Synthesis and Reactivity of the Octahedral d⁶ Parent Amido Complexes TpRu(L)(L‘)(NH₂) (Tp = Hydridotris(pyrazolyl)borate; L = L‘ = PMe₃, P(OMe)₃; L = CO, L‘ = PPh₃) and [TpRu(PPh₃)(NH₂)₂][Li]

A series of octahedral ruthenium(II) parent amido complexes of the type TpRu(L)(L‘)(NH2) (L/L‘ = neutral and two-electron-donor ligands) and [TpRu(PPh3)(NH2)2][Li] (Tp = hydridotris(pyrazolyl)borate) have been prepared. Preliminary reactivity studies indicate that the amido moieties are highly basic:  for example, TpRu(L)(L‘)(NH2) complexes deprotonate phenylacetylene at room temperature to form [TpRu(L)(L‘)(NH3)][PhC2] ion pairs, as determined by 1H NMR spectroscopy

Synthesis and Reactivity of a Coordinatively Unsaturated Ruthenium(II) Parent Amido Complex: Studies of X−H Activation (X = H or C)

The five-coordinate parent amido complex (PCP)Ru(CO)(NH2) (2) (PCP = 2,6-(CH2PtBu2)2C6H3) has been prepared by two independent routes that involve deprotonation of Ru(II) ammine complexes. Complex 2 reacts with phenylacetylene to yield the Ru(II) acetylide complex (PCP)Ru(CO)(C⋮CPh) (5) and ammonia. In addition, complex 2 rapidly activates dihydrogen at room temperature to yield ammonia and the previously reported hydride complex (PCP)Ru(CO)(H). The ability of the amido complex 2 to cleave the H−H bond is attributed to the combination of a vacant coordination site for binding/activation of dihydrogen and a basic amido ligand. Complex 2 also undergoes an intramolecular C−H activation of a methyl group on the PCP ligand to yield ammonia and a cyclometalated complex. The reaction of (PCP)Ru(CO)(Cl) with MeLi allows the isolation of (PCP)Ru(CO)(Me) (8), and complex 8 undergoes an intramolecular C−H activation analogous to the amido complex 2 to produce methane and the cyclometalated complex. Determination of activation parameters for the intramolecular C−H activation transformations of 2 and 8 reveal identical ΔH⧧ {18(1) kcal/mol} with ΔS⧧ = −23(4) eu and −18(4) eu, respectively. Density functional theory has been applied to the study of intermolecular activation of methane and dihydrogen by (PCP‘)Ru(CO)(NH2) to yield (PCP‘)Ru(CO)(NH3)(X) (X = Me or H; PCP‘ = 2,6-(CH2PH2)2C6H3). The results indicate that the activation of dihydrogen is both exoergic and exothermic. In contrast, the addition of a C−H bond of methane across the Ru−NH2 bond has been calculated to be endoergic and endothermic. The surprising endoergic nature of the methane C−H activation has been attributed to a large and unfavorable change in Ru−N bond dissociation energy upon conversion from Ru-amido to Ru-ammine

Ruthenium(II) Anilido Complexes TpRuL₂(NHPh): Oxidative 4,4‘-Aryl Coupling Reactions (Tp = Hydridotris(pyrazolylborate); L = PMe₃, P(OMe)₃, or CO)

Reactions of the Ru(II) amido complexes TpRuL2(NHPh) (L = CO, PMe3, or P(OMe)3) with AgOTf (OTf = trifluoromethanesulfonate) yield the binuclear complexes [TpRuL2NH(C6H4−)]2[OTf]2 along with the Ru(II) amine complexes [TpRuL2(NH2Ph)][OTf] in an approximate 1:1 molar ratio. In these reactions, the two ruthenium fragments are coupled via C−H bond cleavage and C−C bond formation at the para position of anilido ligands. A resonance structure corresponding to Ru(II) metal centers linked by a diimine ligand contributes significantly to the bonding. Evidence for such a contribution comes from the diamagnetic nature of the binuclear complexes and a solid-state X-ray crystallographic study of [TpRu{P(OMe)3}2NH(C6H4−)]2[OTf]2. It is proposed that the coupled products are formed via initial single-electron oxidation followed by C−C bond formation. Variable-temperature NMR spectra of the aryl-coupled complexes are consistent with two geometrical isomers around the rigid HN−C6H4−C6H4NH bridges

