agc redox active ligands - princeton...
TRANSCRIPT
![Page 1: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/1.jpg)
Redox-Active Ligands
MacMillan Group MeetingAndrew Capacci
2/4/14
![Page 2: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/2.jpg)
Coordination Chemistry and Metal-Ligand Interactions
! The coordination of metal complexes have been described in the classical terms of Werner complexes
Jørgensen, C. K. Coord. Chem. Rev., 1966, 1, 164.Chirik, P. J. Inorg. Chem., 2011, 50, 9737.
FeNH3
CoNH3
NH3
H3N
H3N
NH3
FeCp2
3+
[Co(NH3)6]Cl3
PtCl
H3N
H3N
Cl
PtCl2(NH3)2
! Considered "innocent" ligands as the metal oxidation state is easily predicted
NH3
CoNH3
NH3
H3N
H3N
NH3
3+
[Co(NH3)6]Cl3
NH3 = L type
overall charge = +3
Co(III)
Fe
FeCp2
PtCl
H3N
H3N
Cl
PtCl2(NH3)2
Cp = X type
overall charge = 0
Fe(II)
Cl = X type
overall charge = 0
Pt(II)
![Page 3: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/3.jpg)
Coordination Chemistry and Metal-Ligand Interactions
! The coordination of metal complexes have been described in the classical terms of Werner complexes
Jørgensen, C. K. Coord. Chem. Rev., 1966, 1, 164.Chirik, P. J. Inorg. Chem., 2011, 50, 9737.
FeNH3
CoNH3
NH3
H3NH3N
NH3
FeCp2
3+
[Co(NH3)6]Cl3
PtCl
H3NH3N
Cl
PtCl2(NH3)2
! Considered "innocent" ligands as the metal oxidation state is easily predicted
! Non-innocent ligands are classified as having experimentally determined oxidation state differ from prediction
N
NN
N
FeIV
SR
O
Fe(IV), ligand radical cation
Which oxidation state doesthe iron center in Compound I
actually exist in?
Me
Me–O2C
–O2CMe
N
NN
N
FeV
SR
OMe
Me–O2C
–O2CMe
Fe(V), neutral ligand
![Page 4: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/4.jpg)
Non-Innocent vs. Redox-Active Ligands
! What's the difference between "noninnocent" and "redox active" ligands?
Chirik, P. J., Wieghardt, K. Science, 2010, 327, 794.Chirik, P. J. Inorg. Chem., 2011, 50, 9737.
"Oftentimes, the two descriptions 'redox-active' and 'noninnocent' ligands are used interchangeablyin the literature. However, care must be used when using the latter because clearly defined physicaloxidation states have often been established for a case where ambivalence has been implied."
-Chirik (2011)
! Non-innocent ligands are classified as having experimentally determined oxidation state differ from prediction
N
NN
N
FeIV
SR
O
Fe(IV), ligand radical cation
Which oxidation state doesthe iron center in Compound I
actually exist in?
Me
Me–O2C
–O2CMe
N
NN
N
FeV
SR
OMe
Me–O2C
–O2CMe
Fe(V), neutral ligand
"Redox-active, or 'noninnocent,' ligands have more energetically accessible levels that allow redoxreactions to change their charge state."
-Chirik, Weighardt (2010)
![Page 5: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/5.jpg)
Non-Innocent vs. Redox-Active Ligands
! What's the difference between "noninnocent" and "redox active" ligands?
Chirik, P. J., Wieghardt, K. Science, 2010, 327, 794.Chirik, P. J. Inorg. Chem., 2011, 50, 9737.
"Oftentimes, the two descriptions 'redox-active' and 'noninnocent' ligands are used interchangeablyin the literature. However, care must be used when using the latter because clearly defined physicaloxidation states have often been established for a case where ambivalence has been implied."
-Chirik (2011)
! Non-innocent ligands are classified as having experimentally determined oxidation state differ from prediction
N
NN
N
FeIV
SR
O
Fe(IV), ligand radical cation
Which oxidation state doesthe iron center in Compound I
actually exist in?
Me
Me–O2C
–O2CMe
N
NN
N
FeV
SR
OMe
Me–O2C
–O2CMe
Fe(V), neutral ligand
"Redox-active, or 'noninnocent,' ligands have more energetically accessible levels that allow redoxreactions to change their charge state."
