FORMATION OF ETA(2)-AROYL, ETA(1)-HALOGENOCARBYNE OR STERICALLY CROWDED ARYLDIAZENIDE LIGANDS IN THE REACTIONS OF RING-SUBSTITUTED TRICARBONYL[HYDROTRIS(PYRAZOLYL)BORATO]-MOLYBDATE AND TRICARBONYL[HYDROTRIS(PYRAZOLYL)BORATO]-TUNGSTATE ANIONS WITH ARENEDIAZONIUM CATIONS AND RELATED OXIDANTS
Fj. Lalor et al., FORMATION OF ETA(2)-AROYL, ETA(1)-HALOGENOCARBYNE OR STERICALLY CROWDED ARYLDIAZENIDE LIGANDS IN THE REACTIONS OF RING-SUBSTITUTED TRICARBONYL[HYDROTRIS(PYRAZOLYL)BORATO]-MOLYBDATE AND TRICARBONYL[HYDROTRIS(PYRAZOLYL)BORATO]-TUNGSTATE ANIONS WITH ARENEDIAZONIUM CATIONS AND RELATED OXIDANTS, Journal of the Chemical Society. Dalton transactions, (10), 1995, pp. 1709-1726
Although the hydrotris(pyrazolyl)borato complex [Mo{HB(pz)(3)}(CO)(3)]
(-) reacted with 3- or 4-substituted arenediazonium cations [R'N-2](+)
yielding carbonyl-substitution (ie, aryldiazenido) products [Mo{HB(pz
)(3)}(CO)(2)(N(2)R')], reaction of the methyl-substituted analogue [ML
(CO)(3)](-) [L* = tris(3,5-dimethylpyrazolyl)hydroborate: M = Mo or W
] led, via oxidative formation of aryl radicals and [ML(CO)(3)](.), t
o eta(2)-aroyl complexes [ML(CO)(2)(eta(2)-COR')] [R' = C(6)H(4)X-4 (
X = NO2, CN, COMe, CF3, H, Me, OMe or NMe(2)) or C(6)H(4)X-3 (X = NO2
or OMe)] in acetonitrile or to the halogenocarbyne complexes [ML(CO)(
2)(=CX)] (X = Cl, Br or I) in the presence of the halogenoalkanes CH2C
l2 or CHX(3) (X = Br or I). The complex [MoL(CO)(3)](-) reacted simil
arly with diphenyliodonium or triphenylsulfonium cations, but in the l
atter case anion-cation redox is very slow in the dark but rapid upon
irradiation with sunlight. Comparison of these results with those obta
ined for [ML(CO)(3)](-) analogues with different substituents in the
pyrazolyl rings demonstrates that oxidation of the former by arenediaz
onium cations occurs in response to the steric rather than the electro
nic effect of the 3-methyl substituents. However further steric crowdi
ng in either the hydrotris(pyrazolyl)borate ligand or the diazonium ca
tion promotes a reversion to the carbonyl-substitution pathway. A mech
anism to account for these observations is proposed. Attempts to exten
d the chlorocarbyne synthesis to systems other than [ML(CO)(3)](-) me
t with only limited success. Spectroscopic data for the new complexes
are reported and discussed. Two aryldiazenido complexes, [MoL(CO)(2)(
N-2,R')] (R' = 2.6-Me(2)C(6)H(3) or 2,3-dimethyl-5-oxo-1-phenyl-3-pyra
zolin-4-yl) have been characterised by single-crystal X-ray diffractio
n studies and are found to differ in the manner in which the aryldiaze
nide ligand accommodates to steric crowding in the molybdenum co-ordin
ation sphere.