Synthesis and characterization of cationic tungsten(V) methylidynes

Article abstract of DOI:10.1021/ic0611342

Cationic tungsten(V) methylidynes [L₄W(X)≡CH] ⁺[B(C₆F₅)₄]^- [L = PMe₃, 0.5dmpe (dmpe = Me₂PCH₂CH ₂PMe₂), X = Cl, OSO₂CF₃] have been prepared in high yield by a one-electron oxidation of the neutral tungsten(IV) methylidynes L₄W(X)≡CH with [Ph₃C] ⁺[B(C₆F₅)₄]^-. The ease and reversibility of the one-electron oxidation of L₄W(X)≡CH were demonstrated by cyclic voltammetry in tetrahydrofuran (E_1/2 ≈ -0.68 to -0.91 V vs Fc). The paramagnetic d¹ (S = 1/2) complexes were characterized in solution by electron spin resonance (g = 2.023-2.048, quintets due to coupling to ³¹P) and NMR spectroscopy and Evans magnetic susceptibility measurements (μ = 2.0-2.1 μ_B). Single-crystal X-ray diffraction showed that the cationic methylidynes are structurally similar to the neutral precursor methylidynes. In addition, the neutral (PMe₃)₄W(Cl)≡CH was deprotonated with a strong base at the trimethylphosphine ligand to afford (PMe₃) ₃(Me₂PCH₂)W≡CH, a tungsten(IV) methylidyne complex that features a (dimethylphosphino)methyl ligand.

Full text of DOI:10.1021/ic0611342

Inorg. Chem. 2007, 46, 14−21
Synthesis and Characterization of Cationic Tungsten(V) Methylidynes
Edwin F. van der Eide,† Warren E. Piers,*,† Masood Parvez,† and Robert McDonald‡
Department of Chemistry, UniVersity of Calgary, 2500 UniVersity DriVe NW, Calgary, Alberta,
Canada T2N 1N4, and X-ray Structure Laboratory, Department of Chemistry, UniVersity of
Alberta, Edmonton, Alberta, Canada T6G 2G2
Received June 22, 2006
Cationic tungsten(V) methylidynes [L4W(X)
Cl, OSO2CF3] have been prepared in high yield by a one-electron oxidation of the neutral tungsten(IV)
methylidynes L4W(X)
CH with [Ph3C]+[B(C6F5)4]-. The ease and reversibility of the one-electron oxidation of
t ) PMe3, 0.5dmpe (dmpe ) Me2PCH2CH2PMe2),
CH]+[B(C6F5)4]- [L
X
)
t
L4W(X)
t
CH were demonstrated by cyclic voltammetry in tetrahydrofuran (E1 ≈ −0.68 to
−
0.91 V vs Fc). The
/
2
paramagnetic d1 (S
)
1/2) complexes were characterized in solution by electron spin resonance (g
)
2.023 2.048,
−
quintets due to coupling to 31P) and NMR spectroscopy and Evans magnetic susceptibility measurements (µ )
2.0 2.1 B). Single-crystal X-ray diffraction showed that the cationic methylidynes are structurally similar to the
neutral precursor methylidynes. In addition, the neutral (PMe3)4W(Cl) CH was deprotonated with a strong base at
CH, a tungsten(IV) methylidyne complex that features
−
µ
t
the trimethylphosphine ligand to afford (PMe3)3(Me2PCH2)W
t
a (dimethylphosphino)methyl ligand.
Introduction
Schrock and co-workers’ original methylidynes (L)4W(X)t
CH are the most studied. The reactivity of (L)4M(X)tCH
has been widely explored, particularly their reactions with
electrophiles.6-8 Furthermore, Hopkins et al. have extensively
probed their electronic and vibrational structure9 in connec-
tion with studies aimed at incorporating the XsWtCH axis
into conjugated metallopolymers.10
In light of these materials’ applications, the redox behavior
of alkylidynes and methylidynes of this general formula is
of interest. In this context, Hopkins et al. have prepared the
paramagnetic d1 benzylidyne complex [(dmpe)2W(Br)tCPh]-
[PF6] (dmpe ) Me2PCH2CH2PMe2) via one-electron oxida-
tion of the neutral d2 benzylidyne using the tropylium
cation as the oxidizing agent.11 Isolated paramagnetic alkyli-
dynes are rare species,12 and they possess the capacity for
dimerization,7a a situation that would presumably be
Although examples of complexes containing a terminal
methylidyne ligand, LnMtCH, have been known for some
time,1 their occurrence remains scarce, and examples are
restricted to the group 6 metals Mo and W. Two general
classes (based on d electron count) have been identified. The
Schrock,2 Chisholm,3 and Cummins4 groups have each
produced variants on the d0 X3MtCH motif (where X is a
bulky anionic donor), while both the Templeton5 and
Schrock1,6 groups have introduced d2 methylidynes, of which
* To whom correspondence should be addressed. E-mail: wpiers@
ucalgary.ca. Phone: 403-220-5746. Fax: 403-289-9488.
† University of Calgary.
‡ University of Alberta.
(1) (a) Sharp, P. R.; Holmes, S. J.; Schrock, R. R.; Churchill, M. R.;
Wasserman, H. J. J. Am. Chem. Soc. 1981, 103, 965.
(2) (a) Seidel, S. W.; Schrock, R. R.; Davis, W. M. Organometallics 1998,
17, 1058. (b) Schrock, R. R.; Seidel, S. W.; Mo¨sch-Zanetti, N. C.;
Dobbs, D. A.; Shih, K.-Y.; Davis, W. M. Organometallics 1997, 16,
5195.
(3) Chisholm, M. H.; Folting, K.; Hoffman, D. M.; Huffman, J. C. J.
Am. Chem. Soc. 1984, 106, 6794.
(4) (a) Peters, J. C.; Odom, A. L.; Cummins, C. C. Chem. Commun. 1997,
1995. (b) Greco, J. B.; Peters, J. C.; Baker, T. A.; Davis, W. M.;
Cummins, C. C. J. Am. Chem. Soc. 2001, 123, 5003. (c) Agapie, T.;
Diaconescu, P. L.; Cummins, C. C. J. Am. Chem. Soc. 2002, 124,
2412.
(7) (a) Holmes, S. J.; Schrock, R. R.; Churchill, M. R.; Wasserman, H. J.
Organometallics 1984, 3, 476. (b) Manna, J.; Geib, S. J.; Hopkins,
M. D. Angew. Chem., Int. Ed. Engl. 1993, 32, 858.
(8) van der Eide, E. F.; Piers, W. E.; Romero, P. E.; Parvez, M.;
McDonald, R. Organometallics 2004, 23, 314.
(9) (a) Manna, J.; Kuk, R. J.; Dallinger, R. F.; Hopkins, M. D. J. Am.
Chem. Soc. 1994, 116, 9793. (b) Manna, J.; Dallinger, R. F.;
Miskowski, V. M.; Hopkins, M. D. J. Phys. Chem. B 2000, 104, 10928.
