gr a m
for [Tp x(CO)(P h CtCR)WdCH2][P F 6] (3) a n d (4)
(R ) P h , Me; Tp x ) Tp , Tp ′)
(L ) PPh3, P(OPh)3; Cp* ) pentamethylcyclopenta-
dienyl).12c The rhenium methylene carbenes are formed
from a methyl precursor and triphenylcarbenium hexaflu-
orophosphate.
We have previously communicated the conversion of
the methyl complex Tp′(CO)(PhCtMe)W-Me (1) (Tp′
) hydridotris(3,5-dimethylpyrazolyl)borate) to a meth-
ylene complex via net hydride abstraction from the
methyl moiety.14 We now report the complementary
carbene complex [Tp(PhC≡CPh)(CO)WdCH2][PF6] (4)
(Tp ) hydridotris(pyrazolyl)borate) as well as details
of the reactivity of both methylene complexes. These
carbene complexes bind nucleophiles, act as methylene
transfer reagents to form cyclopropanes, and catalyze
aziridine formation from imines and EDA (ethyl diaz-
oacetate). The focus of this report is centered upon
elucidation of the nature of the methylene fragment, the
stability of the Tp′ carbene 3 compared to the facile
decomposition of the Tp carbene 4, and the mechanism
by which 3 or 4 catalyzes the formation of aziridines
from N-arylimines and EDA.
Resu lts a n d Discu ssion
Syn th esis a n d Sta bility of Meth ylen e Ca r ben es.
Trityl cation reacts with Tp′(CO)(PhCtCMe)W-Me (1)
at -78 °C in methylene chloride to form the correspond-
ing methylene complex, [Tp′(CO)(PhCtCMe)WdCH2]-
[PF6] (3) (eq 1). A color change from blue to reddish-
ated. However, reports of stable methylene complexes
remain rare.
Although attempts to observe the putative [Cp-
(CO)2FedCH2]+ complex proposed by Pettit and J olly
were unsuccessful, Brookhart et al. were able to
spectroscopically observe the methylene complex [Cp-
(Ph2PCH2CH2PPh2)FedCH2]+.11d The ruthenium ana-
log has also been spectroscopically identified as have
the group VI carbenes [Cp(CO)2(L)MdCH2]+ (L ) PPh3,
PEt3; M ) Mo, W).11b
brown accompanies the formation of 3. The IR spectrum
exhibits a high-energy CO stretching frequency at 2073
cm-1 in methylene chloride (cf. 2073 cm-1 for [Tp′(CO)-
(PhCtCH)2W][BF4]).15 The 13C and 1H NMR spectra
display classical methylene carbene features, including
low-field chemical shifts for the protons and carbon of
the [W]dCH2 unit. Thus, two doublets (12.33, 12.04
ppm, 2J HH ) 12 Hz, 2J WH ) 7 Hz, 183W (14% abundance),
Gladysz et al. have reported the extraordinarily
robust methylene complexes [Cp*(NO)(L)RedCH2][PF6]
1
1
I ) /2) are observed in the H NMR spectrum, while a
low-field triplet (308.2 ppm, 1J CH ) 140 Hz, 1J WC ) 110
Hz) is revealed in the 13C NMR spectrum. In order to
achieve an 18-electron count, the alkyne must serve as
a four-electron donor, consistent with the downfield
chemical shifts in the 13C NMR spectrum (213.8, 211.5
ppm). The absence of methylene rotation on the NMR
time scale is compatible with optimal back-bonding
from the metal dπ orbitals to the carbene, alkyne,
and carbonyl. It is expected that the plane of the
CH2 fragment will be orthogonal to the W-CO axis
(Scheme 2).
Rapid decomposition is common among methylene
complexes. Decomposition often occurs through a bi-
molecular route that results in the coupling of two
methylene units to form ethylene. However, carbene 3
decomposes slowly in methylene chloride at room tem-
(11) (a) Brookhart, M; Liu, Y. Advances in Metal Carbene Chemistry;
Schubert, U., Ed.; Kluwer Academic Publishers: Norwell, MA, 1989,
p 251. (b) Kegley, S. E.; Brookhart, M. Organometallics 1982, 1, 760.
(c) Studabaker, W. B.; Brookhart, M. J . Organomet. Chem. 1986, 310,
C39. (d) Brookhart, M.; Tucker, J . R.; Flood, T. C.; J ensen, J . J . Am.
Chem. Soc. 1980, 102, 1203. (e) Brookhart, M.; Nelson, G. O. J . Am.
Chem. Soc. 1977, 99, 6099.
(12) (a) Kiel, W. A.; Gong-Yu, L.; Bodner, G. S.; Gladysz, J . A. J .
Am. Chem. Soc. 1983, 105, 4958. (b) Wang, Y.; Gladysz, J . A. Chem.
Ber. 1995, 128, 213. (c) Patton, A. T.; Strouse, C. E.; Knobler, C. B.;
Gladysz, J . A. J . Am. Chem. Soc. 1983, 105, 5804. (d) Merrifield, J .
H.; Gong-Yu, L.; Kiel, W. A.; Gladysz, J . A. J . Am. Chem. Soc. 1983,
105, 5811. (e) Wong, W.; Tam, W.; Gladysz, J . A. J . Am. Chem. Soc.
1979, 101, 5440. (f) Buhro, W. E.; Etter, M. C.; Georgiou, S.; Gladysz,
J . A.; McCormick, F. B. Organometallics 1987, 6, 1150. (g) Buhro, W.
E.; Patton, A. T.; Strouse, C. E.; Gladysz, J . A.; McCormick, F. B.; Etter,
M. C. J . Am. Chem. Soc. 1983, 105, 1056.
(13) For some representative examples of electrophilic methylene
carbenes, see: (a) Guerchais, V.; Astruc, D. J . Chem. Soc., Chem.
Commun. 1985, 835. (b) Barefield, E. K.; McCarten, P.; Hillhouse, M.
C. Organometallics 1985, 4, 1682. (c) Davison, A.; Krusell, W. C.;
Michaelson, R. C. J . Organomet. Chem. 1974, 72, C7. (d) Brandt, S.;
Helquist, P. J . Am. Chem. Soc. 1979, 101, 6473. (e) O’Connor, E. J .;
Brandt, S.; Helquist, P. J . Am. Chem. Soc. 1987, 109, 3739. (f) Mattson,
M. N.; Bays, J . P.; Zakutansky, J .; Stolarski, V.; Helquist, P. J . Org.
Chem. 1989, 54, 2467. (g) Riley, P. E.; Capshew, C. E.; Pettit, R.;
Davies, R. E. Inorg. Chem. 1978, 17, 408. (h) Flood, T. C.; DiSanti, F.
J .; Miles, D. L. Inorg. Chem. 1976, 15, 1910.
(14) Gunnoe, T. B.; White, P. S.; Templeton, J . L.; Casarrubios, L.
J . Am. Chem. Soc. 1997, 119, 3171.
(15) Feng, S. G.; White, P. S.; Templeton, J . L. J . Am. Chem. Soc.
1992, 114, 2951.

Tungsten(II) Methylene Carbene Complexes
Organometallics, Vol. 16, No. 22, 1997 4867
perature (t1/2 ≈ 3700 min) and persists for days in the
solid state. While the presence of the electron-rich Tp′
ligand should provide electronic stabilization to the
carbene moiety, the presence of other π-acids (CO,
PhCtCMe) in the coordination sphere likely compro-
mises this electronic contribution. If a bimolecular
decomposition pathway is operative, the steric bulk of
the borate ligand could serve to deter degradation and
account for the kinetic stability of 3. Synthesis of the
Tp analogue of 3 provides an opportunity to investigate
the relative roles of electronic and steric factors. In
comparison to Tp′, the unsubstituted Tp ligand provides
less electron density and is sterically less bulky (cone
angle ) 224° for Tp′, 184° for Tp).16
1
of the green oil in CD2Cl2 allowed observation of the H
NMR spectrum, which displayed the four multiplets we
have assigned above to the ethylene complex 6. Con-
sistent with earlier observations, this complex decom-
poses over a period of hours.
