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New Results in the Chemistry of Chromium.

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New Results in the Chemistry of Chromium
Reactions of Boron Compounds with Metal
Chelates and CheIating Agents
By H . L. Krauss [*I
By F. Um/and[*J
1. Chromium peroxides
CrC13 or CrC13.aq in tetrahydrofuran reacts with an excess
of concentrated Hz02 to form first CrCI3.3THF and then a
deep blue chromium(v1) peroxide. The blue compound is
spectroscopically identical with “CrOS”, which is quite stable
in THF. The substance shows the same broad absorption
maximum at 580 nm in water, ether, alcohol, and THF.
Electrophoresis of “CrOs” in THF/HzO/HzOz with LiC104
as conducting salt showed, surprisingly, that the blue compound is anionic. It is assumed that the anions Cr06H- and
Cr05X- [1**1 are present, their absorption being identical
with that of CrOs (at the same pH).
Decomposition of “CrOs” in water (PH = 1)with an excess of
H202 [eq. (a)] or of chromate [eq. (b)] gives different amounts
of oxygen but with the same rate of reaction:
Cr@Cr&-
+ 5 H202 + 8 H+
+ 3 H z 0 +~ 8 H+
+ 9 H20 f 4 Oz
2 Cr3++ 7 H20 + 3 0 2
+ 2 Cr3+
(a)
+
(b)
The rates of reactions (a) and (b) are determined by attack of
the protons; the rate of decomposition is thus dependent on
the proton concentration. The apparent catalytic decomposition of Hz02 is explained by a redox reaction between
chromium peroxide and hydrogen peroxide.
Phenylboric acids, PhzBOH and PhS(OH)z, react with
chelating agents to form chelate rings with quadri- or triligating boron. From consideration of the bond angle
between the ligands on the boron and the bond angle in the
ring it is to be expected that quadriligating boron will be
favored in five-membered ring chelates because of the tetrahedral angle (% 105O; cf. bond angle in the ring 10S0),
whereas triligating boron (120 ”) should be favored in sixmembered-ring chelates. Five-membered diphenylboron chelate rings occur with, e.g., 8-hydroxyquinoline or nitrosophenylhydroxylamine“1. Quasiaromatic systems,however,always
lead to great stability, independently of the bond angles. Thus
the diphenylboron chelate of o-aminophenol splits off benzene, with formation of 2-phenyl-1,3,2-oxazaboroline(1).
Very stable quasi-aromatic six-membered ring compounds of
PhzBOH are obtained with chelating agents such as salicylaldehyde or the corresponding azomethines 121. The hydroxydiphenylboron-salicylaldehydechelate is suitable as a reagent
for primary amines; NH3, NHzOH, and NHzNHz also
react. Loss of benzene and formation of boric acid derivatives
occur only when a more condensed ring system can be
obtained, e.g., with hydrazine, giving (2). Free boric acids
also give chelates of these types [31.
B
2. Surface Chemistry of Chromium
In continuation of work concerned with chromium(v1) and
chromium(u1) compounds on the surface of amorphous
aluminum silicates with various Si/Al ratios the magnetic
and the optical behavior have been studied at various temperatures, oxygen partial pressures, and concentrations. In
all cases it was possible to distinguish chromium chemisorbed
on the surface from that retained in capillaries.
Only the surface chromium has catalytic activity, e.g. for
polymerization of ethylene. With corresponding supply of
oxygen and on “activation” at 400 to 600°C the oxidation
number of surface chromium always lies between 5 and 6 ,
the highest value (5.95) being achieved on pure SiOyaq.
Comparison of quantitative ESR measurements with the
analytical findings shows that the paramagnetic components
appearing in surface chromium cannot be identical with
chromium(v). It is assumed that the ESR-active species
consists of chromium(u1)ions in special crystal environments ;
the band form leads to the same conclusion.
The redox reactions were studied optically by use of a hightemperature cell for reflection measurements in the visible
and near-IR region. This work gave complete agreement with
the analytical results concerning the reduction-reoxidation
sequence in the activation process. Chromium(v1) is present
as dichromate in the active material. The catalytic reaction
with ethylene was also studied optically. The initial step
clearly consists in reduction of the surface chromium(vr),
which leads to formation of the catalytically active centers.
[VB 63 IE]
Lecture at Kiel on December 15th, 1966
German version: Angew. Chem. 79, 538 (1967)
[*] Prof. Dr. H. L. Krauss
Anorganisch-chemisches Laboratorium
der Technischen Hochschule
Arcisstr. 21
8 Munchen 2 (Germany)
[I J W. P . Griflith, J . chem. SOC.(London) 1962, 3948.
[2] D. G . Tuck,J. chem. Soc. (London) 1965,5753.
574
However, when o-aminothiophenol is used as amine component, a diphenylboron chelate (3) of the benzothiazole is
formed with evolution of hydrogen.
The PhzBf group may replace the proton of metal chelates
of the bis(dimethylglyoxime)nickel(n) type, Ni(DMGH)z,
containing an intramolecular hydrogen bridge L41. A special
study was made of whether analogous cationic complexes
with triligating boron can be prepared. So far the following
a boroxole
types are known: [Ni(DMG)z(BOH)z]~[B~06]2with
anion, [N~(DMC)~P~Z(BOH)Z]C~Z,
and [Ni(DMG)3(BPh)z1.
Attempts to introduce elements othgr than boron into
Ni(DMGH)Z succeeded with SnV1, the trinuclear complex
[(HDMG)Ni(DMG)SnClz(DMG)Ni(DMGH)J being formed.
Lecture at Marburg on February 3rd. 1967
[VB 64 IE]
German version: Angew. Chem. 79,583 (1967)
I*] Prof. Dr. F. Umland
Anorganisch-chemisches Institut der Universitat
Hindenburgplatz 55
44 Munster (Germany)
[l] F. Umland and C. Schleyerbach, Angew. Chem. 77, 169
(1965); Angew. Chem. internat. Edit. 4,151 (1965).
[2] F. Umland and C. SchIeyerbach, Angew. Chem. 77, 426
(1965); Angew. Chem. internat. Edit. 4, 432 (1965).
[3] F. Urnlandand B. K. Poddar, Angew. Chem. 77, 1012 (1965);
Angew. Chem. internat. Edit. 4, 958 (1965).
141 F. Umland and D.Thierig, Angew. Chem. 74, 388 (1962);
Angew. Chem. internat. Edit. I , 333 (1962).
Angew. Chem. internat. Edit.
Vol. 6 (1967) /No.6
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