(c) Da Re, R. E.; Hopkins, M. D. Coord. Chem. ReV. 2005, 249, 1396.
(10) (a) Manna, J.; Geib, S. J.; Hopkins, M. D. J. Am. Chem. Soc. 1992,
114, 9199. (b) See also: Mayr, A.; Yu, M. P. Y.; Yam, V. W.-W. J.
Am. Chem. Soc. 1999, 121, 1760.
(5) (a) Enriquez, A. E.; White, P. S.; Templeton, J. L. J. Am. Chem. Soc.
2001, 123, 4992. (b) Jamison, G. M.; Bruce, A. E.; White, P. S.;
Templeton, J. L. J. Am. Chem. Soc. 1991, 113, 5057.
(6) Holmes, S. J.; Clark, D. N.; Turner, H. W.; Schrock, R. R. J. Am.
Chem. Soc. 1982, 104, 6322.
(11) Manna, J.; Gilbert, T. M.; Dallinger, R. F.; Geib, S. J.; Hopkins, M.
D. J. Am. Chem. Soc. 1992, 114, 5870.
14 Inorganic Chemistry, Vol. 46, No. 1, 2007
10.1021/ic0611342 CCC: $37.00
© 2007 American Chemical Society
Published on Web 09/02/2006

Cationic Tungsten(V) Methylidynes
simulations; giso values, hyperfine coupling constants, and line
widths can be found in Table 2. The giso values of the radicals
were calculated using the field/frequency ratio of each sample.
UV-visible spectra were obtained on a Cary 100 Bio spectropho-
tometer operating in double-beam mode. Elemental analyses were
performed by Olivera Blagojevic and Roxanna Smith (University
of Calgary).
exacerbated in the less sterically protected parent methylidyne
compounds, where even diamagnetic examples dimerize.3,5b
Nonetheless, in the context of our continuing interest in the
reactions of archetypal organometallic fragments with elec-
trophiles,8,13 we discovered that the reaction of Schrock and
co-workers’ methylidynes (L)4W(X)tCH (L ) PMe3 or
0.5dmpe; X ) Cl or OTf) with the trityl borate reagent
[Ph3C][B(C6F5)4]14 leads to facile one-electron oxidation to
the cationic d1 methylidynes [(L)4W(X)tCH][B(C6F5)4], the
first monomeric paramagnetic methylidyne complexes to be
characterized.
Synthesis of [(PMe3)4W(Cl)tCH]+[B(C6F5)4]- (2a). (PMe3)4-
W(Cl)tCH (0.153 g, 0.285 mmol) and [Ph3C]+[B(C6F5)4]- (0.265
g, 0.287 mmol) were placed in a 50-mL flask attached to a swivel-
frit assembly, and toluene (20 mL) was condensed onto the yellow
solids at -78 °C. The orange suspension was allowed to warm to
room temperature, during which a color change to green was
observed, as well as the formation of a green precipitate. The
supernatant had a yellow color. The suspension was stirred at room
temperature for another 30 min, after which the green solids were
collected on the frit and washed with several portions of toluene.
Drying in vacuo gave a bright-green powder, which was isolated.
Yield: 0.320 g (0.263 mmol, 93%). Crystals of 2a‚C6D6 suitable
for X-ray analysis were obtained from an NMR tube reaction
between (PMe3)4W(Cl)tCH and 1 equiv of [Ph3C]+[B(C6F5)4]-
in C6D6, from which 2a precipitated as a green oil. Dark-green
prismatic crystals had grown on the oil/C6D6 interface after 30 min.
1H NMR (THF-d8, 400 MHz, 300 K): δ 8.2 (v br, ∆ν1/2 ≈ 2500
Hz, 36H, CH3), WtCH not observed, probably very broad. 19F
NMR (THF-d8, 282.4 MHz, 300 K): δ -132.6 (o-F), -164.7 (p-
F), -168.2 (m-F). 11B NMR (THF-d8, 128.2 MHz, 300 K): δ -17.4
(B(C6F5)4). 31P{1H} and 13C{1H} NMR spectra are silent. µ (THF,
298 K) ) 2.0 µB. IR: 3011 (w), 2985 (w), 2920 (w), 2850 (w),
2804 (w), 1643 (m), 1515 (s), 1464 (s), 1420 (m), 1292 (m), 1275
(m), 1087 (s), 980 (s), 951 (s), 775 (m), 756 (m), 684 (m), 662
(m). Anal. Calcd for C37H37BClF20P4W: C, 36.56; H, 3.07.
Found: C, 36.69; H, 3.01.
Experimental Section
Reagents and General Procedures. All operations were per-
formed under a purified Ar atmosphere using glovebox or vacuum-
line techniques. Toluene, hexanes, and tetrahydrofuran (THF) sol-
vents were dried and purified by passing through activated alumina
and Q5 columns.15 Acetonitrile and dichloromethane were dried
over CaH2 and distilled under reduced pressure. Diethyl ether and
pentane were dried over Na/benzophenone and distilled under re-
duced pressure. Methylidynes (PMe3)4W(Cl)tCH (1a) and (dmpe)2-
W(Cl)tCH (1b) were prepared as described in the literature,6 while
the compound (dmpe)2W(OTf)tCH (1c) was prepared by treatment
of 1b with Me3SiOTf.7b Isotopomers (PMe3)4W(Cl)t13CH ([13C]-
1a) and (PMe3)4W(Cl)tCD (1a-d1) and derivatives were prepared
16
by reacting (PMe3)4WCl2 with Al(13CH3)3 or Al(CD3)3 instead
of unlabeled Al(CH3)3.
Instrumentation. 1H, 2H{1H}, 11B, 13C, 19F, and 31P NMR
spectra were collected on a Bruker AC-200, AMX-300, or DRX-
400 spectrometer in dry, O2-free C6D6, C7D8, CD2Cl2, THF-d8,
C6D5Br, or CD3CN. Chemical shifts are given in ppm relative to
residual solvent signals for 1H and 13C NMR spectra. 11B, 19F, and
31P NMR spectra were referenced to external Et2O‚BF3, C6F6, and
85% H3PO4, respectively. Electrochemical studies were carried out
using an EG&G model 283 potentiostat in conjunction with a three-
electrode cell. The auxiliary electrode was a Pt wire, the pseudo-
reference electrode a Ag wire, and the working electrode a Pt disk
(1.6 mm diameter). Solutions (in THF or acetonitrile) were 1 mM
in the tungsten compound and 0.1 M in [nBu4N][PF6] as the
supporting electrolyte. IR spectra were recorded as KBr pellets
on a Nicolet Nexus 470 FT-IR spectrometer in the range 4000-
400 cm-1. Solution magnetic moments were determined at 298 K
in THF/THF-d8 (3:1) according to the Evans method.17 Elec-
tron spin resonance (ESR) spectra were recorded on a Bruker
EMX 113 spectrometer. WINEPR SimFonia18 was used to simu-
late the spectra, and Lorentzian line shapes were used in the
Synthesis of [(dmpe)2W(Cl)tCH]+[B(C6F5)4]- (2b). (dmpe)2-
W(Cl)tCH (0.150 g, 0.282 mmol) and [Ph3C]+[B(C6F5)4]- (0.260
g, 0.282 mmol) were placed in a 50-mL flask attached to a swivel-
frit assembly, and toluene (20 mL) was condensed onto the yellow
solids at -78 °C. The orange suspension was allowed to warm to
room temperature, during which a color change to light green was
observed, as well as the formation of a green precipitate. The
supernatant had a light-yellow color. The suspension was stirred
at room temperature for another 30 min, after which the green solids
were collected on the frit and washed with several portions of
toluene. Drying in vacuo afforded a yellow/green powder, which
was isolated. Yield: 0.320 g (0.264 mmol, 94%). Light-green
crystals of 2b suitable for X-ray analysis were grown by slow
1
evaporation of solvent from a CH2Cl2 solution of 2b. H NMR
(CD2Cl2, 400 MHz, 300 K): δ 2.71 (br, ∆ν1/2 ≈ 160 Hz, 12H,
CH3), 1.34 (br, ∆ν1/2 ≈ 160 Hz, 12H, CH3), -11 (v br, ∆ν1/2
≈
(12) (a) Xue, W.-M.; Chan, M. C. W.; Mak, T. C. W.; Che, C.-M. Inorg.