-Chirik, Weighardt (2010)
Fe(IV) state
![Page 6: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/6.jpg)
Non-Innocent vs. Redox-Active Ligands
! What's the difference between "noninnocent" and "redox active" ligands?
Chirik, P. J., Wieghardt, K. Science, 2010, 327, 794.Chirik, P. J. Inorg. Chem., 2011, 50, 9737.
"Oftentimes, the two descriptions 'redox-active' and 'noninnocent' ligands are used interchangeablyin the literature. However, care must be used when using the latter because clearly defined physicaloxidation states have often been established for a case where ambivalence has been implied."
-Chirik (2011)
! Non-innocent ligands are classified as having experimentally determined oxidation state differ from prediction
"Redox-active, or 'noninnocent,' ligands have more energetically accessible levels that allow redoxreactions to change their charge state."
-Chirik, Weighardt (2010)
Milstein cat. (0.1 mol%)
toluene, ! N
RuEt2N PtBu2
CO
H
OH
R'H2N
R"
O
NH
R'R"
–2 H2
! Non-redox-active cooperative ligation is interesting but beyond the scope of this discussion
![Page 7: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/7.jpg)
Coordination Chemistry and Metal-Ligand Interactions
! Early discovery of noninnocent ligands: metal dithiolene complexes (1960s)
Eisenberg, R., Gray, H. B. Inorg. Chem., 2011, 50, 9741.
! Dithiolene complexes were examined for their spectroscopic and redox properties
SM
S
S
SR
R
R
R
R = Ph, CN, CF3
M = Ni, Cu, Co, Pd, Pt
The conventional assignmentof V(S2C2Ph2)3 would require aV(VI) metal center! (3p5 valency)
S
SS
V
S
SS
PhPh
Ph
Ph Ph
Ph
SNi
S
S
SPh
Ph
Ph
Ph SNi
S
S
SPh
Ph
Ph
Ph
Ni(II), d8 Ni(IV), d6
SNi
S
S
SPh
Ph
Ph
Ph
Ni(0), d10
![Page 8: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/8.jpg)
Coordination Chemistry and Metal-Ligand Interactions
! Early discovery of noninnocent ligands: metal dithiolene complexes (1960s)
Eisenberg, R., Gray, H. B. Inorg. Chem., 2011, 50, 9741.
! Dithiolene complexes have applications in catalysis: Mo oxotransferases
SM
S
S
SR
R
R
R
R = Ph, CN, CF3
M = Ni, Cu, Co, Pd, Pt
The conventional assignmentof V(S2C2Ph2)3 would require aV(VI) metal center! (3p5 valency)
S
SS
V
S
SS
PhPh
Ph
Ph Ph
Ph
MoSS S
S
OSerine
RR
RRMe
SMe
OMe
SMe
![Page 9: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/9.jpg)
Advantages of Redox-Active Ligands
! Confering noble reactivity to non-noble metals
Blackmore, K. J., Ziller, J. W., Heyduk, A. F. Inorg. Chem., 2005, 44, 5559.Haneline, M. R., Heyduk, A. F. J. Am. Chem. Soc., 2006, 128, 8410.
! Reductive elimination from a Zr(IV) center is also possible with redox-active ligands
O
tBuNO
Zr
O
OtBuN
tBu
tBu
tBu
tBu
Cl
tBuNO
Zr
Cl
OtBuN
tBu
tBu
tBu
tBu
Cl2
Ph
tBuNO
Zr
Ph
OtBuN
tBu
tBu
tBu
tBu
O
tBuNO
Zr
O
OtBuN
tBu
tBu
tBu
tBu
2–
[Cp2Fe]PF6 (2 equiv.)
THF, -78 °C then-78 °C to rt
Oxidative additionwith a d0 metal complex
reductive eliminationfrom Zr(IV)
![Page 10: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/10.jpg)
Advantages of Redox-Active Ligands
! Generation of novel reactivity:
Prier, C. K., Rankic, D. A., MacMillan, D. W. C. Chem. Rev., 2013, 113, 5322.
