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. Ru 3 (CO) 12 1.Carbonyl complexes which are generally derived from Ru 3 (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 RuCl 2 L 4, RuHClL 4, or RuH 2 L 4 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 RuCl 3. 3H 2 O and Ru 3 (CO) 12 They are relatively inexpensive and stable against oxygen.

10 Dichlororuthenium Complexes RuCl 2 (PPh 3 ) 3 Coordinatively unsaturated. Agostic C-H bond A common Ru precursor

11 Dichlororuthenium complexes Dichlororuthenium complexes are formed by the reduction of RuCl 3.3H 2 O in the presence of the ligand. RuCl 2 (PPh 3 ) 3 is obtained by treatment of RuCl 3. 3H 2 O with an excess of PPh 3 in methanol as air-stable shiny black crystals. Reaction of RuCl 3.3H 2 O with PRR’ 2 or PR 2 R’ (R = phenyl, R’ = alkyl) gives cationic dinuclear complexes [Ru 2 Cl 3 (PR n R’ 3-n ) 6 ]Cl under similar conditions.

12 RuCl 2 (PPh 3 ) 3 The X-ray crystallography of RuCl 2 (PPh 3 ) 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 RuCl 2 (PPh 3 ) 3

14 N-Alkylation of Amines by Primary Alcohols RuCl 2 (PPh 3 ) 3 or RuCl 3. 3H 2 O/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 RuH 2 (PPh 3 ) 4 as catalyst.

15 Preparation of heterocycles N-alkyl piperidine pyrrolidine pyrrole

16 Oxidation of Amines, Amides, and Diols RuCl 2 (PPh 3 ) 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 RuCl 2 (CO) 2 (P t Bu 2 Me) 2 with magnesium affords an isolable 16e ruthenium(0) complex Ru(CO) 2 (P t Bu 2 Me) 2. Highly reactive toward hydrogen, acetylenes and phosphines to give coordinatively saturated complexes. Trans phosphines Two COs are bent.

18 RuHCl(CO)(PPh 3 ) 3 Formed by the reduction of RuCl 3.3H 2 O with alcohol in the presence of tertiary phosphines. Similarly prepared as Vaska's complex, IrCl(CO)(PPh 3 ) 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 RuH 2 (PPh 3 ) 4 RuH 2 (PPh 3 ) 4 is prepared by the reaction of RuCl 2 (PPh 3 ) 3 with NaBH 4 in the presence of PPh 3 in refluxing methanol. Or by the direct reaction of RuCl 3.3H 2 O with NaBH 4 and PPh 3 in refluxing ethanol. It is formed as an off-yellow powder and should be kept under argon, not nitrogen, because a PPh 3 ligand is readily replaced by dinitrogen.

24 Reactivities of RuH 2 (PPh 3 ) 4

25 Chemoselective aldol reactions

26 Coupling reactions of acetylenes with dienes The reaction of l-octyne with 1,3-butadiene catalyzed by RuH 2 (PBu 3 ) 4 affords 2- dodecen- 5-yne. A similar coupling reaction is also catalyzed by RuCl(C 5 H 5 )(C 8 H 12 ). Mechanism?

27 Tishchenko-type dimerization. RuH 2 (PPh 3 ) 4 reacts with aldehydes to give esters via Tishchenko-type dimerization. For example, benzaldehyde is converted to benzyl benzoate by RuH 2 (PPh 3 ) 4. This reaction involves C—H bond activation of the formyl proton followed by formation of a ruthenium acyl alkoxide complex Ru(OCH 2 Ph)(COPh)(PPh 3 ) 4. Mechanism?

28 RuH 2 (CO)(PPh 3 ) 3 catalyze olefin coupling reactions of aromatic ketones via C—H bond activation

29 A possible intermediate in the olefin coupling reaction of aromatic ketone catalyzed by RuH 2 (CO)(PPh 3 ) 3. Other ligands are omitted.

30 Reactivities of RuH 2 (PPh 3 ) 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

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34 Ruthenium Complexes Having Cyclopentadienyl Ligands Ruthenocene is relatively un-reactive The dinuclear complex [RuCl 2 (C 5 Me 5 )] 2 is a versatile reagent. prepared by the reaction of RuCl 3. 3H 2 O with pentamethylcyclopentadiene in ethanol

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36 Treatment of Ru 2 H 4 (C 5 Me 5 ) 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 RuCl 3. 3H 2 O 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

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