1. CHEM 522 Chapter 04 Carbonyl, Phosphine complexes and Ligand Substitution Reaction

2. Bonding σ Donation π Back bonding

6. From IR it is possible to tell how good is the metal as a π base

7. Preparation of CO Complexes Direct reaction of metal with CO CO replace weakly bonded ligands

8. Preparation of CO Complexes From CO and a reducing agent (like Na, S 2 O 4 2- and CO)

9. Preparation of CO Complexes From a reactive carbonyl compound followed by desertion

10. Metal Carbonyls Reactions Nucleophilic attack at carbon Reaction wit Me - give carbenes Reaction with Me 3 NO give a free bonding site for metal

11. Metal Carbonyls Reactions Nucleophilic attack at carbon [Cp(NO)(PPh 3 )ReCO] + Cp(NO)(PPh 3 )Re(CHO)

12. Metal Carbonyls Reactions Electrophilic attack at oxygen Cl(PR 3 ) 4 ReCO Cl(PR 3 ) 4 ReCOAlMe 3

13. Metal Carbonyls Reactions Migratory insertion MeMn(CO) 5 (PMe 3 )(CO) 4 Mn

14. Bridging CO Groups

15. Unequivalent Bridging CO

16. triply Bridging CO

17. Isonitriles M=C=N-R Stabilize higher oxidation state [Pt(CNPh) 4 ] 2+ no [Pt(CO) 4 ] 2+ is known The lone pair in CO is almost nonbonding while in CNR it is more of antibonding, so when σ donation take place the CN bond become stronger, π back donation weaken the bond, so the shift in the IR will depend on the strength of σ or π donation. (unlike CO)

18. Isonitriles M=C=N-R If back bonding is not strong, M-CΞNR should be linear M=C=N-R bent molecule is also known which means strong back bonding NbCl(CO)(CNR)(dmpe). The ligand is bent at N (129 o -144 o )

19. Thiocarbonyls CS ligand CS is not stable by itself above -160 o C It is known in some compounds as a ligand bonding through C Also bridging CS is also known Usually prepared from CS 2 RhCl(PPh 3 ) 3 Trans-RhCl(CS)(PPh 3 ) 2 + SPPh 3

20. Thiocarbonyls Frequency range Free CS is 1273 μ 3 CS 1040-1080 μ 2 CS 1100-1160 M-CS 1160-1410

21. Nitrosyls NO is a stable free radical Also as NO + in NOBF 4 NO + is isoelectronic with CO It can bind as NO + and it will be three electron donor When NO is bent then it will be one electron donor

22. NO is a fifteen electron molecule with one unpaired electron residing in the π* molecular orbital: (σ1)2(σ1*)2(σ2)2(σ2*)2(σ3)2(πx, πy)4(πx*, πy*)1(σ*3) This electronic configuration explains the high reactivity of the NO molecule, particularly the formation of nitrosonium cation (NO+) on oxidation and the reduction to nitroxide anion (NO–), making it a "non-innocent" ligand Most of the known stable "nitrosyl" complexes are assumed to contain the diamagnetic π acceptor ligand nitrosonium, NO+,but there are cases when NO or NO– (nitroxide) can be reasonably postulated as ligands in transition metal complexes. Establishing the actual form of coordinated NO often requires a variety of physical methods such as IR, EPR, NMR, UV/VIS, X-rays, resonance Raman, magnetic circular dichroism (MCD), etc., and theoretical calculations.

23. NO Bonding NO binds in two ways Either as NO + then it will give linear molecule and will be three electron donor Or as NO - then it will give bent molecule and will be one electron donor

24. Reaction When NO + is added it makes reaction with Nu - more probable

25. Electron Count When NO change from linear to bent both the number of electron on the metal and the oxidation state of the metal will change CoCl 2 L 2 (lin-NO) CoCl 2 L 2 (bent-NO)

27. Electron Count

28. Preparation - NO+ is a powerful oxidation agent - Migratory insertion is also possible for NO

29. Phosphine Ligands Phosphine ligands have the general formula PR 3 where R = alkyl, aryl, H, halide etc. Closely related are phosphite ligands which have the general formula P(OR) 3. Both phosphines and phosphites are neutral two electron donors that bind to transition metals through their lone pairs. There are many examples of polydentate phosphine ligands, some common examples of which are shown below.