Chem. 1997, 36, 6437. (b) Felixberger, J. K.; Kiprof, P.; Herdtweck,
E.; Herrmann, W. A.; Jakobi, R.; Gu¨tlich, P. Angew. Chem., Int. Ed.
Engl. 1989, 28, 334. (c) Lemos, M. A. N. D. A.; Pombeiro, A. J. L.;
Hughes, D. L.; Richards, R. L. J. Organomet. Chem. 1992, 434, C6.
(13) For example, see: (a) Spence, R. E. v. H.; Piers, W. E.; Sun, Y.;
Parvez, M.; MacGillivray, L. R.; Zaworotko, M. J. Organometallics
1998, 17, 2459. (b) Cook, K. S.; Piers, W. E.; McDonald, R. J. Am.
Chem. Soc. 2002, 124, 5411.
(14) Chien, J. C. W.; Tsai, W.-M.; Rausch, M. D. J. Am. Chem. Soc. 1991,
113, 8570.
(15) Pangborn, A. B.; Giardello, M. A.; Grubbs, R. H.; Rosen, R. K.;
Timmers, F. J. Organometallics 1996, 15, 1518.
(16) Sharp, P. R.; Bryan, J. C.; Mayer, J. M. Inorg. Synth. 1990, 28, 326.
(17) (a) Evans, D. F. J. Chem. Soc. 1959, 2003. (b) Schubert, E. M. J.
Chem. Educ. 1992, 69, 62. (c) Grant, D. H. J. Chem. Educ. 1995, 72,
39.
(18) WINEPR SimFonia, version 1.25; Bruker Analytische Messtechnik
GmbH: Karlsruhe, Germany, 1996.
1
1600 Hz, 1H, WtCH). H NMR (C6D5Br, 400 MHz, 300 K):
δ 2.20 (br, 12H, -CH3), 1.10 (br, 12H, -CH3), -11 (v br, 1H,
WtCH). Resonances for the methylene protons could not be
observed; these are probably buried underneath the methyl reso-
nances as broad lines. 11B NMR (CD2Cl2, 128.2 MHz, 300 K): δ
-17.3 (B(C6F5)4). 19F NMR (CD2Cl2, 282.4 MHz, 300 K): δ
-132.5 (o-F), -163.5 (p-F), -167.3 (m-F). 19F NMR (C6D5Br,
282.4 MHz, 300 K): δ -133.2 (o-F), -163.4 (p-F), -167.2
(m-F). 31P{1H} and 13C{1H} NMR spectra are silent. µ (THF, 298
K) ) 2.1 µB. IR: 2977 (w), 2938 (w), 2907 (w), 1643 (m), 1515
(s), 1465 (s), 1421 (m), 1372 (w), 1292 (m), 1275 (m), 1090 (s),
977 (s), 951 (m), 934 (m), 895 (m), 777 (m), 758 (m), 686 (m),
664 (m). Anal. Calcd for C37H33BClF20P4W: C, 36.68; H, 2.75.
Found: C, 36.93; H, 2.60.
Inorganic Chemistry, Vol. 46, No. 1, 2007 15

van der Eide et al.
Table 1. Data Collection and Structure Refinement Details for 2a‚C6D6, 2b, and 3
2a‚C6D6
2b
3
formula
fw
C43H37D6BClF20P4W
1299.80
C37H33BClF20P4W
1211.62
C13H36P4W
500.15
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
Z
triclinic
P1h
orthorhombic
Pca21
27.5938(18)
11.9743(8)
13.3408(9)
90
90
90
4408.0(5)
4
monoclinic
C2/c
30.889(11)
8.924(2)
15.485(6)
90
94.582(17)
90
4255(2)
8
13.667(2)
14.036(3)
15.665(2)
64.577(8)
68.486(9)
73.640(8)
2497.2(7)
2
T, K
123
193
173
λ, Å
0.710 73
1.729
1274
0.710 73
1.826
2364
0.710 73
1.562
1984
F
calc, g cm-3
F(000)
µ, mm-1
2.601
2.940
5.72
cryst size, mm3
transm factors
θ range, deg
data/restraints/param
GOF
0.10 × 0.08 × 0.07
0.781-0.839
3.0-30.0
14484/0/656
1.06
0.68 × 0.26 × 0.07
0.2397-0.8206
2.25-26.38
8964/0/597
1.007
0.16 × 0.12 × 0.05
0.462-0.763
3.2-27.5
4857/0/177
1.04
R1 [I > 2σ(I)]
wR2 (all data)
residual density, e Å-3
0.037
0.076
1.04 and -1.07
0.0243
0.0548
1.260 and -0.322
0.032
0.076
0.99 and -1.15
4
2
1
Synthesis of [(dmpe)2W(OTf)≡CH]+[B(C6F5)4]-‚PhCH3 (2c‚
PhCH3). (dmpe)2W(OTf)tCH (0.111 g, 0.172 mmol) and
[Ph3C]+[B(C6F5)4]- (0.160 g, 0.173 mmol) were placed in a 50-
mL flask attached to a swivel-frit assembly, and toluene (20 mL)
was condensed onto the yellow solids at -78 °C. The orange
suspension was allowed to warm to room temperature, during which
clumps of a green material precipitated. These clumps were
sonicated into a green powder. After the green solids were stirred
at room temperature for another 30 min, they were collected on
the frit and washed with several portions of toluene. Drying in vacuo
afforded a green powder, which was isolated. Yield: 0.199 g (0.150
mmol, 82%). 1H NMR (THF-d8, 400 MHz, 300 K): δ 7.21-7.05
(m, 5H, CH3C6H5), 5.28 (br, ∆ν1/2 ≈ 400 Hz, 12H, CH3), 2.30 (s,
3H, CH3C6H5), -0.3 (br, 8H, CH2), -1.23 (br, ∆ν1/2 ≈ 350 Hz,
12H, CH3), -10.2 (v br, ∆ν1/2 ≈ 1100 Hz, 1H, WtCH). 19F NMR
(THF-d8, 282.4 MHz, 300 K): δ -75.2 (br, OSO2CF3), -130.9
(o-F), -163.1 (p-F), -166.6 (m-F). 11B NMR (THF-d8, 128.2 MHz,
300 K): δ -17.4 (B(C6F5)4). 31P{1H} and 13C{1H} NMR spectra
are silent. µ (THF, 298 K) ) 2.1 µB. IR: 2992 (w), 2908 (w),
1643 (w), 1515 (m), 1464 (s), 1423 (w), 1322 (w), 1235 (w), 1207
(m), 1087 (m), 1025 (m), 980 (s), 949 (m), 775 (w), 756 (w), 684
(w), 662 (w), 635 (m). Anal. Calcd for C45H41BF23O3P4SW: C,
38.13; H, 2.92. Found: C, 37.61; H, 2.92.
