Insertion reactions of six-membered cyclopalladated N, N′, N″ -Triarylguanidine, [Pd{κ2(C, N)-C6H 3Me-3(NHC(NHAr)(=NAr))-2}(μ-Br)]2 (Ar = 2-MeC 6H4) with PhC≡C - C(O)OR (R = Me and Et): A gateway to second orthopalladation through novel rearrangements

Article abstract of DOI:10.1021/om4010719

The reaction of [Pd{κ²(C,N)-C₆H ₃Me-3(NHC(NHAr)(=NAr))-2}(μ-Br)]₂ (Ar = 2-MeC ₆H₄; 1) with 4 equiv of PhC≡C - C(O)OMe in CH ₂Cl₂ afforded [Pd{κ²(C,N)-C(Ph)=C(C(O) OMe)C(Ph)=C(C(O)OMe)C₆H₃Me-3(N=C(NHAr)₂)-2}Br] (Ar = 2-MeC₆H₄; 2) in 70% yield, and the aforementioned reaction carried out with 10 equiv of PhC≡C - C(O)OR (R = Me, and Et) afforded an admixture of two regioisomers of [Pd{κ³(N,C,O)-O= C(OR)C₅Ph₃(C(O)OR)C(C(O)OR)C₆H ₃Me-3(N=C(NHAr)₂)-2}Br] (Ar = 2-MeC₆H ₄; R = Me (3a/3b), Et (4a/4b)) in 80 and 87% yields, respectively. In one attempt, the minor regioisomer, 4b, was isolated from the mixture in 6% yield by fractional crystallization. Palladacycles 3a/3b and 4a/4b, upon stirring in CH₂Cl₂/MeCN (1/1, v/v) mixture at ambient condition for 5 days, afforded [Pd{(η³-allyl, κ¹N)-C₅(C(O)OR)₂Ph₃C(C(O)OR) C₆H₃Me-3(N=C(NHAr)₂)-2}Br] (Ar = 2-MeC ₆H₄; R = Me (5a/5b), Et (6a/6b)) in 94 and 93% yields, respectively. Palladacycles 3a/3b and 4a/4b, upon reaction with AgOTf in CH ₂Cl₂/Me₂C(O) (1/1, v/v) mixture at ambient temperature for 15 min, afforded [Pd{κ³(N,C,O)-O=C(OR)C ₅Ph₃(C(O)OR)C(C(O)OR)C₆H₃Me-3(N= C(NHAr)₂)-2}(OTf)] (Ar = 2-MeC₆H₄; R = Me (7a/7b), Et (8a/8b)) in 79 and 77% yields, respectively. Palladacycles 7a/7b and 8a/8b, upon reflux in PhCl separately for 6 h, or palladacycles 5a/5b and 6a/6b, upon treatment with AgOTf in CH₂Cl₂/Me ₂C(O) (7/3, v/v) mixture for 15 min, afforded [Pd{(η²- Ph)C₅Ph₂(C(O)OR)₂κ²(C,N)- C(C(O)OR)C₆H₃Me-3(N=C(NHAr)₂)-2}(OTf)] (Ar = 2-MeC₆H₄; R = Me (9a/9b), Et (10a/10b)) in ≥87% yields. Palladacycles 9a/9b, upon stirring in MeCN in the presence of excess NaOAc followed by crystallization of the reaction mixture in the same solvent, afforded [Pd{κ³(N,C,C)-(C₆H₄)C ₅Ph₂(C(O)OMe)₂C(C(O)OMe)C₆H ₃Me-3(N=C(NHAr)₂)-2}(NCMe)] (Ar = 2-MeC₆H ₄; 11a/11b) in 82% yield. The new palladacycles were characterized by analytical, IR, and NMR (¹H and ¹³C) spectroscopic techniques, and the molecular structures of 2, 3a, 4a, 4b, 5a, 6a, 7a, 9a, 10a, and 11a-d₃ were determined by single crystal X-ray diffraction. The frameworks in the aforementioned palladacycles, except that present in 2, are unprecedented. Plausible pathways for the formation of new palladacycles and the influence of the guanidine unit in 1, substituents in alkynes, reaction conditions, and electrophilicity of the bromide and the triflate upon the frameworks of the insertion products have been discussed.

Full text of DOI:10.1021/om4010719

Article
pubs.acs.org/Organometallics
Insertion Reactions of Six-Membered Cyclopalladated N,N′,N″-
Triarylguanidine, [Pd{κ2(C,N)‑C6H3Me-3(NHC(NHAr)(NAr))-2}(μ-Br)]2
(Ar = 2‑MeC6H4) with PhCCC(O)OR (R = Me and Et): A Gateway to
Second Orthopalladation through Novel Rearrangements
Priya Saxena,† Natesan Thirupathi,*,† and Munirathinam Nethaji‡
†Department of Chemistry, University of Delhi, Delhi 110 007, India
‡Department of Inorganic and Physical Chemistry, Indian Institute of Science, Bangalore 560 012, Karnataka, India
S
* Supporting Information
ABSTRACT: The reaction of [Pd{κ2(C,N)-C6H3Me-3-
(NHC(NHAr)(NAr))-2}(μ-Br)]2 (Ar = 2-MeC6H4; 1)
with 4 equiv of PhCCC(O)OMe in CH2Cl2 afforded
[Pd{κ2(C,N)-C(Ph)C(C(O)OMe)C(Ph)C(C(O)-
OMe)C6H3Me-3(NC(NHAr)2)-2}Br] (Ar = 2-MeC6H4; 2)
in 70% yield, and the aforementioned reaction carried out with
10 equiv of PhCCC(O)OR (R = Me, and Et) afforded an
admixture of two regioisomers of [Pd{κ3(N,C,O)-OC(OR)-
C5Ph3(C(O)OR)C(C(O)OR)C6H3Me-3(NC(NHAr)2)-
2}Br] (Ar = 2-MeC6H4; R = Me (3a/3b), Et (4a/4b)) in 80
and 87% yields, respectively. In one attempt, the minor
regioisomer, 4b, was isolated from the mixture in 6% yield by fractional crystallization. Palladacycles 3a/3b and 4a/4b, upon
stirring in CH2Cl2/MeCN (1/1, v/v) mixture at ambient condition for 5 days, afforded [Pd{(η3-allyl,κ1N)-C5(C(O)OR)2Ph3C-
(C(O)OR)C6H3Me-3(NC(NHAr)2)-2}Br] (Ar = 2-MeC6H4; R = Me (5a/5b), Et (6a/6b)) in 94 and 93% yields,
respectively. Palladacycles 3a/3b and 4a/4b, upon reaction with AgOTf in CH2Cl2/Me2C(O) (1/1, v/v) mixture at ambient
temperature for 15 min, afforded [Pd{κ3(N,C,O)-OC(OR)C5Ph3(C(O)OR)C(C(O)OR)C6H3Me-3(NC(NHAr)2)-
2}(OTf)] (Ar = 2-MeC6H4; R = Me (7a/7b), Et (8a/8b)) in 79 and 77% yields, respectively. Palladacycles 7a/7b and 8a/
8b, upon reflux in PhCl separately for 6 h, or palladacycles 5a/5b and 6a/6b, upon treatment with AgOTf in CH2Cl2/Me2C(O)
(7/3, v/v) mixture for 15 min, afforded [Pd{(η2-Ph)C5Ph2(C(O)OR)2κ2(C,N)-C(C(O)OR)C6H3Me-3(NC(NHAr)2)-
2}(OTf)] (Ar = 2-MeC6H4; R = Me (9a/9b), Et (10a/10b)) in ≥87% yields. Palladacycles 9a/9b, upon stirring in MeCN in the
presence of excess NaOAc followed by crystallization of the reaction mixture in the same solvent, afforded [Pd{κ3(N,C,C)-
(C6H4)C5Ph2(C(O)OMe)2C(C(O)OMe)C6H3Me-3(NC(NHAr)2)-2}(NCMe)] (Ar = 2-MeC6H4; 11a/11b) in 82% yield.
The new palladacycles were characterized by analytical, IR, and NMR (1H and 13C) spectroscopic techniques, and the molecular
structures of 2, 3a, 4a, 4b, 5a, 6a, 7a, 9a, 10a, and 11a-d3 were determined by single crystal X-ray diffraction. The frameworks in
the aforementioned palladacycles, except that present in 2, are unprecedented. Plausible pathways for the formation of new
palladacycles and the influence of the guanidine unit in 1, substituents in alkynes, reaction conditions, and electrophilicity of the
bromide and the triflate upon the frameworks of the insertion products have been discussed.
insertion and the frameworks of the products differ depending
upon the electronic and steric effects of the donor atoms in the
C,N chelate and ancillary ligands around the palladium, as well
as substituents in alkynes, among other factors.
The commonly observed frameworks in alkyne-inserted
products of [C,N] palladacycles wherein the nitrogen atom is
part of an amine, imine, amidine or heterocyclic unit are shown
in Chart 1. A five-membered [C,N] palladacycle, for example,
upon monoinsertion with alkyne affords a seven-membered
[C,N] palladacycle of the type I while upon diinsertion affords a
nine-membered [C,N] palladacycle of the type II. Triinsertion
INTRODUCTION
■
Insertion reaction of small molecules such as alkenes and
alkynes into the M−C bond of organometallic compounds is
one of the fundamentally important reactions in the field of
organometallic chemistry and catalysis.1,2 Insertion reactions of
alkynes into the Pd−C bond of [C,E] palladacycles (E =
nitrogen,3−14 oxygen,15 and sulfur16) and organopalladium
complexes17−20 have been studied intensively in the past, as
these reactions pave the way to numerous alkyne-inserted
products, and such products upon depalladation under suitable
conditions afford novel carbocycles and heterocycles, which are
otherwise difficult to prepare by conventional organic
syntheses.3−5,9i,j,10a,13e,14c,d,21 [C,N] palladacycles insert up to
three molecules of alkynes, and the degree and rate of alkyne
Received: November 5, 2013
Published: November 23, 2013
© 2013 American Chemical Society
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Chart 1. Commonly Observed Frameworks of Alkyne-
Inserted Products of [C,N] Palladacycles
Chart 3. Line Drawing Pictures of 2, 4b, and 3a−11a (Ar =
2-MeC6H4)
reaction of [C,N] palladacycles is much less well investigated
than mono- and diinsertion reactions.9m,n,q,10c,12a,13a,14b,c,21a
Two types of frameworks are observed for triinserted products,
namely, η2 CC-coordinated cyclopentadiene-containing
palladacycle of the type III9q,13a,21a and spirocyclic palladacycle
of the type IV,9m,n,q,10c,12a,14b,c depending upon whether the
substituent in alkyne is alkyl or ester (see Chart 1). Alkyne
insertion reactions of six-membered [C,N] palladacycles are less
well studied than those of their five-membered counter-
parts.10,12,14
Symmetrical N,N′,N″-trisubstituted guanidines are one of the
versatile nitrogen donor ligands for metal ions.22,23 Recently,
we have reported synthetic, reactivity aspects and solution
behavior of six-membered cyclopalladated N,N′,N″-triarylgua-
nidines of the types [(C,N)Pd(μ-Br)]2 and [(C,N)PdBrL] (C,N
= guanidine derived monoanionic κ2C,N scaffold; L = Lewis
base).24 We have carried out insertion reaction of 1 shown in
Chart 2 with PhCCC(O)OR (R = Me (MPP), and Et
Chart 2
bond in 2 is reactive enough for further insertion and 2 is
probably one of the intermediates in the formation of 3a/3b.
This result is in line with that obtained by Vicente and co-
workers in the formation of triinserted product obtained from
the corresponding diinserted product and 4 equiv of alkyne.9n
The insertion reaction of 1 with 10 equiv of EPP in CH2Cl2 at
ambient condition for 72 h afforded a mixture of 4a/4b and 6a/
6b in 87 and 5% yields, respectively.
Insertion reaction of 1 with 2 equiv of MPP afforded 2 and
3a/3b in 27 and 6% yields, respectively, while the reaction with
4 and 2 equiv of EPP afforded 4a/4b in 59 and 25% yields,
respectively (see the Supporting Information). Thus, the
formation of 2, 3a/3b, or 4a/4b was independent of the
ratio of the reactants used. That MPP upon insertion with 1
afforded a mixture of 2, 3a/3b, and 5a/5b, while the same
reaction with EPP afforded a mixture of 4a/4b and 6a/6b,
indicates higher nucleophilicity of the CC unit in EPP
than that present in MPP leading to enhancement in the rate of
insertion,9k which results in tri- rather than diinserted products.
It has been shown that electron-rich alkynes are prone to
undergo diinsertion rather than monoinsertion with [C,N]
palladacycles.4,8,9a,c,e,n,q,10c,11i,12a,13c,d,14b Insertion reaction of
six-membered cyclopalladated phentermine or homoveratryl-
amine, N,N′-diphenylethanimidamide, and 2-benzylpyridine of
the type [(C,N)Pd(μ-X)]2 (X = Cl or Br) with MPP and EPP
afforded mono- or diinserted palladacycles,10d,12a,14b while the
reaction of 1 with the same alkynes afforded 2, 3a/3b, or 4a/
4b. This suggests high reactivity of the Pd−C bond in 1
presumably due to the basic nature of the guanidine moiety.22
The regioisomeric pairs, 3a/3b and 4a/4b, could not be
separated from each other, although in one attempt the
regioisomers of the latter pair were separated by fractional
crystallization.
(EPP)) and isolated one diinserted palladacycle 2 and several
triinserted palladacycles, namely, 3a, 4a,b and 5a−11a, which
are grouped in Chart 3, and 3b and 5b−11b, which are grouped
in in Chart S1 in the Supporting Information. The letters a and
b denote the major and the minor regioisomers of the
triinserted palladacycles, respectively. The objectives of the
present investigation are to understand the influence of the six-
membered “[C,N]Pd” ring in 1, and the substituents in alkynes
upon the degree and regioselectivity of alkyne insertion, and
frameworks of the products. The molecular structures of 10
new palladacycles with five distinct frameworks are reported in
the manuscript, and out of these, four frameworks are novel in
alkyne insertion chemistry. Further, plausible mechanisms of
formation of new palladacycles have been outlined.
