Novel dinuclear and trinuclear ruthenium clusters derived from 2‐aryl‐substituted indenylphosphines via C─H bond cleavage

Treatment of Ru₃(CO)₁₂ with an equivalent of (2‐phenyl‐1H ‐inden‐3‐yl)dicyclohexylphosphine ( 1 ) and (2‐pyridyl‐1H ‐inden‐1‐yl)dicyclohexylphosphine ( 4 ) in refluxing heptane gave the novel trinuclear ruthenium clusters (μ₃‐η¹:η²:η⁵–2‐phenyl‐3‐Cy₂PC₉H₄)Ru₃(CO)₈ ( 1c ) and [μ₂‐η¹–2‐(pyridin‐2‐yl)‐3‐Cy₂PC₉H₆]Ru₃(CO)₉ ( 4a ), respectively, via C ─ H bond cleavage. (2‐Mesityl‐1H ‐inden‐3‐yl)dicyclohexylphosphine ( 2 ) reacted with Ru₃(CO)₁₂ in refluxing heptane to give the trinuclear ruthenium cluster [μ‐2‐mesityl‐(3‐Cy₂PC₉H₅)](μ₂‐CO)Ru₃(CO)₉ ( 2c ) via C ─ H bond cleavage and carbonyl insertion. 2‐(Anthracen‐9‐yl)‐1H –inden‐3‐yldicyclohexylphosphine ( 3 ) reacted with Ru₃(CO)₁₂ in refluxing heptane to give the dinuclear ruthenium cluster [μ₂‐η³:η³–2‐(anthracen‐9‐yl)‐3‐Cy₂PC₉H₆]Ru₂(CO)₅ ( 3a ). The structures of 1c , 2c , 3a and 4a were fully characterized using IR and NMR spectroscopy, elemental analysis and single‐crystal X‐ray diffraction. These results suggest that the 2‐aryl substituent on the indenyl ring has a pronounced effect on the reaction and coordination modes of Ru₃(CO)₁₂.     

Addition of H2 Across a Cobalt–Phosphorus Bond

Addition of H₂ across the cobalt–phosphorus bond of (PPP)CoPMe₃ ( 3 ) is demonstrated, where PPP is a monoanionic diphosphine pincer ligand with a central N‐heterocyclic phosphido (NHP^?) donor. The chlorophosphine Co^II complex (PP^ClP)CoCl₂ ( 2 ) can be generated through coordination of the chlorophosphine ligand (PP^ClP, 1 ) to CoCl₂. Subsequent reduction of 2 with KC₈ in the presence of PMe₃ generates (PPP)CoPMe₃ ( 3 ), in which both the phosphorus and cobalt centers have been reduced. The addition of 1 atm of H₂ to complex 3 cleanly affords (PP^HP)Co(H)PMe₃ ( 4 ), in which H₂ has ultimately been added across the metal–phosphorus bond. Complex 4 was characterized spectroscopically and using computational methods to predict its geometry.     

Reaction of ruthenium carbonylcarbide cluster Ru6C(CO)17 with nickelocene and pentamethylcyclopentadiene

The reaction of cluster Ru₆C(CO)₁₇ (1) with nickelocene is studied. Five CO ligands rather than a metal-ligand crown are substituted for two cyclopentadienyl groups to give a new complex Ru₆C(⁵-Cp)₂(CO)₁₂ (2). The reaction of cluster1 with entamethylcyclopentadiene leads to new complex Ru₆C(-¹⁵-CH₂C₅Me₄)(CO)₁₄ (3) containing the cr-bond CH₂-Ru, along with an ⁵-coordinated cyclopentadienyl ring.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1171–1172, June, 1995.     

Synthesis and characterisation of nonclassical ruthenium hydride complexes containing chelating bidentate and tridentate phosphine ligands

The synthesis and characterisation of nonclassical ruthenium hydride complexes containing bidentate PP and tridentate PCP and PNP pincer-type ligands are described. The mononuclear and dinuclear ruthenium complexes presented have been synthesised in moderate to high yields by the direct hydrogenation route (one-pot synthesis) or in a two-step procedure. In both cases [Ru(cod)(metallyl)(2)] served as a readily available precursor. The influences of the coordination geometry and the ligand framework on the structure, binding, and chemical properties of the M--H(2) fragments were studied by X-ray crystal structure analysis, spectroscopic methods, and reactivity towards N(2), D(2), and deuterated solvents.     

