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J. G. Rudick
CHE 322: Organic Chemistry IIA
Spring 2017
Lecture 15 (2/24/17)
Electron Counting for Transition-Metal
Complexes
Chapter 18 in Loudon, M.; Parise, J.
Organic Chemistry, 6th Ed. W. H. Freeman: New York, NY, 2016
Prof. Jon Rudick
Office Hours: CHEM 775
Mondays 1:30–2:30p
Tuesdays 1:30–2:30p
Thursdays 2:30p–3:30p
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J. G. Rudick
Transition-Metal Complexes
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Spring 2017
J. G. Rudick
Transition-Metal Complexes
Spring 2017
The 18-electron rule: transition metals like to have 18 valence
electrons
The valence orbitals of transition metals include
one s-orbital, five d-orbitals, and three p-orbitals
that can hold up to 18 electrons
Ti: [Ar] 4s2 3d2
Cr: [Ar] 3d5 4s1
Mo: [Kr] 5s1 4d5
Fe: [Ar] 4s2 3d6
Ru: [Kr] 5s1 4d7
Ni: [Ar] 4s2 3d8
Pd: [Kr] 4d10
The 18-electron rule is analogous to
the “octet rule” for main group elements
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J. G. Rudick
L
L
halides
hydride
acetate
cyanide
alkyl
vinyl
aryl
Transition-Metal Complexes
X-Type Ligands
L
L
L M
L
L
L
L
M X
L
Cl–, Br–, I–, F–
H–
O
+
Spring 2017
X
(can be a bidentate ligand
that doneate 4e– and –1q)
R
O
NC–
R 3C –
R
Ar –
These ligands donate 2e– and a negative charge (–1q)
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Transition-Metal Complexes
Spring 2017
L-Type Ligands
L
L
L
L
M L
ML5
+
L
L
amines
:NR3
(R = H, alkyl)
carbon monoxide
:C≡O:
(usually through carbon)
phosphines
:PR3
(R = H, alkyl, aryl)
water (aquo)
H2O:
(bonds through 1 lone pair)
acetonitrile
H3C–C≡N:
Neutral (0q) ligands that donate 2e–
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Transition-Metal Complexes
Spring 2017
Some ligands use electrons in π-orbitals to bind metals
Alkenes donate 2e– and no charge (0q): L-Type Ligand
L
L
ML5 +
L M
L
L
Benzenes donate 6e– (or 4e– or 2e–) and no charge (0q)
L3-Type ligand
M
L
L
L
Cyclopentadienyl anion (Cp) donates 6e– and –1 charge (–1q)
M
L
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L
L
L2X-Type ligand
J. G. Rudick
Transition-Metal Complexes
Spring 2017
Nickel tetracarbonyl: Ni(CO)4
O
Ni
O
O
O
Ni: [Ar] 4s2 3d8
Ni(0) has 10
valence electrons
C O
each CO donates the
lone pair (2e–) from C
Counting all of the electrons involved in bonds to Ni
(8e–) and the non-bonding electrons on Ni (10e–)
we conclude that Ni(CO)4 is an 18-electron complex
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Clicker Question #1
Spring 2017
(Pre-lecture Quiz Question)
CO
CO
OC Cr CO
OC
CO
Cr: [Ar]
3d5
4s1
Cr(0) has 6
valence electrons
each CO donates the
lone pair (2e–) from C
C O
What is the total electron count on the metal in
Cr(CO)6 (i.e., chromium hexacarbonyl)?
A. 6
B. 12
C. 16
D. 18
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PPh3
Pd
Ph3P
PPh3
PPh3
Clicker Question #2
Pd: [Kr]
P
4d10
Ph
Ph
Ph
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Pd(0) has 10
valence electrons
each PR3 donates the
lone pair (2e–) from P
What is the total electron count on the metal in
Pd(PPh3)4 (i.e., palladium tetrakis(triphenylphosphine)?
A. 6
B. 12
C. 16
D. 18
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Transition-Metal Complexes
Spring 2017
Palladium tetrakis(triphenylphosphine): Pd(PPh3)4
PPh3
Pd
Ph3P
PPh3
PPh3
Pd: [Kr]
P
4d10
Ph
Ph
Ph
Pd(0) has 10
valence electrons
each PR3 donates the
lone pair (2e–) from P
Counting all of the electrons involved in bonds to Pd (8e–)
and the non-bonding electrons on Pd (10e–)
we conclude that Pd(PPh3)4 is an 18-electron complex
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Transition-Metal Complexes
Spring 2017
Cis-platin: Pt(NH3)2Cl2
Cl
Cl
NH3
Pt NH3
For the complex to be
neutral (i.e., 0 charge),
the metal must be
Pt(II) (i.e., Pt2+)
H
N
H
H
L-type ligand (2e–, 0q)
X-type ligand (2e–, –1q)
Cl
Pt(II) has (10 – 2 =) 8 valence electrons
Counting all of the electrons involved in bonds to Pt
(8e–) and the non-bonding electrons on Pt(II) (8e–)
we conclude that cis-platin is an 16-electron complex
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Clicker Question
Spring 2017
(Pre-lecture Quiz Question)
#3 What is the oxidation state of the metal in
PdCl2(PPh3)2?
Cl
Ph3P Pd PPh3
Cl
A. –2
B. 0
C. +2
D. +4
#4 Palladium(II) has how many valence electrons?
(What is the dn count for Pd in the complex?)
A. 8
B. 10
C. 16
D. 18
#5 What is the total electron count on the metal in
PdCl2(PPh3)2?
