2. Outline
Introduction
The Chemistry of Pd(I) & other Low Valent Transition Metals
Applications of Pd Chains(containing Pd(I))
Challenges
Hetero metals in Pd(I) Chains
First paper: Stepwise Expansion of Pd Chains via Binuclear Pd(I) Complexes
Supported by Tetraphosphine Ligands
Previous Studies
Results & Discussions
Conclusion
Second paper: Multinuclear Metal-binding ability of a Carotene
Previous Studies
Results & Discussions
Conclusion
Critics & New ideas
2
3. Introduction
The Chemistry of Pd(I) & other Low Valent Transition Metals
Pd: Group 10
Principal oxidation states II & IV
Metal clusters (M-M bonds & π-acidic ligands like PR₃) I & III
Pd(I) like [Pd₂(PMe₃)₆]²⁺: Coordination number 4
Square planar
Pd(I) complexes* : Pd(0) + Pd(II) 2 Pd(I)
Pd(II) + Reducing conditions Pd(I)
Pd(0) + Oxidizing conditions Pd(I)
* Cotton. F., Wilkinson. G., Murillo. C., Bochmann. M., Advanced Inorganic Chemistry, Sixth Edition, 1063-1070
3
4. Introduction
The Chemistry of Pd(I) & other Low Valent Transition Metals
Pd(I) – Pd(I) clusters :
non-bridged entities , SP environment for each metal center
[PdCl₄]²⁻ + Pd(CO)₂
Bridged entities,
ligands like chelating phosphines
such as Ph₂PCH₂PPh₂(dppm) ,
allenyl (Organopalladium complex)
* Cotton. F., Wilkinson. G., Murillo. C., Bochmann. M., Advanced Inorganic Chemistry, Sixth Edition, 1063-1070
4
5. Introduction
The Chemistry of Pd(I) & other Low Valent Transition Metals
Pt(I) : Behavior similar to Pd(I)
Greater density & Higher melting point
Less abundant , more expensive
Ni(I) : Mostly contain phosphine ligands
Coordination number 4
Tetrahedral or tbp
Less stable in air
5
6. Introduction
Applications of Pd Chains(containing Pd(I))
Pd chains
EMACs (Extended Metal Atom Chains)
Mixed-valence compounds with delocalized unpaired electrons
Conductivity along chain , Electronic devices , Quantum tunneling
6
8. Introduction
Challenges
The longer metal chain > The more synthetic difficulties
Lower yield
Instability of EMAC due to high flexibility of large ligand
8
9. Solutions
I. Stepwise methodology
rather than Template synthesis
II. Substitution of rigid &
potentially redox active ligands
9
10. Introduction
Hetero metals in Pd(I) chains
Manipulation of the conductivity along chain
Conformation control , Preference of M bonding , Avoiding regioisomers
Different energy gap between d orbitals , Different current flow
[CuCuPd(npa)₄Cl]⁺ (3d)(4d) [CuCuPt(npa)₄Cl]⁺ (3d)(5d)*
Large energy gap , One-direction current flow , Rectifier-like behavior
* Liu. I., Wang. W., Peng. S., Chem. Commun, 2009, 29, 4323-4331.
10
12. First paper: Stepwise Expansion of Pd Chains via Binuclear Pd(I) Complexes Supported by
Tetraphosphine Ligands
Previous Studies
[Pt₂(RNC)₆](PF₆)₂ + 2 dpmp
[Pt₃(XylNC)₆] NaBH₄/EtOH
1a
* Goto. E., Begum. R., Hosokawa. A., Yamamoto. C., Kure. B. , Organometallics, 2012, 31, 8482.
12
1a
13. Previous Studies
dpmppm *
L = dmf , T >100 ͦC
* Nakamae. K., Takemura. Y., Kure. B., Nakajima. T., Kitagawa. Y., Tanase. T., Angew. Chem., Int. Ed. 2015, 54, 1016.
