Structural and reaction chemistry of tungstenocene boryl complexes

Article abstract of DOI:10.1021/om9606303

The structural and reaction chemistry of Cp₂W(H)(Bcat) (cat = O₂C₆H₄) (1) and Cp₂W-(Bcat′)2 (cat′ = O₂C₆H₃-t-Bu or O₂C₆H₂-t-Bu₂

Full text of DOI:10.1021/om9606303

5350
Organometallics 1996, 15, 5350-5358
Str u ctu r a l a n d Rea ction Ch em istr y of Tu n gsten ocen e
Bor yl Com p lexes
J ohn F. Hartwig* and Xiaoming He
Department of Chemistry, Yale University, P.O. Box 208107,
New Haven, Connecticut 06521-8107
Received J uly 29, 1996X
The structural and reaction chemistry of Cp2W(H)(Bcat) (cat ) O2C6H4) (1) and Cp2W-
(Bcat′)2 (cat′ ) O2C6H3-t-Bu or O2C6H2-t-Bu2) (2a ,b) is reported. Compound 1 was prepared
by reaction of the anion [Cp2WH]- with ClBcat, and 2a ,b were prepared by oxidative addition
of cat′BBcat′ by photochemical or thermal generation of tungstenocene. The X-ray structures
of 1 and 2a are reported, and they display geometries indicating dπ-pπ interaction. The
reaction chemistry of these compounds with small molecules involves protonation by alcohols,
water-catalyzed protonation by amines, halogenation of the hydride in 1, and resistance
toward formation of Lewis acid-base complexes. In addition, 1 undergoes photochemically
induced reductive elimination of HBcat. Remarkably, generation of tungstenocene in the
presence of cat′BBcat′ in benzene solvent led to the formation of 2 rather than oxidative
addition of the solvent.
In tr od u ction
covalent bond has become uncertain in light of the more
recent 11B NMR data of crystallographically character-
ized examples.
The chemistry of transition metal boryl compounds
has been pursued recently because of the intermediacy
of such complexes in transition metal-catalyzed hydro-
borations, the fundamental interest in electrophilic,
covalently bound ligands, and the ability of a transition
metal to stabilize the -BR2 reactive intermediate.1-21
In the late 1960’s and early 1970’s a number of metal
boryl complexes were reported,22 although the identity
of these compounds and the presence of an M-B
We and others have recently described the structural
properties of a series of metallocene boryl complexes.5,11,23
The X-ray diffraction study of Cp2W(H)(Bcat) (1) (Bcat
) B(O2C6H4)) in our work provided evidence for dπ-pπ
bonding. The group 5 complexes with metal-boron
bonding show an interesting combination of hydroborate
and boryl structural types in the case of niobium3 and
distinct endo and exo isomers in the case of tantalum.11
Little reaction chemistry of metallocene boryl complexes
has been reported.
The formation and cleavage of B-H and B-B bonds
is important in metal-catalyzed and -mediated chemis-
try of boranes. B-H oxidative addition is believed to
be a key step in catalytic hydroboration,1 and the
oxidative addition of B-B bonds may led to metal-
catalyzed diborations.12,18,24-28 On a more fundamental
level, transition metals that are not capable of cleaving
C-H or C-C bonds in hydrocarbons do add the B-B
bonds of diborane(4) derivatives. It is unclear if this
greater reactivity for borane additions is a result of
thermodynamic or kinetic effects.
X Abstract published in Advance ACS Abstracts, November 15, 1996.
(1) For a review of metal-catalyzed hydroboration see: Burgess, K.;
Ohlmeyer, M. J . Chem. Rev. 1991, 91, 1179.
(2) Hartwig, J . F.; Huber, S. J . Am. Chem. Soc. 1993, 115, 4908.
(3) Hartwig, J . F.; De Gala, S. R. J . Am. Chem. Soc. 1994, 116, 3661.
(4) He, X.; Hartwig, J . F. Organometallics 1995, 15, 400.
(5) Hartwig, J . F.; He, X. Angew. Chem., Int. Ed. Engl. 1996, 315.
(6) Waltz, K. M.; He, X.; Muhoro, C. N.; Hartwig, J . F. J . Am. Chem.
Soc. 1995, 117, 11357.
(7) Baker, T.; Ovenall, D. W.; Calabrese, J . C.; Westcott, S. A.;
Taylor, N. J .; Williams, I. D.; Marder, T. B. J . Am. Chem. Soc. 1990,
112, 9399.
(8) Basil, J . D.; Aradi, A. A.; Nripendra, K. B.; Nigam, P. R.;
Eigenbrot, C.; Fehlner, T. P. Inorg. Chem. 1990, 29, 1260-1270.
(9) Braunschweig, H.; Wagner, T. Agnew. Chem., Int. Ed. Engl.
1995, 34, 825.
(10) Knorr, J . R.; Merola, J . S. Organometallics 1990, 9, 3008.
(11) Lantero, D. R.; Motry, D. H.; Ward, D. L.; Smith, M. R., III. J .
Am. Chem. Soc. 1994, 116, 10811.
(12) Iverson, C. N.; Smith, M. R. J . Am. Chem. Soc. 1995, 117, 4403.
(13) Lu, Z.; J un, C.-H.; de Gala, S. R.; Sigalas, M.; Eisenstein, O.;
Crabtree, R. H. J . Chem. Soc., Chem. Commun. 1993, 1877-1880.
(14) Burgess, K.; van der Donk, W. A.; Westcott, S. A.; Marder, T.
B.; Baker, R. T.; Calabrese, G. C. J . Am. Chem. Soc. 1992, 114, 9350.
(15) Westcott, S. A.; Marder, T. B.; Baker, R. T.; Calabrese, J . C.
Can. J . Chem. 1993, 71, 930.
We report studies on diverse reaction chemistry with
a set of tungstenocene boryl compounds. This reactivity
demonstrates weak boryl Lewis acidity and robust
metal-boron linkages.29 Further, we report the re-
markable selectivity of the metal fragment Cp2W for
addition of B-B bonds in benzene or toluene solvent,
(16) Westcott, S. A.; Marder, T. B.; Baker, R. T. Organometallics
1993, 12, 975.
(17) Baker, R. T.; Calabrese, J . C.; Westcott, S. A.; Nguyen, P.;
Marder, T. B. J . Am. Chem. Soc. 1993, 115, 4367-4368.
(18) Nguyen, P.; Lesley, G.; Taylor, N. J .; Marder, T. B.; Pickett, N.
L.; Clegg, W.; Elsegood, M. R. J .; Norman, N. C. Inorg. Chem. 1994,
33, 4623.
(19) Wilkey, J . D.; Schuster, G. B. J . Org. Chem. 1987, 52, 2118.
(20) Eisch, J . J . J . Org. Chem. 1989, 54, 1627.
(21) Eisch, J . J .; Tamao, K.; Wilcsek, R. J . J . Am. Chem. Soc. 1975,
97, 895.
(23) Hartwig, J . F.; De Gala, S. R. J . Am. Chem. Soc. 1994, 116,
3661.
(24) Ishiyama, T.; Matsuda, N.; Miyaura, N.; Suzuki, A. J . Am.
Chem. Soc. 1993, 115, 11018-11019.
(25) Ishiyama, T.; Matsuda, N.; Murata, M.; Ozawa, F.; Suzuki, A.;
Miyaura, N. Organometallics 1996, 15, 713-720.
(26) Baker, R. T.; Nguyen, P.; Marder, T. B.; Westcott, S. A. Angew.
Chem., Int. Ed. Engl. 1995, 34, 1336.
(27) Brown, S. D.; Armstrong, R. W. J . Am. Chem. Soc. 1996, 118,
6331-6332.
(28) Maderna, A.; Pritzkow, H.; Siebert, W. Angew. Chem., Int. Ed.
Engl. 1996, 35, 1501.
