Synthesis, cis/trans isomerization, and reactivity of palladium alkyl complexes that contain a chelating N-Heterocyclic-carbene sulfonate ligand

Article abstract of DOI:10.1021/om200482a

The chemistry of palladium alkyl complexes that incorporate the NHC-sulfonate ligand N-(2,6-ⁱPr₂-Ph)-N′-2- benzenesulfonate-NHC ([C-O]^-, NHC = cyclo-CNCH₂CH ₂N) is described. The reaction of {C-O}Ag (2) with Pd ₂(μ-Cl)₂Me₂(PPh₃)₂ affords cis-C,C-{C-O}PdMe(PPh₃) (3, 79%). The reaction of 2 with Pd₂(μ-Cl)₂Me₂(2,6-lutidine)₂ at 25 °C in CH₂Cl₂ gives a 4/1 mixture of trans-C,C-{C-O}PdMe(2,6-lutidine) (4a) and cis-C,C-{C-O}PdMe(2,6-lutidine) (4b), which were isolated in 62% and 18% yield, respectively, by recrystallization. The NHC-sulfonate ligands bind in a κ²-C,O fashion in 3 and 4a,b. 4a isomerizes to 4b by dissociation of the Ar-SO₃^- unit to form a configurationally labile three-coordinate intermediate. This process is accelerated by hydrogen bond donors (CD₃OD, lutidinium) and Lewis acids (B(C₆F₅)₃) that can labilize the sulfonate group. 4a and 4b react with 1 equiv of B(C₆F ₅)₃ to yield the O-bound adduct cis-C,C-{C-O-B(C ₆F₅)₃}PdMe(2,6-lutidine) (5). 5 decomposes at 40 °C by C-C reductive elimination to afford (in the presence of pyridine to trap the B(C₆F₅)₃) N-(2,6-ⁱPr ₂-Ph)-N′-2-benzenesulfonate-imidazolium methyl (6). trans-C,C-4a reacts with CO and ^tBuNC to yield the insertion products {C-O}Pd{C(=O)Me}(2,6-lutidine) (7) and {C-O}Pd{C(=N^tBu)Me}( ^tBuNC) (9), in which the acyl and iminoacyl ligands are cis to the NHC ligand, via stereospecific displacement of Ar-SO₃^- by the substrate followed by migratory insertion. The bis-isocyanide adduct {κ¹-C-C-O}PdMe(^tBuNC)₂, in which the ^tBuNC ligands are trans, is an intermediate in the formation of 9. ^tBuNC reversibly displaces the Ar-SO₃^- ligand of 9 to form {κ¹-C-C-O}Pd{C(=N^tBu)Me}( ^tBuNC)₂ (10). In contract, cis-C,C-4a does not undergo net reaction with CO and reacts with ^tBuNC via reductive elimination to yield 6. Displacement of the ArSO₃^- ligand of cis-C,C-4b by potential substrates yields adducts in which the substrate and Me group are trans and insertion is not possible.

Full text of DOI:10.1021/om200482a

ARTICLE
pubs.acs.org/Organometallics
Synthesis, cis/trans Isomerization, and Reactivity of Palladium Alkyl
Complexes That Contain a Chelating N-Heterocyclic-Carbene
Sulfonate Ligand
Xiaoyuan Zhou and Richard F. Jordan*
Department of Chemistry, The University of Chicago, 5735 South Ellis Avenue, Chicago, Illinois 60637, United States
S Supporting Information
b
ABSTRACT: The chemistry of palladium alkyl complexes that
incorporate the NHC-sulfonate ligand N-(2,6-iPr2-Ph)-N0-2-ben-
zenesulfonate-NHC ([C-O]ꢀ, NHC = cyclo-CNCH2CH2N) is
described. The reaction of {C-O}Ag (2) with Pd2(μ-Cl)2Me2-
(PPh3)2 affords cis-C,C-{C-O}PdMe(PPh3) (3, 79%). The reac-
tion of 2 with Pd2(μ-Cl)2Me2(2,6-lutidine)2 at 25 °C in CH2Cl2
gives a 4/1 mixture of trans-C,C-{C-O}PdMe(2,6-lutidine) (4a) and cis-C,C-{C-O}PdMe(2,6-lutidine) (4b), which were isolated
in 62% and 18% yield, respectively, by recrystallization. The NHC-sulfonate ligands bind in a k2-C,O fashion in 3 and 4a,b. 4a
isomerizes to 4b by dissociation of the Ar-SO3ꢀ unit to form a configurationally labile three-coordinate intermediate. This process is
accelerated by hydrogen bond donors (CD3OD, lutidinium) and Lewis acids (B(C6F5)3) that can labilize the sulfonate group. 4a
and 4b react with 1 equiv of B(C6F5)3 to yield the O-bound adduct cis-C,C-{C-O-B(C6F5)3}PdMe(2,6-lutidine) (5). 5 decomposes
at 40 °C by CꢀC reductive elimination to afford (in the presence of pyridine to trap the B(C6F5)3) N-(2,6-iPr2-Ph)-N0-2-
benzenesulfonate-imidazolium methyl (6). trans-C,C-4a reacts with CO and tBuNC to yield the insertion products {C-O}Pd{C-
(dO)Me}(2,6-lutidine) (7) and {C-O}Pd{C(dNtBu)Me}(tBuNC) (9), in which the acyl and iminoacyl ligands are cis to the
NHC ligand, via stereospecific displacement of Ar-SO3ꢀ by the substrate followed by migratory insertion. The bis-isocyanide adduct
t
t
{k1-C-C-O}PdMe(tBuNC)2, in which the BuNC ligands are trans, is an intermediate in the formation of 9. BuNC reversibly
displaces the Ar-SO3ꢀ ligand of 9 to form {k1-C-C-O}Pd{C(dNtBu)Me}(tBuNC)2 (10). In contract, cis-C,C-4a does not undergo
net reaction with CO and reacts with tBuNC via reductive elimination to yield 6. Displacement of the ArSO3ꢀ ligand of cis-C,C-4b by
potential substrates yields adducts in which the substrate and Me group are trans and insertion is not possible.
’ INTRODUCTION
Palladium(II) alkyl complexes that contain ortho-phosphino-
arenesulfonate ligands ({PO}ꢀ, A, Figure 1) exhibit unique
behavior in olefin polymerization. {PO}Pd(R)(L) species (L =
labile ligand) polymerize ethylene to linear polyethylene and
copolymerize ethylene with a variety of polar vinyl monomers to
functionalized linear polymers.1 One interesting feature of
{PO}Pd species is the electronic asymmetry that results from
the cis arrangement of the phosphine ligand, a strong donor, and
the sulfonate ligand, a very weak donor. This property may
inhibit β-H elimination, thus disfavoring chain-walking and
leading to the formation of linear polymers, and β-X elimina-
tions, thus enabling the incorporation of CH2dCHX monomers
in ethylene polymerization. N-Heterocyclic carbenes (NHCs)
are stronger donors than typical phosphines and have been
widely used in organometallic chemistry.2 Chelating NHC-sul-
fonate ligands may provide enhanced electronic asymmetry and
lower metal electrophilicity compared to phosphine-sulfonate
Figure 1. Metal complexes that contain ortho-phosphino-arenesulfo-
nate or chelating NHC-sulfonate ancillary ligands.
ligands and, thus, are potentially interesting as ancillary ligands
for late transition metal catalysts.
asymmetric conjugate addition, allylic alkylation, hydroboration,
and diboronation reactions.3 Nozaki reported the palladium alkyl
Hoveyda reported a series of chiral ortho-NHC-arenesulfonate
ligands, one example of which is shown as the dinuclear silver salt
B in Figure 1, and described their application in copper-catalyzed
Received: June 6, 2011
Published: August 17, 2011
r
2011 American Chemical Society
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Scheme 1
Figure 2. Molecular structure of 3. Hydrogen atoms are omitted.
Selected bond lengths (Å) and angles (deg): Pd(1)ꢀC(26) 2.019(4),
Pd(1)ꢀC(1) 2.014(4), Pd(1)ꢀP(1) 2.331(1), Pd(1)ꢀO(1) 2.179(3),
S(1)ꢀO(1) 1.472(3), S(1)ꢀO(2) 1.438(3), S(1)ꢀO(3) 1.440(3);
C(1)ꢀPd(1)ꢀC(26) 86.32(16), C(1)ꢀPd(1)ꢀP(1) 93.48(12), O-
(1)ꢀPd(1)ꢀC(26) 93.76(13), O(1)ꢀPd(1)ꢀP(1) 86.34(8).
Scheme 2a
a Ar = 2,6-iPr2-Ph.
complex C, which contains an NHC-sulfonate ligand in which
the NHC and sulfonate units are linked by a methylene spacer
(Figure 1).4 Here we describe the syntheses of an achiral
Hoveyda-type ortho-NHC-arenesulfonate ligand and several Pd-
(II) complexes of this ligand and studies of the dynamic proper-
ties and insertion reactivity of these species.
Figure 3. Molecular structure of one independent molecule of 4b.
Hydrogen atoms are omitted. Selected bond lengths (Å) and angles
(deg): Pd(1)ꢀC(9) 1.964(11), Pd(1)ꢀC(29) 2.068(9), Pd(1)ꢀN(3)
2.124(9), Pd(1)ꢀO(1) 2.163(6), S(1)ꢀO(1) 1.483(7), S(1)ꢀO(2)
1.455(7), S(1)ꢀO(3) 1.431(7); C(9)ꢀPd(1)ꢀC(29) 89.1(4), C-
(29)ꢀPd(1)ꢀN(3) 90.0(4), C(9)ꢀPd(1)ꢀO(1) 93.7(3), O(1)ꢀPd-
(1)ꢀN(3) 87.4(3).
