View
151
Download
3
Category
Tags:
Preview:
DESCRIPTION
PINCER COMPLEXES. A SPECIAL TOPIC. Pincer Complexes. Complexes of mixed donor polydentate ligands pioneered by Shaw in mid-70s. Generic Structure of Pincer Complex. Dehydrogenation of Alkanes. Palladium Pincer Complexes as Catalysts for the Heck Reaction. - PowerPoint PPT Presentation
Citation preview
PINCER COMPLEXES
A SPECIAL TOPIC
Ir
PtBu2
PtBu2
Cl
H
Pd
P(CMe3)2
P(CMe3)2
Cl
Pincer Complexes
Complexes of mixed donor polydentate ligands pioneered by Shaw in mid-70s
M
DR
DR
XnLm
R'
*cavity for metal bonding with tunable accessibility*sites for counterions or ancillary ligand
*hardness/softness*metal-binding rigidity*steric constraints of substituents*coordinating 2e- donor or free Lewis base
*anchoring site*remote electronic modulations
*chiral pocket*steric constraints
Generic Structure of Pincer Complex
Dehydrogenation of Alkanes
I + COOMeCOOMe
140oC, N-methyl pyrrolidone, Na2CO3
Pd
PiPr2
PiPr2
TFA
Palladium Pincer Complexes as Catalysts for the Heck Reaction
+
O
Pd
O
PiPr2
PiPr2
Cl
Cl
180oC, Dioxane, CsOAc
Palladium Phosphinito PCP Pincer Complex in Heck Reactions Involving Aryl Chlorides
CsOAC, 180oC, Dioxane
The Classical Mechanism PdL4 precatalyst
Pd(0)L2
R'-Pd(II)L2-X
R'X
Pd(II)L2X
R''
R'
H
H
R''
H
Pd(II)L2X
H
R'
H
R''
H
H-Pd(II)L2-X
R'R''
HX-BaseBase
oxidative addition
coordination
internal rotation
elimination
reductive elimination
ligand dissociation
R'-Pd(II)L2-X
R''
alkyl migration
The Pd(II)/Pd(IV) Mechanism
O
Pd
O
PPri2
PPri2
Cl
O
Pd
O
PPri2
PPri2
O
Pd
O
PPri2
PPri2
Ar
O
Pd
O
PPri2
PPri2
H
Cl
Ph
Ph
Ph
Cl
HCl
Ar
Ph
Ph
ArCl
II
IV
II
IV
Platinum NCN and PCP pincer complexes as catalysts for alkane CH bond activation
and functionalization
OH OH+HO OH
OH
+ CH3CH2CO2H
Pt
NEt2
NEt2
ClPt
PPri2O
O PPri2
Cl
PtII
+ RHa)
PtII + H+
BA
PtIV
PtII
PtIV
b)
C
R
R
H2O
ROH + H+
c)
Cl-
RCl
Mechanism for the Shilov system
OH
OHHO
POP-Pd-Cl (1 mol %)
CuCl2.2H2O (2 mol %), HCl (2 mol %)
Air, H2O
OHCl
+
OH OH
Pd
PiPr2O
O PiPr2
Cl
TFA, H2O, Oxidant, 95oC
Pd
PiPr2
PiPr2
Cl Pd
NEt2
NEt2
Br Pd
StBu
StBu
Cl
HO1 or 2 or 3 or 4
1 2 3 4
OH
OHHO
POP-Pd-Cl (1 mol %)
CuCl2.2H2O (2 mol %), HCl (2 mol %)
Air, H2O
OHCl
+
OH
OHHO
POP-Pd-Cl (1 mol %)
CuCl2.2H2O (2 mol %), HCl (2 mol %)
Air, H2O
OHCl
+
Pd
PiPr2O
O PiPr2
Cl Pd
PiPr2
PiPr2
Cl Pd
NEt2
NEt2
Br Pd
StBu
StBu
Cl
1 2 3 4
Preparation of Pincer Complex
synthesis of pincer ligand
synthesis of metal precursor
Metalation of pincer ligand
A solution of resorcinol (0.36 g, 3.28 mmol) and DMAP (0.81 g, 6.60 mmol) in THF (30 ml) was added a solution of ClPPri
2 (1.0 g, 6.55 mmol) in THF (20 ml), while stirring at 0°C. The resulting mixture was allowed to reach room temperature (r.t.) and stirred for an additional 24 h. Following removal of the solvent in vacuo, the solid residue was extracted with toluene (220 ml). The combined extracts were filtered through a short plug of Celite and the toluene removed in vacuo to yield the product (1.1 g, 95%) as a colorless oil. NMR spectroscopy showed the product to be greater than 98% pure and it was used in further steps without further purification. 1H NMR (400.03 MHz, CDCl3): d 7.10–6.80 (m, 4H, arom.); 2.00–1.80 (m, 4H, CH(CH3)2); 1.15–1.00 (m, 24H, CH(CH3)2). 13C NMR (100.59 MHz, CDCl3): d 160.22 (s, ArC), 129.38 (s, ArC), 111.77 (s, ArC), 109.25 (s, ArC), 28.26 (d, 1JPC 17.9 Hz, PCH(CH3)2), 17.71 (s, PCH(CH3)2), 16.98 (s, PCH(CH3)2). 31P{1H} NMR (161.93 MHz, CDCl3): d 149.0. Anal. Calc. for C18H32O2P2 (342.40.): C, 63.14; H, 9.42. Found: C, 63.42; H, 9.74%.
Preparation of C6H4 -2,6 -(OPPri2)2
DMAP = 4 dimethylaminopyridine
A toluene (50 ml) solution of C6H4-2,6-(OPPri2)2 (500 mg,
1.46 mmol), and PdCl2(COD) (417 mg, 1.46 mmol) was refluxed for 5 h. The solvent was evaporated under vacuum and the crude product was extracted with pentane. Following recrystalization from diethyl ether, a purified product was obtained (Yield 630 mg, 90 %). 1H NMR (400.03 MHz, CDCl3): d 1.20–1.40 (m, 24H, CH(CH3)2), 2.40–2.52 (sep m, 3JHH7.2 Hz, 4H, CH(CH3)2), 6.54 (d, 3JHH8.0 Hz, 2H, arom), 6.96 (t, 3JHH8.0 Hz, 1H, arom); 13C NMR (100.59 MHz, CDCl3) d 166.29 (bs, ArC), 149.84 (s, ArC), 128.02 (s, ArC), 105.94 (vt, JPC14.48 Hz, ArC), 28.78 (vt, JPC23.14 Hz, PCH(CH3)2), 17.26 (s, PCH(CH3)2), 16.69 (s, PCH(CH3)2); 31P NMR (161.93 MHz, CDCl3): d 187.68 (s, 1P). Anal. Calc. for C18H31Cl1O2P2Pd (483.24): C, 44.74; H, 6.47. Found: C, 44.49; H, 6.15%.
Preparation PdCl{C6H3 -2,6 -(OPPri2)}
Single-crystal X-ray diffraction study
Recommended