A. 8
B. 14
C. 16
D. 18
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J. G. Rudick
Transition-Metal Complexes
Spring 2017
Dichlorobis(triphenylphosphine)palladium(II): PdCl2(PPh3)2
Ph
P
L-type ligand (2e–, 0q)
Ph
Ph
Cl
Ph3P Pd PPh3
Cl
Cl
X-type ligand (2e–, –1q)
Pd2+ has (10 – 2 =) 8 valence electrons
For the complex to be neutral (i.e., 0 charge),
the metal must be Pd(II) (i.e., Pd2+)
Counting all of the electrons involved in bonds to Pd (8e–)
and the non-bonding electrons on Pd(II) (8e–)
we conclude that PdCl2(PPh3)2 is a 16-electron complex
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Clicker Question
#6 What is the oxidation state of the metal in
[Rh(CO)2I2]–?
CO
I Rh CO
I
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A. –2
B. –1
C. +1
D. +2
#7 Rhodium(I) has how many valence electrons? (What A. 7
is the dn count for Rh in the complex?)
B. 8
C. 9
D. 10
#8 What is the total electron count on the metal in
[Rh(CO)2I2]–?
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A. 15
B. 16
C. 17
D. 18
J. G. Rudick
Transition-Metal Complexes
Spring 2017
[Rh(CO)2I2]–
This is an
anionic complex
CO
I Rh CO
I
C O
I
L-type ligand (2e–, 0q)
X-type ligand (2e–, –1q)
Rh1+ has (9 – 1 =) 8 valence electrons
For the complex to be anionic (i.e., –1 charge),
the metal must be Rh(I) (i.e., Rh1+)
Counting all of the electrons involved in bonds to Rh (8e–)
and the non-bonding electrons on Rh(I) (8e–)
we conclude that [Rh(CO)2I2]– is a 16-electron complex
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J. G. Rudick
Clicker Question
Spring 2017
#9 What is the oxidation state of the metal in
Cl2Ru(=CHPh)(PCy3)2?
PCy3
Cl Ru
Cl
Ph
PCy3
#10 Ruthenium(IV) has how many valence electrons?
(What is the dn count for Ru in the complex?)
A. +4
B. +2
C. –2
D. –4
#11 What is the total electron count on the metal in
Cl2Ru(=CHPh)(PCy3)2?
A. 18
B. 16
C. 14
D. 12
16
A. 0
B. 4
C. 8
D. 12
J. G. Rudick
Transition-Metal Complexes
Spring 2017
Grubbs 1st-Generation Catalyst: Cl2Ru(=CHPh)(PCy3)2
(J. Am. Chem. Soc. 1996, 118, 100–110)
PCy3
Cl Ru
Cl
Ph
PCy3
CHR
X2-type ligand (4e–, –2q)
PCy3
L-type ligand (2e–, 0q)
Cl
X-type ligand (2e–, –1q)
Ru4+ has (8 – 4 =) 4 valence electrons
For the complex to be neutral (i.e., 0 charge),
the metal must be Ru(IV) (i.e., Ru4+)
Counting all of the electrons involved in bonds to Ru (12e–)
and the non-bonding electrons on Ru(IV) (4e–) we conclude that
Cl2Ru(=CHPh)(PCy3)2 is a 16-electron complex
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Clicker Question
Spring 2017
#12 What is the oxidation state of the metal in ZrCp2HCl A. –4
(a.k.a., Schwartz’s reagent)?
B. –2
C. +2
D. +4
Zr H
Cl
#13 Zirconium(IV) has how many valence electrons?
(What is the dn count for Zr in the complex?)
A. 0
B. 1
C. 2
D. 4
#14 What is the total electron count on the metal in
ZrCp2HCl (a.k.a., Schwartz’s reagent)?
A. 12
B. 14
C. 16
D. 18
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Transition-Metal Complexes
Spring 2017
Schwartz’s Reagent: ZpCp2HCl
(Chem. Commun. 1969, 1105; J. Am. Chem. Soc. 1974, 96, 8115–8116)
L2X-type ligand (6e–, –1q)
Zr
H
Cl
Cl , H
X-type ligand (2e–, –1q)
Zr4+ has (4 – 4 =) 0 valence electrons
For the complex to be neutral (i.e., 0 charge),
the metal must be Zr(IV) (i.e., Zr4+)
Counting all of the electrons involved in bonds to Zr (8e–)
and the non-bonding electrons on Zr(IV) (0e–)
we conclude that ZrCp2HCl is a 16-electron complex
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Clicker Question
Spring 2017
Pre-lecture Quiz Question
#15 What is the oxidation state of the metal in
NiCl2(PPh3)2?
Cl
Ph3P Ni PPh3
Cl
A. –2
B. 0
C. +2
D. +4
#16 Nickel(II) has how many valence electrons?
(What is the dn count for Ni in the complex?)
A. 8
B. 10
C. 16
D. 18
#17 What is the total electron count on the metal in
NiCl2(PPh3)2?
A. 8
B. 10
C. 16
D. 18
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J. G. Rudick
Transition-Metal Complexes
Spring 2017
Dichlorobis(triphenylphosphine)nickel(II): NiCl2(PPh3)2
Cl
Ph3P Ni PPh3
Cl
PPh3
L-type ligand (2e–, 0q)
Cl
X-type ligand (2e–, –1q)
Ni2+ has (10 – 2 =) 8 valence electrons
For the complex to be neutral (i.e., 0 charge),
the metal must be Ni(II) (i.e., Ni2+)
Counting all of the electrons involved in bonds to Ni (8e–)
and the non-bonding electrons on Ni(II) (8e–)
we conclude that NiCl2(PPh3)2 is a 16-electron complex
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