RESULTS AND DISCUSSION
■
Syntheses. Insertion reaction of 1 with 4 equiv of MPP in
CH2Cl2 at ambient condition for 72 h afforded 2 and 3a/3b in
70 and 16% yields, respectively, while the same reaction carried
out with 10 equiv of MPP afforded a mixture of 2, 3a/3b, and
5a/5b in 5, 80, and 6% yields, respectively. Interestingly, 2
upon reaction with 5 equiv of MPP in CH2Cl2 at ambient
condition for 7 days afforded 3a/3b in 70% yield (see the
Supporting Information). This result indicates that the Pd−C
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Palladacycles 3a/3b and 4a/4b, upon (i) stirring in CH2Cl2/
MeCN mixture at ambient condition for 5 days and (ii) reflux
in MeCN or PhCl for 7 and 8 h, respectively, rearranged to 5a/
5b and 6a/6b, respectively, in ≥88% yields (see also the
Supporting Information). These results indicate that the
presence of either strongly coordinating solvent or weakly
coordinating solvent at elevated temperature facilitates the
formation of 5a/5b and 6a/6b.
Palladacycles 3a/3b upon treatment with AgOTf in CH2Cl2/
acetone mixture for 15 min afforded a mixture of 7a/7b and
9a/9b in 79 and 16% yields, respectively. The yield of 9a/9b
increased to 73% and that of 7a/7b decreased to 16% when the
duration of the aforementioned reaction was extended to 24 h
(see Method 2 for 9a/9b in the Supporting Information).
Similarly, 4a/4b upon treatment with AgOTf in CH2Cl2/
acetone mixture for 15 min afforded 8a/8b and 10a/10b in 77
and 20% yields, respectively, but upon extending the reaction
period to 24 h, the yield of the former pair decreased to 13%
while that of the latter pair increased to 74% (see Method 2 for
10a/10b in the Supporting Information). Palladacycles 7a/7b
and 8a/8b upon stirring in either MeOH or MeCN at ambient
condition for 24 h afforded 9a/9b and 10a/10b in 88 and 87%
yields, respectively (see Methods 3 and 4 for 9a/9b and 10a/
10b in the Supporting Information). Pleasingly, 7a/7b and 8a/
8b upon reflux in PhCl for 6 h separately afforded 9a/9b and
10a/10b in 87 and 89% yields, respectively (see Method 1 for
9a/9b and 10a/10b). Palladacycles 5a/5b and 6a/6b upon
treatment with AgOTf separately in CH2Cl2/acetone mixture
for 15 min also afforded 9a/9b and 10a/10b in 92 and 90%
yields, respectively (see Method 5 for 9a/9b and 10a/10b in
the Supporting Information). During the course of our
Figure 1. The ORTEP representation of 2 at the 50% probability level.
Solvent molecules and all hydrogen atoms except those on the amino
nitrogen atoms are removed for clarity. Selected bond distances (Å)
and angles (deg): Pd(1)−N(1) = 2.183(3), Pd(1)−Br(1) =
2.4518(5), Pd(1)−C(36) = 1.997(3), Pd(1)−X = 2.027, C(23)−
C(26) = 1.424(4), C(33)−C(36) = 1.344(5), N(1)−C(1) = 1.319(4),
N(2)−C(1) = 1.360(4), N(3)−C(1) = 1.361(4), C(36)−Pd(1)−
Br(1) = 93.78(9), N(1)−Pd(1)−Br(1) = 101.59(7), N(1)−Pd(1)−X
= 88.54, C(36)−Pd(1)−X = 75.37, C(36)−Pd(1)−N(1) = 162.9(1),
Br(1)−Pd(1)−X = 167.80. X represents the midpoint of the double
bond C(23)−C(26).
1
attempts to measure H NMR spectrum of 9a/9b in CD3CN
The molecular structures and bond parameters of 3a, 4a, 4b,
and 7a are shown in Figures 2−4. The palladium atom
possesses a distorted square planar geometry. Three of the four
coordination sites around the palladium atom are occupied by
the monoanionic terdentate [N,C,O] bischelate via the imine
nitrogen atom of rearranged guanidine moiety, the anionic
carbon atom of a trimerised alkyne unit, and the ketonic oxygen
atom of the ester group present adjacent to the sp3 carbon of a
cyclopentadiene unit, while the fourth coordination site is
occupied by bromide (3a, 4a, and 4b) or the oxygen atom of
triflate (7a). The framework of the trimerised alkyne unit in 3a,
4a, 4b, and 7a is identical to the corresponding unit found in
[Pd{κ2(C,O)-OC(OMe)C5(C(O)OMe)4C(C(O)OMe)Cl}-
(acac)], obtained from the trimerization of DMAD in the
presence of (PhCN)2PdCl2 followed by the reaction of the
product with Tl(acac) as reported by Maitlis and co-workers.25
The Ph ring and the ester substituent are located α and β,
respectively, to the sp3 carbon of the cyclopentadiene unit in 3a
and 4a, but the position of these substituents is reversed in 4b.
Thus, 4a and 4b are regioisomers formed because of a
nonregioselective migratory insertion of the third alkyne into
the Pd−C bond of 1 (see later). The annulated framework in
3a, 4a, 4b, and 7a as compared with the known spirocyclic
framework, IV, found in triinserted products obtained from
palladacycles and an ester containing alkyne, which is
DMAD,9m,q,10c,14b arises because of the presence of Ph rather
than the ester substituent in MPP and EPP used in the present
investigation. Thus, the framework of 3a, 4a, 4b, and 7a is
novel for triinserted products. Nonregioselective monoinsertion
of alkynes with [C,N] palladacycles is known in few instances,
but nonregioselective diinsertion is known in several
instances.9a,c,p,10a,c,14b,21b However, to the best of our knowl-
in a 5 mm NMR tube, 11a-d3 crystallized as yellow crystals in
42% yield after several days. Subsequently, the yield of 11a/11b
was optimized to 82% by stirring 9a/9b in MeCN in the
presence of 10 equiv of NaOAc as an external base for 1 h and
subsequent crystallization of the reaction mixture without work
up.
Molecular Structures. The molecular structures of 2, 3a,
4a, 4b, 5a, 6a, 7a, 9a, 10a, and 11a-d3 were determined by
single crystal X-ray diffraction. The atom connectivity and
selected bond parameters of 2 are shown in Figure 1.
Palladacycle 2 consists of an eight-membered “[C,N]Pd” ring
wherein the palladium atom is surrounded by the imine
nitrogen atom of rearranged guanidine unit, bromide, one of
the carbon atoms of the CC unit of a butadienyl moiety
through a σ bond, and the remaining CC unit through a π
bond. The imine nitrogen atom and the σ-bonded carbon atom
of the butadienyl moiety are located trans to each other, as are
the bromide and the midpoint of the π-bonded CC unit. The
CC distance, 1.424(4) Å of the π-bonded olefinic unit is
longer than the CC distance, 1.344(5) Å of the σ-bonded
olefinic unit because of back-donation of electrons from the
palladium to the CC π* orbital of the π-bonded olefinic unit.
The π-bonded olefinic unit forms an angle of 63.6(1)° with the
coordination plane of the palladium atom. The substituents in
the π-bonded olefinic unit are trans to each other, while those
in the σ-bonded olefinic unit are cis to each other as observed in
the related diinserted products.9a,d,h,k,l,n,10b,c,11a−g,k,l As can be
seen in the structure, the two molecules of MPP have inserted
in a head to tail fashion.
The structural aspects of 3a, 4a, 4b, and 7a are discussed
together as these palladacycles possess an identical framework.
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Figure 4. The ORTEP representation of 7a at the 50% probability
level. Solvent molecules and all hydrogen atoms except those on the
amino nitrogen atoms are removed for clarity. Selected bond distances
(Å) and angles (deg): Pd(1)−N(1) = 2.020(4), Pd(1)−O(7) =
2.214(7), Pd(1)−O(5) = 2.039(3), Pd(1)−C(23) = 2.050(4), N(1)−
C(1) = 1.335(6), N(2)−C(1) = 1.341(6), N(3)−C(1) = 1.354(6),
N(1)−Pd(1)−O(7) = 102.3(2), N(1)−Pd(1)−C(23) = 81.2(2),
O(5)−Pd(1)−C(23) = 97.6(2), O(5)−Pd(1)−O(7) = 79.3(2),
C(23)−Pd(1)−O(7) = 169.9(2), N(1)−Pd(1)−O(5) = 177.2(1).
Figure 2. The ORTEP representation of 3a at the 50% probability
level. Solvent molecules and all hydrogen atoms except those on the
amino nitrogen atoms are removed for clarity. Selected bond distances
(Å) and angles (deg): Pd(1)−N(1) = 2.004(5), Pd(1)−Br(1) =
2.5309(8), Pd(1)−O(5) = 2.048(4), Pd(1)−C(23) = 2.087(6),
N(1)−C(1) = 1.320(8), N(2)−C(1) = 1.353(7), N(3)−C(1) =
1.362(8), N(1)−Pd(1)−Br(1) = 96.0(1), N(1)−Pd(1)−C(23) =
80.0(2), O(5)−Pd(1)−C(23) = 96.6(2), O(5)−Pd(1)−Br(1) =
87.4(1), C(23)−Pd(1)−Br(1) = 175.0(2), N(1)−Pd(1)−O(5) =
176.4(2).
Figure 3. The ORTEP representations of 4a (left) and 4b (right) at the 50% probability level. Solvent molecules and all hydrogen atoms except
those on the amino nitrogen atoms are removed for clarity. Selected bond distances (Å) and angles (deg) for 4a/4b: Pd(1)−N(1) = 2.002(3)/
2.017(2), Pd(1)−Br(1) = 2.5300(5)/2.5341(9), Pd(1)−O(5) = 2.035(3)/2.058(2), Pd(1)−C(23) = 2.092(3)/2.099(3), N(1)−C(1) = 1.317(5)/
1.320(4), N(2)−C(1) = 1.357(5)/1.348(4), N(3)−C(1) = 1.347(5)/1.350(4), N(1)−Pd(1)−Br(1) = 96.40(8)/97.11(7), N(1)−Pd(1)−C(23) =
80.5(1)/80.5(1), O(5)−Pd(1)−C(23) = 96.2(1)/96.1(1), O(5)−Pd(1)−Br(1) = 86.82(8)/86.02(6), C(23)−Pd(1)−Br(1) = 175.69(9)/
176.05(8), N(1)−Pd(1)−O(5) = 176.7(1)/174.50(9).
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edge, no pair of regioisomers such as 4a and 4b have been
structurally characterized together in alkyne insertion chem-
istry, and hence our work represents the first such report.
The molecular structures and bond parameters of 5a and 6a
are given in Figure 5 and Figure S1 in the Supporting
an endocyclic η3-allylic form.26 To the best of our knowledge,
no structurally characterized palladacycle is known that
contains an exocyclic η3-allylic unit as that present in 5a and
6a, and hence the molecular structures of these palladacycles
are also unique.
Two molecules crystallized in an asymmetric unit of 9a, but
the molecular structure and bond parameters are given only for
one molecule in Figure 6, and structural features are discussed
Figure 5. The ORTEP representation of 5a at the 50% probability
level. Hydrogen atoms except those on the amino nitrogen atoms are
removed for clarity. Selected bond distances (Å) and angles (deg):
Pd(1)−N(1) = 2.115(2), Pd(1)−Br(1) = 2.4789(4), Pd(1)−C(23) =
2.088(3), Pd(1)−C(26) = 2.079(3), Pd(1)−C(50) = 2.183(3),
C(23)−C(26) = 1.439(4), C(26)−C(50) = 1.435(4), N(1)−C(1) =
1.308(4), N(2)−C(1) = 1.352(4), N(3)−C(1) = 1.360(4), N(1)−
Pd(1)−Br(1) = 101.87(7), C(50)−Pd(1)−Br(1) = 106.37(7), N(1)−
Pd(1)−C(50) = 151.6(1).
Figure 6. The ORTEP representation of 9a at the 50% probability
level. Solvent molecules and all hydrogen atoms except those on
amino nitrogen atoms are removed for clarity. Selected bond distances
(Å) and angles (deg): Pd(1)−N(1) = 2.046(3), Pd(1)−C(23) =
2.069(3), Pd(1)−C(47) = 2.367(3), Pd(1)−C(48) = 2.301(3),
Pd(1)−O(7) = 2.197(2), C(47)−C(48) = 1.412(5), N(1)−C(1) =
1.318(4), N(2)−C(1) = 1.353(4), N(3)−C(1) = 1.354(4), N(1)−
Pd(1)−C(23) = 80.4(1), N(1)−Pd(1)−O(7) = 92.9(1), C(23)−
Pd(1)−O(7) = 173.0(1).
Information, respectively. The palladium atom in 5a, and 6a is
surrounded by the imine nitrogen atom of rearranged guanidine
unit, η3-allylic unit of a trimerised alkyne moiety, and bromide
and thus revealed a distorted square planar geometry. The two
carbon atoms of the allylic unit are part of a five-membered ring
skeleton. The presence of η3-allylic coordination mode in the
trimerised alkyne unit is apparent from the approximately equal
Cterminal−Ccentral bond distances in 5a (1.435(4) and 1.439(4)
Å) and 6a (1.434(3) and 1.439(3) Å). Surprisingly, two phenyl
rings are located on the sp3 carbon of the five-membered ring,
which suggests a series of transformations as shall be discussed
later.
The trimerised alkyne unit in 5a/5b and 6a/6b, in principle,
can have three resonance forms in solution, namely, endo- and
exocyclic η3-allylic forms and η2,σ-allylic form as found in the
related palladium complexes reported by Brookhardt and
Maitlis and co-workers (see Scheme 1).20a,26 The molecular
structure of Pd{η3-C1(Me3CC2H)3}Cl(PPh3)]·AcOH revealed
below for the same molecule. The molecular structure and
bond parameters for 10a are given in Figure S2 in the
Supporting Information. The palladium atom in 9a and 10a is
surrounded by the imine nitrogen atom of rearranged guanidine
unit, monoanionic carbon atom of a trimerised alkyne unit, and
oxygen atom of the triflate as analogously observed in 7a, but
the fourth coordination site is occupied by the CC unit
involving an ipso and an ortho carbon atoms of one of the
phenyl rings that is bound to the sp3 carbon atom of a
cyclopentadiene ring. Thus, the palladium atom revealed a
distorted square planar geometry. Palladium complexes that
possess η2 arene have been characterized by single crystal X-ray
diffraction. In these complexes, the Pd−C distance associated
with the ipso carbon varies from 2.34−2.49 Å, and that
associated with ortho carbon varies from 2.33−2.59 Å.13b,20b,27
The Pd−Cipso distance in all complexes except two is shorter
than the Pd−Cortho distance.27c,e The minimum and the
maximum difference between the Pd−Cipso and the Pd−Cortho
distances in η2 arene palladium complexes are 0.022 and 0.161
Å, respectively. Remarkably, one of the Pd−Cortho distances in
Scheme 1
9a and 10a is shorter than the Pd−Cipso distance (Pd−Cortho
:
2.301(3) Å (9a), 2.312(3) Å (10a); Pd−Cipso: 2.367(3) Å (9a),
2.388(3) Å (10a)), which may be responsible for the proclivity
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of ortho-carbon of the coordinated phenyl ring to undergo
intramolecular cyclopalladation as found in the conversion of
9a to 11a-d3. Small difference between two Pd−C distances in
9a and 10a (0.066(3) Å (9a), 0.076(3) Å (10a)) suggests η2-
phenyl coordination to the palladium. Only one η2-phenyl
bound palladium complex has been structurally characterized in
alkyne insertion chemistry.13b
arene palladium complexes have been suggested as one of the
intermediates in depalladation of alkyne-inserted palladacycle-
s9i,13d and intramolecular C−H activation,28−30 to the best of
our knowledge there is no unequivocal proof for the proposal,
and thus the molecular structures of 9a and 11a-d3 together
serve as a proof.