’ RESULTS AND DISCUSSION
Synthesis of {C-O}Pd Alkyl Complexes. The zwitterion
N-(2,6-iPr2-Ph)-N0-2-benzenesulfonate-imidazolium (1, {C-O}H,
Scheme 1) was prepared using the route developed by Hoveyda for
the chiral analogue in B.3a Pd-catalyzed coupling of isobutyl
2-bromobenzenesulfonate with N-2,6-iPr2-phenyl-ethylenediamine
yields the corresponding isobutyl-2-(2-arylaminoethylamino)-
benzenesulfonate. Condensation of this intermediate with triethyl
orthoformate in the presence of acetic acid affords 1 as a white -
solid (Scheme 1). The reaction of 1 with Ag2O yields the {C-O}Ag
complex (2, {C-O}ꢀ = N-(2,6-iPr2Ph)-N0-2-benzenesulfonate-
NHC). 2 may have a dinuclear structure analogous to that of B,
but this issue was not addressed. The reaction of 2 with Pd2(μ-
Cl)2Me2(PPh3)2 affords cis-C,C-{C-O}PdMe(PPh3) (3, Scheme 2)
in 79% yield. The reaction of 2 with Pd2(μ-Cl)2Me2(2,6-lutidine)2 at
25 °C in CH2Cl2 gives a 4/1 mixture of trans-C,C-{C-O}PdMe(2,6-
lutidine) (4a) and cis-C,C-{C-O}PdMe(2,6-lutidine) (4b) as a white
powder (Scheme 2). 4a and 4b were separated by recrystallization
and isolated in 62% and 18% yield, respectively.
Structures of {C-O}PdMe(L) Complexes. The molecular
structure of 3 is shown in Figure 2. The seven-membered {C-
O}Pd chelate ring adopts a twist-boat conformation,5 with an
angle of 87.5(2)o between the Pd square plane (O(1)ꢀPd-
(1)ꢀC(26)) and the backbone plane of the {C-O}ꢀ ligand
(S(1)ꢀC(20)ꢀC(25)ꢀN(1)). The NHC ligand is rotated out
of the Pd square plane by 62.8(4)o, as measured by the angle
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Table 1. Kinetics of Isomerization of 4a to 4b
entry
conditions (22 °C)
k1 (10ꢀ5 sꢀ1 a
)
1
2
3
4
5
6
CD2Cl2
3.2(1)
5.2(1)
1.4(1)
53(1)
22(1)
38(1)
CD2Cl2 with 2,6-lutidine (20 equiv)
60% v/v acetone-d6 in CD2Cl2
60% v/v CD3OD in CD2Cl2
CD2Cl2 with [2,6-lutidinium][B(C6F5)4] (0.1 equiv)
CD2Cl2 with B(C6F5)3 (0.1 equiv)
a First-order rate constant for isomerization.
Figure 4. Molecular structure of 4a. Hydrogen atoms are omitted.
Selected bond lengths (Å) and angles (deg): Pd(1)ꢀC(15) 2.114(3),
Pd(1)ꢀC(1) 2.075(3), Pd(1)ꢀN(1) 2.029(3), Pd(1)ꢀO(3) 2.083(2),
S(1)ꢀO(3) 1.492(2), S(1)ꢀO(2) 1.436(2), S(1)ꢀO(1) 1.442(2);
C(15)ꢀPd(1)ꢀN(1) 100.14(12), C(15)ꢀPd(1)ꢀO(3) 90.58(11),
N(1)ꢀPd(1)ꢀC(1) 85.88(12), O(3)ꢀPd(1)ꢀC(1) 83.44(12).
between the N(1)ꢀC(26)ꢀN(2) and O(1)ꢀPd(1)ꢀC(26)
planes.
Complex 4b crystallizes with two independent molecules in
the asymmetric unit cell, both of which are structurally similar to
3. The structure of one molecule of 4b is shown in Figure 3. The
{C-O}Pd chelate ring of 4b is puckered with an angle of 89.4(4)o
between the O(1)ꢀPd(1)ꢀC(9) and S(1)ꢀC(1)ꢀC(6)ꢀ
N(1) planes and 85.9(4)o between the O(4)ꢀPd(2)ꢀC(38)
and S(2)ꢀC(30)ꢀC(35)ꢀN(4) planes in the two independent
molecules. The NHC ligand is rotated out of the Pd square
plane by 59.4(9)o and 64.4(9)o in the two independent mol-
ecules (N(1)ꢀC(9)ꢀN(2)/O(1)ꢀPd(1)ꢀC(9) and (N(4)ꢀ
C(38)ꢀN(5)/O(4)ꢀPd(2)ꢀC(38) dihedral angles). The 2,6-
lutidine ligand is trans to the NHC ligand and is oriented
perpendicular to the Pd square plane, as observed in the
Figure 5. Kinetics of isomerization of 4a to 4b at 22 °C. Ao= [4a] at t = 0 s.
A = [4a] at time t.
analogous complex {P-O}PdMe(2,6-lutidine) (D, {P-O}ꢀ
=
2-P(2-OMe-Ph)2-benzenesulfonate).1f The PdꢀN (2.124(9),
2.105(9) Å) and PdꢀMe (2.068(9), 2.050(9) Å) bond lengths
in 4b are similar to those in D (PdꢀN: 2.134(2); PdꢀMe:
2.107(3) Å).
for the ꢀCH(CH3)2 methine hydrogens. The 13C{1H} NMR
spectrum contains doublets for the Pd-CH3 (2JCP = 5 Hz) group
and the NHC carbene carbon (δ = 207, 2JCP = 133 Hz), which
confirms the presence of a coordinated NHC ligand.6 These
results are consistent with the solid-state structure and restricted
rotation around the N(2)ꢀC(29) bond.
The molecular structure of the trans-C,C isomer 4a is shown in
Figure 4. The twist-boat conformation of the {C-O}Pd chelate
ring of 4a is similar to those in 3 and 4b, with an angle of 82.9(1)o
between the O(3)ꢀPd(1)ꢀC(15) and S(1)ꢀC(9)ꢀC(14)ꢀ
N(2) planes and an angle of 64.5(3)o between the NHC and Pd
square planes (N(3)ꢀC(15)ꢀN(2)/O(3)ꢀPd(1)ꢀC(15)).
The PdꢀCNHC distance in 4a (2.114(3) Å) is 0.15 Å longer
than that in 4b (1.964(11) Å), which reflects the difference in
trans influence between the methyl and lutidine ligands that are
trans to the NHC in the two species. The PdꢀN (2.029(3) Å)
and PdꢀO (2.083(2) Å) bonds in 4a are shorter by 0.095 and
0.080 Å than those in 4b. The N(1)ꢀPd(1)ꢀC(15) angle
(100.14(12)°) in 4a is much larger than other bond angles at
Pd due to steric repulsion between 2,6-iPr2-Ph and 2,6-
lutidine rings.
The 1H NMR spectrum of 4b is very similar to that of 3. Two
sharp singlets are observed for the 2,6-lutidine methyl groups
(δ 2.43 and 2.20), indicating that rotation around the PdꢀN
bond is slow on the NMR T2 time scale. However, cross-peaks
linking those resonances are observed in the phase-sensitive
EXSY spectrum, which is indicative of slow rotation (T1 time
scale) around the PdꢀN bond. In contrast, the PdꢀN bond
rotation in D is fast on the NMR time scale.1f
1
The H NMR spectrum of 4a exhibits several differences
compared to that of 4b. In particular, one ꢀCH(CH3)2 reso-
nance (δ 0.01), one ꢀCH(CH3)2 resonance (δ 2.47), and
one 2,6-lutidine ꢀCH3 resonance (δ 1.84) of 4a are shifted
upfield by 0.3ꢀ1.1 ppm from the corresponding resonances in
4b, consistent with the anisotropic shielding expected from the
1
The ambient-temperature H NMR spectrum of 3 contains
a doublet for the Pd-CH3 group (3JHP = 7 Hz), four doublets
for ꢀCH(CH3)2 (3JHH = 7 Hz) hydrogens, and two multiplets
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Scheme 3
Figure 6. Molecular structure of 5. Hydrogen atoms are omitted, and
only the ipso carbons of the C6F5 rings are shown. Selected bond lengths
(Å) and angles (deg): Pd(1)ꢀC(2) 1.968(3), Pd(1)ꢀC(1) 2.002(3),
Pd(1)ꢀN(4) 2.106(2), Pd(1)ꢀO(18) 2.1984(19), S(1)ꢀO(18)
1.4582(19), S(1)ꢀO(16) 1.432(2), S(1)ꢀO(17) 1.5169(19), B-
(1)ꢀO(17) 1.569(4); C(1)ꢀPd(1)ꢀC(2) 89.52(12), C(1)ꢀPd(1)ꢀ
N(4) 89.52(11), C(2)ꢀPd(1)ꢀO(18) 95.58(9), O(18)ꢀPd(1)ꢀN-
(4) 85.40(8).
orientation of the 2,6-iPr2-Ph and 2,6-lutidine rings in the solid-
state structure of 4a. No cross-peaks between the two 2,6-lutidine
methyl resonances were observed in the EXSY spectrum, in-
dicating that PdꢀN bond rotation is slow.
