Net heterolytic cleavage of B-H and B-B bonds across the N-Pd bond in a cationic (PNP)Pd fragment

Article abstract of DOI:10.1021/ic2001283

The use of weakly coordinating anions BAr^F₄ (where Ar^F = 3,5-(CF₃)₂C₆H₃) and CB₁₁H₁₂ allows one to access clean reactions of the [(PNP)Pd]⁺ fragment (PNP = bis(2-ⁱPr₂P4- Me-phenyl)amido) with the B-H bond in catecholborane (CatBH) and catecholdiboron (CatBBCat). In both cases, a net heterolytic cleavage of B-H or B-B takes place, with the nitrogen atom of PNP being a recipient of a boryl fragment. The resultant products [(PN(BCat)P)PdH]⁺ (2) and [(PN(BCat)P)PdBCat] ⁺ (3) were isolated as either BAr^F₄ or CB ₁₁H₁₂ salts and fully characterized. They are susceptible to hydrolysis, with the B-N bond hydrolyzing selectively and rapidly at RT to give [(PN(H)P)PdH]⁺ (1) and [(PN(H)P)PdBCat]⁺ (4). Notably, 4 and 2 are isomers, but they do not interconvert even under thermolysis at 90 °C. The Pd-B bond in 4 can be further hydrolyzed more slowly, to give 1. On the other hand, a Pd-B bond was formed from the Pd-H bond in 2 by reaction with excess CatBH (and evolution of H₂), producing 3.

Full text of DOI:10.1021/ic2001283

ARTICLE
pubs.acs.org/IC
Net Heterolytic Cleavage of BÀH and BÀB Bonds Across the NÀPd
Bond in a Cationic (PNP)Pd Fragment
Yanjun Zhu,† Chun-Hsing Chen,‡ Claudia M. Fafard,‡ Bruce M. Foxman,‡ and Oleg V. Ozerov*,†
†Department of Chemistry, Texas A&M University, 3255 TAMU, College Station, Texas 77842, United States
‡Department of Chemistry, Brandeis University, MS 015, 415 South Street, Waltham, Massachusetts 02454, United States
S Supporting Information
b
ABSTRACT: The use of weakly coordinating anions BArF
4
(where ArF = 3,5-(CF3)2C6H3) and CB11H12 allows one to
access clean reactions of the [(PNP)Pd]+ fragment (PNP =
bis(2-iPr2P4-Me-phenyl)amido) with the BÀH bond in cate-
cholborane (CatBH) and catecholdiboron (CatBBCat). In both
cases, a net heterolytic cleavage of BÀH or BÀB takes place,
with the nitrogen atom of PNP being a recipient of a boryl
fragment. The resultant products [(PN(BCat)P)PdH]+ (2)
and [(PN(BCat)P)PdBCat]+ (3) were isolated as either BArF
4
or CB11H12 salts and fully characterized. They are susceptible to
hydrolysis, with the BÀN bond hydrolyzing selectively and
rapidly at RT to give [(PN(H)P)PdH]+ (1) and [(PN(H)P)-
PdBCat]+ (4). Notably, 4 and 2 are isomers, but they do not interconvert even under thermolysis at 90 °C. The PdÀB bond in 4 can
be further hydrolyzed more slowly, to give 1. On the other hand, a PdÀB bond was formed from the PdÀH bond in 2 by reaction
with excess CatBH (and evolution of H2), producing 3.
’ INTRODUCTION
undergoing 1,2-addition of nonpolar or weakly polar bonds,19À22
there is no π bond in the [(PNP)Pd]+ fragment because the
empty and the filled orbitals are orthogonal to each other and
dimerization is presumably unfavorable on steric grounds. In this
sense, [(PNP)Pd]+ resembles the so-called frustrated Lewis pairs
(FLPs) recently popularized by Stephan et al.23
The activation of BÀH and BÀB bonds by transition-metal
complexes to give boryls is of great interest to chemists because
of its direct relevance to homogeneous catalysis. Transition-metal
boryl complexes are important as intermediates in transition-
metal-catalyzed hydroboration with boranes, diboration with
diboron reagents, and borylation of alkanes and arenes.1À10
MetalÀboryl complexes are typically generated through oxida-
tive addition (OA)11 of boranes or diboron substrates. For ex-
ample, Marder et al. have reported examples of oxidative addition
of borane/diboron compounds to Pt(0),12 and oxidative addi-
tion of BÀH and BÀB bonds to Rh(I) and Ir (I) is also well-
known.8,13
Classical OA of an XÀY bond (such as BÀH or BÀB) to the
metal center can be contrasted with and complemented by 1,
2-addition of an XÀY bond across a metal ligand bond (Scheme 1).
Both cases necessitate the presence of a filled and of an empty
orbital in the metal complex to rupture the XÀY bond and form
new bonds to X and Y. For the classical OA, both orbitals are
metal-based, whereas for the 1,2-addition, the ligand orbital
contributes a lone pair and the metal an empty orbital. We have
recently reported14 1,2-addition of HÀH, alkynyl CÀH, and
thiolic SÀH bonds cross the PdÀN moiety in a cationic, three-
coordinate [(PNP)Pd]+ fragment where PNP15À17 is a diaryla-
mido/bis(phosphine) pincer ligand (Scheme 2). This 1,2-addi-
tion can be viewed as heterolysis of the corresponding HÀX
bonds.18 In contrast to most other common examples of complexes
In the present paper, we report our investigation of the 1,
2-addition of the BÀH bond in catecholborane (CatBH) and the
BÀB bond in bis(catecholate)diboron (CatB-BCat) across the
PdÀN moiety in [(PNP)Pd]+. In contrast to our previous report
(Scheme 2) on the net heterolytic cleavage of HÀX by [(PNP)-
Pd]+,14 here, the nitrogen atom is the recipient of X (boron) in
the net heterolytic cleavage of HÀX, not of hydrogen. Addition
of BÀH and BÀB bonds across metalÀoxygen functionalities is
rather common. 1,2-Addition of BÀH across the metalÀoxygen
bond in oxo-rhenium complexes and peroxo-rhodium complexes
has been reported.24,25 Addition of BÀB bonds across late metal
alkoxides with the release of free alkoxyboron molecules has been
used for the synthesis of a variety of late metal boryls.26À29
Another closely related precedent is the very recent report by
Clark et al.30 describing the net heterolytic cleavage of BÀB (and
BÀH) bonds by a ruthenium center and a pendant oxygen in a
Shvo-type31 system, albeit that does not constitute 1,2-addition.
