Pd(II) and Pt(II) complexes of cyclic bidentate (S)PNP(S) ligands: Synthesis, structure and catalytic activity in the Suzuki reaction

Article abstract of DOI:10.1016/j.ica.2012.11.005

The synthetic approach to the novel cyclic (S)PNP(S) ligands (5a-c, R = EtO, Me, Ph), i.e. 1-thiophosphoryl-2-thioxo-1,2-azaphospholanes having different surrounding at the exocyclic phosphorus atom, has been developed. Compounds bearing two asymmetric ph

Full text of DOI:10.1016/j.ica.2012.11.005

Inorganica Chimica Acta 395 (2013) 203–211
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Pd(II) and Pt(II) complexes of cyclic bidentate (S)PNP(S) ligands: Synthesis,
structure and catalytic activity in the Suzuki reaction
Inga M. Aladzheva a, Olga V. Bykhovskaya a, Yulia V. Nelyubina a, Zinaida S. Klemenkova a,
Oleg I. Artyushin a, Pavel V. Petrovskii a, Andrei A. Vasil’ev b, Irina L. Odinets a,
⇑
a A.N. Nesmeyanov Institute of Organoelement Compounds, Russian Academy of Sciences, Vavilova str. 28, Moscow 119991, Russia
b N.D. Zelinsky Institute of Organic Chemistry, Russian Academy of Sciences, 47 Leninsky prosp., 117913 Moscow, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
Received 25 May 2012
The synthetic approach to the novel cyclic (S)PNP(S) ligands
(5a–c, R = EtO,
PhP(S)(CH2)3NP(S)(R)(Ph)
Received in revised form 13 September 2012
Accepted 11 November 2012
Available online 19 November 2012
Me, Ph), i.e. 1-thiophosphoryl-2-thioxo-1,2-azaphospholanes having different surrounding at the exocy-
clic phosphorus atom, has been developed. Compounds bearing two asymmetric phosphorus atoms were
obtained as individual (R⁄,R⁄)- and (R⁄,S⁄)-diastereomers. Reacting with (PhCN)2MCl2 (M = Pd, Pt) in MeCN
under ambient conditions the ligands readily form complexes MLCl2 [6a–c (M = Pd), 7b (M = Pt)] via
bidentate chelating coordination mode. The structures and stereochemistry both of the ligands and their
complexes were confirmed by IR, multinuclear NMR and X-ray diffraction study. The palladium com-
plexes demonstrated high activity as precatalysts for the Suzuki cross-coupling reaction, which was
found to increase in the series 6a < 6b < 6c.
Keywords:
1-Thiophosphoryl-2-thioxo-1,2k5-
azaphospholane
Diastereomer
Palladium
Ó 2012 Elsevier B.V. All rights reserved.
Platinum
Complex
Catalysis
1. Introduction
or their alkaline metal salts with transition metal precursors lead
to the formation of the complexes containing the corresponding
Bidentate (X)PNP(X) ligands (X = lone pair, O, S, Se) and their
complexes with a variety of metals are the subject of intensive
studies for decades due to the range of practically useful properties
[1]. Thus, the ligands bearing pentavalent (thio)phosphoryl groups
can be used as selective metal extractants [2], lanthanide
complexes of O,O-imidodiphosphinates possess high luminescent
properties [3] and find application as NMR shift reagents [4],
whereas their silver and palladium ones are promising for
homogeneous catalysis [5]. Furthermore, Pd(II) complexes of triva-
lent phosphorus PNP ligands such as N-diphenylphosphino-N-fur-
furylamine and N,N-bis(diphenylphosphino)-N-furfurylamine [6],
N,N,N0,N0-tetrakis(diphenylphosphino)ethylenediamine [7], and
tris{2-(N,N-bis(diphenylphosphino)aminoethyl)amine} [8], were
found to be active catalysts in the Suzuki cross-coupling and Heck
reaction.
[(X)PR2]2Nꢀ anion such as for example bis(bidentate) chelate com-
plexes [M{(XPR2)2N}2] (X = O, S, Se) with Pd(II), Pt(II) and Ni(II)
[1,9,10]. Only one palladium complex [Pd{(SPPh2)2NH}Br2] con-
taining a neutral NH ligand has been reported [11]. Moreover,
the complexes with neutral ligands [1a,11] are unstable com-
pounds quantitatively converted to the complexes with the anionic
ligand. However, if a ligand contains other substituent instead of
the hydrogen, for example [Ph2P]2N-Alk [6–8] or [Ph2P(S)]2-
NCH(Me)COOR [12], they provide the corresponding complexes
with neutral ligands possessing X,X-bidentate coordination mode.
Taking into account that even small variations in the ligand
structure can cause significant changes in their coordination
behavior and the properties of the resulting complexes, recently
we have developed the convenient synthesis of 1-(thio)phos-
phoryl-2-oxo-1,2k5-azaphospholanes being the first cyclic biden-
tate (O)PNP(X) ligands. The general synthetic procedure is based
on the intramolecular Arbuzov reaction of N,N-bis-P(III)-substi-
tuted 3-bromopropylamines, [R(R’O)P]2NCH2CH2CH2Br, generated
in situ followed by the oxidation or intermolecular Arbuzov reac-
tion (X = O) or sulfur addition (X = S) [13]. These compounds lack-
ing hydrogen at the nitrogen atom and having rigid cyclic skeleton,
were of undoubted interest as neutral ligands for transition metals.
Noteworthy, all (X)PNP(X) ligands derived before the beginning
of our investigations present the acyclic compounds bearing
mostly the NH linking group. Typically, reactions of such ligands
⇑
Corresponding author. Tel.: +7 499 135 9356.
E-mail address: odinets@ineos.ac.ru (I.L. Odinets).
0020-1693/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.ica.2012.11.005

204
I.M. Aladzheva et al. / Inorganica Chimica Acta 395 (2013) 203–211
Indeed, the corresponding O,O-derivatives were found to form sta-
ble complexes with f-elements (uranyl and lanthanide nitrates)
which structure depended on the ligand nature and, in some cases,
on the experimental conditions [13,14].
4JPC = 2.9 Hz, Cp), 131.84 (d, 4JPC = 2.9 Hz, Cp), 132.26 (d, 2JPC = 11.3 -
2
Hz, Co), 132.43 (Ci), 132.56 (Ci), 133.06 (d, JPC = 12.0 Hz, Co). 31P
2
NMR (162 MHz, CDCl3): d = 45.3 (d, JPP = 1.6 Hz, P@O), 60.5 (d,
2JPP = 1.6 Hz, P@S).
In continuation of this study, herein we report on the synthesis
of the corresponding cyclic S,S-ligands, their platinum(II) and
palladium(II) complexes, their spectroscopic and structural charac-
terization as well as briefly tested discuss the activity of Pd(II)
complexes in the Suzuki–Miyaura cross-coupling between aryl
bromides and phenylboronic acid.