Isomerization of 4a to 4b. The trans-C,C complex 4a
isomerizes to the cis-C,C isomer 4b at 22 °C in CD2Cl2 solution
(eq 1). 1H NMR kinetic studies show that this isomerization is
first-order in 4a, with a first-order rate constant k1 = 3.2(1) ꢁ
10ꢀ5 sꢀ1 (Table 1, entry 1, and Figure 5). The addition of free
2,6-lutidine (20 equiv) has only a minimal effect on the isomer-
ization rate (Table 1, entry 2). Under these conditions, no line
uncatalyzed cis/trans isomerization of square-planar platinum com-
plexes by kinetic studies.8
1
The influence of additives on the rate of isomerization of 4a
to 4b was studied with the expectation that additives that can
solvate or stabilize the sulfonate group would accelerate the
isomerization if mechanism III is operative but have little
effect on this process if mechanism I or II is operative. The
addition of acetone-d6 (60 vol %) inhibits the isomerization
process slightly (Table 1, entry 3). In contrast, the addition of
CD3OD (60 vol %), a hydrogen-bond donor, or [2,6-
lutidinium][B(C6F5)4] (0.1 equiv), a noncoordinating hydro-
gen-bond donor, results in significant acceleration of the
isomerization rate (Table 1, entries 4, 5). These effects can
be ascribed to labilization of the sulfonate group through
hydrogen bonding and are consistent with mechanism III. A
similar specific solvent effect was observed for the thermo-
dynamics of tautomerization of N,N-dimethylvaline; 95% of
this amino acid exists as the zwitterion form in methanol, while
81% is in the neutral form in acetone.9 The addition of
B(C6F5)3 (0.1 equiv) also results in a significant acceleration
of the isomerization of 4a to 4b. This effect is ascribed to
labilization of the sulfonate group by O---B(C6F5)3 coordina-
tion and is also consistent with mechanism III. Collec-
tively, these results support mechanism III over mechanisms
I and II.
broadening was observed in the H NMR spectrum, indicating
the exchange between free and coordinated 2,6-lutidine is slow
on the NMR time scale. These results rule out isomerization
mechanisms that involve the formation of three- or five-coordi-
nate intermediates through dissociation or association of 2,6-
lutidine.1o
Three plausible isomerization mechanisms for the isomer-
ization of 4a to 4b that are consistent with the first-order
behavior in 4a and lack of influence of free 2,6-lutidine on the
isomerization rate are shown in Scheme 3. Mechanism I
involves movement of the 2,6-lutidine and methyl groups by
about 90° from their positions in the ground-state structure to
form a transition state in which the geometry at Pd may be
described as square pyramidal with one basal vacancy. Mech-
anism II involves bidentate coordination of the sulfonate
group to generate a five-coordinate intermediate or transition
state that undergoes Berry pseudorotation. Mechanisms I and
II are analogous to the mechanism of isomerization of
{PO}PdR(ethylene) species proposed by Ziegler and by
Nozaki and Morokuma on the basis of DFT calculations.7,1j
Mechanism III involves dissociation of the sulfonate group
to form a configurationally labile, three-coordinate intermedi-
ate and is analogous to the mechanism implicated for the
Reaction of 4a,b with B(C6F5)3. The reaction of 4a or 4b with
1 equiv of B(C6F5)3 in CD2Cl2 generates the cis-C,C O-bound
B(C6F5)3 adduct 5 (eq 2), which was isolated by crystallization
from CD2Cl2/hexane. The molecular structure of 5 is shown in
Figure 6. The PdꢀMe (2.002(3) Å) bond in 5 is ca. 0.06 Å
shorter, and the SꢀOB (1.5169(19) Å) bond is ca. 0.07 Å longer
than the corresponding distances in 4b, but the other metrical
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Scheme 4a
Scheme 5a
a L = 2,6-lutidine.
a Ar = 2,6-iPr2C6H3, L = 2,6-lutidine.
the Pd-CH3 resonance is shifted 0.2 ppm downfield from
the corresponding resonances of 4b. The 11B NMR resonance
(δ ꢀ1.5) is consistent with a BꢀO interaction and a four-
coordinate boron center.10 The two 2,6-lutidine methyl reso-
nances of 5 are only slightly shifted but are strongly broadened
compared to those of 4b, indicating that rotation around the
PdꢀN bond is faster in the former species.
Compound 5 decomposes at 40 °C by CꢀC reductive
elimination to generate the O-bound B(C6F5)3 adduct of the
zwitterion N-(2,6-iPr2-Ph)-N0-2-benzenesulfonate-imidazolium
methyl (6 B(C6F5)3), which was converted to 6 by reaction
3
with pyridine (eq 3). This reaction is complete within 30 h at
40 °C. In contrast, only ca. 50% of 4b decomposes to 6 after 30 h
at 40 °C. The increase in effective charge at Pd due to O-bound
B(C6F5)3 may promote the reductive elimination. The 13C NMR
spectrum of 6 contains a resonance (δ 169), which is character-
istic of the [ꢀNC(CH3)Nꢀ]+ unit.11 A similar decomposition
pathway was observed for [(NHC)2PdMe(DMSO)][NO3] and
[(NHC)PdMe(COD)][BF4] complexes.11d
Figure 7. Molecular structure of 7. Hydrogen atoms are omitted.
Selected bond lengths (Å) and angles (deg): Pd(1)ꢀC(16) 2.006(5),
Pd(1)ꢀC(1) 1.954(5), Pd(1)ꢀN(1) 2.126(4), Pd(1)ꢀO(2) 2.231(3),
S(1)ꢀO(2) 1.482(3), S(1)ꢀO(3) 1.449(3), S(1)ꢀO(4) 1.447(3),
C(1)ꢀO(1) 1.213(5); C(1)ꢀPd(1)ꢀC(16) 90.84(19), C(1)ꢀPd-
(1)ꢀN(1) 90.18(18), C(16)ꢀPd(1)ꢀO(2) 90.67(16), O(2)ꢀPd-
(1)ꢀN(1) 88. 42(13).
parameters of 5 are only minimally perturbed by the presence of
the borane.
Reaction of 4a,b with CO. {PO}PdR species readily insert
CO and ethylene, which is the basis for copolymerization of these
substrates.12 The reactions of 4a,b with CO were investigated for
comparison with {PO}PdR species. 4a reactswithCO(200mmHg,
25 °C, CD2Cl2) immediately to produce the acyl complex {C-
O}Pd{C(dO)Me}(2,6-lutidine) (7, Scheme 4) in quantitative
yield. In contrast, 4b does not react with CO under these conditions.
This difference is consistent with initial stereospecific substitution of
the sulfonate by CO (Scheme 4). For 4a, CO binds cis to the Pd-Me
group, which leads to insertion, while for 4b, CO binds trans to the
Pd-Me group, and insertion is not possible.13
1
The H and 19F NMR spectra of 5 in CD2Cl2 solution are
slightly different from those of 4b and free B(C6F5)3, consistent
with retention of the BꢀO interaction in solution. In particular,
1
the H NMR resonance for the hydrogen that is ortho to the
sulfonate group (δ 8.15 in 4b) is shifted >0.3 ppm upfield and
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Figure 9. Molecular structure of 9. Hydrogen atoms and the three
methyl groups on C(8) are omitted. Selected bond lengths (Å) and
angles (deg): Pd(1)ꢀC(18) 2.061(5), Pd(1)ꢀC(1) 2.004(6), Pd-
(1)ꢀC(6) 2.019(6), Pd(1)ꢀO(1) 2.204(4), S(1)ꢀO(1) 1.487(4),
S(1)ꢀO(2) 1.435(4), S(1)ꢀO(3) 1.445(4), C(1)ꢀN(1) 1.149(7),
C(6)ꢀN(2) 1.248(8); C(1)ꢀPd(1)ꢀC(6) 84.8(2), C(1)ꢀPd(1)ꢀO-
(1) 86.8(2), C(6)ꢀPd(1)ꢀC(18) 96.3(2), C(18)ꢀPd(1)ꢀO(1)
92.15(18).
Figure 8. Molecular structure of 8. Hydrogen atoms are omitted. Selected
bond lengths (Å) and angles (deg): Pd(1)ꢀC(12) 2.096(2), Pd(1)ꢀC-
(11) 2.106(2), Pd(1)ꢀC(1) 1.981(3), Pd(1)ꢀC(6) 1.980(2), S(1)ꢀO-
(1) 1.4546(19), S(1)ꢀO(2) 1.455(2), S(1)ꢀO(3) 1.4535(19); C(1)ꢀ
Pd(1)ꢀC(12) 98.49(10), C(1)ꢀPd(1)ꢀC(11) 83.82(10), C(6)ꢀPd-
(1)ꢀC(11) 87.78(10), C(6)ꢀPd(1)ꢀC(12) 89.86(10).
The solid-state structure of 7 is shown in Figure 7 and is very
similar to that of the methyl analogue 4b. The acyl ligand in 7 is
rotated out of the Pd square plane by 64.9(5)o, as measured by
the angle between the Pd(1)ꢀC(1)ꢀO(1) and C(1)ꢀPd-
(1)ꢀC(16) planes.14
t
Reaction of 4a with BuNC. The proposed adducts 4a CO
3
and 4b CO were not observed in NMR monitoring experiments.
3
In order to provide support for the formation of these inter-
mediates and further probe the reactivity difference between 4a
and 4b, the reactions of these species with tert-butyl isocyanide
were studied (Scheme 5).
Complex 4a reacts with tBuNC (2 equiv) within 5 min at ꢀ30 °C
to form the zwitterionic bis-tBuNC adduct 8, presumably by the
stepwise displacement of the sulfonate and 2,6-lutidine ligands by
tBuNC. The presumed mono-tBuNC intermediate was not ob-
served by NMR under these conditions or at lower temperatures.
These results indicate that the second tBuNC substitution reaction
(presumably of 2,6-luditine) is faster than the first.
Complex 8 was crystallized by layering a solution of 4a and
tBuNC (2ꢀ3 equiv) in CH2Cl2 with cold hexane at ꢀ30 °C. The
molecular structure of 8 is shown in Figure 8. The PdꢀC(NHC)
distance is 0.018 Å shorter and the PdꢀMe distance is 0.031 Å
longer than the corresponding distances in 4a, which may
partially reflect the release of the constraints to Pd-NHC
coordination imposed by the chelation in 4a. One sulfonate
oxygen (O(2)) makes a close contact with one of the methylene
hydrogens of the NHC ring (O(2)---H(13A), 2.513(2) Å;
C(13)---O(2), 3.384(4) Å; C(13)ꢀH(31A)---O(2), 146.8(2)o),
consistent with the presence of a weak CH---O hydrogen bond.15 In
Figure 10. Molecular structure of 10. Hydrogen atoms are omitted.
Selected bond lengths (Å) and angles (deg): Pd(1)ꢀC(17) 2.060(4),
Pd(1)ꢀC(11) 2.063(4), Pd(1)ꢀC(1) 1.992(4), Pd(1)ꢀC(6) 2.056-
(4), S(1)ꢀO(1) 1.434(3), S(1)ꢀO(2) 1.433(3), S(1)ꢀO(3) 1.453
(3); C(17)ꢀPd(1)ꢀC(11) 94.52(14), C(17)ꢀPd(1)ꢀC(6) 94.05-
(15), C(1)ꢀPd(1)ꢀC(6) 90.41(16), C(1)ꢀPd(1)ꢀC(11) 81.16(15).