What is the identity of the second decomposition
product? Decomposition via transfer of a methylene
fragment between two metal carbene centers to form
the ethylene complex 6 would open a coordination site
at the metal. We have previously found that fluorinated
Reaction of Tp(CO)(PhCtCPh)W-Me (2) with trityl
cation in CD2Cl2 at -78 °C yields the corresponding
methylene complex, [Tp(CO)(PhCtCPh)WdCH2][PF6]
(4). A CO stretching absorption at 2100 cm-1, the
appearance of two low field doublets (12.4 and 12.1 ppm;
anions (PF6 and BF4-) are willing σ-donor ligands
-
for W(II) d4 metal fragments of the type [Tpx(CO)-
(RCtCR′)W]+.19 Therefore, a likely product is Tp(CO)-
(PhCtCPh)W-FPF5 (5). The CO stretching frequency
of 1937 cm-1 is consistent with previously reported Tp′
species (for example, Tp′(CO)(PhC≡CMe)W-FBF3, νCO
) 1917 cm-1).19 Unfortunately, as with the ethylene
complex 6, complex 5 decomposes to intractable prod-
ucts.
1
2J HH ) 12 Hz) in the H NMR, and a color change from
dark green to bright yellow characterize the formation
of 4. Between -50 and -40 °C, carbene 4 undergoes
rapid decomposition.
We tentatively attribute the stability of the Tp′
carbene 3 relative to the Tp carbene 4 to the steric bulk
of the substituted borate. The electronic difference
between the two borate ligands may play some role in
the stability of 3. However, given the large difference
in steric factors between Tp and Tp′, the electronic
contribution is probably secondary.
Rea ction s w ith P Me3. Addition of PMe3 to a CH2-
Cl2 solution of [Tp′(CO)(PhCtCMe)WdCH2][PF6] (3)
yields the phosphine adduct [Tp′(CO)(PhCtCMe)W-
CH2PMe3][PF6] (7) (eq 3). Attack of PMe3 on carbene
Decom p osition of [Tp (CO)(P h CtCP h )WdCH2]-
[P F 6] (4). Decomposition of 4 initially forms two
products, as indicated by 1H NMR and IR spec-
troscopies. 1H NMR spectroscopy indicates that the Tp
ligand and alkyne remain intact, while IR spectroscopy
reveals two carbonyl stretching frequencies (1937
and 2043 cm-1). On the basis of literature prece-
dents11b,e,12d and spectroscopic data, we propose that the
two products are Tp(CO)(PhCtCPh)W-FPF5 (5) and
[Tp(CO)(PhCtCPh)W(CH2dCH2)][PF6] (6).
The 1H NMR spectrum of the decomposition products
of 4 exhibits four broad multiplets with approximate
triplet character (4.7, 4.0, 2.4, and 1.8 ppm). This
pattern is consistent with the formation of ethylene
complex 6 in which olefin rotation is slow on the NMR
time scale. Hindered rotation of ethylene would result
in four non-equivalent olefinic protons and could yield
the four observed resonances. The high-energy CO
stretching frequency at 2043 cm-1 is congruous with a
cationic complex with three π-acids in the coordination
sphere (CO, alkyne, and olefin).
complex 3 demonstrates the electrophilic nature of the
carbene fragment. Formation of 7 is accompanied by a
vivid color change to purple and the appearance of a
CO stretch at 1893 cm-1 (CH2Cl2) in the IR spectrum.
The 1H NMR spectrum of 7 reveals a doublet of doublets
for one of the diastereotopic methylene protons (0.79
2
2
ppm, J HH ) 14 Hz, J PH ) 22 Hz), a doublet for the
2
PMe3 methyl groups (1.57 ppm, J PH ) 13 Hz), and
signature features for the ancillary ligands. The second
methylene proton lies between 1.5 and 1.6 ppm and is
obscured by methyl peaks. A COSY was used to assign
the resonances of the second methylene proton. The 13
C
NMR reveals a definitive triplet of doublets (1J CH ) 125
1
Hz, J PC ) 33 Hz) for the methylene carbon and a
Efforts were made to independently synthesize eth-
ylene complex 6. In the presence of excess ethylene
(-78 °C), Tp(CO)(PhCtCPh)W-Me (2) was treated
with HBAr4′ (BAr4′ ) tetrakis[3,5-bis(trifluoromethyl)-
phenyl]borate). Elimination of methane17 should gener-
ate an open coordination site suitable for binding
ethylene (eq 2). The result was the formation of a
complex which exhibited a CO stretching frequency at
1
quartet of doublets (1J CH ) 130 Hz, J PC ) 55 Hz) for
the phosphine moiety.
Reaction of the Tp carbene 4 with PMe3 forms the
complex [Tp(CO)(PhCtCPh)W-CH2PMe3][PF6] (8). A
2
2
triplet (2.01 ppm, J HH ) 14, J PH ) 14 Hz), a doublets
2
2
of doublets (1.19 ppm, J HH ) 14 Hz, J PH ) 20 Hz),
and a doublet (1.59 ppm, 2J PH ) 13 Hz) are observed in
1
the H NMR spectrum for the diastereotopic methylene
2043 cm-1 18
Evaporation of the solvent and dissolution
.
protons and the phosphine methyl groups. The 13C
NMR of 8 reveals a triplet of doublets centered at 23.2
(16) Trofimenko, S. Chem. Rev. 1993, 93, 943.
1
ppm (1J CH ) 120 Hz, J PC ) 38 Hz) and a quartet and
(17) Loss of methane upon reaction of Tp′(CO)(PhCtCMe)W-CH3
with acid has been observed, see: Caldarelli, J . L.; Wagner, L. E.;
White, P. S.; Templeton, J . L. J . Am. Chem. Soc. 1994, 116, 2878.
(18) In addition to the putative ethylene complex, other products
are observed for this reaction.
(19) Caldarelli, J . L. Optical Resolution and Reactivity of Chiral
Tungsten(II) Alkyne Complexes. Ph.D. Dissertation, University of
North Carolina at Chapel Hill, Chapel Hill, NC, 1993.

4868 Organometallics, Vol. 16, No. 22, 1997
Gunnoe et al.
