Introduction to Organometallic Compounds. Metal. R MgX. Wilkinson s catalyst is used for hydrogenation of alkene and alkyne. Wilkinson's catalyst

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1 Introduction to rganometallic mpounds 1 Chapter 1 Introduction to rganometallic mpounds 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, gx Carbon compound etal gx Wilkinson s catalyst is used for hydrogenation of alkene and alkyne. Wilkinson's catalyst + H Ligand P P 3 h Wilkinson's Catalyst During the catalytic cyclic, a stage comes where the metal h is attached with carbon. Therefore, it is said to be an organometallic compound. P 3 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: Lone pair donor > -donor > -donor : N CH H Bonding may be ionic, coordinate and it may be covalent. The covalent bonding are of the two types (i) Localized (ii) delocalised assification of an organometallic compounds: n 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, gx, e Hg, TEL, n-buli, Al( ) 3. () Transition metal organometallic compound: If the metal is from transition metals. e.g. h(p 3 ) 3, Pd(P 3 ) 4, CuLi, Fe(C). (3) Lanthanide/Actinide organometallic compound : If metal is from f-block metals. CH H

2 Introduction to rganometallic mpounds + K + K + K C H Deep green. THF ºC where, can also be replaced by Pa, Nd. First main group organometallic compounds was Cacodyl oxide CH As H 3 C As As H 3 C First T.S. metal organometallic compound was Zeise s Salt 3 Square planar Pt or K Pt C H 3 4 Formula for calculation of.s. in organometallic compound: C = + L (where,.s. = oxidation state) Where, C = charge on co-ordination sphere =.S. of metal L = formal charge on ligand. e.g. xidation state of zeise s salt 3 4 Trichloro ethylene platinate II ion Pt C H 1 x 3 x Effective Atomic Number (EAN) rule: Sidgwick proposed this rule. The sum of the electrons on the metal plus electrons donated by ligands is called EAN. When EAN is equal to 36(Kr), 4(Xe), 86(n) then it is said that EAN ule is obeyed and the compound is found to be stable. In this concept metal is consider to be Lewis Acid and ligand is consider to be Lewis Base. (1) Ni(C) 4 () Cr(C) 6 (3) (C H ) Fe EAN = 8+8 = 36 EAN= = 36 EAN = = 36 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. e.g. 1 CH A ligand which joins two /more metals is said to be bridged. It is represented by µ n this indicates the number of metals bridges, where n is number of metal bridged.

3 Introduction to rganometallic mpounds 3 1 C µ (C) C C 1 1 nly one donor atom of ligand attached, so hapticity is one 1 C 1 H C CH -phenyl or H C CH N C 1 1 ( ) ( ) 1 -allyl 3 allyl 3 allyl A ligand which can show more than one hapticity is called fluxonial. 1 3 e.g. allyl shows &, Sb C 3 H 4 Cyclopentadienyl: 3 C 3 H 3 1 Cp 3 Cp Cp 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 conventionally considered as being supplied by the surrounding ligands equals 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. mplex which follow 17 electron rule and 19 electron rule are paramagnetic 6 10 rganometallic compound which follows this configuration e ns np n 1 d than complex is stable. For complex, total number of electron = the number of valence electron donated by the metal + number of electron donated by the ligand charge.

4 4 Introduction to rganometallic mpounds There are two methods for calculation of 18 electron (1) xidation state method () Neutral atom method e.g. (i) Ferrocene xidation State ethod : Neutral atom method :.S. of Fe Cp = = 10 = Fe = 8 1 = 8 = + Fe 18 e Fe = 6 1 = 6 Cp = 6 = 1 18 e Ferrocene follows 18 electron rule. (ii) n(c). Neutral atomic method := = 18 electron.s. ethod = = 18 electron 0 = 1, = +1 Note : Why 16 electron is stable? etals with d 8 electrons : The d 8 metals have a tendency to form square planar 16-electron complexes. This tendency is weak for group 8 (Fe, u and s in zero oxidation state) and strong for group 9, 10 and 11 (h(i), Pd(II), Pt(II), Au(III). A square planar complexes TVE = 16. This is due to the fact that the d 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. x y z L d x y x L L L d xy y d xz d z d yz Soln. Note: mplex which follows 17 electron rule is strong oxidizing agent. mplex which follows 19 electron rule is strong reducing agent. e.g. Which of the following complex is strong oxidizing agent and strong reducing agaent? (a) FeC 18 e (b) VC 19 e (c) C 4 18 e (d) n C 17 e (d) is strong oxidizing agent because follows 17 electron rule. (b) is strong reducing agent because follows 19 electron rule. 6

