The Influence of N‐Heterocyclic Carbenes (NHC) on the Reactivity of [Ru(NHC)4H]+ With H2, N2, CO and O2

The five‐coordinate ruthenium N‐heterocyclic carbene (NHC) hydrido complexes [Ru(IiPr₂Me₂)₄H][BAr^F₄] ( 1 ; IiPr₂Me₂=1,3‐diisopropyl‐4,5‐dimethylimidazol‐2‐ylidene; Ar^F=3,5‐(CF₃)₂C₆H₃), [Ru(IEt₂Me₂)₄H][BAr^F₄] ( 2 ; IEt₂Me₂=1,3‐diethyl‐4,5‐dimethylimidazol‐2‐ylidene) and [Ru(IMe₄)₄H][BAr^F₄] ( 3 ; IMe₄=1,3,4,5‐tetramethylimidazol‐2‐ylidene) have been synthesised following reaction of [Ru(PPh₃)₃HCl] with 4–8 equivalents of the free carbenes at ambient temperature. Complexes 1 – 3 have been structurally characterised and show square pyramidal geometries with apical hydride ligands. In both dichloromethane or pyridine solution, 1 and 2 display very low frequency hydride signals at about δ ?41. The tetramethyl carbene complex 3 exhibits a similar chemical shift in toluene, but shows a higher frequency signal in acetonitrile arising from the solvent adduct [Ru(IMe₄)₄(MeCN)H][BAr^F₄], 4 . The reactivity of 1 – 3 towards H₂ and N₂ depends on the size of the N‐substituent of the NHC ligand. Thus, 1 is unreactive towards both gases, 2 reacts with both H₂ and N₂ only at low temperature and incompletely, while 3 affords [Ru(IMe₄)₄(η²‐H₂)H][BAr^F₄] ( 7 ) and [Ru(IMe₄)₄(N₂)H][BAr^F₄] ( 8 ) in quantitative yield at room temperature. CO shows no selectivity, reacting with 1 – 3 to give [Ru(NHC)₄(CO)H][BAr^F₄] ( 9 – 11 ). Addition of O₂ to solutions of 2 and 3 leads to rapid oxidation, from which the Ru^III species [Ru(NHC)₄(OH)₂][BAr^F₄] and the Ru^IV oxo chlorido complex [Ru(IEt₂Me₂)₄(O)Cl][BAr^F₄] were isolated. DFT calculations reproduce the greater ability of 3 to bind small molecules and show relative binding strengths that follow the trend CO ? O₂ > N₂ > H₂.     

Preparation and Structural Characterization of [CpRu(1,10-phenanthroline)(CH3CN)][X] and Precursor Complexes (X=PF6, BArF,TRISPHAT-N)

Cationic [Ru(η⁵-C₅H₅)(CH₃CN)₃]⁺ complex, tris(acetonitrile)(cyclopentadienyl)ruthenium(II), gives rise to a very rich organometallic chemistry. Combined with diimine ligands, and 1,10-phenanthroline in particular, this system efficiently catalyzes diazo decomposition processes to generate metal-carbenes which undergo a series of original transformations in the presence of Lewis basic substrates. Herein, syntheses and characterizations of [CpRu(Phen)(L)] complexes with (large) lipophilic non-coordinating (PF₆⁻ and BAr_F⁻) and coordinating TRISPHAT-N⁻ anions are reported. Complex [CpRu(η⁶-naphthalene)][BAr_F] ( [1][BAr_F] ) is readily accessible, in high yield, by direct counterion exchange between [1][PF₆] and sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (NaBAr_F) salts. Ligand exchange of [1][BAr_F] in acetonitrile generated stable [Ru(η⁵-C₅H₅)(CH₃CN)₃][BAr_F] ( [2][BAr_F] ) complex in high yield. Then, the desired [CpRu(Phen)(CH₃CN)] ( [3] ) complexes were obtained from either the [1] or [2] complex in the presence of the 1,10-phenanthroline as ligand. For characterization and comparison purposes, the anionic hemilabile ligand TRISPHAT−N (TTN) was introduced on the ruthenium center, from the complex [3][PF₆] , to quantitatively generate the desired complex [CpRu(Phen)(TTN)] ( [4] ) by displacement of the remaining acetonitrile ligand and of the PF₆⁻ anion. Solid state structures of complexes [1][BAr_F] , [2][BAr_F] , [3][BAr_F] , [3][PF₆] and [4] were determined by X-ray diffraction studies and are discussed herein.     

