Synthesis of Organometallic Compounds

1. Synthesis of Organometallic Compounds Advanced Inorganic Chemistry 92/2

2. Ruthenium Complexes • Recently, the chemistry of ruthenium complexes has been extensively explored. • less application in organic synthesis than palladium compounds, probably because their chemistry is more complicated.

3. Ruthenium Complexes • Ruthenium complexes generally have 5- or 6-coordinated geometry and their oxidation state can vary between -2 to 6. • This complexity, however, leads to many interesting reactions and further developments in this field are expected.

4. Ruthenium Complexes • A wide variety of organoruthenium complexes is known. • They can be roughly divided into 4 groups according to their supporting ligands.

5. 1. Ru3(CO)12 • Carbonyl complexes which are generally derived from Ru3(CO)12. • Air stable compound, easy to handle • The precursor of an active catalyst for reduction of nitro groups, C—H bond activation or carbonylation.

6. 2. Ruthenium complexes with tertiary phosphine ligands • RuCl2L4, RuHClL4, or RuH2L4 • useful for organic synthesis, catalytic reactions, asymmetric reactions.

7. 3. Cyclopentadienyl complexes • Cyclopentadienyl and pentamethylcyclopentadienyl ligands effectively stabilize alkyl-ruthenium bonds, whereas in phosphine complexes the alkyl group tends to undergo b-hydrogen elimination.

8. Ruthenium complexes having arenes or dienes • Low valent ruthenium starting materials via replacement of arene or diene ligands • Catalysts for olefin dimerization, hydrogenation of arenes, or C—C bond cleavage reaction.

9. Preparation of these ruthenium complexes • RuCl3.3H2O and Ru3(CO)12 • They are relatively inexpensive and stable against oxygen.

10. Dichlororuthenium Complexes • RuCl2(PPh3)3 • Coordinatively unsaturated. • Agostic C-H bond • A common Ru precursor

11. Dichlororuthenium complexes • Dichlororuthenium complexes are formed by the reduction of RuCl3.3H2O in the presence of the ligand. • RuCl2(PPh3)3 is obtained by treatment of RuCl3.3H2O with an excess of PPh3 in methanol as air-stable shiny black crystals. • Reaction of RuCl3.3H2O with PRR’2 or PR2R’ (R = phenyl, R’ = alkyl) gives cationic dinuclear complexes [Ru2Cl3(PRnR’3-n)6]Cl under similar conditions.

12. RuCl2(PPh3)3 • The X-ray crystallography of RuCl2(PPh3)3 showed that it has a distorted octahedral geometry with a vacant site which is occupied by an agostic proton of a phenyl group.

13. Reactivities of RuCl2(PPh3)3

14. N-Alkylation of Amines by Primary Alcohols • RuCl2(PPh3)3 or RuCl3.3H2O/P(OBu)3 effectively catalyze the N-alkylation of aromatic amines. • N-alkylation of aliphatic amines with a primary alcohol is carried out in high yield by the use of RuH2(PPh3)4 as catalyst.

15. Preparation of heterocycles N-alkyl piperidine pyrrolidine pyrrole

16. Oxidation of Amines, Amides, and Diols • RuCl2(PPh3)3 is also a catalyst for the oxidation of nitriles, amides and lactams under moderate conditions.

17. A coordinatively unsaturated 16e- ruthenium(0) complex • Reduction of RuCl2(CO)2(PtBu2Me)2 with magnesium affords an isolable 16e ruthenium(0) complex Ru(CO)2(PtBu2Me)2. • Highly reactive toward hydrogen, acetylenes and phosphines to give coordinatively saturated complexes. Trans phosphines Two COs are bent.

18. RuHCl(CO)(PPh3)3 • Formed by the reduction of RuCl3.3H2O with alcohol in the presence of tertiary phosphines. • Similarly prepared as Vaska's complex, IrCl(CO)(PPh3)2 • Where does the CO ligand come from? • Mechansim? • Stereochemistry: Cl trans to CO

19. Recent developments

20. C-H Bond activation • The generation of coordinatively unsaturated species play an important role. • These species are usually produced by thermal or photo-mediated reductive elimination of dihydrogen, alkanes, alkenes or arenes.

