Cationic palladium(II)–acetylacetonate complexes containing phosphine and aminophosphine ligands and their catalytic activities in telomerization of 1,3-butadiene with methanol

Cationic palladium(II)–acetylacetonate complexes containing phosphine and

aminophosphine ligands and their catalytic activities in telomerization of 1,3-

butadiene with methanol

a

b

D.S. Suslov †, M.V. Bykov , Z.D. Abramov , I.A. Ushakov , T.N. Borodina , V.I. Smirnov ,

a

G.V. Ratovskii , V.S. Tkach

a

Irkutsk State University, ul. K.Marksa, 1, Irkutsk, Russia, 664003

b

A.E. Favorsky Irkutsk Institute of Chemistry SB RAS, Favorsky st., 1, Irkutsk, Russia, 664033,

†

Correspondence should be addressed: e-mail: suslov@chem.isu.ru; suslov.dmitry@gmail.com.

Keywords: palladium, acetylacetonate, 1,3-butadiene, telomerization, methanol

1

CONTENTS

1

2

Introduction ................................................................................................................................3

Experimental Section..................................................................................................................5

2

.1 General procedures and materials.......................................................................................5

.2 Telomerization experiments ...............................................................................................5

.3 Synthesis of Palladium Complexes.....................................................................................6

2

.3.1 Preparation of (acetylacetonate-κ O,O')bis[cyclohexyl(diphenyl)phosphine-

κP]palladium(II) tetrafluoroborate, [Pd(acac)(PCyPh ) ]BF (2)..........................................6

2

4

2

.3.2 Preparation of (acetylacetonate-κ O,O')bis[dicyclohexyl(phenyl)phosphine-

κP]palladium(II) tetrafluoroborate, [Pd(acac)(PCy Ph) ]BF (3)..........................................7

2

4

2

.3.3 Preparation of (acetylacetonate-κ O,O')bis[tris(dimethylamino)phosphine-

κP]palladium(II) tetrafluoroborate, [Pd(acac){P(NMe ) } ]BF (5) .....................................8

2

3

2

4

2

.3.4 Preparation of (acetylacetonate-κ O,O')bis[tris(diethylamino)phosphine-

κP]palladium(II) tetrafluoroborate, [Pd(acac){P(NEt ) } ]BF (6).......................................9

2

3

2

4

2

.3.5 Preparation of (acetylacetonate-κ O,O')bis(tri-2-furylphosphine-κP)palladium(II)

tetrafluoroborate, [Pd(acac)(TFP) ]BF (TFP = tri-2-furylphosphine) (7) ............................9

2

4

2

.3.6 Preparation of (acetylacetonate-κ O,O')bis(tri-2-thienylphosphine-κP)palladium(II)

tetrafluoroborate, [Pd(acac)(TTP) ]BF (TTP = tri-2-thienylphosphine) (8) ......................10

2

4

2

.3.7 Preparation of (acetylacetonate-κ O,O')(2-dicyclohexylphosphino-2',6'-

dimethoxybiphenyl-κP)palladium(II) tetrafluoroborate, [Pd(acac)(SPhos)]BF , (SPhos = 2-

4

dicyclohexylphosphino-2',6'-dimethoxybiphenyl) (10) .......................................................11

2

.3.8 Preparation of (acetylacetonate-κ O,O')(2-dicyclohexylphosphino-2′,4′,6′-

triisopropylbiphenyl-κP)palladium(II) tetrafluoroborate, [Pd(acac)(XPhos)]BF , (XPhos =

4

2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl) (11)..............................................12

2

.4 Calculations ......................................................................................................................14

.5 X-ray crystallographic studies ..........................................................................................14

2

3

4

Results and Discussion.............................................................................................................16

3.1 Synthesis of Palladium(II) Complexes. ............................................................................16

3.2 X-ray Crystal Structures of 2 and 3 ..................................................................................18

3.3 Catalytic Studies ...............................................................................................................20

Conclusions ..............................................................................................................................24

References .....................................................................................................................................26

Highlights ......................................................................................................................................35

CRediT author statement...............................................................................................................36

2

1

Introduction

Telomerization, linear dimerization of 1,3-dienes with simultaneous addition of a

nucleophile in a catalytic reaction, is a very efficient organic transformation. The telomerization

process which allows the synthesis of functionalized octadienyl substrate with a potentially

1

00% atom efficiency [1,2], fulfils most of the principles of the green chemistry. Complexes of

palladium are known to effectively catalyze the reaction of dienes with a variety of nucleophiles.

Since its discovery 45 years ago [3,4], telomerization has attracted significant interest by many

industrial and academic laboratories due to its robustness and versatility in the production of a

wide variety of valuable products. The resulting products of telomerization have been used as

intermediates in the total synthesis of several natural products, as well as precursors for

plasticizer alcohols, industrial monomers, solvents, corrosion inhibitors, and non-volatile

herbicides [1,2]. Pd-catalyzed telomerization is also explored as a potential route for the

valorization of biomass-derived feedstock [5,6].

Telomerization of 1,3-butadiene (BD) with methanol developed by Dow Chemical

represent a commercial route to produce 1-octene [7] (Figure 1). The telomerization of 1,3-

butadiene with methanol in the presence of a palladium catalyst modified with triarylphosphine,

yields 1-methoxy-2,7-octadiene, which is hydrogenated and cracked to give 1-octene and

methanol [7]. It is also known that apart from telomerization (products: 1-methoxy-2,7-

octadiene, 3-methoxy-2,7-octadiene) the palladium catalyzed dimerization or Diels-Alder

reaction of butadiene can take place, leading to 1,3,7-octatriene and 4-vinylcyclohexene, with

chemoselectivity depending on the nature of nucleophiles and ligands coordinated to the reactive

palladium center (Figure 2) [1,2,8–10].

Figure 1 – Simplified Scheme of the Dow Process

A series of palladium complexes with various monodentate phosphines [11–16],

diphosphines [17], zwitterionic phosphonium alkylsulfonate ligands [18] and NHC (NHC — N-

heterocyclic carbene) ligands [19–21] were reported for the telomerization of BD with methanol.

Nevertheless, the search still continues for new ligands and catalysts, due to the high

requirements in terms of the stability, reactivity and selectivity of the resulting catalyst [2].

3

Figure 2 – Telomerization of 1,3-Butadiene with Methanol

We reported synthesis of cationic acetylacetonate palladium complexes with phosphine

ligands as well as the results of their usage as efficient precursors (usually activated with

BF ·OEt ) for the polymerization of norbornene and its derivatives [22–25], polymerization of

3

2

phenylacetylene [26], selective dimerization or hydroamination of vinylarenes [25,27],

telomerization of butadiene and isoprene with diethylamine [28,29]. It should be noted, that

application of [Pd(acac)(PPh ) ]BF as precatalyst for the telomerization of isoprene with amines

3

2

4

was reported by Röper et al [30].

In this work we report the results of synthesis of the novel palladium complexes as well

as results of [Pd(acac)(L) ]BF -catalyzed telomerization of 1,3-butadiene with methanol under

n

4

base-free conditions (n = 2: L = PPh , PCyPh , PCy Ph, PCy , P(NMe ) , P(NEt ) , tri-2-

3

2

3

2 3

furylphosphine, tri-2-thienylphosphine, tris(2-methoxyphenyl)phosphine; n = 1: L = 2-

dicyclohexylphosphino-2',6'-dimethoxybiphenyl, 2-dicyclohexylphosphino-2′,4′,6′-

triisopropylbiphenyl). The eight new compounds have been fully characterized, and crystal

structures of [Pd(acac)(L) ]BF (L = PCyPh , PCy Ph) have been determined by means of X-ray

2

4

2

diffraction. NMR spectroscopy features of the prepared cationic complexes are discussed.

4

2

Experimental Section

.1 General procedures and materials

All air- and/or moisture-sensitive compounds were manipulated by using standard high-

vacuum line, Schlenk, or cannula techniques under an argon atmosphere. Argon (Arnika-Prom-

Service) was purified before feeding to the reactor by passing through columns packed with

oxygen scavenger and molecular sieve 4A (Aldrich), respectively. Diethyl ether, petroleum

ether, toluene (ZAO Vekton) were distilled from sodium−benzophenone. CH Cl (ZAO Vekton),

2

CH CN (ZAO Vekton), methanol (ZAO Vekton) were distilled from CaH . Solvents were stored

3

2

over molecular sieves. Other chemicals were purchased from Acros Organic, Sigma-Aldrich,

ABCR and employed without drying or any further purification. All glassware and steel reactors

was dried for at least 3 h in a 150°C oven and cooled under an argon atmosphere. Pd(acac) was

2

synthesized according to a literature procedure [31] and recrystallized from acetone. Complexes

[

Pd(acac)(PPh ) ]BF (1), [Pd(acac)(PCy ) ]BF (4), {Pd(acac)[P(o-MeOC H ) ] }BF (9),

3 2 4 3 2 4 6 4 3 2 4

Pd(acac)(MeCN) ]BF (12) were prepared according to literature procedures [25,26,28]. All

2

4

other reagents were obtained commercially and used as received. All NMR spectra were

recorded at room temperature on Bruker DPX-400 spectrometer. IR spectra were recorded on a

Simex Infralum FT 801 spectrometer. GC-FID and GC–MS analyses were performed on

Chromatec Crystall 5000.2 (SGE BPX-5 capillary column, internal standard benzene) and

Shimadzu QP2010 Ultra (GSBP-5MS capillary column), respectively.

