Palladacycles of sulfated and selenated Schiff bases of ferrocene-carboxaldehyde as catalysts for O-arylation and Suzuki-Miyaura coupling

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SHARMA, H. Joshi, R. Bhaskar and S. Kumar, Dalton Trans., 2017, DOI: 10.1039/C7DT00083A.

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ISSN 1477-9226

PAPER

Joseph T. Hupp, Omar K. Farha et al.

Eﬃcient extraction of sulfate from water using

framework

a Zr-metal–organic

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ARTICLE

Palladacycles of sulfated and selenated Schiff bases of ferroceneꢀ

carboxaldehyde as catalysts for Oꢀarylation and Suzuki–

Miyaura coupling

Received

Accepted

Alpesh K. Sharma, Hemant Joshi, Renu Bhaskar, Satyendra Kumar and Ajai K. Singh*

DOI: 10.1039/x0xx00000x

Schiff base ligands (L1: sulfated and L2: selenated) having ferrocene core synthesized by reacting ferroceneꢀ

carboxaldehyde with 2ꢀ(phenylthio/seleno)ethylamine on treatment with Na₂PdCl₄in the presence of NaOAc give

cyclopalladated complexes [Pd(L1/L2ꢀH)Cl] (1/2). The complex 1 of sulfated Schiff base L1, on reacting with one

equivalent of triphenylphosphine gives complex [Pd(L1ꢀH)PPh₃Cl] (3), formed due to cleavage of PdꢀS bond. With 2 such

reaction does not occur, as PdꢀSe bond being stronger than that of its sulfur analogue, does not cleave. The L1, L2 and their

complexes 1ꢀ3 were authenticated with HRꢀMS, ¹H, ¹³C{¹H} and ⁷⁷Se{¹H} NMR spectra. Single crystal structures of 1–3

were determined with Xꢀray diffraction. Palladium in all three complexes has nearly square planar geometry. The Pd−S,

Pd−Se and Pd−P bond distances are 2.4249(12), 2.5058(14) and 2.2445(17) Å respectively. The catalytic activity of

complexes 1–3 was explored for Oꢀarylation of phenol and Suzuki Miyaura coupling (SMC) of phenylboronic acid with aryl

bromides and chlorides. The optimum reaction time for SMC of ArBr is 3 h whereas for ArCl it is 6 h.The TON values of

Oꢀarylation catalyzed with complexes 1ꢀ3 are up to ~ 170 (TOF, 28 h^ꢀ1) and SMC ~9300 (TOF, 3100 h^ꢀ1) for reaction time

of the order of 3 and 6 h respectively. The catalytic process is some what more efficient with 2 (Pd bonded with selenoether

group), than 3, followed by 1.

www.rsc.org/

palladium(II) complexes are known.⁴These ligands prepared

by multistep protocols are unsuitable to make palladacycles.

Introduction

The deployment of ferrocene and its derivatives is immense

in various fields including materials science^1aꢀcand medicinal

chemistry.^1dꢀgThe unique electrochemical and structural

properties and insensitivity towards oxygen, moisture and

several chemicals are among the reasons for their presence in

diverse areas. The ferrocene derivatives are used in a wide

range of catalysis,²including homogeneous asymmetric ones.^1h

Bis(diphenylphosphino)ferrocene

and

ferrocenylphosphines have been applied as transitionꢀmetal

complexes in diverse catalytic processes successfully.^2dꢀf

Ferrocene based chiral ligands are interesting due to their novel

enantioselective applications and high asymmetric efficiency.^1h

The existence of various methods to functionalize Cp rings

bonded to iron in ferrocene has resulted in ligands with

ferrocene core. The (P, P), (P, N) and (N, N) ligands result

when; phosphorus and nitrogen containing groups functionalize

Cp ring of ferrocene. Similarly (P, S), (S, S) and (P, O) ligands

with ferrocene core are afforded.^1h,3Few ligands, having

ferrocene core and selenium donor groups (Chart 1) and their

Chart 1

Similarly many sulfur ligands with ferrocene core can not be

cyclopalladated. Palladacycles have emerged as promising

catalysts for many C–C and C–heteroatom bond forming

reactions⁵and considered as good alternative to palladium(0)

complexes,^5bbecause they are often easy to handle due to their

stability. The airꢀstable complexes of Pd(II) are known to show

good catalytic activity e.g. phosphine adduct of a (C, N)ꢀ

palladacycle activates chloroarenes.^5fFor organochalcogen

Department of Chemistry, Indian Institute of Technology, Delhi, New Delhi 110016,

India. *e-mail, aksingh@chemistry.iitd.ac.in, ajai57@hotmail.com,

Fax: +91-01- 26581102; Tel: +91-011-26591379;

Electronic Supplementary Information (ESI) available: Spectral data for L1

1

, L2 and

–

3

; single crystal data for complexes 1–3. CCDC 1487503-1487505. For ESI and

crystallographic data in CIF or other electronic format see DOI:

10.1039/c6dt01406b

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ligands, cyclopalladated species outperform their other NMR and mass spectra

complexes many times.²¹The palladacycles resulting from

The ¹H, ¹³C{¹H} and ⁷⁷Se{¹H} NMR spectra and HRꢀMS

authenticating L1 L2 and are given in ESI. Ferroceneꢀ

carboxaldehyde on reaction with 2ꢀ(phenylthio/seleno)

ethylamine gives Schiff bases L1 and L2 The signal of H₉

(attached to C₉) appearing at ~10.00 ppm, in ¹H NMR spectrum

of the ferroceneꢀcarboxaldehyde is shifted to 8.1 ppm on the

formation of a Schiff base. The signal of C₉in ¹³C{¹H} NMR

spectra of Schiff bases L1 and L2 (appearing at 162.8 and

cyclopalladation of organochalcogen group bearing ferrocene

are not in our knowledge. Schiff bases of ferroceneꢀ

carboxaldehyde with sulfated/ selenated amine are appropriate

ligands to fill this gap. Therefore, palladacycles of ligands

having S/Se donor groups present in an arm anchored on Cp

ring of ferrocene and their catalytic applications in crossꢀ

coupling reactions are reported herein.

,

1−3

.

The CꢀO cross coupling reaction viz.

Oꢀarylation, resulting

162.5 ppm respectively

respect to that of the aldehyde. In ¹³C{¹H} NMR spectra of

complexes 1, 2 and the signal of C₉appears at 172.2, 172.5

) is at ~30 ppm lower frequency with

diaryl ether is important in the synthesis of several biologically

active compounds and natural products.⁶Palladiumꢀcatalyzes

such reactions and their protocols are improved using various

ligands.^7ꢀ11,13aThe efficient catalyst for CꢀO coupling continues

to be of current interest as diaryl ether formation is more

challenging compared to its alkyl analogue. The nucleophilicity

of phenoxide ion is lower than that of alkoxide ion, and

consequently reductive elimination from aryl palladium

phenoxide is less favorable. A ligand attached to Pd may play

an important supporting role in the formation of diaryl ether

e.g. the presence of sterically hindered ligand in a metal

complex is known to drive CꢀO coupling. The strongly

donating S / Se group in the palladcycles reported herein may

facilitate reductive elimination, resulting CꢀO coupling.