Addition of excess tBuNC to 9 yields the zwitterion 10, in which
the sulfonate group has been displaced by tBuNC. Removal of the
excess tBuNC results in reversion of 10 to 9 with the release of
tBuNC over the course of several days at 25 °C. The molecular
structure of 9 is shown in Figure 9. The iminoacyl group is cis to
the NHC, as expected for migratory insertion of 8, and is rotated
such that the imine unit is perpendicular to the Pd square plane
(angle between the Pd(1)ꢀC(6)ꢀN(2) and O(1)ꢀPd(1)ꢀC-
(18) planes: 86.4(5)o). The molecular structure of 10 is shown
in Figure 10. The sulfonate group is engaged in a CH---O hydro-
gen bond with a NHC methylene hydrogen (O(3)---H(24B),
1
the H NMR spectrum of 8 in CD2Cl2 solution (ꢀ30 °C), one
NHC methylene resonance (δ 5.53) is shifted downfield by ca. 1.2
ppm from the range observed for the resonances of 4a (δ 4.3ꢀ3.8),
indicating that this interaction is maintained in solution. This effect
can be used as a probe for sulfonate dissociation in these species.
Complex 8 undergoes tBuNC insertion at ꢀ10 °C to form the
Pd-iminoacyl complex {C-O}Pd{C(dNtBu)Me}(tBuNC) (9).
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Scheme 6a
Figure 11. Numbering scheme used for NMR assignments.
’ CONCLUSION
The NHC-sulfonate ligand 1 binds to PdII in a k2-C,O mode to
form square-planar {C-O}PdMe(2,6-lutidine) complexes 4a,b,
in which the seven-membered {C-O}Pd chelate rings adopt
puckered conformations. The reactivity of 4a,b is dominated by
ꢀ
dissociation or displacement of the ArSO3 group from Pd.
Isomerization of trans-C,C-4a to cis-C,C-4b proceeds by dissocia-
tion of the ArSO3ꢀ unit to form a configurationally labile three-
coordinate intermediate and is strongly accelerated by hydrogen
bond donors (CD3OD, lutidinium) and Lewis acids (B(C6F5)3)
that can labilize the sulfonate group. trans-C,C-4a reacts with CO
t
and BuNC to yield the insertion products {C-O}Pd{C-
(dO)Me}(2,6-lutidine) (7) and {C-O}Pd{C(dNtBu)Me}-
(tBuNC) (9), in which the acyl and iminoacyl ligands are cis to
the NHC ligand, via stereospecific displacement of ArSO3ꢀ by
the substrate followed byꢀmigratory insertion. In contrast,
displacement of the ArSO3 ligand of cis-C,C-4b by potential
substrates yields adducts in which the substrate and Me group are
trans and insertion is not possible. Thus CO does not undergo
net reaction with cis-C,C-4b and tBuNC induces reductive CꢀC
elimination of the NHC and Me ligands to produce the methyl
imidazolium zwitterion 6. The difference in the chemistry of {C-
O}PdMeL species, in which ArSO3ꢀ dissociation/displacement
plays a central role, and that of ortho-phosphino-arenesulfonate
{PO}PdMeL species, in which sulfonate decoordination has
been observed only rarely, reflects the greater lability of the
seven-membered chelate rings in {C-O}PdMeL species com-
pared to the six-membered chelate rings in {PO}PdMeL species.
a Ar = 2,6-iPr2C6H3, L = 2,6-lutidine.
2.285(3) Å; C(24)---O(3), 3.144(5) Å; C(24)ꢀH(24B)---O(3),
144.5(3)o) as observed for 8.16 In the 1H NMR spectrum of 10 in
CD2Cl2 solution, one NHC methylene resonance (δ 5.47) is
shifted downfield from the range observed for the resonances of 9
(δ 4.3ꢀ3.9). The reaction of 4a with 1 equiv of tBuNC at 25 °C
yields a 1/1 mixture of 4a and 9.
Reaction of 4b with tBuNC. In contrast, 4b reacts with tBuNC
(5 equiv) at ꢀ20 °C via stereospecific displacement of the
sulfonate ligand to yield the zwitterionic BuNC adduct {k1-C-
t
O}PdMe(tBuNC)(2,6-lutidine) (11, Scheme 5). The 1H NMR
spectrum of 11 (CD2Cl2, ꢀ20 °C) contains one low-field NHC
methylene resonance (δ 5.57), which is ca. 1.4 ppm downfield
from the range observed for 4b, and, as noted above, is
characteristic of a dissociated sulfonate group in this system. In
addition, the inequivalence of the two ꢀCH3 resonances (δ 2.26
and 1.98) of 2,6-lutidine reveals the coordination of this ligand.
’ EXPERIMENTAL SECTION
Complex 11 is the analogue of the proposed CO adducts 4a CO
3
General Procedures. All experiments were performed using dry-
box or Schlenk techniques under a purified nitrogen atmosphere unless
otherwise noted. Nitrogen was purified by passage through activated
molecular sieves and Q-5 oxygen scavenger. CD2Cl2 was distilled from
P2O5. THF and CH2Cl2 were purified by passage through activated
alumina. Hexane and toluene were purified by passage through activated
alumina and BASF R3-11 oxygen scavenger. All workup and purification
procedures of organic compounds were carried out with reagent grade
solvents in air. Pd2(μ-Cl)2Me2(PPh3)2, Pd2(μ-Cl)2Me2(2,6-lutidine)2,18
and N-2,6-diisopropylphenyl-(1,2-diaminoethane)19 were prepared by
literature procedures. 2-Bromobenzenesulfonyl chloride was purchased
from Lancaster and purified by a literature method.3a Other chemicals were
purchased from Sigma-Aldrich and used as received.
and 4b CO in Scheme 4 and the proposed intermediate in the
3
reaction of 4a with tBuNC to generate 8. Complex 11 does not
undergo insertion but rather undergoes CꢀC reductive elimina-
tion at 25 °C to produce 6.17
Reaction of 4a,b with Ethylene. In contrast to {PO}PdR
species, neither 3 nor 4a,b react with ethylene, at least under
mild conditions. NMR analysis showed that no reaction occurs
between 4a or 4b and ethylene (30 equiv) at 25 °C in CD2Cl2
solution or under polymerization conditions (400 psi) at 25 or
50 °C in toluene. These results show neither the 2,6-luditine nor
the sulfonate ligand is displaced by ethylene. Interestingly
however, ethylene promotes CꢀC reductive elimination of the
B(C6F5)3 adduct 5 (Scheme 6). As noted above, the decom-
position of 5 to 6 (after addition of pyridine to trap the B(C6F5)3,
eq 3) requires 30 h for completion at 40 °C. Addition of ethylene
(30 equiv) accelerates this process significantly (completion in
12 h at 40 °C). The sulfonate ligand in 5 is more labile than that
in 4b due to the presence of the borane, which promotes
displacement of the sulfonate by ethylene to generate a zwitter-
ionic intermediate that is more susceptible to reductive elimina-
tion than 4b itself.
NMR spectra were recorded at ambient probe temperature unless
otherwise indicated. 1H and 13C chemical shifts are reported relative to
1
SiMe4 and were determined by reference to the residual H and 13C
solvent resonances. 31P chemical shifts are reported relative to external
85% H3PO4. The numbering scheme for NMR assignments is given in
Figure 11. NMR assignments for complexes 3, 4a, and 4b are based on
COSY, HMQC, and NOESY experiments. NMR assignments for other
compounds were made by analogy to the assignments for 3, 4a, and 4b.
GC-MS and ESI-MS were recorded on freshly prepared samples. The
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listed m/z value corresponds to the most intense peak in the isotope
pattern.
(ꢀNCH2ꢀ), 29.0 (ꢀCH(CH3)2), 25.0 (ꢀCH(CH3)2). GC-MS: calcd
m/z = 386, found 386.
Ag [N-(2,6-iPr2-Ph)-N0-2-benzenesulfonateNHC] (2). A flask
was charged with imidazolium salt 1 (0.45 g, 1.2 mmol), Ag2O (0.81 g,
3.5 mmol), and CHCl3 (10 mL). The black mixture was stirred at 60 °C
in the dark for 20 h and then allowed to cool to room temperature. The
mixture was filtered through a Celite bed, and the bed was washed with
CH2Cl2 (10 mL). The colorless filtrate and wash were combined and
concentrated to ca. 3 mL. Hexane (30 mL) was added to afford a white
precipitate, which was collected by filtration and dried under vacuum.
Yield: 0.54 g, 94%. 1H NMR (CD2Cl2): δ 7.47 (br, 3H), 7.33ꢀ7.24 (m,
3H), 7.10 (d, 3JHH = 8 Hz, 1H), 4.70 (m, 1H), 3.92 (m, 3H), 3.04 (m,
2H), 1.37 (d, 3JHH = 6 Hz, 3H), 1.27 (d, 3JHH = 7 Hz, 3H), 1.11 (d, 3JHH
= 7 Hz, 3H), 0.48 (br, 3H). This material was used without further
purification.
