Synthesis of porphyrin-spacer-quinone compounds via metal-mediated cross-coupling: new systems for probing the relative magnitudes of axial and equatorial electronic coupling at the porphyrin macrocycle in thermal and photoactivated electron transfer

摘要

Two classes of (porphinato) zinc(II) -spacer-quinone electron transfer compounds were fabricated through metal-mediated cross-coupling reactions using appropriately derivatized polphyrin, dimethoxybenzene and phenylene spacer moieties. The syntheses of these electron transfer model systems utilized either a (2,5-dimethoxyphenyl)boronic acid or a boronic acid derivative of a 2,5-dimethoxyphenyl-substituted spacer compound which was subsequently coupled to either [5-(4'-bromophenyl) -10, 15,20-triphenylporphinato] zinc(LI) or 4-bromopyridine; the former species define compounds in which to probe the magnitude of electronic coupling between the meso-appended spacer moiety and the porphyrin carbon framework, while the latter constitute acceptor-modified, rigid axial ligands, that will facilitate a comparison of this coupling to that enabled by the zinc(II)-coordinated pyridyl moiety orthogonal to the porphyrin pi system. These compounds further underscore the utility of combining the modular syntheses of donor, acceptor and spacer molecules with Pd-catalyzed carbon-carbon bond forming reactions to elaborate porphyrin-based donor-spacer-acceptor systems. (C) 1998 Elsevier Science S.A. All rights reserved. [References: 51]