2

.2 Telomerization experiments

All reactions were performed in a 20 mL custom-made stainless steel autoclave. The 1,3-

butadiene (39 mmol) was condensed to the reactor and controlled volumetrically. The catalyst

was added as solution in CH Cl directly into the reactor pot. Then methanol (39 mmol) was

2

added via syringe. Afterwards the reactor was closed and placed in an oil bath at 70 °C. The

reaction was magnetically stirred at 900 rpm. After 2 h the reaction was stopped using an ice-

bath. Analyses of the catalytic reactions have been performed on a GC-FID

5

2

.3 Synthesis of Palladium Complexes

2

.3.1 Preparation of (acetylacetonate-κ O,O')bis[cyclohexyl(diphenyl)phosphine-

κP]palladium(II) tetrafluoroborate, [Pd(acac)(PCyPh ) ]BF (2)

2

4

PCyPh (0.2147 g, 0.800 mmol) was dissolved in 10 mL of CH Cl , and to this solution

2

was added [Pd(acac)(MeCN) ]BF (0.1497 g, 0.400 mmol), forming a yellow solution. The

2

4

reaction mixture was then stirred for 1.5 h at room temperature. The resulting yellow solution

was concentrated to 2 mL under vacuum. Addition of diethyl ether (10 mL) formed an lemon

precipitate, which was collected, washed with diethyl ether (2×10 mL), and dried (8 h) under

vacuum to afford complex 2 as a yellow powder (300 mg, 90.6%). Vapor diffusion of mixture of

petroleum ether and diethyl ether (1:1 v/v) into a 1,2-dichloroethate solution of 2 afforded yellow

crystals suitable for single-crystal X-ray analysis. Anal. Calcd for C H BF O P Pd: C, 59.40;

4

1

49

4

2 2

1

H, 5.96. Found: C, 58.17; H, 6.00. H NMR (400 MHz, CDCl , 25°C): δ 7.63 – 7.55 (m, 4H,

3

H ), 7.40 –7.13 (m, 16H, H ), 5.64 (s, 1H, H ), 2.74 – 2.59 (m, 2H, H ), 2.02 (s, 6H, H ),

Phi

acac

Cyi

Me

1

4

1

.91 – 1.79 (m, 4H, H ), 1.75 – 1.65 (m, 4H, H ), 1.65 – 1.54 (m, 2H, H ), 1.29 – 1.12 (m,

Cyi Cyi Cyi

1

3

H, H ), 1.11 – 0.82 (m, 6H, H ). C NMR (101 MHz, CDCl , 25°C): δ 186.69 (s, C_C_O_-_a_c_a_c),

Cyi

3

33.74 (observed as virtual triplets (vt) due to virtual coupling [32,33], J = 5.0 Hz, C_P_h_,_o_r_t_h_o),

1

32.39 (s, C_P_h_,_p_a_r_a), 129.08 (vt, J = 5.3 Hz, C_P_h_,_m_e_t_a), 124.42 (d, J(P,C_i_p_s_o) = 51.9 Hz), 101.10 (s,

C_C_H_-_a_c_a_c), 35.99 – 35.54 (m, C ), 29.21 (s, C ), 27.51 – 27.29 (m, C ), 27.26 – 27.00 (m,

Cyi

31

1

C ), 25.70 (s, C ). P{ H} NMR (162 MHz, CDCl , 25°C): δ 35.78 (s). IR (nujol, NaCl

Cyi

Me

3

−

1

2

···

plates, cm ): (acetylacetonate-κ O,O')-group: 1570 ν(C O and C C); 1516 ν(C C and C O);

1

282 (sh) and 1274 (sh) ν (C–CH ) and chelate deformations; 1196 δ(C–H from CH, plane) and

s 3

chelate deformations; 1004 chelate deformations and δ(C–CH rocking); 938 ν (C–CH ) and

3

,

as

3

chelate deformations; 843 (sh) δ(C–H from CH, off-plane); 668 chelate deformations and ν (Pd–

s

···

O); 665 π(CH –C(O) C); 604 chelate deformations. (PCyPh )-group: 3068, 3047, 3033 ν(C–H

3

2

from CH, Ph); 1589, 1550, 1482, 1438, 1432 ν (C=C, Ph) and phenyl ring deformations; 1448

as

(

sh) δ(C–H from CH , scissoring); 1344, 1340 (sh), 1329, 1314, 1300, 1289, 1269, 1252, 1208

2

δ(C–H from CH , Cy, wagging); 1321 δ(C–H from CH , Cy, wagging) and δ(C–H from CH,

2

Cy); 1190, 1165, 1160 (sh), 1119, 1113, 1085, 1077, 1062 δ(C–H from CH , Cy, twisting); 1185,

2

1

178, 1101 δ(C–H, Ph, plane); 1049 ν(C–C, Cy) and cyclohexyl ring deformations and δ(C–H

from CH , Cy, twisting); 1027 ν (C=C, Ph) and ring deformations; 998 ν(C–C, Cy) and ν (C=C,

2

s

Ph), with cyclohexyl and phenyl rings deformations; 974, 918, 892, 885, 850 δ(C–H from CH₂,

Cy, rocking); 933, 888 δ(C–H, Ph, off-plane); 858, 806 phenyl ring deformations; 816 δ(C–H

from CH , Cy, rocking) and cyclohexyl ring deformations; 743, 721, 695 δ(C–H, Ph, off-plane);

2

6

7

6

52 ν (P–C , Ph); 705 ν (P–C , Ph); 687 ν(P–C, Cy); 655, 651, 648, 644, 639, 635, 631, 630,

as Ar s Ar

22, 615, 609, 607 cyclohexyl and phenyl rings deformations. (BF )-group: 1093, 1054, 1035

4

ν (B–F); 782 partially resolved in the IR bands of the symmetric ν (B–F) vibrations, which

as

s

appear in the spectrum due to violation of the symmetry of the environment.

2

.3.2 Preparation of (acetylacetonate-κ O,O')bis[dicyclohexyl(phenyl)phosphine-

κP]palladium(II) tetrafluoroborate, [Pd(acac)(PCy Ph) ]BF (3)

2

4

PCy Ph (0.2195 g, 0.800 mmol) was dissolved in 10 mL of CH Cl , and to this solution

2

was added [Pd(acac)(MeCN) ]BF (0.1497 g, 0.400 mmol), forming a yellow solution. The

2

4

reaction mixture was then stirred for 1.5 h at room temperature. The resulting yellow solution

was concentrated to 2 mL under vacuum. Addition of diethyl ether (10 mL) formed an lemon

precipitate, which was collected, washed with diethyl ether (2×10 mL), and dried (8 h) under

vacuum to afford complex 3 as a yellow powder (276 mg, 82.0%). Vapor diffusion of mixture of

petroleum ether and diethyl ether (1:1 v/v) into a 1,2-dichloroethate solution of 3 afforded yellow

crystals suitable for single-crystal X-ray analysis. Anal. Calcd for C H BF O P Pd: C, 58.55;

4

1

61

4

2 2

1

H, 7.31. Found: C, 57.89; H, 7.14. H NMR (400 MHz, CDCl , 25°C): δ 7.47 (t, J = 7.6 Hz, 2H,

3

H ), 7.32 (t, J = 7.7 Hz, 4H, H ), 7.14 (m, 4H, H ), 5.64 (s, 1H, H_a_c_a_c), 2.43 – 2.28 (m, 4H,

Phi

H ), 2.12 – 1.95 (m, 4H, H ), 2.04 (s, 6H, H ), 1.94 – 1.67 (m, 18H, H ), 1.55 – 1.10 (m,

Cyi

Me

Cyi

1

3

1

8H, H ). C NMR (101 MHz, CDCl , 25°C): δ 186.12 (s, C_C_O_-_a_c_a_c), 132.36 (vt, J = 4.1 Hz,

Cyi 3

1

C_P_h_,_o_r_t_h_o), 131.95 (s, C_P_h_,_p_a_r_a), 129.08 (vt, J = 4.9 Hz, C_P_h_,_m_e_t_a), 123.65 (d, J(P,C_i_p_s_o) = 47.4 Hz),

1

00.83 (s, C_C_H_-_a_c_a_c), 34.53 – 33.84 (m, C ), 30.60 – 29.94 (m, C ), 27.90 – 27.46 (m, , C ),

Cyi Cyi Cyi

3

1

2

7.27 – 27.00 (m, C ), 25.84 (s, C ). P{ H} NMR (162 MHz, CDCl , 25°C): δ 41.95 (s). IR

Cyi

Me

3

-1

2

···

(

nujol, NaCl plates, cm ): (acetylacetonate-κ O,O')-group: 1571 ν(C O and C C) and ν (C=C,

as

···

Ph from PCy Ph); 1525 ν(C C and C O); 1281 (sh) and 1273 (sh) ν (C–CH ) and chelate

2

s

3

deformations; 1197 δ(C–H from CH, plane) and chelate deformations; 1006 (sh) chelate

deformations and δ(C–CH rocking); 938 ν (C–CH ) and chelate deformations; 840 δ(C–H from

3

,

as

3

···

CH, off-plane); 668 chelate deformations and ν (Pd–O); 663 π(CH –C(O) C); 602 chelate

s

3

deformations. (PCy Ph)-group: 3084, 3067, 3042 ν(C–H from CH, Ph); 1550, 1485 (sh), 1436