(29) Rablen, P. R.; Hartwig, J . F.; Nolan, S. P. J . Am. Chem. Soc.
1994, 116, 4121.
(22) A number of similar complexes were reported previously. Their
spectroscopic characteristics make it unlikely that they are true metal-
boryl species: Schmid, G. Angew. Chem., Int. Ed. Engl. 1970, 9, 819.
S0276-7333(96)00630-9 CCC: $12.00 © 1996 American Chemical Society

Tungstenocene Boryl Complexes
Organometallics, Vol. 15, No. 25, 1996 5351
Ta ble 1. Cr ysta l a n d Da ta Collection P a r a m eter s
for 1
A. Crystal Data
empirical formula
fw
C16H15O2BW
433.95
cryst color
habit
pale yellow
prism
cryst dimens (mm)
cryst system
no. reflcns used for unit cell
determinatn (2θ range (deg))
ω scan peak width at half-height 0.23
lattice param (Å, deg)
0.10 × 0.20 × 0.40
monoclinic
24 (30.2-38.4)
a ) 10.118(4), b ) 10.539(2),
c ) 13.193(2), â ) 100.46(2)
1383.6(7)
V (Å3)
space group
Z value
D
P21/n (No. 14)
4
2.083
824
85.23
calc (g/cm3)
F igu r e 1. ORTEP drawing of 1.
F000
µ(Mo KR) (cm-1
)
Sch em e 1
B. Intensity Measurements
Rigaku AFC5S
Mo KR (0.710 69)
-125
diffractometer
radiation (λ (Å))
temp (°C)
attenuators
Zr foil (factors: 2.3, 5.3, 11.7)
take-off angle (deg)
detector aperture
cryst to detector dist (cm)
scan type
6.0
6.0 mm hor, 6.0 mm vert
28.5
ω-2θ
scan rate (deg/min)
scan width (deg)
2θmax (deg)
no. of reflcns measd
total
8.0 (in ω) (3 rescas)
1.52 + 0.30 tan θ
60.0
which are known to react with the Cp2W fragment. The
structural details of a hydrido boryl and bis(boryl) com-
plex of tungstenocene are also reported. Portions of this
work have been reported in communication form.3,5
4133
unique
corrs
3918 (Rint ) 0.078)
Lorentz-polarization, abs
(transm factors: 0.73-1.00)
Resu lts a n d Discu ssion
The formation of the tungstenocene hydrido boryl
C. Structure Solution and Refinement
struct solution
Patterson method
complex 1 is shown in Scheme 1. Addition of ClBcat to
30
refinement
full-matrix least squares
a slurry of the anion {Li{Cp2WH]}4 in benzene or
function minimized
least-squares weights
p-factor
∑w(|Fo| - |Fc|)2
toluene solution led to formation of the hydrido boryl
compound 1 in 28-70% yield after filtration, concentra-
tion, and layering with pentane. Higher yields were ob-
tained by crystallization from toluene/pentane mixtures
at -35 °C. Crystallization from benzene/pentane at
room temperature gave lower yields but led to the form-
ation of crystals suitable for an X-ray diffraction study.
X-r a y Str u ctu r e of 1. Compound 1 crystallized in
space group P21/n, and the structure was solved by
Patterson methods. An ORTEP drawing is provided in
Figure 1; tables of crystal parameters, bond distances,
and bond angles are given in Tables 1-3. The structure
consisted of well-separated monomeric units with no
short intermolecular contacts. The overall pseudotet-
rahedral geometry of 1 has similar bond angles to an
alkyl hydride of tungsten,31 and the B-H distance is
greater than 2 Å. Thus, no B-H interaction exists. The
boryl ligand geometry is similar to those of the isoelec-
tronic alkyl alkylidenes of tantalum.32 The well-
developed molecular orbital description of the bent
metallocene fragment dictates that the carbene substit-
uents be directed toward the Cp ligands in a sterically
disfavored geometry. In order for a π-interaction be-
tween the tungsten and boryl ligand to occur, a similar
geometry must be adopted. Indeed the boryl oxygens
are directed toward the Cp ligands in a carbene-like
geometry. Moreover, the tungsten boryl distance ap-
4Fo2/σ2(Fo
)
2
0.01
anomalous dispersion
no. observns (I > 3.00σ(I))
no. variables
all non-hydrogen atoms
2571
185
reflcn/param ratio
residuals: R, Rw
13.90
0.027, 0.028
1.50
goodness of fit indicator
max shift/error in final cycle
0.00
max peak in final diff map (e/Å3) 0.83
min peak in final diff map (e/Å3) -1.17
Ta ble 2. Bon d Dista n ces for 1a
2.291(6) C1C6
W-C7
W-C8
W-C9
W-C10
W-C11
W-C12
W-C13
W-C14
W-C15
W-C16
W-B
1.404(8)
1.417(9)
1.399(9)
1.391(9)
1.390(9)
1.39(1)
1.40(1)
1.40(1)
1.41(1)
1.43(1)
1.41(1)
1.38(1)
1.41(1)
1.40(1)
1.37(1)
2.294(8) C2C3
2.310(8)
2.328(7)
2.280(6)
2.288(6)
2.288(6)
2.297(7)
2.310(7)
2.326(7)
2.190(7)
1.375(7)
1.444(8)
1.370(7)
1.444(8)
1.381(9)
C3C4
C4-C5
C5C6
C7-C8
C7-C11
C8-C9
C9-C10
C10-C11
C12-C13
C12-C16
C13-C14
C14-C15
C15-C16
O1-C1
O1-B
O2-C6
O2-B
C1-C2
a
Distances are in angstroms. Estimated standard deviations
in the least significant figure are given in parentheses.
pears shorter than predicted from a combination of
covalent radii for the tungstenocene metal and boryl
boron atoms. In addition to the alkyl hydride of
tungestenocene, a number of Cp2W-C(sp2) bond dis-
(30) Francis, B. R.; Green, M. L. H.; Luong-thi, T.; Moser, G. A. J .
Chem. Soc., Dalton Trans. 1976, 1339.
(31) Herberich, G. E.; Barlage, W.; Linn, K. J . Organomet. Chem.
1991, 414, 193.
(32) Schrock, R. R. J . Am. Chem. Soc. 1990, 112, 1642.

5352 Organometallics, Vol. 15, No. 25, 1996
Hartwig and He
Ta ble 3. Selected Bon d An gles (d eg) for 1
Cp centroid 1-W-Cp centroid 2 144 W-B-O1
127.2(4)
127.1(4)
Cp centroid 1-W-B
Cp centroid 1-W-H1
Cp centroid 2-W-B
Cp centroid 2-W-H1
105 W-B-O2
105 O1-B-O2 105.7(5)
105 B-W-H
78(2)
101
Sch em e 2
F igu r e 2. ORTEP drawing of 2a . Hydrogen atoms are
omitted for clarity.
Ta ble 4. Cr ysta l a n d Da ta Collection P a r a m eter s
for 2a
A. Crystal Data
empirical formula
fw
cryst color/habit
cryst dimens (mm)
cryst system
no. reflcns used for unit cell
determinatn (2θ range (deg))
lattice params (Å, deg)
C36H40O4B2W
742.18
pale yellow plates
0.08 × 0.10 × 0.12
monoclinic
tances are known.33-35 The metal-boryl distance is
similar to those of the Cp2W-C(sp2) bond lengths.
Thus, the W-B distance is shortened by the difference
in covalent radii between sp2-hybridized carbon and
three-coordinate boron, which is approximately 0.05-
0.1 Å.36 This small difference alone would not support
the presence of a π-interaction. However, the combina-
tion of sterically disfavored geometry and slightly
shortened W-B distance suggests the presence of a
weak interaction. Consistent with this interaction being
weak, the unsymmetric 4-methylcatecholate version of
25 (10.3-18.0)
a ) 14.829(4), b ) 7.976(2),
c ) 27.282(5), â ) 98.76(2)
3189(2)
P2/n (No. 13)
4
1.546
1488
37.34
V (Å3)
space group
Z value
D
calc (g/cm3)
F000
µ(Mo KR) (cm-1
)
1
1 showed no hindered rotation of the boryl group by H
B. Intensity Measurements
or 13C NMR spectrometry down to -80 °C that would
be detected by observation of a broadened Cp resonance.
