Post on 05-Feb-2018
RECENT DEVELOPMENTS IN
CHALCOGEN CHEMISTRY: 4
Tristram Chivers
Department of Chemistry,
University of Calgary,
Calgary, Alberta, Canada
S S
P P h 2
C
P h 2 P 2 -
S e S e
P P h 2
H C
P h 2 P -
E E
P P h 2
C
P h 2 P 2 -
E '
Theme: Carbon-Centred Reactivity – Compare with PNP-Bridged Anions
Outline:
• Formation of stable carbenoids by oxidation of 1
• Synthesis and metal complexes of diseleno monoanion 2
• Formation of complexes of triseleno dianion 3a by Se-H+ exchange
• Redox behaviour of trichalcogeno dianions 3b and 3c
1 2 3a (E = E’ = Se) 3b (E = S, E’ = Se) 3c (E = E’ = S)
2
Chalcogen-Centred PCP-Bridged Ligands
Double Deprotonation: Metal Complexes: (Le Floch et al. 2004-2011)
• Methanediide complexes with TMs, lanthanides and actinides
• All complexes exhibit S,C,S coordination
• M-C bond: Highly polar, ca. single bond for early and late TMs
Significant multiple bonding for Ln and An
Recent review: S. T. Liddle, D. P. Mills, A. J. Wooles, Chem. Soc Rev. 2011, 40, 2164.
Le Floch et al. ACIE, 2004, 43, 6382.
3
A Dithio PCP-Bridged Dianion: Synthesis
S S
P P h 2
C
P h 2 P 2 -
( L i + ) 2 S S
P P h 2
H 2 C
P h 2 P 2 MeLi
toluene, -80 o C
Li 2 1 ( in situ reagent)
..
P h 2 P P P h 2
C
S
C
S
P P S S P h 2 P h 2
(a) Le Floch et al. ACIE, 2007, 46, 5947. (b) Konu and Chivers, Chem. Commun., 2008, 4995.
Li21 (a) (b)
C2Cl6 I2
- LiI
A Dithio PCP-Bridged Dianion: Oxidation
Formation of Stable Carbenoids upon Two-Electron Oxidation • Mild oxidation produces a monomeric carbenoid • Oxidation with I2 gives a dimeric carbenoid and a C2P2S2 ring comprised of two carbenes
4
L i +
S
S P
C
P
L i +
I
S
S P
C
P
I
( E t 2 O ) P h 2 P h 2
P h 2 P h 2
S S
P P h 2
C
P h 2 P
L i ( E t 2 O ) 2
C l
Synthesis: • Metallation first to avoid P=Se cleavage by RLi • iPr derivative (XRD) prepared from Cl2PCH2PCl2 • Deprotonation of Li2 accompanied by P=Se cleavage
Homoleptic Group 12 Complexes:
2 Li2 + MCl2
(M = Zn, Hg)
M = Zn, pale yellow (48%)
M = Hg, pale yellow (77%)
Diseleno PCP-Bridged Monoanion
L i
P P h 2
H C
P h 2 P
( T M E D A )
P P h 2
H 2 C
P h 2 P
MeLi
Et2O, TMEDA
2 Se
toluene
Li2
(XRD)
S e S e
P P h 2
H C
P h 2 P
L i ( T M E D A )
J. Konu, H. M. Tuononen, T. Chivers, Inorg. Chem., 2009, 48, 11788. 5
Oxidation with I2: Produces C-H rather than Se-Se bond, cf. PNP system
(R = Ph, iPr) [Dark red intermediate]
One-electron Oxidation: Hydrogen Abstraction
6
+ ½ I2
THF THF S e S e
P R 2
H C
R 2 P
L i ( T M E D A )