2

ν (C=C, Ph) and phenyl ring deformations; 1449 (sh) δ(C–H from CH , scissoring); 1350, 1342,

as

2

1

330, 1316, 1307, 1293, 1269, 1264, 1211, 1204 (sh) δ(C–H from CH , Cy, wagging); 1189,

2

170, 1122 (sh), 1115, 1085, 1072, 1038 δ(C–H from CH , Cy, twisting); 1181, 1162, 1154,

2

099 δ(C–H, Ph, plane); 1051 ν(C–C, Cy) and cyclohexyl ring deformations and δ(C–H from

CH , Cy, twisting); 1026 ν (C=C, Ph) and ring deformations; 998 ν(C–C, Cy) and ν (C=C, Ph),

2

s

with cyclohexyl and phenyl rings deformations; 981, 914, 892, 851 δ(C–H from CH , Cy,

2

7

rocking); 932, 920, 887 δ(C–H, Ph, off-plane); 859, 806 phenyl ring deformations; 817 δ(C–H

from CH , Cy, rocking) and cyclohexyl ring deformations; 735, 692 δ(C–H, Ph, off-plane); 748

2

ν(P–C , Ph); 723 ν (P–C, Cy); 705 ν (P–C, Cy); 660, 653, 650, 646, 642, 638, 633, 631, 629,

Ar

as

s

6

25, 622, 616, 610, 607 cyclohexyl and phenyl rings deformations. (BF )-group: 1093, 1054,

4

1

033 ν (B–F).

as

2

.3.3 Preparation of (acetylacetonate-κ O,O')bis[tris(dimethylamino)phosphine-

κP]palladium(II) tetrafluoroborate, [Pd(acac){P(NMe ) } ]BF (5)

2

3

2

4

P(NMe ) (0.16 mL, 0.800 mmol) was dissolved in 10 mL of CH Cl , and to this solution

2

3

2

was added [Pd(acac)(MeCN) ]BF (0.1497 g, 0.400 mmol), forming a yellow solution. The

2

4

reaction mixture was then stirred for 1.5 h at room temperature. The resulting yellow solution

was concentrated to 2 mL under vacuum. Addition of diethyl ether (10 mL) formed an lemon

precipitate, which was collected, washed with diethyl ether (2×10 mL), and dried (8 h) under

vacuum to afford complex 5 as a yellow powder (218 mg, 88.0%). Anal. Calcd for

1

C H BF N O P Pd: C, 33.00; H, 7.00; N, 13.58. Found: C, 32.41; H, 6.77; N, 13.15. H NMR

17

43

4

6

2 2

(

400 MHz, CDCl , 25°C): δ 5.51 (s, 0.3H, H_a_c_a_c), 5.48 (s, 0.7H, H_a_c_a_c), 2.80 (vt, J = 5.1 Hz, 6H,

3

2

13

NCH ), 2.76 (d, J(P,H) = 9.6 Hz, 30H, NCH ), 2.05 (s, 1H, H ), 1.99 (s, 5H, H ). C NMR

3

Me

(

101 MHz, CDCl , 25°C): δ 187.45 (s, C_C_O_-_a_c_a_c), 100.69 (s, C_C_H_-_a_c_a_c), 39.35 (vt, weak, J = 3.8 Hz,

3

1

NCH ), 38.76 (vt, J = 3.8 Hz, NCH ), 26.30 (vt, J = 5.7 Hz, C ). P{ H} NMR (162 MHz,

3

Me

-1

CDCl , 25°C): δ 90.81 (s), 85.04 (s, weak). IR (nujol, NaCl plates, cm ): (acetylacetonate-

3

2

···

κ O,O')-group: 1582 ν(C O and C C); 1520 ν(C C and C O); 1185 δ(C–H from CH, plane)

and chelate deformations, and ν (C–N–C from P(NMe ) ); 998 chelate deformations and δ(C–

s

2 3

CH , rocking) and ν (P–N from P(NMe ) ); 934 ν (C–CH ) and chelate deformations; 820 δ(C–

3

as

2 3

as

3

···

H from CH, off-plane); 673 chelate deformations and ν (Pd–O); 665 π(CH –C(O) C).

s

3

(

P(NMe ) )-group: 2817, 2805 ν(C–H from N(CH ) ); 1298 (sh) δ (C–H from N(CH ) , plane);

2 3 3 2 s 3 2

1

280 and 1268 ν (C–N–C from N(CH ) ), overlapping ν (C–CH from acac) and acac-chelate

as 3 2 s 3

deformations; 1185 ν (C–N–C from N(CH ) ) and δ(C–H from CH from acac) and acac-chelate

s

3 2

deformations; 1160 and 1141 (sh) ν (C–N–C from N(CH ) ); 1065 (sh) δ(N–CH , rocking); 998

s

3 2

3

ν (P–N) and acac-chelate deformations and δ(C–CH , from acac); 972, 957 ν (P–N); 717 ν (P–

as

3

as

s

N); 734, 703 δ(N–CH ) and δ(C–N–C); 652 δ(C–N–H) and δ(P–N–C). (BF )-group: 1095, 1052,

3

4

1

035 ν (B–F); 788 and 779 partially resolved in the IR bands of the symmetric ν (B–F)

as s

vibrations, which appear in the spectrum due to violation of the symmetry of the environment.

8

2

.3.4 Preparation of (acetylacetonate-κ O,O')bis[tris(diethylamino)phosphine-

κP]palladium(II) tetrafluoroborate, [Pd(acac){P(NEt ) } ]BF (6)

2

3

2

4

P(NEt ) (0.23 mL, 0.800 mmol) was dissolved in 10 mL of CH Cl , and to this solution

2

3

2

was added [Pd(acac)(MeCN) ]BF (0.1497 g, 0.400 mmol), forming a yellow solution. The

2

4

reaction mixture was then stirred for 2 h at room temperature. The resulting yellow solution was

concentrated to 2 mL under vacuum. Addition of petroleum ether (30 mL) formed an oily

precipitate. The reaction mixture was cooled to −18°C and stored for 24 h. The crude product

was then filtered, and the yellow solid was washed twice with petroleum ether (2×10 mL), and

dried (8 h) under vacuum to afford complex 6 as a yellow powder (263 mg, 83.6%). Anal. Calcd

1

for C H BF N O P Pd: C, 44.25; H, 8.58; N, 10.68. Found: C, 44.05; H, 8.54; N, 9.45. H

2

9

67

4

6

2 2

NMR (400 MHz, CDCl , 25°C): δ 5.45 (s, 1H, H_a_c_a_c), 3.53 – 2.92 (m, 24H, NCH CH ), 1.98 (s,

3

2

3

6

H, H ), 1.24 (t, J(H,H) = 7.1 Hz, 3H, NCH CH ), 1.16 (t, J(H,H) = 7.1 Hz, 33H, NCH CH ).

Me 2 3 2 3

1

3

C NMR (101 MHz, CDCl , 25°C): δ 186.52(s, C_C_O_-_a_c_a_c), 101.19 (s, C_C_H_-_a_c_a_c), 41.80 (weak,

3

NCH CH ), 40.89 (vt, J = 4.6 Hz, NCH CH ), 25.63 (vt, J = 5.9 Hz, C ), 13.32 (s, NCH CH ).

2

3

2

3

Me

2

3

1

P{ H} NMR (162 MHz, CDCl , 25°C): δ 99.56 (s, weak), 93.69 (s). IR (nujol, NaCl plates,

3

-1

2

···

cm ): (acetylacetonate-κ O,O')-group: 1576 ν(C O and C C); 1514 ν(C C and C O); 955

ν (C–CH ) and chelate deformations; 820 δ(C–H from CH, off-plane); 677 chelate deformations

as

3

···

and ν (Pd–O); 668 π(CH –C(O) C). (P(NEt ) )-group: 1348 (sh) δ (C–H from CH ); 1295, 1265

s

3

2 3

s

3

ν (C–N–C), overlapping ν (C–CH from acac) and acac-chelate deformations; 1199 ν (C–N–C);

as

s

3

s

1

171 ν (C–N–C) and δ(C–H from CH from acac, plane) and acac-chelate deformations; 1024

s

(

sh) and 1013 ν (P–N), overlapping acac-chelate deformations and δ(C–CH from acac,

a

s

3

rocking); 938, 922, 916 ν (P–N); 808, 800, 793, 770 δ(C–H from СH , rocking); 721, 690, 686

as

2

ν (P–N); 654 and 639 δ(P–N–C) and δ(N–C–C). (BF )-group: 1090, 1052, 1034 ν (B–F); 787

s

4

as

and 780 partially resolved in the IR bands of the symmetric ν (B–F) vibrations, which appear in

s

the spectrum due to violation of the symmetry of the environment.