Boron Lewis Acid‐Catalyzed Hydroboration of Alkenes with Pinacolborane: BArF3 Does What B(C6F5)3 Cannot Do!

The transition‐metal‐free hydroboration of various alkenes with pinacolborane (HBpin) initiated by tris[3,5‐bis(trifluoromethyl)phenyl]borane (BAr^F₃) is reported. The choice of the boron Lewis acid is crucial as the more prominent boron Lewis acid tris(pentafluorophenyl)borane (B(C₆F₅)₃) is reluctant to react. Unlike B(C₆F₅)₃, BAr^F₃ is found to engage in substituent redistribution with HBpin, resulting in the formation of Ar^FBpin and the electron‐deficient diboranes [H₂BAr^F]₂ and [(Ar^F)(H)B(μ‐H)₂BAr^F₂]. These in situ‐generated hydroboranes undergo regioselective hydroboration of styrene derivatives as well as aliphatic alkenes with cis diastereoselectivity. Another ligand metathesis of these adducts with HBpin subsequently affords the corresponding HBpin‐derived anti‐Markovnikov adducts. The reactive hydroboranes are regenerated in this step, thereby closing the catalytic cycle.     

Isolation and Structure of Germylene‐Germyliumylidenes Stabilized by N‐Heterocyclic Imines

The ditopic germanium complex FGe(NIPr)₂Ge[BF₄] ( 3 [BF₄]; IPr=1,3‐bis(2,6‐diisopropylphenyl)imidazolin‐2‐ylidene) is prepared by the reaction of the amino(imino)germylene (Me₃Si)₂NGeNIPr ( 1 ) with BF₃?OEt₂. This monocation is converted into the germylene‐germyliumylidene 3 [BAr^F₄] [Ar^F=3,5‐(CF₃)₂‐C₆H₃] by treatment with Na[BAr^F₄]. The tetrafluoroborate salt 3 [BF₄] reacts with 2 equivalents of Me₃SiOTf to give the novel complex (OTf)(GeNIPr)₂[OTf] ( 4 [OTf]), which affords 4 [BAr^F₄] and 4 [Al(OR^F)₄] [R^F=C(CF₃)₃] after anion exchange with Na[BAr^F₄] or Ag[Al(OR^F)₄], respectively. The computational, as well as crystallographic study, reveals that 4 ⁺ has significant bis(germyliumylidene) dication character.     

Reactivity of the Latent 12‐Electron Fragment [Rh(PiBu3)2]+ with Aryl Bromides: Aryl?Br and Phosphine Ligand C?H Activation

Oxidative addition of aryl bromides to 12‐electron [Rh(PiBu₃)₂][BAr^F₄] (Ar^F=3,5‐(CF₃)₂C₆H₃) forms a variety of products. With p‐tolyl bromides, Rh^III dimeric complexes result [Rh(PiBu₃)₂(o/p‐MeC₆H₄)(μ‐Br)]₂[BAr^F₄]₂. Similarly, reaction with p‐ClC₆H₄Br gives [Rh(PiBu₃)₂(p‐ClC₆H₄)(μ‐Br)]₂[BAr^F₄]₂. In contrast, the use of o‐BrC₆H₄Me leads to a product in which toluene has been eliminated and an isobutyl phosphine has undergone C? H activation: [Rh{PiBu₂(CH₂CHCH₃C H₂)}(PiBu₃)(μ‐Br)]₂[BAr^F₄]₂. Trapping experiments with ortho‐bromo anisole or ortho‐bromo thioanisole indicate that a possible intermediate for this process is a low‐coordinate Rh^III complex that then undergoes C? H activation. The anisole and thioanisole complexes have been isolated and their structures show OMe or SMe interactions with the metal centre alongside supporting agostic interactions, [Rh(PiBu₃)₂(C₆H₄O Me)Br][BAr^F₄] (the solid‐state structure of the 5‐methyl substituted analogue is reported) and [Rh(PiBu₃)₂(C₆H₄S Me)Br][BAr^F₄]. The anisole‐derived complex proceeds to give [Rh{PiBu₂(CH₂CHCH₃C H₂)}(PiBu₃)(μ‐Br)]₂[BAr^F₄]₂, whereas the thioanisole complex is unreactive. The isolation of [Rh(PiBu₃)₂(C₆H₄O Me)Br][BAr^F₄] and its onward reactivity to give the products of C? H activation and aryl elimination suggest that it is implicated on the pathway of a σ‐bond metathesis reaction, a hypothesis strengthened by DFT calculations. Calculations also suggest that C? H bond cleavage through phosphine‐assisted deprotonation of a non‐agostic bond is also competitive, although the subsequent protonation of the aryl ligand is too high in energy to account for product formation. C? H activation through oxidative addition is also ruled out on the basis of these calculations. These new complexes have been characterised by solution NMR/ESIMS techniques and in the solid‐state by X‐ray crystallography.     

