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Crystal and Molecular Structure of Tricarbonyl(hexaethylborazine)chromium(0).

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from the infrared data given in the Table. According to
previous analyses of the spectra of related complexes[g1,
these compounds contain OCIO, of C,, symmetry, and
( 4 ) and (5) an uncomplexed CIO,(T,) unit. The molecular
structures of (1) and (2) must prevail also in nonpolar
solvents as suggested by their electronic spectra in benzene,
which are identical with those of the respective complexes
in the solid state as well as very similar to the spectra
(solution and crystals) of the structurally well-established
tran~-[MA(C0)L,]['~.
Note also the striking solubility
difference in benzene between the ionic complexes [( 4 )
and ( S ) , insoluble] and the neutral species [ ( I ) and ( 2 ) ,
soluble]. The latter, by analogy with tr~ns-[MA(C0)L,][~~,
undergo oxidative addition reactions to produce sixcoordinated molecular complexes of tervalent metals['. '].
Perchloratodicarbonyltris(triphenylphosphane)cobalt(I)
(3), a five-coordinated complex, is obtained from a
benzene solution of the reactants and precipitated with
hexane.
[CoCI(CO),(Ph,P),]
+AgCIO,
-t
[Co(OCIO,)(CO),(Ph,P),1 +AgCI
(4)
It appears that the method of synthesis for ( l ) , (2), and
(3) represents a general route to organometallic
perchlorato compounds[' 'I.
Received: January 13,1971 [Z 417 IE1
German version: Angew. Chem. 83,497 (1971)
[l] L. Vaska and J . Peone, Jr., Suomen Kemistilehti, in press.
[2] L Vaska and J . W DiLuzio, J . Amer. Chem. SOC.83,2784 (1961).
[3] ( I ) and (2) can also be prepared from [MF(CO)(Ph,P),] and
NaCIO, [ 5 ] , but in poorer yields.
[4] L. Vaska, Accounts Chem. Res. I , 335 (1968), and references quoted
therein.
[ S ] L. Vaska and J . Peone, Jr., Chem. Commun. 1971,418.
[6] W Strohineier, Structure and Bonding 5, 96 (1968), and references
cited.
[7] J . Peone, J r . , Ph. D.Thesis, Clarkson College of Technology 1971.
[8] L. Vaska and D . L . Catone, J. Amer. Chem. SOC.88, 5324 (1966).
[9] H. Cohn, J. Chem. SOC.1952,4282; A . R . Dauis, C .J . Murphy, and
R . A. Plane, Inorg. Chem. 9,423 (1970); K . Nakamoto: Infrared Spectra
o f Inorganic and Coordination Compounds. 2nd ed. Wiley-Interscience,
New York, N.Y. 1970, pp. 175, 176, and references quoted.
[lo] Although we have thus far experienced no accidents in our work
with these complexes, it should be mentioned that crystalline trans[Ir(OC103)(CO)(Ph,P)2] reacts violently with chlorine gas. Needless
to add that all these materials are potentially hazardous and one should
employ only small amounts, avoid high temperatures and provide
adequate shielding and other protective measures. See M . Burton,
Chem. and Eng. News 28, No. 53, p. 55 (1970).
Crystal and Molecular Structure of
Tricarbonyl(hexaethylborazine)chromium(0)l**l
By Gottfried Huttner and Bernhard Krieg[*]
It is to be expected that investigation of the structure of
x-complexes of transition metals with heterocyclic x-ligands
will give an insight into the bonding in x-complexes,
[*] Dr. G. Huttner and Dip1.-Chem. B. Krieg
Anorganisch-Chemisches Laboratorium
der Technischen Universitat
8 Miinchen, Arcisstrasse 21 (Germany)
We thank the Deutsche Forschungsgemeinschaft for their support
and the Bayerische Akademie der Wissenschaften for computer time.
[**I
512
particularly on comparison with analogous complexes of
carbocyclic systems. Replacing a carbon atom by a hetero
atom amounts, in a first approximation, to a change in the
electron density distribution in the ligands, and the
influence of such changes can be studied in structural
investigations.
The first structure determination that we report in this
connection is the X-ray analysis of tricarbonyl(hexaethy1borazine)chromium(O), a compound that is isosteric with
tricarbonyl(hexaethylbenzene)chromium(O). Because of its
bulky ethyl groups, the complex is not the ideal representative of the borazine-metal n-complexes, but it was selected
for investigation because it is the onlv borazine complex
prepared so far that has been obtained in usable single
crystak-1.