Hz, JHH ) 0.9 Hz, JHW ) 74 Hz, JCH ) 125 Hz, 1H, WtCH),
1.54 (dd, 2JHP ) 8.1 Hz, 4JHP ) 1.3 Hz, 6H, WCH2P(CH3)2), 1.52
(ps t, 18H, PMe3), 1.49 (d, 2JHP ) 6.9 Hz, 9H, PMe3), -1.26 (dddt,
2JHP ) 4.1 Hz, 3JHP ) 13.0 and 2.8 Hz, 4JHH ) 0.9 Hz, 2H, WCH2-
1
P(CH3)2). H NMR (THF-d8, 300 MHz, 300 K): δ 8.13 (m, 1H,
WtCH), 1.60 (d, 9H, PMe3), 1.53 (dd, overlapping, 6H, WCH2-
P(CH3)2), 1.51 (ps t, 18H, PMe3), -1.58 (ps tt, 2H, WCH2P(CH3)2).
1H NMR (C7D8, 400 MHz, 300 K): δ 8.58 (ddtt, 1H, WtCH),
1.53 (dd, 6H, WCH2P(CH3)2), 1.50 (ps t, 18H, PMe3), 1.49 (d,
overlapping, 9H, PMe3), -1.35 (dddt, 2H, WCH2P(CH3)2). 1H NMR
(C7D8, 400 MHz, 185 K): δ 8.97 (br, 1H, WtCH), 1.83 (br, 6H,
1 CH3 of PMe3), 1.74 (br, 6H, 1 CH3 of PMe3), 1.58 (br d, 6H,
WCH2P(CH3)2), 1.45 (br, 9H, PMe3), 1.09 (br, 6H, 1 CH3 of PMe3),
-1.16 (br, 2H, WCH2P(CH3)2). 31P{1H} NMR (C6D6, 161.8 MHz,
2
2
300 K): δ -14.0 (dt, JPP(cis) ) 13.5 Hz, JPP(pseudo-trans) ) 26.5
1
2
Hz, JPW ) 339 Hz, 1P, PMe3), -31.0 (ps t, JPP(cis) ) 13.5 and
14.0 Hz, 1JPW ) 281 Hz, 2P, PMe3), -52.8 (dt, 2JPP(cis) ) 14.0 Hz,
2JPP(pseudo-trans) ) 26.5 Hz, JPW ) 249 Hz, 1P, WCH2PMe2). 13C-
1
{1H} NMR (C6D6, 100.5 MHz, 300 K): δ 264.8 (ddt, WtCH),
28.6 (ps t, 2 PMe3), 26.9 (d ps q, PMe3), 19.8 (d ps q, WCH2-
P(CH3)2), -23.1 (ddt, WCH2P(CH3)2). IR: 2959 (m), 2927 (m),
2901 (s), 2798 (w), 1415 (m), 1292 (m), 1279 (m), 930 (s), 872
(m), 840 (m), 704 (m), 652 (m). Anal. Calcd for C13H36P4W: C,
31.22; H, 7.25. Found: C, 29.99; H, 7.62. This was the best result
of several analyses; the compound was quite sensitive and also
contained variable amounts (<5%) of an impurity believed to be
(Me3P)4WH4, based on reported NMR data for this compound.19
Single-Crystal X-ray Analyses. Crystals of 2a‚C6D6 and 2b
were coated with Paratone 8277 oil, those of 3 with perfluoropoly-
alkyl ether (1600 cSt), and mounted on a glass fiber. Measurements
for 2a‚C6D6 and 3 were made on a Nonius Kappa CCD diffracto-
meter (University of Calgary) and those for 2b on a Bruker
PLATFORM/SMART 1000 CCD diffractometer (University of
Alberta), using graphite-monochromated Mo KR radiation for all
measurements. Table 1 gives further details, and the crystallographic
data (CIF) are available as Supporting Information. The CCDC
contains the supplementary crystallographic data for the crystal
Synthesis of (PMe3)3(Me2PCH2)WtCH (3). (PMe3)4W(Cl)t
CH (0.311 g, 0.580 mmol) and KCH2Ph (0.101 g, 0.776 mmol)
were placed in a 25-mL flask attached to a swivel-frit assembly.
THF (10 mL) was condensed onto the solids at -78 °C, and the
mixture was allowed to warm to room temperature. The dark-red
solution was stirred for 30 min at room temperature, after which
the volatiles were removed in vacuo. Pentane (5 mL) was condensed
onto the residue at -78 °C, and the mixture was sonicated at room
temperature for 5 min, after which the volatiles were removed in
vacuo. Pentane (20 mL) was condensed onto the residue at -78
°C, and filtering at room temperature afforded a yellow solution.
Removal of the pentane in vacuo afforded a yellow/orange solid,
which was isolated. Yield: 0.240 g (0.480 mmol, 83%). Yellow
crystals of 3 suitable for X-ray analysis were grown by cooling a
saturated pentane solution of 3 to -35 °C for several days. 1H NMR
3
(C6D6, 400 MHz, 300 K): δ 8.72 (ddtt, JHP ) 5.2, 2.3, and 2.2
(19) Lyons, D.; Wilkinson, G. J. Chem. Soc., Dalton Trans. 1985, 587.
16 Inorganic Chemistry, Vol. 46, No. 1, 2007

Cationic Tungsten(V) Methylidynes
Scheme 1
and multiplet resonances at (among others) 4.93, 5.91, and
6.43 ppm clearly indicate the formation of the known dimer
resulting from head-to-tail coupling of the trityl radical.22
The oxidation reaction also goes very cleanly in THF-d8, in
which the products stay dissolved. Although Cooper’s WV
cations [Cp2WRR′]+ undergo H• radical abstraction from an
alkyl R-C in the presence of trityl radicals to form triphen-
ylmethane, the methylidyne cations do not react with trityl
radicals under any conditions we tried.