Catalytic Methylation of CH Bonds Using CO2 and H2

Formation of C? C bonds from CO₂ is a much sought after reaction in organic synthesis. To date, other than C? H carboxylations using stoichiometric amounts of metals, base, or organometallic reagents, little is known about C? C bond formation. In fact, to the best of our knowledge no catalytic methylation of C? H bonds using CO₂ and H₂ has been reported. Described herein is the combination of CO₂ and H₂ for efficient methylation of carbon nucleophiles such as indoles, pyrroles, and electron‐rich arenes. Comparison experiments which employ paraformaldehyde show similar reactivity for the CO₂/H₂ system.     

Binding N2, N2H2, N2H4, and NH3 to transition-metal sulfur sites: modeling potential intermediates of biological N2 fixation

In the quest for low-molecular-weight metal sulfur complexes that bind nitrogenase-relevant small molecules and can serve as model complexes for nitrogenase, compounds with the [Ru(PiPr(3))('N(2)Me(2)S(2)')] fragment were found ('N(2)Me(2)S(2)'(2-)=1,2-ethanediamine-N,N'-dimethyl-N,N'-bis(2-benzenethiolate)(2-)). This fragment enabled the synthesis of a first series of chiral metal sulfur complexes, [Ru(L)(PiPr(3))('N(2)Me(2)S(2)')] with L=N(2), N(2)H(2), N(2)H(4), and NH(3), that meet the biological constraint of forming under mild conditions. The reaction of [Ru(NCCH(3))(PiPr(3))('N(2)Me(2)S(2)')] (1) with NH(3) gave the ammonia complex [Ru(NH(3))(PiPr(3))('N(2)Me(2)S(2)')] (4), which readily exchanged NH(3) for N(2) to yield the mononuclear dinitrogen complex [Ru(N(2))(PiPr(3))('N(2)Me(2)S(2)')] (2) in almost quantitative yield. Complex 2, obtained by this new efficient synthesis, was the starting material for the synthesis of dinuclear (R,R)- and (S,S)-[micro-N(2)[Ru(PiPr(3))('N(2)Me(2)S(2)')](2)] ((R,R)-/(S,S)-3). (Both 2 and 3 have been reported previously.) The as-yet inexplicable behavior of complex 3 to form also the R,S isomer in solution has been revealed by DFT calculations and (2)D NMR spectroscopy studies. The reaction of 1 or 2 with anhydrous hydrazine yielded the hydrazine complex [Ru(N(2)H(4))(PiPr(3))('N(2)Me(2)S(2)')] (6), which is a highly reactive intermediate. Disproportionation of 6 resulted in the formation of mononuclear diazene complexes, the ammonia complex 4, and finally the dinuclear diazene complex [micro-N(2)H(2)[Ru(PiPr(3))('N(2)Me(2)S(2)')](2)] (5). Dinuclear complex 5 could also be obtained directly in an independent synthesis from 1 and N(2)H(2), which was generated in situ by acidolysis of K(2)N(2)(CO(2))(2). Treatment of 6 with CH(2)Cl(2), however, formed a chloromethylated diazene species [[Ru(PiPr(3))('N(2)Me(2)S(2)')]-micro-N(2)H(2)[Ru(Cl)('N(2)Me(2)S(2)CH(2)Cl')]] (9) ('N(2)Me(2)S(2)CH(2)Cl'(2-) =1,2-ethanediamine-N,N'-dimethyl-N-(2-benzenethiolate)(1-)-N'-(2-benzenechloromethylthioether)(1-)]. The molecular structures of 4, 5, and 9 were determined by X-ray crystal structure analysis, and the labile N(2)H(4) complex 6 was characterized by NMR spectroscopy.     

Hydrolysis of dinuclear ruthenium complexes [{CpRu(PPh3)2}2(micro,eta(1:1)-L)][CF3SO3]2 (L=P4, P4S3): simple access to metal complexes of P2H4 and PH2SH

