Expanding the allyl analogy: accessing η^3-P,B,P diphosphinoborane complexes of group 10

Using the diphosphinoborane, (PPh_2)_2BMes (Mes = 2,4,6-Me_3C_6H_3), we report the first examples of η^3-P,B,P-ligated complexes using Ni(0) and Pt(II). Reaction of (PPh_2)_2BMes with Ni(COD)_2 or Pt(COD)Me_2 (COD = 1,5-cyclooctadiene) results in gradual COD displacement to give [η^3-P,B,P-(PPh_2)_2BMes]Ni(COD) (3) or [η^3-P,B,P-(PPh_2)_2BMes]Pt(CH_3)_2 (6). Complex 3 serves as a versatile Ni-containing synthon for the preparation of square planar or tetrahedral Ni(0) complexes. Notably, the M–B interaction in these systems is non-negligible – with coordination resulting in an upfield shift of ca. 80 ppm in the ^(11)B NMR spectrum. We also show that treatment of the Pt^(IV) halide precursor, [PtMe_3I]_4 with this ligand framework results in migration of X-type ligands (CH_3− and I−) to boron and reductive elimination of ethane (C_2H_6) to give a distorted square planar zwitterionic Pt^(II) complex, Pt[κ^2-P,P-(PPh_2)_2B(Mes)(CH_3)][κ^2-P,P-(PPh_2)_2B(Mes)(I)] (10). This reactivity suggests the feasibility of (PPh_2)_2BMes-ligand-induced labilization of M–X ligands

Generating Potent C–H PCET Donors: Ligand-Induced Fe-to-Ring Proton Migration from a Cp*Fe^(III)–H Complex Demonstrates a Promising Strategy

Highly reactive organometallic species that mediate reductive proton-coupled electron transfer (PCET) reactions are an exciting area for development in catalysis, where a key objective focuses on tuning the reactivity of such species. This work pursues ligand-induced activation of a stable organometallic complex toward PCET reactivity. This is studied via the conversion of a prototypical Cp*Fe^(III)–H species, [Fe^(III)(η⁵-Cp*)(dppe)H]⁺ (Cp* = C₅Me₅⁻, dppe = 1,2-bis(diphenylphosphino)ethane), to a highly reactive, S = 1/2 ring-protonated endo-Cp*H–Fe relative, triggered by the addition of CO. Our assignment of the latter ring-protonated species contrasts with its previous reported formulation, which instead assigned it as a hypervalent 19-electron hydride, [Fe^(III)(η⁵-Cp*)(dppe)(CO)H]⁺. Herein, pulse EPR spectroscopy (^(1,2)H HYSCORE, ENDOR) and X-ray crystallography, with corresponding DFT studies, cement its assignment as the ring-protonated isomer, [Fe^I(endo-η⁴-Cp*H)(dppe)(CO)] ⁺. A less sterically shielded and hence more reactive exo-isomer can be generated through oxidation of a stable Fe0(exo-η⁴-Cp*H)(dppe)(CO) precursor. Both endo- and exo-ring-protonated isomers are calculated to have an exceptionally low bond dissociation free energy (BDFE_(C–H) ≈ 29 kcal mol⁻¹ and 25 kcal mol⁻¹, respectively) cf. BDFE_(Fe–H) of 56 kcal mol⁻¹ for [Fe^(III)(η⁵-Cp*)(dppe)H] ⁺. These weak C–H bonds are shown to undergo proton-coupled electron transfer (PCET) to azobenzene to generate diphenylhydrazine and the corresponding closed-shell [Fe^(II)(η⁵-Cp*)(dppe)CO]⁺ byproduct

A review and road map of entrepreneurial equity financing research

Equity financing in entrepreneurship primarily includes venture capital, corporate venture capital, angel investment, crowdfunding, and accelerators. We take stock of venture financing research to date with two main objectives: (a) to integrate, organize, and assess the large and disparate literature on venture financing; and (b) to identify key considerations relevant for the domain of venture financing moving forward. The net effect is that organizing and assessing existing research in venture financing will assist in launching meaningful, theory-driven research as existing funding models evolve and emerging funding models forge new frontiers