Isobutyl-2-bromobenzenesulfonate. A solution of pyridine
(14.3 mL, 176 mmol) and 2-bromobenzenesulfonyl chloride (20.7 g,
81.0 mmol) in CHCl3 (40 mL) was added dropwise to a solution of
iBuOH (8.0 mL, 86 mmol) in CHCl3 (60 mL) at 0 °C. The resulting
mixture was stirred at room temperature for 12 h. The solution was
quenched with aqueous HCl (60 mL, 0.1 M). The organic phase was
separated, washed with aqueous HCl (50 mL, 0.1 M), H2O (2 ꢁ
35 mL), and brine (35 mL), and then dried over MgSO4, filtered, and
taken to dryness under vacuum. The residue was purified by flash
chromatography (20% ethyl acetate/hexane) to give the product as a
colorless oil. Yield: 18.2 g, 76%. 1H NMR (CD2Cl2): δ 8.08 (m, 1H),
7.81 (m, 1H), 7.50 (m, 2H), 3.84 (d, 3JHH = 7 Hz, 2H, ꢀSO3CH2ꢀ),
2.00 (m, 1H, ꢀSO3CH2CHMe2), 0.93 (d, 3JHH = 7 Hz, 6H, ꢀMe). GC-
MS: calcd m/z = 294, found 294.
cis-C,C-{C-O}PdMe(PPh3) (3). A flask was charged with Ag-NHC
complex 2 (60 mg, 0.12 mmol), Pd2(μ-Cl)2Me2(PPh3)2 (50 mg, 0.06
mmol), and CH2Cl2 (3 mL). The suspension was stirred at 25 °C for 20
min and filtered through a Celite bed. The colorless filtrate was mixed
with hexanes (10 mL) to afford a white precipitate, which was collected
by filtration and dried under vacuum. Yield: 73 mg, 79%. Crystals
suitable for X-ray diffraction were obtained by diffusion of hexane into a
CH2Cl2 solution of the product at ꢀ30 °C. 1H NMR (CD2Cl2): δ 7.96
(d, 3JHH = 8 Hz, 1H, H3-ArSO3), 7.62 (t, 3JHH = 8 Hz, 1H, H5-ArSO3),
Isobutyl-2-(2,6-diisopropylphenylaminoethyl)-amino-
benzenesulfonate. A flask was charged with tris(dibenzylideneacetone)
dipalladium(0) (0.59 g, 0.65 mmol), rac-2,20-bis(di-p-tolylphos-
phino)-1,10-binaphthyl (1.21 g, 1.94 mmol), and NaOtBu (1.86 g,
19.40 mmol) and fitted with a reflux condenser. A solution of
isobutyl-2-bromobenzenesulfonate (3.16 g, 10.8 mmol) and N-
2,6-diisopropylphenyl-1,2-diaminoethane (2.38 g, 10.8 mmol) in
THF (70 mL) was added by cannula transfer. The brown mixture
was refluxed at 80 °C for 6 h. The resulting deep red mixture was
allowed to cool to 25 °C and filtered through Celite, and the Celite
bed was washed with CH2Cl2 (50 mL). The filtrate and wash were
combined and dried under vacuum to afford a deep red sticky oil,
which was purified by flash chromatography (10% ethyl acetate/
hexane) to give a yellow oil. Yield: 2.46 g, 53%. 1H NMR (CD2Cl2):
δ 7.76 (d, 3JHH = 8 Hz, 1H, H3-ArSO3), 7.48 (t, 3JHH = 8 Hz, 1H, H5-
ArSO3), 7.10 (m, 3H, H9-Ar, H10 and H11-Ar), 6.85 (d, 3JHH = 8 Hz,
1H, H6-ArSO3), 6.76 (t, 3JHH = 7 Hz, 1H, H4-ArSO3), 6.25 (br, 1H,
3
3
7.52 (d, JHH = 8 Hz, 1H, H6-ArSO3), 7.46 (t, JHH = 8 Hz, 1H, H4-
ArSO3), 7.42 (t, JHH = 8 Hz, 1H, H10-ArSO3), 7.35 (m, 4H, H9(11)
-
-
3
ArSO3, p-PPh3), 7.23 (m, 6H, m-PPh3), 7.19ꢀ7.15 (m, 7H, H9(11)
ArSO3, o-PPh3), 4.36ꢀ4.27 (m, 2H, ꢀNCH2ꢀ), 4.16ꢀ4.05 (m, 3H,
3
ꢀNCH2ꢀ, ꢀCH(CH3)2), 3.07 (septet, JHH = 7 Hz, 1H, ꢀCH-
(CH3)2), 1.39 (d, 3JHH = 7 Hz, 3H, ꢀCH(CH3)2), 1.28 (d, 3JHH = 7
Hz, 3H, ꢀCH(CH3)2), 1.21 (m, 6H, ꢀCH(CH3)2), ꢀ0.39 (d, 3JPH = 7
Hz, 3H, Pd-CH3). 13C{1H} NMR (CD2Cl2): δ 206.7 (d, 2JPC = 133 Hz,
ꢀNCNꢀ), 149.5 (C8(12)-Ar), 146.9 (C8(12)-Ar), 144.0 (C7-Ar), 139.3
(C1-ArSO3), 135.6 (C2-ArSO3), 134.8 (d, 2JPC = 13 Hz, o-PPh3), 131.6
(C5-ArSO3), 131.3 (d, 1JPC = 40 Hz, ipso-PPh3), 130.6 (d, 4JPC = 2 Hz, p-
PPh3), 129.7 (C3-ArSO3), 129.5 (C10-Ar), 128.7 (d, 3JPC = 10 Hz, m-
PPh3), 128.3 (C4-ArSO3), 127.3 (C6-ArSO3), 125.4 (C9(11)-Ar), 124.3
(C9(11)-Ar), 55.8 (ꢀNCH2ꢀ), 55.0 (ꢀNCH2ꢀ), 29.1 (ꢀCH(CH3)2),
28.0 (ꢀCH(CH3)2), 26.9 (ꢀCH(CH3)2), 26.7 (ꢀCH(CH3)2), 24.9
(ꢀCH(CH3)2), 23.7 (ꢀCH(CH3)2), ꢀ8.7 (d, 2JPC = 5 Hz, Pd-CH3).
31P{1H} NMR (CD2Cl2): δ 24.9. Anal. Calcd for C40H44N2O3PPdS: C,
62.37; H, 5.76. Found: C, 62.58; H, 5.61.
3
ꢀNHꢀ), 3.76 (d, JHH = 6 Hz, 2H, ꢀSO3CH2ꢀ), 3.48 (m, 2H,
ꢀNCH2ꢀ), 3.33 (m, 2H, ꢀCH(CH3)2), 3.16 (m, 2H, ꢀNCH2ꢀ),
3.07 (br, 1H, ꢀNHꢀ), 1.93 (m, 1H, ꢀSO3CH2CHMe2), 1.22 (d,
3
3JHH = 6 Hz, 12H, ꢀCH(CH3)2), 0.88 (d, JHH = 7 Hz, 6H,
ꢀSO3CH2CH(CH3)2). 13C{1H} NMR (CD2Cl2): δ 147.3 (C1-
ArSO3), 143.9 (2C, C8 and C12-Ar), 143.0 (C2-ArSO3), 136.0 (C5-
ArSO3), 131.5 (C3-ArSO3), 124.9 (C10-ArSO3), 124.1 (2C, C9 and
C
11-Ar), 117.2 (C7-ArSO3), 116.0 (C4-ArSO3), 112.8 (C6-ArSO3),
77.0 (ꢀSO3CH2ꢀ), 51.0 (ꢀNCH2ꢀ), 44.3 (ꢀNCH2ꢀ), 28.6
(ꢀSO3CH2CHMe2), 28.1 (ꢀCH(CH3)2), 24.7 (ꢀCH(CH3)2),
18.9 (ꢀSO3CH2CH(CH3)2). GC-MS: calcd m/z = 432, found 432.
N-(2,6-iPr2-Ph)-N0-2-benzenesulfonateimidazolium ({C-O}-
H, 1). A mixture ofisobutyl-2-(2,6-diisopropylphenylaminoethyl)-amino-
benzenesulfonate (0.48 g, 1.1 mmol) and triethyl orthoformate (4 mL,
30 mmol) was stirred at 100 °C for ca. 5 min to afford a brownish-yellow
solution. Glacial acetic acid (0.96 mL) was added, and the solution was
stirred for 10 min at 100 °C. During this period, some white precipitate
formed. The mixture was cooled to 25 °C, and Et2O (5 mL) was added to
precipitate the product. The product was collected by filtration, washed
with Et2O (10mL), and dried under vacuum. Yield:0.29 g, 68%. 1H NMR
(CD2Cl2): δ 8.60 (s, 1H, ꢀNCHNꢀ), 8.13 (d, 3JHH = 8 Hz, 1H, H3-
ArSO3), 7.52 (m, 2H, H4 and H5-ArSO3), 7.49 (t, 3JHH = 8 Hz, 1H, H10-
Ar), 7.42 (d, 3JHH = 8 Hz, 1H, H6-ArSO3), 7.31 (d, 3JHH = 8 Hz, 2H, H9
andH11-Ar), 4.68 (t, 3JHH =10Hz, 2H, ꢀNCH2ꢀ), 4.31 (t, 3JHH = 10Hz,
2H, ꢀNCH2ꢀ), 3.24 (septet, 3JHH = 7 Hz, 2H, ꢀCH(CH3)2), 1.32 (d,
3JHH = 7 Hz, 6H, ꢀCH(CH3)2), 1.29 (d, 3JHH = 7 Hz, 6H, ꢀCH(CH3)2).
13C{1H} NMR (CD2Cl2): δ 160.3 (ꢀNCHNꢀ), 147.5 (2C, C8 and C12-
Ar), 144.2 (C7-Ar), 132.5 (C1-ArSO3), 131.8 (C10-Ar), 131.1 (C4-
ArSO3), 130.4 (C5-ArSO3), 130.2 (C2-ArSO3), 129.8 (C3-ArSO3),
126.6 (C6-ArSO3), 125.6 (2C, C9 and C11-Ar), 54.5 (ꢀNCH2ꢀ), 53.9
trans-C,C-{C-O}PdMe(2,6-lutidine) (4a). A flask was charged
with Ag-NHC complex 2 (200 mg, 0.41 mmol), Pd2(μ-Cl)2Me2(2,6-
lutidine)2 (110 mg, 0.21 mmol), and CH2Cl2 (12 mL). The mixture was
stirred at 25 °C for ca. 10 min and filtered through a Celite bed. The
colorless filtrate was mixed with hexanes (20 mL) and concentrated to
ca. 10 mL under vacuum to afford a white precipitate, which was
collected by filtration and dried under vacuum. NMR analysis showed
that this material was a 4/1 mixture of 4a and 4b. Yield: 0.22 g, 89%. The
mixture was dissolved in a mixture of CH2Cl2 (5 mL) and hexanes (ca.