Werner Complexes with ω‐Dimethylaminoalkyl Substituted Ethylenediamine Ligands: Bifunctional Hydrogen‐Bond‐Donor Catalysts for Highly Enantioselective Michael Additions

The racemic carbonate complex [Co(en)₂O₂CO]⁺ Cl^? (en=1,2‐ethylenediamine) and (S)‐[H₃NCH((CH₂)_nNHMe₂)CH₂NH₃]³⁺ 3 Cl^? (n=1–4) react (water, charcoal, 100 °C) to give [Co(en)₂((S)‐H₂NCH((CH₂)_nNHMe₂)CH₂NH₂)]⁴⁺ 4 Cl^? ( 3 a – d H⁴⁺ 4 Cl^?) as a mixture of Λ/Δ diastereomers that separate on chiral‐phase Sephadex columns. These are treated with NaOH/Na⁺ BAr_f^? (BAr_f=B(3,5‐C₆H₃(CF₃)₂)₄) to give lipophilic Λ‐ and Δ‐ 3 a–d ³⁺ 3 BAr_f^?, which are screened as catalysts (10 mol %) for additions of dialkyl malonates to nitroalkenes. Optimal results are obtained with Λ‐ 3 c ³⁺ 3 BAr_f^? (CH₂Cl₂, ?35 °C; 98–82 % yields and 99–93 % ee for six β‐arylnitroethenes). The monofunctional catalysts Λ‐ and Δ‐[Co(en)₃]³⁺ 3 BAr_f^? give enantioselectivities of <10 % ee with equal loadings of Et₃N. The crystal structure of Δ‐ 3 a H⁴⁺ 4 Cl^? provides a starting point for speculation regarding transition‐state assemblies.     

The Simplest Amino‐borane H2B=NH2 Trapped on a Rhodium Dimer: Pre‐Catalysts for Amine–Borane Dehydropolymerization

The μ‐amino–borane complexes [Rh₂(L^R)₂(μ‐H)(μ‐H₂B=NHR′)][BAr^F₄] (L^R=R₂P(CH₂)₃PR₂; R=Ph, ⁱPr; R′=H, Me) form by addition of H₃B?NMeR′H₂ to [Rh(L^R)(η⁶‐C₆H₅F)][BAr^F₄]. DFT calculations demonstrate that the amino–borane interacts with the Rh centers through strong Rh‐H and Rh‐B interactions. Mechanistic investigations show that these dimers can form by a boronium‐mediated route, and are pre‐catalysts for amine‐borane dehydropolymerization, suggesting a possible role for bimetallic motifs in catalysis.     

Influence of Cyclopentadienyl Ring‐Tilt on Electron‐Transfer Reactions: Redox‐Induced Reactivity of Strained [2] and [3]Ruthenocenophanes