On the other hand, addition of BÀB bonds across a metalÀnitrogen
Received: January 19, 2011
Published: August 05, 2011
r
2011 American Chemical Society
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Inorganic Chemistry
ARTICLE
moiety remains unusual. It is also worth noting that relatively few
palladium boryl complexes are known, mainly prepared by oxi-
dative addition of a boronÀhalogen bond to a Pd center.32
convenient precursor did not work well in the reaction with the
CatB-H substrate, which produced a mixture of unidentified species.
Thus, we were prompted to turn to more weakly coordinating anions
[BArF ]À (ArF = 3,5-(CF3)2C6H3)33,34 and monocarba-
4
closo-dodecaborate [CB11H12]À (also known as “carborane”)35
’ RESULTS AND DISCUSSION
in place of triflate. Reaction of A with Na[BArF ] in THF furnished
4
Synthesis of [(PNP)Pd]+ Synthons B and C. In our previously
reported work on the net heterolytic cleavage of HÀX bonds in
thiols, H2, or an alkyne, (PNP)PdOTf (A) functioned well as
a synthon for [(PNP)Pd]+ (Scheme 2).14 Unfortunately, this
[(PNP)Pd(THF)]BArF (B, Scheme 3) as a blue solid in 60%
4
isolated yield. An analogous reaction of A with Cs[CB11H12] in
fluorobenzene yielded (PNP)Pd(CB11H12) (C, Scheme 3) as a
solid of a different shade of blue in 83% yield. Both B and C were
1
characterized by H, 31P, and 13C NMR spectroscopies and
Scheme 1. Oxidative Addition to a Metal Center and the
Nonoxidative 1,2-Addition
elemental analysis. They display apparent C2v symmetry in their
room-temperature NMR spectra, as is expected of simple square-
planar adducts of [(PNP)Pd]+. We were not able to grow an
X-ray quality crystal of C. However, using the same synthetic
strategy, we prepared (FPNP)PdCB11H12 (FC, Scheme 3), a very
similar compound bearing fluorine substituents on the ligand
backbone and obtained its single crystal for an XRD study. The
solid-state structure of FC (vide infra) revealed coordination of
CB11H12À to the [(FPNP)Pd]+ fragment, and presumably that is
the case for C, as well.
Although B and C are adducts of the authentic [(PNP)Pd]+
fragment, the coordination of the THF molecule in B or of the
carborane anion in C was sufficiently weak that B and C readily
functioned as synthons of [(PNP)Pd]+ in the reactions with
BÀH, BÀB, and HÀH bonds described below. We selected two
different weakly coordinating anions in order to increase the
chances of obtaining X-ray quality crystals containing the cations
of interest and of obtaining analytically pure solid products. In
Scheme 2. Reactions of Certain HÀX Substrates with
(PNP)PdOTf
the products of net heterolytic splitting, both [BArF ]À and
4
[CB11H12]À behave as noncoordinating anions.
Net BÀH and BÀB Heterolytic Splitting Reactions. Both B
and C readily reacted with 1.0À1.1 equiv of CatB-H (Scheme 4),
with the reaction complete in 1À3 h, as evidenced by the evo-
lution of the blue color of B or C into yellow with the formation
of the products [(PN(BCat)P)PdH]BArF4 (2-BArF ) and [(PN-
4
(BCat)P)PdH]CB11H12 (2-CB11H12). In both cases, the reac-
tion mixtures also contained small amounts of the [(PN(H)-
P)PdH]+ (1-BArF or 1-CB11H12) impurities. Nonetheless,
4
workup allowed isolation of pure 2-BArF in ca. 60% yield,
4
whereas 2-CB11H12 was characterized in the presence of 1-
CB11H12. 1H, 31P, and 13C NMR spectroscopies confirmed the
Scheme 3. Synthesis of Compounds B, C, and FC
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Inorganic Chemistry
ARTICLE
Scheme 4. Synthesis of Compounds 1À5 and Their
and elemental analysis data, and it was also characterized by
Interconversion
single-crystal X-ray diffraction (vide infra). 3-BArF possesses
4
better solubility in aromatic solvents than 3-CB11H12. 3-CB11H12
is barely soluble in benzene, toluene, or fluorobenzene at room
temperature and precipitated from the toluene reaction mixture.
This low solubility is presumably responsible for the fortuitous
separation of the likely impurities.
The origin of the formation of salts of 1 in the reaction of B and
C with CatB-H and of 4 in reactions of B and C with CatB-BCat
is not clear. It is likely the result of the protolysis of the NÀB
bonds in the expected products (see the Hydrolysis section
below). The nature of the protic source responsible is at this
point unknown. Consistent observation of apparent protolysis
products after different drying precautions taken casts doubt (but
does not eliminate) the possibility of adventitious water. It is also
possible that the difficulty in removing BÀOH impurities in
CatB-H and CatB-BCat is the culprit.
Hydrolysis of BÀN and PdÀB Bonds. The BÀN and PdÀB
bonds in complexes 3-BArF as well as 3-CB11H12 were easily
4
hydrolyzed (Scheme 4). The hydrolysis of the BÀN bond took
place more rapidly: reaction of 3-BArF with 1 equiv of water
4
produced complex 4-BArF . The PdÀB bond was hydrolyzed
4
more slowly, and excess water effected conversion of 3-BArF4 or
3-CB11H12 to complex 1-BArF or 1-CB11H12, respectively.
4
Thus, in the course of the hydrolysis, the NÀB and PdÀB bonds
were converted to the corresponding NÀH and PdÀH bonds,
with concomitant production of CatBOBCat (Scheme 4).36 The
structure and formulation of products 2. Complex 2-BArF4 was
also characterized by single-crystal X-ray diffraction (vide infra)
and elemental analysis. It is worth noting that the BÀH bond of
CatB-H added to the PdÀN bond in the opposite direction
compared with the CÀH and SÀH substrates mentioned
above;14 that is, B added to N while H added to Pd. This is
consistent with the reversal of polarity of a BÀH bond versus a
CÀH or a SÀH bond. The most telling spectroscopic evidence
of this regiochemistry in salts of 2 was the Pd-H resonance at
ultimate hydrolysis products 1-BArF and 1-CB11H12 were
4
synthesized independently via reaction of B or C with H2 and
1
characterized by H, 13C, and 31P NMR spectroscopies (and
elemental analysis for 1-BArF ). These syntheses parallel the
4
previously reported synthesis of 1-OTf from (PNP)PdOTf and
H2.14 Complexes 1-BArF4 and 1-CB11H12 have the same cation
as 1-OTf and only differ in the anion. Not surprisingly, they
resonated at the same chemical shift (56.3 ppm) in the 31P NMR
δ À12.7 (2-BArF ) or À12.6 ppm (2-CB11H12) in the 1H NMR
spectra and displayed the same number and symmetry of H
1
4
spectrum.