The substituted complex was prepared in analogy to the
preparation of 1, and since no variable-temperature
behavior was observed, further studies with this com-
plex were not pursued.
diffractometer
radiation (λ (Å))
temp (°C)
Enraf-Nonius CAD-4
Mo KR (0.710 69)
-119
Zr foil (factor ) 20.4)
2.8°
2.0-2.5 mm hor/2.0/mm vert
21 cm
ω-2θ
attenuator
take-off angle (deg)
detector aperture
cryst to detector dist (cm)
scan type
Syn th esis of Bis(bor yl) Com p lexes Cp 2W(Bca t′)2
(2a ,b). The synthesis of bis(boryl) complex 2a ,b by
oxidative addition of diboron compounds is shown in
Scheme 2. Irradiation of a mixture of Cp2WH2 and the
diboron compounds Cat′BBCat′ in benzene solvent gave
2a ,b in 92% yields by NMR spectroscopy and 45-57%
yields of isolated material. Photolysis of Cp2WH2 is
known to generate the reactive intermediate Cp2W,
which readily inserts into aromatic C-H bonds. This
intermediate does not insert into C-C bonds, and few
complexes are known to add C-C bonds including those
between two sp2-hybridized C-C bonds. However,
photolysis of Cp2WH2 in the presence of only 1 equiv of
cat′BBcat′ in benzene solvent led to the high yield
formation of Cp2W(Bcat′)2 (2a , cat′ ) 4-t-BuC6H3O2B;
2b, cat′ ) 3, 5-t-Bu2C6H2O2B). The products were
isolated in analytically pure form, suitable for X-ray
analysis in the case of 2a , by concentration of the
reaction solution and layering with pentane. The 11B
NMR chemical shifts were similar to, but shifted slightly
downfield of, that for 1. Photolysis of phenyl hydride
complex Cp2W(Ph)(H), the product of solvent oxidative
addition, in the presence of cat′BBcat′, for 3 h, did not
give 2a , demonstrating that 2a was formed as a kinetic
product. This kinetic selectivity is not simply a steri-
scan rate (deg/min)
scan width (deg)
2θmax (deg)
no. of reflcns measd
total
1.0-16.5 (in ω)
0.53 + 1.10 tan θ
52.6
7198
unique
corrs
6929 (Rint ) 0.078)
Lorentz-polarization, abs
(transm factors: 0.77-1.00)
C. Structure Solution and Refinement
struct solution
refinement
function minimized
least-squares weights
p-factor
anomalous dispersion
no. observns (I > 3.00σ(I))
no. variables
Patterson method
full-matrix least squares
∑w(|Fo| - |Fc|)2
4Fo2/σ2(Fo
0.03
)
2
all non-hydrogen atoms
4244
388
10.94
0.041, 0.050
1.69
reflcn/param ratio
residuals: R, Rw
goodness of fit indicator
max shift/error in final cycle
0.001
max peak in final diff map (e/Å3) 1.29
min peak in final diff map (e/Å3) -2.71
cally driven phenomenon, considering the lack of addi-
tion of sp2-sp2 C-C bonds, and most likely results from
the ability of the nucleophilic Cp2W fragment to coor-
dinate to the electrophilic boron center as part of the
reaction mechanism.
X-r a y Str u ctu r e of 2a . An X-ray diffraction study
of 2a was conducted on a sample obtained from a
benzene/pentane solvent mixture. Compound 2a crys-
tallized in space group P2/n and showed well-separated
monomeric units with no intermolecular contacts. An
(33) Couldwell, C.; Prout, K. Acta Crystallogr. 1979, 35B, 335.
(34) J ernakoff, P.; Cooper, N. J . J . Am. Chem. Soc. 1987, 109, 2173.
(35) J ernakoff, P.; Cooper, N. J . J . Am. Chem. Soc. 1989, 111, 7424.
(36) Odum, J . D. In Comprehensive Organometallic Chemistry;
Wilkinson, G., Stone, F. G. A., Abel, E. W., Eds.; Pergamon Press:
Oxford, U.K., 1982; Vol. 6, pp 256-263.

Tungstenocene Boryl Complexes
Ta ble 5. Bon d Dista n ces for 2a
Organometallics, Vol. 15, No. 25, 1996 5353
Sch em e 3
W-C21
W-C22
W-C23
W-C24
W-C25
W-C26
W-C27
W-C28
W-C29
W-C30
W-B1
2.274(8)
2.309(8)
2.295(9)
2.318(9)
2.332(8)
2.262(8)
2.301(8)
2.33(1)
2.34(1)
2.324(8)
2.19(1)
2.23(1)
1.40(1)
1.42(1)
1.40(1)
1.45(1)
1.38(1)
1.43(1)
1.35(1)
1.38(1)
1.36(1)
1.37(1)
1.41(1)
1.38(1)
1.40(1)
1.54(1)
1.32(2)
1.43(3)
C5-C6
1.37(1)
1.55(1)
1.55(1)
1.52(1)
1.37(1)
1.38(1)
1.42(1)
1.39(1)
1.39(1)
1.54(1)
1.41(1)
1.52(1)
1.54(1)
1.54(1)
1.42(1)
1.42(1)
1.40(1)
1.44(1)
1.43(1)
1.41(1)
1.41(1)
1.43(1)
1.44(1)
1.40(1)
1.35(2)
1.36(3)
1.34(3)
1.34(3)
C7-C8
C7-C9
C7-C10
C11-C12
C11-C16
C12-C13
C13-C14
C14-C15
C14-C17
C15-C16
C17-C18
C17-C19
C17-C20
C21-C22
C21-C25
C22-C23
C23-C24
C24-C25
C26-C27
C26-C30
C27-C28
C28-C29
C29-C30
C31-C32
C31-C36
C33-C34
C35-C36
Sch em e 4
W-B2
O1-C1
O1-B1
O2-C6
O2-B1
O3-C11
O3-B2
O4-C16
O4-B2
C12-C2
C1-C6
C2-C3
C3-C4
C4-C5
C4-C7
C32-C33
C34-C35
is more electrophilic and sterically hindered than ClB-
30
cat, with {Li[Cp2WH]}4 gave only the product of
addition to the Cp-ring 3a rather than addition to the
metal center. This compound was isolated in 60% yield.
Catecholboryl complex 1 was converted to a similar
borylcyclopentadienyl compound 3b, in 82% yield by
addition of a catalytic amount (ca. 0.1 equiv) of ClBcat
to a C6D6 solution of 1. Addition of 0.1 equiv of methyl-
substituted B-chlorocatecholborane, ClB(O2C6H3-3-Me),
led to incorporation of the methylcatecholboryl group
into the rearranged product. Trace amounts of cationic
tungestenocene trihydride product39 were observed upon
addition of stoichiometric quantities of ClBcat to 1,
suggesting the presence of free HCl during the reaction.
Alternatively, catecholborylcyclopentadienyl complex 3b
was prepared in 21% isolated yield without isolation of
the boryl intermediate 1. Addition of 1.2 equiv of ClBcat
to Li[Cp2WH] followed by stirring for 2 h gave 3b.
Borylcyclopentadienyl compounds have been sought for
their ability to act as a ligand-based coordination site
for substrates.40,41
It is likely that the electrophilicity of the haloborane
controls the rate of the borane-catalyzed formal migra-
tion, and the rearrangement is certainly not a simple,
intramolecular migration. Rather it appears to occur
by an electrophilic addition to the coordinated cyclo-
pentadienyl ring and elimination of HCl or HBr that
subsequently reacts at the M-B bond to provide the
tungsten hydride and regenerate the haloborane cata-
lyst (Scheme 4). An electrophilic addition of BI3 to
ferrocene has been observed,42 and a recent structure
of the product of addition of an alkyl dichloroborane to
Cp2WH2, (i-PrBCl2C5H5)CpWH2,43 has been reported.
