Iit Jam Inorganic Chemistry
Iit Jam Inorganic Chemistry
Iit Jam Inorganic Chemistry
CHAPTER-11
Introduction :
Edward Frankland was father of organometallic chemistry for a complex to be organometallic compound,
there should be atleast one metal-carbon bond. For example, RMgX
PPh3
Metal
Ph
Ph P Rh PPh3
Carbon compound R MgX
Ph
Cl
Wilkinson's Catalyst
NaCN : It has metal-carbon bond but dispite of this, NaCN is not organometallic compound.
So, the above given definition of organometallic compound is not rigid, it is flexible.
Bonding in organometallic complexes:
Ligands are of three types:
Ligand
R CH2 H
M :N R M M
R CH2 H
Bonding may be ionic, coordinate and it may be covalent. The covalent bonding are of the two types
(i) Localized (ii) delocalised
Classification of an organometallic compounds:
On the basis of metal present in organometallic compounds
(1) If metal is main group element then it is said to be main group compound.
e.g. t-BuLi, RMgX, Me2Hg, TEL, n-BuLi, Al(CH3)3.
Introduction to Organometallic Compounds 273
(2) Transition metal organometallic compound: If the metal is from transition metals.
e.g. Rh(Ph3)3Cl, Pd(PPh3)4, R2CuLi, Fe(CO)5.
(3) Lanthanide/Actinide organometallic compound : If metal is from f-block metals.
+ 2K
THF
2K 2C8 H8 MCl4 M Deep green.
0C
H3C CH3
O
As As
H3C CH3
First T.S. metal organometallic compound was Zeises Salt
Cl Cl
Square planar Pt or K PtCl3 C2 H 4
Cl
Hapticity :
It is the property of ligand. It is represented by . The number of donor atom of a ligand is directly attached
with the metal is said to be the hapticity.
n Number of donar atom attached with metal.
CH3
M M N C CH3
1
1 -phenyl
O
H2C CH2 H2C CH2 M O O M
M or O
M
2
2 2 1 (O2) (O2)
M M
M
2 1 -allyl 3 allyl 3 allyl
A ligand which can show more than one hapticity is called fluxonial.
e.g. allyl shows 1 & 3
Cl
SbCl5
,
M M
2 3
C3H4 C3H3
Cyclopentadienyl:
M M M
1Cp 3Cp 5Cp
Introduction to Organometallic Compounds 275
18 electron rule :
The rule states that thermodynamically stable transition metal organometallic compounds are formed when the
sum of the metal d electrons and the electrons converntionally considered as being supplied by the surrounding
ligands equals 18.
18 electron rule is only applicable for transition metal organometallic compound.
The main group organometallic compound follows octet rule.
Square planar complex follows 16 electron rule.
The complex which follow 16 and 18 electron rule are stable.
Complex which follow 17 electron rule and 19 electron rule are paramagnetic
Organometallic compound which follows this configuration ns 2 np6 n 1 d10 than complex is stable.
2 6 10 18 e
For complex, total number of electron = the number of valence electron donated by the metal + number of
electron donated by the ligand charge.
(ii) Mn(CO)5CH3.
Neutral atomic method := 7 + 10 + 1 = 18 electron
O.S. Method = 6 + 2 + 10 = 18 electron
0 = M 1, M = +1
Note : Why 16 electron is stable?
Metals with d8 electrons : The d8 metals have a tendency to form square planar 16-electron complexes. This
tendency is weak for group 8 (Fe, Ru and Os in zero oxidation state) and strong for group 9, 10 and 11 (Rh(I),
Pd(II), Pt(II), Au(III). A square planar complexes TVE = 16. This is due to the fact that the d x2 y 2 orbital
cannot be occupied in the square-planar geometry, because it has a high energy. Thus, the complexes are
stable with the 16-electron count.
z d x2y2
L
L M L y
2
dz
L
dxz dyz
x dxy
276 Introduction to Organometallic Compounds
Note:
Complex which follows 17 electron rule is strong oxidizing agent.
Complex which follows 19 electron rule is strong reducing agent.
e.g. Which of the following complex is strong oxidizing agent and strong reducing agaent?
2
(a) Fe CO 5 18 e
(b) V CO 6 19 e
(d) Mn CO 17 e
(c) Co CO 4 18 e 5
SOLVED PROBLEMS
Soln. Cr CO 6
TVE = 6 + 62 = 6 + 12 = 18
Correct option is (d)
2. The complex which obeys the 18 electron rule is [GATE 2002]
(a) Fe(CO)4 (b) Ni(CO)3(PPh3) (c) Cr(CO)5 (d) Cr(C5H5)2
Soln. Ni(CO)3(PPh3)
TVE = 10 + 32 + 2 = 18
Correct option is (b)
3. The bonding of cyclopentadienyl in Ti(Cp)4 is such that [GATE 2002]
(a) all Cp rings are pentahapto
(b) one Cp ring is pentahapto and the other three rings are monohapto
(c) two Cp rings are monohapto and the other two rings are pentahapto
(d) All Cp rings are monohapto
Soln. Structure of Ti(Cp)4 d follow 16 electron rule.