452 nm
t2g
eg
t2g
eg
!* (bpy)
t2g
eg
!* (bpy)
t2g
eg
!* (bpy)strong oxidant
Ru(bpy)33+
Ru(bpy)3+
E1/2 = +.79 V
strong reductant
E1/2 = –.83 V
Ru(bpy)32+ *Ru(bpy)32+
N
NN
N
N
NRu
2+
N
NN
N
N
NRu
2+*
![Page 11: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/11.jpg)
Classes of Redox-Active Ligands
M+nLSpectator Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.
![Page 12: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/12.jpg)
Classes of Redox-Active Ligands
M+nL
M+nL
-e–
S
M+nL
S
M+(n+2)L-2
S
Modification of metal electronicsvia ligand modification
Electron transfer to ligand
Spectator Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.
![Page 13: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/13.jpg)
Classes of Redox-Active Ligands
M+nL
M+nL
-e–
S
M+nL
S
M+(n+2)L-2
S
Modification of metal electronicsvia ligand modification
Electron transfer to ligand
Spectator Ligand Actor Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.
![Page 14: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/14.jpg)
Classes of Redox-Active Ligands
M+nL
M+nL M+nL
M+(n+1)L
SX
SX
S
S•
M+nL
S
-e–
S
M+nL
S
M+(n+2)L-2
S
Modification of metal electronicsvia ligand modification Ligand assisted substrate activation
Redox-active substrate complexElectron transfer to ligand
Spectator Ligand Actor Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.
![Page 15: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/15.jpg)
M+nL
M+(n+1)L
SX
SX
S
S•
M+nL
S
S
M+nL
S
M+(n+2)L-2
S
Ligand assisted substrate activation
Redox-active substrate complexElectron transfer to ligand
Actor Ligand
Classes of Redox-Active Ligands
M+nL
M+nL
-e–
Modification of metal electronicsvia ligand modification
Spectator Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.
![Page 16: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/16.jpg)
Ligand Controlled Modification of Catalytic Activity
! Early studies by Wrighton in rhodium catalyzed processes
Lorkovic, I. M., Duff, R. R., Wrighton, M. S. J. Am. Chem. Soc., 1995, 117, 3617.
CoII
P
P
Rh
PhPh
PhPh
Solv. CoIII
P
P
Rh
PhPh
PhPh
Solv.
2++
–e–
+e–
! Reduced catalyst complex is 16 times more reactive towards alkene hydrogenation
! Oxidized catalyst complex was found to be more reactive for ketone hydrosilylation
![Page 17: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/17.jpg)
Ligand Controlled Modification of Catalytic Activity
! Use of redox-active ligands as switches in Lewis acid mediated polymerizations
! An efficient redox switch would be desirable for thecontrolled synthesis of block copolymers
Ti NNOO
tBu tBu
OiPr
OiPrFeIIFeII
Gregson, C. K. A., Gibson, V. C., Long, N. J. Marshall, E. L., Oxford, P. J., White, A. J. P. J. Am. Chem. Soc., 2006, 128, 7410.
Ti NNOO
tBu tBu
OiPr
OiPrFeIIIFeIII
–2e–
+2e–
Active catalyst Inactive catalyst
O
O
O
O
Me
Me
HO
O
OHMe n
Ti-salen cat.
![Page 18: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/18.jpg)
Ligand Controlled Modification of Catalytic Activity
! Use of redox-active ligands as switches in Lewis acid mediated polymerizations
! Rate of polymerization decreases with increasedLewis acidity of the metal comlex
Ti NNOO
tBu tBu
OiPr
OiPrFeIIFeII
Gregson, C. K. A., Gibson, V. C., Long, N. J. Marshall, E. L., Oxford, P. J., White, A. J. P. J. Am. Chem. Soc., 2006, 128, 7410.
Ti NNOO
tBu tBu
OiPr
OiPrFeIIIFeIII
–2e–
+2e–
Active catalyst Inactive catalyst
O
O
O
O
Me
Me
HO
O
OHMe n
Ti-salen cat.