Figure 1. Cyclic voltammogram (scan rate 10 mV s-1) of 1 mM 1a in
THF at room temperature with 0.1 M [n-Bu4N][PF6] as the supporting
electrolyte.
structures reported in this paper (CCDC 605925, 2a‚C6D6; CCDC
605926, 2b; CCDC 605927, 3). These data can be obtained, free
of charge, via www.ccdc.cam.ac.uk/conts/retrieving.html (or from
the Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, U.K.; fax 44-1223-336033; or e-mail
deposit@ccdc.cam.ac.uk).
-
B(C6F5)4 salts 2 (Scheme 1) were synthesized on a
preparative scale by the reaction of 1 with 1 equiv of
[Ph3C]+[B(C6F5)4]- in toluene. The ion pairs are insoluble
in toluene and precipitate as green microcrystalline materials
in the course of the reaction. Filtration and washing of the
precipitate with toluene removes the soluble organic byprod-
uct and affords 2a (green) and 2b (bright green/yellow) as
analytically pure powders in ca. 90% yield. Triflate derivative
2c (green) is obtained in a yield of 82%, and its combustion
analysis and 1H NMR spectrum suggest that approximately
1 equiv of toluene is retained in the isolated solid material.
In the solid state at -35 °C, the ion pairs are indefinitely
stable, and also after days at room temperature, there is no
sign of decomposition. Ion pairs 2 are soluble in polar
solvents, such as halobenzenes, CH2Cl2, THF, and CH3CN.
While dmpe-containing 2b and 2c are stable in all of these
solvents, 2a decomposes within 24 h in CH2Cl2 and CH3-
CN to unknown products. The solutions are highly O2-
sensitive; opening them to air results in a disappearance of
the green or yellow color and decomposition to unidentified
products. Complexes 2 are the first stable, monomeric
paramagnetic methylidynes to be isolated. Churchill et al.
synthesized a formally tungsten(V) phosphinomethylidyne7a
by the reaction of 1a with AlCl3/C2Cl6, but the product is
dimeric and diamagnetic and the methylidyne proton is
somehow lost in the reaction.
Single-crystal X-ray analysis of 2a‚C6D6 (Figure 2) cor-
roborates its formulation as a cationic tungsten(V) methyli-
dyne complex. The methylidyne and chloride ligands are
disordered (Cl and C atoms were included with 0.5 oc-
cupancy factors on either side of the WP4 plane), which does
not justify a discussion of metrical data associated with the
ClsWtCH axis. The same type of disorder was found to
be operative in the crystal structure of the parent 1a,23
determined by Churchill and co-workers. In both 1a and 2a,
the W(PMe3)4 part is ordered, with the PMe3 ligands situated
alternately above and below the least-squares WP4 plane.
Results and Discussion
One-Electron Oxidation of Tungsten(IV) Methylidynes.
Methylidynes L4W(X)tCH (L, X ) PMe3, Cl, 1a; 0.5dmpe,
Cl, 1b; 0.5dmpe, OTf, 1c) can be reversibly oxidized, as
was found by cyclic voltammetry in THF (Figure 1; [W] )
1 mM, 0.1 M [n-Bu4N][PF6] electrolyte, Cp2Fe as the internal
standard). One-electron oxidations to the WV radical cations
[L4W(X)tCH]+ (1+) were found in all cases, with E1/2 values
of -0.88, -0.91, and -0.68 V vs Fc ([Cp2Fe]+1/0 couple)
for the couples 1a+/1a, 1b+/1b, and 1c+/1c, respectively.
These data indicate that the denticity of the phosphine ligand
has a negligible effect on the E1/2 value, whereas substitution
of Cl for OTf significantly increases the redox potential by
ca. 0.20 V. This can be attributed to a greater positive charge
on W in 1c vs 1b due to the more weakly coordinating or
electron-withdrawing nature of OTf- vs Cl-. The d1 cations
1+ generated in the cyclic voltammetry experiments were
found to be persistent in a THF solution because reversible
oxidations were observed also at low scan rates. The redox
potentials of the methylidyne complexes are comparable to
the potentials found for tungsten(IV) dialkyl complexes Cp2-
WRR′ (ca. -0.80 to -0.64 V vs Fc, MeCN solvent, [Et4N]-
[ClO4] electrolyte), as determined by Cooper and co-
workers.20
Clean chemical oxidation of methylidynes 1 is readily
achieved by reaction with the trityl cation Ph3C+ (E1/2
)
-0.11 V vs Fc in MeCN21). NMR tube reactions of yellow
1 with 1 equiv of [Ph3C]+[B(C6F5)4]- in C6D6 result in the
precipitation of green oils or solids, leaving a light-yellow
supernatant (Scheme 1). In each case, 1H NMR spectroscopy
reveals the absence of W-containing products in solution,
(20) Asaro, M. F.; Cooper, S. R.; Cooper, N. J. J. Am. Chem. Soc. 1986,
108, 5187.
(21) Connelly, N. G.; Geiger, W. E. Chem. ReV. 1996, 96, 877.
(22) McBride, J. M. Tetrahedron 1974, 30, 2009.
(23) Churchill, M. R.; Rheingold, A. L.; Wasserman, H. J. Inorg. Chem.
1981, 20, 3392.
Inorganic Chemistry, Vol. 46, No. 1, 2007 17

van der Eide et al.
of 0.75 and 0.25, respectively (in Figure 3, the A position is
displayed). Such a dmpe disorder is the rule rather than the
exception for (dmpe)2W complexes and has been discussed
elsewhere.25 The methylidyne hydrogen H1 was located and
refined; the linearity of the ClsWtCH unit is evidenced
by W-C1-H1 and Cl-W-C1 angles of 175(4)° and 176.6-
(2)°, respectively. The W-Cl bond length in 2b is 2.556(1)
Å, shorter than the 2.606(3) Å determined26 for 1b, while
the WtC length of 1.776(5) Å is statistically almost identical
with the length of 1.797(10) Å in 1b.26 This shortening of
the W-Cl bond upon oxidation is expected for the electron-
donating chloride ligands. Again, the average W-P bond
length is ca. 0.06 Å longer in 2b than in 1b. The W-P and
WtC bond lengths found here for 2b compare very well to
those found for [(dmpe)2W(Br)tCPh]+[PF6]-, a closely
related tungsten(V) benzylidyne complex reported by Hop-
kins and co-workers.11
Figure 2. Crystalmaker depiction (50% probability thermal ellipsoids) of
the molecular structure of 2a‚C6D6. The anion, cocrystallized C6D6, and H
atoms, except the methylidyne H (arbitrary radius), are omitted for clarity,
and the disorder of the methylidyne and chloride ligands is not shown.
Selected bond lengths (Å): W1-P1, 2.5430(9); W1-P2, 2.5347(9); W1-
P3, 2.5280(8); W1-P4, 2.5301(8). Selected bond angles (deg): P1-W1-
P2, 165.39(3); P3-W1-P4, 164.70(3).