The degree of n−π conjugation involving the lone pair of
electrons on the amino nitrogen atoms with the CN π*
orbital of the guanidine moiety can be assessed from the values
of ΔCN, ΔCN′, and ρ as defined in Chart S2 in the Supporting
Information. The values of ΔCN and ΔCN′ = 0.0, and ρ = 1.0
indicate a maximum n−π conjugation, and any deviation from
these values indicates a hampered n−π conjugation.31,32 The
aforementioned parameters for the structurally characterized
palladacycles in the present investigation are given in Table S1
in the Supporting Information. As can be seen from Table S1
(Supporting Information), the values of ΔCN, ΔCN′ and ρ
indicate a moderate to strong n−π conjugation in new
palladacycles.
The molecular structure and bond parameters of 11a-d3 are
given in Figure 7. The palladium atom in 11a-d3 is surrounded
1
1H and 13C{1H} NMR Spectroscopy. H and 13C{1H}
NMR spectra of 2 revealed the presence of a single species in
solution and thus suggest a regioselective insertion of the first
and the second molecule of MPP into the Pd−C bond of 1 in
the formation of 2. 1H NMR spectra of 3a/3b, 4a/4b, and 7a/
7b−10a/10b revealed the presence of two isomers in solution
with one of them being predominant. The successful isolation
1
of 4b in one attempt permitted us to record its H NMR
1
spectrum, which helped us to confidently assign the H NMR
signals of 4a and 4b in the isomeric mixture, 4a/4b. The two
species observed for 3a/3b and 7a/7b−10a/10b in solution are
assigned to two regioisomers based on the molecular structure
1
of 4b and H NMR spectra of 4b and 4a/4b.
1
The H NMR spectrum of 5a/5b revealed the presence of
two species, possibly two regioisomers, in about 1.0:0.08 ratio
at 0.010 mM and 0.004 mM concentrations. However, the H
1
Figure 7. The ORTEP representation of 11a-d3 at the 50% probability
level. Solvent molecules and all hydrogen atoms except those on
amino nitrogen atoms are removed for clarity. Selected bond distances
(Å) and angles (deg): Pd(1)−N(1) = 2.138(4), Pd(1)−C(23) =
2.077(4), Pd(1)−C(52) = 1.987(5), Pd(1)−N(4) = 2.097(4), N(1)−
C(1) = 1.303(6), N(2)−C(1) = 1.371(6), N(3)−C(1) = 1.346(6),
N(1)−Pd(1)−C(23) = 82.1(2), N(1)−Pd(1)−N(4) = 98.7(2),
N(4)−Pd(1)−C(52) = 88.9(2), C(23)−Pd(1)−C(52) = 90.2(2),
N(1)−Pd(1)−C(52) = 172.2(2), N(4)−Pd(1)−C(23) = 179.1(2).
NMR spectrum of 6a/6b revealed the presence of two species,
possibly two regioisomers, in about 1.0:0.28 ratio at 0.012 mM
concentration but three species in about 1.0:0.25:0.15 ratios at
0.004 mM concentration. The presence of three species of 6a/
6b at a lower concentration suggests the presence of two
regioisomers 6a and 6b and a rotamer, 6c, which possibly arises
from 6a through the restricted C−N(H)Ar single bond rotation
of the CN3 unit of the guanidine moiety as illustrated in
Scheme 2. The intermolecular interactions could be weakened
at 0.004 mM concentration, thereby facilitating the formation
of rotamer, 6c. The difference in the number of isomers
between 5a/5b and 6a/6b at 0.004 mM concentration is
probably ascribed to the difference in the strength of inter- and
intramolecular interactions present in 5a/5b as compared to
those present in 6a/6b. Variable temperature 1H NMR
by a [N,C,C] bischelate constituted by the imine nitrogen atom
of rearranged guanidine unit, monoanionic carbon atom of a
trimerised alkyne unit, and ortho carbon atom of one of the two
phenyl rings bound to the sp3 carbon of a cyclopentadiene ring.
The fourth coordination site is fulfilled by the nitrogen atom of
CD3CN. Thus, the phenyl ring that was previously coordinated
to the palladium atom through the η2 CC double bond in 9a
has undergone orthopalladation to afford a biscyclopalladated
11a-d3. The palladium atom revealed a distorted square planar
geometry. The imine nitrogen atom of the rearranged
guanidine unit and the cyclopalladated carbon of the phenyl
ring are trans to each other, as are the sp3 carbon of the
trimerised alkyne unit and the nitrogen atom of CD3CN. The
six-membered “[C,C]Pd” ring revealed a pseudoboat con-
formation with the palladium atom and the sp3 carbon, C(40)
lying at 0.7511(3) and 0.7467(41) Å, respectively, out of the
mean plane defined by the remaining four basal atoms. The
five-membered “[C,N]Pd” ring revealed a nonplanar con-
formation with the palladium atom lying 0.8165(3) Å from the
mean plane defined by the remaining four atoms. Although η2
Scheme 2. Pathway for the Formation of Third Isomer of
6a/6b in Solution
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Scheme 3. Plausible Mechanism of Formation of Di- and Triinserted Products
measurements carried out on the samples of 8a/8b and 9a/9b
from 298−218 at 10 K interval in CD2Cl2 revealed no
significant change in the spectral pattern and thus confirmed
our proposal that the two isomers observed in each case are
regioisomers (see Figures S3−S9 in the Supporting Informa-
tion).
variously substituted monoanionic benzylamine derived κ2C,N
scaffold).9k The intermediate A upon ring contraction affords
an intermediate B. The framework present in the intermediate
B is analogous to that present in the product obtained from the
bridge-splitting reaction of an eight-membered monoinserted
palladacycle with pyridine, the monoinserted palladacycle being
the product of the insertion reaction of F3CCCCF3
with the six-membered palladacycle of the type [(C,O)Pd(μ-
Cl)]2 (C,O = monoanionic acetanilide derived κ2C,O
scaffold).12a Subsequently, the intermediate B undergoes
amine-imine tautomerization to afford an intermediate C.
The reaction of 1 with 2 equiv of CNXy afforded five-
membered palladacycle, [Pd{κ2(C,N)-CNXyC6H3Me-3(N
C(NHAr)2)-2}Br(CNXy)] (Ar = 2-MeC6H4; Xy = 2,6-
Me2C6H3) via the bridge-splitting, insertion, ring contraction,
The degree of alkyne insertion and sometimes the number of
regioisomers of a given palladacycle can be identified not only
1
from the number and types of H NMR signals but also from
the number of 13C NMR signals of the CO carbon of the
ester moieties. For example, the 13C{1H} NMR spectrum of
8a/8b revealed three singlets at δ = 164.28, 170.91, and 176.19
assignable to the CO carbon of the ester moieties of 8a and
three distinct singlets at δ = 167.63, 170.73, and 174.47
assignable to the same carbon atom of the same moieties of 8b.
Palladacycle 11a can give rise to four isomers in solution
through the combination of (i) inversion of the six-membered
“[C,C]Pd” ring and (ii) folding and unfolding of the five-
membered “[C,N]Pd” and the six-membered “[C,C]Pd” rings
along the common Pd−Csp3 bond. Thus, in principle, eight
isomers are anticipated for 11a/11b in solution, but only six
were observed in about 0.26:0.59:0.61:1.00:2:00:3.00 ratios as
and amine-imine tautomerisation events.26 Moreover, we
a,b
have isolated a family of monoinserted palladacycles of the type
C wherein the Lewis base such as 3,5-lutidine or CNtBu
occupies the fourth coordination site in place of η2 coordinated
alkyne,35 and this further serves as an indirect evidence for the
proposed structure of C. [C,N] Palladacycles that possess an
amino nitrogen atom (NH) as part of the six-membered
“[C,N]Pd” unit upon insertion reaction with alkynes afford
eight-membered diinserted products,12a,14c which were pre-
sumed to arise from the ring contraction cum amine-imine
tautomerization or only ring contraction process. Several eight-
membered monoinseretd [C,N] palladacycles are
known,10d,12b,c,14b and therefore, ring contraction and amine-
imine tautomerisation upon alkyne insertion reaction appear to
be intrinsic properties of the cyclopalladated complexes such as
1 rather than ring strain associated with the intermediate A.
In the absence of third equivalent of alkyne, the intermediate
C rearranges to 2 through the regioselective migratory insertion
1
identified by H NMR spectroscopy, probably because of very
low intensity of some of the isomers that arise out of 11b.
Mechanism. The mechanism of alkyne insertion of
organopalladium complexes has been widely studied and
discussed.4−6,9b,c,k,p,14a,b,d,17a,33,34 A plausible mechanism of
the formation of 2, 3a/3b, and 4a/4b is shown in Scheme 3.
The first step involves bridge-splitting cum insertion reactions
of 1 with alkynes to afford an intermediate A, which is in
conjunction with the pathway proposed by Ryabov and co-
workers for mono- and diinsertion of alkynes with the five-
membered palladacycles of the type [(C,N)Pd(μ-Cl)]2 (C,N =
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Scheme 4. Plausible Mechanism of Formation of Rearranged Triinserted Products and Biscyclopalladated Product
of the coordinated alkyne, cis → trans isomerization4,9k of the
CC unit of the first inserted alkyne and coordination of the
same CC unit to the palladium. In the presence of the third
equivalent of alkyne, the intermediate C undergoes regiose-
lective migratory insertion of the coordinated alkyne to afford
an intermediate D. The intermediate D undergoes migratory
insertion of the coordinated alkyne to afford an intermediate E
wherein the carbon atom bound to the palladium possesses R1
substituent while the adjacent carbon atom possesses R2
substituent. Alternatively, and to a lesser probability, the
intermediate D undergoes migratory insertion of the
coordinated alkyne to afford an intermediate F wherein the
carbon atom bound to the palladium possesses R2 substituent
while the adjacent carbon atom possesses R1 substituent. The
formation of 10-membered “[C,N]Pd” intermediates, E and F,
is in line with the hypothesis discussed in the literature to
explain the formation of triinserted palladacycles.14b That the
palladacycle 2 can be transformed to 3a/3b in the presence of
alkyne indicates decoordination and trans → cis isomer-
ization9c,e of the of the first inserted alkyne. The molecular
structure of 4b and the fact that 2 upon reaction with 5 equiv of
MPP affords 3a/3b in 70% yield, albeit slowly, support
nonregioselective migratory insertion of the coordinated alkyne
in D in the formation of intermediates E and F. Intermediates
E/F upon the Pd−C bond cleavage followed by cyclization
afford zwitterionic intermediates G/H,14b and these inter-
mediates upon ring closure via the carbanion and the ketonic
oxygen atom of the ester group, which is present β to the sp3
carbon of the cyclopentadiene ring, afford annulated 3a/3b or
4a/4b. Conceivably, the presence of Ph ring rather than the
ester substituent on the sp3 carbon of the cyclopentadiene unit
in the intermediates G/H, indicated as R1, completely
eliminates the possibility of the formation of a spirocyclic
framework such as that present in IV.
K/L, when X is less electrophilic Br, undergo σ → π allylic
rearrangement of the trimerised alkyne unit, followed by the
1
loss of solvent molecule, S, to afford 5a/5b and 6a/6b. H
NMR spectra of 5a/5b in CD3CN indicated the presence of
only one species while in CDCl3 indicated the presence of two
species in about 1.0:0.08 ratio. Presumably, this observation
indicates the reversible formation of species K and L upon
dissolution of 5a/5b in CD3CN. Intermediates K/L, when X is
more electrophilic triflate, undergo cyclopentadienyl ring flip by
180° along the CCp−CPd (Cp = cyclopentadienyl) single bond
followed by coordination of one of the phenyl rings attached to
the sp3 carbon atom of the cyclopentadienyl ring to the
palladium and subsequent elimination of S to afford 9a/9b and
10a/10b. The more electrophilic triflate appears to stabilize
intermediates K/L long enough to facilitate the formation of
9a/9b and 10a/10b. Thus, coordinating ability of the solvent
molecule, S, and the difference in the electrophilicity of X are
the driving forces in the formation of 5a/5b, 6a/6b, 9a/9b, and
10a/10b.
Palladacycles 9a/9b upon storing in CD3CN afforded 11a/
11b-d3 in 42% yield, but upon reaction with NaOAc in MeCN
and crystallization of the reaction mixture without work up
afforded 11a/11b in 82% yield. Since CD3CN/MeCN are
coordinating solvents and the triflate is a weakly coordination
anion, the formation of ionic intermediates such as M/N and
O/P in the absence and in the presence of NaOAc,
respectively, prior to the formation of 11a/11b-d3 and 11a/
11b is possible (see Chart 4). To prove this hypothesis, molar
Chart 4
The plausible mechanism of the formation of 5a/5b, 6a/6b,
9a/9b, and 10a/10b and subsequent conversion of 9a/9b to
11a/11b is outlined in Scheme 4. The first step involves
decoordination of the ketonic oxygen atom of the ester moiety
by the solvent molecule, S, to afford intermediates, I/J, which
upon 1,2 phenyl shift afford intermediates K/L. Intermediates
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4a/4b, 5a/5b, 6a/6b, 9a/9b, and 10a/10b may be found in the
Supporting Information.
conductivity was measured for 9a/9b in MeCN, and the
obtained molar conductivity value of 159.3 Ω−1 cm2 mol−1
indicated the presence of a 1:1 electrolyte,36 and this data
supports the formation of intermediates such as O/P. The
molar conductivity value of 0.0 Ω−1 cm2 mol−1 for the CHCl3
solution of 9a/9b indicated the presence of a neutral species,
which further validates the formation of intermediates O/P in
MeCN.