Palladium catalyzed SMC, a versatile method of CꢀC bond

formation between aryl groups is widely used in organic

synthesis.¹²Palladium(II) complexes of phosphine ligands^13aꢀe

are well known catalysts for SMC. However, due to air

sensitivity, cost and toxicity of many phosphine ligands, there

is an interest in alternatives giving equally efficient catalysts.^13f

Palladacycles and Pd(II) complexes of organosulfur/selenium

ligands (including Schiff base type),^14ꢀ16have emerged as a

family of airꢀmoisture insensitive efficient catalysts. Thus good

catalytic performance is envisaged for the palladacycles 1ꢀ3 for

CꢀO coupling as a well as SMC.

3

and 174.0 ppm respectively. Its shift to higher frequency

relative to the corresponding signal of ligands L1 and L2

implies their coordination to palladium. In ⁷⁷Se{¹H} NMR

spectrum of L2, signal appearing at 273.2 ppm, is shifted to

336.9 ppm on its coordination with Pd. The signals of C₇(CH₂)

in ¹³C{¹H} NMR spectra of complexes

1 and 2 have been found

shifted to higher frequency (~ 4.6 and 6.2 ppm respectively)

with respect to those of corresponding free L1 and L2. The

two

L1 and L2, show four signals whereas in the spectra of

complexes and 3, they show six signals which are at higher

frequencies relative to those of free L1 and L2. This implies

binding of palladium with

⁵ꢀCp ring via CꢀH activation.

η

⁵ꢀCp rings of ferrocene core in ¹³C{¹H} NMR spectra of

1, 2

η

³¹P{¹H} NMR spectrum of complex

3 shows a signal at 37.1

ppm indicating bonding of phosphorus with palladium.³¹

In mass spectra of ligands L1, and L2, peaks appearing at

m/z 350.0660 and 398.0093 respectively may be ascribed to [

+ H]⁺(see ESI, Figs. S1−S2). In the spectra of complexes

and

respectively due to [

L

2

1

,

3

peaks appear at m/z, 453.9561, 501.8974, and 716.0448

ꢀCl]⁺(see ESI, Figs. S3−S5).

M

Results and discussion

The syntheses of L1

, L2, 1, 2 and 3 are summarized in Scheme

1. The ligands L1 and L2 synthesized by the reaction of

ferroceneꢀcarboxaldehyde with 2ꢀ(phenylthio/seleno)ethylꢀ

amine on treatment with Na₂PdCl₄in presences of sodium

acetate result in complexes

1

and

2

respectively. The complex

1

on treatment with 1 equivalent of PPh₃gives complex

3

by

substitution of sulfur donor group with PPh₃. On treatment of

complex with 1 equivalent of PPh_3,there was no reaction and

recovered. Probably this happened due to strong coordination

2

of Se with Pd. The L1 and L2 have good solubility in CHCl₃,

CH₂Cl₂, CH₃OH, EtOAc and CH₃CN. On contrary complexes

Scheme 1. Synthesis of ligands L1 and L2 and complexes 1–3

1−

3

are moderately soluble in first four of these solvents and

have good solubility in CH₃CN, DMF and DMSO. The

complexes and their ligands L1 and L2 are insensitive to

Crystal structures

1−3

The single crystals of 1–3 suitable for Xꢀray diffraction were

grown by slow evaporation of their solutions made in ethyl

acetate:hexane (3:1) mixture. The crystal structure data and

refinement parameters for complexes 1ꢀ3 are given in Table S1

of ESI. The ORTEP diagrams (30% probability of ellipsoids) of

air and moisture, as they can be stored at room temperature for

several months under ambient conditions. However examples

of air stable palladium complexes of phosphine ligands.^5,13a,14

which are efficient as catalyst in aerobic conditions^5aare also

known.

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complexes 1ꢀ3 with selected bond lengths and angles are shown

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Figs. 1ꢀ3. Palladium has nearly a square planar geometry with

S/Se/P and C(Cp) disposed trans to each other. The L1 and L2

bind in a tridentate (C‾, N, S/Se) mode with Pd(II) in

complexes

1 and 2, whereas in complex 3 bonding mode of L1

is (C‾, N,) leaving S free. The Pdꢀtriphenylphosphine bond

replaces the cleaved PdꢀS bond. The Pd−N bond lengths of 1, 2

and

3 are 2.012(4), 2.025(5), and 2.131(6) Å respectively,

consistent with the values, 2.012(5)Åꢀ2.182(3)Å reported for

Pd(II) complexes of tridentate chalcogenated Schiff bases^17,15f,26

and palladium complexes with bidentate phosphineꢀimine (P,

N) ligands.^20bThe Pd−C distances of complex 1, 2 and

3

[1.973(4), 1.956(6), and 2.003(7) Å respectively] are consistent

with the values 1.970(7)ꢀ2.022(4)Å reported earlier for

palladacycles of chalcogenated ligands.^14c,21

Fig. 3 Structure of complex

3

. Bond lengths (Å): Pd1—P1

2.2445(17), Pd1—N1 2.131(6), Pd1—Cl1 2.370(2), Pd1—C11

2.003(7), C9—N1 1.272(10), C6—S1 1.775(9); Bond angles

(deg.): N1—Pd1—Cl1 92.36(18), C11—Pd1—P1 92.00(2),

C11—Pd1—Cl1 173.1(2), N1—Pd1—P1 172.07(19)

The Pd−S bond distance [2.4249(12)Å] of

1 is consistent with

value [2.428(2)Å]¹⁹reported for a palladium complex of

tridentate thioether ligand. The PdꢀSe bond length [2.5058(14)

Å] of complex

2 is longer than the value of 2.4627(14) Å

reported for the Pd(II) complex of a bisꢀpincer ligand, 1,2,4,5ꢀ

tetrakis(phenyselenomethyl)benzene.^20aThe Pd−P distance of

complex

3 [2.2445(17) Å] is consistent with the values of

2.235(3)ꢀ2.236(1) Å reported for palladium complexes with

bidentate phosphineꢀimine (P, N) ligands.^20bꢀ31The lengths of

Pd−Cl bond of complexes 1, 2 and

3 [2.2870(14), 2.286(2) and

Fig. 1 Structure of complex

1, Bond lengths (Å): Pd1—S1

2.370(2) Å respectively] are within the range of [2.284(4)ꢀ

2.3980(2)Å] reported for palladacycles having coordinated

2.4249(12), Pd1—N1 2.012(4), Pd1—Cl1 2.2870(14), Pd1—

C11 1.973(4)), C—N1 1.274(6), C6—S1 1.785(5) Bond angles

(deg.): N1—Pd1—Cl1 174.00(11), C11—Pd1—S1 165.62(14),

C11—Pd1—Cl1 93.74(15), N1—Pd1—S1 84.68(11), C11—

Pd1—N1 81.03(18).

selenium/sulfur donor group and Pd(II) complex of Fe[η⁵

ꢀ

C₅H₄NC(H)Ph]₂.^14d,20c,21In the crystals of

1–3 C–H⋯Cl

secondary interactions make chains as shown in Figs. 4, 5 and

6. Between these chains the same interaction exists. However,

in case of

3 there is no C–H⋯Cl secondary interaction between

the chains. The steric blocking by PPh₃and pendent SPh group

appears to be responsible for it. For distances of nonꢀcovalent

interactions see ESI (Table S3).