2.2.2. Synthesis of the ligands 5a–c (general procedure)
The corresponding reactant 4a–c (individual diastereomer in
the case of 4a or 4b) (1.50 mmol) was refluxed with the Lawesson
reagent (1.58 mmol) in toluene (15 mL) for 7 h. Then toluene was
evaporated in vacuo. For isolation of the (R⁄,S⁄)- and (R⁄,R⁄)-
diastereomers 5a,b, the residue was subjected to column chroma-
tography (silica gel, hexane–acetone, gradient elution from 99:1 to
92:8) followed by Et2O treatment of the appropriate fractions to
give the crystalline solids. The ligand 5c was isolated by the treat-
ment of the residue with benzene and subsequently with Et2O.
2. Experimental
2.1. Materials and methods
The NMR spectra were recorded on a Bruker AMX-300, AMX-
400 and AMX-600 instrument in CHCl3, CDCl3, MeCN, and MeNO2
solutions. The solvent CDCl3 was used as the internal standard rel-
ative to tetramethylsilane (1H and 13C) and 85% H3PO4 as the exter-
nal standard (31P). The 13C NMR spectra were registered using the
JMODECHO mode; the signals for the C atoms bearing odd and
even numbers of protons have opposite polarities. IR spectra were
recorded on a Magna-IR 750 FTIR-spectrometer (Nicolet Co., reso-
lution 2 cmꢀ1, scan number 128, KBr pellets or Nujol). Melting
points were determined with an Electrothermal IA9100 Digital
Melting Point Apparatus and were uncorrected. Ph(EtO)PCl was
obtained via the known procedure [15], other reagents were used
as purchased (Acros) without additional purification.
2.2.2.1. 1-[Ethoxy(phenyl)thiophosphoryl]-2-thioxo-2-phenyl-1,2k5-
azaphospholane (5a).
2.2.2.1.1. Data for (R⁄,S⁄)-5a. Yield 68%. Mp 122.0–124.0 °C (diethyl
ether). Anal. Calc. for C17H21ONP2S2: C, 53.54; H, 5.55; N, 3.67; P,
16.26. Found: C, 53.54; H, 5.44; N, 3.65; P, 16.20%. IR (KBr):
m
= 3063, 2988, 2937, 2880, 1436, 1116, 1109, 1065, 1027, 1010,
1003, 997, 986, 961, 864, 789, 747, 727, 695, 646 (w, P@S), 635
(w, P@S), 614, 506, 479. 1H NMR (400 MHz, CDCl3): d = 0.86 (t,
3JHH = 7.0 Hz, 3H, CH3), 2.10–2.57 (m, 4H PCH2CH2), 3.25–3.36
(m, 1H, NCH2), 3.58–3.68 (m, 2H, OCH2), 3.72–3.81 (m, 1H,
NCH2), 7.40–7.60, 8.03–8.20 (2 m, 10H, 2 ꢁ C6H5). 13C NMR
3
(151 MHz, CDCl3): d = 15.19 (d, JPC = 7.7 Hz, CH3), 23.08 (d,
1
3
2JPC = 9.3 Hz, PCH2CH2), 38.56 (dd, JPC = 68.5 Hz, JPC = 4.2 Hz,
2
2
PCH2), 49.84 (dd, JPC = 13.1 Hz, JPC = 6.4 Hz, NCH2), 62.28 (d,
2JPC = 4.9 Hz, OCH2), 128.00 (d, JPC = 15.5 Hz, Cm), 128.14 (d, JPC
3
3
2.2. Synthesis of the ligands
= 13.3 Hz, Cm), 131.56 (d, 2JPC = 12.5 Hz, Co), 131.69 (d, 4JPC = 3.2 Hz,
2
4
The ligand precursors 2-oxo-2-phenyl-1,2-azaphospholanes
4a,b as individual (R⁄,S⁄)- and (R⁄,R⁄)-diastereomers were obtained
via the previously reported procedure [13].
Cp), 131.82 (d, JPC = 12.8 Hz, Co), 131.94 (d, JPC = 3.2 Hz, Cp),
133.02 (d, JPC = 133.0 Hz, Ci), 134.75 (d, JPC = 95.5 Hz, Ci). 31P
1
1
2
NMR (162 MHz, CDCl3): d = 77.8 (d, JPP = 3.4 Hz, Pexo@S), 79.8 (d,
2JPP = 3.4 Hz, Pendo@S). 31P NMR (162 MHz, CH3CN): d = 75.4 (s, Pexo-
@S), 78.2 (s, Pendo@S).
2.2.1. 1-Diphenylthiophosphoryl-2-oxo-2-phenyl-1,2k5-
azaphospholane (4c)
2.2.2.1.2. Data for (R⁄,R⁄)-5a. Yield 52%. Mp 125.0–127.0 °C (ace-
tone). Anal. Calc. for C17H21ONP2S2: C, 53.54; H, 5.55; N, 3.67; P,
16.26. Found: C, 53.49; H, 5.54; N, 3.61; P, 16.15%. IR (KBr):
A solution of freshly prepared Ph(EtO)PCl (2.35 g, 12.5 mmol) in
benzene (10 mL) was added dropwise at ꢀ10 °C to a stirred solu-
tion of HBr NH2(CH2)3Br (2.70 g, 12.5 mmol) and Et3N (2.88 g,
28.6 mmol) in CHCl3 (25 mL). The reaction mixture was refluxed
for 1 h, cooled again to ꢀ10 °C, and after addition of Et3N (1.44 g,
14.3 mmol), a solution of Ph2PCl (2.75 g, 12.5 mmol) was added
dropwise with stirring at ꢀ10 °C. The mixture was allowed to
warm and stirred at ambient temperature for 1 h, the precipitate
of Et3N HHal was filtered off, washed with hot benzene. A solution
of sulfur (0.40 g, 12.5 mg-atom) in benzene (10 mL) was added to
filtrate at 20 °C followed by stirring for 2 h. The mixture was kept
overnight under ambient conditions. Then, the solvent was re-
moved in vacuo, the residue was treated with acetone to give the