Ta ble 2. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [Tp ′(CO)(P h CtCMe)W-CH2P Me3][P F 6] (7)
W(1)-C(1)
W(1)-C(3)
W(1)-C(4)
W(1)-C(5)
W(1)-N(21)
W(1)-N(31)
W(1)-N(41)
C(1)-O(1)
1.938(14)
2.055(11)
2.041(11)
2.232(11)
2.257(8)
2.202(8)
2.249(9)
1.168(16)
C(2)-C(3)
C(3)-C(4)
C(4)-C(11)
C(11)-C(12)
P(1)-C(5)
P(1)-C(6)
P(1)-C(7)
P(1)-C(8)
1.494(17)
1.301(18)
1.432(17)
1.39(2)
1.744(10)
1.763(13)
1.783(12)
1.779(12)
C(1)-W(1)-C(3)
C(1)-W(1)-C(4)
C(1)-W(1)-C(5)
C(1)-W(1)-N(21)
C(1)-W(1)-N(31)
72.7(5) N(21)-W(1)-N(31)
109.3(5) N(21)-W(1)-N(41)
94.6(4) N(31)-W(1)-N(41)
84.8(4) C(5)-P(1)-C(6)
79.3(3)
80.7(3)
84.8(3)
110.8(6)
114.3(5)
111.3(6)
105.6(6)
106.2(6)
108.2(6)
176.0(9)
149.6(9)
70.9(7)
139.4(11)
72.1(7)
148.8(10)
138.7(11)
125.9(6)
93.4(4) C(5)-P(1)-C(7)
C(1)-W(1)-N(41) 165.5(4) C(5)-P(1)-C(8)
C(3)-W(1)-C(4)
C(3)-W(1)-C(5)
C(3)-W(1)-N(21) 157.4(4) C(7)-P(1)-C(8)
C(3)-W(1)-N(31)
C(3)-W(1)-N(41) 121.7(4) W(1)-C(3)-C(2)
C(4)-W(1)-C(5) 103.6(4) W(1)-C(3)-C(4)
C(4)-W(1)-N(21) 163.5(4) C(2)-C(3)-C(4)
C(4)-W(1)-N(31)
C(4)-W(1)-N(41)
C(5)-W(1)-N(21)
C(5)-W(1)-N(31) 159.9(4) W(1)-C(5)-P(1)
C(5)-W(1)-N(41) 82.9(3)
37.0(5) C(6)-P(1)-C(7)
101.0(4) C(6)-P(1)-C(8)
99.0(4) W(1)-C(1)-O(1)
F igu r e 1. ORTEP diagram for [Tp′(CO)(PhCtCMe)W-
CH2PMe3][PF6] (7).
91.0(4) W(1)-C(4)-C(3)
85.1(4) W(1)-C(4)-C(11)
83.1(3) C(3)-C(4)-C(11)
Ta ble 1. Cr ysta llogr a p h ic Da ta a n d Collection
P a r a m eter s for
[Tp ′(CO)(P h CtCMe)W-CH2P Me3][P F 6] (7)
formula
mol wt
cryst syst
space group
a, Å
C29H41BF6ON6P2W
860.27
monoclinic
P21/n
17.005(4)
13.3937(25)
17.704(3)
96.458(23)
4006.6(13)
4
bonds.21 The carbon-phosphorus bond length is 1.744-
(10) Å, and the W-C-P bond angle is 125.9(6)°.
Cyclop r op a n e Syn th esis. Transition metal medi-
ated carbene transfer to olefins to form cyclopropanes
is a well-established synthetic methodology.2,22-25 Enan-
tioselective cyclopropane formation with substituted
carbene entities, CHR, has been achieved both catalyti-
cally and stoichiometrically. However, transfer of the
parent CH2 methylene fragment from a transition metal
complex to a prochiral olefin with high enantioselectivity
has not been achieved.
In order to explore the possible use of chiral tungsten
carbenes [Tpx(CO)(PhCtCR)WdCH2]+ (R ) Ph, Me) for
enantioselective cyclopropane synthesis, we investigated
reactions of the racemic carbene complexes 3 and 4 with
olefins. Cyclopropane yields for a range of olefins are
presented in Table 3.
b, Å
c, Å
â, deg
V, Å3
Z
D
calcd, g cm-3
1.426
F(000)
cryst dimens, mm
temp, °C
1711.70
0.15 × 0.20 × 0.40
20
Mo KR (0.710 73)
5.00 < θ < 46.00
3.02
ω
6630
5571
3528
radiation (λ, Å)
2θ range, deg
µ, mm-1
scan mode
total no. of data
total no. of unique data
no. of obsd data (I > 2.5σ(I))
RF
0.042
Initially, CH2 transfer to the monosubstituted olefins
styrene and 4-methylstyrene was explored. In each
reaction, the corresponding carbene complex was re-
acted with 10 equiv of olefin. Cyclopropane yields,
particularly for disubstituted olefins (vide infra), de-
creased with a decrease in the ratio of olefin to metal
complex. Methylene transfer from either 3 or 4 to
styrene occurred with almost identical yield. In addi-
tion, production of norcarane from cyclohexene was
achieved in 51% yield with either 3 or 4. The Tp
carbene 4 is significantly more reactive than 3, as
manifested by its rapid reaction with olefins.26
Rw
GOF
0.048
1.71
doublets at 13.6 ppm (1J CH ) 130 Hz, J PC ) 53 Hz).
The IR spectrum of 8 shows a CO absorption at 1914
cm-1 (KBr). Complex 8 could not be obtained in
analytically pure form.
1
Recrystallization upon layering a methylene chloride
solution of 7 with hexanes at room temperature pro-
vided a suitable single crystal (0.15 × 0.20 × 0.40 mm)
for an X-ray diffraction study. A labeled ORTEP
diagram of 7 is shown in Figure 1, while crystal-
lographic data and collection parameters are given in
Table 1. Selected bond distances and angles for 7 are
presented in Table 2. The alkyne is aligned parallel to
the W-CO axis with the alkyne phenyl substituent syn
to Tp′, both typical structural features for d4 metal
complexes of this class.20 The PMe3 moiety is bound to
the former carbene carbon. The W-C(5) bond distance
of 2.232(11) Å is typical for tungsten-carbon single
(21) See, for example: (a) Schrock, R. R.; Kolodziej, R. M.; Liu, A.
H.; Davis, W. M.; Vale, M. G. J . Am. Chem. Soc. 1990, 112, 4338. (b)
O’Regan, M. B.; Liu, A. H.; Finch, W. C.; Schrock, R. R.; Davis, W. M.
J . Am. Chem. Soc. 1990, 112, 4331. (c) Schrock, R. R.; Glassman, T.
E.; Vale, M. G.; Kol, M. J . Am. Chem. Soc. 1993, 115, 1760. (d) Liu, A.
H.; Murray, R. C.; Dewan, J . C.; Santarsiero, B. D.; Schrock, R. R. J .
Am. Chem. Soc. 1987, 109, 4282.
(22) Brookhart, M.; Humphrey, M. B.; Kratzer, H. J .; Nelson, G. O.
J . Am. Chem. Soc. 1980, 102, 7802.
(23) Friedrich, E. C.; Lunetta, S. E.; Lewis, E. J . J . Org. Chem. 1989,
54, 2388.
(24) Du, H.; Yang, F.; Hossain, M. M. Synth. Commun. 1996, 26,
1371.
(25) Casey, C. P.; Polichnowski, S. W.; Shusterman, A. J .; J ones, C.
R. J . Am. Chem. Soc. 1979, 101, 7282.
(20) (a) Feng, S. G.; Philipp, C. C.; Gamble, A. S.; White, P. S.;
Templeton, J . L. Organometallics 1991, 10, 3504. (b) Feng, S. G.; White,
P. S.; Templeton, J . L. Organometallics 1993, 12, 2131.

Tungsten(II) Methylene Carbene Complexes
Organometallics, Vol. 16, No. 22, 1997 4869
Ta ble 3. Yield s for Cyclop r op a n a tion Rea ction s
Sch em e 4. Ca ta lytic Azir id in e F or m a tion
metal complex
olefin
% yield
refa
Tp′ 3
Tp 4
Tp′ 3
Tp 4
Tp′ 3
Tp 4
Tp′ 3
Tp 4
Tp′ 3
Tp 4
styrene
styrene
cyclohexene
73%
74%
51%
51%
57%
85%
32%
44%
19%
54%
22
22
23
23
24
24
25
25
25
25
cyclohexene
4-methylstyrene
4-methylstyrene
cis-â-methylstyrene
cis-â-methylstyrene
trans-â-methylstyrene
trans-â-methylstyrene
a
References give 1H NMR data for the resulting cyclopropane.
