1. Chapter 13 Lecture 2 More Ligand Types
Ligands with Extended p Systems
Linear p Systems
Ethylene (C2H4)
Single p-bond composed of two overlapping p-orbitals
One bonding and one antibonding p molecular orbital
Allyl Radical (C3H5)

2. 1,3-Butadiene
Other extended p systems

3. Cyclic p Systems
Cyclopropene
Similar construction of orbitals as in linear systems
Degenerate orbitals have the same number of nodes
Polygon Method for finding cyclic p system MO’s
Draw molecule as a polygon with vertex down
One MO per vertex gives energy ordering and degeneracy
Number of nodes increases as energy increases

5. Bonding Between Metals and Linear p Systems
Ethylene Complexes
Sidebound geometry is most common
Bonding: s-donation from p MO, p-acceptance from p* MO
Coordination weakens C=C bond (137.5 pm, 1516 cm-1) compared to free ethylene (133.7 pm, 1623 cm-1)
p-Allyl Complexes
Can be trihapto: both s- and p-bonding
Can be monohapto: s-bonding only from sp2 hybrid orbital (120o bond angle)

6. Other linear p-system coordination
c) The lowest energy MO provides s-bonding, highest energy MO = p-acceptor
Other linear p-system coordination
p3 is a p-acceptor
p2 can be donating
or accepting depending
on metal e- distribution
p1 is a s-donor

7. Bonding in Cyclic p Systems
Cyclopentadienyl = Cp = C5H5- is the most important cyclic ligand
Ferrocene Synthesis: FeCl NaC5H (h5-C5H5)2Fe NaCl
Called metallocene or sandwich complex
18-electron complex: Fe2+ = d6 and 2 Cp x 6 e-
Bonding Group Orbitals of 2 eclipsed Cp rings
D5h
0-Node Group Orbitals

8. Matching with metal d-orbitals: dyz orbital example
MO Description
6 strongly bonding MO’s hold electrons from Cp ligands
8 antibonding orbitals are empty
5 mid-range energy orbitals holding metal d-electrons
Reactivity
Follows 18-electron rule, but not inert
Ligand reactions on Cp ring are most common reactions

9. D5h

10. M—C Single, Double, and Triple Bonds
Metal Alkyl Complexes
Grignard Reagents: X—M—CH2CH2CH2CH3
Bonding in Transition Metal Complexes
s-donation from C sp3 hybrid orbital
2 electron, -1 charge for electron counting
Synthesis
ZrCl PhCH2MgCl Zr(CH2Ph)4
Na[Mn(CO)5] + CH3I CH3Mn(CO)5 + NaI
Other M—C single bond ligands

11. Metal Carbene Complexes
M=C counted as 2 electron, neutral ligand in electron counting
Schrock Alkylidenes: only H or C attached to the carbene Carbon
Fisher Carbenes: heteroatom attached to the carbene Carbon (our focus)
s-bond from C sp2 hybrid to metal
p-bond from C p-orbital(s)
Heteroatom delocalizes p-system to 3 atoms, stabilizing it by resonance

12. Metal Carbyne Complexes
First synthesis in 1973 by Lewis Acid attack on carbene complex
Bonding
180o bond angle and short bond length confirm triple bond
3 electron, 0 charge for electron counting

13. Spectroscopy of Organometallic Complexes
Infrared Spectroscopy
Number of Bands is determined by group theory (chapter 4 procedure)
Monocarbonyl = 1 band only
Dicarbonyl
Linear arrangement = 1 band only
Bent arrangement = 2 bands
3 or more Carbonyls: table 13.7 in your book
Position of IR Bands
Electron Density determines Wavenumbers
Cr(CO)6 n = 2000 cm-1 [V(CO)6]- n = 1858 cm-1 [Mn(CO)6]+ n = 2095 cm-1
Bonding Mode
Other ligands

14. NMR Spectroscopy
Proton NMR
Hydride Complexes M—H hydrogen strongly shielded (-5 to –20 ppm)
M—CH3 hydrogens 1-4 ppm
Cyclic p system hydrogens 4-7 ppm and large integral because all the same
13C NMR
Useful because “sees” all C ligands (CO) and has wide range (ppm)
CO: terminal = ppm, bridging slightly larger

15. Examples
[(Cp)Mo(CO)3]2 + tds Product?
Data: 1H NMR: 2 singlets at 5.48 (5H) and 3.18 (6H)
IR: 1950, 1860 cm-1
Mass = 339
Solution: proton nmr 5.48 = Cp, 3.18 = ½ tds
IR: at least 2 CO’s
Mass: (Mo=98) – (Cp=65) – 2(CO) = 120 = ½ tds
Product = (Cp)Mo(CO)2(S2CN(CH3)2)
I: proton = 4.83 (4H), carbon = 224, 187, 185, 184, 73
II: proton = m (15H), 4.19 (4H) carbon: 231, 194, 189, 188, ,72
III: proton = m (15H), 3.39 s (2 H) carbon: 237, 201,193, , 69
Solution: 224 = M=C; = CO; 73 = CH2CH2
tds