The partial formation of 11a/11b-d3 in CD3CN in the
absence of NaOAc via intermediates M/N is due to the weakly
basic nature of OTf−, but the complete formation of 11a/11b
in MeCN in the presence of NaOAc via intermediates O/P is
due to the strongly basic nature of OAc−. Cyclopalladation can
occur through one of the following pathways:37 (i) base
unassisted, (ii) base-assisted intramolecular, and (iii) base-
assisted intermolecular, and which one of these operates for a
given reaction depends upon several factors. From the
experimental results we have obtained, it appears that both
11a/11b-d3 and 11a/11b pairs are formed from intermediates
M/N and O/P through an intramolecular anion assisted
pathway via intermediates Q/R and S/T, respectively (see
Chart 5).
Palladacycle 2. Method 1: To a solution of 1 (200 mg, 0.194
mmol) in CH2Cl2 (20 mL) was slowly added CH2Cl2 solution (10
mL) of MPP (124 mg, 0.774 mmol), and the resulting solution stirred
at ambient temperature for 72 h. The solution was concentrated under
a vacuum to about 5 mL, layered with n-hexane, and stored at ambient
temperature for several days to afford a mixture of 2·CH2Cl2 as yellow
cuboidal crystals and 3a/3b as orange needle shaped crystals. The two
types of crystals were separated with the aid of a brush and dried under
a vacuum. Yields: 70% (250 mg, 0.272 mmol, 2·CH2Cl2), 16% (62 mg,
0.062 mmol, 3a/3b). Data for 2·CH2Cl2: mp (DSC) 172.02 °C; IR
(KBr, cm−1) ν(NH) 3384 (w), 3251 (w); ν(CO) 1719 (s); ν(C
1
N) 1611 (vs); H NMR (CDCl3, 400 MHz) δ 1.60 (br, 3 H, CH3),
2.06, 2.23 (each s, 2 × 3 H, CH3), 3.44, 3.83 (each s, 2 × 3 H,
C(O)OCH3), 6.19 (br, 1 H, NH), 6.64−6.80 (m, 7 H, ArH), 6.89 (d,
JHH = 7.0 Hz, 1 H, ArH), 7.04−7.07 (m, 2 H, ArH), 7.27−7.30 (m, 3
H, ArH), 7.36−7.42 (m, 4 H, ArH), 7.47 (dd, JHH = 6.1, 3.0 Hz, 2 H,
ArH), 7.96 (d, JHH = 7.3 Hz, 2 H, ArH), 8.94 (br, 1 H, NH); the
13C{1H} NMR signals were assigned with the aid of 1H−13C
HETCOR NMR spectroscopy (see Figures S10−S12 in the
Supporting Information); 13C{1H} NMR (CDCl3, 100.5 MHz) δ
18.00, 18.06, 19.54 (CH3), 51.30, 53.24 (OCH3), 90.79 (br, C), 105.21
(C), 119.90 (br, CH), 121.48 (CH), 124.16 (CH), 124.39 (CH),
124.59 (CH), 125.31 (CH), 126.02 (CH), 127.05 (CH), 127.36 (CH),
127.92 (CH), 128.05 (CH), 128.99 (CH), 129.65 (CH), 129.91 (C),
130.32 (CH), 130.38 (CH), 130.87 (CH), 132.05 (CH), 132.48 (C),
134.98 (C), 135.79 (C), 137.52 (C), 139.05 (C), 148.70 (C), 152.82
(C), 159.02 (C) (ArC, ArCH, CC and CN), 160.20, 169.79 (C
O); MS (ESI+) m/z, (relative intensity %), [ion] 820 (9) [M−Me]+,
776 (100) [M−C(O)OMe]+, 329 (26) [LH22‑tolyl]+. Anal. Calcd for
C42H38N3O4BrPd·CH2Cl2 (Mw 835.1 + 84.94): C, 56.14; H, 4.38; N,
4.57%. Found: C, 56.27; H, 4.51; N, 4.47.
Chart 5
Palladacycles 3a/3b. Method 1: To a solution of 1 (200 mg,
0.194 mmol) in CH2Cl2 (20 mL) was added CH2Cl2 solution (10 mL)
of MPP (311 mg, 1.94 mmol), and the resulting solution stirred at
ambient temperature for 72 h. The solution was concentrated under a
vacuum to about 5 mL, layered with n-hexane, and stored at ambient
temperature for several days to afford a mixture that consisted of 2·
CH2Cl2 as yellow irregular crystals, 3a/3b as orange needle shaped
crystals, and 5a/5b·H2O as reddish-orange cuboidal crystals. The three
types of crystals were separated with the aid of a brush and each of
them washed with several aliquots of n-hexane and dried under a
vacuum. Yields: 80% (310 mg, 0.311 mmol; 3a/3b), 5% (18 mg, 0.019
mmol; 2·CH2Cl2) and 6% (23 mg, 0.023 mmol; 5a/5b·H2O). Data for
3a/3b: mp (DSC) 194.52 °C (decomp); IR (KBr, cm−1) ν(NH) 3400
(br), 3362 (w); ν(CO) 1734 (w), 1673 (w); ν(CN) 1596 (vs);
the 1H NMR spectrum of 3a/3b revealed the presence of 3a and 3b in
about 1:0.13 ratio as estimated from the integrals of alkyl protons; 1H
NMR (CDCl3, 400 MHz) δ 2.10 (s, 3H, CH3, 3a), 2.14, 2.20 (each s,
2 × 3H, CH3, 3b), 2.25, 2.35 (each s, 2 × 3H, CH3, 3a), 2.38 (s, 3H,
CH3, 3b), 3.34 (s, 2 × 3H, C(O)OCH3, 3a), 3.39, 3.41, 3.86 (each s, 3
CONCLUSION
■
One diinserted and a variety of triinserted palladacycles have
been synthesized and characterized. The molecular structures of
10 new palladacycles have been determined by X-ray
diffraction. The frameworks of the five-membered “[C,N]Pd”
ring and the six-membered “[C,O]Pd” ring in 3a, 4a, 4b, and 7a
are unanticipated partly because of ring contraction cum amine-
imine tautomerisation and partly because of the unsymmetrical
nature of MPP and EPP used in the present investigation.
Through the molecular structures of 4a and 4b, non-
regioselective triinsertion of 1 with MPP and EPP has been
confirmed. The frameworks of 5a and 6a are unprecedented in
the literature. The role of η2 arene complexes as genuine
intermediates in intramolecular C−H activation is confirmed
through the isolation and structural characterization of 9a and
11a-d3. From the results we have obtained, it is concluded that
the substituents in alkynes affect the degree of insertion,
whereas coordinating ability of solvents and temperature
determine the duration of the formation of rearranged
products. The electrophilicity of the bromide and the triflate
determines the type of rearrangement of the triinserted
palladacycles. Factor that increases the electrophilicity of the
palladium atom induces cyclopalladation.
× 3H, C(O)OCH3, 3b), 3.94 (s, 3H, C(O)OCH3, 3a), 5.49 (d, JHH
=
8.1 Hz, 2 × 1H, ArH, 3a/3b), 5.83 (t, JHH = 8.1 Hz, 2 × 1H, ArH, 3a/
3b), 6.50 (d, JHH = 7.3 Hz, 2 × 1H, ArH, 3a/3b), 6.65 (s, 2 × 1H, NH,
3a/3b), 6.72 (t, JHH = 7.3 Hz, 2 × 1H, ArH, 3a/3b), 6.78 (apparent q,
JHH = 7.6 Hz, 2 × 3 H, ArH, 3a/3b), 6.84−6.89 (m, 2 × 2H, ArH, 3a/
3b), 6.95 (t, JHH = 7.3 Hz, 2 × 2H, ArH, 3a/3b), 7.08 (d, JHH = 7.3 Hz,
2H, ArH, 3b), 7.14 (d, JHH = 8.0 Hz, 2H, ArH, 3a), 7.18−7.24 (m, 2 ×
5H, ArH, 3a/3b), 7.27−7.28 (m, 2 × 3H, 3a/3b), 7.31−7.35 (m, 2 ×
5H, 3a/3b), 9.23 (s, 1H, NH, 3a), 9.29 (s, 1H, NH, 3b); the 13C{1H}
NMR spectrum could not be recorded for 3a/3b because of their poor
solubility in most of the common deuterated NMR solvents; MS
(ESI+) m/z, (relative intensity %), [ion] 995 (2) [M]+, 928 (5) [M +
Li − C(O)OMe, Me], 914 (100) [M − HBr]+, 780 (9) [M + H − Br,
Ph, C(O)OMe], 754 (46) [M − HBr, MPP]+, 679 (80) [M − HBr,
MPP, Ph]+, 648 (22) [M + H − Br, MPP, Ph, OMe]+, 330 (25)
[LH32‑tolyl]+. Anal. Calcd for C52H46N3O6BrPd (Mw 995.27): C, 62.75;
H, 4.66; N, 4.22%. Found: C, 62.99/63.05; H, 4.30/4.40; N, 3.98/3.94.
EXPERIMENTAL SECTION
Full experimental details pertinent to general considerations as well as
alternate low yielding or circuitous synthetic procedures for 2, 3a/3b,
■
7588
dx.doi.org/10.1021/om4010719 | Organometallics 2013, 32, 7580−7593

Organometallics
Article
Palladacycles 4a/4b. Method 1: To a solution of 1 (200 mg,
0.194 mmol) in CH2Cl2 (20 mL) was added CH2Cl2 solution (10 mL)
of EPP (338 mg, 1.94 mmol), and the resulting solution was stirred at
ambient temperature for 72 h. The solution was concentrated under a
vacuum to about 5 mL, layered with n-hexane, and stored at ambient
temperature for several days to afford a mixture of 4a/4b·1/2CH2Cl2
as orange cuboidal crystals and 6a/6b as red cuboidal crystals. The two
types of crystals were separated with the aid of a brush, washed with
several aliquots of n-hexane, and dried under a vacuum. Yields: 87%
(366 mg, 0.339 mmol; 4a/4b·1/2CH2Cl2), 5% (10 mg, 0.010 mmol;
6a/6b). Crystals of 4a·C7H8 suitable for X-ray diffraction were grown
from CHCl3/toluene mixture in a span of several days. Data for 4a/4b·
1/2CH2Cl2: mp (DSC) 244.81 °C (decomp); IR (KBr, cm−1) ν(NH)
3400 (br), 3361 (w); ν(CO) 1733 (m), 1670 (m); ν(CN) 1593
(vs); the 1H NMR spectrum of 4a/4b revealed the presence of 4a and
4b in about 1:0.20 ratio as estimated from the integrals of CH3 protons
1H, ArH, 5b), 6.62−6.69 (m, 2 × 2H, ArH, 5a/5b), 6.72−7.00 (m, 2
× 12H, ArH, 5a/5b), 7.04 (d, JHH = 8.3 Hz, 2H, ArH, 5a), 7.23 (s, 1H,
ArH, 5b), 7.24 (s, 1H, ArH, 5a), 7.28−7.31 (m, 2H, ArH, 5a), 7.36 (t,
JHH = 6.4 Hz, 4H, ArH, 5b), 7.43−7.48 (m, 3H, ArH, 5a), 7.57 (d, JHH
= 7.8 Hz, 1H, ArH, 5b), 7.62 (t, JHH = 7.5 Hz, 2H, ArH, 5b), 7.76 (d,
JHH = 6.9 Hz, 2H, ArH, 5a), 8.07 (dd, JHH = 6.8, 1.8 Hz, 2H, ArH, 5a),
8.18 (d, JH1H = 8.7 Hz, 1H, ArH, 5b), 8.73 (s, 1H, NH, 5a), 8.92 (s, 1H,
NH, 5b); H NMR (CD3CN, 400 MHz) δ 1.88, 1.90, 2.27 (each s, 3
× 3H, CH3), 2.27 (br, 3H, CH3), 3.27, 3.38, 3.78 (each s, 3 × 3H,
OCH3), 6.44 (s, 1H, NH), 6.59 (d, JHH = 7.3 Hz, 1H, ArH), 6.68 (t,
JHH = 7.3 Hz, 1H, ArH), 6.75−6.79 (m, 4H, ArH), 6.84−6.92 (m, 4H,
ArH), 6.94−6.97 (m, 2H, ArH), 6.99−7.04 (m, 3H, ArH), 7.21 (d, JHH
= 8.1 Hz, 1H, ArH), 7.31 (d, JHH = 2.2 Hz, 2H, ArH), 7.32 (d, JHH
=
1.5 Hz, 1H, ArH), 7.47−7.48 (m, 3H, ArH), 7.63 (d, JHH = 2.2 Hz, 1H,
ArH), 7.64 (d, JHH = 4.4 Hz, 1H, ArH), 7.00−8.02 (m, 2H, ArH), 8.39
(br, 1H, NH); MS (ESI+) m/z, (relative intensity %), [ion] 996 (20)
[M + H]+, 914 (35) [M − HBr]+, 810 (100) [M − 2Ph, OMe]+, 747
(9) [M + Li − Br, MPP, Me]+; the 13C{1H} NMR signals were
assigned with the aid of DEPT 90 and 1H−13C HETCOR NMR
spectroscopy and the assignments of the signals to 5a and 5b were
made wherever possible (see Figures S13−S18 in the Supporting
Information); 13C{1H} NMR (CDCl3, 100.5 MHz) δ 17.3 (5a), 17.5
(5b), 17.6 (5a), 17.8 (5b), 18.3 (5b), 18.4 (5a) (CH3), 50.9 (5b), 51.2
(5a), 51.3 (5b), 52.0 (5b), 52.8 (5a), 53.1 (5a) (C(O)OCH3), 68.2
(C, 5a), 75.2 (C, 5b), 84.5 (C), 90.5 (C), 95.8 (CH), 120.2 (CH),
121.8 (CH, 5a), 121.9 (CH, 5b), 123.0 (CH), 123.9 (CH), 124.2 (CH,
5a), 124.4 (CH, 5b), 124.7 (CH, 5b), 124.8 (CH, 5a), 125.0 (CH, 5b),
125.5 (CH), 125.6 (CH), 125.8 (CH, 5a), 125.9 (CH, 5b), 126.1
(CH), 126.2 (CH), 126.8 (br, C), 127.6 (CH), 127.9 (CH), 128.1
(CH), 128.3 (CH), 128.5 (CH), 128.6 (C), 129.3 (C), 129.4 (CH),
129.8 (CH), 130.4 (CH), 130.7 (C), 131.4 (CH), 132.2 (C), 132.5
(CH), 133.8 (CH), 133.9 (C), 134.5 (CH), 134.6 (C, 5a), 135.0 (C,
5b), 135.4 (C, 5a), 136.0 (C, 5b), 136.5 (C, 5a), 136.7 (C, 5a), 136.9
(C, 5b), 137.0 (C, 5b), 137.5 (C, 5b), 137.7 (C, 5b), 138.0 (C, 5a),
138.3 (C, 5a), 140.3 (C), 151.1 (C), 152.9 (C), 153.1 (C), 153.3 (C),
155.0 (C), 155.3 (C), 162.7 (C) (ArC, CC and CN), 164.4 (5b),
164.6 (5a), 165.7 (5a), 168.4 (5a), 173.1 (5b), 174.6 (5b) (CO).