13
L = C H3C N, D MF,
X ylNC
14. Results and Discussions - (Homonuclear complex)
Preparation of [Pd₂(μ-dpmppm)₂]X₂ (X= PF₆ ,BF₄)
[Pd₂(XylNC)₆]X₂ + 2 dpmppm
XylNC :
. Pd(I)-Pd(I) : 2.7379 Å
. Asymmetrical fashion , 5 & 6-membered rings , 4 types P
. UV-Vis : 458 nm for σ → σ*
. ESI –MS : (m/z(=2))= 735.082 for [Pd₂(dpmppm)₂]²⁺
14
CH₂Cl₂ , 2hrs, rt
15. Results and Discussions - (Homonuclear complex)
Preparation of [Pd₄(μ-dpmppm)₂(L)n]X₂ (X= PF₆ ,BF₄), (n=2 , 3), (L=XylNC ,L= ͭBuNC)
15
Symmetrical Asymmetrical low Thigh T
+ L
16. Results and Discussions - (Homonuclear complex)
Temperature-dependent NMR spectra of [Pd₄(μ-dpmppm)₂(XylNC)n]X₂ in CD₃CN
16
¹H{³¹P} NMR ³¹P{¹H} NMR
P
Pd
P
Pd Pd Pd
P
P
P
P
P
P
L L
X2
17. Results and Discussions - (Homonuclear complex)
Temperature-dependent NMR spectra of [Pd₄(μ-dpmppm)₂(ͭBuNC)n]X₂ in CD₃CN
17
³¹P{¹H} NMR
P
Pd
P
Pd Pd Pd
P
P
P
P
P
P
L L
X2
18. Results and Discussions - (Homonuclear complex)
Variable-temperature UV-Vis changes
in CH₃CN for [Pd₄(μ-dpmppm)₂(XylNC)n]X₂
(reversible upon changing ratio of [L]/[Pd₄])
18
19. Results and Discussions - (Homonuclear complex)
Variable-temperature UV-Vis changes
in CH₃CN for [Pd₄(μ-dpmppm)₂(ͭBuNC)n]X₂
(reversible upon changing ratio of [L]/[Pd₄])
19
20. Results and Discussions - (Homonuclear complex)
Preparation of [Pd₈(μ-dpmppm)₄(CH₃CN)₂]X₄ (X= PF₆ ,BF₄)
20
³¹P{¹H} NMR
68%
22. Pd1-Pd2 < Pd2-Pd3 < Pd3-Pd4 > Pd4-Pd5 Pd – Pd distance range : (2.6249 – 2.7921 Å)
Space group : P-1
22
23. 1. Results proved that [Pd₂(μ-dpmppm)₂].(BF₄)₂ or (PF₆)₂ is a good precursor
for Pd chains , either extension to [Pd₈]⁴⁺ in acetonitrile
or
termination to [Pd₄]²⁺ in the presence of isocyanides .
2. All spectroscopic features of octanuclear complex for both (PF₆)₄ and
(BF₄)₄ are identical ,indicating that the counteranions have no influence on the
[Pd₈]⁴⁺ structure.
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24. Results and Discussions - (Heteronuclear complex)
Preparation of Pd₂M₂ Complexes, [Pd₂Cl(Cp*MCl)(Cp*MCl₂)(μ-dpmppm)₂](PF₆)₂
(M= Rh, Ir)
M= Rh (Pd(I)-Pd(I) = 2.6932 Å)
M= Ir (Pd(I)-Pd(I) = 2.710 Å)
24
4
26. Conclusion
Results demonstrating that the binuclear palladium(I) complexes with two
dpmppm ligands are viable precursors to extend low-valent Palladium chains and
Pd-involved mixed-metal multinuclear systems in stepwise procedures.
26
42. Critics & new ideas :
. In both articles, only synthetic pathways were investigated . Although
successful, no computational studies were done to consider how charge is
delocalized along the chain.
. No studies on physical & chemical properties of EMACs were reported.
* Computational studies deeply investigating charge delocalization along chain
* Studies on conductivity of homo & heterometallic chains.
* Comparison among different functional groups on ligands & physical
properties of produced EMACs.
42
43. Thanks
Advisor : Dr. Grapperhaus Lab mates & friends
Committee : Dr. Buchanan
Dr. Liu
Dr. Li
Seminar coordinator : Dr. Kozlowski
43
44. Introduction – explanation slide 8
Applications of Pd(I) Chains (EMAC)
EMACs
Mixed-valence compounds with delocalized unpaired electrons (symmetric
coordination sphere > indistinguishable valence)
Quantitatively explored conductance
Different arrangement of metal ions > Various interactions > Change in
extent of charge delocalization > Different ET efficiency
The stronger M-M interaction > The better conductivity
Longer chain > greater electron mobility > higher conductance
Less anionic ligand > Low valent MV > greater electron mobility
Heteronuclear EMAC > Charge disproportional framework > Rectifier
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45. Introduction –explanation slide 8
Applications of Pd Chains(containing Pd(I))
Properties :Linearly ordered, high-nuclearity, electron rich
Electron-transporting along metal string based on
quantum conducting phenomena (quantum tunneling)
An electron wavepacket directed at
a potential barrier. The dim spot at
right represents tunnelling electrons
4
5
46. Previous Studies – explanation slide 13 & 14
Linear tetraphosphine ligand (dpmppm) :
1 . dpmp (linear triphosphine ligand) effective in stabilizing Pt₂Pd centers in EMACs*
2 . dpmp leading to reductive coupling to generate low valent EMACs
Pd :
1 . Relatively weak Pd-L & Pd-Pd bonds > easier formation of Pd-M(hetero metal) chains
2 . More feasible to undergo convergent metal assembly **
* Goto. E., Begum. R., Ueno. C., Hosokawa. A., Yamamoto. C., Nakamae. K., Kure. B., Organometallics, 2014, 33, 1893.
** Mednikov. E., Dahl. L., J. Chem. Edu., 2009, 86, 1135.
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