desired product as white crystalline solid. Yield: 2.42 g (49%). Mp
217–218 °C (ethanol). Anal. Calc. for C21H21ONP2S: C, 63.48; H,
5.29; N, 3.53; P, 15.62; S, 8.06. Found: C, 63.19; H, 5.23; N, 3.58;
m
= 3049, 2975, 2932, 2882, 1438, 1119, 1108, 1053, 1023, 1013,
999, 991, 958,860, 798, 752, 739, 729, 699, 690, 647 (w, P@S),
636 (s, P@S), 515. 1H NMR (400 MHz, CDCl3): d = 1.28 (t, 3JHH = 7.2 -
Hz, 3H, CH3), 2.08–2.24, 2.25–2.60 (2 m, 4H PCH2CH2), 3.53–3.70
3
3
(m, 2H, NCH2), 4.14 (dq, JHH = 7.2 Hz, JPH = 9.0 Hz, 2H, OCH2),
7.20–7.55, 7.75–8.00 (2 m, 10H, 2 ꢁ C6H5). 13C NMR (75.5 MHz,
3
2
CDCl3): d = 15.81 (d, JPC = 10.2 Hz, CH3), 23.21 (d, JPC = 8.2 Hz,
1
3
PCH2CH2), 38.42 (dd, JPC = 76.7 Hz, JPC = 4.4 Hz, PCH2), 50.67 (dd,
2JPC = 13.7 Hz, JPC = 3.3 Hz, NCH2), 62.15 (d, JPC = 5.5 Hz, OCH2),
2
2
3
3
127.81 (d, JPC = 11.0 Hz, Cm), 128.00 (d, JPC = 10.3 Hz, Cm),
131.28 (d, JPC = 12.1 Hz, Co), 131.32 (d, JPC = 12.1 Hz, Co), 131.54
2
2
4
4
(d, JPC = 3.3 Hz, Cp), 131.69 (d, JPC = 3.3 Hz, Cp), 132.76 (d,
1JPC = 139.4 Hz, Ci), 134.67 (d, JPC = 95.5 Hz, Ci). 31P NMR
1
2
2
(162 MHz, CDCl3): d = 73.8 (d, JPP = 6.7 Hz, Pexo@S), 74.6 (d, JPP
=
P, 15.56, S, 8.05%. IR (KBr,
m
, cmꢀ1): 3051, 2972, 2819, 1480,
6.7 Hz, P
endo@S). 31P NMR (162 MHz, CH3NO2): d = 72.3 (d,
2
1438, 1262, 1215 (vs P@O), 1148, 1118, 1109, 1056, 1017, 994,
977, 834, 755, 726, 717, 705, 687, 663, 623 (m, P@S), 613 (m, P@S),
527, 509, 485, 460. 1H NMR (400 MHz, CDCl3): d = 1.97–2.12,
2.15–2.44 (2 m, 4H PCH2CH2), 3.45–3.57, 3.80–4.00 (2 m,
1H + 1H, NCH2), 6.87–7.05, 7.10–7.28, 7.29–7.45, 7.47–7.68,
8.15–8.35 (5 m, 15H, 3 ꢁ C6H5). 13C NMR (100 MHz, CDCl3):
2JPP = 10.0 Hz, Pexo@S), 77.5 (d, JPP = 10.3 Hz,. Pendo@S).
2.2.2.2. 1-[Methyl(phenyl) thiophosphoryl]-2-thioxo-2-phenyl-1,2k5-
azaphospholane (5b).
2.2.2.2.1. Data for (R⁄,S⁄)-5b. Yield 45%. Mp 124.5–125.0 °C (diethyl
ether). Anal. Calc. for C16H19NP2S2: C, 54.70; H, 5.41; N, 3.99; P,
17.66. Found: C, 54.48; H, 5.51; N, 3.97; P, 17.47%. IR (KBr):
2
1
d = 22.08 (d, JPC = 8.4 Hz, PCH2CH2), 30.46 (dd, JPC = 85.7 Hz,
3JPC = 3.3 Hz, PCH2), 50.06 (dd, JPC = 14.6 Hz, JPC = 3.6 Hz, NCH2),
127.12 (d, JPC = 13.5 Hz, Cm), 128.00 (d, JPC = 13.1 Hz, Cm),
128.37 (d, JPC = 98.4 Hz, Ci), 128.66 (d, JPC = 13.6 Hz, Cm), 131.16
(d, JPC = 10.9 Hz, Co), 131.43 (d, JPC = 2.9 Hz, Cp), 131.57 (d,
m = 3051, 2941, 2876, 1436, 1296, 1164, 1106, 1051, 1014, 981,
2
2
3
3
897, 887, 857, 776, 748, 734, 717, 709, 691, 623 (s, P@S), 612 (s,
P@S), 569, 536, 485, 455. 1H NMR (400 MHz, CDCl3): d = 1.96 (d,
2JPH = 14.0 Hz, 3H, CH3), 2.08–2.30 (m, 2H, PCH2CH2), 2.41–2.60
1
3
2
4

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205
(m, 2H, PCH2CH2), 3.08–3.20, 3.92–4.00 (2 m, 1H + 1H, NCH2),
7.45–7.65, 8.11–8.29 (2 m, 10H, 2 ꢁ C6H5). 13C NMR (100 MHz,
3.82; N, 2.51; P, 11.17%. IR (KBr):
m
= 3054, 2976, 2910, 1439,
1155, 1121, 1112, 1035, 1018, 1008, 991, 981, 967, 858, 767,
2
3
CDCl3): d = 22.67 (dd, JPC = 8.1 Hz, JPC = 1.1 Hz, PCH2CH2), 22.69
727, 714, 683, 583 (w, PS), 558 (m, PS), 510, 470. 31P NMR
1
3
1
2
(dd, JPC = 61.0 Hz, JPC = 1.3 Hz, CH3), 38.99 (dd, JPC = 67.7 Hz,
(162 MHz, CH3CN): d = 64.0 (d, JPP = 12.1 Hz, Pexo@S), 84.9 (d,
3JPC = 2.9 Hz, PCH2), 49.87 (dd, JPC = 13.0 Hz, JPC = 4.3 Hz, NCH2),
128.30 (d, JPC = 13.5 Hz, Cm), 128.64 (d, JPC = 13.3 Hz, Cm),
131.42 (d, JPC = 13.5 Hz, Co), 131.65 (d, JPC = 13.5 Hz, Co), 131.70
2JPP = 12.1 Hz, Pendo@S).
2
2
3
3
2
2
2.3.2. [Pd{(R⁄,R⁄)-5a}Cl2] (R⁄,R⁄)-6a
Yield 93%. Mp 232 °C (decomp.). Anal. Calc. for C17H21Cl2ONP2-
PdS2: C, 36.55; H, 3.79; N, 2.51; P, 11.10. Found: C, 36.42; H,
4
4
(d, JPC = 3.2 Hz, Cp), 132.40 (d, JPC = 3.2 Hz, Cp), 133.38 (d,
3JPC = 1.1 Hz, Ci), 134.30 (d, JPC = 91.0 Hz, Ci). 31P NMR (162 MHz,
1
2
2
CDCl3): d = 63.2 (d, JPP = 4.3 Hz, Pexo@S), 79.4 (d, JPP = 4.6 Hz,
3.76; N, 2.54; P, 11.18%. IR (KBr):
m = 3052, 2990, 2916, 1439,
2
P
P
endo@S). 31P NMR (162 MHz, CH3CN): d = 62.4 (d, JPP = 2.5 Hz,
1157, 1120, 1107, 1052, 1017, 1006, 995, 860, 752, 726, 715,
2
705, 694, 685, 594, 584 (w, PS), 557 (w, PS), 511, 502. 31P NMR
exo@S), 79.9 (d, JPP = 2.5 Hz,. Pendo@S).