15 mL), resulting in the precipitation of 4a as a white solid. 4a was
collected by filtration and dried under vacuum. (The filtrate was used to
afford 4b; see below.) Yield of 4a: 0.15 g, 62%. Crystals of 4a suitable for
X-ray diffraction were obtained by diffusion of hexane into a CH2Cl2
solution of 4a at ꢀ30 °C. 1H NMR (CD2Cl2): δ 8.19 (d, 3JHH = 8 Hz,
1H, H3-ArSO3), 7.61 (t, 3JHH = 8 Hz, 1H, H5-ArSO3), 7.52ꢀ7.48 (m,
2H, H4 and H6-ArSO3), 7.44ꢀ7.39 (m, 2H, H10 and H9(11)-Ar), 7.32 (t,
3JHH = 8 Hz, 1H, p-2,6-Me2-py), 7.01 (d, 3JHH = 7 Hz, 1H, H9(11)-Ar),
6.88 (d, 3JHH = 8 Hz, 1H, m-2,6-Me2-py), 6.78 (d, 3JHH = 8 Hz, 1H, m-
2,6-Me2-py), 4.27 (m, 1H, -NCH2ꢀ), 4.12 (m, 1H, ꢀNCH2ꢀ), 3.95
(m, 2H, ꢀNCH2ꢀ, ꢀCH(CH3)2), 3.82 (m, 1H, ꢀNCH2ꢀ), 2.47 (m,
1H, ꢀCH(CH3)2), 2.42 (s, 3H, 2,6-Me2-py), 1.84 (s, 3H, 2,6-Me2-py),
3
3
1.70 (d, JHH = 7 Hz, 3H, ꢀCH(CH3)2), 1.26 (d, JHH = 7 Hz, 3H,
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ꢀCH(CH3)2), 1.07 (d, 3JHH = 7 Hz, 3H, ꢀCH(CH3)2), 0.01 (d, 3JHH
=
1H, ꢀNCH2ꢀ), 4.16 (m, 1H, ꢀNCH2ꢀ), 4.05 (m, 2H, ꢀNCH2ꢀ),
7 Hz, 3H, ꢀCH(CH3)2), ꢀ0.25 (s, 3H, Pd-CH3). 13C{1H} NMR
(CD2Cl2): δ 215.1 (ꢀNCNꢀ), 161.6 (o-2,6-Me2-py), 160.0 (o-2,6-
Me2-py), 150.0 (C8(12)-Ar), 147.2 (C8(12)-Ar), 143.6 (C7-Ar), 140.2
(C1-Ar), 137.5 (p-2,6-Me2-py), 136.7 (C2-Ar), 131.7 (C5-ArSO3), 129.9
(C9(11)-Ar), 129.4 (C3-ArSO3), 128.1 (C4-ArSO3), 127.4 (C6-ArSO3),
126.0 (C10-Ar), 124.2 (C9(11)-Ar), 122.8 (m-2,6-Me2-py), 122.0 (m-2,6-
Me2-py), 55.3 (ꢀNCH2ꢀ), 55.0 (ꢀNCH2ꢀ), 28.5 (ꢀCH(CH3)2),
28.3 (2,6-Me2-py), 27.8 (ꢀCH(CH3)2), 26.8 (2,6-Me2-py), 26.3
(ꢀCH(CH3)2), 25.8 (ꢀCH(CH3)2), 24.8 (ꢀCH(CH3)2), 22.3
3
3.45 (septet, JHH = 7 Hz, 1H, ꢀCH(CH3)2), 3.00 (m, 1H, ꢀCH-
(CH3)2), 2.44 (br, 3H, 2,6-Me2-py), 2.16 (br, 3H, 2,6-Me2-py), 1.44 (d,
3JHH = 6 Hz, 3H, ꢀCH(CH3)2), 1.29ꢀ1.24 (m, 6H, ꢀCH(CH3)2),
1.18 (d, 3JHH = 7 Hz, 3H, ꢀCH(CH3)2), ꢀ0.16 (s, 3H, Pd-CH3). 11
B
NMR (CD2Cl2): δ ꢀ1.5. 19F NMR (CD2Cl2): δ ꢀ132.5, ꢀ160.1,
ꢀ166.0. Crystals of 5 suitable for X-ray diffraction were obtained by
diffusion of hexane into a CH2Cl2 solution of 5 at ꢀ30 °C.
Decomposition of cis-C,C-{C-O}PdMe(2,6-lutidine)B(C6F5)3
(5) to Produce 6. An NMR tube was charged with 4a or 4b (6 mg, 10
μmol) and B(C6F5)3 (5 mg, 10 μmol). CD2Cl2 (0.5 mL) was added by
vacuum transfer at ꢀ193 °C. The tube was warmed to 40 °Candkeptatthis
temperature for 30 h. Pyridine (5 equiv) was added. The 1H NMR showed
that 6, free 2,6-lutidine, and py-B(C6F5)3 were present. Pd(0) was also
present. 1HNMRof6(CD2Cl2):δ8.18 (dd, 3JHH =8Hz, 4JHH = 2 Hz, 1H,
H3-ArSO3), 7.58 (td, 3JHH = 8 Hz, 4JHH = 2 Hz, 1H, H5-ArSO3), 7.53 (td,
3JHH = 8 Hz, 4JHH = 2 Hz, 1H, H4-ArSO3), 7.45 (t, 3JHH = 8 Hz, 1H, H10-
Ar), 7.37 (dd, 3JHH = 8 Hz, 4JHH = 2 Hz, 1H, H9(11)-Ar), 7.32 (m, 2H, H6-
ArSO3, H9(11)-Ar), 5.17 (m, 1H, ꢀNCH2ꢀ), 4.37 (m, 1H, ꢀNCH2ꢀ),
4.25 (m, 1H, ꢀNCH2ꢀ), 4.10 (m, 1H, ꢀNCH2ꢀ), 3.54 (septet, 3JHH = 7
Hz, 1H, ꢀCH(CH3)2), 2.88 (septet, 3JHH = 7 Hz, 1H, ꢀCH(CH3)2), 1.91
(s, 3H, ꢀNC(CH3)Nꢀ), 1.35 (d, 3JHH = 7 Hz, 3H, ꢀCH(CH3)2), 1.30
(d, 3JHH = 7 Hz, 3H, ꢀCH(CH3)2), 1.27 (m, 6H, ꢀCH(CH3)2). 13C{1H}
NMR of 6 (CD2Cl2): δ 169.5 (ꢀNC(CH3)Nꢀ), 148.9 (C8(12)-Ar), 146.4
(C8(12)-Ar), 146.3 (C7-Ar), 131.9 (C1-ArSO3), 131.8 (C10-Ar), 131.5 (C4-
ArSO3), 131.2 (C5-ArSO3), 130.6 (C3-ArSO3), 130.2 (C2-ArSO3), 128.5
(C6-ArSO3), 126.5 (C9(11)-Ar), 125.4 (C9(11)-Ar), 55.2 (ꢀNCH2ꢀ), 55.0
(ꢀNCH2ꢀ), 29.5 (ꢀCH(CH3)2), 28.2 (ꢀCH(CH3)2), 25.5 (ꢀCH-
(CH3)2), 25.3 (ꢀCH(CH3)2), 24.7 (ꢀCH(CH3)2), 24.5 (ꢀCH(CH3)2),
13.4 (ꢀNC(CH3)Nꢀ). ESI-MS: calcd m/z = 401, found 401.1.
1
1
(ꢀCH(CH3)2), 2.4 (Pd-CH3). Hꢀ H NOE correlations (CD2Cl2):
δ/δ 4.27 (ꢀNCH2ꢀ)/3.95 (ꢀNCH2ꢀ); 4.27 (ꢀNCH2ꢀ)/3.82
(ꢀNCH2ꢀ); 4.12 (ꢀNCH2ꢀ)/3.95 (ꢀNCH2ꢀ); 3.95 (ꢀCH(CH3)2-
(2))/1.70 (ꢀCH(CH3)2); 3.95 (ꢀCH(CH3)2)/1.26 (ꢀCH(CH3)2);
3.82 (ꢀNCH2ꢀ)/2.47 (ꢀCH(CH3)2); 3.82 (ꢀNCH2ꢀ)/1.07 (ꢀCH
(CH3)2); 2.47 (ꢀCH(CH3)2)/1.07 (ꢀCH(CH3)2); 2.47 (ꢀCH
(CH3)2)/0.01 (ꢀCH(CH3)2); 2.42 (2,6-Me2-py)/ꢀ0.25 (Pd-CH3);
1.84 (2,6-Me2-py)/ꢀ0.25 (Pd-CH3); 1.70 (ꢀCH(CH3)2)/1.26 (ꢀCH
(CH3)2); 1.07 (ꢀCH(CH3)2)/0.01 (ꢀCH(CH3)2). Anal. Calcd for
C29H38N3O3PdS: C, 56.63; H, 6.23. Found: C, 56.88; H, 6.06.
cis-C,C-{C-O}PdMe(2,6-lutidine) (4b). The filtrate from the
isolation of 4a above was allowed to stand at 25 °C for 12 h and then
concentrated to ca. 5 mL under vacuum, resulting in the precipitation of
4b as a white solid. 4b was isolated by filtration and dried under vacuum.
Yield of 4b: 44 mg, 18%. Crystals of 4b suitable for X-ray diffraction were
obtained by diffusion of hexane into a CH2Cl2 solution of 4b at ꢀ30 °C.
