Synthesis of Monomeric Fe(II) and Ru(II) Complexes of Tetradentate Phosphines

rac-Bis[{(diphenylphosphino)ethyl}-phenylphosphino]methane (DPPEPM) reacts with iron(II) and ruthenium(II) halides to generate complexes with folded DPPEPM coordination. The paramagnetic, five-coordinate Fe(DPPEPM)Cl2 (1) in CD2Cl2 features a tridentate binding mode as established by 31P{1H} NMR spectroscopy. Crystal structure analysis of the analogous bromo complex, Fe(DPPEPM)Br2 (2) revealed a pseudo-octahedral, cis-α geometry at iron with DPPEPM coordinated in a tetradentate fashion. However, in CD2Cl2 solution, the coordination of DPPEPM in 2 is similar to that of 1 in that one of the external phosphorus atoms is dissociated resulting in a mixture of three tridentate complexes. The chloro ruthenium complex cis-Ru(κ4-DPPEPM)Cl2 (3) is obtained from rac-DPPEPM and either [RuCl2(COD)]2 [COD = 1,5-cyclooctadiene] or RuCl2(PPh3)4. The structure of 3 in both the solid state and in CD2Cl2 solution features a folded κ4-DPPEPM. This binding mode was also observed in cis-[Fe(κ4-DPPEPM)(CH3CN)2](CF3SO3)2 (4). Addition of an excess of CO to a methanolic solution of 1 results in the replacement of one of the chloride ions by CO to yield cis-[Fe(κ4-DPPEPM)Cl(CO)](Cl) (5). The same reaction in CH2Cl2 produces a mixture of 5 and [Fe(κ3-DPPEPM)Cl2(CO)] (6) in which one of the internal phosphines has been substituted by CO. Complexes 2, 3, 4, and 5 appear to be the first structurally characterized monometallic complexes of κ4-DPPEPM

Synthesis of Monomeric Fe(II) and Ru(II) Complexes of Tetradentate Phosphines

rac-Bis[{(diphenylphosphino)ethyl}-phenylphosphino]methane (DPPEPM) reacts with iron(II) and ruthenium(II) halides to generate complexes with folded DPPEPM coordination. The paramagnetic, five-coordinate Fe(DPPEPM)Cl2 (1) in CD2Cl2 features a tridentate binding mode as established by 31P{1H} NMR spectroscopy. Crystal structure analysis of the analogous bromo complex, Fe(DPPEPM)Br2 (2) revealed a pseudo-octahedral, cis-α geometry at iron with DPPEPM coordinated in a tetradentate fashion. However, in CD2Cl2 solution, the coordination of DPPEPM in 2 is similar to that of 1 in that one of the external phosphorus atoms is dissociated resulting in a mixture of three tridentate complexes. The chloro ruthenium complex cis-Ru(κ4-DPPEPM)Cl2 (3) is obtained from rac-DPPEPM and either [RuCl2(COD)]2 [COD = 1,5-cyclooctadiene] or RuCl2(PPh3)4. The structure of 3 in both the solid state and in CD2Cl2 solution features a folded κ4-DPPEPM. This binding mode was also observed in cis-[Fe(κ4-DPPEPM)(CH3CN)2](CF3SO3)2 (4). Addition of an excess of CO to a methanolic solution of 1 results in the replacement of one of the chloride ions by CO to yield cis-[Fe(κ4-DPPEPM)Cl(CO)](Cl) (5). The same reaction in CH2Cl2 produces a mixture of 5 and [Fe(κ3-DPPEPM)Cl2(CO)] (6) in which one of the internal phosphines has been substituted by CO. Complexes 2, 3, 4, and 5 appear to be the first structurally characterized monometallic complexes of κ4-DPPEPM

Formation and Transmetalation Mechanisms of Homo- and Heterometallic (Fe/Zn) Trinuclear Triple-Stranded Side-by-Side Helicates