5 Introduction to rganometallic mpounds Table: mmon ligands and their electron contributions. Ligand Carbonyl ( C) osphine ( P 3 ) Amine N 3 ) Amide (-N ) Hydrogen (-H) Alkene (Sidewise). Alkyne (sidewise) Neutral xidation State Ligand Neutral xidation State atom Electron Formal atom Electron Formal contribution charge contribution charge 0 Halogen 1-1 (-X) 0 Alkyl 1-1 ( ) 0 Aryl 1-1 (-Ar) 1-1 Acyl 1-1 ( C() Cyclopenta dienyl 0 1 -Allyl Allyl C Cyclopenta dienyl Nitrosyl Benzene bent Nitrosyl Linear Carbene (=C ) Cycloheptat rienyl 4 - Carbyne C Alkoxide 1-1 Thiolate 1-1 ( ) ( S) -C ( 0 -H 1-1 (C) ) Alkyne X( X ) X=Halogen Alkyl 1-1 Amido (-(N ) osphi do ( (P ) Alkoxide (-()

6 6 Introduction to rganometallic mpounds SLVED PBLES 1. The compound which obeys 18-electron rule is: [GATE 000] (a) n C 3 (b) Fe C 4 (c) VC 6 (d) Cr C 6 Cr C TVE = = = 18 rrect option is (d) Soln. 6. The complex which obeys the 18 electron rule is [GATE 00] (a) Fe(C) 4 (b) Ni(C) 3 (P 3 ) (c) Cr(C) (d) Cr(C H ) Soln. Ni(C) 3 (P 3 ) TVE = = 18 rrect option is (b) 3. The bonding of cyclopentadienyl in Ti(Cp) 4 is such that [GATE 00] (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 dº follow 16 electron rule. TVE = = 16 Ti rrect option is (c) 4. Among the complexes (i) C6H6 Cr, (ii) Hn C, (iii) CpFeC CH CH C h C I 3 3 and (iv) 3, the 18-electron rule is not followed in [GATE 003] (a) iii only (b) ii and iii (c) i and iv (d) ii only. Soln. (i) C H 6 6 (ii) Cr, TVE = = 18 Hn C, TVE = = 18 CH3C h C I3 (iii) (iv) CpFeC CH 3 rrect option is (a), TVE = = 16, TVE = = 18. The neutral complex which follows the 18-electron rule is [GATE 00] (a) CH FeC (b) CH oc3 (c) CH C (d) C 6 H e C6H6 Soln. C 6 H e C6H6 TVE = = 18 rrect option is (d)

7 Introduction to rganometallic mpounds 7 6. Find oxidation state of the following compounds? [TIF 01] (a) Pd (b) Pd(P 3 ) 4 (c) Pd(Ac) (d) Pd(Br) Soln. (a) Pd (b) Pd(P 3 ) 4 x = 0, x = x+0 = 0, x = 0 xidation state = + xidation state = 0 (c) Pd(Ac) (d) Pd(Br) x+( 1) =0, x = x+( 1) + ( 1) = 0 x = 0, x = xidation state = + xidation state = + 7. For in oxidation state II, predict the overall charges of the coordination complexes shown in the reactions below: [TIF 01] Soln. H H H H H H z NaH H H H H H H (a) z = +; x = ; y = + (b) z = 0; x = +; y = (c) z = 0; x = +; y = + (d) z = ; x = +; y = H H H H H H z NaH H H H H H H + L = C + L = C + L = C (+) + ( 1) + 4(0) = Z (+) + 6(0) = X (+) + 4( 1) = Y Z = 0 X = + Y = rrect answer is (b) 8. n the basis of 18 electron rule, find out the value of n. (i) TcBr C n (ii) Na FeC (iii) n C n (v) h C 3 n (iv) Ir CS P n 3 H x x n Soln. (i) TcBr C n (ii) Na FeC n n = n = 18, n = 8 n = n = 4 (iii) n C n (iv) Ir CS P H y y + 6H + 6H n n + 1 = n = 18, n = n = 10 = n = 1 (v) h C 3 n n = 18 n = 18-1, n = 3