Fig. 2 Structure of complex 2, Bond lengths (Å): Pd1—Se1

2.5058(14), Pd1—N1 2.025(5), Pd1—Cl1 2.286(2), Pd1—C11

1.956(6), C9—N1 1.286(8), C6—Se1 1.912(6) Bond angles

Fig. 4 Nonꢀcovalent C–H⋯Cl interactions in 1.

(deg.):

N1—Pd1—Cl1

174.53(15),

93.8(2),

C11—Pd1—Se1

N1—Pd1—Se1

166.61(18),

85.25(16).

C11—Pd1—Cl1

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3

Cs₂CO₃

1,4ꢀ

2

58

Dioxane

Toluene

DMSO

4

Cs₂CO₃

K₂CO₃

NaOH

KOH

NaO^tBu

KO^tBu

ꢀ

2

ꢀ

40

61

12

18

24

31

nd

11

85

61

52

68

78

80

5

6

7

8

9

10

11

12^b

13^c

14^d

15^e

16^f

17^g

18^h

Fig. 5 Nonꢀcovalent C–H⋯Cl interactions in 2.

Cs₂CO₃

2

Fig.6 Nonꢀcovalent C–H⋯Cl interactions in 3

.

^aReaction condition: 4ꢀbromobenzaldehyde, 1.0 mmol; phenol, 1.2

C‒O coupling of aryl/heteroaryl bromides with phenol

mmol; Base, 1.2 mmol.; catalyst 2, 0.5 mol%; solvent, 4 mL; time,

c

6 h; temperature, 110

̊

The coupling of phenol with different aryl bromides, catalyzed

f

^dcatalyst 2, 0. 1mol%; ^etemperature, 60 C

̊ ; temperature, 80 C̊ ; ;

with complexes

1ꢀ3 was explored. The reaction given in

^gcatalyst 2: Hg (1:400); ^hPPh_3,0.5 mol%;ⁱisolated yield; nd = not

Scheme 2 was used to optimize the conditions for catalysis. The

yield was ~ 83% at 110⁰C in the presence of base, Cs₂CO₃

(Table 1, Entry 1) and reduced to ~61% when K₂CO₃was used

as a base (Table 1, Entry 5). The NaOH and KOH were

detected.

0

The yield of reaction (Scheme 2) at 80 and 60 C. was 68 and

52% respectively (Table 1, Entry 15 and 16). At room

temperature the yield was ~11% (Table 1, Entry 12). On

lowering the loading of the catalyst to 0.1 mol% the yield

decreased (Table 1, Entry 14). The increase in catalyst loading

to 1.0 mol% did not result significant increment in the yield of

the desired coupled product (Table 1, Entry 13).

unsuitable as a base for the coupling reaction catalyzed with 1ꢀ

3, as product yield was~12 and 18% respectively in their

presence (Table 1, Entries 6 and 7). In the presence of NaO^tBu

and KO^tBu, yield was low and the coupled product associated

with several intricate impurities. (Table 1, Entries 8 and 9). The

reason for good results with cesium carbonate is probably the

good solubility of cesium phenoxide in organic solvents.²²

Among various organic solvents (Table 1) evaluated for the Cꢀ

O coupling reaction, the best yield (~83%) was achieved in

DMSO (Table 1, Entry 1). The yield in 1,4ꢀdioxane and DMF

were almost similar and low (Table 1, Entries 2 and 3). In

toluene also yield was low (Table 1, Entry 4).

Table 2 C‒O coupling reaction of aryl/heteroaryl bromides

with phenol^a

O

MeOC

3b

O₂N

3c

OHC

3a

1 = 72%, 2 = 80%, 3 = 79%

1 = 74%, 2 = 83%, 3 = 80%

1 = 72%, 2 = 83%, 3 = 82%

HO

O

Complex 2, 110^o

C

1.4ꢀ1.6 x 10²(TON)

2.3ꢀ2.6 x10¹(TOF)

1.4ꢀ1.6 x 10²(TON)

2.3ꢀ2.6 x10¹(TOF)

1.4ꢀ1.7 x 10²(TON)

2.3ꢀ2.8 x10¹(TOF)

OHC

Br

+

Base, Solvent

O

OHC

O

CHO

COMe

NC

3d

3e

3f

Scheme2 C‒O coupling reaction of 4ꢀbromobenzaldehyde

1 = 65%, 2 = 75%, 3 = 70%

1 = 75%, 2 = 81%, 3 = 81%

1 = 64%, 2 = 74%, 3 = 68%

with phenol

1.5ꢀ1.6 x 10²(TON)

2.5ꢀ2.8 x10¹(TOF)

1.3ꢀ1.5 x 10²(TON)

2.1ꢀ2.5 x10¹(TOF)

1.3ꢀ1.5x 10²(TON)

2.1ꢀ2.5 x10¹(TOF)

No significant coupling was observed in 6 h under optimum reaction

conditions in the absence of catalyst (Table 1, Entry 11). The

reaction did not proceed in the absence of base (Table 1, Entry 10).

O

3h

MeO

3i

3g

1 = 68%, 2 = 72%, 3 = 71%

1 = 62%, 2 = 71%, 3 = 67%

1 = 74%, 2 = 78%, 3 = 78%

Table 1: Optimization of solvent and base^a.

1.3ꢀ1.4 x 10²(TON)

2.1ꢀ2.3 x10¹(TOF)

1.3ꢀ1.6 x 10²(TON)

2.1ꢀ2.8 x10¹(TOF)

1.2ꢀ1.4 x 10²(TON)

2.0ꢀ2.3 x10¹(TOF)

O

S.N. Base

Solvent

DMSO

DMF

Catalyst

Yieldⁱ%

N

3j

1

2

Cs₂CO₃

2

83

56

1 = 74%, 2 = 80%, 3 = 78%

1.4ꢀ1.6 x 10²(TON)

2.3ꢀ2.8 x10¹(TOF)

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^aReaction condition: ArBr, 1.0 mmol; phenol, 1.2 mmol; Cs₂CO_3,1.2 ferrocenylꢀdiꢀtertꢀbutylphosphine or P(tꢀBu)₃(2ꢀ5 mol%) and (v)

mmol; catalyst, 0.5 mol%; DMSO, 4 mL; Time 6 h; temperature, 110 Pd(OAc)₂ꢀNꢀ(2,6ꢀdiisopropylphenyl)ꢀ2ꢀdiꢀ1ꢀadamantylphosphinoꢀ

°C. Isolated yield in % are below each structure, TOF is in h^ꢀ1

imidazole (2 mol %). The optimum loading for 1ꢀ3 is 0.5 mol%. It

is lower in comparison to all catalytic systems mentioned above ( iꢀ

v) . Reaction time for the catalytic systems mentioned above (iꢀv), is

of the order of 10ꢀ24 h whereas with 0.5 mol% of 1ꢀ3 good yield of

coupled product is afforded in 6 h. The present catalytic CꢀO

coupling reactions are largely homogeneous, as supported by Hg²⁶

and triphenylphosphine²⁶poisoning tests. The mercury and PPh₃

poisoning tests were applied to coupling of 4ꢀbromobenzaldehyde

with phenol catalyzed with 2. The change in the yield of coupled

product in the presence of Hg was insignificant (Table 1, Entry 17).