32. Bonding

33. π Acidity

34. Ti2+ is a d2 ion in octahedral field so it should be paramagnetic, however it is diamagnetic. The reason is because of the strong back bonding

35. Tolman Cone Angle

36. The stronger donor phosphine increase the electron density on metal which increase it on CO by back donation

37. Cone angles for some common phosphine ligands are: Phosphine LigandCone Angle PH 3 87 o PF 3 104 o P(OMe) 3 107 o PMe 3 118 o PMe 2 Ph122 o PEt 3 132 o PPh 3 145 o PCy 3 170 o P(t-Bu) 3 182 o P(mesityl) 3 212 o

38. Factors Effecting Bonding There are two important factors effecting the bonding of the phosphines –Electronic –Steric The advantage of using bulky ligands compounds of low coordination number can be formed [Pt(PCy 3 ) 2 ]

39. Chelates Cis and trans phosphines

40. Dissociative Substitution

41. Usually the larger the cone angle the faster the dissociation This mechanism is usually preferred for 18- electron molecule Transition state has a positive ΔS ‡ and in the range 10-15 eu (entropy unit)

42. stereochemistry O h can go to SP or distorted TBP (DTBP)

43. stereochemistry O h can go to SP or distorted TBP ML 6 d 6 seems to prefer SP or DTBP ML 6 d 8 seems to prefer TBP

44. stereochemistry Phosphines usually do not replace all CO in the complex The fac structure is usually prefer over the mer for electronic reason

45. Dissociative Substitution Bulky ligands usually enhance dissociation Protonation can be used to remove an alkyl or hydride group Weakly bonded solvent is a good leaving group W(CO) 5 (thf) + PPh 3  W(CO) 5 (PPh 3 )

46. Associative Mechanism L n M  L n M-L’  L n-1 M-L’ This mechanism is usually adapted for 16 e complexes

47. The Trans Effect This is observed in square planar complexes where the incoming ligand will occupy certain position depending on the ligand trans to it

48. The Trans Effect The solvent may have some effect

49. Ligand Rearrangement This take place for 18-e complexes

50. Ligand Rearrangement This also observed for indenyl complexes better than their Cp analogs because of the benzene ring

51. Ligand Rearrangement This also observed for other complexes

52. Redox Effects Sometime mechanism can be catalyzed by oxidation The 17, and 19 e species are very difficult to study they are unstable and usually only a transition state

53. Redox Effects This could lead to chain reaction

54. Redox Effects A trace of a free radical can abstract a 1e ligand

55. The Interchange Mechanism It is intermediate state in which the ligand will be in the area around the complex but will not substitute before the leaving of one of the ligands from the complex (I d ) this is usually observed when an 18 electron complex exist and it is thought that an associative mechanism take place There is also interchange associative mechanism (I a )

56. Rearrangement This take place with coordinatively unsaturated species

57. Rearrangement This take place with coordinatively unsaturated species

58. Rearrangement Coordinatively unsaturated species is using a ligand from other specie

59. Cyclometallation This is one of the reductive elimination process W (IV)  W (III)

60. Cyclometallation This is one of the oxidative addition process

61. Agostic Ligand Substitution This is one of the ligand substitution process

62. Photochemical Substitution Usually used for carbonyl complexes

63. Photochemical Substitution Charge transfer process W(CO) 4 (Phen) at 546 nm there will be charge transfer transition to give W.+ (CO) 4 (Phen.- ) Then irradiation will lead to substitution by PPh 3 to give W(CO) 3 (PPh 3 )(Phen)

64. Hydride Cp 2 WPhH + H 2 Cp 2 WH 2 Reductive elimination enforced by hv followed by oxidative addition

65. Hydride ReH 5 (PR 3 ) 2 + PR 3 ReH 5 (PR 3 ) 3 Some times loss of phosphine can occur instead

66. M-M Bond Disproportionation The metal when bonded to the NH 3 it can not take the electron density no more. electron density will be provided by NH3 to an extent it may be oxidized

67. Solvents DMSO DMF THF Diethylether Acetone Ethanol Halocarbon

68. Solvents