In contrast to ruthenocene [Ru(η⁵‐C₅H₅)₂] and dimethylruthenocene [Ru(η⁵‐C₅H₄Me)₂] ( 7 ), chemical oxidation of highly strained, ring‐tilted [2]ruthenocenophane [Ru(η⁵‐C₅H₄)₂(CH₂)₂] ( 5 ) and slightly strained [3]ruthenocenophane [Ru(η⁵‐C₅H₄)₂(CH₂)₃] ( 6 ) with cationic oxidants containing the non‐coordinating [B(C₆F₅)₄]^? anion was found to afford stable and isolable metal?metal bonded dicationic dimer salts [Ru(η⁵‐C₅H₄)₂(CH₂)₂]₂[B(C₆F₅)₄]₂ ( 8 ) and [Ru(η⁵‐C₅H₄)₂(CH₂)₃]₂[B(C₆F₅)₄]₂ ( 17 ), respectively. Cyclic voltammetry and DFT studies indicated that the oxidation potential, propensity for dimerization, and strength of the resulting Ru?Ru bond is strongly dependent on the degree of tilt present in 5 and 6 and thereby degree of exposure of the Ru center. Cleavage of the Ru?Ru bond in 8 was achieved through reaction with the radical source [(CH₃)₂NC(S)S?SC(S)N(CH₃)₂] (thiram), affording unusual dimer [(CH₃)₂NCS₂Ru(η⁵‐C₅H₄)(η³‐C₅H₄)C₂H₄]₂[B(C₆F₅)₄]₂ ( 9 ) through a haptotropic η⁵–η³ ring‐slippage followed by an apparent [2+2] cyclodimerization of the cyclopentadienyl ligand. Analogs of possible intermediates in the reaction pathway [C₆H₅ERu(η⁵‐C₅H₄)₂C₂H₄][B(C₆F₅)₄] [E=S ( 15 ) or Se ( 16 )] were synthesized through reaction of 8 with C₆H₅E?EC₆H₅ (E=S or Se).     

Synthesis,crystal structure and electrochemical properties of three isocloso eleven‐vertex ferrocenecarboxylate ruthenaborane clusters

The reaction of [RuCl₂(PPh₃)₃] with closo‐[B₁₀H₁₀]^2? and C₅H₅FeC₅H₄COOH (FcCO₂H) in refluxing CH₂Cl₂ solution affords three ruthenaborane clusters: [PPh₃(H₂O)(FcCO₂)RuB₁₀H₈Cl] (1), [(PPh₃)₂ClRu(PPh₃)(FcCO₂)RuB₁₀H₉]·0.5CH₂Cl₂ (2 × 0.5CH₂Cl₂) and [PPh₃(FcCO₂)₂RuB₁₀H₈] (3). All of these compounds are characterized by FT‐IR, NMR spectroscopic techniques, elemental analysis and single‐crystal X‐ray analysis. They are all based on a closo‐type 1:2:4:2:2 {RuB₁₀} stack with the metal occupying the unique six‐connected apical position and can be considered as having isocloso structures derived from the complete capping of the open face of an arachano geometry to give a completely closed deltahedral cluster. Compounds 1 and 2 both have an exo‐polyhedral ferrocenecarboxylate that is attached with one {Ru? O} and one {B? O} bond each, resulting in one exo‐cyclic five‐membered Ru? O? C? O? B ring. There is in addition one exo‐polyhedral ruthenium atom bonded to the center {RuB₁₀} cluster via one {Ru? Ru} linkage and two {RuH_µB} bridges, which forms a closed exo‐polyhedral tetrahedron configuration in compound 2. Compound 3 has two exo‐polyhedral ferrocenecarboxylates to form two five‐membered Ru? O? C? O? B rings engendering a symmetrical conformation. All of these new 11‐vertex ruthenaboranes can be considered as having isocloso structures derived from the complete capping of the open face of an arachano geometry to give a completely closed deltahedral cluster. Copyright © 2006 John Wiley & Sons, Ltd.     

PC‐Activated Bimetallic Rhodium Xantphos Complexes: Formation and Catalytic Dehydrocoupling of Amine–Boranes

{Rh(xantphos)}‐based phosphido dimers form by P? C activation of xantphos (4,5‐bis(diphenylphosphino)‐9,9‐dimethylxanthene) in the presence of amine–boranes. These dimers are active dehydrocoupling catalysts, forming polymeric [H₂BNMeH]_n from H₃B?NMeH₂ and dimeric [H₂BNMe₂]₂ from H₃B?NMe₂H at low catalyst loadings (0.1 mol %). Mechanistic investigations support a dimeric active species, suggesting that bimetallic catalysis may be possible in amine–borane dehydropolymerization.     