Magnetic moments of 2 in a THF solution were determined
by the Evans method17 to be 2.0-2.1 µB, relatively close to
the spin-only value of 1.7 µB expected for a complex with a
single unpaired electron. As a consequence, the NMR spectra
1
are paramagnetically broadened. The H NMR spectrum of
2a in THF-d8 shows a very broad (∆ν1/2 ≈ 2500 Hz) signal
at 8.2 ppm for the 36 equivalent PMe3 protons, which
sharpens slightly upon heating of the sample to 335 K and
which broadens upon cooling. The single methylidyne proton,
which may be broadened to an even larger extent because
of its closer proximity to the W center, could not be observed.
2H NMR spectroscopy on 2a-d1, deuterated at the methyli-
dyne position, also afforded a featureless spectrum. Likewise,
paramagnetic broadening prevented the observation of signals
in the 13C and 31P NMR spectra. In contrast, resonances for
the B(C6F5)4- anion in the 19F and 11B NMR spectra are sharp
and are located at unperturbed chemical shift values, which
suggests that the diamagnetic anion is solvent-separated from
the paramagnetic cation. NMR spectra of 2a in other solvents
such as C6D5Br and CD2Cl2 are very similar to those recorded
in THF-d8. The 1H NMR resonances for 2b and 2c are much
less broadened than those of 2a, although 13C and 31P NMR
spectra are still featureless. For example, the methylidyne
protons of 2b and 2c are now visible at ca. -9 to -11 ppm
Figure 3. Crystalmaker depiction (50% probability thermal ellipsoids) of
the molecular structure of 2b. The anion and H atoms, except the
methylidyne H (arbitrary radius), are omitted for clarity, and the disorder
in the P21/P22 dmpe ligand is not shown. Selected bond lengths (Å):
W-C1, 1.776(5); W-Cl, 2.5561(12); W-P11, 2.5198(9); W-P12, 2.5018-
(8); W-P21, 2.5069(11); W-P22A, 2.471(3); C1-H1, 0.88(7). Selected
bond angles (deg): Cl-W-C1, 176.63(16); P11-W-P12, 79.91(3); P21-
W-P22A, 77.72(5); P11-W-P21, 94.34(3); P12-W-P22A, 107.02(5).
1
Interestingly, in going from the neutral 1a to the cationic
2a, the average W-P bond length [d(W-P)av] increases from
2.467(2) to 2.534(6) Å, i.e., by 2.7%. While the opposite
trend might have been expected on the basis of an increased
electrophilicity of the W atom, the increase in d(W-P)av
reflects the diminished W d-(P-C) σ* back-donation24 in
the WV d1 product compared to the WIV d2 starting material.
Methylidyne/chloride ligand disorder is absent in the
crystal structure of 2b, displayed in Figure 3, although in
this case one of the dmpe ligands is disordered. This disorder
was satisfactorily dealt with by placing several of the dmpe
atoms in the two positions A and B with occupancy factors
in the H NMR spectra as broad (∆ν1/2 ≈ 1100-1500 Hz)
resonances, just distinguishable from the baseline. Further-
more, the two sets of inequivalent methyl protons (2b, δ
2.71 and 1.34 ppm; 2c, δ +5.28 and -1.23 ppm) have widths
at half-height of only 160-400 Hz (cf. 2500 Hz for 2a).
Complexes 2 were further characterized in a THF solution
([2] ≈ 1 mM) by variable-temperature X-band ESR spec-
troscopy. Simple symmetric spectra were obtained for each
of the complexes; those of 2b at temperatures of 295 and
220 K are displayed in Figure 4. The giso value of 2.048
indicates that the radical is W-based, and hyperfine coupling
(25) Me´noret, C.; Spasojevic-de Bire´, A.; Quy Dao, N.; Cousson, A.; Kiat,
J.-M.; Manna, J. D.; Hopkins, M. D. J. Chem. Soc., Dalton Trans.
2002, 3731.
(26) Manna, J.; Mlinar, L. A.; Kuk, R. J.; Dallinger, R. F.; Geib, S. J.;
Hopkins, M. D. In Transition Metal Carbyne Complexes; Kreissl, F.
R., Ed.; Kluwer Academic Publishers: Dordrecht, The Netherlands,
1993; pp 75-77.
(24) (a) Orpen, A. G.; Connelly, N. G. Organometallics 1990, 9, 1206. (b)
The average P-C bond length, which is 1.818(6) Å in 2a‚C6D6 and
1.832(11) Å in 1a, exhibits the expected trend for a lower population
of antibonding P-C σ* orbitals in the former complex, but caution
should be used in interpreting this observation because of the larger
estimated standard deviations associated with these bonds.
18 Inorganic Chemistry, Vol. 46, No. 1, 2007

Cationic Tungsten(V) Methylidynes
Figure 5. Experimental (top) and simulated ESR spectra of [13C]2c‚PhCH3
in THF at 200 K.
Figure 4. Variable-temperature X-band ESR spectra of 2b in THF.
Table 2. ESR Parametersa for Tungsten(V) Methylidyne Radicals in
THF
the bent metallocene type [Cp2WRR′]+ and bear little
relevance to the octahedral methylidynes studied here.
However, a somewhat related phosphine ligated WV radical
31P
183W
13C
a
T (K)
giso
line width
a
a
is [WCl2(H)2(PMe3)4]+ (giso ) 2.00, a ) 22 and 25 G),
31P
2a
2b
2c
290
200
295
200
295
200
2.0234
2.0259
2.0479
2.0503
2.0444
2.0478
20.0
10.0
23.5
9.5
17.0
7.8
34.5
35.0
31.0
31.5
31.0
31.5
52
52
45
45
45
45
b
8.0
b
8.0
b
8.0
reported by Sharp and Frank.27
The UV-visible spectra of compounds 2 were recorded
in C6H5F, THF, and MeCN solutions, in concentration ranges
of 0.3-1.0 mM, and exhibited three bands in the visible
range of 300-500 nm with ꢀ values of ca. 1000 M-1 cm-1.
These are the expected bands based on the electronic
structure treatment presented by Da Re and Hopkins for a
d1 complex of the general formula L5MtCR9c and can be
assigned as dxy f π*, π f dxy, and π f π* transitions in a
[πMtCR]4[dxy]1 ground-state configuration.
Attempted Deprotonation of 2a. While Schrock et al.
originally reported that the neutral d2 methylidynes 1 are not
susceptible to deprotonation using alkyllithium or alkoxide
bases in aromatic solvents,7a we felt that the cationic d1
systems described above might be more acidic. Somewhat
surprisingly, treatment of 2a with a range of strong bases,
including lithium diisopropylamide (LDA), benzylpotassium
(KBn), and the phosphazene base [(Me2N)3PdN]3PdNtBu,28
led to reduction rather than deprotonation, and the major
product recovered was the neutral d2 methylidyne 1a; the
a Line widths and HFCCs are in gauss. Estimated standard deviations:
31
13
1
183
(0.0001 for giso, (0.5 G for line width, a P, a C, and a H, (2 G for a
.
W
b Coupling is hardly visible because of broad lines.