2

.3.5 Preparation of (acetylacetonate-κ O,O')bis(tri-2-furylphosphine-κP)palladium(II)

tetrafluoroborate, [Pd(acac)(TFP) ]BF (TFP = tri-2-furylphosphine) (7)

2

4

TFP (0.2000 g, 0.800 mmol) was dissolved in 10 mL of CH Cl , and to this solution was

2

added [Pd(acac)(MeCN) ]BF (0.1497 g, 0.400 mmol), forming a yellow solution. The reaction

2

4

mixture was then stirred for 2 h at room temperature. The resulting yellow solution was

concentrated to 2 mL under vacuum. Addition of diethyl ether (7 mL) formed an yellow oily

precipitate, which was dissolved in toluene (10 mL). The reaction mixture was cooled to −18°C

9

and stored for 24 h. The crude product was then filtered, and the yellow solid was washed twice

with Et O (2×10 mL), and dried (8 h) under vacuum to afford complex 7 as a yellow powder

2

(

279 mg, 92.4%). Anal. Calcd for C H BF O P Pd: C, 46.03; H, 3.33. Found: C, 46.69; H,

29 25 4 8 2

1

3

.20. H NMR (400 MHz, Acetone-d , 25°C): δ 7.98 (s, 6H, H_F_u_r₅) (Fur – furyl ring), 7.19 (d, J

6

1

3

=

3.6 Hz, 6H, H_F_u_r₃), 6.67 (s, 6H, H_F_u_r₄), 5.69 (s, 1H, H_a_c_a_c), 1.83 (s, 6H, H ). C NMR (101

Me

1

MHz, Acetone-d , 25°C): δ 186.93 (s, C_C_O_-_a_c_a_c), 151.00 (vt, J = 3.6 Hz, C_F_u_r₅), 137.54 (d, J(P,C)

6

=

99.2 Hz, C_F_u_r₂), 126.20 (vt, J = 10.2 Hz, C_F_u_r₃), 112.24 (vt, J = 4.3 Hz, C_F_u_r₄), 100.64 (s, C_C_H_-

4

19

_a_c_a_c), 25.14 (vt, J(P,C) = 5.9 Hz, C ). F NMR (376 MHz, Acetone-d , 25°C): δ −151.14,

Me

6

1

0

−151.19 (intensity ratio of approximately 20:80 corresponding to the natural abundances of

B

1

31

1

and B, respectively). P{ H} NMR (162 MHz, Acetone-d , 25°C): δ −18.63 (s). IR (nujol,

6

-1

2

···

NaCl plates, cm ): (acetylacetonate-κ O,O')-group: 1575 ν(C O and C C); 1517 ν(C C and

···

C O); 1281 (sh) and 1272 ν (C–CH ) and chelate deformations; 1196 δ(C–H from CH, plane)

s

3

and chelate deformations; 1006 (sh) chelate deformations and δ(C–CH , rocking); 937 ν (C–

3

as

CH ) and chelate deformations; 847 δ(C–H from CH, off-plane); 687 chelate deformations and

3

···

ν (Pd–O); 668 π(CH –C(O) C); 602 chelate deformations. TFP-group: 3147, 3124, 3084 ν(C–H

s

3

from Fur); 1549 ν(C=C from Fur) and ring deformations, 1580 ν(C=C from Fur) overlapped by

···

ν(C O and C C) from acac-group; 1226, 1216 and 1169 δ(C–H from Fur, plane) and ring

deformations, including ν(C–O–C, quasi ν ); 1138 and 1128 ν(C–O–C, quasi ν ) with ring

as

deformations and δ(C–H from Fur, plane); 1067 δ(C–H from Fur, plane) and ring deformations

including ν(C–O–C, quasi ν ); 1009 ring deformations and δ(C–H from Fur, plane); 911 ν(C–C

s

from Fur) and δ(C–H from Fur, off-plane); 907, 883, 859 ring deformations and δ(C–H from

Fur, off-plane); 768 ν(P–C); 786 (sh), 756 (sh), 723 δ(C–H from Fur, off-plane); 655, 643, 637

ring deformations, 589 ring deformations with δ(C–O–C). (BF )-group: 1079, 1053, 1035 ν (B–

4

as

F).

2

.3.6 Preparation of (acetylacetonate-κ O,O')bis(tri-2-thienylphosphine-κP)palladium(II)

tetrafluoroborate, [Pd(acac)(TTP) ]BF (TTP = tri-2-thienylphosphine) (8)

2

4

TTP (0.411 mmol, 3.2 mL of solution in 1,2-dichloroethane) was diluted in 10 mL of

CH Cl , and to this solution was added [Pd(acac)(MeCN) ]BF (0.0770 g, 0.206 mmol. The

2

4

reaction mixture was then stirred for 2 h at room temperature. The resulting yellow solution was

concentrated to 2 mL under vacuum. Addition of diethyl ether (7 mL) formed oily precipitate,

which was filtered and dried (1 h) under vacuum. The obtained powder was washed with toluene

(

2×10 mL), Et O (1×10 mL) and dried (8 h) under vacuum to afford complex 8 as a brown

2

powder (146 mg, 83.5%). Anal. Calcd for C H BF O P PdS : C, 40.83; H, 2.95 Found: C,

2

9

25

4

2

6

1

0

1

4

0.86; H, 3.02. H NMR (400 MHz, Acetone-d , 25°C): δ 8.12 – 8.05 (m, 6H, H_T_h_i₅) (Thi –

6

thienyl ring), 7.64 – 7.56 (m, 6H, H_T_h_i₃), 7.28 – 7.22 (m, 6H, H_T_h_i₄), 5.67 (s, 1H, H_a_c_a_c), 1.74 (s,

1

3

6

H, H ). C NMR (101 MHz, Acetone-d , 25°C): δ 186.96 (s, C_C_O_-_a_c_a_c), 139.73 (vt, J = 6.5 Hz,

Me 6

C_T_h_i₅), 136.79 (s, C_T_h_i₄), 128.99 (vt, J = 7.0 Hz, C_T_h_i₃), 127.21 (d, J = 70.5 Hz, C_T_h_i₂), 100.94 (s,

4

19

C_C_H_-_a_c_a_c), 25.41 (vt, J(P,C) = 5.5 Hz, C ). F NMR (376 MHz, Acetone-d , 25°C): δ −151.25,

Me

6

1

0

−151.30 (intensity ratio of approximately 20:80 corresponding to the natural abundances of

B

1

31

1

and B, respectively). P{ H} NMR (162 MHz, Acetone-d , 25°C): δ 3.83 (s). IR (nujol, NaCl

6

-1

2

···

plates, cm ): (acetylacetonate-κ O,O')-group: 1563 ν(C O and C C); 1519 ν(C C and C O);

282 (sh) and 1272 ν (C–CH ) and chelate deformations; 1200 δ(C–H from CH, plane) and

1

s

3

chelate deformations; 1011 chelate deformations and δ(C–CH , rocking) and thienyl ring

3

deformations; 937 ν (C–CH ) and chelate deformations; 845 (sh) δ(C–H from CH, off-plane);

as

3

···

6

84 chelate deformations and ν (Pd–O); 668 π(CH –C(O) C); 602 chelate deformations. TTP-

s 3

group: 3107, 3092, 3077 ν(C–H from Thi); 1494 and 1401 ν(C=C from Thi) and ring

deformations; 1332 δ(C–H from Thi, plane); 1226 (sh), 1218 and 1110 (sh) δ(C–H from Thi,

plane) and ring deformations; 1011 ring deformations and δ(C–H from Thi, plane) and acac-

chelate deformations; 914 δ(C–H from Thi, off-plane); 854 ν(C–S–C, quasi ν ) with ring

as

deformations and δ(C–H from Thi, off-plane); 806 ν(C–S–C, quasi ν ) with ring deformations

s

and δ(C–H from Thi, off-plane); 743, 698 δ(C–H from Thi, off-plane); 734 δ(C–H from Thi, off-

plane) and ν(C–S) with ν(P–C); 721 ν(P–C) with ν(C–S), 665, 648, 641, 637, 621, 618, 611, 596,

5

87 ring deformations; 572 ring deformations with ν(C–S–C). (BF )-group: 1100, 1052, 1036

4

ν_a_s(B–F).

2

.3.7 Preparation of (acetylacetonate-κ O,O')(2-dicyclohexylphosphino-2',6'-

dimethoxybiphenyl-κP)palladium(II) tetrafluoroborate, [Pd(acac)(SPhos)]BF , (SPhos =

4

2

-dicyclohexylphosphino-2',6'-dimethoxybiphenyl) (10)

SPhos (0.1693 g, 0.400 mmol) was dissolved in 10 mL of CH Cl , and to this solution

2

was added [Pd(acac)(MeCN) ]BF (0.1497 g, 0.400 mmol), forming a yellow solution. The

2

4

reaction mixture was then stirred for 2 h at room temperature. The resulting yellow solution was

concentrated to 4 mL under vacuum. Addition of diethyl ether (10 mL) followed by addition of

petroleum ether (6 mL) formed a precipitate, which was collected, washed with diethyl ether

(2×10 mL), and dried (8 h) under vacuum to afford complex 10 as a orange powder (274 mg,

1

9

7.3%). Anal. Calcd for C H BF O PPd: C, 52.97; H, 6.02. Found: C, 51.57; H, 5.98. H NMR

31

42

4

(

400 MHz, CDCl , 25°C): δ 8.28 – 8.15 (m, 1H, H ), 7.62 – 7.40 (m, 3H, H ), 6.80 – 6.66 (m,

3 Ari Ari

1

H, H ), 6.57 – 6.47 (m, 2H, H ), 5.26 – 5.22 (two peaks, 1H, H_a_c_a_c), 3.85 – 3.70 (two peaks,

Ari Ari

1

6

H, H_O_M_e), 2.27 – 2.16 (m, 2H, H ), 2.13 – 2.04 (m, 2H, H ), 1.93 (s, 3H, H ), 1.89 (s, 3H,