2.2.2.2.2. Data for (R⁄,R⁄)-5b. Yield 48%. Mp 134.5–135.0 °C (diethyl
ether). Anal. Calc. for C16H19NP2S2: C, 54.70; H, 5.41; N, 3.99; P,
17.66. Found: C, 54.87; H, 5.41; N, 3.91; P, 17.56%. IR (KBr):
2
(162 MHz, CH3NO2): d = 72.0 (d, JPP = 13.4 Hz, Pexo@S), 90.3 (d,
2JPP = 13.4 Hz,. Pendo@S).
2.3.3. [Pd{(R⁄,S⁄)-5b}Cl2] (R⁄,S⁄)-6b
Yield 80%. Mp 234–238 °C. Anal. Calc. for C16H19Cl2NP2PdS2: C,
36.34; H, 3.60; N, 2.65; P, 11.73. Found: C, 36.07; H, 3.60; N,
m
= 3060, 2978, 2952, 2890, 1439, 1401, 1288, 1145, 1105, 1049,
999, 971, 910, 885, 854, 833, 764, 745,733, 710, 688, 620 (vs
P@S), 612 (vs P@S), 574, 537, 496, 474. 1H NMR (400 MHz, CDCl3):
2
d@2.24 (d, JPH = 13.6 Hz, 3H, CH3), 2.12–2.29, 2.30–2.45 (2 m,
2.61; P, 11.87%. IR (KBr):
m = 3053, 2969, 2896, 1438, 1108, 1052,
1H + 1H, PCH2CH2), 2.45–2.62 (m, 2H, PCH2), 3.57–3.73, 3.77–
1018, 1010, 990, 899, 886, 854, 745, 715, 685, 667, 585, 574 (w,
PS), 552 (w, PS), 533, 476, 453. 31P NMR (162 MHz, CH3CN):
3.92 (2 m, 1H + 1H, NCH2), 7.10–7.50, 7.67–7.80 (2 m, 10H,
1
2 ꢁ C6H5). 13C NMR (100 MHz, CDCl3): d = 21.90 (d, JPC = 70.1 Hz,
2
2
d = 63.0 (d, JPP = 11.0 Hz, Pexo@S), 83.9 (d, JPP = 11.0 Hz, Pendo@S).
2
3
CH3), 23.30 (dd, JPC = 8.3 Hz, JPC = 1.3 Hz, PCH2CH2), 39.00 (dd,
1JPC = 68.4 Hz, JPC = 2.6 Hz, PCH2), 50.30 (dd, JPC = 13.2 Hz,
3
2
2.3.4. [Pd{(R⁄,R⁄)-5b}Cl2] (R⁄,R⁄)-6b
Yield 79%. Mp 240–242 °C. Anal. Calc. for C16H19Cl2NP2PdS2: C,
36.34; H, 3.60; N, 2.65; P, 11.73. Found: C, 36.19; H, 3.57; N,
2JPC = 3.7 Hz, NCH2), 127.70 (d, JPC = 13.3 Hz, Cm), 128.20 (d,
3
3JPC = 13.5 Hz, Cm), 130.58 (d, JPC = 1.1 Hz, Ci), 131.30 (d,
3
2JPC = 10.9 Hz, Co), 131.40 (d, JPC = 10.3 Hz, Co), 131.80 (d,
2
2.71; P, 11.68%. IR (KBr):
m = 3048, 2971, 2904, 1438, 1111, 1045,
4JPC = 2.9 Hz, Cp), 131.90 (d, 4JPC = 3.2 Hz, Cp), 134.00 (d, 1JPC = 93.7 -
1021, 1011, 987, 901, 883, 767, 756, 712, 692, 669, 579 (m, PS),
Hz, Ci). 31P NMR (162 MHz, CDCl3): d = 61.9 (s, Pexo@S), 73.9 (s,
554 (m, PS), 531, 489, 480, 457. 31P NMR (162 MHz, CH3CN):
2
endo@S). 31P NMR (162 MHz, CH3CN): d = 61.2 (d, JPC = 2.6 Hz,
2
2
P
P
d = 63.6 (d, JPP = 11.0 Hz, Pexo@S), 84.6 (d, JPP = 11.0 Hz, Pendo@S).
2
exo@S), 75.8 (d, JPC = 2.6 Hz, Pendo@S).
2.3.5. [Pd(5c)Cl2] 6c
2.2.2.3. 1-Diphenylthiophosphoryl-2-thioxo-2-phenyl-1,2k5-azaphos-
pholane (5c). Yield 81%. Mp 166.0–167.0 °C (benzene–diethyl
ether). Anal. Calc. for C21H21NP2S2: C, 61.02; H, 5.08; N, 3.39; P,
15.01. Found: C, 60.97; H, 5.04; N, 3.33; P, 14.78%. IR (KBr):
Yield 75%. Mp 236–238 °C. Anal. Calc. for C21H21Cl2NP2PdS2: C,
42.68; H, 3.56; N, 2.37; Cl, 12.03; P, 10.50; S, 10.84. Found: C,
42.59; H, 3.53; N, 2.37; Cl, 12.20; P, 10.67; S, 11.00%. IR (KBr):
m
= 3053, 2921, 1437, 1148, 1111, 1103, 1044, 1006, 995, 987,
m
= 3044, 2963, 1437, 1405, 1105, 1049, 1008, 972, 867,
867, 747, 729, 710, 688, 679, 595 (m, PS), 563 (m, PS), 509, 494,
838,744,735, 721,715, 694, 684, 637 (vs P@S), 613 (m, P@S), 582,
543, 513, 505, 475, 443. 1H NMR (400 MHz, CDCl3): d = 2.25–
2.40, 2.42–2.55, 2.58–2.70 (3 m, 4H PCH2CH2), 3.47–3.60, 4.03–
4.12 (2 m, 1H + 1H, NCH2), 6.92–7.02, 7.18–7.26, 7.31–7.40, 7.42–
7.52, 7.53–7.62, 7.63–7.74, 8,20–8.32 (7 m, 15H, 3 ꢁ C6H5). 13C
475. 31P NMR (162 MHz, CH3CN): d = 56.6 (d, JPP = 11.0 Hz, Pexo-
2
2
@S), 85.9 (d, JPP = 11.0 Hz, Pendo@S).