In the presence of PPh₃only 3% decrease in the yield was noticed

(Table 1, Entry 18).

The reactions of several aryl bromides with phenol under the

optimized conditions were studied and the scope of the present

protocol is shown in Table 2. To our delight most of the C–O

coupling reactions catalyzed with 1ꢀ3 culminated in good or high

yield. Functional groups NO₂, CN, CHO, COMe. OMe, and Me on

ArBr were tolerated under the optimum reaction conditions. The

nature and position of the substituent on aryl bromide have shown

some effect on the yield of the coupled product. The aryl bromides

having electron donating groups show less reactivity in comparison

to those having electron withdrawing groups. Thus substrates having

CN, NO₂, COMe and CHO groups are coupled with good yield

(Table 2, Entries 3aꢀ3d). When electron withdrawing groups are at a

The mechanism for Oꢀarylation proposed in Scheme 3 is adopted

position ortho to bromo group, the yield is less in comparison to from earlier reports^7a,24b,24cand based on Pd(0) species protected by

those substrates having a substituent at a para position (Table 2, ligand. Its formation is due to presumed dissociation of Cl and

Entries 3eꢀ3f). The reaction of phenol with 2ꢀbromopyridine (Table cleavage of PdꢀC bond. The latter is supported by ¹³C {¹H} NMR

2, Entry 3j) also gave good yield. The yield of coupled product spectrum of catalytic reaction mixture (having 2 as a catalyst) after

(Table 2) was found highest in the case of 4ꢀbromobenzaldehyde (up 30 minutes of reaction. It shows four NMR signals (see ESI Fig S19)

to 83 %, Table 2, Entry 1), with all the three complexes 1−3 used as instead of six for two η⁵ꢀCp rings of ferrocene, which are slightly

a catalyst. The 2 (having PdꢀSe bond) was found somewhat more deshielded compared to those of free ligand (L2).

efficient as a catalyst among all the three complexes, as its 0.5%

loading was sufficient for high yield of the coupled product. Time

profile of CꢀO coupling of 4ꢀbromobenzaldehyde (1 mmol ) shown

in Fig. 7 indicates that on increasing reaction time from 6 h to 10 h

increment in yield of the coupled product is not significant and ~

60% yield results in 3 h. On adding fresh substrates to the reaction

mixture the quantity of coupled product did not increase. Most

probably catalyst loses its activity in one cycle.

Scheme 3: Proposed mechanism for C‒O coupling

C‒C coupling of aryl/heteroaryl halides with phenyl boronic

acid

Fig.

7

Time profile of C‒O coupling reaction of 4ꢀ

bromobenzaldehyde: catalyst, 2 (0.5 mol %) phenol, 1.2 mmol.; The complexes 1ꢀ3 were explored as catalysts for Suzuki−Miyaura

Cs₂CO₃, 1.2 mmol.; DMSO, 4 mL; temperature, 110 °C;

C−C coupling (SMC) reaction of several aryl bromides. The

optimum conditions were established using reaction shown in

Scheme 4. The K₂CO₃was found better base than cesium carbonate,

sodium acetate and NaOH, on the basis of yield under similar

reaction conditions (Table 3 Entries 2, 6, 7 and 8). A mixture of

DMF and water (3:1) as a reaction medium gave best result. In the

solvents EtOH + water mixture (3:1) and 1,4 dioxane yield was low

(Table 3 Entries 4 and 5). No coupled product was obtained when

THF was used as a solvent (Table 3 Entry 3). On lowering the

loading of the catalyst to 0.001 mol% the yield of product decreased

(Table 3, Entry 13).The increase in catalyst loading to 0.1mol% did

The comparison of performance of complexes 1ꢀ3 as a catalyst for

Oꢀarylation with the literature reports reveals that reaction time and

catalyst loading with the present complexes are reasonably low. The

amount of the catalyst required for the reaction in earlier

reports^11a,23,24are: (i) Pd(OAc)₂+ diꢀtertꢀbutylphosphino group

containing ligands (2 mol%) (ii) Pd(dba)₂+ ferrocene or its

derivative having diꢀtertꢀbutylphosphino group (5 mol%) (iii)

Pd(OAc)₂+ aryldialkylphosphine ligand (2 mol%) (iv) Pd(OAc)₂ꢀ

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not result in significant increase in the yield of the desired coupled On adding fresh substrates to the reaction mixture the quantity of

product (Table 3, Entry 12). At room temperature yield was very low coupled product did not increase. Most probably catalyst loses its

and therefore elevated temperature for the reaction was optimized activity in one cycle only

0

(Table 3 Entry 10). At 70 C yield increased to a good level and at

90 ⁰C it became maximum(Table 3 Entry 2, 14).

Scheme 4: C‒C coupling reaction of 4ꢀbromobenzaldehyde with

phenyl boronic acid

Table 3: Optimization of reaction conditions^a

S.no

Base

K₂CO₃

Cs₂CO₃

KOH

Solvent

Catalyst

Yield%^h

67

1

DMF

2

ꢀ

Fig. 8 Time profile of SMC of 4ꢀbromobenzaldehyde (1 mmol);

catalyst (complex 2), 0.01 mol %.; phenyl boronic acid, 1.5 mmol;

K₂CO₃, 2 mmol; solvent: DMF + water (3:1), 4 mL; bath

temperature, 90 °C; isolated yield in %.

2

DMF:Water(3:1)

THF

93

3

nd

4

1,4ꢀDioxane

44

Table 4 SuzukiꢀMiyaura coupling of aryl bromide

5

Ethanol:Water(3:1)

DMF:Water(3:1)

80

6

72

7

21

8

NaOAc

K₂CO₃

ꢀ

25

9

nd

10^b

11

12^c

2

13

nd

K₂CO₃

87

13^d

14^e

15^f

16^g

K₂CO₃

DMF:Water(3:1)

2

76

81

87

89

^aReaction conditions: 4ꢀbromobenzaldehyde, 1.0 mmol; phenylboronic

acid, 1.5 mmol; base, 2 mmol; catalyst, 0.01 mol%; solvent, 4mL; time, 3

h; temperature, 90 °C;^broom temperature; ^c4ꢀbromobenzene, 1.0 mmol

d

e

^aReaction condition: ArBr, 1.0 mmol; phenylboronic acid, 1.5 mmol;

K₂CO₃, 2 mmol; catalyst, 0.01 mol %; DMF:water(3:1), 4 mL; temperature

catalyst, 0.1 mol%; catalyst, 0.001 mol%; temperature, 70°C;^fcatalyst 2:

Hg (1:400); ^gPPh_3,0.5 mol%;^hisolated yield; nd = not detected.

0

of bath, 90 C; time 3 h; Isolated yield in % are given below each structure.