![Page 19: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/19.jpg)
M+nL
M+(n+1)L
SX
SX
S
S•
M+nL
S
S
M+nL
S
M+(n+2)L-2
S
Ligand assisted substrate activation
Redox-active substrate complexElectron transfer to ligand
Actor Ligand
Classes of Redox-Active Ligands
M+nL
M+nL
-e–
Modification of metal electronicsvia ligand modification
Spectator Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.
![Page 20: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/20.jpg)
M+nL M+nL
M+(n+1)L
SX
SX
S
S•
M+nL
S
-e–
Modification of metal electronicsvia ligand modification Ligand assisted substrate activation
Redox-active substrate complex
Actor Ligand
Classes of Redox-Active Ligands
M+nL
S
M+nL
S
M+(n+2)L-2
S
Electron transfer to ligand
Spectator Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.
![Page 21: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/21.jpg)
Redox Active Bis(imino)-Pyridine Ligand with Iron(II)
! Brookhart developed bulky pyridine diimine ligands for use in polymerization
! In 2006, involvement of the PDI ligand upon two-electron reduction of the iron complex was established
Small, B. L., Brookhart, M., Bennett, A. M. A. J. Am. Chem. Soc., 1998, 120, 4049.Bart, S. C., Chlopek, K., Bill, E., Bouwkamp, M. W., Lobkovsky, E., Neese, F., Wieghardt, K., Chirik, P. J. J. Am. Chem. Soc., 2006, 128, 13901.
NFe
N
N
Me
Me
Ar
Ar
XX
Ar = 2,6-(iPr)2-C6H3
nMAO
NFeII
N
N
Me
Me
Ar
Ar
XX
NFe0
N
N
Me
Me
Ar
Ar
N2N2
NFeI
N
N
Me
Me
Ar
Ar
N2N2
NFeII
N
N
Me
Me
Ar
Ar
N2N2
2 e–
major resonanceform
![Page 22: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/22.jpg)
Redox Active Bis(imino)-Pyridine Ligand with Iron(II)
! Brookhart developed bulky pyridine diimine ligands for use in polymerization
! In 2006, involvement of the PDI ligand upon two-electron reduction of the iron complex was established
Small, B. L., Brookhart, M., Bennett, A. M. A. J. Am. Chem. Soc., 1998, 120, 4049.Bart, S. C., Chlopek, K., Bill, E., Bouwkamp, M. W., Lobkovsky, E., Neese, F., Wieghardt, K., Chirik, P. J. J. Am. Chem. Soc., 2006, 128, 13901.
NFe
N
N
Me
Me
Ar
Ar
XX
Ar = 2,6-(iPr)2-C6H3
nMAO
NFeII
N
N
Me
Me
Ar
Ar
N2N2
major resonanceform
NFeII
N
N
Me
Me
Ar
Ar
N
NMe2
vs.
![Page 23: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/23.jpg)
Redox Active Bis(imino)-Pyridine Ligand with Iron(II)
! Chirik has developed bis(imino)-pyridine iron(II) dinitrogen complexes with unique reactivity
Bouwkamp, M. W., Bowman, A. C., Lobkovsky, E., Chirik, P. J. J. Am. Chem. Soc., 2006, 128, 13340.
NFe
N
N
Me
Me
Ar
Ar
N2N2Ar = 2,6-(iPr)2-C6H3
E E
H
H
10 mol%
E =
CH2
NBn
NtBu
C(CO2Et)2
Time (min) Conv. (%) TOF (h-1)
300 92 1.8
26 90 21
< 5 > 95 > 240
141 > 95 4
benzene, 23 °C
![Page 24: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/24.jpg)
Redox Active Bis(imino)-Pyridine Ligand with Iron(II)
! Chirik has developed bis(imino)-pyridine iron(II) dinitrogen complexes with unique reactivity
Bouwkamp, M. W., Bowman, A. C., Lobkovsky, E., Chirik, P. J. J. Am. Chem. Soc., 2006, 128, 13340.