Sch em e 3. Tw o Meth od ologies for Azir id in e
Syn th esisa
transfer to imines (Scheme 3, Path A).28-30 In prelimi-
nary reports, the source of the carbene fragment is ethyl
diazoacetate (EDA) to give dinitrogen and C(H)(CO2Et).
J ørgensen and Rasmussen have reported that the
addition of EDA to a solution of an imine and a catalytic
amount of Cu(OTf)2 results in aziridine formation.28 The
addition of EDA to arylimines in the presence of a
catalytic amount of Cu(I) and chiral bis(dihydrooxazole)
ligands yields aziridines along with low yields of a
pyrrolidine.29 Mechanistic speculation included initial
formation of a Cu(I) carbene complex (via reaction with
EDA) followed by nucleophilic attack of the imine on
the carbene fragment. At this stage, ring closure and
copper-carbon bond cleavage would yield aziridine.
Methylrhenium trioxide catalyzes the production of
aziridines from alkyl, or arylimines and EDA.30 Mecha-
nistic consideration again invokes a metal-carbenoid
intermediate in the catalytic cycle.
EDA can attack imines which are activated by simple
Lewis acids (BF3, TiCl4, or AlCl3).31 Two major products
are typically observed for these systems: aziridines and
enamines. The ratio of these products was found to be
dependent on both the Lewis acid and the identity of
the arylimine.
Addition of 10 equiv of N-benzylideneaniline and EDA
to the Tp carbene 4 at -78 °C followed by allowing the
solution to reach room temperature resulted in the
observation of gas evolution (presumably dinitrogen).
1H NMR analysis of the reaction mixture indicated the
formation of three major organic products: cis and trans
aziridine and enamine (10a ) (60%, 6% and 25% yield,
respectively) (Scheme 4).
a
Path A: carbene transfer to an imine. Path B: nitrene
transfer to an alkene.
The disparate yields between reaction of the Tp
carbene 4 and the Tp′ carbene 3 with 4-methylstyrene
were unexpected (85% vs 57% yield, respectively). At
the completion of reaction of the Tp′ carbene with
4-methylstyrene, only a small amount of starting olefin
is observed in the GC analysis. Given 4-methylstyrene’s
proclivity to undergo electrophilic polymerization, po-
lymerization of 4-methylstyrene may be responsible for
consumption of this olefin and the reduced cyclopropane
yields. The higher yield of cyclopropane incurred with
the Tp carbene 4 can be explained by the high reactivity
of this complex. In this case, the kinetics of methylene
transfer presumably compete favorably with electro-
philic polymerization.
Reaction of carbene 3 or 4 with cis- or trans-â-
methylstyrene proceeded to form cyclopropanes in vary-
ing yields. In either case, the Tp′ carbene 3 produced
cyclopropane in lower yields than Tp carbene 4. This
can be rationalized by steric inhibition between the Tp′
ligand and the disubstituted olefins. In each reaction,
the original stereochemistry of the olefin is conserved
in the cyclopropane products, i.e., cis-olefin yields cis-
cyclopropane.
Both 3 and 4 were found to catalyze aziridine forma-
tion from imines and EDA. Yields for aziridine and
enamine production for a range of imines are shown in
Table 4. Three trends are noteworthy. For reasons that
we have not been able to elucidate, the catalytic
synthesis of aziridines in these systems works only with
N-arylimines. Use of the Tp carbene 4 as the catalyst
results in higher overall yields of aziridine and enamine.
Azir id in e Ca ta lysis. A recently discovered route to
aziridine synthesis is metal-mediated nitrene transfer
to olefins (Scheme 3, Path B).27 A new development in
aziridine synthesis is an extension of the nitrene-to-
olefin transfer methodology to metal-catalyzed carbene
(28) Rasmussen, K. G.; J ørgensen, K. A. J . Chem. Soc., Chem.
Commun. 1995, 1401.
(29) Hansen, K. B.; Finney, N. S.; J acobsen, E. N. Angew. Chem.,
Int. Ed. Engl. 1995, 34, 676.
(26) Reaction of the Tp′ carbene complex 3 with olefins typically
requires several hours at room temperature, while the Tp carbene
complex 4 reacts in e1 h at room temperature.
(27) See, for example: (a) Evans, D. A.; Faul, M. M.; Bilodeau, M.
T.; Anderson, B. A.; Barnes, D. M. J . Am. Chem. Soc. 1993, 115, 5328.
(b) Li, Z.; Conser, K. R.; J acobsen, E. N. J . Am. Chem. Soc. 1993, 115,
5326.
(30) (a) Zhu, Z.; Espenson, J . H. J . Org. Chem. 1995, 60, 7090. (b)
Zhu, Z.; Espenson, J . H. J . Am. Chem. Soc. 1996, 118, 9901.
(31) Casarrubios, L.; Pe´rez, J . A.; Brookhart, M.; Templeton, J . L.
J . Org. Chem. 1996, 61, 8358.

4870 Organometallics, Vol. 16, No. 22, 1997
Gunnoe et al.
Ta ble 4. Yield s a n d Ra tios for Azir id in e Ca ta lysis
Ta ble 5. In fr a r ed a n d 1H NMR Da ta for Im in iu m
Com p lexes
metal
complex
infrared
iminium
complex
imine
1H NMR (ppm)a
(cm-1
)
3
3
3
3
4
4
4
4
12a
12b
12c
12d
12a
12b
12c
12d
4.43, 3.98 (13Hz)b
1894
1894
1894
13a
13b
13c
13d
13e
13f
13g
13h
4.41 (14 Hz)b
4.60, 4.00 (13 Hz)b
4.85, 4.03 (13 Hz)b
4.50, 4.10 (13 Hz)
4.66, 3.71 (14 Hz)
1929
1927
1925
1916
catalyst
imine
total yielda
cis
trans
enamine
4
4
4
4
3
3
3
3
12a
12b
12c
12d
12a
12b
12c
12d
91.0%
93.4%
90.5%
89.8%
67.5%
64.6%
87.5%
71.2%b
60.0
62.0
71.7
32.9
45.0
41.3
65.0
27.7
6.0
17.3
25.0
14.1
18.8
13.2
18.0
8.9
1H NMR data for the methylene protons. NMR data for the
major isomer of two observed isomers (at room temperature).
a
b
43.7
4.5
14.4
activate the imine toward attack by EDA. Subsequent
loss of dinitrogen and formation of aziridine would
regenerate the carbene catalyst.
Reaction of the carbene complexes 3 and 4 with
N-arylimines in the absence of EDA results in the
spectroscopic observation of iminium complexes (13a -
h ) (eq 4). No aziridine products are observed in these
22.5
13.4
30.1
a
As determined by integration (versus an internal standard)
of well-resolved peaks in the 1H NMR. Isolated yield: reaction
b
performed in CH2Cl2 with products purified by chromatography
on silica gel (10:1 hexanes:ethyl acetate).
Sch em e 5. P ossible Mech a n ism for Azir id in e
Ca ta lysis
reactions. The formation of Tp complexes (13e-h )
results in a decrease in the CO stretching frequency
from 2100 to 1916-1929 cm-1 (Table 5). For the Tp′
carbene, the corresponding CO stretching frequency is
reduced from 2073 to 1894 cm-1. Diagnostic doublets
can be observed for diastereotopic methylene protons
1
for most iminium complexes in the H NMR (Table 5).
Only [Tp(CO)(PhCtCPh)W-CH2-N(Ph)dC(H)(Ph)]-
[PF6] (13e) could be isolated in the solid state.