Generating Potent C–H PCET Donors: Ligand-Induced Fe-to-Ring Proton Migration from a Cp*Fe^(III)–H Complex Demonstrates a Promising Strategy

Highly reactive organometallic species that mediate reductive proton-coupled electron transfer (PCET) reactions are an exciting area for development in catalysis, where a key objective focuses on tuning the reactivity of such species. This work pursues ligand-induced activation of a stable organometallic complex toward PCET reactivity. This is studied via the conversion of a prototypical Cp*Fe^(III)–H species, [Fe^(III)(η⁵-Cp*)(dppe)H]⁺ (Cp* = C₅Me₅⁻, dppe = 1,2-bis(diphenylphosphino)ethane), to a highly reactive, S = 1/2 ring-protonated endo-Cp*H–Fe relative, triggered by the addition of CO. Our assignment of the latter ring-protonated species contrasts with its previous reported formulation, which instead assigned it as a hypervalent 19-electron hydride, [Fe^(III)(η⁵-Cp*)(dppe)(CO)H]⁺. Herein, pulse EPR spectroscopy (^(1,2)H HYSCORE, ENDOR) and X-ray crystallography, with corresponding DFT studies, cement its assignment as the ring-protonated isomer, [Fe^I(endo-η⁴-Cp*H)(dppe)(CO)] ⁺. A less sterically shielded and hence more reactive exo-isomer can be generated through oxidation of a stable Fe0(exo-η⁴-Cp*H)(dppe)(CO) precursor. Both endo- and exo-ring-protonated isomers are calculated to have an exceptionally low bond dissociation free energy (BDFE_(C–H) ≈ 29 kcal mol⁻¹ and 25 kcal mol⁻¹, respectively) cf. BDFE_(Fe–H) of 56 kcal mol⁻¹ for [Fe^(III)(η⁵-Cp*)(dppe)H] ⁺. These weak C–H bonds are shown to undergo proton-coupled electron transfer (PCET) to azobenzene to generate diphenylhydrazine and the corresponding closed-shell [Fe^(II)(η⁵-Cp*)(dppe)CO]⁺ byproduct

Snapshots of a Migrating H-Atom: Characterization of a Reactive Iron(III) Indenide Hydride and its Nearly Isoenergetic Ring-Protonated Iron(I) Isomer

We report the characterization of an S=1/2 iron π‐complex, [Fe(η⁶‐IndH)(depe)]⁺ (Ind=Indenide (C₉H₇⁻), depe=1,2‐bis(diethylphosphino)ethane), which results via C−H elimination from a transient Fe^(III) hydride, [Fe(η³:η²‐Ind)(depe)H]⁺. Owing to weak M−H/C−H bonds, these species appear to undergo proton‐coupled electron transfer (PCET) to release H₂ through bimolecular recombination. Mechanistic information, gained from stoichiometric as well as computational studies, reveal the open‐shell π‐arene complex to have a BDFE_(C‐H) value of ≈50 kcal mol⁻¹, roughly equal to the BDFE_(Fe‐H) of its Fe^(III)−H precursor (ΔG°≈0 between them). Markedly, this reactivity differs from related Fe(η⁵‐Cp/Cp*) compounds, for which terminal Fe^(III)−H cations are isolable and have been structurally characterized, highlighting the effect of a benzannulated ring (indene). Overall, this study provides a structural, thermochemical, and mechanistic foundation for the characterization of indenide/indene PCET precursors and outlines a valuable approach for the differentiation of a ring‐ versus a metal‐bound H‐atom by way of continuous‐wave (CW) and pulse EPR (HYSCORE) spectroscopic measurements

Expanding the allyl analogy: accessing η^3-P,B,P diphosphinoborane complexes of group 10

