Selective oxidation of Mo(CO)3 complexes of
tritertiary 1,5,9-triphosphacyclododecane macrocycles (R3L)
by
halogens (X2 = Cl2, Br2,
I2) to Mo(II) triphospha macrocycle complexes of the
type (R3L)Mo(CO)2X2 [R
=
(CH3)2CH (2),
(CH3)3SiCH2 (3),
C2H5 (4),
(CH3)2CHCH2 (5)]
allows the high yield and stereoselective liberation
of the corresponding tritertiary macrocycles
[syn,syn-R3L, R =
(CH3)2CH (6),
(CH3)3SiCH2 (7),
C2H5 (8),
(CH3)2CHCH2 (9)] in good yield (75−80%) by
digestion in strong base. This method fails for the parent
trisecondary
macrocycle (H3L) and also for the intermediate Mo(II)
salts,
[(R3L)Mo(CO)3X]A-
[X = halide, A- = halide,
BPh4 (1)]. Addition of halogen to
(H3L)Cr(CO)3 gives rise to the new
blue-violet complexes
(H3L)Cr(CO)2X2
[X = Cl2 (11), Br2
(12)]. Paramagnetic susceptibilities indicate that
11 and 12 are low-spin d4 six
coordinate
dicarbonyl halo−halide complexes of the type
[(H3L)Cr(CO)2X]X. In this
case, the trisecondary 1,5,9-triphosphacyclododecane (H3L, 13) may be
liberated stereoselectively and in reasonable yield (60−70%)
from
11 or 12. The macrocycles may alternatively
be liberated from the Mo(II) dihalo complexes by action of
CN-.
The free trisecondary macrocycle can be alkylated
nonstereoselectively to give the tritertiary macrocycles
[syn,anti-R3L; R = CH3 (24),
C2H5 (8b),
(CH3)3C (25)]. The inversion
of phosphorus in the syn,syn isomer 8 to
its
syn,anti analogue, 8b, was shown to be slow
at 156 °C. Exhaustive oxidation of the Mo(0) macrocycle
complexes
with H2O2 or O3 results in
liberation of the corresponding macrocycle trioxides in good yield.
All free macrocycles
(and oxides) have been characterized by spectroscopic methods and as
the hydrochlorides for selected ligands.