8 8 Introduction to rganometallic mpounds 9. n the basis of 18 electron rule find out the value of, where is first row (3d series element) and then find out the element (i) () (iii) 3 -allyl -Cp C (ii) C H -C H Soln. (i) (C) (iii) 3 -allyl -Cp C 1 st row (3d) = = 18 = = 6 = 7 So, = Cr. So, = n (ii) C H -C H = 18 = 10 So, = Ni UNSLVED PBLES 1. What change could be necessary for the following complex to obey 18 electrons rule. (a) [(C) 3 ] z (c) [( Cp)Fe (C) (C H) z (b) [Ni(C) 3 (N)] z Ans. (a) z 3 (b) z 1 (c) z 1. n the basis of 18 electrons rule, identify the first row transition metal for each of the following complexes. (a) (b) (c) [(CF 3 )(C) ] Ans. (a) = Cr (b) = Ni (c) = n 3. rganometallic compound [o(cp) (C) ] follow 18 electrons rule the heptacity of two cp group are Ans (a), (b), (c), (b) 4. The complex that does not obey 18 electrons rule Ans. (a) [u(n)(br )(Pe 3 )(Ne )] (c) [CpTi(C) 4 ] (a) (b) [CpCr(N) e] (d) none of these (d) [(C) (CS)(P 3 )(Br)]. What is the heptacity of cycloheptatrienyl ligand in a complex [(C 7 H 7 )o(c) 3 ] Ans. (a) (b) (c) 6 (d) 7 (c)

9 Introduction to rganometallic mpounds 9 PACTICE SET 1. atch each of the compounds in List-I with appropriate oxidation state from List-II and the coordination number from List-III. [GATE 199] List-I List-II List-III (1) Zeise s salt 0 3 () Ni(C) (3) [(NH 3 ) ] 3 6 List-I List-II List-III (a) (1,, 3) (, 0, 1) (3, 4, 6) (b) (1,, 3) (, 3, 1) (3, 4, ) (c) (1,, 3) (3, 0, 1) (, 4, 6) (d) (1,, 3) (, 0, 3) (3, 4, ). Which case of the following is most easily reduced? [GATE 1996] (a) V(C) 6 (b) Cr(C) 6 (c) Fe(C) (d) Ni(C) 4 3. The organometallic compound W(C H ) (C) follows the 18-electron rule. The hapticities of the two cyclopentadienyl groups are [GATE 1996] (a) and (b) 3 and (c) 3 and 3 (d) 1 and 4. Which one of the following molecules does not obey the 18-electron rule? [GATE 1997] (a) n C 6 (b) Fe C (c) Cr C 3 (d) n C. Among the following, the unstable carbonyl species is [GATE 1998] (a) n(c) (b) [n(c) ] (c) [n(c) ] + (d) n(c) 6. Which of the following does not obey 18 electron rule? [GATE 1999] (a) Cr(C) 6 (b) Fe(C) (c) V(C) 6 (d) n (C) Which of the following obey 18 electron rule? [GATE 000] (a) n(c) 3 (b) Fe (C) 4 (c) V(C) 6 (d) Cr(C) 6 8. Which of the following complex do not obey 18 electron rule. (a) Cpu CP 3 (b) W C Sie NCe (c) Ir P As Which of the following Beryllium complex is stable? (a) Be Cp (c) 1 3 Be Cp Cp 3 (d) As N Br Pe Ne 3 (b) 1 Be Cp Cp Note: ain group elements follow octet rule, Valence electron of Be =, So, to complete octet, Needs 6 electrons. (d) 1 Be Cp Cp ANSWE KEY Questions ption (a) (a) (b) (d) (d) Questions ption (c) (d) (d) (d) 4