Reaction of 1 equiv of EDA with the iminium complex
13e results in the production of cis and trans aziridine
in a 10:1 ratio. In addition, formation of the enamine
product is noted with an aziridine/enamine ratio con-
sistent with the aziridine catalysis performed with the
Tp methylene carbene 4.
On the basis of these observations, we propose that
the methylene carbene complexes 3 and 4 are acting as
Lewis acids for the activation of imines (Scheme 6).
When bound to the carbene fragment, the imine be-
comes susceptible to nucleophilic attack by EDA. The
formation of enamine is rationalized by migration of the
R′ group on the imine carbon to form a bound imine,
which could undergo facile tautomerization to the
observed enamine. As an alternate route, carbon-
nitrogen bond formation from the putative complex 14
would yield aziridine and re-form the carbene catalyst.
As already mentioned, of the N-arylimine adducts
(13a -h ) only [Tp(CO)(PhCtCPh)W-CH2-N(Ph)dC-
(H)(Ph)][PF6] (13e) could be isolated in the solid state.
Attempts to produce X-ray quality crystals of 13e were
ineffectual. Reaction of [Tp′(CO)(PhCtCMe)WdCH2]-
[PF6] (3) with excess N-benzylidenemethylamine yields
the iminium complex [Tp′(CO)(PhCtCMe)WsCH2-
N(Me)dC(H)(Ph)][PF6] (15) (eq 5). 1H NMR data for
15 include two doublets (4.45, 2.00 ppm, 2J HH ) 12 Hz)
assigned to the diastereotopic methylene protons. The
iminic carbon resonates as a doublet at 161.6 ppm
The cis/trans ratios of aziridine and aziridine/enamine
ratios seem to be more dependent upon the identity of
the imine than the catalyst.
Two plausible mechanisms deserve consideration in
the catalytic formation of aziridines described above.
One possibility is that the carbene complexes 3 and 4
initially lose the methylene fragment, regardless of
mechanistic details, resulting in the formation of a
transient five-coordinate intermediate of the type [Tpx-
(CO)(PhCtCR)W]+ (11) (Scheme 5). Fragment 11 could
combine with EDA to form a highly reactive carbene
complex with elimination of dinitrogen. Nucleophilic
attack of the imine upon the carbene carbon would yield
a transient intermediate, which could ring close to form
aziridine and regenerate 11. This mechanism is remi-
niscent of that reported for a Cu(I) complex.29
The discovery of Lewis-acid-catalyzed aziridine for-
mation from EDA and imines prompted us to consider
a second possible mechanism. The tungsten carbene
complexes could be acting as Lewis acids to bind and

Tungsten(II) Methylene Carbene Complexes
Organometallics, Vol. 16, No. 22, 1997 4871
Sch em e 6. P r op osed Mech a n ism for Azir id in e
Ca ta lysis
(1J CH ) 170 Hz), while the methylene carbon is observed
as a triplet at 66.4 ppm (1J CH ) 135 Hz) in the 13C NMR.
The infrared spectrum exhibits a CO stretching fre-
quency at 1886 cm-1
.
Recrystallization of 15 was achieved by layering a
CH2Cl2 solution with hexanes at room temperature.
X-ray data were collected as outlined in Table 6.
Selected bond distances and angles are presented in
Table 7. Figure 2 depicts an ORTEP diagram of 15.
The W-C(5) bond length of 2.237(13) Å is typical of
tungsten-carbon single bonds.21 The imine fragment
is bound to the former carbene carbon with a bond
length of 1.468(17) Å. The imine NdC bond length is
1.318(19) Å. Phenyl rings demonstrate a propensity for
juxtaposition between two pyrazolyl rings of the borate
ligand (see, for example, the phenyl ring of Tp′-phenyl
alkyne complexes).20 In agreement with this observa-
tion, the phenyl ring of N-benzylidenemethylamine is
positioned proximal to the pyrazolyl rings of the Tp′
ligand, a counterintuitive location based on steric
considerations.
The tungsten carbene [Tp′(CO)(PhC≡CMe)WdCH2]-
[PF6] (3) possesses a chiral metal center. With the
ultimate goal of metal-mediated enantioselective cyclo-
propane and aziridine synthesis, we attempted resolu-
tion of the methyl complex 1 into single enantiomers.
The immediate precursor to the methyl complex 1,
Tp′(CO)(PhCtCMe)W-I (16), has been isolated as a
single enantiomer.32 Reaction of 16 with LiMe2Cu
yields the methyl complex 1, and HPLC on a chiral
column provides a convenient means to assay the
enantiomeric purity of the product. Figure 3 shows the
results of HPLC of racemic 1 and of complex 1 produced
from opposite enantiomers of the iodide complex 16.
Conversion of a single enantiomer of 16 to the methyl
complex 1 reproducibly yields a 4:1 ratio of enantiomers.
Further enantiomeric enrichment of 1 can be achieved
by recrystallization from CH2Cl2/hexanes. Collection of
the supernatant from a single recrystallization yields
two enantiomers of 1 in a 9:1 ratio, but loss of the
racemic precipitate is costly in time and effort.
Ta ble 6. Cr ysta llogr a p h ic Da ta a n d Collection
P a r a m eter s for [Tp ′(CO)(P h CtCMe)WsCH2sN-
(Me)dC(H)(P h )][P F 6] (15)
formula
mol wt
cryst syst
space group
a, Å
b, Å
c, Å
C37H47BCl6F6ON7PW
1158.16
triclinic
P1h
13.026(6)
14.770(9)
15.012(8)
64.26(5)
88.38(4)
66.93(4)
2358.2(22)
2
R, deg
â, deg
γ, deg
V, Å3
Z
Dcalcd, g cm-3
F(000)
1.631
1151.97
0.40 × 0.30 × 0.15
-120
cryst dimens, mm
temp, °C
An alternate route to the methyl complex 1 was
sought. To date, the only other route to 1 from 16 is
reaction with Me2Mg. However, this reaction results
in racemization of the metal center.
Although the current methodology for the preparation
of enantiomerically enriched 1 is tedious, we were able
to isolate enough enriched 1 to probe enantioselective
aziridine synthesis. The aziridine was formed from
N-benzylideneaniline and EDA, and the enantiomeric
ratio of products was determined by enantiomorph
separation on a chiral HPLC column.
radiation (λ, Å)
2θ range, deg
µ, mm-1
Mo KR (0.710 73)
5.00 < θ < 46.00
2.94
ω
6712
6586
4842
0.062
0.065
scan mode
total no. of data
total no. of unique data
no. of obsd data (I > 2.5σ(I))
RF
Rw
GOF
1.79
solution followed by addition of EDA. The solution was
then allowed to come to room temperature and stirred
for 30 min. Purification of the aziridine products was
performed by chromatography on a silica gel column
(20:1 hexanes/ethyl acetate), and the enantioselectivity
was assayed by HPLC. Unexpectedly, a 1:1 ratio of the
two enantiomers of cis-aziridine was observed.
The tungsten carbene complex 3 was generated at low
temperature (-78 °C). The imine was added to this
(32) Separation of the two diastereomers resulting from coordination
of optically pure (S)-(-)-R-methylbenzylamine to the racemic fragment
[Tp′(CO)(PhCtCMe)W]+ allows access to enantiomerically enriched
Tp′(CO)(PhCtCMe)W-I, see: Caldarelli, J . L.; White, P. S.; Temple-
ton, J . L. J . Am. Chem. Soc. 1992, 114,10097.
Investigation of this unanticipated and disappointing
result is in progress. One possible explanation involves

4872 Organometallics, Vol. 16, No. 22, 1997
Gunnoe et al.