NMR resonances for the cation. On the other hand, the chemical
1
Analogous reactions of B and C with CatB-BCat proceeded
more slowly, requiring >18 h and/or mild heating for completion
shifts of the resonances in the H NMR spectra in CD2Cl2 of
these three compounds were quite distinct from each other,
(Scheme 4). The products [(PN(CatB)P)PdBCat]BArF
especially for the N-H resonances (δ 8.75, 6.96, 7.07 ppm for
4
(3-BArF ) and [(PN(CatB)P)Pd(BCat)]CB11H12 (3-CB11H12)
1-OTf, 1-BArF , and 1-CB11H12, respectively).37 However, the
4
4
1
were characterized by H, 31P, and 13C NMR spectroscopies.
chemical shifts in the 1H NMR spectra in the more polar solvent
Like the salts of 2, both salts of 3 possess Cs symmetry in the
NMR spectra at ambient temperature. The NMR spectroscopic
signatures of 3-BArF4 and 3-CB11H12 were nearly identical. For
example, 3-CB11H12 gave rise to a 31P NMR resonance at δ 45.0
acetone-d6 were only slightly different (δ 9.15, 9.09, 9.08 ppm for
the N-H resonances for 1-OTf, 1-BArF , and 1-CB11H12,
4
respectively). These discrepancies can be rationalized by the
notion that triflate, albeit not coordinated to the metal, maintains
ppm, very similar to 3-BArF (44.7 ppm). We did not observe
a closer interaction with the cation in solution than [BArF ]À or
4
4
the 11B signals for 3-BArF and 3-CB11H12 corresponding to the two
[CB11H12]À.38 The difference is greater in the less polar solvent
(CD2Cl2) and nearly disappears in acetone. This notion is
reinforced by the observation of hydrogen bonding between
NH of the cation and the triflate anion in the solid-state structure
of 1-OTf.14 Most likely, this is the interaction most important for
the downfield shift of the NH resonance in solutions of 1-OTf
versus 1-BArF4 or 1-CB11H12.
4
different BCat groups, even upon cooling to À30 °C. This was
surprising to us because the 11B NMR resonances of the anions in
salts of 3 were easily detected in the same experiments, and
because the N-B resonance in 2-BArF4 and the Pd-B resonance in
4-BArF were also readily detected at 21.2 and 37.1 ppm, res-
4
pectively, in their 11B{1H} NMR spectra. Presumably, the 11B
NMR resonances of the CatB groups in 3-BArF4 and 3-CB11H12
are substantially broadened, but the origin of this broadening is
unclear to us. Nonetheless, the expected 1H NMR and 13C NMR
The intermediate hydrolysis product 4-BArF4 (Scheme 4) was
isolated in 68% yield from selective reaction of 4-BArF4 with 1
equiv of water, and we were able to obtain single crystals suitable
for X-ray diffraction studies (vide infra) using this route. Alter-
resonances for the two distinct CatB groups for 3-BArF and
4
3-CB11H12 were observed. Compound 3-BArF4 was found to be
natively, 4-BArF4 could be prepared via thermolysis of 1-BArF
4
contaminated with 4-BArF , and our best attempts at removing
with excess CatB-H. Thermolysis with excess CatB-H also served
4
to convert 2-BArF to 3-BArF . These reactions converted
this impurity failed. On the other hand, compound 3-CB11H12 was
4
4
isolated in a pure solid form, as supported by NMR spectroscopy
PdÀH into Pd-BCat (and H2) but did not affect the NH bond
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ARTICLE
Figure 1. ORTEP drawing48 (50% probability ellipsoids) of FC show-
ing selected atom labeling. Hydrogen atoms of the FPNP ligand are
omitted for clarity. Disorder of one of the iPr groups is not shown. Selected
bond distances (Å) and angles (deg) follow: Pd1ÀN1, 2.0072(19);
Pd1ÀP1, 2.2969(5); Pd1ÀP2, 2.3449(6); Pd1ÀH512, 1.69(3); B12À
H512, 1.22(3); P1ÀPd1ÀP2, 161.68(2); N1ÀPd1ÀH512, 171.0(10);
B12ÀH512ÀPd1, 133(2).
Figure 2. ORTEP drawing48 (50% probability ellipsoids) of 2-BArF
4
showing selected atom labeling. Hydrogen atoms (except PdÀH) and
the BArF counterion are omitted for clarity. Selected bond distances
4
(Å) and angles (deg) follow: Pd1ÀP1, 2.2624(7); Pd1ÀP2, 2.2838(7);
Pd1ÀN1, 2.202(2); Pd1 B1, 2.746(3); Pd1ÀH1, 1.43(4); P1À
3 3 3
Pd1ÀP2, 163.66(3); N1ÀPd1ÀH1, 175.9(14).
Complexes 4-BArF4 and 2-BArF4 are isomers. Both can be for-
mally viewed as products of 1,2- versus 2,1-addition of CatB-H to
[(PNP)Pd]+, with 2-BArF4 having PdÀH and NÀB bonds and
in 4-BArF . 4-BArF4 displayed Cs symmetry in its NMR spectra
4
and a single 11B resonance for the cation (37.1 ppm).
4-BArF having PdÀB and NÀH bonds. As mentioned above,
The formation of a metalÀboryl bond upon treatment of a
metal hydride with boranes is not without precedent39 Dehy-
drogenative borylation of CÀH bonds with R2BH reagents must
also involve conversion of metal hydrides to metal boryls as part
of the catalytic cycle.40 In another study using the PNP ligand,
Mindiola reported the formation of the neutral (PNP)NiBCat by
treatment of (PNP)NiH with CatB-H.41
Select Mechanistic Considerations. Without more extensive
data, it is difficult to speculate on the possible mechanism of the
BÀH and BÀB cleavage, but several observations can be made.
For the H2 splitting,14 we hypothesized that a likely mechanism
involves intermolecular proton transfer from the dihydrogen
ligand in [(PNP)Pd(H2)]+ to the N of PNP by an external base
(triflate, solvent, possibly adventitious water). However, an ana-
logous transfer of a CatB+ seems a more exotic proposition,42
especially considering the absence of triflate and the demon-
strated deleterious role of water as an impurity.
It is possible that the reaction is initiated by the formation of a
σ complex of a BÀH or a BÀB bond with [(PNP)Pd]+. σ
complexes of BÀH bonds are well-precedented.43 Recent com-
putational investigations by Bo, Peris, and Fernandez argued in
favor of a viable BÀB σ-complex intermediate in the BÀB oxidative
addition to a CNC pincer-supported Pd(II) cation.44 In our
previous work with H2 splitting,14 we computationally investi-
gated the possibility of H2 oxidative addition to [(PNP)Pd]+ and
concluded that it was too unfavorable to play a role in the
heterolytic splitting reaction. However, boryl is a more donating
ligand than a hydride and it is possible that BÀH or BÀB OA to
[(PNP)Pd]+ is more accessible.
