Ruthenium nucleophilic addition reactions

The addition of a phosphine group to the organic fragment has been studied in some detail in compounds with cluster-bound vinyl ligands. The zwitterionic adducts which are formed can then undergo nucleophilic addition reactions (411, 461, 462). A reaction of this type also occurs with amine-substituted alkynes coordinated to osmium and ruthenium complexes (117). 

Beck and co-workers (84,8.5) utilized the anionic carbonylmetallates [M(C0)5] (M = Mn, Re) and [WCp(CO),] in nucleophilic addition reactions with cationic hexadienyl, cyclohexadienyl, cycloheptadienyl, and cyclooctadienyl complexes of iron and ruthenium to give heterobimetal lie complexes with rj iV-hydrocarbon bridges. The reaction of [Fe(i7 -... 

On the other hand, a nucleophilic addition reaction of a jt(-allyl)ruthenium complex to a ketone is also reversible. The deallylation of a tertiary homoallylic... 

Thiolate-bridged dirutheniutn complexes catalyze the [3-f3] cycloaddition reaction between propargylic alcohols and cyclic 1,3-dicarbonyl compounds to afford 4,6,7,8-tetrahydrochromen-5-ones or 4//-cyclopenta[b]pyran-5-ones [193] and with 2-naphthols or phenols to afford l//-naphtho[2,l-b]pyrans and 4//-l-benzo-pyrans, respectively [194]. This cycloaddition is considered to proceed by stepwise propargylation and intramolecular cyclization (carbon and oxygen nucleophile additions) reactions, where ruthenium allenylidene and vinylidene complexes are the key intermediates (Scheme 57). Enantioselective mthenium-catalyzed [3-f3] cycloaddition of propargylic alcohols with 2-naphthols has also been described [195]. 

This aldol condensation is assumed to proceed via nucleophilic addition of a ruthenium enolate intermediate to the corresponding carbonyl compound, followed by protonation of the resultant alkoxide with the G-H acidic starting nitrile, hence regenerating the catalyst and releasing the aldol adduct, which can easily dehydrate to afford the desired a,/3-unsaturated nitriles 157 in almost quantitative yields. Another example of this reaction type was reported by Lin and co-workers,352 whereas an application to solid-phase synthesis with polymer-supported nitriles has been published only recently.353... 

Otherwise, the reactions of indenyl-ruthenium(II) allenylidenes [RuCty -CgHy) =C=C=C(R )Ph (PPh3)2][PF6] (R = H, Ph) with ynamines R C CNEtj (R = Me, SiMea) have been reported to yield the alkenyl(amino)allenylidene complexes 41 via insertion of the ynamine into the Cp=Cy allenylidene bond (Scheme 10) [52, 53], This insertion process involves an initial nucleophilic addition of the ynamine at Cy atom of the cumulene, which leads to the cationic alkynyl intermediate complexes 39. Further ring closing, involving the Cp atom, generates the [2+2]... 

Highly reactive organic vinylidene and allenylidene species can be stabilized upon coordination to a metal center [1]. In 1979, Bruce et al. [2] reported the first ruthenium vinylidene complex from phenylacetylene and [RuCpCl(PPh3)2] in the presence of NH4PF6. Following this report, various mthenium vinylidene complexes have been isolated and their physical and chemical properties have been extensively elucidated [3]. As the a-carbon of ruthenium vinylidenes and the a and y-carbon of ruthenium allenylidenes are electrophilic in nature [4], the direct formation of ruthenium vinylidene and ruthenium allenylidene species, respectively, from terminal alkynes and propargylic alcohols provides easy access to numerous catalytic reactions since nucleophilic addition at these carbons is a viable route for new catalysis (Scheme 6.1). 

The isomerization of terminal epoxyalkynes into furans catalyzed by RuCl(Tp)(PPh3) (MeCN) inthe presence of Et3N as abase at 80 °C in 1,2-dichloroethaneis explained by a related intramolecular nucleophilic addition of the oxygen atom of the epoxide to the a-carbon atom of a ruthenium vinylidene intermediate, as shovm by deuteration in the 3-position of the furan (Scheme 10.10) [45]. This reaction is specific for terminal alkynes and tolerates a variety of functional groups (ether, ester, acetal, tosylamide, nitrile). 

In addition to allylsilanes, CM can also be applied to allylstannanes, which serve as valuable reagents for nucleophilic additions and radical reactions.To date, only eatalyst 1 has been shown to demonstrate CM reactivity in the preparation of 1,2-disubstituted allylstannanes, as ruthenium catalysts were found to be inactive in the presence of this substrate class.Poor stereoselectivities were generally observed, with the exeeption of one instance of >20 1 Z-selectivity in the reaction of allyltributylstannane with an acetyl-protected allyl gluco-side. 

Coordinated nitrogen donor atoms can be involved in chelate-forming template reactions by virtue of nucleophilic addition to carbonyl compounds. An early and rather specific example does not allow the possibility of elimination following the addition step (equation 46).171 More recent work on ruthenium(III) and osmium(III) results in the formation of a-diimine chelate rings... 