Synthesis and Structures of Ruthena-octahydrotetraborane Complexes

The reactivity of κ²-N,S-chelated ruthenium borate complexes, [Ru(PPh₃)(κ²-N,S-(NC₇H₄S₂)Ru{κ³-H,S,S′-H₂B (NC₇H₄S₂)₂}] ( 1 a ) and [Ru(PPh₃)(κ²-N,S-(NC₅H₄S){κ³-H,S,S′-H₂B(NC₅H₄S)₂}] ( 1 b ) with monoboranes have been explored. The prolonged room temperature reaction of [Ru(PPh₃){κ²-N,S-(NC₇H₄S₂)}{κ³-H,S,S′-H₂B(NC₇H₄S₂)₂}], 1 a with an excess of [BH₃ ⋅ THF] led to the formation of hydrogen-rich complex, arachno-[PPh₃(κ²-B₃H₈)Ru{κ³-H,S,S′-H₂B(NC₇H₄S₂)₂] ( 2 ). In a similar fashion, the isomeric ruthenatetraborane complexes of [Ru(PPh₃)(κ²-N,S-(B₃H₈){κ³-H,S,S′-H₂B(NC₅H₄S)₂}], 4 and 5 were isolated from the room temperature reaction of 1 b with [BH₃ ⋅ THF]. In complex 2 , the borate ligand, [H₂B(NC₅H₄S)₂] and the PPh₃ occupy the endo and exo sites of the butterfly-shaped RuB₃ core, respectively. In contrast, the borate unit [H₂B(NC₅H₄S)₂] in 4 sits on the exo position of the butterfly core, while the phosphine ligand occupies the endo site. Multinuclear spectroscopic analyses were done to characterize all new complexes and the structures were further confirmed by single-crystal X-ray diffraction analysis. Density functional theory (DFT) calculations were performed to probe into the bonding modes of these complexes.     

Hydroboration of Alkynes with Zwitterionic Ruthenium–Borate Complexes: Novel Vinylborane Complexes

Building upon previous studies on the synthesis of bis(sigma)borate and agostic complexes of ruthenium, the chemistry of nido‐[(Cp*Ru)₂B₃H₉] ( 1 ) with other ligand systems was explored. In this regard, mild thermolysis of nido‐ 1 with 2‐mercaptobenzothiazole (2‐mbzt), 2‐mercaptobenzoxazole (2‐mbzo) and 2‐mercaptobenzimidazole (2‐mbzi) ligands were performed which led to the isolation of bis(sigma)borate complexes [Cp*RuBH₃L] ( 2 a – c ) and β‐agostic complexes [Cp*RuBH₂L₂] ( 3 a – c ; 2 a , 3 a : L=C₇H₄NS₂; 2 b , 3 b : L=C₇H₄NSO; 2 c , 3 c : L=C₇H₅N₂S). Further, the chemistry of these novel complexes towards various diphosphine ligands was investigated. Room temperature treatment of 3 a with [PPh₂(CH₂)_nPPh₂] (n=1–3) yielded [Cp*Ru(PPh₂(CH₂)_nPPh₂)‐BH₂(L₂)] ( 4 a – c ; 4 a : n=1; 4 b : n=2; 4 c : n=3; L=C₇H₄NS₂). Mild thermolysis of 2 a with [PPh₂(CH₂)_nPPh₂] (n=1–3) led to the isolation of [Cp*Ru(PPh₂(CH₂)_nPPh₂)(L)] (L=C₇H₄NS₂ 5 a – c ; 5 a : n=1; 5 b : n=2; 5 c : n=3). Treatment of 4 a with terminal alkynes causes a hydroboration reaction to generate vinylborane complexes [Cp*Ru(R?C?CH₂)BH(L₂)] ( 6 and 7 ; 6 : R=Ph; 7 : R=COOCH₃; L=C₇H₄NS₂). Complexes 6 and 7 can also be viewed as η‐alkene complexes of ruthenium that feature a dative bond to the ruthenium centre from the vinylinic double bond. In addition, DFT computations were performed to shed light on the bonding and electronic structures of the new compounds.     

Ir(PCy3)2(H)2(H2B-NMe2)]+ as a latent source of aminoborane: probing the role of metal in the dehydrocoupling of H3B⋅NMe2H and retrodimerisation of [H2BNMe2]2

