Organometallic Chemistry

1
Advanced Inorganic Chemistry

• Paula Diaconescu (pld_at_chem.ucla.edu)
• office hours Friday 4 5 pm, MSB 3515

• TAs Marisa Monreal (rio_at_chem.ucla.edu) Tu,
  9-10, YH 1336
• Erin Broderick (ebroderi_at_chem.ucla.edu) Th, 5-6,
  YH 1336
• office hours (YH 1336) MM, Mo, 6-7pm EB, We,
  12-1pm

www.inorganic-chemistry.net
2
Textbooks

• Required texts
• Introduction to Molecular Symmetry by J. S. Ogden
  (Oxford Primers)
• Inorganic Chemistry by Gary L. Miessler and
  Donald A. Tarr, Prentice Hall, Inc., 2004
• Recommended
• Basic Inorganic Chemistry by F. Albert Cotton et
  G. Wilkinson, Wiley not in the library
• Advanced Inorganic Chemistry by F. Albert Cotton
  et al., Wiley 6th edition 1999 on hold
• Chemical Applications of Group Theory by F.
  Albert Cotton et al., Wiley 3rd edition 1990
  in the library
• Inorganic Chemistry by D. F. Shriver et al.,
  Freeman 3rd edition 1999 permanent reserves

3
Grading

• Midterms 25 30 55
• Midterm 1 April 24
• Midterm 2 May 18
• Final 45
• Extra credit 5
• 10-15 students critical study of a paper / DFT
  calculations
• Presentation to a high school on inorganic
  chemistry letter from instructor
• Personal choice if approved

4
Course content

• Introduction
• Hard and soft acids and bases
• Introduction to Molecular Symmetry (both
  textbooks)
• Symmetry elements and point groups
• Representations
• Molecular vibrations and vibrational spectroscopy
• Chemical bonding
• Electronic spectra
• Inorganic Reaction Mechanisms
• Substitution reactions
• Electron transfer reactions
• Ligand-based reactions
• Introduction to organometallic chemistry

Notes will be posted on http//vohweb.chem.ucla.ed
u/voh
5
Introduction

• Chapters 1-3, 6, 9 (Miessler Tarr)

6
d orbitals
dxy
dxz
dyz
dx2-y2
dz2
http//www.rsc.org/chemsoc/visualelements/orbital/
orbital_d.html
7
Learn to love f-Orbitals
The High Nodality of f - Orbitals is Scary
f z3
f xz2 f yz2
f xyz f z(x2-y2)
f x(x2-3y2) f y(3x2-y2)
s
p
d
f
8
Different metals general properties

• From left to right, the electronegativity
  increases substantially
• Early TM are electropositive
• often found in the highest permissible oxidation
  state
• d2 are very easily oxidized very p basic
• Late TM are relatively electronegative
• Often found in low oxidation states
• Back donation is not so marked ligands are
  subject to nucleophilic attack

Electronegativity
9
Transition metals in nature

• As active sites of enzymes hemoglobin (oxygen
  transport), nitrogenases (nitrogen fixation),
  hydrogenases, etc.

Hemoglobin Green shows Fe-containing site
Heme b
10
Nitrogen fixation

• Heterogeneous catalysis Haber-Bosch process
• Homogeneous catalysis

Nitrogenase structure
11
Vitamin B12
Methylcobalamin is an example of an
organometallic compound (containing metal-carbon
bonds).
12
Gemstones
Sapphire Fe(II) and Ti(IV) impurities in Al2O3
Hydrous phosphate of Cu(II) and Al(III)
Ruby Cr(III) impurities in Al2O3
Hematite A mineral form of Fe2O3
13
Coordination chemistry
Alfred Werner (1866 1919) Nobel prize 1913
The understanding of valence bonding and geometry
in metal-amine complexes such as Co(NH3)6Cl3.
14
Coordination chemistry Definitions

• A coordination compound, sometimes called a
  coordination complex, contains a central metal
  atom or ion surrounded by a number of oppositely
  charged ions or neutral molecules (possessing
  lone pairs of electrons) which are known as
  ligands.
• If a ligand is capable of forming more than one
  bond with the central metal atom or ion, then
  ring structures are produced which are known as
  metal chelates, the ring forming groups are
  described as chelating agents or polydentate
  ligands.
• The coordination number of the central metal atom
  or ion is the total number of sites occupied by
  ligands. Note a bidentate ligand uses two sites,
  a tridentate three sites etc.