Cyi Cyi Me

1

3

H ), 1.85 – 1.62 (m, 9H, H ), 1.60 – 1.06 (m, 9H, H ). C NMR (101 MHz, CDCl , 25°C) δ

Me

Cyi

3

1

3

89.23 (d, J(C,P) = 3.5 Hz, C_C_O_-_a_c_a_c), 183.10 (s, C_C_O_-_a_c_a_c), 170.55, 147.77, 145.77, 145.60,

33.68, 133.20, 132.71, 131.28, 131.17, 128.71, 128.64, 105.03, 100.07 (s, C_C_H_-_a_c_a_c), 56.99,

5.69, 35.43, 29.72, 29.64, 28.32, 28.11, 27.16, 27.02, 26.99, 26.87, 25.79, 25.63, 25.60

19

[

observed complexity due to C−P coupling]. F NMR (376 MHz, CDCl , 25°C): δ −153.94,

3

1

0

−154.03 (intensity ratio of approximately 20:80 corresponding to the natural abundances of

B

1

31

1

and B, respectively). P{ H} NMR (162 MHz, CDCl , 25°C): δ 66.20 (s). IR (nujol, NaCl

3

-1

2

···

plates, cm ): (acetylacetonate-κ O,O')-group: 1573 ν(C O and C C); 1509 ν(C C and C O);

273 (sh) and 1281 (sh) ν (C–CH ) and chelate deformations; 1183 (sh) δ(C–H from CH, plane)

1

s

3

and chelate deformations; 1012 chelate deformations and δ(C–CH rocking); 958 ν (C–CH )

3

,

as

3

and chelate deformations; 841 δ(C–H from CH, off-plane); 668 chelate deformations and ν (Pd–

s

···

O); 663 π(CH –C(O) C); 604 chelate deformations. (SPhos)-group: 3095, 3071, 3034 ν(C–H

3

from CH, Ar); 1592, 1576, 1559, 1550, 1487, 1437 (sh), 1416 δ (O–CH ) and ν (C=C, Ar) and

s

3

as

aryl rings deformations; 1449 (sh) δ(C–H from CH , scissoring); 1341, 1337, 1330, 1296, 1208

2

δ(C–H from CH , Cy, wagging); 1258 ν (C–O–C ); 1189 (sh) δ(C–H, Ar, plane) and δ(O–CH

3,

2

as

Ar

rocking); 1172, 1115 (sh), 1110 (sh) δ(C–H from CH , Cy, twisting); 1161 δ(C–H, Ar, plane);

2

1

140 δ(O–CH rocking); 1057 ν (C–O–C ) and δ(C–H from CH , Cy, twisting) with ν(C–C,

3, as Ar 2

Cy) and cyclohexyl ring deformations; 1002 ν(C–C, Cy) and ν (C=C, Ar), with cyclohexyl and

s

aryl rings deformations; 989, 917, 896, 892, 886, 869 δ(C–H from CH , Cy, rocking); 934 δ(C–

2

H, Ar, off-plane) and δ(C–H from CH , Cy, rocking); 824, 767 (sh) aryl rings deformations; 821

2

cyclohexyl ring deformations; 778, 765, 757, 753, 746 δ(C–H, Ar, off-plane); 760 ν (P–C ,

as

Ar

Ar); 737 ν (P–C, Cy); 725 ν (P–C, Cy); 699, 695, 690, 686, 684, 681, 677, 674, 657, 655, 649,

as

s

6

45, 642, 638, 636, 632, 628, 623, 620, 613, 606 cyclohexyl and aryl rings deformations. (BF )-

4

group: 1097, 1053, 1036 ν (B–F).

as

2

.3.8 Preparation of (acetylacetonate-κ O,O')(2-dicyclohexylphosphino-2′,4′,6′-

triisopropylbiphenyl-κP)palladium(II) tetrafluoroborate, [Pd(acac)(XPhos)]BF , (XPhos

4

=

2-dicyclohexylphosphino-2′,4′,6′-triisopropylbiphenyl) (11)

XPhos (0.1966 g, 0.400 mmol) was dissolved in 10 mL of CH Cl , and to this solution

2

was added [Pd(acac)(MeCN) ]BF (0.1497 g, 0.400 mmol), forming a yellow solution. The

2

4

reaction mixture was then stirred for 2 h at room temperature. The resulting yellow solution was

concentrated to 4 mL under vacuum. Addition of diethyl ether (15 mL) formed a precipitate,

which was collected, washed with diethyl ether (2×10 mL), and dried (8 h) under vacuum to

1

2

afford complex 11 as a orange powder (270 mg, 87.7%). Anal. Calcd for C H BF O PPd: C,

38

56

4

2

1

5

9.35; H, 7.34. Found: C, 58.84; H, 7.54. H NMR (400 MHz, CDCl , 25°C): δ 7.84 – 7.74 (m,

3

1

H, H ), 7.63 – 7.48 (m, 2H, H ), 7.09 (s, 2H, H ), 6.72 – 6.65 (m, 1H, H ), 5.19 (s, 1H,

Ari

3

H_a_c_a_c), 3.03 (dq, J(H,H) = 6.7 Hz, 1H, (CH )CH), 2.46 – 2.27 (m, 4H, H +(CH )CH), 2.25 –

3

Cyi

3

2

.15 (m, 2H, H ), 2.11 – 1.99 (m, 2H, H ), 1.93 (s, 3H, H ), 1.87 – 1.77 (m, 4H, H ), 1.74

Cyi Cyi Me Cyi

3

(

s, 3H, H ), 1.70 – 1.56 (m, 6H, H ), 1.53 (d, J(H,H) = 6.8 Hz, 6H, (CH )CH), 1.33 (d,

Me Cyi 3

3

J(H,H) = 6.9 Hz, 6H, (CH )CH), 1.45 – 1.03 (m, 6H, H ), 0.90 (d, J(H,H) = 6.7 Hz, 6H,

3

Cyi

1

3

(

CH )CH). C NMR (101 MHz, CDCl , 25°C): δ 189.11 (d, J(C,P) = 3.5 Hz, C_C_O_-_a_c_a_c), 183.19

3 3

(s, C_C_O_-_a_c_a_c), 163.95, 158.25, 145.23, 145.07, 133.29, 132.91, 132.24, 132.09, 131.90, 131.44,

1

3

2

29.50, 129.43, 124.83, 104.37, 104.34, 100.24 (s, C_C_H_-_a_c_a_c), 39.92, 39.66, 37.78, 37.53, 34.60,

2.85, 29.08, 29.06, 28.82, 28.79, 27.78, 27.70, 27.31, 27.21, 27.18, 27.09, 25.71, 25.49, 25.17,

1

9

3.10 [observed complexity due to C−P coupling]. F NMR (376 MHz, CDCl , 25°C): δ

3

−154.32, −154.37 (intensity ratio of approximately 20:80 corresponding to the natural

1

0

11

31

1

abundances of B and B, respectively). P{ H} NMR (162 MHz, CDCl , 25°C): δ 61.43 (s).

3

-1

2

···

IR (nujol, NaCl plates, cm ): (acetylacetonate-κ O,O')-group: 1564 ν(C O and C C); 1514

···

ν(C C and C O); 1270 ν (C–CH ) and chelate deformations and ν (C–CH , i-Pr from XPhos);

s

3

s

3

1

193 δ(C–H from CH, plane) and chelate deformations; 1007 chelate deformations and δ(C–

CH₃_,rocking) and δ(C–CH₃_,rocking, i-Pr from XPhos); 938 ν (C–CH ) and chelate

as

3

deformations and ν (C–CH , i-Pr from XPhos); 843 δ(C–H from CH, off-plane); 670 chelate

s

3

···

deformations and ν (Pd–O); 663 π(CH –C(O) C); 602 chelate deformations. (XPhos)-group:

s

3

056, 3045 ν(C–H from CH, Ar); 1604, 1571, 1540, 1490, 1422 (sh), 1419 (sh) ν (C=C, Ar) and

as

aryl rings deformations; 1447 (sh) δ(C–H from CH , scissoring); 1356 δ(C–CH i-Pr); 1326,

2

3,

1

316, 1303, 1296, 1248, 1242, 1228 δ(C–H from CH , Cy, wagging); 1213 ν(C–C from i-Pr) and

2

δ(C–H from CH , Cy, wagging); 1183, 1162, 1136, 1115, 1087 δ(C–H from CH , Cy, twisting);

2

1

176, 1153 δ(C–H, Ar, plane); 1047 ν(C–C, Cy) and cyclohexyl ring deformations and δ(C–H

from CH , Cy, twisting); 1028 ν (C=C, Ar) and ring deformations; 1002 ν(C–C, Cy) and ν (C=C,

2

s

Ar), with cyclohexyl and aryl rings deformations; 995, 905, 895, 889, 880, 853 δ(C–H from CH₂,

Cy, rocking); 931, 920 δ(C–H, Ar, off-plane) and δ(C–H from CH , Cy, rocking); 874 δ(C–H,

2

Ar, off-plane); 822, 797 aryl rings deformations; 840, 816 cyclohexyl ring deformations; 772,

7

6

54 δ(C–H, Ar, off-plane); 746 ν(P–C , Ar); 732 ν (P–C, Cy); 722 ν (P–C, Cy); 710, 707, 702,

Ar as s

93, 688, 684, 681, 677, 659, 656, 652, 648, 642, 638, 630, 622, 616, 613, 608 cyclohexyl and

aryl rings deformations. (BF )-group: 1091, 1051, 1034 ν (B–F).

