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Tetrakis(trimethylphosphane)cobalt(0) Preparation and Reactions.

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Tetrakis(trimethylphosphane)cobalt(O):
Preparation and Reactions
By Hans-Friedrich Klein['l
Only occasional complexes of zerovalent cobalt with phosphane ligands have been described so far". 'I. Attempts to
prepare them often gave, instead, phosphane-substituted
cobalt hydrides of the type (R,P),COH'~~.Since the CoH
stretching vibration of these compounds absorbs more or
less strongly according to the nature of the phosphane
ligands and in some cases cannot be observed at all, the
possible existence of phosphane-substituted cobalt(0) complexes under any conditions has been placed in doubt in
very recent publication^^^!
However, we have been able, for the first time, to obtain
paramagnetic tetrakis(trimethylphosphane)cobalt(O) ( I ) ,
by reduction of anhydrous cobalt halides with sodium
amalgam in presence of trimethylphosphane.
Coxz
+
4 (CH,)3P
+
2 Na(Hg)
THF
20%
After removal of volatile materials from the reaction
mixture, the compound ( I ) was extracted with hexane;
it crystallized at -50°C or was sublimed at 8O0C/1 torr.
In an atmosphere of nitrogen the dark brown needles
decompose only at 18C185"C and they dissolve very
readily in hydrocarbons, ethers, or other apolar solvents.
Cryoscopic determinations of molecular weight in benzene
gave the simple formula weight. Thus in solution ( I )
shows little of the tendency to dimerize that is observed
with, for instance, CO(CO),'~]and CO(PF,),[~].In accordance with this, NMR-spectroscopic determination of the
paramagnetic susceptibility'"] (in benzene containing 5%
of cyciohexane, at 30°C) gave a magnetic moment I .J of
1.70 B. M., as expected for the d9 configuration in a tetrahedral ligand field.
The intense EPR signal''] (at 77 "K, 1% in a toluene matrix)
shows complex hyperline structure caused by the cobalt
nucleus with 1=7/2. The total of 16 lines corresponds to
the two g factors that are expected under these conditions
and they imply Jahn-Teller distortion of the tetrahedron.
These details must be studied at still lower temperatures.
In the absence of a catalyst, ( 1 ) does not react with molecular hydrogen: However, if ( I ) is synthesized by the above
reaction in a H, atmosphere the ( I ) produced is accompanied by some [(CH,),P],COH[~' which becomes the
main product after 8 hours' reaction.
Solutions of ( 1 ) rapidly absorb one equivalent of nitric
oxide with formation of diamagnetic nitrosyltris(trimethy1ph0sphane)cobalt (2).
spectrum shows pseudotriplet structure for the (A&), - C,,
system of the phosphane ligands, lJAx+ JAx.I = 5.8 Hzr9].
In the IR spectrum the NO stretching vibration at 1605
cm-' is at the longest wavelength so far observed for
compounds of the type L,CO(NO)[''~.
The compound ( I ) reacts with azobenzene analogously
to tetrakis(trirnethylphosphane)nickel(O)*' 'I, giving a
quantitative yield of azobenzenebis(trimethy1phosphane)cobalt (3),which forms dark violet leaflets,m. p. 126-127°C
(dec.), from tetrahydrofuran.
'3
The LR spectrum of ( 3 ) differs only slightly from that of
the analogous nickel complex in the positions and intensities of the bands. This finding, together with the result
of magnetic measurements [p=2.02 B. M. for (311, indicates coordination of the cobalt only to the azo group,
without an additional o-bond to the ortho-position of a
benzene ring['31.
It is thus shown that not only are paramagnetic cobalt(0)
compounds with phosphane ligands surprisingly stable,
but also that they are amenable to replacement reactions
with retention of their paramagnetic valence state.
Received: February 22, 1971 [Z 381 IE]
German version: Angew. Chem. 83, 363 (1971)
[I]
J . Chatt, F. A. Hart, and D. 7: Rosevear, J. Chem. SOC.1961,5504.
[2] Th. Kruck and W Lang, Z. Anorg. Allg. Chem. 343,181 (1966).
[3] R. A . Shunn, Inorg. Chem. 9, 2567 (1970), and literature cited
therein.
[4] H . J. Keller and H. Wawersik, 2. Naturforsch. 20b, 938 (1965).
151 Th. Kruck, Angew Chem. 79, 27 (1967); Angew. Chem. internat.
Edit. 6, 53 (1967).
[6] Method of direct replacement as described by K . D.Bartle, D. W
Jones, and S. Maricic, Croatica Chem. Acta 40, 227 (1968).
[7] I thank Dr. H . J . Keller and Dr. D. N6the of the Institute of In-
organic Chemistry of the Technical University, Munich, for determining
the EPR spectra.
[8] H . F . Klein, Angew. Chem. 82,885 (1970); Angew. Chem. internat.
Edit. 9, 903 (1970).
[9] R. K . Harris, Can. J. Chem. 42, 2275 (1964).
[lo] W Hieber and K . Heinicke, Z. Anorg. Allg. Chem. 316,305 (1962).
[I13 H . F. Kiein and J . F. Nixon, Chem. Commun. 1971, 42.
[I21 H . F. Klein and H . Schmidbaur, Angew. Chem. 82, 885 (1970);
Angew. Chem. internat. Edit. 9,903 (1970).
[13] R. F. Heck, J. Amer. Chem. Soc. 90, 313 (1968).
Restricted Rotation in N-Silylated Hydrazines
By Otto Josef Scherer and Uwe BiiZtjer["
The compound (2) crystallizes as slightly sensitive red
needles (m. p. 107-108"C, from hexane) and can be sublimed without decomposition at 6 0 6 5 OC/l torr. The NMR
In continuation of our investigations concerning restricted
rotation around sulfur-['], arsenic- and antimony-nitrogen['] bonds in compounds containing as ligand to nitrogen an organic derivative of a Group IV b element, we have
studied N-silylated hydrazines of type (I).
[*] Prof Dr. 0. J. Scherer and Dipl.-Chem. U. Bultjer
Universitat Trier-Kaiserslautern
[*] Dr. H -i-. Ktein
Institut fur Anorganische Chemie der Universitat
87 Wurzburg, Rontgenring 11 (Germany)
Angew. Chem. internat. Edit. J Vol. 10 (1971)
1 No. 8
Present address: Institut Fir Anorganische Chemie der Universitat
87 Wurzburg, Rontgenring 11 (Germany)
343
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preparation, reaction, trimethylphosphine, cobalt, tetrakis
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