A novel linear hybrid tris-bidentate neutral ligand having 2,2′-bipyridine and two terminal triazolylpyridine coordination sites (<b>L</b>) was efficiently synthesized and explored in the synthesis of trinuclear triple-stranded homometallic side-by-side helicates <b>L</b>₃Fe₃(OTf)₆ (<b>1</b>) and <b>L</b>₃Zn₃(OTf)₆ (<b>2</b>), in which the three metal centers display alternating Λ and Δ configurations. Selective formation of the analogous heterometallic side-by-side helicate <b>L</b>₃Fe₂Zn­(OTf)₆ (<b>3</b>) was achieved from a mixture of <b>L</b>, Fe­(CH₃CN)₂(OTf)₂, and Zn­(OTf)₂ (1:1:1) in acetonitrile at room temperature. Various analytical techniques, i.e., single-crystal X-ray diffraction and NMR and UV/vis spectroscopy, were used to elucidate the sequence of the metal atoms within the heterometallic helicate, with the Zn²⁺ at the central position. The formation of <b>3</b> was also achieved starting from either <b>L</b>₃Zn₃(OTf)₆ or <b>L</b>₃Fe₃(OTf)₆ by adding Fe­(CH₃CN)₂(OTf)₂ or Zn­(OTf)₂, respectively. ESI-MS and ¹H NMR studies elucidated different transmetalation mechanisms for the two cases: While a Zn²⁺-to-Fe²⁺ transmetalation occurs by the stepwise exchange of single ions on the helicate <b>L</b>₃Zn₃(OTf)₆ at room temperature, this mechanism is almost inoperative for the Fe²⁺-to-Zn²⁺ transmetalation in <b>L</b>₃Fe₃(OTf)₆, which is kinetically trapped at room temperature. In contrast, dissociation of <b>L</b>₃Fe₃(OTf)₆ at higher temperature is required, followed by reassembly to give <b>L</b>₃Fe₂Zn­(OTf)₆. The reassembly follows an interesting mechanistic pathway when an excess of Zn­(OTf)₂ is present in solution: First, <b>L</b>₃Zn₃(OTf)₆ forms as the high-temperature thermodynamic product, which is then slowly converted into the thermodynamic heterometallic <b>L</b>₃Fe₂Zn­(OTf)₆ product at room temperature. The temperature-dependent equilibrium shift is traced back to significant entropy differences resulting from an enhancement of the thermal motion of the ligands at high temperature, which destabilize the octahedral iron terminal complex and select zinc in a more stable tetrahedral geometry

Piano-Stool Lutetium Amido and Imido Compounds Supported by a Constrained Bis(oxazoline)cyclopentadienyl Ligand

{Bo^MCp^tet}­Lu­(CH₂Ph)₂ (<b>1</b>; Bo^MCp^tet = MeC­(Ox^Me2)₂C₅Me₄; Ox^Me2 = 4,4-dimethyl-2-oxazoline) was prepared in 95% yield from the reaction of Bo^MCp^tetH and Lu­(CH₂Ph)₃THF₃. Compound <b>1</b> reacts with 1 or 2 equiv of H₂NCH₂R (R = C₆H₅, 1-C₁₀H₇) to give the corresponding imido complexes [{Bo^MCp^tet}­LuNCH₂R]₂ (R = C₆H₅ (<b>2a</b>), 1-C₁₀H₇ (<b>2b</b>)) or amido complexes {Bo^MCp^tet}­Lu­(NHCH₂R)₂ (R = C₆H₅ (<b>3a</b>), 1-C₁₀H₇ (<b>3b</b>)). Once isolated, the imido species are insoluble in nonprotic organic solvents. Crystallographic characterization reveals dimeric [{Bo^MCp^tet}­LuNCH₂(1-C₁₀H₇)]₂ in the solid state. The reaction of <b>1</b> and NH₃B­(C₆F₅)₃ affords crystallographically characterized {Bo^MCp^tet}­Lu­{NHB­(C₆F₅)₂}­C₆F₅. This species is proposed to form via a transient lutetium imido, which undergoes C₆F₅ migration to the lutetium center

Piano-Stool Lutetium Amido and Imido Compounds Supported by a Constrained Bis(oxazoline)cyclopentadienyl Ligand