Addition of borane to the heteroatom first has been proposed
for the net heterolytic splitting reaction of a RhÀperoxo complex
with pinacolborane.25 However, this pathway appears less likely
with [(PNP)Pd]+ because the basicity of the N site in it should be
quite low, whereas the empty coordination site on Pd is clearly a
very reactive moiety.
4
only 2-BArF4 could, in fact, be synthesized in this fashion. There
was no conversion between these two isomers upon thermolysis
of one or the other at 90 °C. Thus, we were unable to determine
which is the more favorable isomer, but the lack of interconver-
sion shows that 2-BArF4 is not accessible from 4-BArF4 under the
reaction conditions.
Solid-State Structures of Complexes 2-BArF , 3-CB11H12, FC,
4
and 4-BArF . We were able to obtain single crystals of com-
4
pounds 2-BArF , 3-CB11H12, FC, and 4-BArF4 that were suitable
4
for X-ray diffraction studies. The ORTEP representations of the
molecular structures in the solid state are given in Figures 1À4.
An X-ray diffraction study for FC (Figure 1) found that the Pd
center was four-coordinate, with the BÀH unit at the 12-position
of [CB11H12]À interacting with the metal center, and the geo-
metry about the metal being approximately square-planar. Co-
ordination of the CB11H12À anion to a metal center via the 12-H
substituent has been reported by Weller et al.45 Coordination via
12-H seems reasonable since this BH unit is the most remote
from the carbon and is the most electron-rich site in the cage.35
F
Complex C (and presumably C) can be viewed as a σ-BH
complex (cf. A in Scheme 4). It is interesting to note that it does
not undergo BÀH cleavage, which is probably an illustration of
the different nature of the BÀH bond in the CB11H12À cage and
in CatB-H, in both the electronic and steric sense.
In the structures of 2-BArF4 (Figure 2), 3-CB11H12 (Figure 3),
and 4-BArF4 (Figure 4), the Pd center adopts a slightly distorted
square-planar geometry, and all three structures contain a PNP
ligand with a central amine nitrogen donor. The PdÀNPNP
distances are notably longer in these compounds (2.202(2) Å
in 2-BArF , 2.2517(11) Å in 3-CB11H12, 2.194(3) Å in 4-BArF )
4
4
than the corresponding distances in the compounds containing
the PNP ligand with a central amido, sp2-hybridized nitrogen donor
(for example, 2.0072(19) Å in 5, 2.0258(19) Å in (PNP)PdCl,16
2.086(4) Å in (FPNP)PdH,46 and 2.0938(15) Å in (FPNP)-
PdMe46). It is also instructive to analyze how the PdÀN bond
length depends on the nature of X and Y in [(PN(X)P)PdÀY]+.
With regard to the regioselectivity of the BÀH addition,
4-BArF4 can be ruled out as an intermediate en route to 2-BArF .
4
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Inorganic Chemistry
ARTICLE
The boryl moieties (as defined by the OÀBÀO planes)
attached to Pd in complexes 3-CB11H12 and 4-BArF4 are oriented
almost perpendicularly to the Pd coordination plane. Interest-
ingly, the two boryl moieties (BÀN and BÀPd) in 3-CB11H12
are almost perpendicular to each other, too. Both determined
PdÀB bond lengths (1.9879(16) Å in 3-CB11H12 and 1.993(4)
Å in 4-BArF ) are in the expected range for the palladium boryl
complexes.324 The other bond distances and angles associated
with the (PNP)Pd system in 2-BArF , 3-CB11H12, and 4-BArF
4
4
are unremarkable. The PÀPdÀP angle varies within ca. 157À
164°, and the PdÀP distances in all three compounds are in the
2.26À2.29 Å range.
’ CONCLUSION
Figure 3. ORTEP drawing48 (50% probability ellipsoids) of 3-CB11-
H12 showing selected atom labeling. Hydrogen atoms, the CB11H12
counterion, and the PhCF3 solvent molecule are omitted for clarity.
Selected bond distances (Å) and angles (deg) follow: Pd1ÀP1,
2.2753(4); Pd1ÀP2, 2.2880(4); Pd1ÀN1, 2.2517(11); Pd1ÀB1,
1.9879(16); P1ÀPd1ÀP2, 156.521(13); N1ÀPd1ÀB1, 175.16(5).
In conclusion, we have demonstrated that the [(PNP)Pd]+
fragment is capable of net heterolytic cleavage of the BÀH bond
in catecholborane and the BÀB bond in catecholdiboron. We
have isolated and physically characterized cationic palladium
hydrides and palladium boryl complexes. The activation of the
BÀH bond by [(PNP)Pd]+ resulted in the formation of PdÀH
and NÀB bonds. The addition of a BÀB bond across a PdÀN
bond to form a palladium boryl complex is unique. It provides
another route to palladium boryl complexes and to the cleavage
of the BÀB bond where oxidative addition of a BÀB bond to the
palladium center is difficult. Both the NÀB and the PdÀB bonds
are subject to hydrolysis, forming the corresponding NÀH and
PdÀH bonds.
’ EXPERIMENTAL SECTION
General Considerations. Unless specified otherwise, all manip-
ulations were performed under an argon atmosphere using a standard
Schlenk line or glovebox techniques. Ethyl ether, C6D6, and pentane
were dried over NaK/Ph2CO/18-crown-6, distilled or vacuum trans-
ferred, and stored over molecular sieves in an Ar-filled glovebox.
Fluorobenzene and catecholborane (CatBH) were dried with and then
distilled from CaH2. NaBArF ,34 (FPNP)PdOTf,49 and (PNP)PdH16
Figure 4. ORTEP drawing48 (50% probability ellipsoids) of 4-BArF
4
4
were prepared according to the published procedures. All other chemi-
cals were used as received from commercial vendors. NMR spectra were
recorded on a Varian iNova 300, Varian iNova 400, and Mercury 300
spectrometers. Chemical shifts are reported in δ (parts per million). For
1H and 13C NMR spectra, the residual solvent peak was used as an
internal reference. 31P NMR spectra were referenced externally using
85% H3PO4 at δ 0 ppm. 19F NMR spectra were referenced externally
using CF3COOH at δ À78.5 ppm. 11B NMR spectra were referenced
showing selected atom labeling. Hydrogen atoms (except H1), the
BArF4 counterion, and the cocrystallized molecules of CH2Cl2 and H2O
are omitted for clarity. Selected bond distances (Å) and angles (deg)
follow: Pd1ÀP1, 2.2635(8); Pd1ÀP2, 2.2859(8); Pd1ÀN1, 2.194(3);
Pd1ÀB1, 1.993(4); P1ÀPd1ÀP2, 159.94(3); N1ÀPd1ÀB1, 178.45(13).