NFeII
N
N
Me
Me
Ar
Ar E
NFeII
N
N
Me
Me
Ar
ArE
H
H
NFe
N
N
Me
Me
Ar
Ar
N2N2Ar = 2,6-(iPr)2-C6H3
E E
H
H
10 mol%
! PDI ligand acts as an electron sink to enable metallocene formation and reductive elimination
benzene, 23 °C
![Page 25: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/25.jpg)
Redox Active Bis(imino)-Pyridine Ligand with Iron(II)
! Chirik has developed bis(imino)-pyridine iron(II) dinitrogen complexes with unique reactivity
Sylvester, K. T., Chirik, P. J. J. Am. Chem. Soc., 2009, 131, 8772.Bouwkamp, M. W., Bowman, A. C., Lobkovsky, E., Chirik, P. J. J. Am. Chem. Soc., 2006, 128, 13340.
! Reductive enyne cyclizations are also possible via similar mechanism
NTs NTsMe
Me
Me
79% yield, 6.7 TOF
NFe
N
N
Me
Me
Ar
Ar
N2N2Ar = 2,6-(iPr)2-C6H3
E E
H
H
10 mol%
NFe
N
N
Me
Me
Ar
Ar
N2N2Ar = 2,6-(iPr)2-C6H3
10 mol%
H2 (4 atm), benzene, 23 °C
benzene, 23 °C
![Page 26: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/26.jpg)
Redox Active Bis(imino)-Pyridine Ligand with Iron(II)
! Terminal alkene hydrosilylation for use in industrial applications
Tondreau, A. M., Atienza, C. C. H., Weller, K. J., Nye, S. A., Lewis, K. M., Delis, J. G. P., Chirik, P. J. Science, 2012, 335, 6068, 567.
NFe
N
N
Me
Me
Ar
Ar
N2N2
Me MeR3Si
! One of the largest-scale applications of homogeneous catalysis
! Used to produce a range of silicone-based surfactants, fluids, molding products,release coatings, and pressure-sensitive adhesives
! Current production relies upon the use of Nobel metal catalysts (Pt, Pd, Ru, and Rh)
! Estimated that industry consumed 5.6 metric tons of Pt in 2007
R3Si–H, neat, 23 °C
![Page 27: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/27.jpg)
Redox Active Bis(imino)-Pyridine Ligand with Iron(II)
! Terminal alkene hydrosilylation for use in industrial applications
Tondreau, A. M., Atienza, C. C. H., Weller, K. J., Nye, S. A., Lewis, K. M., Delis, J. G. P., Chirik, P. J. Science, 2012, 335, 6068, 567.
NFe
N
N
Me
Me
Ar
Ar
N2N2
Me MeR3Si
Catalyst
1
mol %
0.05
0.04
0.03
Silane
(TMSO)2MeSiH
(EtO)3SiH
Et3SiH
Time Yield (GC)
15 min
15 min
1 hr
> 98%
96%
trace
0.02
0.02
Et3SiH
Et3SiH
15 min
45 min
9%
> 98%
1, Ar = 2,6-(iPr)2-C6H3
NFe
N
N
Me
Me
Ar
ArN2N2 2
Ar = 2,6-(Et)2-C6H3, 2Ar = 2,6-(Me)2-C6H3, 3
R3SiH, [Fe]
2
3
1
1
0.004 (TMSO)2MeSiH 15 min > 98%3 25,000 turnovers
neat, 23 °C
![Page 28: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/28.jpg)
Redox Active Bis(imino)-Pyridine Ligand with Iron(II)
! Terminal alkene hydrosilylation for use in industrial applications
Tondreau, A. M., Atienza, C. C. H., Weller, K. J., Nye, S. A., Lewis, K. M., Delis, J. G. P., Chirik, P. J. Science, 2012, 335, 6068, 567.
C5H11
Et3Si
NFe
N
N
Me
Me
Ar
ArN2N2 2
Ar = 2,6-(Me)2-C6H3
NFeII
N
N
Me
Me
Ar
Ar
C5H11
NFeII
N
N
Me
Me
Ar
Ar
H11C5
NFeII
N
N
Me
Me
Ar
Ar
H
C5H11
Et3Si
NFeII
N
N
Me
Me
Ar
Ar
Et3Si
C5H11
AlkeneHydrosilylation
Et3Si H
![Page 29: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/29.jpg)
Negishi-type Coupling Using Cobalt(III)
! Breakthrough use of Cobalt(III) for alkyl halide oxidative addition and reductive elimination
! Oxidative addition results in formation of semiquinonate complex
Smith, A. L., Hardcastle, K. I., Soper, J. D. J. Am. Chem. Soc., 2010, 132, 14358.