Synthesis and Reactivity of a Coordinatively Unsaturated Ruthenium(II) Parent Amido Complex: Studies of X−H Activation (X = H or C)

The five-coordinate parent amido complex (PCP)Ru(CO)(NH2) (2) (PCP = 2,6-(CH2PtBu2)2C6H3) has been prepared by two independent routes that involve deprotonation of Ru(II) ammine complexes. Complex 2 reacts with phenylacetylene to yield the Ru(II) acetylide complex (PCP)Ru(CO)(C⋮CPh) (5) and ammonia. In addition, complex 2 rapidly activates dihydrogen at room temperature to yield ammonia and the previously reported hydride complex (PCP)Ru(CO)(H). The ability of the amido complex 2 to cleave the H−H bond is attributed to the combination of a vacant coordination site for binding/activation of dihydrogen and a basic amido ligand. Complex 2 also undergoes an intramolecular C−H activation of a methyl group on the PCP ligand to yield ammonia and a cyclometalated complex. The reaction of (PCP)Ru(CO)(Cl) with MeLi allows the isolation of (PCP)Ru(CO)(Me) (8), and complex 8 undergoes an intramolecular C−H activation analogous to the amido complex 2 to produce methane and the cyclometalated complex. Determination of activation parameters for the intramolecular C−H activation transformations of 2 and 8 reveal identical ΔH⧧ {18(1) kcal/mol} with ΔS⧧ = −23(4) eu and −18(4) eu, respectively. Density functional theory has been applied to the study of intermolecular activation of methane and dihydrogen by (PCP‘)Ru(CO)(NH2) to yield (PCP‘)Ru(CO)(NH3)(X) (X = Me or H; PCP‘ = 2,6-(CH2PH2)2C6H3). The results indicate that the activation of dihydrogen is both exoergic and exothermic. In contrast, the addition of a C−H bond of methane across the Ru−NH2 bond has been calculated to be endoergic and endothermic. The surprising endoergic nature of the methane C−H activation has been attributed to a large and unfavorable change in Ru−N bond dissociation energy upon conversion from Ru-amido to Ru-ammine

Ruthenium(II) Anilido Complexes TpRuL₂(NHPh): Oxidative 4,4‘-Aryl Coupling Reactions (Tp = Hydridotris(pyrazolylborate); L = PMe₃, P(OMe)₃, or CO)

Reactions of the Ru(II) amido complexes TpRuL2(NHPh) (L = CO, PMe3, or P(OMe)3) with AgOTf (OTf = trifluoromethanesulfonate) yield the binuclear complexes [TpRuL2NH(C6H4−)]2[OTf]2 along with the Ru(II) amine complexes [TpRuL2(NH2Ph)][OTf] in an approximate 1:1 molar ratio. In these reactions, the two ruthenium fragments are coupled via C−H bond cleavage and C−C bond formation at the para position of anilido ligands. A resonance structure corresponding to Ru(II) metal centers linked by a diimine ligand contributes significantly to the bonding. Evidence for such a contribution comes from the diamagnetic nature of the binuclear complexes and a solid-state X-ray crystallographic study of [TpRu{P(OMe)3}2NH(C6H4−)]2[OTf]2. It is proposed that the coupled products are formed via initial single-electron oxidation followed by C−C bond formation. Variable-temperature NMR spectra of the aryl-coupled complexes are consistent with two geometrical isomers around the rigid HN−C6H4−C6H4NH bridges