S e S e
P R 2
H C
R 2 P
S e S e
P R 2
H 2 C
R 2 P
J. Konu, H. M. Tuononen, T. Chivers, Inorg. Chem., 2009, 48, 11788.
Oxidation with I2: Produces C-H rather than Se-Se bond, cf. PNP system
(R = Ph, iPr) [Dark red intermediate]
One-electron Oxidation: Hydrogen Abstraction
7
SOMOs of Neutral Radicals
PCP: R = iPr
Significant contribution from p-orbital on C
PNP: R = Me
Localized on chalcogens; No contribution from N atom
+ ½ I2
THF THF S e S e
P R 2
H C
R 2 P
L i ( T M E D A )
S e S e
P R 2
H C
R 2 P
S e S e
P R 2
H 2 C
R 2 P
2 SnCl2 4
- 2 - [Sn0]
NMR (1H, 31P, 77Se, cf. Group 12 complexes)
red crystals (51%)
- 4 LiCl
NMR: • Monoselenide (P=Se) is eliminated
XRD:
• Octahedral tin(IV) complex • Two tridentate [SeC(Ph2PSe)2]2- ligands • Se-H+ exchange • Redox process [Sn(II) → Sn(IV)]
A Triseleno PCP-Bridged Tin(IV) Complex
S e S e
P P h 2
H C
P h 2 P
L i ( T M E D A )
S e
S e P
H C
P
S n I I
S e
S e P
C H
P
P h 2 P h 2
P h 2 P h 2
S e
P P h 2
H 2 C
P h 2 P
S n S e
S e S e
S e
S e
S e
C P h 2 P
P h 2 P
C
P P h 2
P P h 2
IV
J. Konu, T. Chivers, Chem. Commun., 2010, 46, 1431. 8
2 TeCl2•TMTU
4 - 2 [H2C(PPh2)(PPh2Se)]
- 4 LiCl
dark red crystals (47%)
IV
C
P P h 2
S e
T e
S e S e
S e S e
P h 2 P C
P h 2 P
S e
P P h 2
S e S e
P P h 2
H C
P h 2 P
L i ( T M E D A )
NMR: • Monoselenide H2C(PPh2)PPh2Se detected • No evidence for intermediate Te(II) complex
XRD: • Te(IV) complex • Two bidentate [SeC(Ph2PSe)2]2- ligands (cf. Sn complex) • Stereochemically active LP on Te: See-saw geometry • Se-H+ exchange • Redox process [Te(II) → Te(IV)]
A Triseleno PCP-Bridged Tellurium(IV) Complex
[J. Konu, T. Chivers, Chem. Commun., 2010, 46, 1431]
9
• Homoleptic Tl(I) complex formed initially • Dark purple Tl(I)/Tl(III) complex on heating
XRD: • Mixed-valent Complex: Octahedral Tl(III) anions and Tl+ cations
• cf. Isovalent neutral Sn(IV) complex
• Polymeric chain in solid state via weak Tl···Se interactions
M. Risto, T. Chivers, J. Konu, Dalton Trans. 2011, 40, 8238.
A Mixed-Valent Tl(I)/Tl(III) Complex
LiOEt
TlOEt
S e S e
P P h 2
H C
P h 2 P
L i ( T M E D A )
S e S e
P P h 2
H C
P h 2 P
Tl ( )
T l S e
S e S e
S e
S e
S e
C P h 2 P
P h 2 P
C
P P h 2
P P h 2
60 °C
toluene
–
Tl+
10
• Is redox capability of metal centre necessary for Se-H+ exchange?
XRD: • Two Hg(II) centres linked by two [SeC(Ph2PSe)2]2- ligands
• Hg···Hg = 3.105(1) Å (cf. 2.49-2.53 Å in Hg2X2)
Conclusion: • Se-H+ exchange can occur without oxidation at metal centre
J. Konu, T. Chivers, Chem. Commun., 2010, 46, 1431. 11
A Triseleno PCP-Bridged Binuclear Hg(II) Complex
THF or toluene,
65 oC, 48h
- 2 [H2C(PPh2)(PPh2Se)] 2 II
II H g
S e
S e S e
S e
S e
S e
P h 2 P
P h 2 P
C
P P h 2
P P h 2
H g
C
S e
S e P
H C
P
H g I I
S e
S e P
C H
P
P h 2 P h 2
P h 2 P h 2
Summary: Proton-Selenium Exchange
• Redox disproportionation [MII → MIV + M0 (M = Sn, Te)]
• Oxidation (TlI → TlIII)
• No change in oxidation state (HgII)
• Mechanism???