TOF is in h^ꢀ1

In Table 4 the results of Suzuki−Miyaura coupling of various ArBr

substrates catalyzed with complexes 1ꢀ3 are given. The efficiency of

palladacycle 2 (having selenated ligand) appears to be somewhat

better than those of 1 and 3. The yield of coupled product was high

when an electron withdrawing group was present on aryl bromide

rather than an electron donating one (Table 4, 6aꢀ6i). The time

profile of catalytic reaction is shown in Fig. 8. The yield increases

almost linearly up to 3 h and thereafter the rate is slowed down. The

yield does not increase on carrying out the reaction for 4 more hours.

The performance of complexes 1ꢀ3 evaluated on the basis of catalyst

loading and reaction time, is better than related Pdꢀbased catalysts

for SMC reported earlier, viz. palladium complexes of (S, N, O⁻)

ligand (0.1 mol%, 24 h),^15a(S, N) ligand (0.1 mol%, 24 h),^15b

(S/Se/Te, N, O−) ligand (0.1ꢀ0.5 mol%, 12ꢀ24 h),^15c,e−g(S, N, S)

ligand^16c(0.1ꢀ 2 mol%, 2.5ꢀ6 h) /(S, C, S) pincer ligand^16eꢀg(1 mol%,

6 | J. Name., 2012, 00, 1-3

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5 h) and (P, N) ligand (0.5 mol%, 16 h).^25aPalladium complex of boronic acid, 1.5 mmol; K₂CO₃, 2 mmol; solvent: DMF + water

ferrocenylhydrazone for Suzuki−Miyaura coupling gave only 15ꢀ (3:1), 4 mL; bath temperature, 90 °C; isolated yield in %.

40% yield of coupled product in case of 4ꢀbromoanisole and 4ꢀ

bromotoluene with 0.5ꢀ1.0 mol% catalyst loading in 4 h.^25b

.

For catalysts reported in the recent past for SMC of aryl chloride

Complexes of cyclopalladateferrocenylimine with triphenylꢀ derivatives, the loading and time of reaction for good yield are as

phosphine catalyze SMC with 0.1 mol% loading.^25cThus follows: (i) Pd(OAc)₂ꢀindolyl phosphine ligands (0.01ꢀ0.1 mol%,

performance of 1ꢀ3 for SMC is better than many catalysts known for 24h)^25d

,

(ii) Pd(OAc)₂ꢀ {^tBu₂PN=P(ⁱBuNCH₂CH₂)₃N} (2ꢀ4 mol%,

this purpose.

10ꢀ18 h)^25e, (iii) Pd(OAc)₂ꢀferrocenyl monophosphine ligands (0.1

mol%, 24 h)^25f(iv) [PdCl₂(PhCN)₂]ꢀphosphine ligand bearing

dodeca(ethylene glycol) chains {EG12ꢀphos} (0.5 mol%, 20 h)^25g

(iv) palladium complexes of ferrocenylhydrazone (no coupling)^25b

(v) tricyclohexylphosphine(PCy₃)ꢀcyclopalladatedꢀ ferrocenylimine

Table 5 SuzukiꢀMiyaura coupling of aryl chloride:

complexes (0.1 mol%

,

12h)^5f

(vi) triphenylphosphineꢀ

cyclopalladateferrocenylmethylimine complexes ^25c(2 mol%, 10 h ).

The complexes (1ꢀ3) stand better if reaction time is compared.

Comparison of loading also rates them superior than most of the

catalytic systems mentioned above. Thus present complexes 1ꢀ3 are

almost equally efficient for ArCl as well as ArBr

NC

O₂

N

OHC

6c

6b

6a

1 = 80%, 2 = 90%, 3 = 90%

1 = 81%, 2 = 92%, 3 = 90%

1 = 85%, 2 = 90%, 3 = 87%

By taking a clue from the mechanism of SMC proposed

earlier.^25hit is proposed that a complex from 1ꢀ3 appears to initiate

SuzukiꢀMiyaura reaction by oxidative addition of ArX at palladium

center after cleavage of (Fc)CꢀPd bond and dissociation of Cl from

complex. The cleavage of PdꢀC(Fc) bond occurs and is supported by

¹³C {¹H} NMR spectrum of catalytic reaction mixture (having 1 as a

catalyst) after 30 min. as number of Cp signal changes from six to

four. The resulting moiety B gives C which undergoes reductive

elimination to give desired coupled product. The formation of C

during the catalysis is supported by ¹H NMR of reaction mixture

taken when reaction between complex 1, 4a (4ꢀbromobenzaldehyde,

5 equiv.) and 5 (phenyl boronic acid, 7 equiv.) under optimum

condition has progressed for 3 h (see ESI Fig S20ꢀS23).

8.5ꢀ9.0 x 10³TON

1.4ꢀ1.5 x 10³TOF

8.1ꢀ9.2 x 10³TON

1.3ꢀ1.5 x 10³TOF

8.0ꢀ9.0 x 10³TON

1.3ꢀ1.5 x 10³TOF

HOOC

MeOC

6f

6e

6d

1 = 74%, 2 = 81%, 3 = 80%

1 = 78%, 2 = 88%, 3 = 82%

1 = 80%, 2 = 86%, 3 = 83%

7.8ꢀ8.8 x 10³TON

1.3ꢀ1.5 x 10³TOF

7.4ꢀ8.1 x 10³TON

1.2ꢀ1.3 x 10³TOF

8.0ꢀ8.6 x 10³TON

1.3ꢀ1.4 x 10³TOF

MeO

N

6i^b

6h^b

6g

1 = 68%, 2 = 82%, 3 = 80%

1 = 72%, 2 = 82%, 3 = 78%

1 = 70%, 2 = 87%, 3 = 82%

7.0ꢀ8.2 x 10³TON

1.2ꢀ1.4 x 10³TOF

7.2ꢀ8.2 x 10²TON

1.2ꢀ1.4 x 10²TOF

6.8ꢀ8.2 x 10²TON

1.1ꢀ1.4 x 10³TOF

Pd^IIC

[(LꢀH)

l]

^aReaction condition: ArCl, 1.0 mmol; phenylboronic acid, 1.5 mmol;

K₂CO₃, 2 mmol; catalyst, 0.01 mol %; DMF:water(3:1), 4 mL; temperature

ꢀCl^ꢀ

[LPd⁰

0

b

of bath, 90 C; time 6 h; catalyst, 0.1 mol %; Isolated yield in % are given

below each structure; TOF is in h^ꢀ1

]

A.

ArX

III

C.

I

The complexes 1ꢀ3 catalyze coupling of aryl chlorides and

phenylboronic acid under optimum conditions (given above for

ArBr) and the results are given in Table 5. The coupling was feasible

in the presence of electron donating as well as withdrawing groups.

For good yield the reaction time was 6 h and the required catalyst

loading between 0.01ꢀ0.1 mol % of palladium.

Ph

II

X

(L)P

d

B.

(L)Pd^II

Ar

II

KX + OHꢀB(OH)₂

K₂CO₃+ PhB(OH)₂

Scheme 4: Proposed mechanism for SuzukiꢀMiyaura coupling

To establish whether the present catalysis of SMC is

heterogeneous or homogeneous Hg²⁶and triphenylphosphine

poisoning²⁶tests were carried out. Both the tests suggest the

homogenous nature of catalysis. The two phase test²⁷(called a threeꢀ

phase when the catalyst is a solid) considered more definitive to

establish whether the catalytically active species is functioning in

homogeneous or heterogeneous manner (Scheme 5) was also

performed to settle further the issue of heterogeneity vs homogeneity

in the activation of SMC with 1ꢀ3. For totally heterogeneous

catalysis the immobilized aryl halide is not expected to give any

Fig.