This compound is analogous to the proposed intermedi-
ate in the haloborane-catalyzed rearrangements of the
boryl complexes. The HCl remained incorporated in this
product. Migration of coordinated boranes44 and silyl
a
Distances are in angstroms. Estimated standard deviations
in the least significant figure are given in parentheses.
Ta ble 6. Selected Bon d An gles (d eg) for 2a
Cp centroid 1-W-Cp centroid 2 142
W-B1-O2 126.1(6)
Cp centroid 1-W-B1
Cp centroid 1-W-H2
Cp centroid 2-W-B1
Cp centroid 2-W-B2
W-B1-O1
105
105
104
105
O1-B1-O2 106.8(7)
W-B2-O3 124.6(6)
W-B2-O4 126.6(7)
O3-B2-O4 108.8(8)
127.0(7) B1-W-B2
78.0(4)
ORTEP drawing is provided in Figure 2, data collection
and crystal parameters are given in Table 4, and
distances and angles are provided in Tables 5 and 6.
The unit cell contained one benzene molecule for each
tungsten complex. The two boryl ligands were oriented
in a fashion that allows for π-bonding between the basic
metal center and each electrophilic boryl, the same
orientation as was observed in boryl hydride 1. Of
course, steric effects also strongly favor the observed
geometry in 2a . Moreover, the metal-boron distances
of 2a were similar to the M-B distances for 1, which
appeared to be shorted by π-bonding. Finally, the
B-W-B angle of 78(2)° was identical to the H-W-B
angle of 78(2)° and the calculated ideal angle for d2 Cp2-
ML2 compounds.37 The B-M-B angles in some pseudo
square planar and octahedral bis(boryl) compounds have
been less than the idealized 90°,4,12 and the angle in a
recently reported Co(II) bis(boryl) was only 68°.38 In
the case of 2a , the small B-W-B angle reflects the ideal
angle of the metallocene system and does not contain
any distortion, relative to the geometry of other metal-
locene compounds, that could be attributed to B-B
interactions. Consistent with this argument, the B-B
distance is 2.78(1) Å, far longer than the 1.678(3) Å B-B
distance in cat′BBcat′ (cat′ ) 1,2-O2C6H3-4-t-Bu).18
(39) Green, M. L. H.; McCleverty, J . A.; Pratt, L.; Wilkinson, G. J .
Chem. Soc. 1961, 4854.
(40) Klang, J . A.; Collum, D. B. Organometallics 1988, 7, 1532.
(41) Herberich, G. E.; Fischer, A. Organometallics 1996, 15, 58-
67.
(42) Ruf, W.; Fueller, M.; Siebert, W. J . Organomet. Chem. 1974,
64, C45-C47.
(43) Braunschweig, H.; Wagner, T. Chem. Ber. 1994, 127, 1613.
(44) Burlitch, J . M.; Burk, J . H.; Leonowicz, M. E.; Hughes, R. E.
Inorg. Chem. 1979, 18, 1702.
Syn th esis of Bor ylcyclopen tadien yl Com pou n ds.
Scheme 3 shows reaction chemistry that forms boryl-
cyclopentadienyl complexes. Reaction of BrBPh2, which
(37) Lauher, J . W.; Hoffmann, R. J . Am. Chem. Soc. 1976, 98, 1729.
(38) Dai, C.; Stringer, G.; Corrigan, J . F.; Taylor, N. J .; Marder, T.
B.; Norman, N. C. J . Organomet. Chem. 1996, 513, 273-275.

5354 Organometallics, Vol. 15, No. 25, 1996
Hartwig and He
Sch em e 5
Sch em e 6
rapid reaction of 1 with water would generate catBOB-
cat and Cp2WH2. We observed that catBOBcat reacts
with diethylamine to generate water and 2 equiv of Et2-
NBcat. The combination of these two reactions provides
a water catalyzed pathway for addition of amines to 1.
Thus, 1 does not react directly with amines. Its weak
Lewis acidity prevents direct N-H bond cleavage by
either participation of the boron p-orbital in a four-
centered transition state involving the amine N-H and
metal complex W-B bond or precoordination of the
amine to 1 through the amine lone pair.
groups to cyclopentadienyl ligands45-47 have also been
observed. The silyl migrations are believed to occur by
migration to a deprotonated cyclopentadienyl ligand46,47
formed in the presence of strong base or by an intramo-
lecular migration triggered by an electronic effect of an
accompanying halide ligand.45 Perhaps the silyl migra-
tions in the absence of base can also be accommodated
by the mechanism in Scheme 4, with the metal halide
and silyl groups generating catalytic amounts of chlo-
rosilanes.
Rea ction Ch em istr y of 1. A survey of the reactivity
of complex 1 with small molecules is shown in Scheme
5. This chemistry includes photochemical reductive
elimination, along with thermal reactions with halogen
sources, with protic reagents, and with Lewis bases.
Ha logen a tion . The boryl ligand was more stable
than its accompanying hydride toward halogenation.
Addition of 1 equiv of CCl4 to 1 led to the formation of
the chloroboryl complex Cp2W(Cl)(Bcat) (4) in 82% yield
by NMR spectroscopy. Compound 4 was isolated in 60-
80% yields as a brown powder by concentration of the
reaction solution after 1 h and addition of pentane.
Alternatively, this compound was crystallized from
toluene/pentane solutions as dark brown, analytically
pure, material.
P r oton a tion . Reactions of compound 1 with proton
donors are consistent with a strong W-B linkage and
weak Lewis acidity. Amines react rapidly with halobo-
ranes such as ClBcat as well as with the metallaborane
CpFe(CO)2Bcat. Reactions with B-H bonds such as
those in catecholborane is slower, however. In contrast
to rapid reactivity of amines with CpFe(CO)2Bcat, the
reaction of diethylamine with 1 showed complete and
quantitative conversion to Et2NBcat and Cp2WH2 only
after warming at 45 °C for several hours. Moreover,
attempts to conduct quantitative kinetic studies of this
reaction led to the conclusion that this reaction of amine
with 1 was catalyzed by trace amounts of water or
catBOBcat. Our rate studies showed a large difference
in rate depending on the water content of the solvent.
Reaction rates varied by roughly 1 order of magnitude
and were slowest when no hydrolysis of 1 was observed
in the initial reaction solution. Addition of trace
amounts of alcohol increased reaction rates with the
amine, as did addition of catBOBcat.
Hydrido boryl complex 1 was more reactive to protic
reagents than chloro boryl complex 4. Addition of 0.1
equiv of MeOH to a 1:1 mixture of the two boryl
complexes, followed by incremental additions of 0.2
equiv, showed relative reactivities of 1 to 4 that were
roughly 2:1. This difference in reactivity can be at-
tributed to either greater steric hindrance in 4 due to
the larger Cl group or to increased π-bonding and
decreased Lewis acidity in 4 due to the ability of the
chloride to act as a π-donor into the same orbital that
donates electron density into the boron p-orbital.37
However, the bis(boryl) compounds 2a ,b were also
less reactive than 1 toward protic reagents. In contrast
to the rapid reaction of 1 with alcohols, 2a ,b required
several hours to react with ethanol and produce Cp2-
1
WH2 (60% yield, H NMR with internal standard) and
EtOBcat′ (67%). Confirming the more rapid reaction
of 1 than 2b, no hydridoboryl complex Cp2WH(Bcat′)
was observed during the course of the reaction. The
hydride signal for Cp2WH2 was the only hydride reso-
nance observed near -12 ppm.
Thus, the greater reactivity of 1 over either 4 or 2b
must be rationalized on steric grounds, since the
chloride and boryl ligands are opposite types of ligands.