Influence of Filled dπ-Manifold and L/L‘ Ligands on the Structure, Basicity, and Bond Rotations of the Octahedral and d⁶ Amido Complexes TpRu(L)(L‘)(NHPh) (Tp = Hydridotris(pyrazolyl)borate; L = L‘ = PMe₃ or P(OMe)₃, or L = CO and L‘ = PPh₃): Solid-State Structures of [TpRu(PMe₃)₂(NH₂Ph)][OTf], [TpRu{P(OMe)₃}₂(NH₂Ph)][OTf], and TpRu{P(OMe)₃}₂(NHPh)

It has been suggested that the reactivity of π-donating ligands bound to late-transition-metal complexes is heightened due to high d-electron counts. Herein, the synthesis and characterization of the Ru(II) amine and Ru(II) amido complexes [TpRuL2(NH2Ph)][OTf] (OTf = trifluoromethanesulfonate) and TpRuL2(NHPh) (L = PMe3 or P(OMe)3) are presented, including solid-state X-ray diffraction studies of [TpRu(PMe3)2(NH2Ph)][OTf], [TpRu{P(OMe)3}2(NH2Ph)][OTf], and TpRu{P(OMe)3}2(NHPh). The pKa's of the Ru(II) amine complexes and the previously reported [TpRu(CO)(PPh3)(NH2Ph)]+ have been estimated to be comparable to that of malononitrile in methylene chloride. In addition, the impact of the filled dπ-manifold (i.e., Ru(II) and d6 octahedral systems) on barriers to rotation of the Ru−NHPh moieties has been studied. For TpRu(PMe3)2(NHPh) and TpRu{P(OMe)3}2(NHPh), evidence for hindered rotation about the amido nitrogen and phenyl ipso carbon has been observed, and the relative N−C and Ru−N bond rotational barriers for the series of three amido complexes are discussed in terms of the π-conflict

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Synthesis, Solid-State Crystal Structure, and Reactivity of a Monomeric Copper(I) Anilido Complex

Synthesis and isolation of the Cu(I) amido complex (dtbpe)Cu(NHPh) (dtbpe = 1,2-bis(di-tert-butylphosphino)ethane) is accomplished upon reaction of [(dtbpe)Cu(μ-Cl)]2 with LiNHPh. The anilido complex has been fully characterized by IR spectroscopy and multinuclear NMR spectroscopy as well as by single-crystal X-ray diffraction study. Salient features of the solid-state structure include an amido orientation that allows π-interaction of the nitrogen-based lone pair with both the empty copper p-orbital and the π*-system of the phenyl substituent. A solid-state X-ray diffraction study of [(dtbpe)Cu(NH2Ph)][BF4] has allowed a direct comparison of the structural features upon conversion of the amine ligand to an amido. The reactivity of the amido ligand of (dtbpe)Cu(NHPh) is consistent with nucleophilic character. For example, the formation of Ph3CNHPh is observed upon treatment with [Ph3C][BF4], and reaction at room temperature with EtX (X = Br or I) yields N-ethylaniline. The reactivity of (dtbpe)Cu(NHPh) is compared to that of the octahedral and d6 complex TpRu(PMe3)2(NHPh) (Tp = hydridotris(pyrazolyl)borate)

Synthesis, Solid-State Crystal Structure, and Reactivity of a Monomeric Copper(I) Anilido Complex