Ta ble 7. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for [Tp ′(CO)(P h CtCMe)WsCH2sN(Me)dC-
(H)(P h )][P F 6] (15)
Sch em e 7. Tw o P r op osed Isom er s for th e Im in iu m
Com p lex 13a
W(1)-C(1)
W(1)-C(3)
W(1)-C(4)
W(1)-C(5)
W(1)-N(31)
W(1)-N(41)
W(1)-N(51)
C(1)-O(1)
1.943(16)
2.076(13)
2.032(12)
2.237(13)
2.198(11)
2.270(11)
2.255(11)
1.183(19)
C(2)-C(3)
C(3)-C(4)
C(4)-C(11)
C(5)-N(6)
N(6)-C(7)
N(6)-C(8)
C(7)-C(21)
1.460(19)
1.304(19)
1.483(18)
1.468(17)
1.318(19)
1.495(20)
1.403(23)
C(1)-W(1)-C(3)
C(1)-W(1)-C(4)
C(1)-W(1)-C(5)
C(1)-W(1)-N(31)
68.4(6) C(5)-W(1)-N(51)
104.7(5) N(31)-W(1)-N(41)
96.0(5) N(31)-W(1)-N(51)
97.0(5) N(41)-W(1)-N(51)
90.1(4)
84.2(4)
75.1(4)
the kinetic tendency to form a nearly 1:1 ratio of cis and
trans isomers around the bound imine could explain the
racemic mixture of aziridine produced with enriched
metal.
Large quantities of enantiomerically enriched 1 would
be required for the exploration of stoichiometric enan-
tioselective CH2 transfer to disubstituted olefins.
83.3(4)
C(1)-W(1)-N(41) 169.9(5) W(1)-C(1)-O(1)
178.3(11)
149.0(11)
69.7(8)
141.3(13)
73.3(8)
145.4(10)
138.8(13)
125.3(9)
127.0(12)
112.9(11)
119.7(12)
127.2(12)
C(1)-W(1)-N(51)
C(3)-W(1)-C(4)
C(3)-W(1)-C(5)
C(3)-W(1)-N(31) 101.6(5) W(1)-C(4)-C(3)
C(3)-W(1)-N(41) 121.2(5) W(1)-C(4)-C(11)
C(3)-W(1)-N(51) 155.1(5) C(3)-C(4)-C(11)
C(4)-W(1)-C(5)
C(4)-W(1)-N(31)
C(4)-W(1)-N(41)
87.3(5) W(1)-C(3)-C(2)
37.0(5) W(1)-C(3)-C(4)
97.6(5) C(2)-C(3)-C(4)
101.3(5) W(1)-C(5)-N(6)
90.3(4) C(5)-N(6)-C(7)
85.3(5) C(5)-N(6)-C(8)
Su m m a r y
Hydride abstraction from the methyl complex Tp′-
(CO)(PhCtCMe)W-Me (1) quantitatively yields the
methylene carbene [Tp′(CO)(PhCtCMe)WdCH2][PF6]
(3). The carbene complex 3 exhibits unusual stability,
showing only slow decomposition in solution at room
temperature. We attribute this kinetic stabilization to
the bulky Tp′ ligand. In agreement with this assess-
ment, the Tp analogue of 3 decomposes rapidly between
-50 and -40 °C.
C(4)-W(1)-N(51) 162.3(5) C(7)-N(6)-C(8)
C(5)-W(1)-N(31) 159.8(4) N(6)-C(7)-C(21)
C(5)-W(1)-N(41)
80.4(4)
Methylene carbene complexes 3 and 4 display elec-
trophilic reactivity at the carbene carbon, as evidenced
by the binding of PMe3 and methylene transfer to
electron-rich olefins to form cyclopropanes. In addition,
3 and 4 catalyze the formation of aziridines from
N-arylimines and EDA. Mechanistic investigations
indicate that binding of the N-arylimine to the carbene
moiety activates the iminic carbon toward nucleophilic
attack by EDA. Subsequent ring closure forms the
aziridine product and regenerates the carbene catalyst.
The development of enantioselective variants of sto-
ichiometric cyclopropane synthesis and catalytic aziri-
dine formation have been frustrated by the circuitous
procedure currently necessary for the resolution of the
methyl complex 1 and by the apparent kinetic tendency
for the formation of two isomers upon binding N-
benzylideneaniline to the carbene 3.
Exp er im en ta l Section
Gen er a l Con sid er a tion s. All reactions were performed
under an atmosphere of dry nitrogen using standard Schlenk
techniques. Infrared spectra were recorded on a Mattson
F igu r e 2. ORTEP diagram for [Tp′(CO)(PhCtCMe)-
WsCH2sN(Me)dC(H)(Ph)][PF6] (15).
1
Polaris FT-IR spectrometer. Routine H and 13C NMR spectra
the stereochemistry of the imine upon binding to the
carbene fragment. Addition of N-benzylideneaniline to
an NMR tube sample of 3 at -78 °C yields two isomers
of the iminium complex 13a , as evidenced by observa-
tion of two sets of doublets for the diastereotopic
methylene protons. We assign these two isomers to cis
and trans geometries around the iminic double bond
(Scheme 7).
After approximately 45 min at room temperature, the
1H NMR of 13a reflects the thermodynamic preference
for one of the stereoisomers, i.e., one of the isomers
becomes dominant. However, if nucleophilic attack of
EDA is rapid (as suggested by the fast reaction time),
were recorded on a Varian XL-400 spectrometer or a Bruker
WM250 spectrometer with 1H and 13C NMR shifts referenced
1
to residual H signals and to the 13C signals of the deuterated
solvents. GC analysis was performed with a Hewlett Packard
5890A gas chromatograph using a J &W Scientific DB-5
capillary column (30 M, 0.25-mm i.d., 0.25-mm film thickness)
and flame ionization detection (temperature program 30 °C
for 4 min; 30-200 °C at 4 deg min-1). Enantiomeric separation
was performed utilizing HPLC on a chiral polysaccharide OD-
type column purchased from Chiral Technologies, Inc. Detec-
tion of enantiomers of Tp′(CO)(PhC2Me)WMe (1) using HPLC
was performed with a mobile phase consisting of 99.7%
hexanes and 0.3% i-PrOH at a flow rate of 0.4 mL/min.
Analysis of the enantiomers of the cis-aziridine produced from

Tungsten(II) Methylene Carbene Complexes
Organometallics, Vol. 16, No. 22, 1997 4873
F igu r e 3. Determination of % ee for enriched Tp′(CO)(PhCtCMe)W-Me (1) Using Chiral HPLC: spectrum A, racemic
mixture; spectrum B, produced from RS-amine; spectrum C, produced from SS-amine (configuration at metal center given
first, see ref 32).
EDA and N-benzylideneaniline was performed with a 99:1
hexanes/i-PrOH mixture at a flow rate of 0.5 mL/min. The
injection volume for both experiments was 0.3 µL.
Decom p osition of [Tp ′(CO)(P h C2Me)WdCH2][P F 6] (3).