The chloride should be a weaker σ-donor than a boryl
ligand, on the basis of the basicity of the two anions,
and would act as a π-donor rather than π-acceptor. It
has been shown that the site of protonation in Cp*2-
WH2 is the orbital located between the hydride ligands.
Protonation at this portion of the molecules 1, 4, and 2
would have a dramatically reduced steric effect for
protonation of 1. Should protonation occur to the metal
on the side of the boryl ligand opposite the ancillary
covalent ligand, then the steric effect would be less
pronounced. These arguments can be explained by the
mechanisms in Scheme 6. Protonation would lead to
an intermediate that does not undergo B-H reductive
elimination, as is common for alkyl complexes, because
of the strong metal-boryl bond.29 Rather, the electro-
philic boryl ligand, albeit weakly so, is subject to attack
by the alkoxide anion, to produce the ethoxyborane and
the tungsten hydride. This process can also occur in
one step, with a four-centered transition state involving
partial protonation and formation of the product by
coordination of the lone pair to the boryl ligand.
Alcohols reacted essentially instantaneously with 1
to yield Cp2WH2 and the alkoxycatecholborane in quan-
1
titative yield by H and 11B NMR spectroscopy. Thus,
(45) Schubert, U.; Schenkel, A. Chem. Ber. 1988, 1988, 939.
(46) Berryhill, S. R.; Clevenger, G. L.; Burduryl, F. Y. Organome-
tallics 1985, 4, 1509.
(47) Pannell, K. H.; Cervantes, J .; Hernandez, C.; Cassias, J .;
Vincenti, S. Organometallics 1986, 5, 1056.

Tungstenocene Boryl Complexes
Organometallics, Vol. 15, No. 25, 1996 5355
Sch em e 7
This photochemical formation of catecholborane from
1 contrasts the formation of bis(boryl) complexes 2a ,b
under photochemical conditions. Thus, we conducted
experiments to determine the origins of this selectivity.
The selectivity for B-B over C-H bond addition in the
photolysis of Cp2WH2 in the presence of cat′BBcat′ and
benzene was independent of whether tungstenocene was
generated photochemically or thermally. Gentle ther-
molysis of [Cp2W(H)(Me)] (5) is known to generate
[Cp2W].49,51 Heating of 5 in benzene solvent for 4 h at
80 °C in the presence of 1-2 equiv of Cat′BBCat′ led to
formation of 2a in 70% yield. No Cp2W(H)(Ph) (6) was
observed during the course of the reaction, and 6 was
stable in benzene solvent at 80 °C in the presence of
cat′BBcat′. Therefore, Cp2W(H)(Ph) could not be either
a reaction intermediate or a kinetic product that is
ultimately converted to a more stable bis(boryl) product.
The clean oxidative addition chemistry of diboron
compounds led us to probe carefully for any potential
oxidative addition chemistry of catecholborane by Cp2W.
Irradiation of Cp2WH2 for 6 h in benzene solvent
containing HBcat (6 equiv) led to the solvent C-H
activation product 6 rather than the borane addition
product 1. At short reaction times (30 and 60 min),
however, we did observe small amounts (10-20% rela-
tive to 6) of the B-H activation product 1. The
formation of this product in benzene medium does
indicate that catecholborane addition is kinetically
preferred over benzene addition. However, at longer
reaction times the small amounts of boryl hydride 1
were converted to phenyl hydride 6, as must occur given
the photochemical lability of 1. Unfortunately, we could
not probe the selectivity of Cp2W for B-H oxidative
addition using methyl hydride 5 as a thermal precursor
to tungstenocene because 5 reacted with catecholborane
faster than it underwent reductive elimination to form
tungstenocene.
P oten tia l Lew is Acid -Ba se Ch em istr y. Com-
pound 1 was less Lewis acidic than catecholborane or
B-chlorocatecholborane. Addition of Lewis bases such
as PPh3, PMe3, NEt3, pyridine, acetonitrile, or THF all
led to no change in the 1H or 11B NMR spectrum of C6D6
solutions of 1. Although catecholborane is less acidic
than B-chlorocatecholborane, it does form a Lewis base
adduct with pyridine.48 Even in THF solvent or in the
presence of excess pyridine, the 11B NMR spectra of 1
were essentially identical to those in pure aromatic
solvents. This reduced Lewis acidity can be attributed
to the dπ-pπ bonding observed in the X-ray structure
and to the increased steric hindrance due to the met-
allocene fragment.
P oten tia l In ser tion Ch em istr y. Boryl complex 1
was resistant to insertion chemistry. Addition of 1-hex-
ene, 1-hexyne, CO, CO2, and acetone led to no reaction
with 1. Compound 1 was also resistant to hydrogen-
olysis and exchange with boranes that were observed
with CpFe(CO)2BPh2.2 Studies concerning the π-bond
strength and total bond energies for these compounds,
as well as the chemistry of molybdenocene analogs that
are likely to display more reactive M-B linkages, will
be the subject of future reports.
Th er m olysis a n d P h otolysis. Consistent with the
presence of haloborane initiating the rearrangement of
1, pure samples of this boryl complex were extremely
stable thermally. This compound did not undergo
rearrangement or reductive elimination even after heat-
ing in toluene at 110 °C for 12 h in a sealed vessel. In
contrast, compound 1 was photochemically reactive. A
comprehensive view of the photochemical reactivity of
the boryl complexes is given in Scheme 7. Irradiation
of a C6D6 solution of 1 with a 450 W mercury arc lamp
for only 10 min at room temperature led to 90% yield
of HBcat and Cp2W(D)(C6D5). These products of borane
reductive elimination and solvent oxidative addition49
were identified and quantified by 1H, 2H, and 11B NMR
spectroscopy. This chemistry was similar to that dis-
played by Cp2WH2, which is also thermally stable but
photochemically labile.49,50 However, compound 1 reacts
much faster under identical photochemical conditions
than does Cp2WH2.
The following series of photochemical stabilities re-
sults from these studies: [Cp2W(Bcat′)2] > [Cp2W(Ph)-
(H)] > [Cp2W(Bcat)(H)]. The selectivities by [Cp2W] for
B-B over C-H bond activation are precedented by the
oxidative addition of diboron compounds with sys-
tems that do not undergo intermolecular C-H activa-
tion.4,12,18,38,52,53 However, the final selectivity for C-H
over B-H activation with Cp2W contrasts the selectivi-
ties of systems that add the B-H bond of catecholborane
but do not add the C-H bond of hydrocarbons.14,54,55
Further, the resulting selectivity for B-B over B-H
activation is exactly the opposite of the preference for
C-H over unactivated and unstrained C-C bond acti-
vation, except in rare cases.56-60
(51) Bullock, R. M.; Headford, C. E. L.; Hennessy, K. M.; Kegley, S.
E.; Norton, J . R. J . Am. Chem. Soc. 1989, 111, 3897-3908.
(52) Dai, C.; Stringer, G.; Marder, T. B.; Baker, R. T.; Scott, A. J .;
Clegg, W.; Norman, N. C. Can. J . Chem., in press.
(53) Lesley, G.; Nguyen, P.; Taylor, N. J .; Marder, T. B.; Scott, A.
J .; Clegg, W.; Norman, N. C. Organometallics, in press.
(54) Kono, H.; Ito, K.; Nagai, Y. Chem. Lett. 1975, 1095.
(55) Westcott, S. A.; Taylor, N. J .; Marder, T. B.; Baker, T.; J ones,
N. J .; Calabrese, J . C. J . Chem. Soc., Chem. Commun. 1991, 304.
(56) Crabtree, R. H. In The Chemistry of Alkanes and Cycloalkanes;
Patai, S., Rappoport, Z., Eds.; J ohn Wiley and Sons: New York, 1992;
p 653.
(57) Gozin, M.; Weisman, A.; Ben-David, Y.; Milstein, D. Nature
1993, 364, 699.