The Ir^III fragment {Ir(PCy₃)₂(H)₂}⁺ has been used to probe the role of the metal centre in the catalytic dehydrocoupling of H₃B?NMe₂H ( A ) to ultimately give dimeric aminoborane [H₂BNMe₂]₂ ( D ). Addition of A to [Ir(PCy₃)₂(H)₂(H₂)₂][BAr^F₄] ( 1 ; Ar^F=(C₆H₃(CF₃)₂), gives the amine‐borane complex [Ir(PCy₃)₂(H)₂(H₃B?NMe₂H)][BAr^F₄] ( 2 a ), which slowly dehydrogenates to afford the aminoborane complex [Ir(PCy₃)₂(H)₂(H₂B? NMe₂)][BAr^F₄] ( 3 ). DFT calculations have been used to probe the mechanism of dehydrogenation and show a pathway featuring sequential BH activation/H₂ loss/NH activation. Addition of D to 1 results in retrodimerisation of D to afford 3 . DFT calculations indicate that this involves metal trapping of the monomer–dimer equilibrium, 2 H₂BNMe₂ ? [H₂BNMe₂]₂. Ruthenium and rhodium analogues also promote this reaction. Addition of MeCN to 3 affords [Ir(PCy₃)₂(H)₂(NCMe)₂][BAr^F₄] ( 6 ) liberating H₂B? NMe₂ ( B ), which then dimerises to give D . This is shown to be a second‐order process. It also allows on‐ and off‐metal coupling processes to be probed. Addition of MeCN to 3 followed by A gives D with no amine‐borane intermediates observed. Addition of A to 3 results in the formation of significant amounts of oligomeric H₃B?NMe₂BH₂?NMe₂H ( C ), which ultimately was converted to D . These results indicate that the metal is involved in both the dehydrogenation of A , to give B , and the oligomerisation reaction to afford C . A mechanism is suggested for this latter process. The reactivity of oligomer C with the Ir complexes is also reported. Addition of excess C to 1 promotes its transformation into D , with 3 observed as the final organometallic product, suggesting a B? N bond cleavage mechanism. Complex 6 does not react with C , but in combination with B oligomer C is consumed to eventually give D , suggesting an additional role for free aminoborane in the formation of D from C .     

Synthesis of organometallic hydrotris(pyrazol-1-yl)boratoruthenium(II) complexes

The reactions of K[HB(pz)₃] (pz = pyrazol-1-yl) with the coordinatively unsaturated σ-vinyl complexes [Ru(CRCHR)Cl(CO)(PPh₃)₂] (R = H, Me, C₆H₅) proceed with loss of a chloride and a phosphine ligand to provide the compounds [Ru(CRCHR)(CO)(PPh₃){HB(pz)₃}] in high yield. Similar treatment of the complex [Ru(C₆H₄Me-4)Cl(CO)(PPh₃)₂] leads to the related σ-aryl derivative [Ru(C₆H₄Me-4)(CO)(PPh₃){HB(pz)₃}] whilst the complex [RuClH(CO)(PPh₃)₃] treated successively with diphenylbutadiyne and K[HB(pz)₃] provides the unusual derivative [Ru{C(CCPh)CHPh}(CO)(PPh₃){HB(pz)₃}].     

Interconversion of Metallabenzenes and Cyclic η2‐Allene‐Coordinated Complexes

Treatment of the osmabenzene [Os{CHC(PPh₃)CHC(PPh₃)CH} Cl₂(PPh₃)₂]Cl ( 1 ) with excess 8‐hydroxyquinoline produces monosubstituted osmabenzene [Os{CH C(PPh₃) CHC(PPh₃)CH}(C₉H₆NO)Cl(PPh₃)]Cl ( 2 ) or disubstituted osmabenzene [Os{CHC(PPh₃)CHC(PPh₃)CH} (C₉H₆NO)₂]Cl ( 3 ) under different reaction conditions. Osmabenzene 2 evolves into cyclic η²‐allene‐coordinated complex [Os{CH?C(PPh₃)CH=(η²‐C?CH₂)}(C₉H₆NO)(PPh₃)₂]Cl ( 4 ) in the presence of excess PPh₃ and NaOH, presumably involving a P? C bond cleavage of the metallacycle. Reaction of 4 with excess 8‐hydroxyquinoline under air affords the S_NAr product [(C₉H₆NO)Os{CHC(PPh₃)CHCHC} (C₉H₆NO)(PPh₃)]Cl ( 5 ). Complex 4 is fairly reactive to a nucleophile in the presence of acid, which could react with water to give carbonyl complex [Os{CH?C(PPh₃)CH?CH₂}(C₉H₆NO) (CO)(PPh₃)₂]Cl ( 6 ). Complex 4 also reacts with PPh₃ in the presence of acid and results in a transformation to [Os {CHC(PPh₃)CHCHC}(C₉H₆NO)Cl (PPh₃)₂]Cl ( 7 ) and [Os{CH?C(PPh₃) CH=(η²‐C?CH(PPh₃))}(C₉H₆NO) Cl(PPh₃)]Cl ( 8 ). Further investigation shows that the ratio of 7 and 8 is highly dependent on the amount of the acid in the reaction.     

