Convenient synthesis of W(≡CR)X3(dme) compounds from W(≡CR)(OBut)3 triple-bond metathesis products

Article abstract of DOI:10.1021/om970394b

Tungsten-alkylidyne complexes of the type W(≡CR)X₃(dme) (R = Bu^t, Prⁿ, Ph; X = Cl, Br; dme = 1,2-dimethoxyethane) are prepared in 77-87% yields from reactions between W(≡CR)(OBu^t)₃ and BX₃

Full text of DOI:10.1021/om970394b

3572
Organometallics 1997, 16, 3572-3573
Con ven ien t Syn th esis of W(tCR)X3(d m e) Com p ou n d s
fr om W(tCR)(OBu t)3 Tr ip le-Bon d Meta th esis P r od u cts
Margaret A. Stevenson and Michael D. Hopkins*
Department of Chemistry, University of Pittsburgh, Pittsburgh, Pennsylvania 15260
Received May 12, 1997X
Sch em e 1
Summary: Tungsten-alkylidyne complexes of the type
W(tCR)X3(dme) (R ) But, Prn, Ph; X ) Cl, Br; dme )
1,2-dimethoxyethane) are prepared in 77-87% yields
from reactions between W(tCR)(OBut)3 and BX3 in the
presence of dme.
Compounds of the type M(tCR)X3(dme) (M ) Mo, W;
X ) Cl, Br; R ) Me, But, CH2But, Ph; dme ) 1,2-
dimethoxyethane)1-4 are of central importance in the
chemistry of group 6 metal-alkylidyne complexes:5 they
are key starting materials for the synthesis of a variety
of high-valent6,7 and low-valent8 metal-alkylidyne com-
pounds; they are precursors to compounds containing
ligands derived from the alkylidyne moiety, including
metallacyclic and cyclopentadienyl compounds,9 olefin-
metathesis catalysts,7 and other derivatives;10 and they
catalyze the polymerization of unsaturated substrates
both in solution11 and when supported on oxide sur-
faces.12 Even broader applications of these compounds
as synthons and catalysts could be envisioned were it
not for the fact that the procedures by which they are
prepared are neither general nor high yielding: the
route to the widely studied compound W(CBut)Cl3(dme)
(Scheme 1a) cannot be adapted to the preparation of
derivatives with alkylidyne R groups other than tert-
butyl and is expensive (multiple neopentyl groups are
consumed en route) and time consuming (involving a
difficult distillation of W(CBut)(CH2But)3),1,3 and the
route to bromo derivatives of the type W(CR)Br3(dme)
(Scheme 1b), while simpler and more flexible, does not
provide the tert-butyl compounds and is unlikely to be
useful for the preparation of derivatives with reactive
alkylidyne R groups because it employs Br2 as a
reagent.4 In at least one case, the limitations imposed
by these syntheses prompted the development of alter-
native starting materials to M(CR)X3(dme) complexes.13
X Abstract published in Advance ACS Abstracts, J uly 1, 1997.
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Our interest in the synthesis and properties of
conjugated materials derived from metal-alkylidyne
building blocks14 led us to seek a more general synthetic
route to W(CR)X3(dme) complexes. Compounds of the
type W(CR)(OR′)3 are attractive precursors in this
regard because derivatives with a wide range of alkyl-
idyne R groups can straightforwardly be prepared by
alkyne and triple-bond metathesis reactions,15 with the
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S0276-7333(97)00394-4 CCC: $14.00 © 1997 American Chemical Society

