The molybdenum tetrahydride species
(Triphos)MoH4PPh3 (Triphos = PhP(CH2CH2PPh2)2) generated from sodium
triethylborohydride addition
to (Triphos)MoCl3 was found to promote CO2 functionalization
to afford acrylate, propionate, and formate species. The formation
of (Triphos)MoH4PPh3 occurs via a (Triphos)Mo(H)Cl(PPh3) intermediate followed by dismutation of an unobserved six-coordinate
molybdenum(II) dihydride complex. Addition of dihydrogen to the dismuation
product mixture affords a nearly quantitative yield of (Triphos)MoH4PPh3. The molybdenum tetrahydride species facilitates
CO2 insertion into a metal hydride to produce a formate
complex, (Triphos)Mo(H)(κ2-CHO2)(PPh3), with an observed rate constant of [2.9(2)] × 10–4 s–1 (25 °C), which is independent
of CO2 pressure. Selective formation of acrylate and propionate
carbon dioxide–ethylene coupling products, (Triphos)Mo(H)(κ2-C3H3O2)(PPh3)
and (Triphos)Mo(H)(κ2-C3H5O2)(PPh3), was achieved by sequential addition of
olefin and heterocumulene to (Triphos)MoH4PPh3. A formally zerovalent TriphosMo(η2-C2H4)3 intermediate was characterized by NMR
spectroscopy and computational analysis along the pathway for carbon
dioxide–ethylene coupling.
In this work, we propose a model to quantify strain induced conductor
discontinuities based on measuring electrical resistance while applying tensile
strain to metal-polymer systems. Under strain, changing conductor geometry and
induced conductor discontinuity increase electrical resistance. On Kapton
substrates strained to ε = .07, evaporated gold films did not
deform and resistance increase was only caused by geometry change. Conversely,
discontinuity caused 31% and 72% of the resistance increase in evaporated and
printed silver films at the same strain. On PDMS substrates, the same magnitude
of discontinuity, causing 31% of the resistance increase, occurred at only
ε = .024 in evaporated silver films. At the same strain,
discontinuity caused 86% of the resistance increase in evaporated gold films.
Printed silver films were inelastic. The results suggest that traditional
fabrication techniques may be more suitable to flexible hybrid electronics
applications than additively manufactured conductors.
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