Fine‐Tuning of Lewis Acidity: The Case of Borenium Hydride Complexes Derived from Bis(phosphinimino)amide Boron Precursors

Reactions of bis(phosphinimino)amines LH and L′H with Me₂S ? BH₂Cl afforded chloroborane complexes LBHCl ( 1 ) and L′BHCl ( 2 ), and the reaction of L′H with BH₃ ? Me₂S gave a dihydridoborane complex L′BH₂ ( 3 ) (LH=[{(2,4,6‐Me₃C₆H₂N)P(Ph₂)}₂N]H and L′H=[{(2,6‐iPr₂C₆H₃N)P(Ph₂)}₂N]H). Furthermore, abstraction of a hydride ion from L′BH₂ ( 3 ) and LBH₂ ( 4 ) mediated by Lewis acid B(C₆F₅)₃ or the weakly coordinating ion pair [Ph₃C][B(C₆F₅)₄] smoothly yielded a series of borenium hydride cations: [L′BH]⁺[HB(C₆F₅)₃]^? ( 5 ), [L′BH]⁺[B(C₆F₅)₄]^? ( 6 ), [LBH]⁺[HB(C₆F₅)₃]^? ( 7 ), and [LBH]⁺[B(C₆F₅)₄]^? ( 8 ). Synthesis of a chloroborenium species [LBCl]⁺[BCl₄]^? ( 9 ) without involvement of a weakly coordinating anion was also demonstrated from a reaction of LBH₂ ( 4 ) with three equivalents of BCl₃. It is clear from this study that the sterically bulky strong donor bis(phosphinimino)amide ligand plays a crucial role in facilitating the synthesis and stabilization of these three‐coordinated cationic species of boron. Therefore, the present synthetic approach is not dependent on the requirement of weakly coordinating anions; even simple BCl₄^? can act as a counteranion with borenium cations. The high Lewis acidity of the boron atom in complex 8 enables the formation of an adduct with 4‐dimethylaminopyridine (DMAP), [LBH ? (DMAP)]⁺[B(C₆F₅)₄]^? ( 10 ). The solid‐state structures of complexes 1 , 5 , and 9 were investigated by means of single‐crystal X‐ray structural analysis.     

Synthesis,Structures, and Reactivities of Pincer‐Type Ruthenium Complexes Bearing Two Proton‐Responsive Pyrazole Arms

A new metal–ligand bifunctional, pincer‐type ruthenium complex [RuCl( L1‐H2 )(PPh₃)₂]Cl ( 1 ; L1‐H2 =2,6‐bis(5‐tert‐butyl‐1H‐pyrazol‐3‐yl)pyridine) featuring two proton‐delivering pyrazole arms has been synthesized. Complex 1 , derived from [RuCl₂(PPh₃)₃] with L1‐H2 , underwent reversible deprotonation with potassium carbonate to afford the pyrazolato–pyrazole complex [RuCl(L1‐H)(PPh₃)₂] ( 2 ). Further deprotonation of 1 and 2 with potassium hexamethyldisilazide in methanol resulted in the formation of the bis(pyrazolato) complex [Ru(L1)(MeOH)(PPh₃)₂] ( 3 ). Complex 3 smoothly reacted with dioxygen and dinitrogen to give the side‐on peroxo complex [Ru(L1)(O₂)(PPh₃)₂] ( 4 ) and end‐on dinitrogen complex [Ru(L1)(N₂)(PPh₃)₂] ( 5 ), respectively. On the other hand, the reaction of [RuCl₂(PPh₃)₃] with less hindered 2,6‐di(1H‐pyrazol‐3‐yl)pyridine ( L3‐H2 ) led to the formation of the dinuclear complex [{RuCl₂(PPh₃)₂}₂(μ₂‐ L3‐H2 )₂] ( 6 ), in which the pyrazole‐based ligand adopted a tautomeric form different from L1‐H2 in 1 and the central pyridine remained uncoordinated. The detailed structures of 1 , 2 , 3 , 3.MeOH , 4 , 5 , 6 were determined by X‐ray crystallography.     