Table 1. PdÀN Distances (from XRD Studies, in Å) for
externally using BF3 Et2O at δ 0 ppm. Elemental analyses were
Compounds [(PN(X)P)PdÀY]+ (1-OTf,14 2-BArF ,
3
4
performed by CALI, Inc. (Parsippany, NJ).
3-CB11H12, and 4-BArF
4
(PNP)PdOTf (A). (PNP)PdH (216 mg, 0.40 mmol) was dissolved in
10 mL of C6H6, followed by the addition of MeOTf (226 μL, 2.0 mmol).
The reaction mixture was allowed to stir at room temperature for 2 h.
The volatiles were removed under vacuum, and the residue was recrys-
tallized from toluene/pentane to give a pure solid. Yield: 225 mg, 85%.
1H NMR (C6D6): δ 7.50 (d, 2H, J = 8 Hz, (PNP)Aryl-H), 6.77 (s, 2H,
(PNP)Aryl-H), 6.60 (d, 2H, J = 8 Hz, (PNP)Aryl-H), 2.42 (m, 4H,
CHMe2), 2.02 (6H, Ar-CH3), 1.38 (dvt, 12H, CHMe2), 1.04 (dvt, 12H,
CHMe2). 13C{1H} NMR (C6D6): δ 163.2 (t), 132.8, 132.7, 127.3,
117.8, 117.5, 25.2 (m), 20.8, 18.7, 18.0. 31P{1H} NMR (C6D6): δ 53.6.
19F NMR (C6D6): δ À79.2.
X = CatB
X = H
Y = CatB
Y = H
2.2517 (11)
2.194(3)
2.202(2)
2.160(4)
The set of four compounds (X = CatB or H; Y = CatB or H) is
completed by considering 1-OTf (2.160(4) Å)14 alongside 2-BArF ,
4
3-CB11H12, and 4-BArF (Table 1). It is apparent that a
4
longer PdÀN bond length results from either X = BCat or Y =
BCat. The elongation of the PdÀN bonds may be attributed to
the greater trans influence of the boryl ligand than the hydride for
Y = BCat,47 and to the greater steric encumbrance of a boryl-
substituted amine for X = BCat.
[(PNP)Pd(THF)]BArF4 (B). (PNP)PdOTf (A) (70 mg, 0.10 mmol)
was dissolved in 5 mL of cold THF, followed by the addition of
Na[BArF ] (88 mg, 0.10 mmol). The reaction mixture was allowed to
4
stir at room temperature for 1 h. All of the volatiles were removed under
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vacuum, and the residue was dissolved in PhF. The mixture was filtered
off Celite, and the filtrate was pumped to dryness. The final pure product
was obtained after recrystallization from PhF/pentane. Yield: 88 mg,
60%. 1H NMR (CD2Cl2): δ 7.73 (s, 8H, BAr4-H), 7.58 (s, 4H, BAr4-H),
7.28 (d, 2H, J = 9 Hz, (PNP)Aryl-H), 6.92 (m, 4H, (PNP)Aryl-H), 3.95
(m, 4H, OCH2), 2.44 (m, 4H, CHMe2), 2.23 (s, 6H, Ar-CH3), 2.02 (m,
4H, CH2), 1.35 (dvt, 12H, CHMe2), 1.26 (dvt, 12H, CHMe2). 13C{1H}
NMR (CD2Cl2): δ 162.5 (q, J = 50 Hz), 162.1 (t), 135.4, 133.8, 132.5,
130.6, 129.6 (q, J = 234 Hz), 126.5, 123.8, 121.1, 118.1, 77.4, 25.6, 23.0,
20.5, 19.0, 18.1. 31P{1H} NMR (CD2Cl2): δ 55.5. 19F NMR (CD2Cl2):
δ À65.7. Elem. Anal. Found (calculated) for C62H60BNOF24P2Pd: C,
50.71 (50.65); H, 4.18 (4.11); N, 0.85 (0.95).
(PNP)PdCB11H12 (C). (PNP)PdOTf (A) (34.8 mg, 0.051 mmol)
was dissolved in 5 mL of PhF. CsCB11H12 (17 mg, 0.062 mmol) was
added to the solution. The mixture was stirred at RT overnight. The
solution was then passed through Celite. The volatiles were removed
under vacuum, and the resulting solid was recrystallized from PhF/
pentane. Yield: 28 mg, 83%. 1H NMR (CD2Cl2): δ 7.30 (d, J = 8 Hz, 2H,
(PNP)Aryl-H), 7.05 (br, 2H, (PNP)Aryl-H), 6.88 (d, J = 8 Hz, 2H,
(PNP)Aryl-H), 2.80 (m, 4H, CHMe2), 2.52À1.50 (br, 12H, CB11H12),
2.21 (s, 6H, Ar-CH3), 1.33 (app. q (dvt), J = 7.2 Hz, 12H, CHMe2)), 1.26
(app. q (dvt), J = 7.2 Hz, 12H, CHMe2). 13C{1H} NMR (C6D6): δ
162.1 (t, J = 9 Hz, (PNP)Aryl-C), 132.9 ((PNP)Aryl-C), 132.7 ((PNP)-
Aryl-C), 117.9 ((PNP)Aryl-C), 117.6 ((PNP)Aryl-C), 117.3 (t, J = 6 Hz,
(PNP)Aryl-C), 54.3, 26.0 (t, J = 11 Hz), 20.3, 20.0, 18.4. 31P{1H} NMR
(CD2Cl2): δ 60.0. 11B{1H} NMR (C6D6): δ À9.4, À13.2, À15.2. Elem.
Anal. Found (calculated) for C27H52B11NP2Pd: C, 47.57 (47.83); H,
7.68 (7.73); N, 2.10 (2.07).
The reaction mixture was passed through Celite, and the filtrate was
transferred to a PTFE-capped flask. H2 was introduced into the flask, and
the reaction was stirred vigorously for 5 min. The initial blue color
disappeared, and white precipitate was formed. The precipitate was col-
lected by filtration and washed three times with pentane. Yield: 72 mg,
1
70%. H NMR (CD2Cl2): δ 7.41À7.34 (m, 6H, (PNP)Aryl-H), 7.07
(br, 1H, N-H), 2.53 (m, 4H, CHMe2), 2.43 (s, 6H, Ar-CH3), 2.25À1.39
(m, 12H, CB11H12), 1.33 (app. q (dvt), J = 7.2 Hz, 6H, CHMe2), 1.17
(app. q (dvt), J = 7.2 Hz, 12H, CHMe2), 0.92 (app. q (dvt), J = 7.2 Hz,
6H, CHMe2), À12.5 (br, 1H, Pd-H). 31P{1H} NMR (CD2Cl2): δ 56.3.