2.3.6. [Pt{(R⁄,S⁄)-5b}Cl2] (R⁄,S⁄)-7b
Yield 65%. Anal. Calc. for C16H19Cl2NP2PtS2: C, 31.12; H, 3.08; N,
2.27; P, 10.05. Found: C, 30.64; H, 2.74; N, 2.24; P, 10.14%. IR (KBr):
2
NMR (100 MHz, CDCl3): d = 23.00 (d, JPC = 8.4 Hz, PCH2CH2),
39.26 (dd, 1JPC = 69.3 Hz, 3JPC = 2.6 Hz, PCH2), 51.56 (dd, 2JPC = 13.0 -
m
= 3052, 2968, 2899, 1438, 1114, 1049, 1006, 991, 899, 876, 854,
2
3
Hz, JPC = 4.0 Hz, NCH2), 126.77 (d, JPC = 13.5 Hz, Cm), 128.00 (d,
745, 727, 688, 667, 553 (w, PS), 530 (m, PS), 476, 454. 31P NMR
1JPC = 98.4 Hz, Ci). 128.05 (d, JPC = 13.9 Hz, Cm), 128.60 (d,
3
2
2
(162 MHz, CH3CN): d = 59.4 (dd, JPP = 7.4 Hz, JPtP = 126 Hz, Pexo-
3JPC = 13.5 Hz, Cm), 131.56 (d, JPC = 12.4 Hz, Co), 131.58 (d,
2
2
2
@S), 79.6 (dd, JPP = 8.1 Hz, JPtP = 126 Hz, Pendo@S).
4JPC = 3.3 Hz, Cp), 131.67 (d, JPC = 3.3 Hz, Cp), 131.87 (d, JPC = 2.9 -
4
4
2
Hz, Cp), 132.60 (d, JPC = 11.7 Hz, Co), 132.80 (Ci), 133.60 (d,
2.3.7. [Pt{(R⁄,R⁄)-5b}Cl2] (R⁄,R⁄)-7b
Yield 70%. Anal. Calc. for C16H19Cl2NP2PtS2: C, 31.12; H, 3.08; N,
2.27; P, 10.05. Found: C, 31.14; H, 3.16; N, 2.41; P, 9.94%. IR (KBr):
2JPC = 12.0 Hz, Co). 31P NMR (162 MHz, CDCl3): d = 62.5 (s, Pexo@S),
78.2 (s,
P
endo@S). 31P NMR (162 MHz, CH3CN): d = 62.0 (d,
2JPP = 2.7 Hz, Pexo@S), 78.3 (d, JPP = 2.7 Hz, Pendo@S).
2
m
= 3055, 2974, 2907, 1438, 1111, 1044, 1021, 1010, 987, 901, 883,
859, 766, 756, 723, 712, 706, 691, 668, 578, 553 (m, PS), 530 (m,
2.3. Synthesis of complexes MLCl2 (M = Pd, Pt) (general procedure)
PS), 478, 456. 31P NMR (162 MHz, CH3NO2): d = 52.0 (dd, 2JPP = 8.8 -
2
2
2
Hz, JPtP = 134 Hz, Pexo@S), 80.5 (dd, JPP = 8.8 Hz, JPtP = 138 Hz,
endo@S).
A solution of [(PhCN)2MCl2] (0.121 mmol) in MeCN (5 mL) was
added dropwise to a solution of the corresponding ligand 5a,b
(individual diastereomer) or 5c (0.121 mmol) in the same solvent
(3 mL). The mixture was left to stand for two days at 20 °C, the
resulting precipitate was collected by filtration, washed twice with
diethyl ether, and dried in vacuo to give palladium complexes as
bright brown and platinum ones as orange crystalline solids.
P
2.4. X-ray crystallography
Single crystals of the ligands (R⁄,S⁄)-5a, (R⁄,R⁄)-5b, 5c suitable
for X-ray experiments were grown from diethyl ether, those of
the complexes (R⁄,S⁄)-6a, (R⁄,S⁄)-6b, (R⁄,R⁄)-6b (6b), 6c, (R⁄,R⁄)-7b
from acetonitrile. The X-ray diffraction experiments were carried
out with a SMART APEX2 CCD diffractometer, using graphite
2.3.1. [Pd{(R⁄,S⁄)-5a}Cl2] (R⁄,S⁄)-6a
Yield 69%. Mp 228 °C (decomp.). Anal. Calc. for C17H21Cl2ONP2-
PdS2: C, 36.55; H, 3.79; N, 2.51; P, 11.10. Found: C, 36.49; H,
monochromated Mo
Ka radiation (k = 0.71073 Å, x-scans) at

206
I.M. Aladzheva et al. / Inorganica Chimica Acta 395 (2013) 203–211
100 K. The structures were solved by direct methods and refined by
the full matrix least-squares against F2 in anisotropic approxima-
tion for non-hydrogen atoms. The positions of hydrogen atoms
were calculated, and they were refined in isotropic approximation
in riding model. ⁄Crystal data and ⁄structure r⁄efinement parameters
for (R⁄,S⁄)-5a, (R ,R⁄)-5b, 5c, (R⁄,S )-6a, (R⁄,S )-6b, (R⁄,R⁄)-6b (6b0),
6c, and (R⁄,R⁄)-7b are given in Table 1. The best available crystal
of the complexes 6b and 6b0 was twinned, and our attempts to
model this twinning were unsuccessful. All calculations were
performed using the SHELXTL software.
solutions in DMF) in 1 mL of DMF was heated at 120 °C from
30 min up to 5 h. To determine the conversion of aryl bromide, ali-
quots of the reaction mixture, taken at the specified time, were
treated with water (3–4 ml), extracted with benzene, and analyzed
by GC (Chrom-5 instrument, 25 m capillary column with SE-30
stationary phase, FID detector, temperature programming
150 ? 250 °C at 15 °C/min). Since both starting aryl bromides
and the cross-coupling products were stable enough and seemed
unlikely to undergo resinification or other loss during the process-
ing, internal standard was not used. To define molar ratios from the
peak areas, a simplified approach basing on FID detector sensitivity
towards carbon ions (acceptable for compounds of close chemo-
types) was used. To this, the observed peak areas were divided
by the number of carbon atoms in the corresponding molecule,
and the thus obtained revised values (theoretically proportional
to molar fractions) for further calculations.
2.5. Catalytic studies
In a typical experiment a solution of 0.25 mmol of aryl bromide,
0.375 mmol of PhB(OH)2, 0.5 mmol of K3PO4, and the mentioned
amount of the corresponding palladium complex (used as titrated
Table 1
Crystal data and structure refinement parameters for (R⁄,S⁄)-5a, (R⁄,R⁄)-5b, 5c, (R⁄,S⁄)-6a, (R⁄,S⁄)-6b, (R⁄,R⁄)-6b, 6c and (R⁄,R⁄)-7b.