Anal. Calcd for C52H46N3O6BrPd·H2O (Mw 995.27 + 18.02): C, 61.64;
H, 4.77; N, 4.15%. Found: C, 61.93; H, 4.71; N, 4.13.
1
of the guanidine moiety; H NMR (CDCl3, 400 MHz) δ 0.57−0.62
(m, 2 × 3H, OCH2CH3, 4a and 4b), 0.75 (t, JHH = 7.1 Hz, 3 H,
OCH2CH3, 4a), 0.88 (t, JHH = 5.9 Hz, 3H, OCH2CH3, 4b), 1.33−1.39
(m, 2 × 3H, OCH2CH3, 4a/4b), 2.10 (s, 3H, CH3, 4a), 2.12, 2.17
(each s, 2 × 3H, CH3, 4b), 2.24, 2.35 (each s, 2 × 3H, CH3, 4a), 2.39
(s, 3H, CH3, 4b), 3.73−3.95 (m, 2 × 4H, OCH2CH3 4a/4b), 4.29−
4.37 (m, 1H, OCH2CH3, 4b), 4.41−4.49 (m, 2 × 1H, OCH2CH3, 4a/
4b), 4.53−4.61 (m, 1H, OCH2CH3, 4a), 5.44 (d, JHH = 8.0 Hz, 1H,
4a), 5.80 (t, JHH = 7.7 Hz, 1H, 4a), 6.24−6.30 (m, 2H, 4b), 6.47 (d,
JHH = 8.1 Hz, 1H, 4a), 6.59 (d, JHH = 6.6 Hz, 1H, 4b), 6.71 (t, JHH
=
7.0 Hz, 2 × 1H, 4a/4b), 6.75−6.84 (m, 2 × 4H, 4a/4b), 6.87−6.89
(m, 1H (4a), 4H (4b)), 6.92−7.00 (m, 2 × 2H, 4a/4b), 7.14−7.18
(m, 1H (4a), 6H (4b)), 7.20−7.25 (m, 7H (4a), 5H (4b)), 7.30−7.36
(m, 8H (4a), 2H (4b)) (NH and ArH), 9.26 (s, 1H, NH, 4a), 9.33 (s,
1H, NH, 4b); the 13C{1H} NMR spectrum could not be obtained for
4a/4b because of their poor solubility in most of the common
deuterated NMR solvents; MS (ESI+) m/z, (relative intensity %),
[ion] 1068 (8) [M + Cs − C(O)OEt, Et], 1038 (12) [M + H]+, 1014
(100) [M + Li − 2Me]+, 933 (5) [M + Li − HBr, Et, H]+, 608 (7) [M
− HBr, 2EPP]+. Anal. Calcd for C55H52N3O6BrPd·1/2CH2Cl2 (Mw
1037.36 + 42.47): C, 61.73; H, 4.95; N, 3.89%. Found: C, 61.55; H,
5.09; N, 3.72.
In one attempt, 4b was obtained as reddish orange cuboidal crystals
in 6% (12 mg, 0.012 mmol) yield from the mother liquor, after the
crystals of 4a/4b·1/2CH2Cl2 had been separated out from CH2Cl2/
toluene mixture, at ambient temperature in a span of several days. Data
for 4b: IR (KBr, cm−1) ν(NH) 3400 (br), 3343 (w); ν(CO) 1708
Palladacycles 6a/6b. Method 1: Palladacycles, 6a/6b were
prepared from 4a/4b (100 mg, 0.096 mmol) following the procedure
described for 5a/5b·H2O with reflux time being 8 h, in 93% (93 mg,
0.090 mmol) yield. Data for 6a/6b: mp (DSC) 215.90 °C; IR (KBr,
cm−1) ν(NH) 3384 (w); ν(CO) 1707 (vs); ν(CN) 1595 (vs);
1
(m), 1676 (m), 1654 (sh); ν(CN) 1596 (vs); H NMR (CDCl3,
1
400 MHz) δ 0.60 (t, JHH = 7.3 Hz, 3H, OCH2CH3), 0.87 (t, JHH = 7.0
Hz, 3H, OCH2CH3), 1.33−1.38 (m, 3H, OCH2CH3), 2.12, 2.16, 2.39
(each s, 3 × 3H, CH3), 3.82−3.97 (m, 4H, OCH2CH3), 4.28−4.37,
4.40−4.48 (each m, 2 × 1H, OCH2CH3), 6.24−6.30 (m, 2H), 6.59 (d,
JHH = 6.6 Hz, 1H), 6.69 (t, JHH = 7.7 Hz, 1H), 6.75−6.83 (m, 4H),
6.86−6.90 (m, 4H), 6.92−7.00 (m, 2H), 7.13−7.19 (m, 6H), 7.19−
7.25 (m, 5H), 7.32−7.39 (m, 2H) (ArH and NH), 9.34 (s, 1H, NH);
MS (ESI+) m/z, (relative intensity %), [ion] 956 (100) [M − HBr]+,
852 (30) [M + H − Br, Ph, Et]+.
the H NMR spectrum of 0.012 mM solution of 6a/6b in CDCl3
revealed the presence of 6a and 6b in about 1:0.28 ratio as estimated
1
from the integrals of CH3 protons of the guanidine moiety; H NMR
(CDCl3, 400 MHz) δ 0.72 (t, JHH = 6.9 Hz, 2 × 3H, OCH2CH3, 6a/
6b), 0.80 (t, JHH = 7.0 Hz, 3H, OCH2CH3, 6a), 0.86 (t, JHH = 7.0 Hz,
3H, OCH2CH3, 6b), 1.33 (t, JHH = 7.3 Hz, 3H, OCH2CH3, 6a), 1.47
(t, JHH = 7.0 Hz, 3H, OCH2CH3, 6b), 1.85, 1.88 (each s, 2 × 3H, CH3,
6a), 2.06, 2.10, 2.19 (each s, 3 × 3H, CH3, 6b), 2.35 (s, 3H, CH3, 6a),
3.68−3.88 (m, 6H, OCH2CH3, 6a (4H) and 6b (2H)), 3.92 (q, JHH
=
Palladacycles 5a/5b. Method 1: Palladacycles 3a/3b (100 mg,
0.100 mmol) were stirred in a mixture of CH2Cl2/CH3CN (1:1 (v/v),
20 mL) for 5 days at ambient condition. Solvents were removed under
a vacuum, and the resulting red solid crystallized from CH2Cl2/n-
hexane mixture at ambient temperature over a span of several days to
afford 5a/5b as hygroscopic reddish-orange cuboidal crystals. Yield:
94% (95 mg, 0.094 mmol; 5a/5b·H2O). Data for 5a/5b·H2O: mp
(DSC) 242.30 °C; IR (KBr, cm−1) ν(NH) 3388 (w), 3199 (w);
7.1 Hz, 2H, OCH2CH3, 6b), 3.99−4.08 (m, 2 × 1H, OCH2CH3, 6a/
6b), 4.25−4.33 (m, 1H, OCH2CH3, 6a), 4.59−4.67 (m, 1H,
OCH2CH3, 6b), 5.74 (s, 2 × 1H, NH, 6a/6b), 6.14 (t, JHH = 7.7
Hz, 1H, ArH, 6b), 6.26 (d, JHH = 8.0 Hz, 1H, ArH, 6b), 6.49 (d, JHH
=
7.3 Hz, 1H, ArH, 6b), 6.57−6.69 (m, 5H, ArH, 6a (2H), 6b (4H)),
6.72 (d, JHH = 7.3 Hz, 2 × 1H, ArH, 6a/6b), 6.77−6.83 (m, 2 × 5H,
ArH, 6a/6b), 6.87−6.90 (m, 2H, ArH, 6a), 6.94 (t, JHH = 7.3 Hz, 2 ×
1H, ArH, 6a/6b), 6.98−7.03 (m, 5H, ArH, 6a (3H), 6b (2H)), 7.12
(br, 1H, ArH, 6a), 7.21−7.23 (m, 2 × 1H, ArH, 6a/6b), 7.27−7.31
(m, 5H, ArH, 6a (1H), 6b (4H)), 7.34 (apparent t, JHH = 5.9 Hz, 1H,
ArH, 6a), 7.42−7.44 (m, 4H, ArH, 6a), 7.47−7.52 (m, 1H, ArH, 6b),
7.58 (q, JHH = 7.6 Hz, 2H, ArH, 6b), 7.70 (d, JHH = 6.6 Hz, 1H, ArH,
6b), 7.79 (d, JHH = 6.6 Hz, 2H, ArH, 6a), 8.10−8.12 (m, 2H, ArH, 6a),
8.21 (br d, JHH = 8.1 Hz, 1H, ArH, 6b), 8.75 (s, 1H, NH, 6a), 8.94 (s,
1H, NH, 6b); the 1H NMR spectrum of 0.004 mM solution of 6a/6b
in CDCl3 revealed the presence of three isomers 6a, 6b and 6c in
about 1:0.25:0.15 ratios as estimated from the integrals of CH3
1
ν(CO) 1719 (s); ν(CN) 1597 (vs); the H NMR spectrum of
5a/5b in 0.010 mM and 0.004 mM solution revealed the presence of
5a and 5b in about 1:0.08 ratio as estimated from the integrals of the
1
alkyl protons; H NMR (CDCl3, 400 MHz) δ 1.88 (s, 2 × 3H, CH3,
5a), 2.07, 2.12, 2.18 (each s, 3 × 3H, CH3, 5b), 2.37 (s, 3H, CH3, 5a),
3.26 (s, 3H, OCH3, 5b), 3.27, 3.37 (each s, 2 × 3H, OCH3, 5a), 3.49
(s, 3H, OCH3, 5b), 3.75 (s, 3H, OCH3, 5a), 3.88 (s, 3H, OCH3, 5b),
5.70 (s, 1H, NH, 5a), 6.16 (t, JHH = 8.0 Hz, 1H, ArH, 5b), 6.24 (d, JHH
= 7.3 Hz, 1H, ArH, 5b), 6.48 (s, 1H, NH, 5b), 6.52 (d, JHH = 7.8 Hz,
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dx.doi.org/10.1021/om4010719 | Organometallics 2013, 32, 7580−7593

Organometallics
Article
protons of the guanidine moiety; 1H NMR (CDCl3, 400 MHz) δ 0.60
(t, JHH = 7.3 Hz, 3H, OCH2CH3, 6c), 0.72 (t, JHH = 6.9 Hz, 2 × 3H,
OCH2CH3, 6a/6b), 0.80 (t, JHH = 7.0 Hz, 3H, OCH2CH3, 6a), 0.87 (t,
JHH = 6.2 Hz, 2 × 3H, OCH2CH3, 6b/6c), 1.33 (t, JHH = 7.3 Hz, 2 ×
3H, OCH2CH3, 6a/6c), 1.47 (t, JHH = 7.3 Hz, 3H, OCH2CH3, 6b),
1.85, 1.89 (each s, 2 × 3H, CH3, 6a), 2.06, 2.10 (each s, 2 × 3H, CH3,
6b), 2.12, 2.17 (each s, 2 × 3H, CH3, 6c), 2.19 (s, 3H, CH3, 6b), 2.35
(s, 3H, CH3, 6a), 2.39 (s, 3H, CH3, 6c), 3.68−3.95 (m, 3 × 4H,
OCH2CH3, 6a/6b/6c), 3.99−4.07 (m, 3 × 1H, OCH2CH3, 6a/6b/
6c), 4.25−4.35 (m, 1H, OCH2CH3, 6a), 4.44 (apparent q, JHH = 5.8
Hz, 1H, OCH2CH3, 6b), 4.63 (apparent q, JHH = 5.9 Hz, 1H,
OCH2CH3, 6c), 5.76 (s, 3 × 1H, NH; 6a/6b/6c), 6.15 (t, JHH = 7.7
Hz, 1H, ArH, 6c), 6.27 (t, JHH = 7.3 Hz, 2 × 1H, ArH, 6b/6c), 6.50 (d,
JHH = 7.3 Hz, 1H, ArH, 6b), 6.60 (d, JHH = 6.6 Hz, 1H, ArH, 6a), 6.62
(s, 1H, ArH, 6a), 6.66 (t, JHH = 7.3 Hz, 3 × 1H, ArH; 6a/6b/6c), 6.71
(t, JHH = 6.6 Hz, 3 × 1H, ArH; 6a/6b/6c), 6.78−6.84 (m, 3 × 6H,
ArH; 6a/6b/6c), 6.87−6.91 (m, 3 × 2H, ArH; 6a/6b/6c), 6.94 (t, JHH
= 7.3 Hz, 3 × 1H, ArH; 6a/6b/6c), 6.98−7.03 (m, 4H, ArH; 6a (2H)/
6b (1H)/6c (1H)), 7.16 (d, JHH = 7.4 Hz, 2 × 1H, ArH, 6b/6c),
7.19−7.24 (m, 4H, ArH; 6a (2H), 6b (1H), 6c (1H)), 7.29−7.31 (m,
2 × 3H, ArH, 6b/6c), 7.34 (s, 2H, ArH, 6b), 7.36 (s, 1H, ArH, 6b),
7.42 (d, JHH = 2.2 Hz, 3H, ArH, 6a), 7.44 (d, JHH = 1.5 Hz, 3 × 2H,
revealed the presence of 7a and 7b in about 1:0.05 ratio as estimated
from the integrals of alkyl protons; H NMR (CDCl3, 400 MHz) δ
1
2.14 (s, 3H, CH3, 7a), 2.18, 2.21 (each s, 2 × 3H, CH3, 7b), 2.25, 2.28
(s, 2 × 3H, CH3, 7a), 2.29 (s, 3H, CH3, 7b), 3.36, 3.40 (each s, 2 ×
3H, C(O)OCH3, 7a), 3.43, 3.45, 3.89 (each s, 3 × 3H, C(O)OCH3,
7b), 3.99 (s, 3H, C(O)OCH3, 7a), 5.57 (d, JHH = 7.7 Hz, 1H, ArH,
7a), 5.86 (t, JHH = 7.7 Hz, 1H, ArH, 7a), 6.29 (d, JHH = 8.0 Hz, 1H,
ArH, 7b), 6.36 (t, JHH = 8.1 Hz, 1H, ArH, 7b), 6.58 (d, JHH = 7.3 Hz, 2
× 1H, ArH, 7a/7b), 6.65 (s, 2 × 1H, NH, 7a/7b), 6.77 (t, JHH = 7.3
Hz, 2 × 1H, ArH, 7a/7b), 6.83 (t, JHH = 7.3 Hz, 2 × 2H, ArH, 7a/7b),
6.90 (t, JHH = 7.3 Hz, 2 × 2H, ArH, 7a/7b), 6.94 (t, JHH = 6.2 Hz, 2 ×
1H, ArH, 7a/7b), 7.01 (d, JHH = 7.3 Hz, 2 × 1H, ArH, 7a/7b), 7.10
(d, JHH = 7.3 Hz, 2 × 1H, ArH, 7a/7b), 7.18−7.25 (br, 2 × 5H, ArH,
7a/7b), 7.27−7.29 (m, 2 × 4H, ArH, 7a/7b), 7.36−7.39 (m, 2 × 6H,
ArH, 7a/7b), 7.89 (s, 1H, NH, 7a), 7.92 (s, 1H, NH, 7b); the 13C{1H}
1
NMR signals were assigned with the aid of H−13C HETCOR NMR
spectroscopy (see Figures S25−S27 in the Supporting Information);
13C{1H} NMR (CDCl3, 100.5 MHz) δ 17.59, 18.47 (CH3), 43.78 (C),
52.03, 52.34, 55.25 (C(O)OCH3), 72.23 (C), 120.80 (CH), 122.05
(CH), 122.17 (CH), 123.42 (q, JCF = 322.3 Hz, CF3), 125.02 (CH),
125.13 (CH), 125.53 (CH), 126.09 (CH), 127.61 (CH), 127.69 (CH),
128.02 (CH), 128.23 (CH), 128.34 (CH), 128.69 (CH), 128.81 (CH),
128.87 (CH), 129.08 (CH), 129.23 (CH), 130.70 (CH), 130.86 (CH),
131.78 (C), 133.33 (C), 135.42 (C), 135.45 (C), 136.15 (C), 141.43
(C), 143.08 (C), 144.87 (C), 150.44 (C), 150.58 (C), 153.52 (C),
156.92 (C), 164.94, 171.58, 176.52 (CO); note that only 2 carbon
resonances were observed for CH3 carbons rather than the expected 3
peaks because of two overlapping peaks at δ = 17.59; MS (ESI+) m/z,
(relative intensity %), [ion] 914 (100) [M − TfOH]+. Anal. Calcd for
C53H46N3O9SF3Pd·2H2O (Mw 1064.44 + 36.03): C, 57.85; H, 4.58; N,
3.82; S, 2.91%. Found: C, 57.48; H, 4.40; N, 3.52; S, 2.69.