4

as

1

3

2

.4 Calculations

All density functional theory calculations were performed with the ORCA program [34].

All geometry optimizations were run with tight convergence criteria, using the BP86 functional

[

35,36], making use of the resolution of the identity technique [37]. The applicability of gradient-

corrected functionals as BP86 for the structural prediction of transition metal compounds and

reliable determination of the kinetic balance are well documented [38–43]. The basis sets that

were used were the Weigend−Ahlrichs basis sets [44,45]. Triple-ξ-quality basis sets with one set

of polarization functions (def2-TZVP) were used for the palladium and phosphorus in

connection with effective core potentials for Pd. The remaining atoms were described by slightly

smaller def2-SVP basis sets.

2

.5 X-ray crystallographic studies

Data were collected on a BRUKER D8 VENTURE PHOTON 100 CMOS diffractometer

with MoK radiation (λ = 0.71073 Å) using the φ and ω scans technique. The structures were

α

solved and refined by direct methods using the SHELX [46]. Data were corrected for absorption

effects using the multi-scan method (SADABS) [47]. All non-hydrogen atoms were refined

anisotropically using SHELX [46]. The coordinates of the hydrogen atoms were calculated from

geometrical positions. Crystal data and experimental details are given in Table 1. Selective bond

lengths, bond angles and torsion angles are given in Table S.1 and S.2 (Electronic

Supplementary Information). Table 1 contains CCDC reference number of the supplementary

crystallographic data for this paper. These data can be obtained free of charge from The

Cambridge Crystallographic Data Centre via http://www.ccdc.cam.ac.uk

1

4

Table 1 – X-ray crystallographic data for compounds 2 and 3.

CCDC number

1997255

1997258

Empirical formula C H O P Pd, BF

C H O P Pd, BF

41

49

2

4

41 61

2

4

Formula weight /

g·mol

-1

828.95

841.04

Crystal system

Space group

a / Å

b / Å

c / Å

Orthorhombic

Pbca

12.6876(5)

18.0564(8)

34.6284(13)

monoclinic

P 2(1)/n

11.6277(7)

15.6915(10)

23.0400(15)

α, β, γ / ˚

Volume / Å

Z

90.00, 90.00, 90.00

7933.1(6)

8

90.00, 98.984(2), 90.00

4152.2(5)

4

3

Density

(

calculated) /

1.388

1.345

-3

g·cm

Absorptions

coefficient / mm

-1

0.601

0.575

Radiation (λ / Å)

Temperature / K

MoKα (0.71073)

296(2)

MoKα (0.71073)

296(2)

2

Θ range / °

2.29 – 28.31

0.36 × 0.31 × 0.14

yellow, prism

3424

2.27 – 27.00

Crystal size / mm

Crystal habit

F(000)

0.28 × 0.11 × 0.10

yellow, prism

1760

-

16<=h<=16, -24<=k<=23,

46<=l<=46

-14<=h<=14, -19<=k<=20,

-29<=l<=29

Index ranges

Reflections

collected

Independent

reflections

7

9

4

0

4643

92634

847 [R(int) = 0.0488]

62

9042 [R(int) = 0.0747]

462

Number of ref.

parameters

R / wR [I >

1

2

.0498 / 0.1131

0.0617 / 0.1260

0.0837 / 0.1345

1.267

2

σ(I)]

R / wR (all data) 0.0760 / 0.1253

1

2

Goodness-of-fit on

2

1.086

F

Completeness [%] 99.8

Largest diff. peak

99.9

-3

and hole / e·Å

0.752/ -0.875

0.463/ -0.674

2

w=1/[σ (F )+(0.0504P) +11.5385P] w=1/[σ (F )+(0.0000P) +15.2241P]

o

Weight scheme

2

where P=(F +2F )/3

o

c

o c

1

5

3

Results and Discussion

.1 Synthesis of Palladium(II) Complexes.

The Pd-complexes used as precatalysts are shown in Figure 3. We report here the

synthesis of the new cationic acetylacetonate palladium complexes 2, 3, 5–8, 10, 11, while 1, 4, 9

are a known compounds. The new compounds were fully characterized by NMR and FTIR

spectroscopy as well as elemental analysis.

Figure 3 – Top: synthesis of cationic acetylacetonate palladium complexes (1–11) with

phosphine ligands (L). Bottom: phosphine ligands used (L1–L11)

The

synthesis

of

the

complexes

1–9

was

achieved

by

reacting

bis(acetonitrile)(acetylacetonate)palladium(II) tetrafluoroborate with two equivalents of L1–L9

in dichloromethane which led to the formation of [Pd(acac)(L) ][BF ] (1–9) as depicted in

2

4

Figure 3. Two phosphines coordinate to the palladium(II) centre, replacing the labile acetonitrile

ligands. In the case of bulky XPhos and SPhos ligands [Pd(acac)(MeCN) ][BF ] reacted with

2

4

1

equiv of the PArCy giving monophosphine complexes [Pd(acac)(L)][BF ] (10, 11). It is most

2 4

likely that in these molecules the ipso-carbon of the diisopropylphenyl or dimethoxyphenyl rings

1

9

from L10, L11 occupies the fourth coordination site of the Pd atom [48–50]. In particular, δ F

−

NMR signals for [BF ] in 10 and 11 are −154.0 and −154.3 ppm, respectively, indicating that

4

tetrafluoroborate anion is non-coordinating in CDCl solutions of the complexes [51–53].

3

In most cases coordination of the phosphines caused a downfield shift Δ(δ_c_o_m_p_l_e_x− δ_l_i_g_a_n_d

)

3

1

of the P{ H} NMR signals in the range of 39.2 to 74.8 ppm (Table 2). In contrast, complexes 5,

31

1

6

with P(NMe ) and P(NEt ) have P{ H} NMR chemical shifts at higher field, by about

2 3 2 3

3

0 ppm, compared with the signals of the free ligands. As was observed for platinum complexes

1

6

with κP ligands bearing electronegative substituents [54], this effect reflects the increase in

electron density at the phosphorus atoms, which is presumably due to the p (N)-σ*(P) interaction

π

as well as the palladium-phosphorus backbonding, which is expected to increase with increasing

electronegativity of the substituents at phosphorus.

3

1

Table 2 – P{ H} Chemical Shift of the Cationic Phosphine-Pd-acac Complexes and

Coordination Induced Shifts Δ for the Complexes

3

1

31

1

31

1

Free ligand δ P{ H} chemical Complex δ P{ H} chemical

shift, ppm shift, ppm

Δ( P{ H})

(δ_c_o_m_p_l_e_x− δ_l_i_g_a_n_d), ppm

PCyPh₂

−3.9 [55] 2

2.7 [55] 3

35.8

41.9

90.8

93.7

−18.3

3.8

39.7

39.2

−31.9

−24.3

56.9

49.4

74.8

72.9

PCy Ph

2

P(NMe₂)₃

P(NEt₂)₃

TFP

TTP

SPhos

XPhos

122.7 [56] 5

118.0 [57] 6

−75.2 [58] 7

−45.6 [59] 8

−8.6 [49] 10

−11.5 [60] 11

66.2

61.4

1

13

Generally, the δ values obtained from H and C NMR spectra of 2, 3, 5–8, 10, 11 are

consistent with NMR data for the ligands or the corresponding transitions metal complexes

1

[

49,55–58,60–63]. The H NMR spectra of 2, 3 show signals at 2.02 and 2.04 ppm for the

methyl-group of the acac ligand non-shielded by phenyl aromatic ring current, indicating the

location of phenyl substituents mainly within ∠P-Pd-P. In contrast, for 7 and 8 the acac-methyl

1

groups signals in H NMR spectra are at 1.83 and 1.74 ppm (shielded by heteroaromatic rings,

cf. the same group signal for [Pd(acac)(PPh ) ]A (A = BF , CF SO , ClO ) is around 1.5 ppm

3

2

4

3

4

[

52,64]).

The formation of the monophosphine complexes 10, 11 was evident from the distinctive

proton signal resonances at 1.93 (10), 1.93 (11) and 1.89 (10), 1.74 (11) ppm (the last two

1

shielded by aromatic ring current) from CH -group of acac ligand in the H NMR spectrum. In

3

1

3

1

addition, the C{ H} NMR spectrum revealed the appearance of diagnostic carbon peaks of acac

3

ligand [189.23 or 189.11 (d, J= 3.5 Hz)] and [183.10 or 183.19 (s)] for carbonyl, which were

split by the adjacent PCy moiety of SPhos or XPhos ligand in the trans- and cis-position,

2

respectively.

The NMR spectra of compounds 5 and 6 suggest that it exist in two isomeric forms in

1

13

solution. In particular, the H and C NMR spectra of 5 display two distinct set of resonances in

methyl group region. The resonances at δ 2.76 (d, J = 9.6 Hz, NCH ) and 38.76 (vt, J = 3.8 Hz,

3

NCH ) are due to the major isomer while those at δ 2.80 (vt, J = 5.1 Hz, NCH ) and 39.35 (vt, J

3

1

=

3.8 Hz, NCH ) are assigned to the minor isomer. Consistent with this the P{ H} NMR

3

spectrum of 5 displays a singlet at δ 90.81 for the major isomer and singlet δ 85.04 for the minor

1

7

isomer in 5:1 intensity ratio. We assume that the isomers observed in solution are due to two

different coordination geometries at nitrogen (pyramidal and planar) in the six NMe groups in

2

two coordinated molecules of P(NMe ) . Previously it was shown that the ground state of

2

3

P(NMe ) has C symmetry, with two different coordination geometries at the nitrogen atoms

2

3

s

[

65,66].