(R⁄,S⁄)-5a
17H21NOP2S2
381.41
100
(R⁄,R⁄)-5b
C16H19NP2S2
351.38
100
5c
(R⁄,S⁄)-6a
C17H21Cl2NOP2PdS2
558.71
100
Empirical formula
Formula weight
T (K)
C
C21H21NP2S2
413.45
100
Crystal system
Space group
Z
monoclinic
P21/n
4
monoclinic
P21
2
monoclinic
C2/c
8
monoclinic
P21/c
4
a (Å)
b (Å)
c (Å)
9.1254(7)
15.8791(12)
12.8702(10)
90.00
6.5674(3)
13.9645(7)
9.4049(5)
90.00
33.7699(16)
8.0103(4)
15.3058(7)
90.00
15.898(5)
9.101(3)
14.642(7)
90.00
a
(°)
b (°)
102.2160(10)
90.00
1822.7(2)
1.390
4.71
800
100.1570(10)
90.00
849.01(7)
1.375
4.95
368
107.0530(10)
90.00
3958.3(3)
1.388
4.36
1728
94.034(13)
90.00
2113.3(14)
1.756
14.88
1120
c
(°)
V (Å3)
Dcalc (g cmꢀ1
)
Linear absorption,
F(000)
l
(cmꢀ1
)
2hmax (°)
58
58
58
56
Reflections measured
Independent reflections
17,406
4838
10,109
4478
15,337
5222
11,305
5070
Observed reflections [with I > 2
r
(I)]
4200
4384
4411
4552
Parameters
R1
wR2
209
191
235
240
0.0364
0.0937
1.008
0.479 and ꢀ0.320
(R⁄,R⁄)-6b (6b0)
0.0213
0.0546
1.006
0.0348
0.1010
1.002
0.493 and ꢀ0.330
0.0253
0.0691
1.009
0.625 and ꢀ0.537
(R⁄,R⁄)-7b
C16H19Cl2NP2PtS2
617.37
100
GOF
D
qmaximum
/
D
qminimum (e Åꢀ3
)
0.280 and ꢀ0.182
(R⁄,S⁄)-6b
C18H22Cl2N2P2PdS2
569.74
6c
Empirical formula
Formula weight
T (K)
C
16H19Cl2NP2PdS2
C21H21Cl2NP2PdS2
590.75
120
528.68
100
100
Crystal system
Space group
Z
orthorhombic
Pbca
8
monoclinic
C2/c
8
monoclinic
P21/n
4
orthorhombic
Pbca
8
a (Å)
b (Å)
c (Å)
9.2546(7)
14.6737(11)
28.612(2)
90.00
18.6599(16)
15.0776(13)
16.9940(15)
90.00
15.4226(19)
9.5848(12)
17.097(2)
90.00
9.2732(4)
14.6194(7)
28.6995(13)
90.00
a
(°)
b (°)
90.00
90.00
3885.5(5)
1.808
16.09
99.890(2)
90.00
4710.1(7)
1.607
13.35
2288
110.481(2)
90.00
2367.5(5)
1.657
13.3
1184
90.00
90.00
3890.8(3)
2.108
78.66
c
(°)
V (Å3)
Dcalc (g cmꢀ1
)
Linear absorption,
F(000)
l
(cmꢀ1
)
2112
2368
2hmax (°)
58
57
58
56
Reflections measured
Independent reflections
42,587
5083
24,558
6172
17,568
6275
40,727
4700
Observed reflections [with I > 2
r
(I)]
4461
5497
3865
3891
Parameters
218
271
262
218
R1
wR2
0.0825
0.2114
2.139
4.096 and ꢀ2.435
0.1016
0.3020
2.333
3.028 and ꢀ2.418
0.0485
0.0834
1.003
1.067 and ꢀ1.476
0.0388
0.1180
1.018
1.502 and ꢀ2.300
Goodness-of-fit (GOF) on F2
D
qmaximum
/
D
qminimum (e Åꢀ3
)

I.M. Aladzheva et al. / Inorganica Chimica Acta 395 (2013) 203–211
207
1. 0.5 HBr.H2N(CH2)3Br/Et3N
1. HBr.H2N(CH2)3Br/Et3N
OEt
Ph
Ph P NH
Ph P N P
Ph(EtO)PCl
2. Δ
2. Δ
O
O
2
1
Ph2PCl/Et3N
[O] or MeI
Ph
S
Ph
N PPh2
P
N P
X
P
Ph
R
O
O
3
a: X=O, R=EtO (R*,R* and R*,S* isomers)
b: X=O, R=Me (R*,R* and R*,S* isomers)
c: X=S, R=Ph
4a-c
RL
toluene
reflux
Ph
R
a: R=EtO (R*,R* and R*,S* isomers)
b: R=Me (R*,R* and R*,S* isomers)
c: R=Ph
Ph
N P
P
S
S
5a-c
Scheme 1. Synthesis of 1-thiophosphoryl-2-thioxo-1,2-azaphospholanes 5a–c.
data, the thionation proceeded with retaining of stereochemical
configuration of chiral phosphorus atom in the starting ligand.
In the IR spectra the ligands 5a–c demonstrated two bands at
646 and 636 cmꢀ1 (5a), 620 and 612 cmꢀ1 (5b), and 637 and
613 cmꢀ1 (5c) characteristic for P@S groups vibrations along with
those attributable for skeletal vibrations of the other groups in
the molecule. In the 31P NMR spectra the ligands 5a,b demon-
3. Results and discussion
3.1. Synthesis of the ligands
The target ligands, namely N-thiophosphorylated 2-thioxo-1,2-
azaphospholanes 5a–c, were obtained by treatment of their
(O)PNP(X) precursors 4a–c with the Lawesson reagent (RL)
(Scheme 1). It should be emphasized that the individual (R⁄,S⁄)-
and (R⁄,R⁄)-diastereomers of the ligands 4a,b were used in the
reaction. The reaction course can be monitored by 31P NMR tech-
nique via the downfield shifting of the resonances of phosphorus
atoms as far as they undergo transformation from phosphoryl to
thiophosphoryl group.
2
strated two signals usually as doublets with JPP in the range of
2.5–10 Hz in the region typical for phosphorus atoms with such
surrounding, the signal of endocyclic phosphorus atom is down-
field shifted compared with that for the exocyclic one. However
in the case of (R⁄,S⁄)-5a (MeCN) and 5b (CDCl3) ligands two singlet
signals were observed. Similar to their precursors bearing either
two or one phosphoryl group in the molecule, the opposite config-
uration of asymmetric centers (R⁄,S⁄) is typical for the diastere-
isomer having downfield chemical shift of the endocyclic
phosphorus atom in the 31P spectra and smaller JPP coupling
constants. The position and multiplicity of the signals in the 1H,
and 13C spectra fit well the depicted structures.