ArH; 6a/6b/6c), 7.48−7.52 (m, 2 × 1H, ArH, 6b/6c), 7.58 (q, JHH
=
7.8 Hz, 2 × 1H, ArH, 6b/6c), 7.70 (d, JHH = 7.3 Hz, 1H, ArH, 6c),
7.78 (dd, JHH = 8.1, 1.5 Hz, 2H, ArH, 6a), 8.09−8.12 (m, 2H, ArH,
6a), 8.20 (d, JHH = 1.4 Hz, 1H, ArH, 6c), 8.22 (br, 1H, ArH, 6c), 8.74
(s, 1H, NH, 6a), 8.94 (s, 1H, NH, 6b), 9.32 (s, 1H, NH, 6c); the
13C{1H} NMR signals were assigned with the aid of DEPT 90 and
1H−13C HETCOR NMR spectroscopy and the assignments of the
signals to 6a and 6b were made wherever possible (see Figures S19−
S24 in the Supporting Information); 13C{1H} NMR (CDCl3, 100.5
MHz, 125.3 μM) δ 13.31 (6a), 13.47 (6a), 13.73 (6b), 13.96 (6a),
14.15 (6b), 14.60 (6b) (C(O)OCH2CH3), 17.15 (6a), 17.28 (6b),
17.51 (6a/6b), 18.22 (6b), 18.31 (6a) (CH3), 59.75 (6b), 59.97 (6a),
60.63 (6b), 61.87, 62.18 (C(O)OCH2CH3), 67.95 (C, 6a), 74.90 (C,
6b), 84.62 (C), 90.85 (C), 95.92 (CH), 119.58 (CH), 121.02 (CH),
121.69 (CH), 123.16 (C), 123.45 (CH), 123.86 (CH), 124.00 (CH),
124.42 (CH), 125.02 (CH), 125.18 (CH), 125.38 (CH), 125.62 (CH),
125.75 (CH), 125.84 (CH), 125.97 (CH), 126.20 (CH), 126.57 (br,
C), 127.29 (CH), 127.67 (CH), 127.82 (CH), 127.97 (CH), 128.18
(CH), 128.37 (CH), 129.12 (C), 129.57 (CH), 129.74 (CH), 130.13
(CH), 130.24 (CH), 130.30 (C), 131.17 (CH), 131.87 (C), 132.29
(C), 132.52 (C), 133.75 (CH), 133.94 (C), 134.47 (CH), 134.84 (C),
135.41 (C), 135.91 (C), 136.36 (C), 136.82 (C), 137.16 (CH), 137.85
(C), 138.18 (C), 138.29 (C), 140.07 (C), 151.09 (C), 152.98 (C),
153.27 (C), 154.76 (C), 154.88 (C), 162.08 (6b), 163.81 (6a), 165.10
(6a), 167.89 (6a), 172.00 (6b), 174.81 (6b) (CO); note that only 5
carbon resonances were observed for CH3 carbons rather than the
expected 6 peaks because of two overlapping peaks at δ = 17.51; MS
(ESI+) m/z, (relative intensity %), [ion] 1037 (52) [M]+, 1015 (9) [M
+ Li − Et]+, 993 (9) [M − Et, Me]+, 957 (7) [M − Br]+, 935 (70) [M
+ Li − Br, Et]+, 850 (25) [M − HBr, Et, Ph]+, 834 (100) [M − EPP,
Et]+, 789 (30) [M + Li − HBr, EPP]+. Anal. Calcd for
C55H52N3O6BrPd (Mw 1037.36): C, 63.68; H, 5.05; N, 4.05%.
Found: C, 63.48/63.34; H, 5.02/4.95; N, 3.90/3.93.
Palladacycles 8a/8b. The title palladacycles were prepared from
4a/4b (100 mg, 0.096 mmol) and AgOTf (26.0 mg, 0.101 mmol) in a
mixture of CH2Cl2/acetone (1:1 (v/v), 15 mL) by a procedure
analogous to that described for 7a/7b. Yield: 77% (82 mg, 0.074
mmol). About 20% of 10a/10b·H2O (22 mg, 0.019 mmol) were also
obtained as thin red crystals from the aforementioned reaction. Data
for 8a/8b: mp (DSC) 205.2 °C; IR (KBr, cm−1) ν(NH) 3394 (w),
1
3284 (w); ν(CO) 1731 (br); ν(CN) 1598 (vs); the H NMR
spectrum of 8a/8b revealed the presence of 8a and 8b in about 1:0.29
ratio as estimated from the integrals of CH3 protons of the guanidine
1
moiety; H NMR (CDCl3, 400 MHz); δ 0.63 (t, JHH = 7.3 Hz, 3H,
OCH2CH3, 8a), 0.66 (t, JHH = 7.3 Hz, 3H, OCH2CH3, 8b), 0.76 (t,
JHH = 7.0 Hz, 3H, OCH2CH3, 8a), 0.87 (t, JHH = 7.0 Hz, 3H,
OCH2CH3, 8b), 1.38 (t, JHH = 7.0 Hz, 3H, OCH2CH3, 8b), 1.41 (t,
JHH = 7.3 Hz, 3H, OCH2CH3, 8a), 2.14 (s, 3H, CH3, 8a), 2.16, 2.18
(each s, 2 × 3H, CH3, 8b), 2.25, 2.27 (each s, 2 × 3H, CH3, 8a), 2.31
(s, 3H, CH3, 8b), 3.83−4.00 (m, 2 × 4H, OCH2CH3, 8a/8b), 4.31−
4.37 (m, 2H, OCH2CH3, 8b), 4.45−4.61 (m, 2H, OCH2CH3, 8a),
5.53 (d, JHH = 7.4 Hz, 1H, ArH, 8a), 5.84 (t, JHH = 8.1 Hz, 1H, ArH,
8a), 6.32 (d, JHH = 2.9 Hz, 1H, 8b), 6.33 (s, 1H, 8b), 6.56 (d, JHH = 7.3
Hz, 1H, 8a), 6.65−6.69 (m, 1H, 8b), 6.76 (apparent t, JHH = 6.6 Hz, 2
× 2H, 8a/8b), 6.82 (t, JHH = 8.8 Hz, 2 × 2H, 8a/8b), 6.88 (d, JHH
7.3 Hz, 2 × 2H, 8a/8b), 6.92 (d, JHH = 8.8 Hz, 1H, 8b), 6.95 (d, JHH
8.8 Hz, 1H, 8a), 7.00 (d, JHH = 7.4 Hz, 2 × 1H, 8a/8b), 7.11 (d, JHH
=
=
=
8.8 Hz, 3H, 8a (1H), 8b (2H)), 7.16 (t, JHH = 8.0 Hz, 3H, 8a (2H), 8b
(1H)), 7.21−7.25 (m, 2 × 6H, 8a/8b), 7.27−7.30 (m, 2 × 2H, 8a/
8b), 7.31−7.39 (m, 2 × 5H, 8a/8b) (NH and ArH), 7.90 (s, 1H, NH,
8a), 7.95 (s, 1H, NH, 8b); the 13C{1H} signals were assigned to 8a
and 8b wherever possible; 13C{1H} NMR (CDCl3, 100.5 MHz) δ
12.99, 13.31 (8b), 13.57, 14.79, 15.09 (8b) (OCH2CH3), 17.37 (8b),
17.60 (8a), 18.42 (8b), 18.52 (8b) (CH3), 43.88 (C, 8a), 46.23 (C,
8b), 61.05 (8a), 61.28 (8b), 61.92, 65.22 (8a), 65.38 (8a)
(OCH2CH3), 70.24 (C, 8b), 72.64 (C, 8a), 119.96, 120.75, 121.91,
122.04, 122.81, 123.46 (q, JCF = 317.2 Hz, CF3), 124.53, 124.90,
125.08, 125.49, 125.60, 125.70, 126.05, 126.15, 127.27 (br), 127.85,
127.89, 128.07, 128.10, 128.49, 128.58, 128.64, 128.69, 128.75, 128.82,
128.97, 129.09, 129.12, 129.57, 130.64, 130.69, 130.77, 130.84, 132.42,
132.47, 133.56, 133.64, 135.54, 135.66, 135.83, 136.16, 141.64, 142.28,
142.82, 143.40, 144.06, 145.00, 148.50, 149.50, 151.00, 151.11, 151.38,
Palladacycles 7a/7b. To a solution of 3a/3b (100 mg, 0.100
mmol) in a mixture of CH2Cl2/acetone (1:1 (v/v), 15 mL) was added
AgOTf (26.0 mg, 0.101 mmol) in the absence of light, and the
resulting solution was stirred at ambient temperature for 15 min.
During the course of the reaction, yellow precipitate deposited. The
reaction mixture was filtered, and the filtrate was concentrated under a
vacuum to afford a red residue. The residue was purified by
crystallization from CH2Cl2/n-hexane mixture at ambient temperature
over a period of several days to afford 7a/7b·2H2O as red cuboidal
crystals and 9a/9b·H2O as thin dark red crystals. The two types of
crystals were separated with the aid of a brush and dried under a
vacuum. Yields: 79% (87 mg, 0.079 mmol, 7a/7b·2H2O), 16% (17
mg, 0.016 mmol, 9a/9b·H2O). Data for 7a/7b·2H2O: mp (DSC)
218.99 °C; IR (KBr, cm−1) ν(NH) 3334 (br); ν(CO) 1735 (m),
1
1689 (m); ν(CN) 1592 (vs); the H NMR spectrum of 7a/7b
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Organometallics
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153.53, 153.74, 157.24 (ArC, CC and CN), 164.28 (8a), 167.63
(8b), 170.73 (8b), 170.91 (8a), 174.47 (8b), 176.19 (8a) (CO);
MS (ESI+) m/z, (relative intensity %), [ion] 957 (100) [M − OTf]+,
852 (10) [M − OTf, Ph, Et]+. Anal. Calcd for C56H52N3O9F3SPd (Mw
1106.53): C, 60.79; H, 4.74; N, 3.80; S, 2.90%. Found: C, 60.59/
60.41; H, 4.82/4.63; N, 3.77/3.61; S, 3.22/3.14.