15
Examples of complexes derived from common ligands
16
Examples of complexes derived from common ligands
17
The hard/soft acid/base principle
Irving-Williams stability series (1953) for a
given ligand, the stability increases in the
following order Ba2 lt Sr2 lt Ca2 lt
Mg2 lt Mn2 lt Fe2 lt Co2 lt Ni2 lt Cu2 lt Zn2
Certain ligands formed their most stable
complexes with metal ions like Al3, Ti4 and
Co3 while others formed stable complexes with
Ag, Hg2 and Pt2.
1958 Ahrland et al.
Type A metal cations Alkali metal cations Li
to Cs Alkaline earth metal cations Be2 to
Ba2 Lighter transition metal cations in higher
oxidation states Ti4, Cr3, Fe3, Co3 The
proton, H Type B metal cations Heavier
transition metal cations in lower oxidation
states Cu, Ag, Cd2, Hg, Ni2, Pd2, Pt2.
Miessler Tarr Chapter 6-3
18
Type A/B ligands
Ligands were classified as type A or type B
depending upon whether they formed more stable
complexes with type A or type B metals

Type A metals prefer to bind to type A ligands.

and
Type B metals prefer to bind to type B ligands.
19
Pearson's hard/soft Lewis acid/base principle
Ralph Pearson (1960s) Lewis acid Lewis
base -gt complex Pearson classified Lewis acids
and Lewis bases as hard, borderline or soft.
According to Pearson's hard soft Lewis acid
base (HSAB) principle Hard Lewis acids
prefer to bind to hard Lewis bases and
Soft Lewis acids prefer to bind to soft
Lewis bases
20
Pearsons acids
21
Pearsons bases
22
Characteristics of hard/soft acids/bases

• Hard Lewis bases Small, highly solvated,
  electronegative atomic centers 3.0-4.0
  Species are weakly polarizable Difficult to
  oxidize High energy HOMO
• Soft Lewis bases Large atoms of
  intermediate electronegativity 2.5-3.0 Easy
  to polarize and oxidize Low energy HOMOs but
  large magnitude HOMO coefficients

• Hard Lewis acids Atomic centers of small
  ionic radius High positive charge Species
  do not contain electron pairs in their valence
  shells Low electron affinity Likely to be
  strongly solvated High energy LUMO
• Soft Lewis acids Large radius Low or
  partial (d) positive charge Electron pairs in
  their valence shells Easy to polarize and
  oxidize Low energy LUMOs, but large magnitude
  LUMO coefficients

Note it is not necessary for species to possess
all properties.
23
Appendix Nomenclature rules. Formulae

• In a coordination formula, the central atom is
  listed first.
• The formally anionic ligands appear next, listed
  in alphabetical order according to the first
  symbols of their formula. The neutral ligands
  follow, also in alphabetical order, according to
  the same principle. The formula of the entire
  coordination entity, whether charged or not, is
  enclosed in square brackets.
• If the coordination entity is negatively charged,
  the formula is preceded by the cation formula.
• When ligands are polyatomic, their formulae are
  enclosed in parentheses. Ligand abbreviations are
  also enclosed in parentheses.

24
Nomenclature rules Names

• 1. In naming the entire complex, the name of the
  cation is given first and the anion second (just
  as for sodium chloride), no matter whether the
  cation or the anion is the complex species.
• 2. In the complex ion, the name of the ligand or
  ligands precedes that of the central metal atom.
  (This procedure is reversed from writing
  formulae.)
• 3. Ligand names generally end with 'o' if the
  ligand is negative ('chloro' for Cl-, 'cyano' for
  CN-, 'hydro' for H-) and unmodified if the ligand
  is neutral ('methanamine' for MeNH2). Special
  ligand names are 'aqua' for water, 'ammine' for
  ammonia, 'carbonyl' for CO, 'nitrosyl' for NO.

25
Nomenclature rules Names

• 4. A Greek prefix (mono, di, tri, tetra, penta,
  hexa, etc.) indicates the number of each ligand
  (mono is usually omitted for a single ligand of a
  given type). If the name of the ligand itself
  contains the terms mono, di, tri, eg
  triphenylphosphine, then the ligand name is
  enclosed in parentheses and its number is given
  with the alternate prefixes bis, tris, tetrakis
  instead.
• Again, one would use diammine, for (NH3)2, but
  bis(methylamine), for (NH2Me)2, to make a
  distinction from dimethylamine. (Note that this
  ambiguity does not arise if the preferred IUPAC
  name, methanamine, is used instead of
  methylamine). There is no elision of vowels or
  use of a hyphen, e.g. in tetraammine and similar
  names. Some texts suggest that if a ligand is
  "complicated" then use the bis, tris multipliers.
  What constitutes "complicated" is not spelled out
  however, so a simpler approach is to use them if
  the name of the ligand is three or more syllables
  long!

26
Nomenclature rules Names

• 5. A Roman numeral or a zero in parentheses is
  used to indicate the oxidation state of the
  central metal atom.
• 6. If the complex ion is negative, the name of
  the metal ends in 'ATE' for example, ferrate,
  cuprate, nickelate, cobaltate, etc.
• 7. If more than one ligand is present in the
  species, then the ligands are named in
  alphabetical order regardless of the number of
  each. For example, NH3 (ammine) would be
  considered an 'a' ligand and come before Cl-
  (chloro).

27
Some additional notes

• Some metals in anions have special names
• B - Borate Au - Aurate Ag - Argentate Fe -
  Ferrate
• Pb - Plumbate Sn - Stannate Cu - Cuprate
• Use of brackets or enclosing marksSquare
  brackets are used to enclose a complex ion or
  neutral coordination species.
• Examples
• Co(en)3Cl3 Co(NH3)3(NO2)3 K2CoCl4 note
  that it is not necessary to enclose the halogens
  in brackets.
• Note that in 2004 it was recommended that anionic
  ligands will end with -ido so that chloro would
  become chlorido, etc.