• Can the dianion [SeC(Ph2PSe)2]2- be generated by direct synthesis? 12
-H+, +Se
+
S e S e
P P h 2
H C
P h 2 P -
Se
Se P P h 2
C
P P h 2
Se
S e
P P h 2
H 2 C
P h 2 P
Formation of Triseleno PCP-Bridged Dianions
Direct Synthesis: • Diseleno PCP-bridged dianion inaccessible (P=Se cleavage)
• Use Le Floch’s dithio PCP-bridged dianion
XRD (E = Se): • S,Se-chelation of both Li+ ions
• Approx. planar C atom (Σ <C = 355°)
• d(C-Se) = 1.970(3) Å (single bond = 1.97 Å; double bond = 1.74 Å)
E, 2 TMEDA, toluene
(85-90%)
-80 oC (E = S)
0 oC (E = Se)
J. Konu, T. Chivers, H. M Tuononen, Chem. Eur. J., 2010, 16, 12977. 13
Trichalcogeno PCP-Bridged Dianions: Lithium Derivatives
S S
P P h 2
C
P h 2 P 2 -
( L i + ) 2 E
C
P h 2 P
S
L i L i
S
P h 2 P
( T M E D A ) ( T M E D A )
Expected products of One and Two-Electron Oxidation: Questions: • Can the anion radicals (B) be stabilized or do they dimerize rapidly? • What is the nature of the chalcogen-chalcogen bonding in these dimers? • Can neutral chalcogenocarbonyls (C) be isolated?
- e- - e-
A (dianion) B (radical anion) C (neutral species)
14
S S
P P h 2
C
P h 2 P
E
S S
P P h 2
C
P h 2 P
E
S S
P P h 2
C
P h 2 P
E
Trichalcogeno PCP-Bridged Dianions: Redox Behaviour?
One-electron oxidation:
• Products are dimers of monoanion radicals [EC(Ph2PS)2]•-
• Long chalcogen-chalcogen distances (compared to single bonds):
S–S = 2.222(2) Ǻ (ca. 8 % elongation)
Se–Se = 2.508(1) Ǻ (ca. 8 % elongation)
• Almost planar carbon atoms (Σ <C = 352-357o) 15
Formation of Chalcogen-Chalcogen Bonded Dimers
I2, toluene
- 2 LiI
(E = S, 60%
E = Se, 74%)
[Li+(TMEDA)]2
2
S
S P P h 2
C
P P h 2
E S
S P h 2 P
C
P h 2 P
E E
C
P h 2 P
S
L i L i
S
P h 2 P
( T M E D A ) ( T M E D A )
• SOMO of anion radical is π* orbital of C=E bond
• Net chalcogen-chalcogen bonding in dimers due to overlap of two SOMOs
• Explains long E–E bonds
[EC(PPh2S)2]•− [(SPh2P)2CEEC(PPh2S)2]2−
16
Frontier Orbitals of Radical Anions and Their Dimers
• Attempted 2e- oxidation of all-sulfur system → monoprotonation
• Also occurs upon removal of Li+ from dianion with 12-crown-4
Monoprotonated Dimer:
• S,S-Chelated [Li(TMEDA)]+ derivative [d(S-S) = 2.140(1) Ǻ]
• Ion-separated [Li(12-crown-4)2]+ salt [d(S-S) = 2.112(2) Ǻ]
• [SC(Ph2PS)2]•- anion radical and [S(H)C(Ph2PS)2]• radical linked by S-S bond
17
THF, CH2Cl2,
[Li+(TMEDA)]2
CH3CN or 12-c-4
[Li+(L)]
(L = TMEDA, (12-c-4)2)
S
S P P h 2
C
P P h 2
S S
S P h 2 P
C
P h 2 P
S
S
S P P h 2
C
P P h 2
S
S
S P
C
P
S
H
P h 2
P h 2
Monoprotonation of Dimeric S-S Bonded Dimer
Two-electron Oxidation: •Occurs cleanly for selenodithio PCP-bridged dianion XRD: • d(Se-I) = 2.722(1) Å, ca. 0.2 Å longer than in RSeI • Planar at C(Se): d(C-Se) = 1.815(4) Å (cf. 1.77-1.84 Å for R2C=Se)
Properties: • Free selone cannot be isolated; Removal of LiI → decomposition
I2, toluene
- LiI
- TMEDA
deep red crystals (71%)
18
Formation and Structure of a Selone-LiI Complex
S e
C
P h 2 P
S
L i L i
S
P h 2 P
( T M E D A ) ( T M E D A )
S
S P P h 2
C
P P h 2
S e ( T M E D A ) L i
I
1. Can the anion radicals (B) be stabilized or do they dimerize rapidly?
The anion radicals dimerize rapidly upon one-electron oxidation of dianions
2. What is the nature of the chalcogen-chalcogen bonding in these dimers?
The dimers form elongated chalcogen-chalcogen bonds (π* - π* interaction}
3. Can neutral chalcogenocarbonyls (C) be isolated?
A LiI-stabilized selenocarbonyl can be isolated.