CoN
NO
O
t-Bu
t-Bu
t-Bu
t-BuPh
Ph
CoN
NO
O
t-Bu
t-Bu
t-Bu
t-BuPh
PhEt
ZnBr
Et
CoIII(Et)(apPh)2[CoIII(apPh)2]–
[CoIII(apPh)2]–
EtBr
10-15% yield
![Page 30: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/30.jpg)
Negishi-type Coupling Using Cobalt(III)
! Breakthrough use of Cobalt(III) for alkyl halide oxidative addition and reductive elimination
! Oxidative addition highly responsive to sterics
Smith, A. L., Hardcastle, K. I., Soper, J. D. J. Am. Chem. Soc., 2010, 132, 14358.
CoN
NO
O
t-Bu
t-Bu
t-Bu
t-BuPh
Ph
CoN
NO
O
t-Bu
t-Bu
t-Bu
t-BuPh
PhEt
ZnBr
Et
CoIII(Et)(apPh)2[CoIII(apPh)2]–
[CoIII(apPh)2]–
EtBr
Alkyl electrophile:
Reaction Time:
CH3I, CH3OTf
< 30 sec
EtI EtBr
<1 min 1 hr
i-PrI
3 hrs
BnBr
24 hrs
BnCl
> 48 hrs
! Oxidative addition likely occurs through an SN2 type mechanism
10-15% yield
![Page 31: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/31.jpg)
Negishi-type Coupling Using Cobalt(III)
! Breakthrough use of Cobalt(III) for alkyl halide oxidative addition and reductive elimination
! Treatment with organozinc reagents induces reductive elimination in low yield
Smith, A. L., Hardcastle, K. I., Soper, J. D. J. Am. Chem. Soc., 2010, 132, 14358.
CoN
NO
O
t-Bu
t-Bu
t-Bu
t-BuPh
Ph
CoN
NO
O
t-Bu
t-Bu
t-Bu
t-BuPh
PhEt
ZnBr
Et
CoIII(Et)(apPh)2[CoIII(apPh)2]–
[CoIII(apPh)2]–
EtBr
CoIII(Et)(apPh)2remaining Ph–Et yield
11%
15%
15%
15%
PhZnBr(equiv.)
2
4
6
10
20%
7%
3%
2%
10-15% yield
![Page 32: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/32.jpg)
M+nL M+nL
M+(n+1)L
SX
SX
S
S•
M+nL
S
-e–
Modification of metal electronicsvia ligand modification Ligand assisted substrate activation
Redox-active substrate complex
Actor Ligand
Classes of Redox-Active Ligands
M+nL
S
M+nL
S
M+(n+2)L-2
S
Electron transfer to ligand
Spectator Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.
![Page 33: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/33.jpg)
Classes of Redox-Active Ligands
M+nL
M+nLSX
SX
Ligand assisted substrate activation
Actor Ligand
M+nL
M+(n+1)L
S
S•
M+nL
S
-e–
S
M+nL
S
M+(n+2)L-2
S
Modification of metal electronicsvia ligand modification
Redox-active substrate complexElectron transfer to ligand
Spectator Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.
![Page 34: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/34.jpg)
Redox-Active Ligand in Actor Role During Catalysis
! Novel reactivity derived from ligand centered radical in nature
Wachter, R. M., Montagne-Smith, M. P., Branchaud, B. P. J. Am. Chem. Soc., 1997, 119, 7743.
O OHOH
HO
OHHO
O OHOH
HO
OHO
Galactose Oxidase, O2
! Galactose oxidase, isolated from a fungal form, is a copper(II) containing enzyme which catalyzes the oxidation of primary alcohols to aldehydes
! This enzyme has been found to utilize a redox active tyrosine residue to facilitate the 2-electron oxidation process
CuIIO
(His496)N
(His581)N
OH2
O S (Tyr272)
(Tyr495)
(Cys228)
Catalytically active form of enzyme:
![Page 35: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/35.jpg)
Redox-Active Ligand in Actor Role During Catalysis
! Novel reactivity derived from ligand centered radical in nature
Wachter, R. M., Montagne-Smith, M. P., Branchaud, B. P. J. Am. Chem. Soc., 1997, 119, 7743.