9

Time profile of catalytic C‒C coupling of 4ꢀ

chlorobenzaldehyde (1 mmol); catalyst (2), 0.01 mol %.; phenyl

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coupled product. The coupling of immobilized substrate implies those of many earlier reports on the catalysis of two coupling

homogeneous catalysis in part or full, depending on the % of reactions. At 0.001 mol% loading of Pd SMC occurs with

immobilized substrate coupled (Scheme 5). The addition of a soluble somewhat lower yield than that of 0.01 mol% loading. The

aryl halide to the reaction mixture ensures the presence of a catalytic complexes 1ꢀ3 as catalyst were found efficient for SMC of

process and its real active species. 4ꢀBromoacetophenone and ArCl also, as yield in 6 h and with catalyst loading of 0.01ꢀ0.1

immobilized 4ꢀbromobenzoic acid (as amide) were reacted with mol % was good. The poisoning and twoꢀphase tests suggest

phenylboronic acid under optimum reaction conditions. The coupled that catalysis with the present complexes of the two coupling

product in solution was separated by filtration and after work up, as reactions is largely homogeneous. The complex

2

is somewhat

and

mentioned in the general procedure of SMC analyzed with ¹H NMR. more efficient for both the catalytic reactions followed by

3

The yield of the crossꢀcoupled product, 4ꢀacetylbiphenyl was ~91%.

The solid phase was hydrolyzed, and the resulting products after

same work up analyzed with ¹H NMR. The immobilized 4ꢀ

bromobenzoic acid (as amide), was converted~88% (Scheme 5) to

the crossꢀcoupled product (biphenylꢀ4ꢀcarboxylic acid). These

results indicate the homogeneous nature of SMC catalyzed with 1ꢀ3.

1.

E

xperimental section

Physical measurements

The ¹H, ¹³C{¹H}, and ⁷⁷Se{¹H} NMR spectra were recorded on

a BrukerSpectrospin DPXꢀ300NMRspectrometer at 300.13,

75.47, and 57.24 MHz respectively. The C, H, and N analyses

were carried out with a Perkin–Elmer 2400 Series II C, H, and

N analyzer. Xꢀray diffraction data on single crystals were

collected using Mo Kα (0.71073 Å) radiation at 298(2) K. The

software SADABS²⁸was used for absorption correction and

SHELXTL for structure determination, and refinements.²⁸

Hydrogen atoms were included in idealized positions with

isotropic thermal parameters set at 1.2 times that of the carbon

atom to which they were attached in all cases. The leastꢀsquares

refinement cycles were performed until the model converged.

High resolution mass spectral measurements were made with

electron spray ionization (10 eV, 180 °C source temperature,

sodium formate as reference) taking sample in CH₃CN. The

commercial nitrogen gas was used after passing it successively

through traps containing solutions of alkaline anthraquinone,

sodium dithionite, alkaline pyrogallol, concentrated H₂SO₄and

KOH pellets. Nitrogen atmosphere if required was created

using Schlenk techniques. All reactions were carried out in

glassware dried in an oven, under ambient conditions.

OR

Si

(i) Catalyst 0.01%

K₂CO₃, Aq. DMF

O

PhB(OH)₂

+

Br

NH

Br

(ii) KOH, EtOH, Water

O

Br

HO

8%

88%

91%

Scheme 5: Two phase test for Suzuki Miyaura coupling

The reaction mixtures of CꢀO and Suzuki Miyaura coupling carried

out under optimum conditions using 2 as a catalyst, were subjected

to TEM studies after completion of the reaction. No sign of

formation of black particles of Pd by decomposition of 2 was noticed

in TEM micrographs or otherwise (see ESI Fig S24). This rule out

formation of Pd aggregates. The real catalytic species are most

probably ligand protected Pd(0) in both the coupling reactions and

originate from 1ꢀ3 by cleavage of ferroceneꢀPd bond and

dissociation of Cl. This supports the mechanism proposed in

Schemes 3 and 4 above for CꢀO and SMC respectively

Chemicals and reagents

The reported methods were used for the synthesis of 2ꢀ

(phenylthio)ethanamine and 2ꢀ(phenylselanyl)ethanamine²⁹.

Thiophenol,

diphenyldiselenide,

2ꢀchloroethylamine

Conclusion

hydrochloride, ferrocenecarboxaldehyde, phenol, aryl bromides

and chlorides, phenyl boronic acid, KOH and NaBH₄were

procured from SigmaꢀAldrich (USA) and used as received. The

solvents were dried and distilled before use by standard

procedures.³⁰The common reagents and chemicals available

commercially within the country were used.

Schiff base ligands (L1 and L2) formed by reaction of

ferroceneꢀcarboxaldehyde with sulfated/selenated amine and

their cyclopalladated complexes (

and characterized by multinuclei NMR and HRꢀMS. The

singleꢀcrystal structures of complexes ( ) were determined

1ꢀ3) have been synthesized

1ꢀ3

with Xꢀray diffraction. They are probably the first examples of

cyclopalladated complexes of chalcogenated Schiff base

ligands having ferrocene core. The disposition of donor atoms

around palladium is nearly square planner. These

Synthesis of L1 and L2

2ꢀ(Phenylthio)ethylamine(0.30 g, 2.0 mmol)

/ 2ꢀ(phenylꢀ

selenyl)ethylamine (0.400 g, 2.0 mmol) was placed in a 100 mL

round bottom flask and stirred with dry ethanol (20 mL) for 30

min at room temperature. Ferrocenecarboxaldehyde (0.428 g,

2.0 mmol), also dissolved in dry ethanol (20 mL), was added

drop wise with stirring. The mixture was stirred further at room

temperature for 2.5 h. After the completion of reaction, the

solvent of reaction mixture was evaporated off under reduced

cyclopalladated complexes have been explored for the

Oꢀ

arylation of phenol and SuzukiꢀMiyura coupling of phenyl

boronic acid with several aryl bromides containing both

activating and deactivating substituent. The complexes 1ꢀ3 as

catalyst show good conversion of ArBr to coupled product with

low catalyst loading (0.5 and 0.01 mol% for CꢀO and SMC

respectively) in 3ꢀ6 h. This reaction time is shorter compared to

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pressure on a rotary evaporator resulting in the ligands L1 and The 1 (0.50 mmol, 0.391 g) was stirred with 40 mL of methanol for

L2 as a wine red precipitate. 30 min at 80 °C. Triphenylphosphine (0.50 mmol, 0.131 g) was

L1: Yield: 0.621g, 89%, Anal. Calc. C₁₉H₁₉FeNS: C, 65.34; H, added and mixture stirred further for 6 h. The red solid formed was

5.48; N, 4.01 Found: C, 65.18; H, 5.36; N, 3.83. ¹H NMR collected by filtration and airꢀdried overnight to get 3. Its single

(CDCl₃, 25 °C vsMe₄Si): δ (ppm):8.10 (s, 1H, H₉), 7.40–7.38 crystals were grown from ethylacetate : hexane mixture (3 : 1).