21. Mechanistic expect

22. Dihydridoruthenium Complexes • Dihydridoruthenum complexes are reported to be catalysts for either the direct or transfer hydrogenation of olefins. • Ruthenium hydride complexes are also catalysts for organic reactions such as the coupling reaction of alkenes with terminal alkynes, the [2 + 2] cycloaddition of norbornene with alkynes, Tishchenko-type reactions, and the catalytic insertion of olefins into the ortho C—H bond of aromatic ketones.

23. Preparation of RuH2(PPh3)4 • RuH2(PPh3)4 is prepared by the reaction of RuCl2(PPh3)3 with NaBH4 in the presence of PPh3 in refluxing methanol. • Or by the direct reaction of RuCl3.3H2O with NaBH4 and PPh3 in refluxing ethanol. • It is formed as an off-yellow powder and should be kept under argon, not nitrogen, because a PPh3 ligand is readily replaced by dinitrogen.

24. Reactivities of RuH2(PPh3)4

25. Chemoselective aldol reactions

26. Coupling reactions of acetylenes with dienes • The reaction of l-octyne with 1,3-butadiene catalyzed by RuH2(PBu3)4 affords 2- dodecen-5-yne. A similar coupling reaction is also catalyzed by RuCl(C5H5)(C8H12). Mechanism?

27. Tishchenko-type dimerization. • RuH2(PPh3)4 reacts with aldehydes to give esters via Tishchenko-type dimerization. For example, benzaldehyde is converted to benzyl benzoate by RuH2(PPh3)4. This reaction involves C—H bond activation of the formyl proton followed by formation of a ruthenium acyl alkoxide complex Ru(OCH2Ph)(COPh)(PPh3)4. Mechanism?

28. RuH2(CO)(PPh3)3 catalyze olefin coupling reactions of aromatic ketones via C—H bond activation

29. A possible intermediate in theolefin coupling reaction ofaromatic ketone catalyzed byRuH2(CO)(PPh3)3. Other ligandsare omitted.A possible intermediate in theolefin coupling reaction ofaromatic ketone catalyzed byRuH2(CO)(PPh3)3. Other ligandsare omitted.

30. Reactivities of RuH2(PPh3)4

31. Catalytic reactions Intermediate:

32. Ruthenium Complexes with Chiral Ligand • the chemistry of ruthenium complexes with the chiral ligands BINAP and PYBOX are described. Atropisomers of the BINAP Ligand

34. Ruthenium Complexes Having Cyclopentadienyl Ligands • Ruthenocene is relatively un-reactive • The dinuclear complex [RuCl2(C5Me5)]2 is a versatile reagent. • prepared by the reaction of RuCl3.3H2O with pentamethylcyclopentadiene in ethanol

36. Treatment of Ru2H4(C5Me5)2 with ethylene results in the formation of a divinyl(ethylene)diruthenium complex under ambient conditions. This is an interesting reaction because there are few examples of vinylic C—H bond activation with metal polyhydride complexes.

37. A unique reaction probably proceeds via an acetylide-vinylidene intermediate.

38. Ruthenium Complexes with Arene/Diene Ligands • Ru(cod)(cot) is prepared by the reduction of RuCl3.3H2O with zinc powder in the presence of 1,5-cyclooctadiene in methanol [192]. It is used in several catalytic reactions and as a convenient precursor to various zero- or multi-valent ruthenium complexes

39. Reactivities of Ru(cod)(cot)

40. Dimerization of NBD

41. For example, ruthenium complexes sometimes show ambiphilic reactivity allyl carbonate

42. Ruthenium-catalyzed allylations are often show quite different reactivities and selectivities from those of palladium-catalyzed allylations. The detailed mechanism of the regiocontrolling step is still unclear.

43. Useful Ru precursors