[(PN(BCat)P)Pd(H)]BArF (2-BArF ). Compound B (40 mg,
4
4
0.029 mmol) was dissolved in about 1 mL of toluene/trifluorotoluene,
followed by the addition of CatB-H (3.0 μL, 0.029 mmol). The reaction
mixture was allowed to stand at room temperature for 1 h, and the
solution color changed to light yellow. Et3N (1 μL, 0.007 mmol) was
added to the mixture (to deprotonate and assist in the removal of the
traces of 1-BArF4 present). The volatiles were removed under vacuum,
and the residue was washed with trifluorotoluene/pentane to give a
white powder after drying under vacuum. Yield: 25 mg, 59%. X-ray
quality crystals were obtained by crystallizing the solid in CH2Cl2/
pentane at À35 °C. 1H NMR (C6D5Br): δ 8.20 (s, 8H, BAr4-H), 7.58 (s,
4H, BAr4-H), 7.26 (m, 4H, (PNP)Aryl-H), 7.02 (d, J = 8 Hz, 2H,
(PNP)Aryl-H), 6.72 (br, 4H, Catechol-H), 2.40 (m, 2H, CHMe2), 2.19
(br, 8H, Ar-CH3 + CHMe2), 1.92 (m, 2H, CHMe2), 1.11 (app. q (dvt),
J = 7.2 Hz, 6H, CHMe2), 0.89 (m, 12H, CHMe2), 0.64 (app. q (dvt),
J = 7.2 Hz, 6H, CHMe2), À12.7 (t, J = 4.8 Hz, 1H, Pd-H). 13C{1H}
NMR (C6D6): δ 162.9 (q, J = 50 Hz, BAr4-C), 147.1 (Catechol-C),
145.9 (t, J = 8 Hz, (PNP)Aryl-C), 139.7 (t, J = 3 Hz, (PNP)Aryl-C),
135.3 (BAr4-C), 134.3 ((PNP)Aryl-C), 133.5 ((PNP)Aryl-C), 129.9 (q,
J = 34 Hz, BAr4-C), 125.1 (d, J = 272 Hz, BAr4-C), 125.8 (t, J = 4 Hz
(PNP)Aryl-C), 124.4 (Catechol-C), 119.7 (BAr4-C), 117.9 (t, J = 4 Hz,
(PNP)Aryl-C), 112.7 (Catechol-C), 26.4 (t, J = 12 Hz), 24.6 (t, J = 13
Hz), 20.3 (t, J = 3 Hz), 20.2, 19.5 (t, J = 4 Hz), 18.9, 18.4. 31P{1H} NMR
(C6D6): δ 53.2. 19F NMR (C6D6): δ À63.1. 11B{1H} NMR (C6D6):
(FPNP)PdCB11H12 (FC). (FPNP)PdOTf (FA) (55 mg, 0.079 mmol)
was dissolved in 3 mL of fluorobenzene, and CsCB11H12 (27 mg, 0.097
mmol) was added with stirring. The solution immediately changed from
purple to dark blue. After approximately 10 min, the solution was passed
through a pad of Celite, the volatiles were removed under vacuum, and
the residue was washed with pentane. The residue was dried under
vacuum. Yield: 37 mg, 76%. 1H NMR (C6D6): δ 7.22 (m, 2H, Ar-H),
6.86 (m, 2H, Ar-H), 6.75 (t, J = 8 Hz, 2H, Ar-H), 3.4À1.4 (br, 12H,
CB11H12), 2.78 (br, 4H, CHMe2), 1.20 (app. q. (dvt), 12H, Hz, CH-
Me2), 1.06 (app. q. (dvt), 12H, Hz, CHMe2). 31P{1H} NMR (C6D6):
δ 58.5. 19F NMR (C6D6): δ À126.4.
δ 21.2 (N-B), À6.3 (BArF -B). Elem. Anal. Found (calculated) for
4
C64H57B2NO2F24P2Pd: C, 50.58 (50.64); H, 3.82 (3.78); N, 0.92 (0.92).
Thermolysis of 2-BArF . 2-BArF (13 mg, 0.009 mmol) was
4
4
dissolved in 0.6 mL of PhF in a J. Young NMR tube, and the solution
was heated at 90 °C for 15 h. 31P NMR spectroscopic analysis indicated
no observable changes.
[(PN(H)P)PdH]BArF (1-BArF ). Compound B (36 mg, 0.026
4
4
Reaction of 2-BArF4 with HBCat. Compound 2-BArF4 (10 mg,
0.0060 mmol) was dissolved in 0.6 mL of PhF in an NMR tube, followed
by the addition of HBCat (4.0 μL, 0.030 mmol). The NMR tube was
placed in a 95 °C oil bath. After 24 h, 31P{1H} NMR analysis indicated
mmol) was dissolved in 0.6 mL of PhF in a J. Young NMR tube. H2
(1 atm) was then introduced into the tube, and the mixture was allowed
to stand at room temperature for 30 min until the color changed to
colorless. All the volatiles were removed under vacuum. The oily residue
was washed with hexanes a few times to obtain an off-white powder. The
solid was dried under vacuum. Yield: 28 mg, 81%. 1H NMR (CD2Cl2):
δ 7.69 (s, 8H, BAr4-H), 7.53 (s, 4H, BAr4-H), 7.37 (m, 4H, (PNP)Aryl-
H), 7.30 (d, J = 6.6 Hz, (PNP)Aryl-H), 6.96 (br, 1H, N-H), 2.53 (m, 4H,
CHMe2), 2.41 (s, 6H, Ar-CH3), 1.34 (app. q (dvt), J = 7.2 Hz, 6H,
CHMe2), 1.13 (app. q (dvt), J = 7.2 Hz, 12H, CHMe2), 0.91 (app. q
(dvt), J = 7.2 Hz, 6H, CHMe2), À12.5 (br, 1H, Pd-H). 13C{1H} NMR
(C6D6): δ 162.9 (q, J = 50 Hz, BAr4-C), 145.5 (t, J = 8 Hz, (PNP)Aryl-
C), 139.3 (t, J = 3 Hz, (PNP)Aryl-C), 135.3 (BAr4-C), 134.2 ((PNP)-
Aryl-C), 133.2 ((PNP)Aryl-C), 129.9 (q, J = 32 Hz, BAr4-C), 125.1 (d,
J = 272 Hz, BAr4-C), 124.8 (t, J = 4 Hz, (PNP)Aryl-C), 119.7 (BAr4-C),
117.9 (t, J = 4 Hz, (PNP)Aryl-C), 25.4 (t, J = 12 Hz), 23.3 (t, J = 13 Hz),
20.3, 19.3 (t, J = 4 Hz), 18.6 (t, J = 4 Hz), 18.4, 17.7. 31P{1H} NMR
(C6D6): δ 56.4. 19F{1H} NMR (C6D6): δ À63.1. Elem. Anal. Found
(calculated) for C58H54BF24NP2Pd: C, 49.67 (49.75); H, 3.95 (3.89);
N, 1.71 (0.96).
full conversion to 3-BArF .