1H NMR (CD2Cl2): δ 8.15 (d, 3JHH = 8 Hz, 1H, H3-ArSO3), 7.59 (t,
3JHH = 8 Hz, 1H, H5-ArSO3), 7.52 (d, 3JHH = 8 Hz, 1H, H6-ArSO3), 7.46
(t, 3JHH = 8 Hz, 1H, H4-ArSO3), 7.44ꢀ7.38 (m, 3H, p-2,6-Me2-py, H10
and H9(11)-Ar), 7.20 (d, 3JHH = 7 Hz, 1H, H9(11)-Ar), 6.90 (d, 3JHH = 7
Hz, 2H, m-2,6-Me2-py), 4.31 (m, 2H, ꢀNCH2ꢀ), 4.17 (m, 1H,
ꢀNCH2ꢀ), 4.07 (m, 2H, ꢀNCH2ꢀ, ꢀCH(CH3)2), 3.08 (septet,
3JHH = 7 Hz, 1H, ꢀCH(CH3)2), 2.43 (s, 3H, 2,6-Me2-py), 2.20 (s,
3H, 2,6-Me2-py), 1.51 (d, 3JHH = 7 Hz, 3H, ꢀCH(CH3)2), 1.30 (d, 3JHH
= 7 Hz, 3H, ꢀCH(CH3)2), 1.26 (d, 3JHH = 7 Hz, 3H, ꢀCH(CH3)2),
Reaction of 4a with Carbon Monoxide. Generation of cis-C,
C-{C-O}Pd(C(dO)Me)(2,6-lutidine) (7). An NMR tube was charged
with 4a (6 mg, 10 μmol). CD2Cl2 (0.5 mL) was added by vacuum
transfer at ꢀ193 °C. The tube was charged with CO (200 mmHg, ca. 22
μmol), warmed to 25 °C, and shaken for 5 min. NMR analysis showed
that cis-C,C-{C-O}Pd(C(dO)Me)(2,6-lutidine) (7) had formed in
quantitative NMR yield. 1H NMR (CD2Cl2): δ 8.18 (d, 3JHH = 8 Hz,
1H, H3-ArSO3), 7.68 (m, 2H, H5 and H6-ArSO3), 7.54 (t, 3JHH = 8 Hz,
1H, H4-ArSO3), 7.45ꢀ7.40 (m, 3H, p-2,6-Me2-py, H10 and H9(11)-Ar),
7.20 (d, 3JHH = 7 Hz, 1H, H9(11)-Ar), 6.96 (d, 3JHH = 8 Hz, 1H, m-2,6-
3
1.19 (d, JHH = 7 Hz, 3H, ꢀCH(CH3)2), ꢀ0.36 (s, 3H, Pd-CH3).
13C{1H} NMR (CD2Cl2): δ 202.6 (ꢀNCNꢀ), 159.4 (2C, o-2,6-Me2-
py), 149.7 (C8(12)-Ar), 147.4 (C8(12)-Ar), 144.1 (C7-Ar), 139.7 (C1-Ar),
138.2 (p-2,6-Me2-py), 136.2 (C2-Ar), 131.7 (C5-ArSO3), 129.7 (C3-
ArSO3), 129.6 (C10-Ar), 128.0 (C4-ArSO3), 127.8 (C6-ArSO3), 125.2
(C9(11)-Ar), 124.0 (C9(11)-Ar), 122.7 (m-2,6-Me2-py), 122.5 (m-2,6-
Me2-py), 55.2 (ꢀNCH2ꢀ), 55.0 (ꢀNCH2ꢀ), 29.1 (ꢀCH(CH3)2),
28.1 (ꢀCH(CH3)2), 27.4 (2,6-Me2-py), 27.3 (2,6-Me2-py), 26.2
(ꢀCH(CH3)2), 25.1 (ꢀCH(CH3)2), 23.8 (ꢀCH(CH3)2), 23.2 (ꢀCH-
3
Me2-py), 6.87 (d, JHH = 8 Hz, 1H, m-2,6-Me2-py), 4.36 (m, 2H,
ꢀNCH2ꢀ), 4.14 (m, 2H, ꢀNCH2ꢀ), 3.96 (septet, 3JHH = 7 Hz, 1H,
ꢀCH(CH3)2), 2.83 (m, 1H, ꢀCH(CH3)2), 2.76 (s, 3H, 2,6-Me2-py),
2.24 (s, 3H, 2,6-Me2-py), 1.74 (s, 3H, PdC(dO)CH3), 1.49 (d, 3JHH = 7
Hz, 3H, ꢀCH(CH3)2), 1.23ꢀ1.19 (m, 9H, ꢀCH(CH3)2). 13C{1H}
NMR (CD2Cl2): δ 222.3 (PdC(dO)Me), 202.9 (ꢀNCNꢀ), 160.3 (o-
1
1
(CH3)2), ꢀ13.6 (Pd-CH3). Hꢀ H NOE correlations (CD2Cl2): δ/δ
4.31 (ꢀNCH2ꢀ)/4.17 (ꢀNCH2ꢀ); 4.31 (ꢀNCH2ꢀ)/4.07 (ꢀNCH2ꢀ);
4.17 (ꢀNCH2ꢀ)/3.08 (ꢀCH(CH3)2); 4.17 (ꢀNCH2ꢀ)/1.26 (ꢀCH-
(CH3)2); 4.07 (ꢀCH(CH3)2)/1.51 (ꢀCH(CH3)2); 4.07 (ꢀCH(CH3)2)/
1.19 (ꢀCH(CH3)2); 3.08 (ꢀCH(CH3)2)/1.30 (ꢀCH(CH3)2); 3.08
(ꢀCH(CH3)2)/1.26 (ꢀCH(CH3)2); 3.08 (ꢀCH(CH3)2)/ꢀ0.36 (Pdꢀ
CH3); 2.43 (2,6-Me2-py)/2.20 (2,6-Me2-py); 2.43 (2,6-Me2-py)/1.51
(ꢀCH(CH3)2); 2.43 (2,6-Me2-py)/ꢀ0.36 (PdꢀCH3); 2.20 (2,6-Me2-py)
/ꢀ0.36 (PdꢀCH3); 1.51 (ꢀCH(CH3)2)/1.19 (ꢀCH(CH3)2); 1.30
(ꢀCH(CH3)2)/ꢀ0.36 (Pd-CH3). Anal. Calcd for C29H38N3O3PdS: C,
56.63; H, 6.23. Found: C, 56.43; H, 5.92.
2,6-Me2-py), 159.4 (o-2,6-Me2-py), 149.4 (C8(12)-Ar), 147.4 (C8(12)
-
Ar), 144.6 (C7-Ar), 139.3 (C1-Ar), 138.7 (p-2,6-Me2-py), 135.6 (C2-Ar),
132.1 (C5-ArSO3), 129.9 (2C, C3-ArSO3, C10-Ar), 128.6 (C6-ArSO3),
124.4 (C4-ArSO3), 125.1 (C9(11)-Ar), 124.0 (C9(11)-Ar), 123.1 (m-2,6-
Me2-py), 122.5 (m-2,6-Me2-py), 55.2 (ꢀNCH2ꢀ), 55.0 (ꢀNCH2ꢀ),
40.1 (PdC(O)CH3), 28.8 (ꢀCH(CH3)2), 28.0 (ꢀCH(CH3)2), 27.6
(2,6-Me2-py), 27.2 (2,6-Me2-py), 25.7 (ꢀCH(CH3)2), 25.3 (ꢀCH-
(CH3)2), 23.8 (ꢀCH(CH3)2), 22.0 (ꢀCH(CH3)2). IR (film, cmꢀ1):
1690 (νCdO). Crystals of 7 suitable for X-ray diffraction were obtained
by diffusion of hexane into a CH2Cl2 solution of 7 at ꢀ30 °C.
Generation of cis-C,C-[C-O]PdMe(2,6-lutidine)B(C6F5)3 (5).
An NMR tube was charged with 4a or 4b (6 mg, 10 μmol) and B(C6F5)3
(5 mg, 10 μmol). CD2Cl2 (0.5 mL) was added by vacuum transfer at
Reaction of 4a with tert-Butyl Isocyanide. Generation of {C-O}-
PdMe(tBuNC)2 (8). An NMR tube was charged with 4a (7 mg, 11 μmol). tert-
Butyl isocyanide (2 mg, 24 μmol) and CD2Cl2 (0.4 mL) were added by
vacuum transfer at ꢀ193 °C. The tube was warmed to ꢀ30 °C. NMR analysis
after 5 min showed that 8 had formed in quantitative NMR yield. 1H NMR
(CD2Cl2, ꢀ30 °C): δ 8.09 (d, 3JHH = 8 Hz, 1H, H3-ArSO3), 7.45 (t, 3JHH = 8
Hz, 1H, H5-ArSO3), 7.39ꢀ7.34 (m, 3H, H4 and H6-ArSO3, H10-Ar), 7.24 (m,
2H, H9 and H11-Ar), 5.53 (m, 1H, ꢀNCH2ꢀ), 4.05 (m, 1H, ꢀNCH2ꢀ),
1
ꢀ193 °C. The tube was warmed to 25 °C for 5 min. The H NMR
spectrum showed that compound 5 had formed in quantitative NMR
yield. 1H NMR (CD2Cl2): δ 7.85 (br, 1H, H3-ArSO3), 7.77 (t, 3JHH = 8
Hz, 1H, H5-ArSO3), 7.61 (d, 3JHH = 8 Hz, 1H, H6-ArSO3), 7.48ꢀ7.40
(m, 4H, H4-ArSO3, p-2,6-Me2-py, H10 and H9(11)-Ar), 7.22 (d, 3JHH = 7
Hz, 1H, H9(11)-Ar), 6.92 (d, 3JHH = 8 Hz, 2H, m-2,6-Me2-py), 4.33 (m,
4640
dx.doi.org/10.1021/om200482a |Organometallics 2011, 30, 4632–4642

Organometallics
ARTICLE
3.86 (m, 2H, ꢀNCH2ꢀ), 3.30 (m, 1H, ꢀCH(CH3)2), 3.17 (m, 1H,
ꢀCH(CH3)2), 1.39 (s, 18H, Pd-CtNCMe3), 1.33 (m, 3H, ꢀCH(CH3)2),
1.25 (m, 6H, ꢀCH(CH3)2), 1.15 (m, 3H, ꢀCH(CH3)2), ꢀ0.17 (s, 3H, Pd-
Me). 13C{1H} NMR (CD2Cl2, ꢀ30 °C): δ 205.1 (ꢀNCNꢀ), 151.0 (Pd-
CtNCMe3), 149.5 (C8(12)-Ar), 147.7 (C8(12)-Ar), 146.1 (C7-Ar), 137.0 (C1-
Ar), 135.2 (C2-Ar), 129.7 (C3-ArSO3), 129.6 (C5-ArSO3), 129.0 (C10-Ar),
128.7 (C4-ArSO3), 128.0 (C6-ArSO3), 124.9 (C9(11)-Ar), 124.2 (C9(11)-Ar),
58.5 (PdꢀCtNCMe3), 54.2 (ꢀNCH2ꢀ), 52.6 (ꢀNCH2ꢀ), 30.4 (Pd-
CtNCMe3), 29.5 (Pd-CtNCMe3), 28.1 (ꢀCH(CH3)2), 27.5 (ꢀCH-
(CH3)2), 26.6 (ꢀCH(CH3)2), 25.3 (ꢀCH(CH3)2), 24.6 (ꢀCH(CH3)2),
24.5 (ꢀCH(CH3)2). Crystals of 8 suitable for X-ray diffraction were obtained
by diffusion of hexane into a CH2Cl2 solution of 4a and tert-butyl isocyanide
(2ꢀ3 equiv) at ꢀ30 °C.
