Cs. Velazquez et al., STAR PORPHYRAZINES - PERIPHERAL CHELATION OF PORPHYRAZINEOCTATHIOLATEBY DIPHOSPHINONICKEL IONS, Journal of the American Chemical Society, 115(22), 1993, pp. 9997-10003
We have synthesized new pentametallic macrocyclic complexes based on t
he polynucleating ligand, porphyrazine-2,3,7,8,12,13,17,18-octathiolat
e, (pzot)8-. This ligand can be thought of as a porphyrazine (tetraaza
porphyrin) bearing four dithiolene moieties peripherally at the beta-p
yrrole positions, and we show that a transition-metal ion can be chela
ted to each of the four peripheral dithiolene moieties. The complexes
[(P-P)Ni]4[Ni(pzot)] (2a, P-P = dppe; 2b, P-P = dppy; 2c, P-P = dppb;
2d, P-P = dcpe) have been synthesized and characterized. Complex 2a cr
ystallizes in the orthorhombic space group Cmc2(1) (No. 36) with 4 mac
rocycles and 16 solvent molecules (N,N-dimethylformamide) in a unit ce
ll of dimensions a = 24.630(5) angstrom, b = 20.607(4) angstrom, c = 3
0.675(6) angstrom. The [Ni(pzot)]8- ligand in 2a coordinates four Ni(P
-P) moieties around its periphery with the two thiolate sulfur atoms o
f each pyrrole binding a nickel ion in a bidentate (S-S) coordination
mode. This is in contrast to the reaction of [Ni(pzot)]8- with SnR2X2,
which yielded Ni(pzot)(SnR2)4 (1), where each tin is coordinated in t
he tridentate (S-N-S) mode, with the thiolate sulfur atoms from two py
rroles and one m-nitrogen atom as ligands from the macrocycle (Velazqu
ez, C. S.; Fox, G. A.; Broderick, W. E.; Andersen, K; Anderson, O. P.;
Barrett, A. G. M.; Hoffman, B. M. J. Am. Chem. Soc. 1992, 114, 7416-7
424). Comparison of the crystal structures of 1,2a, and uo(octakis(met
hylthio)porphyrazinato)magnesium(II) (Mg(omtp)), a structurally uncons
trained reference compound with eight peripheral methylthio groups, sh
ows that [Ni(pzot)]8- adjusts to accommodate either the (S-S) or (S-N-
S) modes of coordinating the metal ions at the periphery by a swing of
the C(beta)-S bond. H-1 and P-31 NMR studies have been used to determ
ine the nature of the coordination of the Ni(P-P) units to the [Ni(pzo
t)]8- macrocycle in solution. Model compounds were synthesized as stru
ctural references to mimic both possible coordination sites of the [Ni
(pzot)]8- ligand. The H-1 and P-31 NMR chemical shifts of macrocycles
2a-d and their respective bidentate model complexes clearly indicate t
hat the macrocycle in solution also binds the Ni(P-P) units in a biden
tate fashion. The electronic absorption spectra of complexes 2a-d show
a red-shift of the absorbance in the Q-band region due to interaction
of the porphyrazine pi-system with the four peripheral metal ions.