In Section 6.3.6, it was emphasized that C02 and secondary amines could add to terminal alkynes in the presence of ruthenium catalysts to afford carbamates. Under comparable conditions (393-413 K, 5 MPa Ru-catalysts), primary amines will afford symmetrical disubstituted ureas in moderate yield [131]. It is worth noting that although the final urea does not contain the starting alkyne, its catalytic formation requires, besides the Ru-catalyst, the presence of a stoichiometric amount of a 1-alkyne (e.g., a propargylic alcohol). A possible mechanism (Scheme 6.32) for this catalytic reaction may involve activation of the alkyne at the metal center, a nucleophilic addition of the carbamate to the activated alkyne to produce... 

The polarisation produced by co-ordination to the metal may be transmitted through a conjugated system. Michael addition reactions of nucleophiles to TV-bonded acrylonitrile are known, and provide a convenient method for the preparation of derivatives. A wide range of nucleophiles may be used in these conjugate additions. For example, the anion of nitromethane (generated in situ) reacts with the ruthenium(m) complex [Ru(NH3)5N=CCH=CH2)]3+, 4.6, to yield a complex of 4-nitrobutyronitrile (Fig. 4-18). 

The stereoselective synthesis of 1,4-disubstituted-l,3-dienes proceeds by head-to-head oxidative coupling of two alkynes with formation of an isolable metallacyclic biscarbene ruthenium complex [23], as shown in Scheme 6. Several key experiments involving labeled reagents and stoichiometric reactions and theoretical studies support the formation of a mixed Fischer-Schrock-type biscarbene complex which undergoes protonation at one carbene carbon atom whereas the other becomes accessible to nucleophilic addition of the carboxylate anion (Scheme 6) [23]. 

The aziridination of olefins, which forms a three-membered nitrogen heterocycle, is one important nitrene transfer reaction. Aziridination shows an advantage over the more classic olefin hydroamination reaction in some syntheses because the three-membered ring that is formed can be further modified. More recently, intramolecular amidation and intermolecular amination of C-H bonds into new C-N bonds has been developed with various metal catalysts. When compared with conventional substitution or nucleophilic addition routes, the direct formation of C-N bonds from C-H bonds reduces the number of synthetic steps and improves overall efficiency.2 After early work on iron, manganese, and copper,6 Muller, Dauban, Dodd, Du Bois, and others developed different dirhodium carboxylate catalyst systems that catalyze C-N bond formation starting from nitrene precursors,7 while Che studied a ruthenium porphyrin catalyst system extensively.8 The rhodium and ruthenium systems are... 

A ruthenacyclopentane 48 has been proposed as an intermediate in this reaction, after coordination of the allene and enone. Exocyclic /1-hydride elimination led to the 1,3-dienes. This ruthenacycle possessed a o-bound ruthenium allyl, allowing nucleophilic additions by alcohols or amines. Alkylative cycloetherification [29] (Eq. 20) and synthesis of pyrrolidine and piperidine [30] were thus achieved. 

The C-C bond formation can also be obtained via a first-step addition of a heteroatom to alkynes. Thus, the reaction of the three components terminal alkyne, water and enone led to 1,5-diketone with atom economy, using the system CpRuCl(COD)/NH4PF6 and In(0S02CF3)3 as a cocatalyst [58,59] (Eq. 43). The mechanism is postulated to proceed by the ruthenium-catalyzed nucleophilic addition of water to alkynes to generate a ruthenium enolate intermediate allowing further insertion of enone and formation of 1,5-diketones after protonation. 

Finally, ruthenium-catalyzed carbocyclization by intramolecular reaction of allylsilanes and allylstannanes with alkynes also led to the formation of vinyl-alkylidenecyclopentanes [81] (Eq. 60). This reaction is catalyzed by RuC13 or CpRuCl(PPh3)2/NH4PF6 in methanol. The postulated mechanism involves the coordination of the alkyne on the ruthenium center to form an electrophilic /f-alkyne complex. This complex can thus promote the nucleophilic addition of the allylsilane or stannane double bond. 

The precatalyst Cp RuCl(COD) allowed the head-to-head oxidative dimerization of terminal alkynes and the concomitant 1,4-addition of carboxylic acid to stereoselectively afford 1-acyloxy-l,3-dienes in one step under mild conditions [89] (Eqs. 67,68). The first step of the reaction consists in the oxidative head-to-head alkyne coupling via the formation of a ruthenacycle intermediate that behaves as a mixed Fischer-Schrock-type biscarbene ruthenium complex, allowing protonation and nucleophilic addition of the carboxylate. 

The selective intramolecular nucleophilic addition of a hydroxy group at Cyof a ruthenium allenylidene generated by activation of propargylic alcohol by RuCl(Cp)(PPh3)2/NH4PF6 provides a ruthenium vinylidene species, which reacts with allylic alcohols as previously described in the section Formation of Unsaturated Ketones (Eq. 11, Scheme 18) [79]. This unprecedented tandem reaction makes possible the construction of tetrahydrofuran derivatives in good yields and has been used as a key step in the synthesis of (-)calyculin A [80]. 

Benzene cyclopentadienyl ruthenium(II) complex 125 undergoes nucleophilic addition at the arene ligand via the addition of sodium borohy-dride or phenyllithium. Reaction with phenyllithium gives the exo-phenyl cyclohexadienyl derivative 249 in 89% yield (154) [Eq. (32)]. 

This chapter will describe various additions to alkynes as a way to generate functional intermediates. In the first section, general additions of O, N, and P nucleophiles will be presented. Ruthenium-catalyzed hydrosilylation of alkynes will be described as an addition reaction to alkynes followed by ruthenium-catalyzed addition of C nucleophiles. 

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