The compound, [(C,H,),B,N,]Cr(CO),,
crystallizes in
the monoSlinic space group P2,/c, with a= 12.05, b= 17.88,
c = 14.79A, f3=138.6", d,,,,=1.214,
dexp=1 . 2 1 8 g ~ m - ~ ,
2 = 4 . The crystal used for the structure determination
measured 0.2x0.3 x0.4mm. For this, a total of 918
independent reflection intensities were measured on a
two-circle diffractometer with Mo,, radiation, h = 0.71069
A. The structure was solved by the heavy atom method and
refined to an R factor of 0.070 by successive approximations ; all the hydrogen atoms were located. The geometry
of the molecular skeleton (Fig. 1) corresponds to that of
tricarbonylbenzenechromium, as predicted by Werner et
a/.[']. However, the structure shows some peculiarities.
Q
Fig. 1. Molecular structure of tricarbonyl(hexaethy1borazine)chromium(0).
The idealized three-fold axis of the tricarbonylchromium
group is perpendicular to the borazine ring. The nitrogen
atoms of the ring are staggered with respect to the carbonyl
groups, and the N-Cr bonds are directed toward the
Cr-(CO) bonds. As in the tricarbonylchromium derivatives of I-methylpyrrole and 1,4-dimethyl-1,2-dihydropyridine, the nitrogen, as the ring atom with the highest
electron density, is trans to a carbonylo group"]. The
mean Cr-N distance amounts to 2.22 A ; this is co!siderably shorter than the Cr-B distances (mean 2.31 A,
Table 1); the difference between these bond lengths
corresponds approximately to the difference between
the covalent radii of boron and nitrogenc3' and it is thus
not permissible to conclude that the boron atoms are
bonded more weakly to the metal than the nitrogen atoms.
Angew. Chem. internat. Edit. 1 Vol. 10 (1971)
No. 7
The differing Cr-B and Cr-N
bond lengths lead to
puckering of the borazine skeleton. In contrast to the
situation in free hexaethylborazine, which is planar
within experimental errorc4], the two parallel planes
formed by the three boron :toms and the three nitrogen
atoms are separated by 0.07A. The six-membered ring thus
assumes a not very pronounced chair conformation (see
the torsion angles in Table I), which has an effect on the
positions of the ethyl groups. Whereas in free hexaethylb ~ r a z i n e ' the
~ ] ethyl groups project alternately above and
Table 1. Bond lengths, bond angles, and torsion angles in tricarbonyl(hexaethylborazine)chromium(O).
Bond lengrhs (A)
Cr-B(1)
Cr-B(2)
Cr-B(3)
2.30k0.02 Cr-N(l)
2.33 10.02 Cr-N(2)
2.31 k 0 0 2 Cr-N(3)
1.46i0.02 N(l)-B(2)
1 45 10.02 W)-B(3)
1.47_f0.02 N(3)-B(I)
B(l)-N(1)
B(2)-N(2)
BI3)-N(3)
2.23 k0.01
2.24 i0.01
2.18 kO.01
1 . 3 6 i 0.02
1.44 5 0.02
1.46 0.02
Bond angles (degrees)
N(l)-B(l)-N(3)
N(2)-B(2)-N
(1)
N (3)-B(3)-N (2)
~
.
- .
113+1 B(l)-N(l)-B(2)
1 1 6 5 1 B(2)-N (2)-B( 3)
115+1 B(3)-N(3)-B(I)
_____
12752
123+2
123+1
Torsion ;inglcs (degrees)
B(l)-N(l)-B(2)--N(2)
B(2)-N(2)-B(3)-N(3)
B(3)-N(3)-B(I)-N(l)
6 N(l)-B(2)-N(2)-B(3)
12 N(2)-B(3)-N(3)-B(I)
12 N(3)-B(l)-N(l)-B(2)
-
8
- 14
-
Stepwise Formation of Bridged Dinuclear
Carbonylmetal Complexes[']
By Heinrich Vahrenkamp and Wnfiied Ehrl[*l
Very few reports have hitherto appeared concerning metal
carbonyls in which two metal atoms are held together only
by an atom that behaves as a Lewis base; their synthesis,
e . g. that of (CO)sW-P(CH3),-Re(CO)sc21 gives rise to
difficulties. In contrast, dinuclear complexes exhibiting
considerable stability, such as (CO)4Fe-P(CH3)zP(CH3)2-Fe(C0),'3], in which the carbonylmetal groups
are linked cia diphosphanes or diarsanes, have been known
for some time. All known complexes of this kind are
symmetrical, i. e. two identical bridging atoms link two
identical metal atoms.