31
1
31
to the four equivalent P atoms ( P, I ) /2, 100%, a P ) 31
G) is observed. Because of significant line broadening at
ambient temperature, the quintet pattern is highly distorted,
but the line width decreases upon cooling of the sample, until
at 220 K an almost regular quintet is obtained. At these low
1
temperatures, the hyperfine coupling to W (183W, I ) /2,
183
14%, a W ) 45 G) also becomes visible, as weak satellites
flank the outer lines of the main I ) 0 signal. The observed
ESR spectra of 2 were successfully simulated; hyperfine
coupling constants (HFCCs), giso values, and line widths
extracted from these simulations are listed in Table 2.
Notably, even though the singly occupied molecular orbitals
of 2 are dxy orbitals oriented perpendicular to the XsWt
CH axes, coupling to the methylidyne C atoms could also
be discerned and simulated in low-temperature spectra of
(27) (a) Sharp, P. R.; Frank, K. G. Inorg. Chem. 1985, 24, 1808. (b) See
also: Saboonchian, V.; Wilkinson, G.; Hussain-Bates, B.; Hursthouse,
M. B. Polyhedron 1991, 10, 595.
the isotopomers [13C]2 (a ≈ 8 G; see Figure 5). This
13C
(28) (a) Swesinger, R.; Schlemper, H.; Hasenfratz, C.; Willaredt, J.;
Dambacher, T.; Breuer, T.; Ottaway, C.; Fletschinger, M.; Boele, J.;
Fritz, H.; Putzas, D.; Rotter, H. W.; Bordwell, F. G.; Satish, A. V.; Ji,
G.-Z.; Peters, E.-M.; Peters, K.; von Schnering, H. G.; Walz, L. Liebigs
Ann. Chem. 1996, 1055. (b) Swesinger, R.; Schlemper, H. Angew.
Chem., Int. Ed. Engl. 1987, 26, 1167. (c) Swesinger, R.; Hasenfratz,
C.; Schlemper, H.; Walz, L.; Peters, E.-M.; Peters, K.; von Schnering,
H. G. Angew. Chem., Int. Ed. Engl. 1993, 32, 1361.
suggests that probably hyperfine coupling to the chloride (for
2a and 2b) and to the methylidyne proton also occurs, but
the line widths are too high to resolve the corresponding
HFCCs. Several other W d1 complexes have been previously
characterized by ESR spectroscopy, but the majority are of
Inorganic Chemistry, Vol. 46, No. 1, 2007 19

van der Eide et al.
Scheme 2
products associated with the reductant were not fully
identified.29 Another, less symmetrical, diamagnetic W-con-
taining product was also observed in minor amounts, and
the proportion of this species was observed to increase when
larger excesses of base were employed. Indeed, it was the
dominant product when 2a was treated with a full 2 equiv
of either LDA or KBn, suggesting that this product arises
from deprotonation of 1a after one-electron reduction of 2a.
Accordingly, it was determined that a methyl group of a
coordinated trimethylphosphine ligand in 1a can be depro-
tonated smoothly in THF by LDA or KBn, yielding the
yellow, highly pentane-soluble product (PMe3)3(Me2PCH2)-
WtCH (3; Scheme 2), a neutral tungsten(IV) methylidyne
complex that contains a formally monoanionic (dimeth-
ylphosphino)methyl ligand.30 With LDA, the reaction pro-
ceeded very slowly, requiring more than 1 week to achieve
>80% conversion, but the more basic KBn furnishes 3 in
30 min in an equally clean reaction. Extraction with pentane,
followed by evaporation of the volatiles, affords 3 in 83%
isolated yield. The identity of 3 was confirmed by X-ray
analysis (vide infra) and multinuclear NMR spectroscopy.
Figure 6. Crystalmaker depiction (50% probability thermal ellipsoids) of
the molecular structure of 3. H atoms, except the methylidyne H (arbitrary
radius), are omitted for clarity. Selected bond lengths (Å): W1-C1, 1.814-
(5); W1-C2, 2.378(5); W1-P1, 2.3914(14); P1-C2, 1.767(6); W1-P2,
2.4353(13); W1-P3, 2.4361(16); W1-P4, 2.4377(14); C1-H1, 0.75(6).
Selected bond angles (deg): C1-W1-P3, 106.65(19); C1-W1-P2, 84.69-
(17); C1-W1-P4, 84.68(16); C1-W1-P1, 121.15(19); C1-W1-C2,
164.6(2); P2-W1-P4, 169.30(4); P1-W1-P3, 132.20(5); C2-W1-P3,
88.71(14); C2-W1-P1, 43.49(14).
-
The incipient PCH2 group that results from deprotonation
of 1a apparently displaces Cl- in a fast intramolecular
nucleophilic substitution reaction. It should be noted that 1a
itself does not engage in bimolecular nucleophilic substitution
reactions with LiMe, LiCH2CMe3, LiBEt3H, or LiOCMe3,
as reported by Schrock and co-workers.7a
Figure 7. 31P{1H} NMR spectrum of 3 in toluene-d8 at 295 K.
The solid-state structure of 3 is displayed in Figure 6.
Although the asymmetric unit consists of one molecule of
3, the molecule, nevertheless, possesses near-Cs symmetry.
The geometry around W is perhaps best described as a highly
distorted octahedron in which C1, P2, and P4 occupy more
or less regular positions and C2, P1, and P3 are distorted
from their regular positions. For P3, this distortion reduces
unfavorable steric interactions between the methyl groups
attached to it and those attached to P2 and P4; obviously,
the bond between P1 and C2 displaces these atoms from the
normal octahedral sites. With regard to the CH2PMe2 ligand,
P1 is located “pseudo-cis” [angle C1-W1-P1 is 121.2(2)°]
and C2 is located “pseudo-trans” [angle C1-W1-C2 is
164.6(2)°] relative to the methylidyne C1. The WtC and
W-C bond lengths are 1.814(5) and 2.378(5) Å, respectively,
rather long for WtC and W-C bonds, probably because of
the strongly σ-donating nature of the opposing alkyl and
methylidyne ligands. The constrained nature of the CH2PMe2
ligand ameliorates this effect somewhat because these bonds
are both shorter than the analogous bonds observed in
(dmpe)2W(nBu)tCH, which are 1.827(5) and 2.405(6) Å,
respectively.7b The bond between W1 and P1 must be quite
strong, judging from the short bond length of 2.3914(14) Å,
but also the average bond length of 2.436(1) Å of the other
three W-P bonds is smaller than the 2.467(2) Å bond length
found in 1a. This shortening of the W-P bonds in 3 relative
to 1a can probably be attributed to a decrease in steric
crowding in 3 due to the loss of the chloride ligand, allowing
the phosphines to move closer to the W center.
(29) LDA as a reductant: (a) Ashby, E. C.; Mehdizadeh, A.; Keshpande,
A. K. J. Org. Chem. 1996, 61, 1322. (b) Newkome, G. R.; Hager, D.
C. J. Org. Chem. 1982, 47, 601. (c) Denny, W. A.; Herbert, J. M.;
Woodgate, P. D. Aust. J. Chem. 1988, 41, 139. (d) Newkome, M.;
Burchill, M. T. J. Am. Chem. Soc. 1984, 106, 8276.