Note that the synthesis of individual (R⁄,S⁄)-and (R⁄,R⁄)-isomers
4a,b used in the study was performed according to the previously
developed procedure [13] by interaction of Ph(EtO)PCl and 3-bro-
mopropylamine in the ratio of 2:1 with subsequent intramolecular
Arbuzov reaction of [Ph(EtO)P]2N(CH2)3Br resulting in the cyclic
product 1 formation. On subsequent oxidation of 1 or the action
of methyl iodide, azaphospholanes 4a,b were produced (Scheme 1).
The new ligand-precursor 4c was obtained via the similar one-pot
methodology with some modifications. Briefly, Ph(EtO)PCl and 3-
bromopropylamine were used at the first stage in stoichiometric
amounts, the intermediate Ph(EtO)PNH(CH2)3Br provided the
monophosphorylated azaphospholane 2 in the result of the intra-
molecular Arbuzov reaction. Subsequent phosphorylation with
diphenylchlorophosphine afforded 1-diphenylphosphino-2-oxo-
1,2-azaphospholane 3 which was transformed to the mixed ligand
4c by sulfur addition in 49% isolated yield (Scheme 1).
3.2. Complexes of cyclic (S)PNP(S) ligands with [(PhCN)2MCl2] (M = Pd,
Pt)
The ligands 5a–c readily react with [(PhCN)2MCl2] (M = Pd, Pt)
in 1:1 M ratio in MeCN solution to afford the corresponding
palladium and platinum complexes 6a–c and 7b, respectively
(Scheme 2).
The composition of the complexes and their structures were
confirmed by elemental analysis, 31P NMR and IR spectroscopy
The (R⁄,S⁄)- and (R⁄,R⁄)-diastereomers of the ligands 5a,b were
purified by column chromatography followed by Et2O treatment
of the desired fractions to give the solid products whereas the li-
gand 5c was precipitated from the benzene-diethyl ether solution.
The compounds 5a–c presented white crystalline solids which
structures were unambiguously confirmed by IR and multinuclear
NMR spectroscopy, elemental analysis data along with X-ray study
for a single crystal (R⁄,S⁄-5a, R⁄,R⁄-5b and 5c). According to these
data. Thus, in the IR spectra of the complexes the m(PS) absorption
bands shifted to the region of 595–555 cmꢀ1 reflecting decreased
P@S band order owing to complexation. The 31P-{1H} NMR spectra
of the complexes 6a–c and 7b exhibit two characteristic doublet
resonances of the exo- and endo-cyclic phosphorus atoms. Note-
worthy that the signals of endocyclic phosphorus atoms in the cor-
responding complexes are shifted downfield for 4–14 ppm
compared with those for the free ligands, whereas the chemical

208
I.M. Aladzheva et al. / Inorganica Chimica Acta 395 (2013) 203–211
(PhCN)2MCl2, MeCN, 20 oC
Ph
R
Ph
R
Ph P N P
Ph P N P
S
S
S
S
M
5a-c
Cl
Cl
6a-c (M=Pd)
7b (M=Pt)
a: R=EtO (R*,R* and R*,S* isomers)
b: R=Me (R*,R* and R*,S* isomers)
c: R=Ph
Scheme 2. Palladium and platinum complexes 6a–c, 7b of N-thiophosphorylated 2-thioxo-1,2-azaphospholanes.
shifts of the exocyclic ones, as a rule, are varied only slightly. At the
same time, the values of 2JPP coupling constants increased by com-
plexation in all cases. Furthermore, the structures of the palladium
complexes (R⁄,S⁄)-6a, both isomers (R⁄,R⁄)- and (R⁄,S⁄)-6b (as a
crystallosolvate with acetonitrile) and 6c as well as platinum com-
plex (R⁄,R⁄)-7b were elucidated by the X-ray diffraction analysis
(see below).
Based on the significant coordination shift of P@S absorption
bands for exo- and endo-phosphorus atoms in the IR spectra on
complexation, considerable downfield shifting of the endocyclic
phosphorus resonances and increasing of the 2JPP coupling constant
values in the 31P-{1H} NMR spectra, the 1:1 bidentate chelating
coordination mode of the ligands to palladium and platinum has
been suggested for the complexes 6a–c and 7b.
pseudo-torsion S(1)P(1)P(2)S(2) angles equal to 179.2(1)°,
164.2(1)° and 176.5(1)°, respectively. Phenyl substituents in
(R⁄,S⁄)-5a and (R⁄,S⁄)-5b are in a transoid and cisoid disposition,
respectively; the angle between their mean planes are 116.1(1)°
and 10.8(1)°. For 5c, the same values involving the P(1)-bound
phenyl group are 66.0(1)° and 13.5(1)°. The absence of any conve-
nient proton donors in these ligands makes them to form weak
intermolecular interactions only: those of the types C–Hꢂ ꢂ ꢂS, C–
Hꢂ ꢂ ꢂ
p, Hꢂ ꢂ ꢂH and also
pꢂ ꢂ ꢂp (5c).
Upon complexation, the molecular geometry of the ligands
changes in the expected manner. The X-ray diffraction study of
the complexes (R⁄,S⁄)-6a, 6b (both isomers), 6c and (R⁄,R⁄)-7b
(Fig. 2) has revealed that in all cases the P@S bonds (being now ci-
soid) became longer by ca. 0.05 Å; the pseudo-torsion angles
S(1)P(1)P(2)S(2) are equal to 63.3(1)° (R⁄,S⁄-6a), 60.9(4)° (R⁄,S⁄-
6b), 53.9(3)° (R⁄,R⁄-6b), 52.7(1)° (6c) and 53.5(4)° (R⁄,R⁄-7b). The
formation of these complexes also causes slight changes in the aza-
phospholane moiety: although its distorted envelope conformation
persists, the atom that deviates mostly (by 0.59(1)–0.62(1) Å) is
C(2). The mutual disposition of the phenyl substituents also varies:
it is cisoid in (R⁄,S⁄)-isomers of complexes 6a and 6b and transoid in
(R⁄,R⁄)-6b and (R⁄,R⁄)-7b (two latter complexes are isostructural).
3.3. Molecular geometry and crystal structures
According to the X-ray diffraction data, azaphospholane moiety
of the ligands (R⁄,S⁄)-5a, (R⁄,S⁄)-5b and 5c (Fig. 1) has a distorted
envelope conformation with the atom C(2) deviated by 0.59(1) Å
in (R⁄,S⁄)-5a or C(1) deviated by 0.76(1) and 0.68(1) Å in the two
other ones. In all cases, the P@S groups are transoid, with the
Fig. 1. General view of the ligands (R⁄,S⁄)-5a, (R⁄,S⁄)-5b and 5c in representation of atoms via thermal ellipsoids at 50% probability level.