(58) Gozin, M.; Aizenberg, M.; Liou, S.-Y.; Weisman, A.; Ben-David,
Y.; Milstein, D. Nature 1994, 370, 42.
(59) Liou, S.-Y.; Gozin, M.; Milstein, D. J . Am. Chem. Soc. 1995,
117, 9774 and references therin.
(48) Hartwig, J . F. Unpublished results.
(49) Green, M. L. H. Pure Appl. Chem. 1978, 50, 27-35.
(50) Green, M. L. H.; O’Hare, D. Pure Appl. Chem. 1985, 57, 1897.

5356 Organometallics, Vol. 15, No. 25, 1996
Hartwig and He
sary for complete reaction. The samples were then brought
into the drybox, the solutions were combined, and the volume
was reduced to 0.5 mL. This benzene solution was layered
with pentane to afford yellow crystals of 2b that were suitable
for X-ray diffraction analysis: yield 52 mg (57%); 1H NMR
(C6D6) δ 7.13 (d, 2.0 Hz, 1H), 6.93 (d, 8.2 Hz, 1H), 6.73 (dd,
8.2 Hz, 2.0 Hz, 1H), 4.70 (s, 10H), 1.16 (s, 9H); 11B NMR δ
59.3; 13C{1H} NMR δ 151.19, 149.14, 143.69, 117.2, 109.5,
108.27, 81.59, 34.42, 31.86.
Syn th esis of Cp 2W(Bca t-3,5-d i-t-Bu )2 (2b). P r ep a r a tive
Sca le. A solution of Cp2WH2 (31.0 mg, 0.0981 mmol) was
dissolved in toluene (3 mL) and placed into an NMR sample
tube. The tube was placed 1 in. from a the photolysis lamp
and was irradiated for 3.5 h. The sample was then brought
into the drybox, the solutions were combined, and the volume
was reduced to 0.5 mL. This toluene solution was layered with
pentane and cooled to -35 °C to afford analytically pure,
yellow crystals of 2b: yield 35 mg (45%); 1H NMR (C6D6) δ
7.07 (s, 1H), 7.00 (s, 1H), 4.711 (s, 10H), 1.50 (s, 9H), 1.25 (s,
9H); 11B NMR δ 58.2; 13C{1H} NMR δ 151.28, 146.81, 143.13,
132.00, 114.10, 106.46, 81.61, 34.81, 34.38, 32.06, 29.99. Anal.
Calcd for C38H50B2O4W‚C7H7: C, 62.31; H, 6.62. Found: C,
62.08; H, 6.64.
We have shown previously with an electron-rich,
third-row system, albeit an iridium system,15 that the
metal-boron bond is stronger thermodynamically than
the corresponding metal-hydride.29 The stability of the
tungsten bis(boryl) compound may be derived from a
similar high bond dissociation energy of the metal-
boron linkage. A kinetic effect that enhances selectivity
for the boranes may result from the favorable matchup
of the nucleophilic d4 Cp2W with the electrophilic
diboron reagent.
Exp er im en ta l Section
Gen er a l Meth od s. Unless otherwise noted, all manipula-
tions were carried out in an inert atmosphere glovebox or by
using standard Schlenk or vacuum line techniques. 1H NMR
spectra were obtained on a GE QE 300 MHz or Ω 300 MHz
Fourier transform spectrometer. 11B, and 31P spectra were
obtained on the Ω 300 MHz Fourier transform operating at
96.38 and 121.65 MHz, respectively. 13C NMR spectra were
obtained on a GE QE 300 NMR spectrometer operating at
75.57 MHz. 1H NMR chemical shifts were recorded relative
to residual protiated solvent. Chemical shifts are reported in
units of parts per million. Positive chemical shifts indicate
resonances located downfield from TMS, 87% H3PO4, or BF3‚-
OEt2 as external standards. Sealed NMR tubes were heated
in Neslab constant-temperature baths.
Unless otherwise specified, all reagents were purchased
from commercial suppliers and used without further purifica-
tion. Catecholborane was distilled under vacuum prior to use.
Diethylamine was dried over a small piece of sodium and was
degassed before vacuum transfer. Carbon tetrachloride was
degassed before use. Pentane (tech grade) was distilled under
nitrogen from purple sodium/benzophenone ketyl made soluble
by addition of tetraglyme to the still. Benzene, toluene, and
tetrahydrofuran were distilled from sodium benzophenone
ketyl under nitrogen. Dichloromethane was vacuum trans-
ferred from CaH2. Deuterated solvents for use in NMR
experiments were dried as their protiated analogs but were
vacuum transferred from the drying agent.
Sm a ll Sca le To Obta in Cr u d e Rea ction Yield .
A
solution of Cp2WH2 (4.2 mg, 0.0133 mmol) was dissolved in
C6H6 (0.5 mL), and the solution was added to a vial containing
roughly 0.5 mg of 1,3,5-(MeO)3C6H3 and exactly 1.0 equiv (4.9
mg) of (t-Bu-C6H3O2B)2. The solution was placed into an NMR
1
sample tube, and an initial H NMR spectrum was obtained.
The tube was placed 1 in. from the photolysis lamp and was
irradiated for 3.5 h. The final 1H NMR spectrum showed
formation of 2b in 92% yield.
X-r a y St r u ct u r a l Det er m in a t ion of 1 a n d 2a . Da t a
Collection . A pale yellow rectangular plate crystal of 1
having approximate dimensions of 0.10 × 0.10 × 0.12 mm or
2a having approximate dimensions of 0.08 × 0.10 × 0.12 was
mounted in a glass capillary (for 1) or on a glass fiber (for 2a ).
All measurements were made on an Enraf-Nonius CAD4
diffactometer with graphite-monochromated Mo KR radiation.
Cell constants and an orientation matrix for data collection
obtained from a least-squares refinement using the setting
angles of 25 carefully centered reflections in the range 17.00°
< 2θ < 29.00° for 1 and 10.30 < 2θ < 18.00° for 2a
corresponded to a monoclinic cell with dimensions a ) 10.161-
(1) Å, b ) 10.597 Å, c ) 13.242(2) Å, â ) 100.023(8) Å, and V
) 1404.1(5) Å3 for 1 and a ) 14.829(4) Å, b ) 7.976(2) Å, c )
27.282(5) Å, â ) 98.76(2)°, and V ) 3189(2) Å3 for 2a . For Z
) 4 and Mr ) 432.95 the calculated density is 2.048 g/cm3 for
1 and for Mr ) 742.18 the calculated density is 1.546 g/cm3
for 2a . On the basis of the systematic absences of h0l, h + 1
) 2n + 1, and 0k0, k ) 2n + 1, and the successful solution
and refinement of the structure, the space group was deter-
mined to be P21/n (No. 14) for 1. On the basis of the systematic
absences of h0l, h + 1 ) 2n + 1, packing considerations, a
statistical analysis of intensity distribution, and the successful
solution and refinement of the structure, the space group was
determined to be P2/n (No. 13) for 2a .
The data were collected at a temperature of 23 ( 1 °C for 1
and -119 ( 5 °C for 2a using the 2θ/ω scan technique to a
maximum 2θ value of 49.9° for 1 and 52.6° for 2a . ω scans of
several intense reflections made prior to data collection had
an average width at half-height of 0.31° with a take-off angle
of 2.8°. Scans of (0.80 + 0.35 tan θ)° for 1 and (0.53 + 1.10
tan θ)° for 2a were made at variable speeds ranging from 1.0
to 5.5 deg/min (in ω) for 1 and from 1.0 to 16.5 deg/min (in ω)
for 2a . Moving crystal moving counter background measure-
ments were made by scanning an additional 25% above and
below the scan range. The counter aperture consisted of a
variable horizontal slit with a width ranging from 2.0 to 2.5
mm and a vertical slit set to 2.0 mm. The diameter of the
incident beam collimator was 1.3 mm for 1 and 0.8 mm for
2a , and the crystal to detector distance was 21 cm for both.