CuIIO
(His496)N
(His581)N
O
O S (Tyr272)
(Tyr495)
(Cys228)
OH
R
H2O
R
CuIIO
(His496)N
(His581)N
OH2
O S (Tyr272)
(Tyr495)
(Cys228)
CuIIO
(His496)N
(His581)N
O
O S (Tyr272)
(Tyr495)
(Cys228)
R
HH
H
CuIO
(His496)N
(His581)NO S (Tyr272)
(Tyr495)
(Cys228)
GalactoseOxidase
H
H
H2O2
O2O
R
![Page 36: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/36.jpg)
Substrate Participation as a Redox-Active Ligand
! Synthetic galactose oxidase mimics enable alcohol oxidation
Chaudhuri, P., Hess, M., Müller, J., Hildenbrand, K., Bill, E., Weyhermüller, T., Wieghardt, K. J. Am. Chem. Soc., 1999, 121, 9599.
1 (1 equiv.), Et3N (2 equiv.)
! The copper(II) complex (1) is capable of quantitatively oxidizingprimary alcohols to the corresponding aldehyde
! Complex 2, with a redox inactive zinc(II) is also capable ofoxidizing primary alcohols (approx. 150 TON in 24 hrs).
NMII
N
OO
t-Bu
t-Bu
t-Bu
t-Bu
M = Cu, 1Zn, 2
CH2Cl2
O
HMeMe
OH
>95% yield
! Kinetic studies show a kH/kD of 54 for methanol oxidation usingcomplex 1 indicating H-atom abstraction as the rate determiningstep in the process
Complex 1
Catalytic ethanol oxidation:
![Page 37: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/37.jpg)
Redox-Active Ligand in Actor Role During Catalysis
! Synthetic galactose oxidase mimics enable alcohol oxidation
Chaudhuri, P., Hess, M., Müller, J., Hildenbrand, K., Bill, E., Weyhermüller, T., Wieghardt, K. J. Am. Chem. Soc., 1999, 121, 9599.
OH
Me
AlcoholOxidation
H2O2
O2O
Me
NZnII
N
OO
t-Bu
t-Bu
t-Bu
t-Bu
NZnII
N
OH
O
t-Bu
t-Bu
t-Bu
t-Bu
OMe
NZnII
N
OH
OH
t-Bu
t-Bu
t-Bu
t-Bu
O
HMe
HH
NZnII
N
OH
OH
t-Bu
t-Bu
t-Bu
t-Bu
Ligand acts as electron donorand sink as well as an actor
in C–H abstraction
![Page 38: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/38.jpg)
Classes of Redox-Active Ligands
M+nL
M+nLSX
SX
Ligand assisted substrate activation
Actor Ligand
M+nL
M+(n+1)L
S
S•
M+nL
S
-e–
S
M+nL
S
M+(n+2)L-2
S
Modification of metal electronicsvia ligand modification
Redox-active substrate complexElectron transfer to ligand
Spectator Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.
![Page 39: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/39.jpg)
M+nL M+nLSX
SX-e–
S
M+nL
S
M+(n+2)L-2
S
Modification of metal electronicsvia ligand modification Ligand assisted substrate activation
Electron transfer to ligand
Spectator Ligand
Classes of Redox-Active Ligands
M+nL
M+(n+1)L
S
S•
M+nL
S
Redox-active substrate complex
Actor Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.
![Page 40: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/40.jpg)
Substrate Participation as a Redox-Active Ligand
! Novel reactivity derived from ligand cetered nitrogen radical
King, E. R., Hennessy, E. T., Betley, T. A. J. Am. Chem. Soc., 2011, 133, 4917.Hennessy, E. T., Betley, T. A. Science, 2013, 340, 591.