Using the diphosphinoborane, (PPh_2)_2BMes (Mes = 2,4,6-Me_3C_6H_3), we report the first examples of η^3-P,B,P-ligated complexes using Ni(0) and Pt(II). Reaction of (PPh_2)_2BMes with Ni(COD)_2 or Pt(COD)Me_2 (COD = 1,5-cyclooctadiene) results in gradual COD displacement to give [η^3-P,B,P-(PPh_2)_2BMes]Ni(COD) (3) or [η^3-P,B,P-(PPh_2)_2BMes]Pt(CH_3)_2 (6). Complex 3 serves as a versatile Ni-containing synthon for the preparation of square planar or tetrahedral Ni(0) complexes. Notably, the M–B interaction in these systems is non-negligible – with coordination resulting in an upfield shift of ca. 80 ppm in the ^(11)B NMR spectrum. We also show that treatment of the Pt^(IV) halide precursor, [PtMe_3I]_4 with this ligand framework results in migration of X-type ligands (CH_3− and I−) to boron and reductive elimination of ethane (C_2H_6) to give a distorted square planar zwitterionic Pt^(II) complex, Pt[κ^2-P,P-(PPh_2)_2B(Mes)(CH_3)][κ^2-P,P-(PPh_2)_2B(Mes)(I)] (10). This reactivity suggests the feasibility of (PPh_2)_2BMes-ligand-induced labilization of M–X ligands

Fusing triphenylphosphine with tetraphenylborate: introducing the 9-phosphatriptycene-10-phenylborate (PTB) anion

In a fusion of two ubiquitous organometallic reagents, triphenylphosphine (PPh_3) and tetraphenylborate (BPh_4−), the 9-phosphatriptycene-10-phenylborate (PTB) anion has been prepared for the first time. This borato species has been fully characterized by a suite of spectroscopic methods, and initial reactivity studies introduce it as a competent ligand for transition metals, including Co(II) and Fe(II)

Nickel complexes of allyl and vinyldiphenylphosphine

Monodentate phosphine-ligated nickel compounds, e.g., [Ni(PPh3)4] are relevant as active catalysts across a broad range of reactions. This report expands upon the coordination chemistry of this family, offering the reactivity of allyl- and vinyl-substituted diphenylphosphine (PPh2R) with [Ni(COD)2] (COD = 1,5-cyclooctadiene). These reactions provide three-coordinate dinickelacycles that are intermolecularly tethered through adjacent {Ni}-olefin interactions. The ring conformation of such cycles has been studied in the solid-state and using theoretical calculations. Here, a difference in reaction outcome is linked to the presence of an allyl vs vinyl group, where the former is observed to undergo rearrangement, bringing about challenges in clean product isolation

Fusing triphenylphosphine with tetraphenylborate: introducing the 9-phosphatriptycene-10-phenylborate (PTB) anion

In a fusion of two ubiquitous organometallic reagents, triphenylphosphine (PPh_3) and tetraphenylborate (BPh_4−), the 9-phosphatriptycene-10-phenylborate (PTB) anion has been prepared for the first time. This borato species has been fully characterized by a suite of spectroscopic methods, and initial reactivity studies introduce it as a competent ligand for transition metals, including Co(II) and Fe(II)

Snapshots of a Migrating H-atom: Characterization of a Reactive Fe(III) Indenide Hydride and its Nearly Isoenergetic Ring-Protonated Fe(I) Isomer

We report the characterization of an S = ½ iron π‐complex, [Fe(η^6‐IndH)(depe)]^+ (Ind = Indenide (C_9H_(7^‐_), depe = 1,2‐bis(diethylphosphino)ethane), which results via C‐H elimination from a transient Fe^(III) hydride, [Fe(η^3:η^2‐Ind)(depe)H]^+. Owing to weak M‐H/C‐H bonds, these species undergo proton‐coupled electron transfer (PCET) to release H_2 through bimolecular recombination. Mechanistic information, gained from stoichiometric as well as computational studies, reveal the open‐shell π‐arene complex to have a BDFE_(C‐H) value of ≈ 50 kcal mol^(‐1), roughly equal to the BDFE_(Fe‐H) of its Fe^(III)‐H precursor (ΔG^o ≈ 0 between them). Markedly, this reactivity differs from related Fe(η^5‐Cp/Cp^*) compounds, for which terminal Fe^(III)‐H cations are isolable and have been structurally characterized, highlighting the effect of a benzannulated (indene) ring. Overall, this study provides a structural, thermochemical, and mechanistic foundation for the characterization of indenide/indene PCET precursors and out‐lines a valuable approach for the differentiation of a ring‐ versus a metal‐ bound H‐atom by way of continuous‐wave (CW) and pulse EPR (HYSCORE) spectroscopic measurements