Cp 2W(H)(Bca t) (1). Li[Cp2WH] (80-400 mg) that was
30
prepared by deprotonation of Cp2WH2 was suspended in
5-10 mL of benzene. To this stirred solution was added
dropwise at room temperature 0.9 equiv of chlorocatecholbo-
rane as a solution in 0.5-1 mL of benzene. The resulting
solution was allowed to react at room temperature for 30 min,
after which time the resulting yellow/orange suspension was
filtered. The filtrate was concentrated to 1-2 mL and
transferred to a small vial. Crystalline 1 was obtained by
vapor diffusion of pentane into the concentrated benzene
solution. Analytically pure 1 was obtained in 28-40% yield
by this method. Alternatively, the reaction was run in toluene
solvent. After reaction under the same conditions, the filtrate
was concentrated to 1-2 mL and layered with pentane.
Cooling to -35 °C for several days led to crystallization of 1
in 70% yield. However, these samples of 1 contained 5-10%
of Cp2WH2 as impurity: 1H NMR (C6D6) δ -10.47 (s, J W-H
)
53.4, 1H), 4.37 (s, 10H), 6.84 (m, 2H), 6.86 (m, 2H); 13C{1H}
NMR (C6D6) δ 76.62 (s), 110.66 (s), 121.06 (s), 151.61 (s); 11B
NMR (C6D6) δ 57.2; IR (Et2O) 1952. Anal. Calcd for C16H15
-
BO2W: C, 44.28; H, 3.48. Found: C, 44.69; H, 3.86.
Syn th esis of Cp 2W(Bca t-4-t-Bu )2 (2a ). A solution of Cp2-
WH2 (42.0 mg, 0.133 mmol) was dissolved in C6H6 (4 mL), and
the solution was added to a vial containing 1.0 equiv (49.5 mg)
of (t-Bu-C6H3O2B)2. The solution was divided into four NMR
sample tubes, and the tubes were placed 1.0 in. from the
photolysis lamp and irradiated for 3.5 h. 11B NMR spectra
taken periodically showed that this reaction time was neces-
(60) Liou, S. Y.; Gozin, M.; Milstein, D. J . Chem. Soc., Chem.
Commun. 1995, 1965.

Tungstenocene Boryl Complexes
Organometallics, Vol. 15, No. 25, 1996 5357
For intense reflections an attenuator was automatically in-
serted in front of the detector.
material. This material was recrystallized before submitting
for microanalysis: 1H NMR (C6D6) δ -10.09 (s, d; J W-H ) 72.5
Hz, 2H, W-H), 3.88 (m, 2H, C5H4BPh2), 4.08 (s, 5H, Cp), 4.75
(m, 2H, C5H4BPh2), 7.20 (t, 7.0 Hz, 2H, BPh2), 7.25 (t, 7.3 Hz,
4H, BPh2), 7.81 (d, J ) 7.2 Hz, BPh2); 11B NMR (C6D6) δ 41;
13C{1H} NMR (C6D6) δ 77.34, 78.63, 85.22, 127.37, 127.43,
134.83; the quaternary carbons bound to boron could not be
observed. Anal. Calcd for C22H21BW: C, 55.04; H, 4.41.
Found: C, 54.77; 4.33.
Cp (C5H4Bca t)WH2 (3b). F r om Li[Cp 2WH]. A procedure
identical to preparation of 1 in toluene solvent was followed
except that 1.2 equiv of chlorocatecholborane was used and
the solution was left to react overnight. Recrystallization from
toluene/pentane solutions gave 3a in 21% yield as a pale yellow
solid: 1H NMR (C6D6) δ -11.31 (s, d; J W-H ) 72 Hz; 2H, W-H),
4.14 (s, 5H, Cp), 4.23 (t, J ) 2.1 Hz, 2H, C5H4Bcat), 4.59 (t, J
) 2.1 Hz, 2H, C5H4Bcat), 6.73 (m, 2H, Bcat), 6.98 (m, 2H, Bcat);
11B NMR (C6D6) δ 33; 13C{1H} NMR (C6D6) δ 73.82, 74.23,
80.23, 111.97, 122.16, 148.81. Anal. Calcd for C16H15BO2W:
C, 44.29; H, 3.48. Found: C, 43.77; H, 3.71.
Da ta Red u ction , Str u ctu r e Solu tion , a n d Refin em en t.
Of the 2770 reflections which were collected for 1, 2641 were
unique (Rint ) 0.033). Of the 7198 reflections which were
collected for 2a , 6929 were unique (Rint ) 0.078). The
intensities of the two representative reflections which were
measured after every 60 min of X-ray exposure time declined
by -50.00% for 1 but were constant for 2a . A linear correction
factor was applied to the data to account for this phenomena
with 1, but no correction was applied for 2a . The linear
absorption coefficient for Mo KR was 84.0 cm-1 for 1 and 37.3
cm-1 for 2a . For 1 an empirical absorption correction using
the program DIFABS was applied, which resulted in transmis-
sion factors ranging from 0.60 to 1.57. The data were corrected
for Lorentz and polarization effects. For 2a , an empirical
absorption correction based on azimuthal scans of several
reflections was applied, which resulted in transmission factors
ranging from 0.77 to 1.00. The data were corrected for Lorentz
and polarization effects.
The structures were solved by the Patterson method.61 This
procedure revealed the position of the W atoms, and subse-
quent difference maps revealed the remaining atoms. The
non-hydrogen atoms were refined anisotropically. The thermal
parameters of the carbon atoms on each cyclopentadienyl ring
of 1 were somewhat larger than normal. The hydrogen atoms
were included in calculated positions. In the case of the methyl
group hydrogens of 2a , one hydrogen atom was located in the
difference map and included in an idealized position to set the
orientation of the other two hydrogen atoms. For 1, the final
cycle of full-matrix least-squares refinement was based on 1456
observed reflections (I > 3.00σ(I)), with 181 variable param-
eters, and converged (the largest parameter shift was 0.00
times its esd) with unwieghted and weighted agreement factors
of R ) Σ||Fo| - |Fc||/Σ|Fo| ) 0.039 and Rw ) [(Σw(|Fo| - |Fc|)2/
Σ|Fo|)]1/2 ) 0.039. For 2a , the final cycle of full-matrix least-
squares refinement was based on 4244 observed reflections (I
> 3.00σ(I)), with 388 variable parameters, and converged (the
largest parameter shift was 0.001 times its esd) with un-
wieghted and weighted agreement factors of R ) ∑||Fo| - |Fc||/
∑|Fo| ) 0.041 and Rw ) [(∑w(|Fo| - |Fc|)2/∑|Fo|)]1/2 ) 0.050.
The standard deviation of an observation of unit weight was
1.42 for 1 and 1.69 for 2a . The weighting scheme was based
on counting statistics and included a factor (p ) 0.03) to
downweight the intense reflections. Plots of Σw(|Fo| - |Fc|)2
versus |Fo| reflection order in data collection, (sin θ)/λ, and
various classes of indices showed no unusual trends. The
maximum and minimum peaks on the final difference Fourier
map corresponded to 1.38 (located 1.77 Å away from the W
atom) and -1.30 e/Å3 for 1 and 1.29 (located 1.04 Å from the
W atom) and -2.71 e/Å3. Neutral atom scattering factors were
taken from Cromer and Waber.62 Anomalous dispersion effects
were included in Fc; the values for ∆f ′ and ∆f ′′ were also those
of Cromer and Waber.63 All calculations were performed using
the TEXSAN crystallographic software package of the Molec-
ular Structure Corp.