3

.2 X-ray Crystal Structures of 2 and 3

Single crystals of 2 and 3 suitable for X-ray crystallography were obtained by slow

diffusion of mixture of petroleum ether and diethyl ether into 1,2-dichloroethane solutions of the

complexes. Complexes 2 and 3 contain a four-coordinate palladium(II) centre with a non-

−

coordinating [BF ] anion.

4

The solid-state molecular structure of 2 is depicted in Figure 4 with selected inter-atomic

distances and angles listed in the figure caption. The Pd–P bond lengths of 2.2835(8) and

2

.2766(9) Å are typical for cationic palladium(II) acetylacetonate complexes [22,28,64,67,68],

but slightly shorter when compared to trans-[PdCl (PPh Cy) ], having a Pd–P bond length of

2

.3256(10) Å [69].

Figure 4 – Molecular structure of [Pd(acac)(PCyPh ) ]BF (2) with atoms represented by thermal

2

4

vibration ellipsoids of 50% probability. Details of the structure refinement are given in Table 1.

Selected bond distances (Å) and angles (°):Pd1-O1 = 2.050(2), Pd1-P1 = 2.2835(8), Pd1-O2 =

2

.051(2), Pd1-P2 = 2.2766(9), ∠O2-Pd1-O1 = 89.97(10), ∠P2-Pd1-P1 = 98.97(3).

1

8

The complex 2 has a distorted square planar geometry for palladium, shown by the ∠O2-

Pd1-O1, ∠P2-Pd1-P1, ∠O1-Pd1-P2 and ∠O1-Pd1-P1 bond angles of 89.97(10)°, 98.97(3)°,

8

9.23(8)° and 170.25(8)° respectively. The average P-C bond distance of 1.845 Å (cyclohexyl

moiety) is somewhat longer than the bond distances for the phenyl moieties, where l(P-C) =

.814 Å. The C-C bond distances in the phenyl rings agree well with the expected value; the

1

cyclohexyl ring has a normal chair conformation. Analysis of the bond lengths and angles of

−

[

BF ] ion (Table S.1) showed distortion of the idealized tetrahedral geometry (e.g. l(B1-Fi) =

4

−

1

.305…1.376Å). In addition short contacts between the fluorine atoms of [BF ] and the

4

hydrogens of the phenyl rings (F…H-C, 2.5Å) are observed in the crystallographic packing of 2,

−

thus presumably forming weak C-H...F hydrogen bonds. Such short contacts between [BF₄]

ions and the hydrogen atoms of the phenyl rings in the crystal structures of transition metal

complexes are known in the literature [70]. Moreover, distortion of idealized tetrahedral

−

geometry of the anion [BF ] leads to appearance in the IR spectrum of 2 the symmetric

4

–

1

stretching vibration at 782 cm , forbidden in the infrared absorption spectrum. The same

infrared spectral feature was reported for the cationic palladium complexes with coordinated

secondary amines, where hydrogen bonding between the NH group of morpholine ligand and

−

[

BF ] anion was observed [29].

4

The results of the X-ray crystal structure analysis of 3 are shown in Figure 5. The main

structural features of 3 appear close to those for 2. The structure of 3 is a four-coordinate

palladium(II) complex with two phosphines and one acetylacetonate ligand coordinated to the

palladium centre. The complex has a distorted square planar geometry as shown by the ∠O2-

Pd1-O1, ∠P2-Pd1-P1, ∠O1-Pd1-P2 and ∠O1-Pd1-P1 bond angles of 89.96(14)°, 102.94(5)°,

1

72.15(11)° and 84.60(11)° respectively; the P2-Pd1-P1 angle is larger than in complex 2. To

gain more insight into the structure of the cationic species, we performed DFT (BP86)

+

calculations for the ions [Pd(acac)(PCyPh ) ] and [Pd(acac)(PCy Ph) ] in gas phase, hence,

2

free from the influence of crystal packing or intermolecular interactions. Within the limits of the

basis set employed, the optimized geometries were good representation of the structures obtained

from the crystallographic studies. Calculated molecular models showed ∠P-Pd-P of 100.52° and

1

06.04° for the cationic species 2 and 3, respectively. Consequently, the P2-Pd1-P1 angle for 3 is

larger than in complex 2 mainly due to the steric bulk of the cyclohexyl groups.

1

9

Figure 5 – Molecular structure of [Pd(acac)(PCy Ph) ]BF (3) with atoms represented by thermal

2

4

vibration ellipsoids of 50% probability. Details of the structure refinement are given in Table 1.

Selected bond distances (Å) and angles (°): Pd1-O1 = 2.068(3), Pd1-P1 = 2.2805(13), Pd1-O2 =

2.053(3), Pd1-P2 = 2.2927(13), ∠O2-Pd1-O1 = 89.96(14), ∠P1-Pd1-P2 = 102.94(5).

3

.3 Catalytic Studies

The cationic palladium complexes 1-11 (Figure 3) with monodentate phosphine ligands

varying steric bulk at the coordinating atoms, and their electronic properties were tested in the

telomerization of 1,3-butadiene with MeOH. The conditions used are 70°C, 2 h, 0.0167 mol% of

catalyst vs butadiene to evaluate their overall productivity and selectivity to the linear product.

The reaction was performed in the presence of an excess of nucleophile relative to the diene

(

[MeOH] :[BD] = 1), so TON is based on butadiene conversion. As shown in Table 3, the

0 0

selectivity and BD conversion largely depended on the nature of the catalyst. As might be

expected from published telomerization results by Beller et al. [11] using an in situ catalyst

mixture [Pd(OAc) /nPPh ], the addition of triethylamine as base has no positive influence on the

2

3

product selectivity or on the catalyst productivity with complex 1 as precatalyst (entries 1–3,

Table 3). So the other complexes were tested using base-free conditions.

2

0

Table 3 – Influence of the Nature of Catalyst on Conversion and Selectivity.

Selectivity, mol%

OCT

3-MOD 1-MOD mol%

16.3

Chemo,

a

^C^oⁿ^v^.b

d

e

f

Entry Pd

c

n/iso E/Z TON

BD %

1

2

3

4

5

6

7

8

9

1

2

3

4

5

6

7

8

9

10

11

12

96.2

6.1

5.2

5.5

5.6

5.8

0.2

0.0

1.6

4.3

4.9

3.8

8.3

7.8

9.1

7.7

0.7

77.6

78.8

80.0

75.9

78.3

4.5

83.7

84.0

85.5

81.5

84.1

4.8

13

15

13

18

—

17

21

18

25

8

12 5800

11 8200

12 8700

18 5800

55 5700

9

11

10

g

68.4

72.7

96.7

95.1

0.1

16.0

14.5

18.5

15.8

95.3

97.3

71.8

6.1

6.6

1.8

26.6

16.0

48.1

3.4

h

5

20

10

0.3

0.1

2.7

26.7

89.5

88.6

94.5

65.2

76.2

42.7

88.9

31.2

28.2

93.9

93.4

98.2

73.5

84.0

51.9

96.6

32.0

17.0

36.3

86.2

6.0

94.7

0.1

12 1000

10 2200

39 5200

0

1

2

3

4

5

6

13

400

i

10

5

12

42

24 5700

8

14

11

5

900

30

j

14.3

0.5

k

1

68.0

a

Reaction conditions: t = 70 °С, 0.0167 mol% of Pd, [BD] /[Pd] = 6000,

0

[

2

MeOH] /[Bd] = 1, n = 6.5 μmol, dichloromethane, V

= 0.5 mL, reaction time –

0

Pd

DCM

b

c

h. 1,3-Butadiene conversion. Chemoselectivity = (1-MOD + 3-MOD)(1-MOD +

−

1

d

−1

3

-MOD + OCT + VCH) . Regioselectivity = (1-MOD)(3-MOD) .

e

−1 f

Stereoselectivity = (trans-1-MOD)(cis-1-MOD) . In units of (mol of BD) (mol of

−

1 g

h

Pd) . 0.0087 mol% of Pd, n = 6.5 μmol, [BD] /[Pd] = 12000. 0.0087 mol% of

Pd, n = 6.5 μmol, [BD] /[Pd] = 12000, 133 eq. of NEt per Pd was added. 1 eq. of

Pd

0

i

Pd

0

3

j

k

SPhos per 10 was added. 1 eq. of XPhos per 11 was added. Catalyst mixture

Pd(acac)(MeCN) ]BF (12)/1PPh were used

[

2

4

3

As one can see from Table 3, for phosphine-ligated complexes catalytic productivity

under the same conditions decreased in the following order: 1, 2, 3, 9 > 8 > 7 > 10 > 4, 5, 6, 11.