TVE = 4 + 21 + 25 = 16
Ti
Correct option is (c)
4. Among the complexes (i) C6 H 6 2 Cr , (ii) HMn CO 5 , (iii) CH 3CO Rh CO I3 and (iv)
CpFe CO 2 CH 3 , the 18-electron rule is not followed in [GATE 2003]
(a) iii only (b) ii and iii (c) i and iv (d) ii only.
Soln. (i) C6 H 6 2 Cr , TVE = 6 + 62 = 18
(c) C5 H5 2 CO (d) 5 C5 H 5 Re 6 C6 H 6
5
Soln. 5
C5 H 5 Re 6 C6 H 6
TVE = 5 + 7 + 6 = 18
Correct option is (d)
Introduction to Organometallic Compounds 279
OH z OH2 x y
H2O OH2 H2O OH2 Cl Cl
NaOH
Co Co Co
+ 6H2O
H2O OH2 H2O OH2 Cl Cl
OH OH2
(a) z = +2; x = 2; y = +2 (b) z = 0; x = +2; y = 2
(c) z = 0; x = +2; y = +2 (d) z = 2; x = +2; y = 2
OH z OH2 x y
H2O OH2 H2O OH2 Cl Cl
NaOH
Co Co Co
Soln. + 6H2O
H2O OH2 H2O OH2 Cl Cl
OH OH2
M+L=C M+L = C M+L=C
(+) 2 + 2(1) + 4(0) = Z (+) 2 + 6(0) = X (+) 2 + 4(1) = Y
Z=0 X = +2 Y = 2
Correct answer is (b)
8. On the basis of 18 electron rule, find out the value of n.
(i) TcBr CO n (ii) Na 2 Fe CO n
(iii) Mn CO n (iv) IrCl2 CS n PPh 3 2 H
n
(v) Rh CO 3
6 + 9 + n = 18
n = 18 - 15, n = 3
280 Introduction to Organometallic Compounds
9. On the basis of 18 electron rule find out the value of M, where M is first row (3d series element) and then
find out the element
OCH3
(i) (Co)5M
Ph
(ii) 4 -C4 H 4 5 -C5 H5 M
(iii) 3 -allyl 5 -Cp M CO
OCH3
Soln. (i) (OC)5M
Ph
(iii) 3 -allyl 5 -Cp M CO
M 1 st row (3d) 3 + 5 + M + 2 + 1 = 18
10 + M + 2 = 18 M = 18 11
M=6 M=7
So, M = Cr. So, M = Mn
(ii) 4 -C4 H 4 5 -C5 H5 M
4 + 5 1 + M = 18
M = 10
So, M = Ni
Introduction to Organometallic Compounds 281
PRACTICE SET
1. Match each of the compounds in List-I with appropriate oxidation state from List-II and the coordination
number from List-III. [GATE 1995]
List-I List-II List-III
(1) Zeises salt 0 3
(2) Ni(CO)4 1 4
(3) [Co(NH3)5Cl]Cl2 2 5
3 6
List-I List-II List-III
(a) (1, 2, 3) (2, 0, 1) (3, 4, 6)
(b) (1, 2, 3) (2, 3, 1) (3, 4, 5)
(c) (1, 2, 3) (3, 0, 1) (5, 4, 6)
(d) (1, 2, 3) (2, 0, 3) (3, 4, 5)
2. Which case of the following is most easily reduced? [GATE 1996]
(a) V(CO)6 (b) Cr(CO)6 (c) Fe(CO)5 (d) Ni(CO)4
3. The organometallic compound W(C5H5)2(CO)2 follows the 18-electron rule. The hapticities of the two
cyclopentadienyl groups are [GATE 1996]
(a) 5 and 5 (b) 3 and 5 (c) 3 and 3 (d) 1 and 5
4. Which one of the following molecules does not obey the 18-electron rule? [GATE 1997]
2 2
(a) Mn CO 6 (b) Fe CO 5 (c) Cr CO 5 (d) Mn CO 4 Cl2
(a) Be Cp 2
5
2 1
(b) Be Cp Cp
1 3
(c) Be Cp Cp 1 5
(d) Be Cp Cp
Note: Main group elements follow octet rule, Valence electron of Be = 2, So, to complete octet, Needs 6
electrons.
ANSWER KEY
Questions 1 2 3 4 5
Option (a) (a) (b) (d) (d)
Questions 6 7 8 9
Option (c) (d) (d) (d)