F r om R ea ct ion of 1 w it h a Ca t a lyt ic Am ou n t of
Ch lor oca tech olbor a n e. Compound 1 (6.0 mg, 0.014 mmol)
was dissolved in 0.6 mL of C6D6. C6H5(t-Bu) (1-2 mg) was
added as an internal standard, and the sample was transferred
to an NMR tube equipped with a Teflon-lined screw cap. An
initial 1H NMR spectrum was obtained to determine the ratio
of 1 to internal standard. Chlorocatecholborane (ca. 0.2 mg,
10 mol %) was weighed into a vial, and the sample of 1 in
C6D6 was added to the vial. The resulting sample was
returned to the NMR tube and was warmed to 45 °C for 2 h.
A second
1H NMR spectrum showed complete consumption of
1 and formation of 3a in 82% yield as determined by integra-
tion of the cyclopentadienyl resonance versus the internal
standard.
Cp 2W(Cl)(Bca t) (4). P r ep a r a tive Sca le. To a solution
of 1 (65 mg, 0.15 mmol) in 5 mL of toluene was added 1.0 equiv
of CCl4 by syringe. The solution turned immediately dark
brown. Addition of pentane to the reaction solution precipi-
tated 4 as a brown powder (55 mg, 78%) that was roughly 90%
1
compound 4 as determined by H NMR spectroscopy. Alter-
natively 4 was prepared as dark brown analytically pure
crystals by concentrating the toluene reaction solution and
cooling to -35 °C. Once isolated, this compound was not
soluble enough in hydrocarbon solvents to obtain satisfactory
signal to noise ratios for 13C NMR spectra and decomposed
slowly in methylene chloride solvent: 1H NMR (C6D6) δ 4.49
(s, 10H), 6.88 (m, 2H), 7.24 (m, 2H); 11B NMR (C6D6): δ 49.
Anal. Calcd for C16H14BClO2W: C, 41.30; H, 3.01. Found: C,
41.29; H, 3.03.
Sm a ll-Sca le Rea ction for NMR Yield Deter m in a tion .
Compound 1 (4.0 mg) was dissolved in C6D6 solvent (0.6 mL),
C6H5(t-Bu) (1-2 mg) was added as an internal standard, and
the sample was transferred to an NMR tube equipped with a
Teflon-lined screw cap. An initial 1H NMR spectrum was
obtained to determine the ratio of 1 to internal standard. A 1
equiv amount of CCl4 was added, and a second 1H NMR
spectrum was obtained that showed complete reaction of 1 and
formation of 4 in 88% yield as determined by integration of
its cyclopentadienyl resonance versus the internal standard.
P h otolysis of 1. A 5.2 mg (0.012 mmol) amount of 1 was
dissolved in 0.6 mL of C6D6. C6H5(t-Bu) (1-2 mg) was added
as an internal standard, and the sample was transferred to
an NMR tube equipped with a Teflon-lined screw cap. An
initial 1H NMR spectrum was obtained to determine the ratio
of 1 to internal standard. The sample was then placed
approximately 2 cm from a 150 W medium-pressure Hanovia
mercury arc lamp located in a water-cooled Pyrex immersion
well. The sample was irradiated for 20 min at room temper-
Cp (C5H4BP h 2)WH2 (3a ). Li[Cp2WH] (80 mg) that was
30
prepared by deprotonation of Cp2WH2 was suspended in
5-10 mL of toluene. To this stirred solution was added
dropwise at room temperature 0.9 equiv of BrBPh2 as a
solution in 0.5 mL of toluene. The resulting solution was
allowed to react at room temperature for 30 min, after which
time the resulting yellow/orange suspension was filtered. The
filtrate was concentrated to 1-2 mL and transferred to a small
vial. The sample was layered with pentane, and 3b was
obtained in 60% yield (65 mg) as spectroscopically pure
(61) Calabrese, J . C. Ph.D. Thesis, WisconsinsMadison, 1972.
(62) Cromer, D. T.; Waber, J . T. In International Tables for X-ray
Crystallography; The Kynoch Press: Birmingham, U.K., 1974; Vol. IV,
Table 2.2A.
(63) Cromer, D. T.; Waber, J . T. In International Tables for X-ray
Crystallography; The Kynoch Press: Birmingham, U.K., 1974; Vol. IV.
1
ature, and a second H NMR spectrum was obtained. All of 1
had been consumed. Catecholborane and Cp2W(D)(C5D5) was
formed in 88% and 90% yields, as determined by comparison
of the ratio of integrals for the two products versus the internal

5358 Organometallics, Vol. 15, No. 25, 1996
Hartwig and He
standard. Catecholborane was also identified by its charac-
teristic doublet resonance at δ 28 in the 11B NMR spectrum.
Rea ction of 1 w ith Eth a n ol. Compound 1 (6 mg) was
dissolved in C6D6 solvent (0.6 mL), C6H5Me (1-2 µl) was added
as an internal standard, and the sample was transferred to
an NMR tube equipped with a Teflon-lined screw cap. An
initial 1H NMR spectrum was obtained to determine the ratio
of 1 to internal standard. A 1 equiv amount of EtOH was
added, and a second 1H NMR spectrum was obtained that
showed complete reaction of 1 and formation of Cp2WH2 and
EtOBcat in quantitative yields as determined by integration
of the cyclopentadienyl resonance and ethoxy methylene
resonance versus the internal standard. EtOBcat was also
identified by its 11B NMR resonance at δ 22.
PPh3, pyridine, acetonitrile, and triethylamine. The resulting
samples were placed into NMR tubes and analyzed by 1H NMR
spectroscopy and 11B NMR spectroscopy. No changes were
observed from samples of pure 1 in C6D6.
Rea ction of 2a w ith EtOH. A 5.3 mg (7.7 mmol) amount
of 2a was weighed into a vial and was dissolved in 0.6 mL of
C6D6. Roughly 0.5 mg of 1,3,5-(MeO)3C6H3 was added as an
internal standard, and the solution was placed in a rubber
septum-capped NMR tube. A 1H NMR spectrum was obtained
and integrated. An excess of EtOH (1.0 µL 17 mmol) was then
added. 1H NMR spectra taken periodically indicated that the
reaction required more than 2 h for completion and that Cp2-
WH2 was formed in 60% yield, while EtOBcat′ was formed in
67% yield.
Kin etic Mea su r em en ts of th e Rea ction of 1 w ith
Dieth yla m in e. A 2 mL volumetric flask was charged with
8-10 mg of 1 and C6D6. This solution (0.62 mL) was
transferred to an NMR tube equipped with a Teflon-lined
screw cap. The desired amount of diethylamine was added
by syringe, typically 10 µL. This sample was then placed in
the NMR spectrometer that was warmed to either 45 or 55
°C. An automated data acquisition program acquired single-
Ack n ow led gm en ts. We are grateful for support
from the National Science Foundation (CHE and NYI
Award program), the Dreyfus Foundation for a New
Faculty Award, DuPont for a Young Faculty Award,
Union Carbide for an Innovative Recognition Award,
and Yale University for a J unior Faculty Fellowship.
We acknowledge the initial observation of the rear-
rangement of 1 to 3a by Sonali Bhandari.
1
pulse H NMR spectra at designated intervals. The decay of
1 was determined by the decay of the integral values for the
cyclopentadienyl resonance of 1. The yields of products, as
determined by comparison of the integrations to the initial
spectrum, were shown to be consistently quantitative. Linear
first-order plots were obtained in all cases, but rate constants
varied by a factor of 2-3 depending on the batch of 1 and the
batch of solvent brought into the drybox after vacuum transfer
from a purple sodium/benzophenone ketyl.
Su p p or tin g In for m a tion Ava ila ble: Tables of positional
parameters, U values, intramolecular distances, intramolecu-
lar bond angles, Cartesian coordinates, and torsion angles for
2a (15 pages). Ordering information is given on any current
masthead page. X-ray data have been provided previously for
1.3
Rea ction of 1 w ith P oten tia l Lew is Ba ses. Samples of
1 (3-6 mg) in C6D6 solvent were treated with 10 equiv of PMe3,
OM9606303