4
[(PN(BCat)P)Pd(H)]CB11H12 (2-CB11H12). Compound C (35 mg,
0.052 mmol) was dissolved in 0.6 mL of PhF, followed by the addition of
CatB-H (5.5 μL, 0.052 mmol). The reaction mixture was allowed to
stand at room temperature for 3 h, and the solution color changed to
light yellow. 31P NMR indicated that there was ∼10% of 1-CB11H12,
besides 90% of 2-CB11H12, in the reaction mixture. White crystals were
formed by carefully layering pentane on top of the PhF solution. Yield:
27 mg, 62%. However, NMR analysis indicated that these crystals still
contain a mixture of both 1-CB11H12 and 2-CB11H12. NMR data for
2-CB11H12: 1H NMR (C6D6) (a drop of CH2Cl2 was added to increase
solubility): δ 7.36 (m, 4H, (PNP)Aryl-H), 7.18 (br, 2H, (PNP)Aryl-H),
6.04 (br, 4H, Catechol-H), 2.51 (m, 2H, CHMe2), 2.30 (s, 6H, Ar-CH3),
2.25 (m, 2H, CHMe2), 2.18À1.60 (br, 12H, CB11H12), 1.14 (app. q
(dvt), J = 8 Hz, 6H, CHMe2), 0.95 (m, 12H, CHMe2), 0.68 (app. q (dvt),
J = 8 Hz, 6H, CHMe2), À12.6 (t, J = 5 Hz, 1H, Pd-H). 31P{1H} NMR
(C6D6): δ 53.3.
[(PN(H)P)PdH]CB11H12 (1-CB11H12). Compound A (104 mg,
0.152 mmol) was dissolved in 6.0 mL of PhF, followed by the addition
of CsCB11H12 (50.0 mg, 0.182 mmol). The reaction mixture was stirred
for 4 h and 31P NMR analysis indicated full conversion to compound C.
[(PN(BCat)P)Pd(BCat)]BArF4 (3-BArF ). Compound B (40 mg,
4
0.029 mmol) was dissolved in ca. 1 mL of toluene/trifluorotoluene,
followed by the addition of CatB-BCat (7.0 μL, 0.029 mmol). The
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reaction mixture was allowed to stir at room temperature for overnight,
and the solution changed to slightly yellow. Et3N (1 μL, 0.007 mmol)
was added to the mixture (to deprotonate and assist in the removal of the
traces of 4-BArF4 present). The volatiles were removed under vacuum,
and the residue was washed with trifluorotoluene/pentane to give a
white powder after drying under vacuum. However, we were not able to
was passed through Celite, and the volatiles were removed under vacuum.
The oily residue was washed with hexanes three times. X-ray quality crystals
were obtained by recrystallizing the off-white solid from CH2Cl2/hexanes.
Method B. Compound 3-BArF4 (63 mg, 0.039 mmol) was dissolved
in ca. 0.6 mL of PhF and then treated with degassed water (0.70 μL,
0.039 mmol). After 40 min at room temperature, 31P NMR observations
get 3-BArF4 in an analytical pure form. 1H NMR analysis indicated the
revealed full conversion to compound 4-BArF . Volatiles were removed
4
1
presence of a small amount of [Et3NH]BArF . Yield: 22 mg, 51%. H
under vacuum. The residue was recrystallized from CH2Cl2/hexanes.
Yield: 40 mg, 68%. 1H NMR (CD2Cl2): δ 7.71 (s, 8H, BAr4-H), 7.54
(s, 4H, BAr4-H), 7.37À7.43 (m, 6H, (PNP)Aryl-H), 7.23 (m, 2H, Cate-
chol-H), 7.06 (m, 2H, Catechol-H), 6.89 (br, 1H, N-H), 2.71 (m, 2H,
CHMe2), 2.58 (m, 2H, CHMe2), 2.43 (s, 6H, Ar-CH3), 1.20À1.07 (m,
18H, CHMe2), 0.92 (app. q (dvt), J = 7.2 Hz, 6H, CHMe2). 13C{1H}
NMR (CD2Cl2): δ 162.6 (q, J = 50 Hz, BAr4-C), 148.9 (Catechol-C),
145.2 (t, J = 8 Hz, (PNP)Aryl-C), 140.1 (t, J = 3 Hz, (PNP)Aryl-C),
135.4 (BAr4-C), 135.2 ((PNP)Aryl-C), 134.1 ((PNP)Aryl-C), 129.6 (q,
J = 34 Hz, BAr4-C), 125.2 (d, J = 272 Hz, BAr4-C), 125.7 (t, J = 4 Hz,
(PNP)Aryl-C), 122.9 (Catechol-C), 121.1 (BAr4-C), 118.0 (t, J = 4 Hz,
(PNP)Aryl-C), 112.5 (Catechol-C), 26.1 (t, J = 12 Hz), 24.3 (t, J = 13
Hz), 21.1, 19.7, 18.5, 18.4, 17.9. 31P{1H} NMR (CD2Cl2): δ 49.8.
4
NMR (C6D6): δ 8.27 (s, 8H, BAr4-H), 7.62 (s, 4H, BAr4-H), 7.10 (m,
2H, Catechol-H), 6.99 (br, 2H, (PNP)Aryl-H), 6.96 (m, 2H), 6.81À
6.85 (m, 4H), 6.70 (br, 4H), 2.23 (m, 4H, CHMe2), 2.03 (s, 6H,
Ar-CH3), 0.84 (app. q(dvt), J = 9 Hz, 6H, CHMe2), 0.70 (app. q(dvt), J = 8
Hz, 12H, CHMe2), 0.52 (app. q (dvt), J = 9 Hz, 6H, CHMe2)). 1H NMR
(CD2Cl2): 7.71 (s, 8H, BAr4-H), 7.55 (s, 4H, BAr4-H), 7.53 (d, 2H,
J = 6 Hz, (PNP)Aryl-H), 7.488 (br, 2H, (PNP)Aryl-H), 7.46 (d, 2H,
J = 6 Hz, (PNP)Aryl-H), 7.22 (m, 2H, Catechol-H), 7.12 (m, 4H,
Catechol-H), 7.06 (m, 2H, Catechol-H), 2.81 (m, 2H, CHMe2), 2.72
(m, 2H, CHMe2), 2.46 (s, 6H, Ar-CH3), 1.11 (m, 18H, CHMe2), 0.88
(app. q (dvt), J = 9 Hz, 6H, CHMe2). 13C{1H} NMR (C6D6): δ 162.9
(q, J = 50 Hz, BAr4-C), 148.3(Catechol-C), 147.1 (Catechol-C), 145.1
(t, J = 8 Hz, (PNP)Aryl-C), 139.7 (t, J = 3 Hz, (PNP)Aryl-C), 135.3
(BAr4-C), 134.5 ((PNP)Aryl-C), 133.7 ((PNP)Aryl-C), 130.0 (q, J = 34
Hz, BAr4-C), 123.3 (Catechol-C), 125.1 (d, J = 272 Hz, BAr4-C), 125.8
(t, J = 4 Hz, (PNP)Aryl-C), 124.5 (Catechol-C), 119.8 (BAr4-C), 117.9
(t, J = 4 Hz, (PNP)Aryl-C), 112.8 (Catechol-C), 112.3 (Catechol-C),
26.0 (t, J = 12 Hz), 24.5 (t, J = 13 Hz), 20.3, 19.9, 18.2, 17.5, 17.2.