{Bo^MCp^tet}­Lu­(CH₂Ph)₂ (<b>1</b>; Bo^MCp^tet = MeC­(Ox^Me2)₂C₅Me₄; Ox^Me2 = 4,4-dimethyl-2-oxazoline) was prepared in 95% yield from the reaction of Bo^MCp^tetH and Lu­(CH₂Ph)₃THF₃. Compound <b>1</b> reacts with 1 or 2 equiv of H₂NCH₂R (R = C₆H₅, 1-C₁₀H₇) to give the corresponding imido complexes [{Bo^MCp^tet}­LuNCH₂R]₂ (R = C₆H₅ (<b>2a</b>), 1-C₁₀H₇ (<b>2b</b>)) or amido complexes {Bo^MCp^tet}­Lu­(NHCH₂R)₂ (R = C₆H₅ (<b>3a</b>), 1-C₁₀H₇ (<b>3b</b>)). Once isolated, the imido species are insoluble in nonprotic organic solvents. Crystallographic characterization reveals dimeric [{Bo^MCp^tet}­LuNCH₂(1-C₁₀H₇)]₂ in the solid state. The reaction of <b>1</b> and NH₃B­(C₆F₅)₃ affords crystallographically characterized {Bo^MCp^tet}­Lu­{NHB­(C₆F₅)₂}­C₆F₅. This species is proposed to form via a transient lutetium imido, which undergoes C₆F₅ migration to the lutetium center

Piano-Stool Lutetium Amido and Imido Compounds Supported by a Constrained Bis(oxazoline)cyclopentadienyl Ligand

{Bo^MCp^tet}­Lu­(CH₂Ph)₂ (<b>1</b>; Bo^MCp^tet = MeC­(Ox^Me2)₂C₅Me₄; Ox^Me2 = 4,4-dimethyl-2-oxazoline) was prepared in 95% yield from the reaction of Bo^MCp^tetH and Lu­(CH₂Ph)₃THF₃. Compound <b>1</b> reacts with 1 or 2 equiv of H₂NCH₂R (R = C₆H₅, 1-C₁₀H₇) to give the corresponding imido complexes [{Bo^MCp^tet}­LuNCH₂R]₂ (R = C₆H₅ (<b>2a</b>), 1-C₁₀H₇ (<b>2b</b>)) or amido complexes {Bo^MCp^tet}­Lu­(NHCH₂R)₂ (R = C₆H₅ (<b>3a</b>), 1-C₁₀H₇ (<b>3b</b>)). Once isolated, the imido species are insoluble in nonprotic organic solvents. Crystallographic characterization reveals dimeric [{Bo^MCp^tet}­LuNCH₂(1-C₁₀H₇)]₂ in the solid state. The reaction of <b>1</b> and NH₃B­(C₆F₅)₃ affords crystallographically characterized {Bo^MCp^tet}­Lu­{NHB­(C₆F₅)₂}­C₆F₅. This species is proposed to form via a transient lutetium imido, which undergoes C₆F₅ migration to the lutetium center

Cyclopentadienyl-bis(oxazoline) Magnesium and Zirconium Complexes in Aminoalkene Hydroaminations

A new class of cyclopentadiene-bis­(oxazoline) compounds and their piano-stool-type organometallic complexes have been prepared as catalysts for hydroamination of aminoalkenes. The two compounds MeC­(Ox^Me2)₂C₅H₅ (Bo^MCpH; Ox^Me2 = 4,4-dimethyl-2-oxazoline) and MeC­(Ox^Me2)₂C₅Me₄H (Bo^MCp^tetH) are synthesized from C₅R₄HI (R = H, Me) and MeC­(Ox^Me2)₂Li. These cyclopentadiene-bis­(oxazolines) are converted into ligands that support a variety of metal centers in piano-stool-type geometries, and here we report the preparation of Mg, Tl, Ti, and Zr compounds. Bo^MCpH and Bo^MCp^tetH react with MgMe₂(O₂C₄H₈)₂ to give the magnesium methyl complexes {Bo^MCp}­MgMe and {Bo^MCp^tet}­MgMe. Bo^MCpH and Bo^MCp^tetH are converted to Bo^MCpTl and Bo^MCp^tetTl by reaction with TlOEt. The thallium derivatives react with TiCl₃(THF)₃ to provide [{Bo^MCp}­TiCl­(μ-Cl)]₂ and [{Bo^MCp^tet}­TiCl­(μ-Cl)]₂, the former of which is crystallographically characterized as a dimeric species. Bo^MCpH and Zr­(NMe₂)₄ react to eliminate dimethylamine and afford {Bo^MCp}­Zr­(NMe₂)₃, which is crystallographically characterized as a monomeric four-legged piano-stool compound. {Bo^MCp}­Zr­(NMe₂)₃, {Bo^MCp}­MgMe, and {Bo^MCp^tet}­MgMe are efficient catalysts for the hydroamination/cyclization of aminoalkenes under mild conditions