(m, 2H, H₁, H₅), 7.32–7.27 (m, 2H, H₂, H₄), 7.21–7.18 (m, 2H, 3: Yield: 0.304g, 85%. Anal. Calc. for C₃₇H₃₃FeClNPdS: C, 61.98;

H₃),4.62 (m, 2H, C₅H₄), 4.37 (m, 2H, C₅H₄), 4.19 (m, 5H, Cp,) H, 4.64; N, 1.95. Found: C, 61.63, H, 4.76, N, 1.87. Mp: 185.0 °C.¹H

3.72–3.67 (t, 2H, H₈), 3.25–3.21 (t, 2H, H₇),. ¹³C{¹H}NMR NMR (CDCl₃,25 °C vsMe₄Si):

(CDCl₃, 25 °C vsMe₄Si): (ppm) 162.8(C₉), 136.3(C₆), 7.42 (m, 12H, PꢀPh), 7.28ꢀ7.20 (m, 3H, PꢀPh), 4.42 (m, 1H, C₅H₃),

δ (ppm) 8.12 (m, 5H, SꢀPh), 7.74ꢀ

δ

129.0(C₁), 128.9(C₂), 125.8(C₃), 80.1 (C₅H₄), 70.5(C₅H₄), 4.27 (m, 1H, C₅H₃), 4.08 (m, 1H, C₅H₃), 3.93 (m, 5H, Cp,), 3.49 (t,

69.1(Cp), 68.4(C₅H₄), 60.6(C₈), 34.0(C₇). HRꢀMS (CH₃CN) 2H, H₈), 3.34 (t, 2H, H₇),¹³C{¹H}NMR (CDCl₃, 25 °C

HRꢀMS (CH₃CN) [C₁₉H₂₀FeNS]⁺(

value for [C₁₉H₂₀FeNS]⁺= 350.0660 (

m/z

)= 350.0660; calculated vsMe₄Si):,¹³C{¹H}NMR (CDCl₃, 25 °C vsMe₄Si): 174.0(C₉),

δ

: 0.2 ppm).

134.9(C₆), 132.0 (PꢀPh₃), 130.5(PꢀPh₃), 129.4 (PꢀPh₃), 129.1 (PꢀPh₃),

L2: Yield:0.667 g, 84%.Anal. Calc. C₁₉H₁₉FeNSe: C, 57.60; H, 128.2(C₁), 128.1(C₂), 126.2 (C₃), 103.4 (C₅H₃), 87.4 (C₅H₃),

4.83; N, 3.54 Found: C, 57.43; H, 4.68; N, 3.43. ¹H NMR 73.18(C₅H₃), 70.3 (Cp), 69.5(C₅H₃), 66.8 (C₅H₃), 57.1 (C₈), 34.5

(CDCl₃, 25 °C vsMe₄Si):

δ

(ppm)8.10 (s, 1H, H₉), 7.55–7.53 (C₇). ³¹P{¹H} NMR (CDCl₃, 25°C, H₃PO₄) δ (ppm): 37.0. HRꢀMS

(m, 2H, H₁, H₅), 7.28–7.26 (m, 3H, H₂, H₃, H₄), 4.62 (m, 2H, (CH₃CN) [C₃₇H₃₃FeNPPdS]⁺(

m

/z)= 716.0448; calculated value for

C₅H₄), 4.37 (m, 2H, C₅H₄), 4.19 (m, 5H, Cp,), 3.78–3.74 (t, [C₃₇H₃₃FeNPPdS]⁺= 716.0465 (

2H, H₈), 3.22–3.17 (t, 2H, H₇), ¹³C{¹H}NMR (CDCl₃, 25 °C

δ: 0.2 ppm).

General procedure for the C‒O coupling reaction of

aryl/heteroaryl halides with phenol

vsMe₄Si):

δ (ppm) 162.5(C₉), 135.7(C₆), 132.4(C₁), 129.0(C₂),

126.7(C₃), 80.1 (C₅H₄), 70.5(C₅H₄), 69.1(Cp), 68.4(C₅H₄),

61.5(C₈), 28.2 (C₇).⁷⁷Se{¹H} NMR (CDCl₃, 25 °C vs Me₂Se) δ

An ovenꢀdried flask was charged with aryl bromide (1.0 mmol),

phenol (1.2 mmol), Cs₂CO₃(1.2 mmol), 1/2/3 (0.5 mol %) and

DMSO (4.0 ml). The flask was fitted with a water condenser and

placed on an oil bath maintained at 110 °C. The reaction mixture

was stirred and the reaction monitored with TLC until maximum

conversion of aryl bromide to the coupled product occurred.

Thereafter the mixture was extracted with ethylacetate (2 × 50 mL).

The organic layer was washed with water (2 × 50 mL) and dried

over anhydrous Na₂SO₄. The solvent of the extract was evaporated

off with a rotary evaporator. The resulting residue was purified with

a column of silica gel using ethylacetate−hexane (2 : 98) as an

eluent. Yield of isolated product was estimated and the product

analyzed with ¹H NMR spectroscopy. The NMR data of each

product was matched with the values reported in literature for its

authentication (ESI, Page no. 17ꢀ18).

(ppm): 273.20. HRꢀMS (CH₃CN) [C₁₉H₂₀FeNSe]⁺

(m/z)=

398.0093; calculated value for [C₁₉H₂₀FeNSe]⁺= 398.0106 (

1.3 ppm).

δ:

Syntheses of complexes 1 and 2

A 0.50 mmol of a ligand (L1: 0.175 g L2: 0.198 g) was stirred

in 40 mL methanol for 15 min. The Na₂[PdCl₄] (0.147 g, 0.50

mmol) and NaOAc (0.041 g, 0.50 mmol) were added to it. The

mixture was stirred further for 6 h at 80˚C. The red solid

formed was collected by filtration and airꢀdried overnight to get

complex

1 and 2. Single crystals of each of the two complexes

were obtained from a mixture of ethylacetate : hexane (3 : 1).