The reaction of [CpRu(PPh(3))(2)Cl] (1) with half an equivalent of P(4) or P(4)S(3) in the presence of AgCF(3)SO(3) as chloride scavenger affords the stable dimetal complexes [{CpRu(PPh(3))(2)}(2)(micro,eta(1:1)-P(4))][CF(3)SO(3)](2).3 CH(2)Cl(2) (2) and [{CpRu(PPh(3))(2)}(2)(micro,eta(1:1)-P(apical)-P(basal)-P(4)S(3))][CF(3)SO(3)](2).0.5 C(7)H(8) (3), in which the tetrahedral P(4) and mixed-cage P(4)S(3) molecules are respectively bound to two CpRu(PPh(3))(2) fragments through two phosphorus atoms. The coordinated cage molecules, at variance with the free ligands, readily react with an excess of water in THF under mild conditions. Among the hydrolysis products, the new, remarkably stable complexes [{CpRu(PPh(3))(2)}(2)(micro,eta(1:1)-P(2)H(4))][CF(3)SO(3)](2) (4) and [CpRu(PPh(3))(2)(eta(1)-PH(2)SH)]CF(3)SO(3) (8) were isolated. In the former, diphosphane, P(2)H(4), is coordinated to two CpRu(PPh(3))(2) fragments, and in the latter thiophosphinous acid, H(2)PSH, is coordinated to the metal centre through the phosphorus atom. All compounds were characterised by elemental analyses and IR and NMR spectroscopy. The crystal structures of 2, 3, 4 and 8 were determined by X-ray diffraction.     

H2 Oxidation Electrocatalysis Enabled by Metal‐to‐Metal Hydrogen Atom Transfer: A Homolytic Approach to a Heterolytic Reaction

Oxidation of H₂ in a fuel cell converts the chemical energy of the H?H bond into electricity. Electrocatalytic oxidation of H₂ by molecular catalysts typically requires one metal to perform multiple chemical steps: bind H₂, heterolytically cleave H₂, and then undergo two oxidation and two deprotonation steps. The electrocatalytic oxidation of H₂ by a cooperative system using Cp*Cr(CO)₃H and [Fe(diphosphine)(CO)₃]⁺ has now been invetigated. A key step of the proposed mechanism is a rarely observed metal‐to‐metal hydrogen atom transfer from the Cr?H complex to the Fe, forming an Fe?H complex that is deprotonated and then oxidized electrochemically. This “division of chemical labor” features Cr interacting with H₂ to cleave the H?H bond, while Fe interfaces with the electrode. Neither metal is required to heterolytically cleave H₂, so this system provides a very unusual example of a homolytic reaction being a key step in a molecular electrocatalytic process.     

Binding H2, N2, H-, and BH3 to transition-metal sulfur sites: synthesis and properties of [RuL(PR3)(N2Me2S2)] Complexes (L=eta2-H2, H-, BH3; R=Cy, iPr)

The reactions of [Ru(N₂)(PR₃)(‘N₂Me₂S₂’)] [‘N₂Me₂S₂’=1,2‐ethanediamine‐N,N′‐dimethyl‐N,N′‐bis(2‐benzenethiolate)(2?)] [ 1 a (R=iPr), 1 b (R=Cy)] and [μ‐N₂{Ru(N₂)(PiPr₃)(‘N₂Me₂S₂’)}₂] ( 1 c ) with H₂, NaBH₄, and NBu₄BH₄, intended to reduce the N₂ ligands, led to substitution of N₂ and formation of the new complexes [Ru(H₂)(PR₃)(‘N₂Me₂S₂’)] [ 2 a (R=iPr), 2 b (R=Cy)], [Ru(BH₃)(PR₃)(‘N₂Me₂S₂’)] [ 3 a (R=iPr), 3 b (R=Cy)], and [Ru(H)(PR₃)(‘N₂Me₂S₂’)]^? [ 4 a (R=iPr), 4 b (R=Cy)]. The BH₃ and hydride complexes 3 a , 3 b , 4 a , and 4 b were obtained subsequently by rational synthesis from 1 a or 1 b and BH₃?THF or LiBEt₃H. The primary step in all reactions probably is the dissociation of N₂ from the N₂ complexes to give coordinatively unsaturated [Ru(PR₃)(‘N₂Me₂S₂’)] fragments that add H₂, BH₄^?, BH₃, or H^?. All complexes were completely characterized by elemental analysis and common spectroscopic methods. The molecular structures of [Ru(H₂)(PR₃)(‘N₂Me₂S₂’)] [ 2 a (R=iPr), 2 b (R=Cy)], [Ru(BH₃)(PiPr₃)(‘N₂Me₂S₂’)] ( 3 a ), [Li(THF)₂][Ru(H)(PiPr₃)(‘N₂Me₂S₂’)] ([Li(THF)₂]‐ 4 a ), and NBu₄[Ru(H)(PCy₃)(‘N₂Me₂S₂’)] (NBu₄‐ 4 b ) were determined by X‐ray crystal structure analysis. Measurements of the NMR relaxation time T₁ corroborated the η² bonding mode of the H₂ ligands in 2 a (T₁=35 ms) and 2 b (T₁=21 ms). The H,D coupling constants of the analogous HD complexes HD‐ 2 a (¹J(H,D)=26.0 Hz) and HD‐ 2 b (¹J(H,D)=25.9 Hz) enabled calculation of the H? D distances, which agreed with the values found by X‐ray crystal structure analysis ( 2 a : 92 pm (X‐ray) versus 98 pm (calculated), 2 b : 99 versus 98 pm). The BH₃ entities in 3 a and 3 b bind to one thiolate donor of the [Ru(PR₃)(‘N₂Me₂S₂’)] fragment and through a B‐H‐Ru bond to the Ru center. The hydride complex anions 4 a and 4 b are extremely Brønsted basic and are instantanously protonated to give the η²‐H₂ complexes 2 a and 2 b .     