NFe
N
Cl
Ar
Ad Ad
Ar = 2,6-Cl2-Ph (1)
PhN3
H H NBoc
Ph
1 (10 mol%)Boc2O (1 equiv.)
benzene, 65 °C
! Highly reactive FeIII–N• system enable the direct functionalization of alkanes in an analagous mannerto cytochrome P450 FeIV–O reactive center
! Dipyrrolomethane ligand is thought to behaveredox-innocently from previous DFT studies
Key intermediate:
NFeIII
N
Cl
Ar
Ad AdNR
![Page 41: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/41.jpg)
Substrate Participation as a Redox-Active Ligand
! Novel reactivity derived from ligand cetered nitrogen radical
King, E. R., Hennessy, E. T., Betley, T. A. J. Am. Chem. Soc., 2011, 133, 4917.Hennessy, E. T., Betley, T. A. Science, 2013, 340, 591.
NFeII
N
Cl
Ar
Ad Ad
NFeII
N
NFeII
N
Cl N N2
Ph
NFeIII
N
Cl N
Ph
FeIIIN
H
HPh
NCl
N
NFeII
N
Cl NPh
Cl L
PhN3
–N2
H
L
NHPh
C–H AminationCycle
FeIIIN
H
Ph
NCl
NH
![Page 42: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/42.jpg)
Substrate Participation as a Redox-Active Ligand
! Novel reactivity derived from ligand-centered carbene radical
Zhu, S., Ruppel, J. V., Lu, H., Wojtas, L., Zhang, X. P. J. Am. Chem. Soc., 2008, 130, 5042.
[Co(1)] (1 mol%)
CH2Cl2, rt
! Generation of carbenes using cobalt porphyrin complexes result in carbene withsignificant ligand centered radical character
PhN2
Ts
PhTs
99% yield, >99:1 dr,92% ee
! Radical nature of the reaction mechanism necessitates large chiral pockets inorder to achieve high selectivity
! Formation of nitrene ligands is also possible and can insert into activated C–H bonds
X = OMe, Y = H, 1
![Page 43: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/43.jpg)
Substrate Participation as a Redox-Active Ligand
! Novel reactivity derived from ligand-centered carbene radical
Zhu, S., Ruppel, J. V., Lu, H., Wojtas, L., Zhang, X. P. J. Am. Chem. Soc., 2008, 130, 5042.
[Co(1)] (1 mol%)
CH2Cl2, rtPh
N2
Ts
Ph
X = OMe, Y = H, 1
Ts
99% yield, >99:1 dr,92% ee
CoII
TsN2H
CoIII
TsH
CoIII
TsH
Ph
! Loss of nitrogen results in electron transfer from Co(II) center and formation of carbon centered radical
![Page 44: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/44.jpg)
Substrate Participation as a Redox-Active Ligand
! Novel reactivity derived from ligand-centered carbene radical
Lu, H., Jiang, H., Wojtas, L., Zhang, X. P., Angew. Chem. Int. Ed., 2010, 49, 10192.Zhu, S., Ruppel, J. V., Lu, H., Wojtas, L., Zhang, X. P. J. Am. Chem. Soc., 2008, 130, 5042.
[Co(1)] (2 mol%)
C6H5Cl, rtMeO2CN2
Ts
MeO2C
X = OMe, Y = H, 1
Ts
96% yield, 94:6 dr,89% ee
[Co(2)] (2 mol%)
C6H5CF3, 40 °C
95% yield
N N3S
OOMe
Me
N NHS
OOMe
Me
Co(2)
! Nitrene based systems proceed through a similar process
![Page 45: AGC Redox Active Ligands - Princeton Universitychemlabs.princeton.edu/.../6/AGC_Redox_Active_Ligands.pdf · 2014. 2. 4. · "Redox-active, or 'noninnocent,' ligands have more energetically](https://reader034.vdocuments.mx/reader034/viewer/2022051922/601053f3b9f87347081ecdc5/html5/thumbnails/45.jpg)
Classes of Redox-Active Ligands
M+nL
M+nL M+nL
M+(n+1)L
SX
SX
S
S•
M+nL
S
-e–
S
M+nL
S
M+(n+2)L-2
S
Modification of metal electronicsvia ligand modification Ligand assisted substrate activation
Redox-active substrate complexElectron transfer to ligand
Spectator Ligand Actor Ligand
Lyaskovskyy, V., de Bruin, B. ACS Catal., 2012, 2, 270.Luca, O. R., Crabtree, R. H. Chem. Soc. Rev., 2013, 42, 1440.