1: Yield: 0.207g, 85% Anal. Calc. C₁₉H₁₈FeClNPdS: C, 46.56; H,

1

General procedure for the C‒C coupling reaction of

aryl/heteroaryl halides with phenyl boronic acid

3.70; N, 2.86 Found: C, 45.76; H, 3.62; N, 2.75. Mp: 190.0 °C. H

NMR (CDCl₃, 25 °C vsMe₄Si):

δ (ppm) 8.06ꢀ8.03 (m, 3H, H₉. H₁,

H₅), 7.44–7.42 (m, 3H, H₂, H₃, H₄), 5.14(m, 1H, C₅H₃), 4.49(m, 1H,

C₅H₃), 4.44(m, 1H, C₅H₃), 4.29 (m, 5H, Cp), 3.56 (t, 2H, H₈), 3.19

(t, 2H, H₇), ¹³C{¹H}NMR (CDCl₃, 25 °C vsMe₄Si): 172.2(C₉),

132.8(C₆), 129.0(C₁), 129.7(C₂), 129.5(C₃), 106.5 (C₅H₃), 89.4

(C₅H₃), 75.96(C₅H₃)_,70.7(Cp), 69.4(C₅H₃), 67.1(C₅H₃), 55.3(C₈),

An oven dried flask was charged with aryl halide (1.0 mmol),

phenylboronic acid (1.5 mmol), K₂CO₃(2.0 mmol), DMF (3.0 mL),

H₂O (1.0 mL) and catalyst (0.01 / 0.1 mol%). The flask was fitted

with a water condenser and placed on an oil bath maintained at

90°C. The reaction mixture was stirred and the reaction monitored

with TLC until maximum conversion of aryl halide to the product

occurred. Thereafter the mixture was extracted with diethyl ether (2

× 20 mL). The extract was washed with water and dried over

anhydrous Na₂SO₄. The solvent of the extract was evaporated off on

a rotary evaporator, and the residue was purified by a column of

silica gel using chloroform−hexane (2:98) as an eluent. Yield of

isolated product was estimated and the product analyzed with ¹H

NMR spectroscopy. The NMR data of each product was matched

with the values reported in literature for its authentication (ESI, Page

no. 18).

40.8(C₇). HRꢀMS (CH₃CN) [C₁₉H₁₈FeNPdS]⁺

calulated value for [C₁₉H₁₈FeNPdS]⁺= 453.9548 (

(

m

/z)= 453.9561;

δ: ꢀ1.3ppm).

2: Yield: 0.091g, 88%. Anal. Calc. for C₁₉H₁₈FeClNPdSe: C, 42.49;

H, 3.38; N, 2.61. Found: C, 42.25; H, 3.49; N, 2.52. Mp: 180 °C. ¹H

NMR (CDCl₃, 25 °C vsMe₄Si):

δ (ppm)8.05 (m, 3H, H₉. H₁, H₅),

7.40 (m, 3H, H₂, H₃, H₄), 5.12(m, 1H, C₅H₃), 4.47(m, 1H, C₅H₃),

4.41(m, 1H, C₅H₃), 4.32 (m, 5H, Cp), 3.56 (t, 2H, H₈), 3.10 (t, 2H,

H₇),¹³C{¹H}NMR (CDCl₃,25 °C vsMe₄Si): 172.6(C₉), 134.4(C₆),

129.8(C₁), 129.5(C₂), 125.9(C₃), 107.2(C₅H₃), 89.4(C₅H₃),

75.63(C₅H₃), 70.6 (Cp), 69.6(C₅H₃), 67.0(C₅H₃), 56.9 (C₈), 33.0

(C₇). ⁷⁷Se{¹H} NMR (CDCl₃, 25 °C, Me₂Se) δ (ppm): 336.86. HRꢀ

Hg poisoning test

MS (CH₃CN) [C₁₉H₁₈FeNPdSe]⁺(

m

/

z

)= 501.8974; calulated value

An excess of Hg (Hg:Pd, 400:1) was taken in the reaction flask

before the addition of reactants. Thereafter the coupling reaction of

for [C₁₉H₁₈FeNPdSe]⁺= 501.8997 (

δ: 2.3 ppm).

Syntheses of complex 3

J. Name., 2013, 00, 1-3 | 9

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Journal Name

204; (d) Z. Weng, S. Teoand T. S. A. Hor, Acc. Chem. Res.

2007, 40 676–684.

,

4ꢀbromobenzaldehyde (1.0 mmol) with phenylboronic acid (1.2

mmol) or phenol (1.2 mmol) using 2 (0.5 mol % for ꢀarylation,

0.01 mol% for Suzuki Miyaura coupling) as a catalyst was carried

under optimum conditions. After 6 h conversion to coupled product

,

O

4

5

(a) S. Jing, C. P. Morley, C. A. Webster and M. D. Vaira,

Dalton Trans., 2006, 4335–4342; (b) S. Jing, C. P. Morley, C.

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was 78% for Oꢀarylation and 87% for SMC.

PPh₃poisoning test

To the coupling reaction of 4ꢀbromobenzaldehyde with

phenylboronic acid/phenol, PPh₃(0.5 mol %) was added under

optimum conditions before addition of catalyst, complex 2 (0.5 mol

% for

Oꢀarylation and 0.01 mol% for SMC). After 5 h of reaction

Hou, H. Yun, X. Cui and R. Yuan, J. Organomet.Chem.

,

crossꢀcoupled products were obtained in 80% (

(SMC) yield.

Oꢀarylation) and 89%

2001, 637–639, 793ꢀ795; (d) F. Yang, X. Cui, Y. N. Li, J.

Zhang, G. Ren and Y. Wu, Tetrahedron, 2007, 63, 1961ꢀ

1969.(e) N. C. Bruno, M. T. Tudge, and S. L. Buchwald,

Chem. Sci., 2013, 4, 916ꢀ920. (f) C. Xu, J. F. Gong, S. F.

Yue, Y. Zhu and Y. J. Wu, Dalton Trans., 2006, 4730–

4739.(g) C. Nájera and D. A. Alonso in Palladacycles:

Synthesis, Characterization and Applications, Eds. J. Dupont

and M. Pfeffer, 2008 Chapter 8, p. 155ꢀ207, WileyꢀVCH. (h)

R. B. Bedford, in Palladacycles: Synthesis, Characterization

and Applications, Eds. J. Dupont and M. Pfeffer, 2008

Chapter 9, p. 209 ꢀ225, WileyꢀVCH.

Twoꢀphase test for SuzukiꢀMiyaura coupling

The 4ꢀbromobenzoic acidꢀimmobilized (as amide) silica (0.20 g)

prepared by standard procedure,²⁹phenylboronic acid (0.36 g, 3

mmol), 4ꢀ bromoacetophenone (0.20 g, 1 mmol), and K₂CO₃(0.56 g,

4 mmol) were taken in a mixture of DMF (8 mL) + water (4 mL).

The reaction mixture was heated at 90 °C for 12 h. Thereafter work

up and analyses of the products were done as reported earlier.^19,26

6

7

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Acknowledgements

A.K.S. thanks Council of Scientific and Industrial Research (CSIR)

of India and BRNS, Department of Atomic Energy(India) for

financial support. A. S. thanks the CSIR of India for SRF, H. J., R.B.

and S.K. thank the University Grants Commission (UGC), India for

JRF/SRF.

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J. Name., 2013, 00, 1-3 | 11

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DOI: 10.1039/C7DT00083A

Palladacycles of sulfated and selenated Schiff bases of ferrocene-

carboxaldehyde as catalysts for O-arylation and Suzuki–Miyaura coupling

Alpesh K. Sharma, Hemant Joshi, Renu Bhaskar and Ajai K. Singh*

Palladacycles of Schiff-bases having ferrocene core catalyze O-arylation of ArBr and Suzuki-Miyaura

coupling of ArBr/Cl with yield up to 93%.

Article Doi

Palladacycles of sulfated and selenated Schiff bases of ferrocene-carboxaldehyde as catalysts for O-arylation and Suzuki-Miyaura coupling

DOI: 10.1039/c7dt00083a

Source and publish data:

Authors:

Article abstract of DOI:10.1039/c7dt00083a

Full text of DOI:10.1039/c7dt00083a

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