Surface-Confined Nickel Mediated Cross-Coupling Reactions: Characterization of Initiator Environment in Kumada Catalyst-Transfer Polycondensation

Abstract

Kumada catalyst-transfer polycondensation (KCTP) has proven to be an excellent strategy toward the synthesis of well-defined conjugated polymers. In this report, Ni(0) species are reacted with surface-bound aryl bromides to yield KCTP initiators of structure (aryl)Ni(II)-Br. Surface-confined Kumada reactions are carried out with a ferrocene functionalized Grignard reagent to quantify initiator coverage, ligand exchange, and Kumada reaction kinetics. In addition, surface-initiated Kumada catalyst-transfer polycondensation (SI-KCTP) is carried out from the fabricated initiators to modify SiO(2) and ITO surfaces. Uniform poly(3-methylthiophene) films with thicknesses between 40 and 65 nm were characterized using a variety of spectroscopic and electrochemical techniques.

Functionalization of Reactive End Groups in Surface‐Initiated Kumada Catalyst‐Transfer Polycondensation

“…Ni-mediated SI-KCTP often suffers from low grafting density, [18] primarily due to interfacial homocoupling reactions facilitated by the close proximity of adjacent Ni(II) species (Scheme 1B). [35] Previous studies by our group have quantified initiator density through cyclic voltammetry with the use of a ferrocene capping agent (1) that can undergo a coupling reaction at the surface (assuming quantitative conversion of the Ni(II) initiators occurs).…”

“…[35] Previous studies by our group have quantified initiator density through cyclic voltammetry with the use of a ferrocene capping agent (1) that can undergo a coupling reaction at the surface (assuming quantitative conversion of the Ni(II) initiators occurs). [18,29] Importantly, cyclic voltammetry can give valuable insight into the integrity of the self-assembled monolayers, as well as the spatial homogeneity of initiators.…”

“…[12][13][14][15][16][17][18] Covalent attachment of the polymer chain to the electrode in photovoltaic devices is advantageous over traditional solution processing methodologies, offering increased mechanical stability as well as increased efficiency in electron/hole injection. [19,20] Additionally, covalent immobilization may offer the ability to produce organized layers of conjugated polymers at the metal oxide interface (such as indium tin oxide, ITO) allowing for increased charged transport.…”

“…Grafting densities are typically limited to around 20% when compared to a full monolayer, possibly due to the high reactivity of the Ni(0) species and the propensity to undergo detrimental side reactions. [18] Higher grafting densities are immensely important for the preparation of oriented films as they force an energetically unfavorable conformation. [29] As far as we know, no current studies examine the combined role of steric congestion and disproportionation at the surface in reducing grafting density.…”

“…[28,32,33] Instead, exchanging a cyclooctadiene (COD) ligand with 2,2 0 -bypyridine (bpy) leads to uniform surface coverage of initiators. [18] In this report, the Ni(COD) 2 /bpy system is used as the catalyst for oxidative addition followed by ligand exchange with dppp for polymerization.…”