Communications
Organometallics, Vol. 16, No. 16, 1997 3573
reactions between alkynes or nitriles and readily avail-
from W(CPh)(OBut)3 in 77% yield. Preliminary evidence
suggests that this synthetic procedure will also afford
more complex compounds relevant to our efforts to
prepare conjugated materials from metal-alkylidyne
building blocks; the reaction between 1,4-C6H4{CW-
(OBut)3}221 and BCl3/dme in 1:1 pentane/dichloromethane
(the latter solvent being required to dissolve the starting
material) provides a compound identified as 1,4-C6H4-
16
able W2(OBut)6 being particularly efficient (80-90%
yield) and versatile (R ) alkyl, aryl, CHdCH2, CtCEt,
CN, SiMe3, NEt2, SBut) routes to W(CR)(OBut)3.17,18 We
report herein a simple procedure for affecting this
transformation: the treatment of W(CR)(OBut)3 with
BX3 (X ) Cl, Br) in the presence of dme provides W(CR)-
X3(dme) in >75% yield (Scheme 1c).
22
The synthesis of W(CPh)Cl3(dme) by this method is
representative of those that we have investigated to
{CWCl3(dme)}2 in 86% yield, although the poor solu-
bility and solution-phase stability of the product have
limited our efforts to fully characterize it. We are
presently working to extend this methodology to deriva-
tives with heteroatom-containing R groups and to the
preparation of Mo(CR)X3(dme) compounds.
17
date. A stirred, -78 °C solution of W(CPh)(OBut)3
(0.250 g, 0.51 mmol) in a mixture of pentane (20 mL)
and dme (0.5 mL, 4.8 mmol) was treated with a room-
temperature solution of BCl3 (1.5 mL, 1 M in heptane,
1.5 mmol). A dark precipitate formed immediately. The
reaction mixture was allowed to slowly warm to room
temperature, during which time its color and appear-
ance underwent several dramatic changes. The dark
precipitate dissolved to give a bright orange solution,
from which an oily brown material was subsequently
deposited. The reaction was complete within 2 h, at
which point the solution was colorless and the crude
product was present as a purple, microcrystalline
precipitate. The product was isolated by filtration and
extracted into toluene. The resulting solution was
filtered through Celite, reduced in volume under vacuum
to ca. 3 mL, and diluted with pentane (ca. 20 mL), which
induced the precipitation of microcrystalline W(CPh)-
Cl3(dme) (0.203 g, 0.43 mmol, 84% yield).19 The product
can also be recrystallized from a concentrated toluene
solution at -40 °C. Because of the air sensitivity of the
starting materials and product, all manipulations were
performed under a nitrogen atmosphere and solvents
were rigorously dried prior to use.
Although attempts to optimize these procedures are
still in progress, we can initially note that use of fewer
than 3 equiv of BX3 is deleterious: treating W(CPh)-
(OBut)3 with 2 equiv of BCl3 under conditions otherwise
identical to those above provides W(CPh)Cl3(dme) in
50% yield (vs 84% when 3 equiv are used), which
precipitates from a yellow (on account of unreacted
W(CPh)(OBut)3) rather than colorless reaction mixture.
The failure of the reaction to go to completion with 2
equiv of BCl3 may be the result of the increased steric
bulk and/or decreased Lewis acidity of the presumed
B(OBut)3-xClx products of alkoxide/halide metathesis
relative to those of BCl3 or of the inherent instability of
B(OBut)3-xClx compounds with respect to disproportion-
ation and decomposition.23
This simple synthesis of W(CR)X3(dme) compounds
from W(CR)(OBut)3 provides the derivatives available
from the two previous routes to these compounds1,3,4 and
would appear to be applicable to the synthesis of
derivatives with other alkylidyne R groups as well. In
addition to being a more general route to this class of
compounds, this procedure also provides them in higher
overall yield; W(CBut)Cl3(dme) and W(CPh)Br3(dme) are
prepared in two steps from W2(OBut)6 (the common
starting material17 for all compounds in this procedure)
in overall yields of 80% (vs 50% yield from WCl6)1,3 and
70% (vs 48% yield from W(CO)6),4 respectively.
This procedure can also be applied to the synthesis
of related W(CR)X3(dme) compounds. Specifically, the
purple compounds W(CBut)Cl3(dme)1,3 and W(CPrn)Cl3-
(dme)20 can be prepared on comparable scales under the
above conditions in yields of 87% and 78%, respectively,
from W(CBut)(OBut)317 and W(CPrn)(OBut)3.17 The use
of BBr3 in place of BCl3 in this procedure provides the
corresponding bromo derivatives, as demonstrated by
the synthesis of the green compound W(CPh)Br3(dme)4
Ack n ow led gm en t. This research was supported by
National Science Foundation Grant No. CHE-9307013.
(16) (a) Akiyama, M.; Chisholm, M. H.; Cotton, F. A.; Extine, M.
W.; Haitko, D. A.; Little, D.; Fanwick, P. E. Inorg. Chem. 1979, 18,
2266-2270. (b) Chisholm, M. H.; Eichhorn, B. W.; Folting, K.;
Huffman, J . C.; Ontiveros, C. D.; Streib, W. E.; Van Der Sluys, W. G.
Inorg. Chem. 1987, 26, 3182-3186.
OM970394B
(20) 1H NMR (C6D6, 300.13 MHz, 25 °C): δ 6.39 (t, 2 H, CH3CH2CH2-
CW), 3.57 (s, 3 H, OCH3), 3.25 (s, 3 H, OCH3), 2.93 (m, 2 H, OCH2),
2.84 (m, 2 H, OCH2), 1.46 (m, 2 H, CH3CH2CH2CW), 1.10 (t, 3 H, CH3-
CH2CH2CW). 13C{1H} NMR (C6D6, 75.46 MHz, 25 °C): δ 332 (s, CtW),
78 (dme), 75 (dme), 70 (dme), 60 (dme), 46 (CH3CH2CH2CW), 28
(17) Listemann, M. L.; Schrock, R. R. Organometallics 1985, 4, 74-
83.
(18) It has been stated that this reaction “promises to make tungsten
alkylidynes among the most readily available of organometallics,
surpassing even Grignard reagents in their ease of preparation” (ref
1e, p 15).
(CH3CH2CH2CW), 15 (CH3CH2CH2CW). Anal. Calcd (found) for C8H17
-
Cl3O2W: C, 22.07 (22.05); H, 3.94 (3.85).
(21) Krouse, S. A.; Schrock, R. R. J . Organomet. Chem. 1988, 355,
(19) 1H NMR (CD2Cl2, 300.13 MHz, 25 °C): δ 7.57 (t, 2 H, Ph), 6.82
(d, 2 H, Ph), 6.74 (t, 1 H, Ph), 4.44 (s, 3 H, OCH3), 4.15 (m, 2 H, OCH2),
3.89 (m, 2 H, OCH2), 3.75 (s, 3 H, OCH3). 13C{1H} NMR (CD2Cl2, 75.46
MHz, 25 °C): δ 322 (CtW), 140 (Ph), 139 (Ph), 134 (Ph), 128 (Ph), 81
257-265.
(22) 1H NMR (CDCl3, 300.13 MHz, 25 °C): δ 7.26 (s, C6H4), 4.24 (s,
OCH3), 4.22 (s, OCH3), 4.11 (m, OCH2), 3.66 (m, OCH2).
(dme), 78 (dme), 73 (dme), 72 (dme). Anal. Calcd (found) for C11H15
Cl3O2W: C, 28.14 (28.21); H, 3.22 (3.24).
-
(23) (a) Gerrard, W.; Lappert, M. F. J . Chem. Soc. 1951, 2545-2550.
(b) Gerrard, W.; Lappert, M. F. J . Chem. Soc. 1955, 3084-3088.