(30) (a) Janak, K. E.; Tanski, J. M.; Churchill, D. G.; Parkin, G. J. Am.
Chem. Soc. 2002, 124, 4182. (b) Baker, R. T.; Calabrese, J. C.; Harlow,
R. L.; Williams, I. D. Organometallics 1993, 12, 830. (c) Cotton, F.
A.; Cannich, J. M.; Luck, R. L.; Vidyasagar, K. Organometallics 1991,
10, 352. (d) Young, S. J.; Olmstead, M. M.; Knudsen, M. J.; Schore,
N. E. Organometallics 1985, 4, 1432. (e) Chiu, K. W.; Howard, C.
G.; Rzepa, H. S.; Sheppard, R. N.; Wilkinson, G.; Galas, A. M. R.;
Hursthouse, M. B. Polyhedron 1982, 1, 441. (f) Karsch, H. H.; Klein,
H.-F.; Schmidbaur, H. Angew. Chem., Int. Ed. Engl. 1975, 14, 637.
(g) Werner, H.; Gotzig, J. Organometallics 1983, 2, 547. (h) Holland,
A. W.; Bergman, R. G. Organometallics 2002, 21, 2149. (i) Harris,
T. V.; Rathke, J. W.; Muetterties, E. L. J. Am. Chem. Soc. 1978, 100,
6966. (j) Werner, H.; Werner, R. J. Organomet. Chem. 1981, 209,
C60. (k) Hajela, S.; Bercaw, J. E. Organometallics 1994, 13, 1147.
(l) Chatt, J.; Davidson, J. M. J. Chem. Soc. 1965, 843.
The 31P{1H} NMR spectrum (toluene-d8; Figure 7) of 3
shows three resonances, all of them accompanied by W
20 Inorganic Chemistry, Vol. 46, No. 1, 2007

Cationic Tungsten(V) Methylidynes
satellites. The doublet of triplets at -52.8 ppm can be
1:1:1 ratio of broad resonances at 1.83, 1.74, and 1.09 ppm,
each integrating to six protons, is finally obtained. We
attribute this low-temperature behavior to a slow (on the
NMR time scale) rate of rotation around the W-P bonds of
the mutually trans PMe3 groups, thereby placing the methyl
groups on each PMe3 ligand in three chemically distinct
positions. It is very well possible that the strong W d-(P-
C) σ* back-bond, which is of π symmetry, is the reason for
the slow rotation.
1
assigned to the CH2PMe2 ligand, on the basis of H{31P}
NMR selective decoupling experiments. This assignment is
supported by the fact that in related complexes containing
both CH2PMe2 and PMe3 ligands the highest-field 31P NMR
resonance is usually assignable to the former ligand.31 The
Cs symmetry of 3 is indicated by the observation of one
signal for the mutually trans PMe3 ligands at -30.7 ppm.
While this resonance appears to be a triplet, it is, in fact, a
doublet of doublets with two nearly identical 2JPP values of
13.5 and 14.0 Hz. The weak coupling between the P atoms
of the CH2PMe2 and the unique PMe3 ligand (2JPP ) 26.5
Hz) can be explained by a significantly bent P1-W1-P3
arrangement; an angle of 132.20(5)° was found in the solid
state. It seems, therefore, that the structure of 3 in solution
is similar to that in the solid state. Any appreciable exchange
of the two types of PMe3 ligands does not occur because
their 31P (and 1H) NMR resonances do not coalesce up to a
temperature of 370 K. The static nature of 3 contrasts with
the dynamic behavior of the tungsten(II) hydride WH-
(PMe3)4(CH2PMe2),31b which displays temperature-dependent
NMR spectra. At elevated temperatures, decomposition of
3 is significant, as free PMe3 becomes visible in the 1H and
31P NMR spectra and a dark-gray material is deposited on
the wall of the NMR tube.
Although 1b also undergoes deprotonation to afford a
product that appears to be similar to 3, we have been unable
to obtain it in pure form. The reaction proceeds only very
slowly with LDA, while with KBn a significant amount of
(dmpe)2W(CH2Ph)tCH is formed by nucleophilic substitu-
tion of the chloride ligand. NMR spectroscopy indicates that
the methyl (as opposed to the methylene) group is depro-
tonated and, as expected, there are no symmetry elements
left in the product. For example, there are four resonances
in the 31P{1H} NMR spectrum and seven distinct methyl
1
resonances in the H NMR spectrum, and the two W-CH2
protons are diastereotopic.
Conclusions
One-electron oxidation of the classical Schrock methyli-
dynes using the trityl cation as the oxidant occurs smoothly
to give the cationic methylidyne compounds 2, the first
monomeric d1 methylidynes. X-ray data and ESR spectros-
copy indicate that the single electron is largely accom-
modated in a metal-based orbital, perhaps offering a rationale
for the stability of these species as monomers rather than
dimers. Attempts to deprotonate the compounds invariably
led to one-electron reduction with the bases employed, but
the neutral methylidyne complex 1a so produced was
deprotonated by further base at one of the Me3P ligands.
In the 1H NMR spectrum, the methylidyne and methylene
protons are located at 8.61 and -1.33 ppm, respectively, as
first-order multiplets due to coupling to the P nuclei as well
as to each other (4JHH ) 0.9 Hz). The methylidyne C-H
1
1
coupling constant JCH was measured directly from the H
NMR spectrum of [13C]3 and is only 125 Hz, even lower
than the already low value of 132 Hz for [13C]1a. The
aliphatic region of the spectrum consists of a doublet of
doublets for the CH2PMe2 group, a doublet for the unique
PMe3 ligand, and a virtual triplet32 for the two mutually trans
PMe3 ligands. Upon cooling of the sample, broadening of
the latter resonance occurs, and at ca. 200 K, it is split into
two broad signals in a 2:1 ratio. Further cooling to 185 K
splits the largest of the two resonances into two, so that a
Acknowledgment. Funding for this work came from the
Natural Sciences and Engineering Research Council of
Canada in the form of a Discovery Grant (to W.E.P.) and
the Alberta Ingenuity Fund in the form of a Studentship (to
E.F.v.d.E.). The authors thank Prof. Michael Hopkins
(Chicago) for useful discussions.
(31) (a) Gibson, V. C.; Grebenik, P.; Green, M. L. H. J. Chem. Soc., Chem.
Commun. 1983, 1101. (b) Gibson, V. C.; Graimann, C. E.; Hare, P.
M.; Green, M. L. H.; Bandy, J. A.; Grebenik, P. D.; Prout, K. J. Chem.
Soc., Dalton Trans. 1985, 2025. (c) Wenzel, T. T.; Bergman, R. G. J.
Am. Chem. Soc. 1986, 108, 4856. (d) Mainz, V. V.; Andersen, R. A.
Organometallics 1984, 3, 675.
Supporting Information Available: Crystallographic data
(CIF) for 2a‚C6D6, 2b, and 3. This material is available free of
charge via the Internet at http://pubs.acs.org.
(32) Harris, R. K. Can. J. Chem. 1964, 42, 2275.
IC0611342
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