Synthesis and isolation of the Cu(I) amido complex (dtbpe)Cu(NHPh) (dtbpe = 1,2-bis(di-tert-butylphosphino)ethane) is accomplished upon reaction of [(dtbpe)Cu(μ-Cl)]2 with LiNHPh. The anilido complex has been fully characterized by IR spectroscopy and multinuclear NMR spectroscopy as well as by single-crystal X-ray diffraction study. Salient features of the solid-state structure include an amido orientation that allows π-interaction of the nitrogen-based lone pair with both the empty copper p-orbital and the π*-system of the phenyl substituent. A solid-state X-ray diffraction study of [(dtbpe)Cu(NH2Ph)][BF4] has allowed a direct comparison of the structural features upon conversion of the amine ligand to an amido. The reactivity of the amido ligand of (dtbpe)Cu(NHPh) is consistent with nucleophilic character. For example, the formation of Ph3CNHPh is observed upon treatment with [Ph3C][BF4], and reaction at room temperature with EtX (X = Br or I) yields N-ethylaniline. The reactivity of (dtbpe)Cu(NHPh) is compared to that of the octahedral and d6 complex TpRu(PMe3)2(NHPh) (Tp = hydridotris(pyrazolyl)borate)

Octahedral Ru(II) Amido Complexes TpRu(L)(L‘)(NHR) (Tp = Hydridotris(pyrazolyl)borate; L = L‘ = P(OMe)₃ or PMe₃ or L = CO and L‘ = PPh₃; R = H, Ph, or ^tBu): Synthesis, Characterization, and Reactions with Weakly Acidic C−H Bonds

The octahedral Ru(II) amine complexes [TpRu(L)(L‘)(NH2R)][OTf] (L = L‘ = PMe3, P(OMe)3 or L = CO and L‘ = PPh3; R = H or tBu) have been synthesized and characterized. Deprotonation of the amine complexes [TpRu(L)(L‘)(NH3)][OTf] or [TpRu(PMe3)2(NH2tBu)][OTf] yields the Ru(II) amido complexes TpRu(L)(L‘)(NH2) and TpRu(PMe3)2(NHtBu). Reactions of the parent amido complexes or TpRu(PMe3)2(NHtBu) with phenylacetylene at room temperature result in immediate deprotonation to form ruthenium−amine/phenylacetylide ion pairs, and heating a benzene solution of the [TpRu(PMe3)2(NH2tBu)][PhC2] ion pair results in the formation of the Ru(II) phenylacetylide complex TpRu(PMe3)2(C⋮CPh) in >90% yield. The observation that [TpRu(PMe3)2(NH2tBu)][PhC2] converts to the Ru(II) acetylide with good yield while heating the ion pairs [TpRu(L)(L‘)(NH3)][PhC2] yields multiple products is attributed to reluctant dissociation of ammonia compared with the tbutylamine ligand (i.e., different rates for acetylide/amine exchange). These results are consistent with ligand exchange reactions of Ru(II) amine complexes [TpRu(PMe3)2(NH2R)][OTf] (R = H or tBu) with acetonitrile. The previously reported phenyl amido complexes TpRuL2(NHPh) {L = PMe3 or P(OMe)3} react with 10 equiv of phenylacetylene at elevated temperature to produce Ru(II) acetylide complexes TpRuL2(C⋮CPh) in quantitative yields. Kinetic studies indicate that the reaction of TpRu(PMe3)2(NHPh) with phenylacetylene occurs via a pathway that involves TpRu(PMe3)2(OTf) or [TpRu(PMe3)2(NH2Ph)][OTf] as catalyst. Reactions of 1,4-cyclohexadiene with the Ru(II) amido complexes TpRu(L)(L‘)(NH2) (L = L‘ = PMe3 or L = CO and L‘ = PPh3) or TpRu(PMe3)2(NHtBu) at elevated temperatures result in the formation of benzene and Ru hydride complexes. TpRu(PMe3)2(H), [Tp(PMe3)2RuCC(H)Ph][OTf], [Tp(PMe3)2RuC(CH2Ph){N(H)Ph}][OTf], and [TpRu(PMe3)3][OTf] have been independently prepared and characterized. Results from solid-state X-ray diffraction studies of the complexes [TpRu(CO)(PPh3)(NH3)][OTf], [TpRu(PMe3)2(NH3)][OTf], and TpRu(CO)(PPh3)(C⋮CPh) are reported