1.50 (t, JHH = 7.3 Hz, 3H, OCH2CH3, 10a), 1.77 (br, 3H, CH3, 10b),
2.09 (s, 3H, CH3, 10a), 2.14 (s, 2 × 3H, CH3, 10a), 2.30 (s, 2 × 3H,
CH3, 10b), 3.75, 3.92 (each apparent q, JHH = 7.1 Hz, 2 × 2 × 2H,
OCH2CH3, 10a/10b), 4.03−4.11, 4.60−4.68 (each m, 2 × 2 × 1H,
OCH2CH3, 10a/10b), 6.15 (t, JHH = 7.7 Hz, 2 × 1H, ArH, 10a/10b),
6.21 (d, JHH = 8.1 Hz, 2 × 1H, ArH, 10a/10b), 6.59 (d, JHH = 7.3 Hz,
2 × 1H, ArH, 10a/10b), 6.67 (s, 2 × 1H, NH, 10a/10b), 6.70 (d, JHH
= 7.3 Hz, 2 × 1H, ArH, 10a/10b), 6.75−6.80 (m, 2 × 3H, ArH, 10a/
Palladacycles 9a/9b. Method 1: Palladacycles 7a/7b (200 mg,
0.188 mmol) were dissolved in PhCl (25 mL) in a 50 mL RB flask to
afford a clear red solution. The flask was fitted to a condenser guard
tube set up, and contents in the flask were refluxed for 6 h, cooled to
ambient temperature, and filtered. The filtrate was concentrated under
a vacuum to afford a red solid. The solid was washed with n-hexane
and subsequently purified by crystallization from CH2Cl2/n-hexane
mixture over a period of several days to afford 9a/9b·H2O as the only
product in the form of thin dark red crystals. Yield: 87% (177 mg,
0.164 mmol). Data for 9a/9b·H2O: mp (DSC) 219.45 °C (decomp);
IR (KBr, cm−1) ν(NH) 3384 (w), 3340 (sh); ν(CO) 1735 (m),
10b), 6.85 (d, JHH = 8.0 Hz, 2 × 1H, ArH, 10a/10b), 6.88 (d, JHH
=
8.0 Hz, 2 × 1H, ArH, 10a/10b), 6.95 (d, JHH = 7.3 Hz, 2 × 1H, ArH,
10a/10b), 7.02 (d, JHH = 8.0 Hz, 2 × 1H, ArH, 10a/10b), 7.09 (d, JHH
= 7.3 Hz, 2 × 1H, ArH, 10a/10b), 7.16 (t, JHH = 7.3 Hz, 2 × 2H, ArH,
10a/10b), 7.21 (br, 2 × 1H, ArH, 10a/10b), 7.30−7.32 (m, 2 × 2H,
ArH, 10a/10b), 7.37−7.40 (m, 2 × 4H, ArH, 10a/10b), 7.59−7.61
(m, 2 × 2H, ArH, 10a/10b), 7.64−7.67 (m, 2 × 2H, ArH, 10a/10b),
8.34 (d, JHH = 8.8 Hz, 2 × 1H, ArH, 10a/10b), 10.61 (br, 2 × 1H, NH,
10a/10b); 13C{1H} NMR signals were assigned with the aid of DEPT
1
1
90 and H−13C HETCOR NMR spectroscopy (see Figures S33−S37
1711 (m), 1701 (s); ν(CN) 1595 (vs); the H NMR spectrum of
in the Supporting Information); 13C{1H} NMR (CDCl3, 100.5 MHz)
δ 13.30 (10b), 13.41 (10a), 13.56 (10a), 14.26 (10b), 14.37 (10b),
14.51 (10a) (OCH2CH3), 17.30, 17.42, 17.74 (CH3), 50.46 (C), 59.98
(10b), 60.09 (10a), 60.97 (10a/10b), 61.30 (10a), 62.76 (10b)
(OCH2CH3), 74.68 (C), 95.93 (CH), 120.51 (CH), 121.77 (CH),
121.89 (C), 122.77 (q, JCF = 320.1 Hz, CF3), 124.37 (CH), 124.62
(CH), 125.55 (CH), 125.99 (CH), 127.57 (CH), 128.06 (CH), 128.20
(CH), 128.52 (CH), 128.70 (C), 129.23 (CH), 130.13 (C), 130.51
(CH), 130.59 (C), 130.64 (CH), 131.34 (br, C), 132.45 (CH), 133.63
(C), 134.32 (CH), 135.16 (CH), 135.76 (C), 135.99 (C), 136.67 (C),
138.75 (C), 139.36 (C), 149.92 (C), 153.79 (C), 154.04 (C), 162.01
(C), 163.81, 172.12, 174.11 (CO); note that 5 carbon resonances
were observed for OCH2 carbons rather than the expected 6 peaks
because of two overlapping peaks at δ = 60.97; MS (MALDI TOF+)
m/z, (relative intensity %), [ion] 958 (65) [M − OTf]+, 852 (50) [M
− OTf, Ph, Et]+. Anal. Calcd for C56H52N3O9F3SPd·H2O (Mw 1106.53
+ 18.02): C, 59.81; H, 4.84; N, 3.74; S, 2.85%. Found: C, 59.87; H,
4.88; N, 3.66; S, 2.65.
9a/9b revealed the presence of 9a and 9b in about 1:0.06 ratio as
estimated from the integrals of CH3 protons of the guanidine moiety
1
and ester group of the alkyne; H NMR (CDCl3, 400 MHz) δ 1.83,
2.01 (each s, 2 × 3H, CH3, 9b) 2.11, 2.14, 2.16 (each s, 3 × 3H, CH3,
9a), 2.30 (s, 3H, CH3, 9b), 3.22 (s, 3 H, C(O)OCH3, 9b), 3.28, 3.49
(each s, 2 × 3H, C(O)OCH3, 9a), 3.51, 3.80 (each s, 2 × 3H,
C(O)OCH3, 9b), 3.91 (s, 3H, C(O)OCH3, 9a), 6.14−6.20 (m, 2 ×
2H, ArH, 9a/9b), 6.57 (s, 2 × 1H, NH, 9a/9b), 6.61 (dd, JHH = 7.3,
1.5 Hz, 2 × 1H, ArH, 9a/9b), 6.71 (t, JHH = 7.3 Hz, 2 × 1H, ArH, 9a/
9b), 6.76−6.80 (m, 2 × 3H, ArH, 9a/9b), 6.88 (t, JHH = 7.3 Hz, 2 ×
2H, ArH, 9a/9b), 6.98 (d, JHH = 8.0 Hz, 2 × 1H, ArH, 9a/9b), 7.01
(d, JHH = 8.8 Hz, 2 × 1H, ArH, 9a/9b), 7.09 (t, JHH = 7.0 Hz, 2 × 1H,
ArH, 9a/9b), 7.15 (t, JHH = 7.3 Hz, 2 × 3H, ArH, 9a/9b), 7.29−7.32
(m, 2 × 2H, ArH, 9a/9b), 7.38 (apparent t, JHH = 5.9 Hz, 2 × 4H,
ArH, 9a/9b), 7.51 (d, JHH = 7.3 Hz, 2 × 1H, ArH, 9a/9b), 7.57 (s, 2 ×
1H, ArH, 9a/9b), 7.62 (t, JHH = 8.1 Hz, 2 × 1H, ArH, 9a/9b), 7.69 (t,
JHH = 7.0 Hz, 2 × 1H, ArH, 9a/9b), 8.32 (d, JHH = 8.8 Hz, 2 × 1H,
ArH, 9a/9b), 10.60 (br, 2 × 1H, NH, 9a/9b); the 13C{1H} NMR
signals were assigned with the aid of DEPT 90 and 1H−13C HETCOR
NMR spectroscopy (see Figures S28−S32 in the Supporting
Information); 13C{1H} NMR (CDCl3, 100.5 MHz) δ 17.36, 17.45,
17.70 (CH3), 49.52 (C), 51.02, 51.42, 52.41 (C(O)OCH3), 74.78 (C),
Palladacycles 11a/11b. Palladacycles 9a/9b (100 mg, 0.094
mmol) were dissolved in MeCN (20 mL) to obtain a clear red
solution. To this solution was added excess of NaOAc (77.0 mg, 0.94
mmol), and the resulting solution was stirred for 1 h to afford a yellow
solution. Thereafter, the reaction mixture was stored at ambient
temperature for 4 days, during which time the volume of the solution
reached about 3 mL, and this resulted in the formation of yellow
crystals. The crystals were separated and washed with distilled water (5
× 20 mL) and subsequently dried under a vacuum to afford 11a/11b·
3H2O as yellow crystals in 82% (77 mg, 0.077 mmol) yield. Crystals of
11a-d3·2H2O suitable for X-ray diffraction were grown by dissolving
9a/9b in CD3CN in a 5 mm NMR tube in a span of several days. Data
for 11a/11b·3H2O: mp (DSC) 212.55 °C (decomp); IR (KBr, cm−1)
ν(NH) 3393 (br); ν(CO) 1718 (s), 1702 (s), 1690 (s); ν(CN)
1618 (vs); the 1H NMR spectrum of 11a/11b revealed the presence of
six isomers in about 0.26:0.59:0.61:1.00:2:00:3.00 ratios as estimated
from the number and integrals of CH3 protons of the guanidine, those
of MeCN and the ester moieties; 1H NMR (CDCl3, 400 MHz) δ 1.65
(s, 3H, CH3, isomer 1), 1.86 (s, 2 × 3H, CH3, isomers 2 and 3), 1.87
(s, 3H, CH3, isomer 4), 1.92 (s, 3H, CH3, isomer 5), 1.95 (s, 2 × 3H,
CH3, isomers 5 and 6), 2.02 (s, 3H, CH3, isomer 2), 2.04 (s, 3H, CH3,
isomer 1), 2.07 (s, 3H, CH3, isomer 3), 2.10 (s, 3H, CH3, isomer 5),
2.11 (s, 2 × 3H, CH3, isomers 4 and 6), 2.15 (s, 3H, CH3, isomer 2),
2.19 (s, 3H, CH3, isomer 3), 2.23 (s, 2 × 3H, CH3, isomers 1 and 6),
2.26 (s, 2 × 3H, CH3, isomers 4 and 5), 2.28 (s, 2 × 3H, CH3, isomers
1 and 6), 2.32 (s, 3H, CH3, isomer 2), 2.33 (s, 3H, CH3, isomer 3),
2.38 (s, 3H, CH3, isomer 4), 2.69 (s, 3H, OCH3, isomer 1), 2.87 (s,
3H, OCH3, isomer 2), 2.95 (s, 3H, OCH3, isomer 3), 3.20 (s, 2 × 3H,
OCH3, isomers 4 and 6), 3.26 (s, 3H, OCH3, isomer 5), 3.27 (s, 3H,
OCH3, isomer 5), 3.32 (s, 2 × 3H, OCH3, isomers 5 and 6), 3.37 (s, 2
× 3H, OCH3, isomers 1 and 4), 3.48 (s, 2 × 3H, OCH3, isomers 2 and
3), 3.55 (s, 2 × 3H, OCH3, isomers 4 and 6), 3.75 (s, 2 × 3H, OCH3,
isomers 1 and 2), 3.88 (s, 3H, OCH3, isomer 3), 5.37 (s, 1H, NH,
isomer 1), 5.68 (s, 1H, NH, isomer 3), 5.87 (d, JHH = 7.32 Hz, 4 × 1H,
95.57 (CH), 120.88 (CH), 121.58 (C), 121.80 (CH), 122.72 (q, JCF
=
320.1 Hz, CF3), 124.44 (CH), 124.62 (CH), 124.66 (CH), 124.82
(CH), 125.57 (CH), 126.00 (CH), 127.64 (CH), 128.09 (CH), 128.29
(CH), 128.33 (CH), 128.57 (CH), 128.90 (C), 129.23 (CH), 130.13
(C), 130.51 (CH), 130.62 (CH), 131.40 (br, C), 132.50 (CH), 133.54
(C), 134.28 (CH), 134.55 (C), 135.00 (CH), 135.54 (CH), 135.62
(C), 135.80 (C), 136.62 (C), 138.28 (C), 139.44 (C), 149.71 (C),
153.71 (C), 153.95 (C), 162.43 (C), 164.18, 173.02, 173.66 (CO);
note that 21 carbon resonances were observed for CH carbons rather
than the expected 22 peaks because of two overlapping peaks at δ =
127.64; MS (ESI+) m/z, (relative intensity %), [ion] 972 (8) [M − Ph,
Me]+, 953 (3) [M + Li − 2C(O)OMe], 914 (100) [M − HOTf]+, 842
(60) [M + H − OTf, C(O)OMe, Me]+, 826 (18) [M − H, MPP,
Ph]+, 809 (18) [M + H − OTf, Ph, 2Me]+, 697 (7) [M + H − OTf,
MPP, C(O)OMe]+. Anal. Calcd for C53H46N3O9F3SPd·H2O (Mw
1064.44 + 18.02): C, 58.81; H, 4.47; N, 3.88; S, 2.96%. Found: C,
59.08; H, 4.59; N, 3.68; S, 2.85.
Palladacycles 10a/10b. Method 1: Palladacycles, 10a/10b·H2O
were prepared from 8a/8b (200 mg, 0.181 mmol) following Method 1
described for 9a/9b in 89% (181 mg, 0.161 mmol) yield. Crystals of
10a·C7H16 suitable for X-ray diffraction were grown from CH2Cl2/
petroleum ether mixture at 10 °C in a span of several days. Data for
10a/10b·H2O: mp (DSC) 230.84 °C; IR (KBr, cm−1) ν(NH) 3319
(w), 3231 (w); ν(CO) 1716 (s), 1697 (vs); ν(CN) 1588 (s); the
1H NMR spectrum of 10a/10b revealed the presence of 10a and 10b
in about 1:0.07 ratio as estimated from the integrals of CH3 protons of
the guanidine moiety and those of the ester groups; 1H NMR (CDCl3,
400 MHz) δ 0.63 (t, JHH = 7.0 Hz, 3H, OCH2CH3, 10b), 0.76 (t, JHH
= 7.3 Hz, 3H, OCH2CH3, 10a), 0.86 (t, JHH = 7.3 Hz, 2 × 3H,
OCH2CH3, 10a/10b), 1.35 (t, JHH = 7.0 Hz, 3H, OCH2CH3, 10b),
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ArH; isomers 2, 4, 5, and 6 or isomers 3, 4, 5 and 6), 6.03 (br, 1H, NH,
isomer 5), 6.11 (s, 1H, NH, isomer 6), 6.17 (d, JHH = 8.8 Hz, 1H, ArH,
isomer 2), 6.23 (d, JHH = 8.0 Hz, 1H, ArH, isomer 3), 6.46 (s, 1H, NH,
isomer 4), 6.52 (d, JHH = 6.6 Hz, 1H, ArH, isomer 3), 6.62−7.24,
7.33−7.46 (each m, 131 H, NH (3 H), isomers 1−3 and ArH (128 H),
Isomers 1−6), 7.51 (d, JHH = 8.0 Hz, 2 × 1H, isomer 5; 2 × 1H,
isomer 6; ArH), 7.57 (d, JHH = 7.3 Hz, 1H, isomers 2 or 3; 2 × 1H,
isomer 6; ArH), 7.63 (d, JHH = 8.0 Hz, 4 × 1H, isomers 1, 2, 3 and 6;
ArH), 7.71 (d, JHH = 6.6 Hz, 1H, ArH, isomer 5), 7.79 (d, JHH = 8.0
Hz, 1H, ArH, isomer 4), 7.94 (br, 2 × 1H, NH, isomers 5 and 6), 8.07
(d, JHH = 5.9 Hz, 1H, ArH, isomer 5), 8.20 (d, JHH = 8.1 Hz, 1H, ArH,
isomer 2), 8.91(s, 1H, NH, isomer 4), 9.31 (s, 1H, NH, isomer 2); the
1H NMR signals of the ArH protons are assigned tentatively and
subjected to correction because of the presence of six isomers with
varying isomeric ratios and, therefore, overlapping peaks; MS
(MALDI) m/z (relative intensity %) [ion] 914 (26) [M −
MeCN]+, 810 (100) [M + Li − Ph, HC(O)OMe, Me]+, 486 (8)
[M − MeCN, 2MPP, Ph, OMe]+. Anal. Calcd for C54H48N4O6Pd·
3H2O (Mw 955.42 + 54.05): C, 64.25; H, 5.39; N, 5.55%. Found: C,
64.37/63.91; H, 5.44/5.58; N, 5.62/5.46.
(9) (a) Bahsoun, A.; Dehand, J.; Pfeffer, M.; Zinsius, M.; Bouaoud,
S.-E.; Le Borgne, G. J. Chem. Soc., Dalton Trans. 1979, 547. (b) Arlen,
C.; Pfeffer, M.; Bars, O.; Grandjean, D. J. Chem. Soc., Dalton Trans.