I.M. Aladzheva et al. / Inorganica Chimica Acta 395 (2013) 203–211
209
Fig. 2. General views of the complexes studied by X-ray diffraction in representation of atoms via thermal ellipsoids at 50% probability level; for clarity, these depict the
inverted isomers.
The angles between their planes are 118.9(1) and 23.4(1) for (R⁄,S⁄)-
6a and (R⁄,R⁄)-7b, as due to a severe disorder of (R⁄,S⁄)-6b and
twinning of (R⁄,R⁄)-6b, the geometry of these complexes cannot
be analyzed in detail. The same values in a crystal of 6c are
59.5(1)° and 20.6(1)° (see above).
Note, that except for (R⁄,S⁄)-6a, the coordination environment of
the metal atom (Pd or Pt) has a square-planar (within 0.04(1) Å)
configuration. In the crystal of (R⁄,S⁄)-6a, it is markedly distorted,
with the largest deviation being 0.48(1) Å (sulfur atom). This fact
cannot be explained by the crystal packing effects: in all cases

210
I.M. Aladzheva et al. / Inorganica Chimica Acta 395 (2013) 203–211
Fig. 3. Plots of conversion vs. time for the couplings of 4-bromoacetophenone (left) and 4-bromoanisole (right) with phenylboronic acid catalyzed by 0.1 mol% of complexes
6a–c.
there are only weak intermolecular interactions, and those do not
differ much along the series of the complexes. With minor varia-
tion – additional Sꢂ ꢂ ꢂS interactions in (R⁄,R⁄)-6b and (R⁄,R⁄)-7b
and C–Hꢂ ꢂ ꢂN contacts with solvent species in (R⁄,S⁄)-6b – the
complex molecules in a crystal are hold together through C–Hꢂ ꢂ ꢂCl,
1 mol% of the additional ligand 2-dicyclohexylphosphino-2’,6’-
dimethoxybiphenyl (S-PHOS) resulted in the formation of the de-
sired products, however conversion over 5 h at 120 °C did not ex-
ceed 17% and 7% for 4- and 2-chloroacetophenones, respectively.
To the best of our knowledge, the data on the catalytic activity
of palladium complexes formed by the related linear (S)PNP(S) li-
gands in the cross-coupling reactions are absent in the literature.
The employment of the different conditions in Suzuki test-reaction
of bromoarenes with phenylboronic acid used in our case
(0.1 mol%, DMF, 120 °C, K3PO4) and for their linear analogs formed
by PN(R)P ligands bearing two trivalent phosphorus atoms
(0.01 mol%, dioxane, 60–80 °C, Cs2CO3) [6–8] did not allow the cor-
rect comparison of the catalytic activity. One may suppose, that in
the view of the same conversion at the lower catalytic loading, the
last-mentioned ligands are more active in the above process.
C–Hꢂ ꢂ ꢂS, Sꢂ ꢂ ꢂ
p, Clꢂ ꢂ ꢂ
p, C–Hꢂ ꢂ ꢂ
p
and Hꢂ ꢂ ꢂH interactions. However,
more close examination of the bonding pattern has shown that
in (R⁄,S⁄)-6a there is also a weak intramolecular contact Pd...H
(3.06 Å) with the hydrogen atom of the CH2 group. The latter, as
it was shown earlier [16], can be responsible for the distortion of
the planar square configuration of the palladium atom in (R⁄,S⁄)-6a.
3.4. Catalytic studies
The catalytic activity of the palladium complexes 6a–c differing
in the surrounding at the exocyclic phosphorus atom, was esti-
mated in the palladium catalyzed Suzuki cross-coupling of aryl ha-
lides with phenylboronic acid, being one of the most powerful
methods for CAr–CAr bond formation [17]. All experiments were
performed under the same conditions: heating in DMF at 120 °C
using K3PO4 as a base.
4. Conclusions
The present study describes the synthesis and characterization
of novel cyclic (S)PNP(S) ligands, namely 1-thiophosphoryl-2-thi-
oxo-1,2-azaphospholanes having different surrounding at the exo-
cyclic phosphorus atom. The synthetic approach starting from their
(O)PNP(O) and (O)PNP(S) precursors provided individual diaste-
reomers in the case of the compounds bearing two chiral phospho-
rus atoms. The ligands formed with palladium(II) and platinum(II)
complexes of MLCl2 composition with 6-membered metallacycle
via S,S-bidentate chelate mode. The corresponding Pd(II) com-
plexes exhibited high activity as precatalysts for the Suzuki
cross-coupling reaction of bromoarenes and phenylboronic acid
and the complex bearing two phenyl substituents at the exocyclic
phosphorus atom was the most active among this series.
Fig. 3 outlines the results as kinetic evolution of the conversions
of two electronically varied substrates, namely, activated 4-bromo-
acetophenone and less reactive 4-bromoanisole bearing electron
donating group in time at the catalyst loading of 0.1 mol%. As is
obvious, in the reaction of 4-bromoacetophenone (Fig. 3, left) com-
plex 6c bearing two phenyl groups at the exocyclic phosphorus
atom appeared to be slightly more active than its analog (R⁄,R⁄)-
6b having methyl and phenyl groups at this P-atom (94% and
87% conversion over 1 h, respectively). In 2 h both complexes pro-
vided almost quantitative conversion of the substrate. At the same
time in the case of complex (R⁄,S⁄)-6a having electron-withdraw-
ing ethoxy group 97% conversion was achieved in 4 h only.
For the less active substrate, 4-bromoanisole (Fig. 3, right), the
same tendency was observed – complex 6c was more active than
(R⁄,R⁄)-6b while complex (R⁄,S⁄)-6a was significantly less active.
However, at this catalyst loading (0.01 mol%) complete conversion
was achieved in none of the cases. These studies revealed the sig-
moidal kinetics and distinct induction period required for the gen-
eration of catalytically active species unambiguously confirming
that these complexes serve as precatalysts being the source of
Pd(0) particles.
Appendix A. Supplementary material
CCDC 881925–881932 contain the supplementary crystallo-
graphic d⁄ata for the ligands (R⁄,S⁄)-5a, (R⁄,R⁄)-5b, 5c, and ⁄com-
plexes (R ,S⁄)-6a, (R⁄,S⁄)-6b, (R⁄,R⁄)-6b (6b0), 6c, and (R⁄,R )-7b.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_re-
quest/cif
References
Taking into account that the main challenges in the cross-cou-
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the catalytic activity of the most active precatalyst 6c in the
cross-coupling of 4- and 2-chloroacetophenones with phenylbo-
ronic acid was examined. However, at the catalyst loading of 0.1
and 1 mol% formation of biaryl product was not observed. The
application of combination of the complex 6c (0.5 mol%) with
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