Ruthenium hydride and vinyl complexes supported by nitrogen–oxygen mixed-donor ligands

Enantioselective Metal-Catalyzed Reductive Coupling of Alkynes with Carbonyl Compounds and Imines: Convergent Construction of Allylic Alcohols and Amines

The use of alkynes as vinylmetal pronucleophiles in intermolecular enantioselective metal-catalyzed carbonyl and imine reductive couplings to form allylic alcohols and amines is surveyed. Related hydrogen auto-transfer processes, wherein alcohols or amines serve dually as reductants and carbonyl or imine proelectrophiles, also are cataloged, as are applications in target-oriented synthesis. These processes represent an emerging alternative to the use of stoichiometric vinylmetal reagents or Nozaki-Hiyama-Kishi (NHK) reactions in carbonyl and imine alkenylation.

Stereo- and Site-Selective Conversion of Primary Alcohols to Allylic Alcohols via Ruthenium-Catalyzed Hydrogen Auto-Transfer Mediated by 2-Butyne

The first enantioselective ruthenium-catalyzed carbonyl vinylations via hydrogen autotransfer are described. Using a ruthenium-JOSIPHOS catalyst, primary alcohols 2a-2m and 2-butyne 1a are converted to chiral allylic alcohols 3a-3m with excellent levels of absolute stereocontrol. Notably, 1°,2°-1,3-diols participate in site-selective C-C coupling, enabling asymmetric carbonyl vinylation beyond premetalated reagents, exogenous reductants, or hydroxyl protecting groups. Using 2-propanol as a reductant, aldehydes dehydro-2a, 2l participate in highly enantioselective 2-butyne-mediated vinylation under otherwise identical reaction conditions. Regio-, stereo-, and site-selective vinylations mediated by 2-pentyne 1b to form adducts 3n, 3o, and epi-3o also are described. The tiglyl alcohol motif obtained upon butyne-mediated vinylation, which is itself found in diverse secondary metabolites, may be converted to commonly encountered polyketide stereodiads, -triads, and -tetrads, as demonstrated by the formation of adducts 4a-4d. The collective mechanistic studies, including deuterium labeling experiments, corroborate a catalytic cycle involving alcohol dehydrogenation to form a transient aldehyde and a ruthenium hydride, which engages in alkyne hydrometalation to form a nucleophilic vinylruthenium species that enacts carbonyl addition. A stereochemical model for carbonyl addition invoking formyl CH···I[Ru] and CH···O≡C[Ru] hydrogen bonds is proposed based on prior calculations and crystallographic data.

The stepwise generation of multimetallic complexes based on a vinylbipyridine linkage and their photophysical properties

The versatile rhenium complex [ReCl(CO)₃(bpyC[triple bond, length as m-dash]CH)] (HC[triple bond, length as m-dash]Cbpy = 5-ethynyl-2,2'-bipyridine) is used to generate a series of bimetallic complexes through the hydrometallation of [MHCl(CO)(BTD)(PPh₃)₂] (M = Ru, Os; BTD = 2,1,3-benzothiadiazole). The ruthenium complex [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}Cl(BTD)(CO)(PPh₃)₂] was characterised structurally. Ligand exchange reactions with bifunctional linkers bearing oxygen and sulfur donors provide access to tetra- and pentametallic complexes such as [{M{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}(CO)(PPh₃)₂}₂(S₂CNC₄H₈NCS₂)] and Fe[C₅H₄CO₂M{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}(CO)(PPh₃)₂]₂. The effect of the group 8 metal on the photophysical properties of the rhenium centre was investigated using the complexes [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}Cl(BTD)(CO)(PPh₃)₂] and [M{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}{S₂P(OEt)₂}(CO)(PPh₃)₂] (M = Ru, Os). This revealed the quenching of the rhenium-based emission in favour of weak radiative processes based on the Ru and Os centres. The potential for exploiting this effect is illustrated by the reaction of [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}Cl(CO)(BTD)(PPh₃)₂] with carbon monoxide, which results in a 5-fold fluorescence enhancement in the dicarbonyl product, [Ru{CH[double bond, length as m-dash]CH-bpyReCl(CO)₃}Cl(CO)₂(PPh₃)₂], as the quenching effect is disrupted.

Gold(I) complexes bearing mixed-donor ligands derived from N-heterocyclic carbenes