We have now accomplished the stepwise formation of such
complexes having two-membered bridges in which the two
metal atoms are different and the two bridge atoms are
also different. We started with derivatives of hexacarbonylchromium and hexacarbonyltungsten with dimethylphosphido and dimethylarsenido ligands. The reactive complexes (CO),M-E(CH,),-Sn(CH,),
(I), which are readily accessible photochemically, react with the halides
(CH,),E'CI to give the organometallic Lewis bases
(CO),M-E(CH,),-E'(CH,),
(3). Reaction of the complexes (CO),M-E(CH,),Cl
(2) with the tin compounds
(CH,),E'-Sn(CH,),
likewise leads to (3). Photochemical
reaction of compounds ( 3 ) with a hexacarbonylmetal
affords the dinuclear complexes ( 4 ) in good yield.
8
below the plane of the ring, in the complex the ethyl group
C(6)-C(16) breaks this alternation. This is possible because
the ring puckering increases the distance between the
methylene carbon atoms C(6) and C(3), and C(6) and C(1),
so that there is no longer strong steric hindrance between
their hydrogen atoms.
As in free borazine['], the bond angles N-B-N
(mean
value 115") are smaller than the B-N-B
anFles (mean
124"). The mean of the B-N separations (1.44A) does not
differ from that (1.435k0.002A) in the free borazine'".
However, one of the B-N distances (Table I),
at 1.36 A,
deviates appreciably from the mean value; a similar strong
deviation was foundc6' for the ring distances within a
n-bonded ring in the case of tricarbonyl(hexamethy1benzene)chr?miurn(O),where the C-C distances differ by up to
9/100A ; in neither case is there any immediately obvious
explanaLion of these observations. The Cr-C,,,
distances,
at 1.80A, are, within experimental error, the samt as in
tricarbonyl(hexamethylbenzene)chromium(O) (1.80 A) and
indicate a similar donor/acceptor behavior of benzene and
borazine.
Received: April 22, 1971 [Z 424 IE]
German version: Angew. Chem. 83, 541 (1971)
[l] H . Werner, R. Piinz, and E . Deckelmann, Chem. Ber. 102,95 (1969).
[Z] G. Hutrner and 0. S . Mills, unpublished.
[3] L. Parrliriy: The Nature of the Chemical Bond. Cornell University
Press, Ithaca, New York 1960.
[4] M . A . Viswamirra and S. N . Vaidya, Z. Krist. Z21, 472 (1965).
[S] W Harshbarger, G. Lee, R. F. Porrer, and S . H . Bauer, Inorg. Chem.
8, 1683 (1969).
[6] M . F. Bailey and L. F. Dahl, Inorg. Chem. 4, 1298 (1965)
[ 7 ] H. Werner, personal communication
Angew. Chem. inlernal. Edit. 1 Vol. 10 (1971) 1 No. 7
Each one of the ten conceivable complexes ( 4 ) with
M = Cr or W and E = P or As has been prepared (see Table).
( 4 a ) - ( 4 c ) have already been describedc4! According to
this method, ( 4 e ) - ( 4 j ) can be prepared by two analogous
routes depending on the reactants.
-r---
Table Properties of compounds ( 4 )
r-
i
~
~
M P'
'H-NMR [a]
IM E E M I ( C)lb(E-CH3) J(P-H)
6(E-CH3)
-- -
J(P-H)
- 1.04
-1.14
- 1.05
- 1.14
- 1.00
- 1.08
- 1.14
- 1.23
7.8
8.2
8.0
6.3
~-
[a] Recorded in benzene; chemical shifts in ppm (TMS internal standard); coupling constants in Hz.
[*] Dr. H. Vahrenkamp and DiplLChem. W. Ehrl
Institut fur Anorganische Chemie der Universitat
8 Miinchen 2, Meiserstrasse 1 (Germany)
513
-
~
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crystals, structure, molecular, tricarbonyl, hexaethylborazine, chromium
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