Cobalt PCP Pincer Complexes via an Unexpected Sequence of Ortho Metalations

The cobalt PCP pincer complexes [Co­{2,6-(CH₂PPh₂-κ<i>P</i>)₂C₆H₃-κ<i>C</i>¹}­(L)₂], where L = PMe₃ (<b>1</b>), CO (<b>2</b>), have been prepared. Complex <b>1</b> is obtained by a transmetalation reaction between 1-lithio-2,6-bis­((diphenylphosphino)­methyl)­benzene and [CoCl­(PMe₃)₃]. Subsequent exposure of <b>1</b> to CO gave complex <b>2</b>. Complexes <b>1</b> and <b>2</b> can also be obtained from 1,3-bis­((diphenylphosphino)­methyl)­benzene and [CoMe­(PMe₃)₄]. Instead of ortho metalation occurring directly at the C2 (pincer) position of the diphosphine, ortho metalation first occurs at the C4 position to form [Co­{2-(CH₂PPh₂-κ<i>P</i>)-4-(CH₂PPh₂)-C₆H₃-κ<i>C</i>¹}­(PMe₃)₃] (<b>4</b>). After reflux of the reaction mixture for 24 h, a rearrangement of <b>4</b> occurs to give pincer complex <b>1</b> with loss of PMe₃ in ca. 50% yield; this rearrangement was accompanied by some decomposition. The mechanism for the conversion of <b>4</b> to <b>1</b> has been probed using 1-deuterio-2,6-bis­((diphenylphosphino)­methyl)­benzene. Unexpectedly, the labeled ligand led to 15% deuterium enrichment of an ortho CH of the terminal PPh₂ group in the product complex <b>1</b>, and the proposed mechanism for this rearrangement involves a four-membered cobaltacyclic intermediate

Cobalt PCP Pincer Complexes via an Unexpected Sequence of Ortho Metalations

The cobalt PCP pincer complexes [Co­{2,6-(CH₂PPh₂-κ<i>P</i>)₂C₆H₃-κ<i>C</i>¹}­(L)₂], where L = PMe₃ (<b>1</b>), CO (<b>2</b>), have been prepared. Complex <b>1</b> is obtained by a transmetalation reaction between 1-lithio-2,6-bis­((diphenylphosphino)­methyl)­benzene and [CoCl­(PMe₃)₃]. Subsequent exposure of <b>1</b> to CO gave complex <b>2</b>. Complexes <b>1</b> and <b>2</b> can also be obtained from 1,3-bis­((diphenylphosphino)­methyl)­benzene and [CoMe­(PMe₃)₄]. Instead of ortho metalation occurring directly at the C2 (pincer) position of the diphosphine, ortho metalation first occurs at the C4 position to form [Co­{2-(CH₂PPh₂-κ<i>P</i>)-4-(CH₂PPh₂)-C₆H₃-κ<i>C</i>¹}­(PMe₃)₃] (<b>4</b>). After reflux of the reaction mixture for 24 h, a rearrangement of <b>4</b> occurs to give pincer complex <b>1</b> with loss of PMe₃ in ca. 50% yield; this rearrangement was accompanied by some decomposition. The mechanism for the conversion of <b>4</b> to <b>1</b> has been probed using 1-deuterio-2,6-bis­((diphenylphosphino)­methyl)­benzene. Unexpectedly, the labeled ligand led to 15% deuterium enrichment of an ortho CH of the terminal PPh₂ group in the product complex <b>1</b>, and the proposed mechanism for this rearrangement involves a four-membered cobaltacyclic intermediate

New Multi-Ferrocenyl- and Multi-Ferricenyl- Materials via Coordination-Driven Self-Assembly and via Charge-Driven Electro-Crystallization

Three new tetra-ferrocenylethynylpyridinyl copper complexes, L₄(CuI)₄ (<b>3</b>), L₄(CuBr)₂ (<b>4</b>), and L₄(CuCl)₂ (<b>5</b>) have been prepared from the reaction of ferrocenyl­ethynyl­pyridine (L)­(<b>2</b>) with copper halides CuX (with X = I^–, Br^–, Cl^–).The ligand <b>2</b> and the complexes <b>3</b>–<b>5</b> have been fully characterized by spectroscopic methods. The structures of <b>2</b>–<b>4</b> have been confirmed by single-crystal X-ray crystallography. <b>2</b> forms a dimer in the crystalline-state through C–H··N hydrogen bonds. <b>4</b> and <b>5</b> are dimers and <b>3</b> a tetramer, in all cases linked through Cu–X··Cu bridging interactions. Cyclic voltammetry in dichloroethane showed chemically reversible multiferrocenyl oxidation signals with evidence for product electro-crystallization. The oxidation products were isolated by electrodeposition onto a Pt disc electrode and investigated by scanning electron microscopy which confirmed the spontaneous formation of crystalline oxidation products with distinctive morphologies. Energy dispersive X-ray elemental analysis shows the presence of hexafluorophosphate (counterion) with the P:Fe ratio of 1:1, 0.5:1, and 1:1 for the electrocrystallized products <b>3</b>, <b>4</b>, and <b>5</b>, respectively, suggesting the formulas [<b>3</b>]⁴⁺(PF₆^–)₄, [<b>4</b>]²⁺(PF₆^–)₂, and [<b>5</b>]⁴⁺(PF₆^–)₄ for the electro-crystallized products

Long-Range Intramolecular Electronic Communication in Bis(ferrocenylethynyl) Complexes Incorporating Conjugated Heterocyclic Spacers: Synthesis, Crystallography, and Electrochemistry

A new series of bis­(ferrocenylethynyl) complexes, <b>3</b>–<b>7</b>, and a mono­(ferrocenylethynyl) complex, <b>8</b>, have been synthesized incorporating conjugated heterocyclic spacer groups, with the ethynyl group facilitating an effective long-range intramolecular interaction. The complexes were characterized by NMR, IR, and UV–vis spectroscopy as well as X-ray crystallography. The redox properties of these complexes were investigated using cyclic voltammetry and spectroelectrochemistry. Although there is a large separation of ∼14 Å between the two redox centers, Δ<i>E</i>_1/2 values in this series of complexes ranged from 50 to 110 mV. The appearance of intervalance charge-transfer bands in the UV–vis–near-IR region for the monocationic complexes further confirmed effective intramolecular electronic communication. Computational studies are presented that show the degree of delocalization across the Fc–CC–CC–Fc (Fc = C₅H₅FeC₅H₄) highest occupied molecular orbital