1983, 1535. (c) Maassarani, F.; Pfeffer, M.; Le Borgne, G.
Organometallics 1987, 6, 2029. (d) Pfeffer, M.; Rotteveel, M. A.;
Sutter, J.-P.; De Cian, A.; Fischer, J. J. Organomet. Chem. 1989, 371,
C21. (e) Tao, W.; Silverberg, L. J.; Rheingold, A. L.; Heck, R. F.
Organometallics 1989, 8, 2550. (f) Maassarani, F.; Pfeffer, M.; van
Koten, G. Organometallics 1989, 8, 871. (g) Beydoun, N.; Pfeffer, M.;
DeCian, A.; Fischer, F. Organometallics 1991, 10, 3693. (h) Sutter, J.-
P.; Pfeffer, M.; De Cian, A.; Fischer, J. Organometallics 1992, 11, 386.
(i) Pfeffer, M.; Sutter, J.-P.; Rotteveel, M. A.; De Cian, A.; Fischer, J.
Tetrahedron 1992, 48, 2427. (j) Pfeffer, M.; Sutter, J. P.; DeCian, A.;
Fischer, J. Organometallics 1993, 12, 1167. (k) Ryabov, A. D.; van
Eldik, R.; Le Borgne, G.; Pfeffer, M. Organometallics 1993, 12, 1386.
(l) Tomita, K.; Caires, A. C.; De Lucca Neto, V. A.; Mauro, A. E. Acta
Crystallogr. 1994, C50, 1872. (m) Vicente, J.; Saura-Llamas, I.; Palin,
M. G.; Jones, P. G. J. Chem. Soc., Dalton Trans. 1995, 2535.
(n) Vicente, J.; Saura-Llamas, I.; Ramírez de Arellano, M. C. J. Chem.
Soc., Dalton Trans. 1995, 2529. (o) Gul, N.; Nelson, J. H.; Willis, A. C.;
̈
X-ray Crystallography. Details of data collections, structure
solutions, and refinements are presented in Tables S2 and S3 in
Supporting Information. Further crystallographic details may also be
found in the Supporting Information.
David Rae, A. Organometallics 2002, 21, 2041. (p) Kelly, A. E.;
Macgregor, S. A.; Willis, A. C.; Nelson, J. H.; Wenger, E. Inorg. Chim.
Acta 2003, 352, 79. (q) Nieto, S.; Arnau, P.; Serrano, E.; Navarro, R.;
Soler, T.; Cativiela, C.; Urriolabeitia, E. P. Inorg. Chem. 2009, 48,
11963.
ASSOCIATED CONTENT
■
(10) (a) Dupont, J.; Pfeffer, M.; Theurel, L.; Rotteveel, M. A. New J.
Chem. 1990, 15, 551. (b) Albert, J.; D’Andrea, L.; Granell, J.; Zafrilla,
J.; Font-Bardia, M.; Solans, X. J. Organomet. Chem. 2007, 692, 4895.
(c) Vicente, J.; Saura-Llamas, I.; Turpín, J.; Bautista, D.; Ramírez de
Arellano, C.; Jones, P. G. Organometallics 2009, 28, 4175. (d) García-
Lopez, J.-A.; Oliva-Madrid, M.-J.; Saura-Llamas, I.; Bautista, D.;
́
Vicente, J. Organometallics 2013, 32, 1094.
(11) (a) Albert, J.; Granell, J.; Sales, J.; Solans, X. J. Organomet. Chem.
1989, 379, 177. (b) Lopez, C.; Solans, X.; Tramuns, D. J. Organomet.
́
Chem. 1994, 471, 265. (c) Lopez, C.; Bosque, R.; Solans, X.; Font-
Bardia, M.; Silver, J.; Fern, G. J. Chem. Soc., Dalton Trans. 1995, 1839.
́
(d) Benito, M.; Lopez, C.; Solans, X.; Font-Bardía, M. Tetrahedron:
Asymmetry 1998, 9, 4219. (e) Zhao, G.; Wang, Q.-G.; Mak, T. C. W.
Tetrahedron: Asymmetry 1998, 9, 2253. (f) Zhao, G.; Wang, Q.-G.;
́
Mak, T. C. W. J. Organomet. Chem. 1999, 574, 311. (g) Lopez, C.;
Caubet, A.; Solans, X.; Font-Bardía, M. J. Organomet. Chem. 2000, 598,
87. (h) Bosque, R.; Benito, M.; Lopez, C. New J. Chem. 2001, 25, 827.
S
* Supporting Information
Contents as described in the manuscript and CIF files for all
structurally characterized palladacycles. These materials are
available free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: tnat@chemistry.du.ac.in, thirupathi_n@yahoo.com.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
N.T. thanks Department of Science and Technology, Delhi, for
a research grant (Grant No. SR/S1/IC-04/2010), and P.S.
thanks Council of Scientific and Industrial Research for a
fellowship. We also thank University Science Instrumentation
Center, University of Delhi, Delhi 110 007, for Instrumental
Facilities, Prof. U. P. Singh, Department of Chemistry, Indian
Institute of Technology-Roorkee, Roorkee 247 667, for X-ray
diffraction data of 2·CH2Cl2 and 3a·2CH2Cl2·H2O, and NMR
research center, Indian Institute of Science, Bangalore 560 012,
(i) Per
́
ez, S.; Lop
́
ez, C.; Caubet, A.; Pawełczyk, A.; Solans, X.; Font-
ez, C.; Perez, S.;
Bardía, M. Organometallics 2003, 22, 2396. (j) Lop
́
́
Solans, X.; Font-Bardía, M. J. Organomet. Chem. 2005, 690, 228.
(k) Albert, J.; D’Andrea, L.; García, G.; Granell, J.; Rahmouni, A.;
Font-Bardia, M.; Calvet, T. Polyhedron 2009, 28, 2559. (l) Lopez, C.;
Salmi, M.; Mas, A.; Piotrowski, P.; Font-Bardía, M.; Calvet, T. Eur. J.
Inorg. Chem. 2012, 1702.
(12) (a) Dupont, J.; Pfeffer, M. J. Chem. Soc., Dalton Trans. 1988,
2421. (b) Benito, M.; Lopez, C.; Morvan, X.; Solans, X.; Font-Bardía,
́
1
for VT H NMR data of 8a/8b and 9a/9b.
M. J. Chem. Soc., Dalton Trans. 2000, 4470. (c) Albert, J.; Granell, J.;
Luque, A.; Font-Bardia, M.; Solans, X. Polyhedron 2006, 25, 793.
(13) (a) Rheingold, A. L.; Wu, G.; Heck, R. F. Inorg. Chim. Acta
1987, 131, 147. (b) Ossor, H.; Pfeffer, M.; Jastrzebski, J. T. B. H.;
Stam, C. H. Inorg. Chem. 1987, 26, 1169. (c) Pereira, M. T.; Pfeffer,
M.; Rotteveel, M. A. J. Organomet. Chem. 1989, 375, 139. (d) Pfeffer,
M.; Rotteveel, M. A.; Le Borgne, G.; Fischer, J. J. Org. Chem. 1992, 57,
2147. (e) Spencer, J.; Pfeffer, M. Tetrahedron: Asymmetry 1995, 6, 419.
(14) (a) Maassarani, F.; Pfeffer, M.; Le Borgne, G. J. Chem. Soc.,
Chem. Commun. 1986, 488. (b) Maassarani, F.; Pfeffer, M.; Le Borgne,
G. Organometallics 1987, 6, 2043. (c) Maassarani, F.; Pfeffer, M.;
Spencer, J.; Wehman, E. J. Organomet. Chem. 1994, 466, 265.
(d) Spencer, J.; Pfeffer, M.; Kyritsakas, N.; Fischer, F. Organometallics
1995, 14, 2214.
REFERENCES
(1) Espinet, P.; Alben
Kurosawa, H., Yamamoto, A., Eds.; Elsevier: New York, 2003; Vol. 3, p
293.
(2) Hartwig, J. F. Organotransition Metal Chemistry: From Bonding to
Catalysis; University Science Books: New York, 2010; Chapter 9, p
349.
■
́
iz, A. C. In Fundamentals of Molecular Catalysis;
(3) Ryabov, A. D. Synthesis 1985, 233.
(4) Pfeffer, M. Recl. Trav. Chim. Pays-Bas 1990, 109, 567.
(5) Pfeffer, M. Pure Appl. Chem. 1992, 64, 335.
(6) Spencer, J.; Pfeffer, M. Adv. Met.-Org. Chem. 1998, 6, 103.
(7) Dupont, J.; Consorti, C. S.; Spencer, J. Chem. Rev. 2005, 105,
2527.
(15) Vicenete, J.; Abad, J. A.; Shaw, K. F.; Gil-Rubio, J.; Ramírez de
Arellano, M. C.; Jones, P. G. Organometallics 1997, 16, 4557 and
references cited therein.
(8) Vila, J. M.; Teresa Pereira, M. In Palladacycles: Synthesis,
Characterization and Applications; Dupont, J., Pfeffer, M., Eds.; Wiley-
VCH Verlag GmbH & Co. KGaA: Weinheim, 2008; Chapter 5, p 87.
7592
dx.doi.org/10.1021/om4010719 | Organometallics 2013, 32, 7580−7593

Organometallics
Article
(16) Spencer, J.; Pfeffer, M.; DeCian, A.; Fischer, J. J. Org. Chem.
1995, 60, 1005 and references cited therein.
́
(17) (a) Vicenete, J.; Abad, J.-A.; Fernandez-de-Bobadilla, R.; Jones,
P. G.; Ramírez de Arellano, M. C. Organometallics 1996, 15, 24.
(b) Vicenete, J.; Abad, J.-A.; Gil-Rubio, J. Organometallics 1996, 15,
3509 and references cited therein.
(18) (a) Lu, G.; Malinakova, H. C. J. Org. Chem. 2004, 69, 4701.
(b) Vicenete, J.; Martínez-Viviente, E.; Fernan
́
dez-Rodríguez, M.-J.;
Jones, P. G. Organometallics 2009, 28, 5845.
(19) Yagyu, T.; Hamada, M.; Osakada, K.; Yamamoto, T.
Organometallics 2001, 20, 1087.
(20) (a) LaPointe, A. M.; Brookhart, M. Organometallics 1998, 17,
1530. (b) Rajender Reddy, K.; Surekha, K.; Lee, G.-H.; Peng, S.-M.;
Liu, S.-T. Organometallics 2001, 20, 5557. (c) Canovese, L.; Visentin,
F.; Chessa, G.; Uguagliati, P.; Santo, C.; Dolmella, A. Organometallics
2005, 24, 3297.
(21) (a) Wu, G.; Rheingold, A. L.; Heck, R. F. Organometallics 1986,
5, 1922. (b) Cuesta, L.; Prat, D.; Soler, T.; Navarro, R.; Urriolabeitia,
E. P. Inorg. Chem. 2011, 50, 8598.
(22) Bailey, P. J.; Pace, S. Coord. Chem. Rev. 2001, 214, 91.
(23) Bazinet, P.; Wood, D.; Yap, G. P. A.; Richeson, D. S. Inorg.
Chem. 2003, 42, 6225 and references cited therein.
(24) (a) Gopi, K.; Thirupathi, N.; Nethaji, M. Organometallics 2011,
30, 572. (b) Gopi, K.; Saxena, P.; Thirupathi, N.; Nethaji, M.
Polyhedron 2013, 52, 1041. (c) Elumalai, P.; Thirupathi, N.; Nethaji,
M. J. Organomet. Chem. 2013, 741−742, 141.
(25) Roe, D. M.; Calbo, C.; Krishnamachari, N.; Moseley, K.; Maitlis,
P. M. J. Chem. Soc., Chem. Commun. 1973, 436.
(26) Bailey, P. M.; Mann, B. E.; Segnitz, A.; Kaiser, K. L.; Maitlis, P.
M. J. Chem. Soc., Chem. Commun. 1974, 567.
(27) (a) Li, C.-S.; Cheng, C. H.; Liao, F.-L.; Wang, S.-L. J. Chem. Soc.,
́
̌
va,
́
Chem. Commun. 1991, 710. (b) Kocovsky, P.; Vyskocil, S.; Císaro I.;
Sejbal, J.; Tislerova, I.; Smrcina, M.; Lloyd-Jones, G. C.; Stephen, S. C.;
̌
́
Butts, C. P.; Murray, M.; Langer, V. J. Am. Chem. Soc. 1999, 121, 7714.
(c) Faller, J. W.; Sarantopoulos, N. Organometallics 2004, 23, 2008.
(d) Chai, D. I.; Thansandote, P.; Lautens, M. Chem.Eur. J. 2011, 17,
́
8175. (e) Ortiz de la Tabla, L.; Matas, I.; Alvarez, E.; Palma, P.;
́
Campora, J. Dalton Trans. 2012, 41, 14524.
(28) Parshall, G. W. Acc. Chem. Res. 1970, 3, 139.
(29) Markies, B. A.; Wijkens, P.; Kooijman, H.; Spek, A. L.; Boersma,
J.; van Koten, G. J. Chem. Soc., Chem. Commun. 1992, 1420.
(30) Liu, C.-H.; Li, C. S.; Cheng, C.-H. Organometallics 1994, 13, 18.
(31) Hafelinger, G.; Kuske, F. K. H. In The Chemistry of Amidines and
̈
Imidates; Patai, S., Rappoport, Z., Eds.; Wiley: Chichester, 1991; Vol.
2.
(32) Raab, V.; Harms, K.; Sundermeyer, J.; Kovace
B. J. Org. Chem. 2003, 68, 8790.
(33) De Vaal, P.; Dedieu, A. J. Organomet. Chem. 1994, 478, 121.
̌ ́ ́
vic, B.; Maksic, Z.
(34) Samsel, E. G.; Norton, J. R. J. Am. Chem. Soc. 1984, 106, 5505.
(35) Saxena, P.; Thirupathi, N.; Nethaji, M. Mono and Dialkyne
Insertion Reactions of Cyclopalladated N,N′,N″-Triarylguanidines,
[(C,N)Pd(μ-Br)]2 and cis/trans-[(C,N)Pd(Lewis base)Br]: Scaffolds
for Enlarged, Rearranged and Zwitterionic Palladacycles through Ring
Contraction cum Amine Imine tautomerisation. Unpublished work.
(36) Geary, W. J. Coord. Chem. Rev. 1971, 7, 81.
(37) García-Cuadrado, D.; de Mendoza, P.; Braga, A. A. C.; Maseras,
F.; Echavarren, A. M. J. Am. Chem. Soc. 2007, 129, 6880.
7593
dx.doi.org/10.1021/om4010719 | Organometallics 2013, 32, 7580−7593