Hydride-phosphoniodithiocarboxylate/ phosphonium-betaine isomerism in Cy3PCS2 complexes of ruthenium

Reaction of Cy₃PCS₂ (Cy = cyclohexyl) with the hydrido complexes [RuClH(CA)(PPh₃)₃] (A  O, S), [RuH(CO)(NCMe)₂(PPh₃)₂]⁺, and [RuH(OClO₃)(CO)(CN^tBu)(PPh₃)₂] leads to the complex cations [RuH(CA)(PPh₃)₂(η²-S₂CPCy₃)]⁺, [Ru(η²-S₂CHPCy₃)(CO) (PPh₃)₂]⁺, [RuH(η¹-S₂CPCy₃)(CO)(CN^tBu)(PPh₃)₂]⁺. The σ-vinyl complex [Ru(CHCHC₆H₄Me-4)Cl(CO)(PPh₃)₂] reacts with Cy₃PCS₂ to give the cationic complex [Ru(CHCHC₆H₄Me-4) (CO)(PPh₃)₂(η²-S₂CPCy₃)]⁺, but this complex is not formed by hydroruthenation of HCCC₆H₄Me-4 by [RuH(CO)(PPh₃)₂(η²-S₂CPCy₃)]⁺. The inter-relationships between the above complexes are discussed.     

Cationic iridium complexes of the Xantphos ligand. Flexible coordination modes and the isolation of the hydride insertion product with an alkene

Reaction of the Ir(I)-Xantphos complex [Ir(κ²-Xantphos)(COD)][BAr^F₄] (Xantphos = 4,5-bis(diphenylphosphino)-9,9-dimethylxanthene, Ar^F = C₆H₃(CF₃)₂) with H₂ in acetone or CH₂Cl₂/MeCN affords the Ir(III)-hydrido complexes [Ir(κ³-Xantphos)(H)₂(L)][BAr^F₄], L = acetone or MeCN, whereas in non-coordinating CH₂Cl₂ solvent dimeric [Ir(κ³-Xantphos)(H)(μ-H)]₂[BAr^F₄]₂ is formed. A common intermediate in these reactions that invokes a (σ, η²-C₈H₁₃) ligand is reported. Addition of excess tert-butylethene (tbe) to [Ir(κ³-Xantphos)(H)₂(MeCN)][BAr^F₄] results in insertion of a hydride into the alkene to form [Ir(κ³-Xantphos)(MeCN)(CH₂CH₂C(CH₃)₃)(H)][BAr^F₄], an Ir(III) alkyl-hydrido-Xantphos complex. This reaction is reversible, and heating (80 °C) results in the reformation of [Ir(κ³-Xantphos)(H)₂(MeCN)][BAr^F₄] and tbe. These complexes have been characterised by NMR spectroscopy, ESI-MS and single-crystal X-ray diffraction. They show variable coordination modes of the Xantphos ligand: cis-κ²-P,P, fac-κ³-P,O,P and mer-κ³-P,O,P with the later coordination mode like that found in related PNP-pincer complexes.     

Planar N‐Heterocyclic Carbene Diarylborenium Ions: Synthesis by Cationic Borylation and Reactivity with Lewis Bases

The NHC–borane adduct (IBn)BH₃ ( 1 ) (NHC= N‐heterocyclic carbene; IBn=1,3‐dibenzylimidazol‐2ylidene) reacts with [Ph₃C][B(C₆F₅)₄] through sequential hydride abstraction and dehydrogenative cationic borylation(s) to give singly or doubly ring closed NHC–borenium salts 2 and 3 . The planar doubly ring closed product [C₃H₂(NCH₂C₆H₄)₂B][B(C₆F₅)₄] is resistant to quaternization at boron by Et₂O coordination, but forms classical Lewis acid–base adducts with the stronger donors Ph₃P, Et₃PO, or 1,4‐diazabicyclo[2.2.2]octane (DABCO). Treatment of 3 with tBu₃P selectively yields the unusual oligomeric borenium salt trans‐[(C₃H₂(NCH₂C₆H₄)₂B)₂(C₃H₂(NCHC₆H₄)₂B)][B(C₆F₅)₄] ( 7 ).