1H, p-2,6-Me2-py), 7.28 (d, 3JHH = 7 Hz, 1H, H9(11)-Ar), 7.21 (d, 3JHH = 7
3
Hz, 1H, H9(11)-Ar), 6.97 (d, JHH = 8 Hz, 1H, m-2,6-Me2-py), 6.90 (d,
3JHH = 8 Hz, 1H, m-2,6-Me2-py), 5.58 (m, 1H, ꢀNCH2ꢀ), 4.23 (m, 1H,
ꢀNCH2ꢀ), 4.03 (m, 1H, ꢀNCH2ꢀ), 3.97 (m, 1H, ꢀNCH2ꢀ), 3.59
(m, 1H, ꢀCH(CH3)2), 3.25 (m, 1H, ꢀCH(CH3)2), 2.26 (s, 1H, 2,6-Me2-
py), 1.98 (s, 1H, 2,6-Me2-py), 1.32 (d, 3JHH = 7 Hz, 3H, ꢀCH(CH3)2),
1.28 (d, 3JHH = 7 Hz, 3H, ꢀCH(CH3)2), 1.19 (m, 15 H, ꢀCH(CH3)2, Pd-
CtNCMe3).
’ ASSOCIATED CONTENT
S
Supporting Information. Additional experimental de-
b
tails and crystallographic data including CIF files. This material
Generation of {C-O}Pd(C(dNtBu)Me)(tBuNC) (9). The above solu-
tion of 8 in CD2Cl2 was warmed from ꢀ30 to ꢀ10 °C and monitored by
NMR, which showed that 8 slowly converts to 9 at this temperature. The
tube was warmed from ꢀ10 to 20 °C over 10 min. NMR analysis after 5
min at 20 °C showed that 9 had formed in quantitative NMR yield. 1H
is available free of charge via the Internet at http://pubs.acs.org.
’ AUTHOR INFORMATION
Corresponding Author
*E-mail: rfjordan@uchicago.edu.
NMR (CD2Cl2): δ 8.09 (d, 3JHH = 8 Hz, 1H, H3-ArSO3), 7.55 (t, 3JHH
=
8 Hz, 1H, H5-ArSO3), 7.47 (t, 1H, H4-ArSO3), 7.41 (m, 3H, H6-ArSO3,
3
H9 and H11-Ar), 7.19 (t, JHH = 7 Hz, 1H, H10-Ar), 4.20 (m, 2H,
ꢀNCH2ꢀ), 3.96 (m, 3H, ꢀNCH2ꢀ, ꢀCH(CH3)2), 2.89 (septet, 3JHH
= 7 Hz, 1H, ꢀCH(CH3)2), 1.75 (d, 3JHH = 7 Hz, 3H, ꢀCH(CH3)2),
1.33 (s, 9H, Pd-CtNCMe3), 1.25 (d, 3JHH = 7 Hz, 9H, ꢀCH(CH3)2),
1.06 (s, 9H, Pd-CMedNCMe3), 0.98 (s, 3H, Pd-CMedNCMe3).
’ ACKNOWLEDGMENT
This work was supported by the National Science Foundation
(CHE-0911180). We thank Ian Steele for assistance with X-ray
crystallography.
13C{1H} NMR (CD2Cl2):
δ
202.8 (ꢀNCNꢀ), 161.7 (Pd-
CtNCMe3), 149.5 (C8(12)-Ar), 147.3 (C8(12)-Ar), 143.8 (C7-Ar),
138.5 (C1-Ar), 136.0 (C2-Ar), 131.1 (C3-ArSO3), 129.9 (C5-ArSO3),
129.3 (C10-Ar), 128.6 (2C, C4-ArSO3, C6-ArSO3), 125.8 (C9(11)-Ar),
124.9 (C9(11)-Ar), 58.2 (Pd-CMedNCMe3), 54.6 (ꢀNCH2ꢀ), 54.0
(ꢀNCH2ꢀ), 53.6 (Pd-CtNCMe3), 31.8 (Pd-CMedNCMe3), 30.8
(Pd-CMedNCMe3), 30.2 (Pd-CtNCMe3), 28.6 (ꢀCH(CH3)2), 28.0
(ꢀCH(CH3)2), 26.6 (ꢀCH(CH3)2), 25.3 (ꢀCH(CH3)2), 23.7
(ꢀCH(CH3)2); the Pd-CMedNCMe3 resonance was not observed.
IR (film, cmꢀ1): 2196 (νCtN), 1652 (νCdN). Crystals of 9 suitable for
X-ray diffraction were obtained by diffusion of hexane into a CH2Cl2
solution of 9 at ꢀ30 °C.
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Generation of {C-O}Pd(C(dNtBu)Me)(tBuNC)2 (10). A solution of 9
and tert-butyl isocyanide (ca. 8 equiv) was allowed to stand at 25 °C for
1
2 h. Complex 10 was produced in quantitative NMR yield. H NMR
(CD2Cl2): δ 8.21 (d, 3JHH = 8 Hz, 1H, H3-ArSO3), 7.47ꢀ7.40 (m, 3H,
H4-ArSO3, H5 and H6-ArSO3), 7.36 (t, 3JHH = 7 Hz, 1H, H10-Ar), 7.25
(d, 3JHH = 8 Hz, 2H, H9 and H11-Ar), 5.47 (br, 1H, ꢀNCH2ꢀ), 4.06 (br,
3H, ꢀNCH2ꢀ), 3.39 (br, 2H, ꢀCH(CH3)2), 1.68 (s, 3H, Pd-
3
CMedNCMe3), 1.44 (br, 18H, Pd-CtNCMe3), 1.33 (d, JHH = 7
Hz, 6H, ꢀCH(CH3)2), 1.24 (d, 3JHH = 7 Hz, 6H, ꢀCH(CH3)2), 0.84
(s, 9H, Pd-CMedNCMe3). 13C{1H} NMR (CD2Cl2): δ 208.5
(ꢀNCNꢀ), 173.8 (Pd-CtNCMe3), 146.0 (2C, C8 and C12-Ar),
137.8 (C7-Ar), 136.1 (C1-Ar), 130.5 (C3-ArSO3), 130.2 (C5-ArSO3),
130.0 (C10-Ar), 129.8 (C4-ArSO3), 128.9 (2C, C6-ArSO3, C2-Ar), 124.9
(2C, C9 and C11-Ar), 58.2 (Pd-CMedNCMe3), 59.4 (Pd-CtNCMe3),
56.4 (Pd-CMedNCMe3), 56.1 (ꢀNCH2ꢀ), 53.3 (ꢀNCH2ꢀ), 34.3
(Pd-CMedNCMe3), 31.5 (Pd-CMedNCMe3), 30.0 (Pd-CtNCMe3),
28.2 (ꢀCH(CH3)2), 28.0 (ꢀCH(CH3)2), 24.3 (ꢀCH(CH3)2); the Pd-
CMedNCMe3 resonance was not observed. IR (film, cmꢀ1): 2192
(νCtN), 1642 (νCdN). Crystals of 10 suitable for X-ray diffraction were
obtained by diffusion of hexane into a CH2Cl2 solution of 10 at ꢀ30 °C.
Generation of {C-O}PdMe(2,6-lutidine)(tBuNC) (11). An NMR tube
was charged with 4b (7 mg, 11 μmol) and tert-butyl isocyanide (ca. 5
equiv). CD2Cl2 (0.4 mL) was added by vacuum transfer at ꢀ193 °C. The
tubewaswarmedtoꢀ20 °C. NMRanalysisafter5minshowedthat11 had
formed in quantitative NMR yield. 1H NMR (CD2Cl2, ꢀ20 °C): δ 8.14
(d, 3JHH = 8 Hz, 1H, H3-ArSO3), 7.56 (d, 3JHH = 7 Hz, 1H, H6-ArSO3),
(4) Nagai, Y.; Kochi, T.; Nozaki, K. Organometallics 2009, 28, 6131.
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T. Organometallics 2006, 25, 4491.
(8) (a) Romeo, R.; Minniti, D.; Trozzi, M. Inorg. Chem. 1976,
15, 1134. (b) Faraone, G.; Ricevuto, V.; Romeo, R.; Trozzi, M. J. Chem.
3
7.48ꢀ7.42 (m, 3H, H4 and H5-ArSO3, H10-Ar), 7.37 (t, JHH = 8 Hz,
4641
dx.doi.org/10.1021/om200482a |Organometallics 2011, 30, 4632–4642

Organometallics
ARTICLE
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(14) Similar structures were observed for other Pd-acyl and Pd-
iminoacyl complexes: (a) Nakazawa, H.; Kashiwamura, T.; Mizuta, T.;
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intra- and intermolecular CH---O hydrogen bonds between the other two
oxygens of the sulfonate group and tBuNC methyl hydrogens are observed
in the solid-state structure of 8.
(16) In addition, intermolecular CH---O hydrogen bonds between
the other oxygen of the sulfonate group and the tBuNC methyl hydrogen
are observed in the solid-state structure of 10.
(17) The Pd products are unknown.
(18) Ladipo, F. T.; Anderson, G. K. Organometallics 1994, 13, 303.
(19) Marshall, C.; Ward, M. F.; Skakle, J. M. S. Synthesis 2006,
6, 1040.
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