An attempt was made to quantitatively follow the decomposi-
tion of methylene carbene 3. To an NMR tube was added
0.0390 g of the methyl complex 2. Complex 2 was dissolved
in 0.75 mL of CD2Cl2 and cooled to -78 °C, and tetramethyl-
silane was added as an internal standard. One equivalent of
[Ph3C][PF6] was added to the solution, and the NMR tube was
warmed to room temperature. Quantitative conversion of 2
to [Tp′(CO)(PhCtCMe)WdCH2][PF6] (3) was noted by 1H
Tp′(CO)(PhC2Me)WMe (1) and Tp(CO)(PhC2Ph)WMe (2)
were prepared according to literature methods.17,33 Methylene
chloride and hexanes were purified under a dry argon atmo-
sphere by passage through a column packed with activated
alumina.34 Ethyl acetate was purged with nitrogen prior to
use. Deuterated methylene chloride was deoxygenated by
several freeze-pump-thaw cycles and stored in a nitrogen
atmosphere over 4 Å (8-12 mesh) molecular sieves. All
solvents were purged with nitrogen prior to use. Triphenyl-
carbenium hexafluorophosphate, N-benzylideneaniline, and
N-benzylidenemethylamine were used as purchased from
Aldrich Chemical Co. Trimethylphosphine was dried over
sodium and transferred to a Kontes tube and stored under a
dry nitrogen atmosphere. Imines (12b-d ) were synthesized
by reaction of the corresponding aldehyde with 1 equiv of
aniline and excess MgSO4 in CH2Cl2. The solution was stirred
for approximately 24 h and filtered, and the solvent was
removed under reduced pressure.
[Tp ′(CO)(P h C2Me)WdCH2][P F 6] (3). In a solution of cold
(-78° C) methylene chloride, 1 equiv of triphenylcarbenium
hexafluorophosphate was added to a known amount of the
tungsten methyl complex 2. Upon addition of the trityl cation,
the solution turned from deep blue to reddish-brown in color.
Solvent removal under reduced pressure allowed isolation of
the methylene carbene 3; however, complex 3 slowly decom-
poses in the solid state. 1H NMR experiments showed
quantitative conversion of the methyl complex 2 to the
1
NMR. The decomposition of carbene 3 was monitored by H
NMR over a period of several days. Unfortunately, reliable
kinetic data was difficult to obtain due to the length of time
for decomposition. However, a rough estimate of t1/2 for 3 could
be obtained (3700 min).
[Tp (CO)(P h C2P h )WdCH2][P F 6] (4). The methylene car-
bene [Tp(CO)(PhC2Ph)WdCH2][PF6] (4) was generated at low
temperature (-78 °C) in an NMR tube in a manner similar to
the synthesis of methylene carbene 3. Upon addition of trityl
cation to a solution of the methyl complex 1, a rapid color
change from dark green to bright yellow was noted. 1H NMR
spectra at low temperature displayed characteristic features
for a methylene carbene. Between -50 and -40 °C, rapid
decomposition of 4 occurred (minutes). Attempts to isolate 4
in the solid state were thwarted by decomposition. IR (CH2-
Cl2): νCO 2100 cm-1
each a d, J HH ) 12 Hz, [W]dCH2).
.
1H NMR (CD2Cl2, δ): 12.4, 12.1 (1H each,
2
[Tp ′(CO)(P h C2Me)WCH2P Me3][P F 6] (7). A Schlenk flask
was charged with Tp′(CO)(PhC2Me)WCH3 (2) (0.101 g, 0.16
mmol) and approximately 30 mL of CH2Cl2. The resulting
solution was cooled to -78 °C, and 0.061 g (0.16 mmol) of
[Ph3C][PF6] was added. To the reddish-brown solution was
added 0.016 mL (0.16 mmol) of PMe3. Solvent removal under
reduced pressure yielded a purple oil. The oil was washed with
hexanes, then washed with ethyl acetate, and finally ab-
stracted with CH2Cl2. Purple crystals (81% yield) were
isolated after slow diffusion of hexanes into the CH2Cl2
methylene carbene complex 3. IR (KBr): νCO 2066 cm-1
.
1H
2
2
NMR (CD2Cl2, δ): 12.33, 12.04 (each a d, J HH ) 12 Hz, J WH
) 7 Hz, 14% 183W, I ) 1/2, [W]dCH2), 7.29, 6.85 (5 H, 3:2 ratio,
phenyl Hs), 6.25, 5.99, 5.78 (3H, Tp′ CH), 4.14 (3H, PhC2CH3),
2.80, 2.63, 2.51, 2.48, 1.32, 1.24 (18 H, Tp′ CH3). 13C NMR
(CD2Cl2, δ): 308.2 (t, 1J CH ) 140 Hz, 1J WC ) 110 Hz, 14% 183W,
1
I ) /2, [W]dCH2), 205.2 (CO), 213.8, 211.5 (PhC2Me), 155.0,
solution. IR (KBr): νCO 1888 cm-1 1H NMR (CD2Cl2, δ): 7.31,
.
154.2, 151.4, 148.8, 147.9, 147.3 (Tp′ CCH3), 134.3, 132.9,
131.0, 129.7 (phenyl Cs), 110.3, 109.3, 108.6 (Tp′ CH), 17.5,
17.0, 14.9, 14.2, 13.2, 13.0, 12.6 (Tp′ CCH3 and alkyne CH3).
6.68 (5 H, 3:2 ratio, phenyl Hs), 6.01, 5.99, 5.71 (3H, Tp′ CH),
2
3.58 (3H, PhC2CH3), 0.79, 1.50-1.60 (2H, each a d of d, J HH
) 14 Hz, 2J PH ) 22 Hz, [W]-CH2PMe3), 1.57 (9H, d, 2J PH ) 13
Hz, [W]-CH2P(CH3)3), 2.75, 2.58, 2.45, 2.39, 1.53, 1.35 (18H,
Tp′ CH3). 13C NMR (CD2Cl2, δ): 238.7 (CO), 218.1, 211.6
(PhC2Me), 152.6, 152.2, 150.5, 146.5, 146.1, 145.5 (Tp′ CCH3),
137.0, 130.0, 129.3, 128.7 (phenyl Cs), 109.1, 108.9, 107.6 (Tp′
CH), 20.1 (t of d, 1J CH ) 125 Hz, 1J PC ) 33 Hz, [W]-CH2PMe3),
23.1, 17.0, 15.9, 15.8, 13.0, 12.8 (1:1:1:1:2:1; Tp′ CCH3 and
(33) Schuster, D. M. Chiral Molybdenum(II) and Tungsten(II)
Aldehyde and Ketone Complexes. Ph.D. Dissertation, University of
North Carolina at Chapel Hill, Chapel Hill, NC, 1996.
(34) For further information concerning the purification of solvents
using activated alumina, see: Pangborn, A. B.; Giardello, M. A.;
Grubbs, R. H.; Rosen, R. K.; Timmers, F. J . Organometallics 1996,
15, 1518.

4874 Organometallics, Vol. 16, No. 22, 1997
Gunnoe et al.
1
1
alkyne CH3), 13.4 (q of d, J CH ) 130 Hz, J PC ) 55 Hz,
[W]-CH2P(CH3)3). Anal. Calcd for [Tp′(CO)(PhC2Me)WCH2-
PMe3][PF6]‚0.5C6H14, (C32H48N6BF6OP2W): C, 42.55; H, 5.36;
N 9.30. Found: C, 42.55; H, 5.10; N, 9.10.
temperature and was stirred for different times for different
samples (approximately 30 min for the Tp complexes and
several hours for the Tp′ complexes). Addition of pentane (∼50
mL) resulted in precipitation of metal decomposition products.
The supernatant was filtered via cannula onto either a column
of alumina or silica gel and washed with additional pentane.
Concentration of the organic products upon removal of pentane
under reduced pressure (0 °C) was performed, and the result-
ing solution was analyzed using GC (undecane added as an
internal standard).
[Tp (CO)(P h C2P h )WCH2P Me3][P F 6] (8). A Schlenk flask
was charged with Tp(CO)(PhC2Ph)WCH3 (1) (0.496 mmol) and
approximately 30 mL of CH2Cl2. The resulting solution was
cooled to -78 °C, and 0.496 mmol of [Ph3C][PF6] was added.
To the bright yellow solution was added 1 equiv of PMe3.
