Silicon and Zinc Coordination to Peripheral Catechol Sites of (2,3,9,10,16,17,23,24-Octahydroxyphthalocyaninato)nickel(II). Phthalocyanine Coordination Chemistry at the Edge

(2,3,9,10,16,17,23,24-Octahydroxyphthalocyaninato)nickel(II)
(NiPc(OH)8) has been prepared by
demethylation
of (octamethoxyphthalocyaninato)nickel(II). Silylation
of peripheral oxygen atoms using
dimethyl-tert-butylsilyl
chloride gave
NiPc(OSi(t-Bu)Me2)8
as a convenient precursor to NiPc(OH)8 with high
solubility in hydrocarbon
solvents. The coordination properties of peripheral catechol sites
were investigated by treating NiPc(OH)8
with
TpCum,MeZn(OH). A model study was first
carried out by adding 5,6-dihydroxyphthalimide
(H2PhtCat) to TpCum,MeZn(OH). Partial deprotonation occurred to give
TpCum,MeZn(HPhtCat). Further deprotonation
with NMe4(OH)
gave (NMe4)[TpCum,MeZn(PhtCat)] as
the methanol solvate. 1H NMR spectra recorded on
TpCum,MeZn(HPhtCat)
show sharp resonances for equivalent arms of the TpCum,Me
ligand, while TpCum,Me resonances for
(NMe4)[TpCum,MeZn(PhtCat)] appear broadened by slow site exchange about the
strongly chelated catecholate ligand. Similarly,
the reaction between NiPc(OH)8 and
TpCum,MeZn(OH) occurred with partial
deprotonation to give NiPc(OH)4(OZnTpCum,Me)4. Structural characterization
on crystals obtained from acetonitrile showed that Zn ions bond
to
single ring oxygen atoms at two sites and that they chelate to adjacent
oxygen atoms at the other two ring sites.
Cumenyl i-propyl substituents of the
TpCum,Me ligands form hydrophobic pockets above and below
the central
metal of the phthalocyanine ring. These sites are occupied by
acetonitrile solvent molecules positioned with
hydrogen atoms directed toward the Ni atom in the crystal structure of
the complex obtained by crystallization
from a dichloromethane/acetonitrile solution. Addition of base to
NiPc(OH)4(OZnTpCum,Me)4
results in deprotonation
of the remaining four OH groups and substantial red shifts for
electronic transitions in the 400 and 600 nm
regions of the phthalocyanine ring. Broadened 1H NMR
resonances for arms of the TpCum,Me ligands point to
a
chelated structure for the Zn atoms of
(NMe4)4[NiPc(O2ZnTpCum,Me)4].