CH Bond Activation during and after the Reactions of a Metallacyclic Amide with Silanes: Formation of a μ‐Alkylidene Hydride Complex,Its H–D Exchange,and β‐H Abstraction by a Hydride Ligand

Metallacyclic complex [(Me₂N)₃Ta(η²‐CH₂SiMe₂NSiMe₃)] ( 3 ) undergoes C?H activation in its reaction with H₃SiPh to afford a Ta/μ‐alkylidene/hydride complex, [(Me₂N)₂{(Me₃Si)₂N}Ta(μ‐H)₂(μ‐C‐η²‐CHSiMe₂NSiMe₃)Ta(NMe₂)₂] ( 4 ). Deuterium‐labeling studies with [D₃]SiPh show H–D exchange between the Ta?D ?Ta unit and all methyl groups in [(Me₂N)₂{(Me₃Si)₂N}Ta(μ‐D)₂(μ‐C‐η²‐CHSiMe₂NSiMe₃)Ta(NMe₂)₂] ([D₂]‐ 4 ) to give the partially deuterated complex [D_n]‐ 4 . In addition, 4 undergoes β‐H abstraction between a hydride and an NMe₂ ligand and forms a new complex [(Me₂N){(Me₃Si)₂N}Ta(μ‐H)(μ‐N‐η²‐C,N‐CH₂NMe)(μ‐C‐η²‐C,N‐CHSiMe₂NSiMe₃)Ta(NMe₂)₂] ( 5 ) with a cyclometalated, η²‐imine ligand. These results indicate that there are two simultaneous processes in [D_n]‐ 4 : 1) H–D exchange through σ‐bond metathesis, and 2) H?D elimination through β‐H abstraction (to give [D_n]‐ 5 ). Both 4 and 5 have been characterized by single‐crystal X‐ray diffraction studies.     

Formation and Reactivity of a Molecular Magnesium Hydride with a Terminal MgH Bond

A complex featuring a terminal magnesium hydride bond supported by an NNNN macrocyclic ligand, [Mg{Me₃TACD ? Al(iBu)₃}H] ( 3 ), was formed from its labile Al(iBu)₃ adduct. Use of Al(iBu)₃ to block the amido nitrogen of the NNNN macrocyclic ligand was essential to prevent aggregation. The structurally characterized compound 3 reacted with BH₃ to give the BH₄ derivative, whereas Me₃SiC?CH and PhSiH₃ led to the corresponding acetylide and silyl derivative under H₂ elimination. Pyridine is inserted into the Mg?H bond to give selectively the 1,4‐dihydropyridinate.     

Ruthenium-Catalyzed Deuteration of Aromatic Carbonyl Compounds with a Catalytic Transient Directing Group

A novel ruthenium-catalyzed C−H activation methodology for hydrogen isotope exchange of aromatic carbonyl compounds is presented. In the presence of catalytic amounts of specific amine additives, a transient directing group is formed in situ, which directs selective deuteration. A high degree of deuteration is achieved for α-carbonyl and aromatic ortho-positions. In addition, appropriate choice of conditions allows for exclusive labeling of the α-carbonyl position while a procedure for the preparation of merely ortho-deuterated compounds is also reported. This methodology proceeds with good functional group tolerance and can be also applied for deuteration of pharmaceutical drugs. Mechanistic studies reveal a kinetic isotope effect of 2.2, showing that the C−H activation is likely the rate-determining step of the catalytic cycle. Using deuterium oxide as a cheap and convenient source of deuterium, the methodology presents a cost-efficient alternative to state-of-the-art iridium-catalyzed procedures.