Attempts to generate the thiocarbonyl resulted in proton abstraction 19
- e- - e-
A (dianion) B (radical anion) C (neutral species)
S S
P P h 2
C
P h 2 P
E
S S
P P h 2
C
P h 2 P
E
S S
P P h 2
C
P h 2 P
E
Trichalcogeno PCP-Bridged Dianions: Redox Behaviour
• Multidentate Chalcogen-centred Dianionic Ligands
• Elongated E–E Bonds (E = S, Se)
Questions:
• What are the possible coordination modes of this dianionic ligand?
• Does the E–E bond remain intact?
• What is the influence of complexation on E–E bond length?
• Does redox occur to give complexes of the monomeric dianion?
Test by carrying out reactions with coinage metals (Cu, Ag, Au)
20
Dichalcogenide Dianions: Coordination Chemistry
+ 2 CuCl2
+ 2 CuCl
2
(dark red)
XRD: (a) Se-Se bond retained, but elongated by 5-6 % compared to Li derivative
(b) Cu–Se bonding approx. symmetrical (c) First example of η2-Se2 bonding for RSe-SeR 21
Binuclear Cu(I) Complex: Retention of Se–Se Bond
Cu
Cu
C
C
P
P
P
P S
Se
S
S
Se
S
Redox
Metathesis
+ 2 CuCl2
+ 2 CuCl
2
(dark blue)
XRD: • Two independent molecules with S···S contacts elongated by 19 and 27 % compared to Li derivative
DFT: • Some diradical character, cf. flexible S-S bond
Konu, Chivers, Tuononen, Chem. Eur. J., 2011, 17, 11844. 22
Binuclear Cu(I) Complex: Retention of S–S Bond
S P
C
Cu
Cu
S
S
S
S
S
P
P
P
C
Redox
Metathesis
XRD: • Unsymmetrical Ag-η2-Se2 bonding d(Ag−Se) = 2.856(1) Å, 3.200(2) Å
• d(Se−Se) = 2.51 Å (cf. 2.51 Å in Li2 complex)
31P NMR: • VT experiments indicate presence of two
isomers in solution • Rapid Ag-Se exchange process?
+ 2 AgOSO2CF3
(red)
23
Binuclear Ag(I) Complex: Retention of Se–Se Bond
C
Ag
Ag
S S
S
Se Se
P
P
P C
P
S
(Metathesis)
XRD:
• Two-electron reduction (cleavage) of E–E bond to form two monomeric dianions
• One AuI centre oxidized to AuIII (square-planar); the other remains as AuI (linear)
• Tridentate [SeC(Ph2PS)2]2- dianions are S,S’-chelated to the Au2 unit and E-
monodentate towards square-planar AuIII centre
24
Binuclear Au(I)/Au(III) Complexes: Redox Behaviour
+ 2 Au(CO)Cl
S
S P P h 2
C
P P h 2
E S
S P h 2 P
C
P h 2 P
E
[ L i + ( T M E D A ) ] 2
(Redox)
E
u
u S A
S
S
S
E P h
2 P
P h 2 P
C
P P h 2
P P h 2
A
C
(E = S, Se)
Summary:
• E–E bond is retained in Cu and Ag complexes
• Metal-dichalcogenide interaction is stronger for Cu
• Pronounced elongation of S–S bond and some diradical character
• Redox reaction occurs with gold(I) reagent to give Au(I)/Au(III) complex • Very flexibile ligand due to labile E–E bond
• Diradical character - activation of small molecules- further studies 25
Dichalcogenide Dianions: Coordination Chemistry
A new feature of the Se-H+ exchange process
NMR: •Monoselenide H2C(PPh2)PPh2Se detected
XRD: •Dimeric CuI/CuI complex with Se-Se bond (2.689(1) Å), cf. single bond ~ 2.33 Å
Conclusion: •Se-H+ exchange, reduction of metal (CuII → CuI) and oxidation of ligand → diselenide
+ 2 CuIICl2
4 - 2 [H2C(PPh2)(PPh2Se)]
(45%)
26
Binuclear Cu(I) Complex via Se-H+ Exchange
Cu
Cu
C
C
P
P
P
P Se
Se
Se
Se
Se
Se
M. Risto, J. Konu, T. Chivers, Inorg. Chem. 2010, 50, 406