Solvent removal under reduced pressure yielded a dark green
oil. The oil was washed with hexanes, then dissolved in ethyl
acetate, and filtered through Celite. The green solid was
extracted with approximately 10 mL of methanol at -78 °C.
Solvent removal from the filtrate yielded a green oil, which
was washed with pentane and dried under vacuum. A green
Ca ta lytic Azir id in a tion Rea ction s. Unless otherwise
noted in Table 4, the following procedure was used in the
aziridination of imines 12a -d : In an NMR tube the tungsten
methyl complex 1 or 2 was dissolved in CD2Cl2. To this
solution was added 5 equiv of imine and an arbitrary amount
powder (45% yield) was isolated. IR (KBr): νCO 1914 cm-1
.
of tetramethylsilane (internal standard). The H NMR of this
1
1H NMR (CD2Cl2, δ): 7.8-7.0 (10H, phenyl protons), 8.08, 7.95,
7.80, 7.75, 6.79 (6H, each a d, Tp CH), 6.40, 6.35, 6.10 (3H,
each a t, Tp CH), 2.01 (1H, d of d, 2J HH ) 14 Hz, 2J PH ) 14 Hz,
sample was obtained prior to cooling the solution to -78 °C.
Triphenylcarbenium hexafluorophosphate (0.5 equiv, dissolved
in CD2Cl2 at -78 °C) was added to the tungsten methyl
complex/imine solution. An NMR spectrum was taken to
confirm complete conversion of the trityl cation to triphenyl-
methane. Via syringe, 5 equiv of EDA (10:1 EDA:catalyst
ratio) was added to the NMR tube, and the solution was slowly
warmed to room temperature. Upon cessation of gas evolution
(20-45 min), another 1H NMR spectrum was recorded and
product ratios and percent yields (utilizing internal standard)
were determined by integration of well-resolved peaks.
2
[W]-C(H)(H)PMe3), 1.59 (9H, d, J PH ) 13 Hz, [W]-CH2P-
(CH3)), 1.19 (1H, d of d, 2J HH ) 14 Hz, 2J PH ) 20 Hz, [W]-C(H)-
(H)PMe3). 13C NMR (CD2Cl2, δ): 241.2 (CO,1J WC ) 130 Hz),
227.2, 211.8 (PhC2Me), 146.3, 144.4, 142.8, 136.9, 136.5, 136.4
(Tp CH), 138.7, 137.8 (ipso phenyl), 131.0, 129.8, 129.3, 128.9,
128.8, 127.3 (phenyl Cs), 107.6, 107.5, 107.2 (Tp′ CH), 23.2 (t
1
1
of d, J CH ) 120 Hz, J PC ) 38 Hz, [W]-CH2PMe3), 13.5 (q of
d, J CH ) 130 Hz, J PC ) 55 Hz, [W]-CH2P(CH3)3).
1
1
+
[Tp ′(CO)(P h C2Me)WCH2N(Me)dC(H)(P h )][P F6] (15). In
a representative synthesis, 0.201 g (0.31 mmol) of 2 was
dissolved in CH2Cl2 and the resulting solution cooled to -78°
C. A CH2Cl2 solution of trityl cation (0.1221 g, 0.31 mmol)
was added to the solution of 2 via cannula. Next, an excess
(0.19 mL, 1.6 mmol) of N-benzylidenemethylamine was added
to the reaction solution. Upon addition of the imine, the
solution color changed from reddish-brown to wine red. After
approximately 15 min, the solution was warmed to room
temperature and the solvent was removed under reduced
pressure. The remaining red oil was washed with hexanes
and then extracted with CH2Cl2. Slow diffusion of hexanes
into the CH2Cl2 solution of the red oil yielded deep red crystals
Con tr ol Rea ction s. While we suggest that the [W]dCH2
fragments play the role of catalyst in these reactions, other
possibilities exist. In a series of control reactions, trityl cation
was found to catalyze the conversion of imines and EDA to
aziridines. However, when compared to carbene-complex-
catalyzed reactions, the syntheses utilizing trityl as catalyst
yield different cis/trans azirdine ratios, as well as different
aziridine:enamine ratios. In addition, all reactions were
performed with 0.5 equiv of trityl cation, assuring that all of
the carbenium is converted to triphenylmethane prior to EDA
addition. The triphenylmethane peak could be observed and
integrated versus internal standard in the 1H NMR prior to
EDA addition.
Addition of EDA and N-benzylideneaniline to a CD2Cl2
solution of the tungsten methyl complex 2 showed no reaction.
Treatment of the tungsten-imine complexes35 with direct
tungsten-nitrogen bonds with EDA showed no reaction after
48 h.
(0.187 g, 66% yield). IR (KBr): νCO 1886 cm-1
.
1H NMR (CD2-
Cl2, δ): 8.13 (1H, [W]-CH2-N(Me)dC(Ph)(H)), 7.44, 7.29, 7.07,
6.84, 6.76 (10H, each a m, phenyl Hs), 6.04, 5.71, 5.47 (3H,
Tp′ CH), 4.05 (3H, [W]-CH2-N(CH3)dC(Ph)(H)), 4.45, 2.00
(2H, each a d, 2J HH ) 12 Hz, [W]-CH2-N(Me)dC(Ph)(H)), 3.62
(3H, PhC2CH3), 2.73, 2.48, 2.46, 2.28, 1.39, 1.33 (18 H, Tp′
CH3). 13C NMR (CD2Cl2, δ): 237.0 (CO), 210.9, 207.3 (PhC2-
Me), 161.6 (d, J CH ) 170 Hz, [W]-CH2-N(Me)dC(H)(Ph)),
154.4, 153.0, 149.9, 147.2, 146.2, 145.1 (Tp′ CCH3), 137.0,
134.3, 132.0, 129.7, 129.0, 128.9, 128.0 (1:1:1:1:2:1:1, phenyl
Cs), 109.7, 109.0, 107.4 (Tp′ CH), 66.4 (t, J CH ) 135 Hz, J WC
) 86 Hz, [W]-CH2-N(Me)dC(Ph)(H)), 22.4 ([W]-CH2-
N(CH3)dC(Ph)(H)), 16.7, 16.2, 15.7, 14.8, 12.9, 12.8 (1:1:1:1:
2:1, Tp′ CCH3 and alkyne CH3). Anal. Calcd for [Tp′(CO)(PhC2-
Me)WCH2N(Me)dC(H)(Ph)][PF6], (C34H41N7BF6OPW): C, 45.21;
H, 4.57; N, 10.85. Found: C, 45.32; H, 4.62; N, 10.75.
Cyclop r op a n e Syn th esis. A general reaction scheme
involved dissolution of the starting methyl complex (1 or 2)
in cold methylene chloride (-78 °C). To this solution was
added 1 equiv of trityl cation, and the resulting solution was
stirred for about 15 min. An excess of olefin (10 equiv) was
syringed into the cold solution and stirred for approximately
30 min. Next, the solution was slowly allowed to warm to room
Ack n ow led gm en t. Special thanks to Dr. J ulio Pe´rez
for informative discussions. This work was supported
by the National Science Foundation (Grant No. CHE-
9208207). T. Brent Gunnoe wishes to thank the Depart-
ment of Education for support through a GAANN
Fellowship.
1
1
1
Su p p or tin g In for m a tion Ava ila ble: Labeled ORTEP
diagrams and tables of crystallographic data and collection
parameters, atomic positional parameters, complete bond
lengths and angles, and anisotropic temperature factors for 7
and 15 (14 pages). Ordering information is given on any
current masthead page.
OM970470A
(35) Francisco, L. W.; White, P. S.; Templeton, J . L. Organometallics
1996, 15, 5127.