The order of decreasing catalytic productivity by these catalysts can be attributed to decreasing

steric bulk in the coordination sphere of the metal and reducing basicity of the phosphine ligands

containing (hetero)aryl moieties (by means of Tolman’s parameters, see Table 4). Complexes 4–

6

with tricyclohexylphosphine and triaminophosphines were not suitable for this telomerization

reaction (entries 6–8, Table 3). For 5 and 6 the presence of phosphorus and nitrogen as chelating

atoms might entail too strong coordination to the metal, inhibiting the catalytic activity [71].

Low conversion was also observed in the presence of 10 and 11 containing “Buchwald-type”

phosphines (entries 12 and 14). However, when 1 eq. of SPhos or XPhos was added to the

reaction mixture, conversion of BD was observed with concomitant formation of products

(entries 13, 15; Table 3). It should be noted that complexes 10 and 11 contain one phosphorus

atom in the coordination sphere of the transition metal and direct comparison of their catalytic

activity with those for complexes 1–9 is not entirely correct. Moreover the catalyst prepared

in situ from the [Pd(acac)(MeCN) ]BF and 1 eq. of PPh was also not active (entry 16, Table 3).

2

4

3

2

1

Thus, it seems that in order to obtain effective telomerization catalysts based on cationic

acetylacetonate palladium (II) complexes, it is required to use [P] :[Pd] ≥ 2.

0

Table 4 – Tolman’s Steric (Cone Angle) and Electronic (ν ) Properties of Phosphines.

CO

a

−1 b

Complex

Phosphine ligand (L)

PPh

PCyPh

PCy Ph

PCy

P(NMe

Cone angle [°]

145

153

162

170

ν(CO) [cm ]

2068.9

2064.8

2060.6

2056.4

2061.9

2060.3

2078.3

–

1

2

3

4

5

6

7

8

9

3

2

3

)

3

157

108

2

P(NEt

TFP

)

2 3

133 [72]

–

176 [73]

204 [74]

173 [74]

TTP

TOMPP

SPhos

2058.3

–

2059 [75]

1

0

1

XPhos

a

b

Ref. [76]. The stretching frequencies ν(CO) of the terminal CO of [Ni(CO) L] in CH Cl ,

3

2

directly measured or estimated values using Tolman’s equation from ref. [76]

By contrast, complexes 1, 2, 3, and 9 are the most productive catalysts of the series,

showing nearly complete conversions. Among the various complexes tested 9 is the more

chemoselective catalyst (entry 11, Table 3), yielding 98% of telomers (with 96% of 1-MOD, the

linear to branched telomers ratio is n/iso = 25/1, trans-/cis- telomers ratio is 39). The results for 9

are close to those found by van Leeuwen et al [15] using Pd(TOMPP)(dvd) (dvd —

2

tetramethyldivinyldisiloxane). Under identical conditions, the catalyst prepared from precursor 2

yielded 81.5% of octadienyl ethers (linear to branched telomers ratio is 13, trans-/cis- telomers

ratio is 18). Remarkably, in the presence of 3 significantly improved trans- to cis-1-

methoxyocta-2,7-diene ratio (98.2% of trans-1-MOD) was obtained (entry 3, Table 3). Catalytic

mechanism of the palladium/phosphine-catalyzed telomerization of 1,3-butadiene with methanol

has been carefully studied by Jolly [77–79] and extended by mechanistic [14,16,80] and DFT

studies [81,82]. It is supposed that under telomerization conditions, active Pd(0) species can be

formed from cationic complexes (Figure 6). In our opinion the observed stereoselectivity in

favor of the trans-linear product is determined by the stability of the intermediates II, III or V

obtained after oxidative coupling of two 1,3-butadiene molecules at the palladium to form the

3

bisallyl complex or after protonation of II to form η -allylpalladium methoxide complexes

(Figure 6).

2

Figure 6 – Mechanism of the Telomerization Reaction

Next, the most interesting precatalysts 3 and 9 were studied under different reaction

conditions, such as palladium concentration, [MeOH] /[BD] ratio, and temperature. Whatever

0

the reaction conditions, some amounts of vinylcyclohexene as a result of Diels-Alder reaction

were detected (>1%). In the case of 3 at 50°C, when only 0.0021 mol% of Pd loading is used,

higher selectivity is obtained compared to the results at higher temperatures, but turnovers do not

exceed 18200 (chemoselectivity up to 94%; entry 18, Table 5). When Pd loading was decreased,

the conversion of BD as well as selectivity substantially droped (entries 19, 20; Table 5). But in

the case of low [MeOH] /[BD] ratios (0.5 instead of 1.0) BD conversion and the selectivity

0

enhanced (TON = 4400 with [MeOH] /[BD] = 1.0 and TON = 38500 with [MeOH] /[BD] =

0

.5; entries 19 and 22, Table 5). Better catalyst performance was observed at lower

substrate:catalyst ratio. In this case, a high catalyst productivity (TON up to 60 000) is achieved

2

3

with 0.0017 mol% of Pd vs BD (entry 21, Table 5). Improvement of catalyst performance at low

methanol concentration have been previously reported for Pd-based catalyst systems containing

triarylphosphines [15,16]. However at 90°C, the conversion of butadiene and the selectivity

decreases, showing that the catalyst formed from 3 is unstable at high temperatures. Similar

trends were observed in the presence of isolated cationic complex 9. Remarkably, in the presence

of 9 improved linear to branched telomers ratios and chemoselectivities were obtained. Using 9

n/iso ratios >27:1 were achieved. Finally, with a [BD] /[Pd] ratio of 96000:1 a modest

0

conversion was achieved (entry 26, TON = 20 200).

Table 5 – Influence of the Catalyst Concentration and Temperature on Conversion and

Selectivity.

a

[BD]

Pd]₀

0

/

t, Conv.

°C BD %

Selectivity, mol%

OCT 3-MOD 1-MOD mol%

Chemo,

d

e

f

Entry

Pd

b

c

n/iso

E/Z TON

[

1

2

7

8

9

0

1

2

3

4

5

6

3

9

24000 50

48000 50

96000 70

960000 70

60000 70

96000 70

48000 90

48000 70

96000 70

88.5

38.0

4.6

5.9

4.7

9,7

0.1

5.3

5.2

4,9

0,4

5,2

5,1

5,3

2,9

3,1

3,0

88.8

89.1

71,2

0,7

71,0

67,6

62,1

84,1

86,8

81,4

94.1

94.3

76,1

1,1

76,2

72,7

67,4

87,0

89,9

84,4

17 109 21200

17

14

2

14

13

12

29

28

27

87 18200

25 4400

g

h

7.7

16 74000

46 60000

35 38500

32 30800

22 11600

19 10600

19 20200

99.9 23,8

40,1 25,1

64,1 28,3

24,1

11,0 10,1

21,0 9,2

7,6

h

2

a

Reaction conditions: n = 78 mmol, [MeOH] /[Bd] = 1, dichloromethane, V = 0.5 mL, reaction

BD

0

DCM

b

c

time – 16 h. 1,3-Butadiene conversion. Chemoselectivity = (1-MOD + 3-MOD)(1-MOD + 3-MOD +

OCT + VCH) . Regioselectivity = (1-MOD)(3-MOD) . Stereoselectivity = (trans-1-MOD)(cis-1-

MOD) . In units of (mol of BD) (mol of Pd) . Reaction time – 160 h. [MeOH] /[Pd] = 48·10 .

−

1

d

−1 e

−

1

f

−1 g

h

3

0

4

Conclusions

We have synthesized eight new cationic acetylacetonate palladium complexes

[

Pd(acac)(L) ][BF ] (n = 2: L = PCyPh , PCy Ph, P(NMe ) , P(NEt ) , tri-2-furylphosphine, tri-

n

4

2

2 3

2

-thienylphosphine; n = 1: L = SPhos, XPhos) by the reaction of [Pd(acac)(MeCN) ][BF ] with 2

2 4

equiv. or 1 equiv. of L. Two palladium(II) complexes have been characterized by X-ray

crystallography. The catalytic potential of [Pd(acac)(L) ][BF ] (L – monodentate phosphine

n

4

ligands) is demonstrated in the industrially important telomerization of 1,3–butadiene with

methanol under base-free conditions. Complexes with phosphines containing (hetero)aryl

moieties catalyzed formation of methoxyocta-2,7-dienes. The other studied palladium complexes

showed substantially lower activities. Complexes [(acac)Pd(PCy Ph) ]BF

and

2

4

[

(acac)Pd(TOMPP) ]BF is highly active for catalytic telomerization. Under optimal conditions

2

4

2

4

in the presence of only 0.001–0.0025 mol% palladium loading the desired telomers were

obtained with chemoselectivities of 76–98 % and TON up to 60000 mol BD per mol Pd. Though

the present research were limited to the telomerization of 1,3-butadiene with methanol, we

believe these novel precatalyst have a broad potential for a variety of other catalytic applications,

too.

Electronic Supplementary Information available: XRD, NMR, FTIR spectral data and

results.

Acknowledgements

This research was supported by the Russian Science Foundation (project No 19-73-

0

0046). The studies were carried out using the equipment of the Baikal Analytical Center of

Collective Use SB RAS (http://ckp-rf.ru/ckp/3050/) as well as the equipment of the Center for

Collective Use of Analytical Equipment of the Irkutsk State University (http://ckp-

rf.ru/ckp/3264/).

.

2

5

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Cationic palladium(II)–acetylacetonate complexes containing phosphine and aminophosphine ligands and their catalytic activities in telomerization of 1,3-butadiene with methanol

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