31P{1H} NMR (C6D6): δ 44.7. 19F NMR (C6D6): δ À63.2. 11B{1H}
11B{1H} NMR (CD2Cl2): δ 37.1 (br, Pd-B), À6.87 (s, BArF -B). Elem.
4
Anal. Found (calculated) for C64H57B2NO2F24P2Pd: C, 50.31 (50.64);
H, 3.59 (3.78); N, 0.93 (0.92).
Thermolysis of 4-BArF . 4-BArF (13 mg, 0.009 mmol) was
4
4
dissolved in 0.6 mL of PhF in a J. Young NMR tube, and the solution
was heated at 90 °C for 15 h. 31P NMR spectroscopic analysis indicated
no observable changes.
NMR (C6D6): δ À6.4 (BArF -B).
4
Hydrolysis of 4-BArF . Compound 4-BArF4 (12 mg, 0.008 mmol)
4
[(PN(BCat)P)Pd(BCat)]CB11H12 (3-CB11H12). Compound C
(62 mg, 0.091 mmol) and CatB-BCat (24 mg, 0.10 mmol) were placed
in a PTFE-capped flask together with 3 mL of toluene. The reaction
mixture was heated at 60 °C overnight. The blue solution changed to
yellow-brown the next day, and white precipitate was visible at the bottom of
the flask. The white precipitate was collected on a glass frit by filtration and
was dried under vacuum. Yield: 47 mg, 57%. X-ray quality crystals were
obtained by slowly cooling down a hot PhCF3 solution of 3-CB11H12. 1H
NMR (C6D6) (a drop of CH2Cl2 was added to increase solubility):
δ 7.19À7.16 (m, 4H, (PNP)Aryl-H), 7.11 (br, 2H, (PNP)Aryl-H), 7.04
(m, 2H, Catechol-H), 6.82 (m, 2H, Catechol-H), 6.78 (br, 4H, Catechol-
H), 2.40 (m, 4H, CHMe2), 2.21 (s, 6H, Ar-CH3), 2.09À1.30 (br, 12H,
CB11H12), 0.84 (m, 18H, CHMe2), 0.61 (app. q (dvt), J = 8 Hz, 6H,
CHMe2). 13C{1H} NMR (C6D6) (a drop of CH2Cl2 was added to
increase the solubility): δ 148.3 (Catechol-C), 147.2 (Catechol-C),
145.1 (t, J = 8 Hz, (PNP)Aryl-C), 139.9 ((PNP)Aryl-C), 134.9 ((PNP)-
Aryl-C), 134.2 ((PNP)Aryl-C), 130.1 (t, J = 14 Hz, (PNP)Aryl-C),
126.3 (t, J = 3 Hz, (PNP)Aryl-C), 124.4 (Catechol-C), 123.0 (Catechol-
C), 113.0 (Catechol-C), 112.3 (Catechol-C), 26.3 (t, J = 13 Hz), 24.8
(t, J = 13 Hz), 20.9, 20.3, 18.6, 18.0, 17.7, one C for CB11H12 anion is
missing. 31P{1H} NMR (C6D6) (a drop of CH2Cl2 was added to
increase solubility): δ 45.0. 11B{1H} NMR (C6D6) (a drop of CH2Cl2
was added to increase solubility): δ À6.6, À12.9, À15.9 (CB11H12-B).
Elem. Anal. Found (calculated) for C39H60B13NO4P2Pd: C, 51.27
(51.15); H, 6.69 (6.60); N, 1.64 (1.53).
was dissolved in 1 mL of toluene in an NMR tube. Degassed water
(1.0 μL, excess) was added. After 4 h, 31P{1H} NMR analysis indicated
ca. 40% conversion to compound 1-BArF . It was fully converted to
4
1-BArF4 after ca. 40 h.
’ ASSOCIATED CONTENT
S
Supporting Information. Crystallographic details for the
b
XRD structural determinations of compounds 2-BArF , 3-CB11-
4
H12, 5, and 4-BArF4 in the form of CIF files and a pictorial 1H
NMR spectrum of select compounds. This material is available
free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: ozerov@chem.tamu.edu.
’ ACKNOWLEDGMENT
This research was supported by the NSF (grants CHE-0809522
and CHE-0944634), the Welch Foundation (grant A-1717), the
Dreyfus Foundation (Camille Dreyfus Teacher-Scholar Award
to O.V.O.), and the Alfred P. Sloan Foundation (Sloan Research
Fellowship to O.V.O.). We also thank the National Science
Foundation for the partial support of this work through grant
CHE-0521047 for the purchase of a new X-ray diffractometer at
Brandeis University. We would like also like to express our
gratitude to Linda Redd for editorial assistance, Samuel Timpa
for help with the creation of graphical NMR spectra, and Daniel
Graham and Gregory Day for contributions to the solution of the
solid-state structure of 3-CB11H12.
Hydrolysis of 3-CB11H12. Compound 3-CB11H12 (5.0 mg, 0.0060
mmol) was dissolved in 1 mL PhCF3, followed by the addition of 1 μL
(excess) of degassed water. Upon addition, 31P{1H} NMR analysis
indicated 15% of 1-CB11H12 and 85% of a signal at 49.7 ppm (likely
4-CB11H12). The reaction mixture was fully converted to 1-CB11H12
after standing overnight.
[(PN(H)P)Pd(BCat)]BArF (4-BArF ). Method A. A solution of
4
4
0.015 mmol of 1-BArF4 in 0.6 mL of PhF in a J. Young tube was treated
with catecholborane (8.0 μL, 0.075 mmol), and the reaction mixture was
allowed to sit in a 90 °C oil bath overnight. 31P NMR observations
revealed quantitative conversion to compound 4-BArF . The mixture
4
7986
dx.doi.org/10.1021/ic2001283 |Inorg. Chem. 2011, 50, 7980–7987

Inorganic Chemistry
ARTICLE
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