The new 2-phenylthiocarbamoyl-1,3-dimesitylimidazolium inner salt (IMes·CSNPh) reacts with [AuCl(L)] in the presence of NH(4)PF(6) to yield [(L)Au(SCNPh·IMes)](+) (L = PMe(3), PPh(3), PCy(3), CNBu(t)). The carbene-containing precursor [(IDip)AuCl] reacts with IMes·CSNPh under the same conditions to afford the complex [(IDip)Au(SCNPh·IMes)](+) (IDip = 1,3-bis(2,6-diisopropylphenyl)imidazol-2-ylidene). Treatment of the diphosphine complex [(dppm)(AuCl)(2)] with one equivalent of IMes·CSNPh yields the digold metallacycle, [(dppm)Au(2)(SCNPh·IMes)](2+), while reaction of [L(2)(AuCl)(2)] with two equivalents of IMes·CSNPh results in [(L(2)){Au(SCNPh·IMes)}(2)](2+) (L(2) = dppb, dppf, or dppa; dppb = 1,4-bis(diphenylphosphino)butane, dppf = 1,1'-bis(diphenylphosphino)ferrocene, dppa = 1,4-bis(diphenylphosphino)acetylene). The homoleptic complex [Au(SCNPh·IMes)(2)](+) is formed on reaction of [AuCl(tht)] (tht = tetrahydrothiophene) with two equivalents of the imidazolium-2-phenylthiocarbamoyl ligand. This product reacts with AgOTf to yield the mixed metal compound [AuAg(SCNPh·IMes)(2)](2+). Over time, the unusual trimetallic complex [Au(AgOTf)(2)(SCNPh·IMes)(2)](+) is formed. The sulfur-oxygen mixed-donor ligands IMes·COS and SIMes·COS (SIMes = 1,3-bis(2,4,6-trimethylphenyl)imidazolin-2-ylidene) were used to prepare [(L)Au(SOC·IMes)](+) and [(L)Au(SOC·SIMes)](+) from [(L)AuCl] (L = PPh(3), CN(t)Bu). The bimetallic examples [(dppf){Au(SOC·IMes)}(2)](2+) and [(dppf){Au(SOC·SIMes)}(2)](2+) were synthesized from the reaction of [(dppf)(AuCl)(2)] with the appropriate ligand. Reaction of [(tht)AuCl] with one equivalent of IMes·COS or SIMes·COS yields [Au(SOC·IMes)(2)](+) and [Au(SOC·SIMes)(2)](+), respectively. The compounds [(Ph(3)P)Au(SCNPh·IMes)]PF(6), [(Cy(3)P)Au(SCNPh·IMes)]PF(6) and [Au(AgOTf)(2)(SCNPh·IMes)(2)]OTf were characterized crystallographically.

The functionalisation of ruthenium(II) and osmium(II) alkenyl complexes with amine- and alkoxy-terminated dithiocarbamates

The complex cis-[RuCl(2)(dppm)(2)] reacts with the amine-terminated dithiocarbamates KS(2)CN(CH(2)CH(2)NEt(2))(2) and KS(2)CN(CH(2)CH(2)CH(2)NMe(2))(2) to form the compounds [Ru{S(2)CN(CH(2)CH(2)NEt(2))(2)}(dppm)(2)](+) and [Ru{S(2)CN(CH(2)CH(2)CH(2)NMe(2))(2)}(dppm)(2)](+), respectively. The methoxy-terminated dithiocarbamate compound [Ru{S(2)CN(CH(2)CH(2)OMe)(2)}(dppm)(2)](+) was also prepared from the same precursor using KS(2)CN(CH(2)CH(2)OMe)(2). The alkenyl complexes [RuRCl(CO)(BTD)(PPh(3))(2)] (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, CH=CHCPh(2)OH), [Ru(C(C[triple bond]CBu(t))=CHBu(t))Cl(CO)(PPh(3))(2)] and [Os(CH=CHC(6)H(4)Me-4)Cl(CO)(BTD)(PPh(3))(2)] also react cleanly with KS(2)CN(CH(2)CH(2)CH(2)NMe(2))(2) and KS(2)CN(CH(2)CH(2)NEt(2))(2) to yield [MR{S(2)CN(CH(2)CH(2)CH(2)NMe(2))(2)}(CO)(PPh(3))(2)] and [MR{S(2)CN(CH(2)CH(2)NEt(2))(2)}(CO)(PPh(3))(2)], respectively. In a similar fashion, the compounds [RuR{S(2)CN(CH(2)CH(2)OMe(2))(2)}(CO)(PPh(3))(2)] (R = CH=CHBu(t), CH=CHC(6)H(4)Me-4, C(C[triple bond]CBu(t))=CHBu(t)) were also prepared. Treatment of [Ru(CH=CHBu(t)){S(2)CN(CH(2)CH(2)CH(2)NMe(2))(2)}(CO)(PPh(3))(2)] and [Ru{S(2)CN(CH(2)CH(2)NEt(2))(2)}(dppm)(2)](+) with trifluoroacetic acid affords the ammonium complexes [Ru(CH=CHBu(t)){S(2)CN(CH(2)CH(2)CH(2)NHMe(2))(2)}(CO)(PPh(3))(2)](2+) and [Ru{S(2)CN(CH(2)CH(2)NHEt(2))(2)}(dppm)(2)](2+), while the same reagent generates the tricationic vinylcarbene complex [Ru(=CHCH=CPh(2)){S(2)CN(CH(2)CH(2)CH(2)NHMe(2))(2)}(CO)(PPh(3))(2)](3+) through loss of water from [Ru(CH=CHCPh(2)OH){S(2)CN(CH(2)CH(2)CH(2)NMe(2))(2)}(CO)(PPh(3))(2)]. The structures of [Ru{S(2)CN(CH(2)CH(2)OMe)(2)}(dppm)(2)]PF(6) and [Ru(CH=CHC(6)H(4)Me-4){S(2)CN(CH(2)CH(2)OMe)(2)}(CO)(PPh(3))(2)] were determined crystallographically.