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Arsinidene Complexes Structure and Electronic Spectrum of C6H5As[Cr(CO)5]2.

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(1 1 7;)of analytically pure product after removal of solvent and
recrystallization from 5 ml CH 2C12/25 ml n-pentane at - 78 "C.
Received: January 31, 1975;
revised: March 19. 1975 [Z 215 a IE]
German version: Angew. Chem. 87,454 (1975)
CAS Registry numbers:
(OC),CrAs(C,H,)H,, 55590-60-8; 11-bulyllithium. 109-72-8;
(OC),CrAs(C,H,)Li,. 55590-59-5; N.N-dichlorocyclohexylamine
26307-01 -7; C,H SAs[Cr(CO),],, 5590-56-2
[I]
[2]
[3]
[4]
[S]
A . Ecker and U . Schmidf, Chern. Ber. 106, 1453 (1973); and references
cited therein.
0.M. Nrfedow and M. N . Manakoiv. Angew. Chem. 78. 1039 (1966);
Angew. Chem. internal. Edit. 5. 102) (1966).
G . Huttner and H:G. Schmid. unpublished.
An analysis of the IR spectrum of CbH5AsH2is reported by H . Stenzenhacher and H . Schindlhauer, Spectrochim. Acta 26 A, 1713 (1970).
G . Hufftier,J . L'OII Sryrri, M. Marsiii. and H.-G. Schniid. Angew. Chem. 87.
455 (1975);Angew. Chem. internat. Edit. 14.434 (1975).
Arsinidene Complexes: Structure and Electronic
Spectrum of C,H,As[Cr(CO),] 7[*t1
By Gotrfried Huttner, Joachini iwn Seyerl, Mario Marsili, and
Hans-Georg Schmidr'l
A structure having a multiply bonded arsinidene bridging
ligand has been considered for phenylarsinidenebis(pentacarbonylchromium), which can be prepared by demetalation of
(OC),CrAs(C,H s)Lil" :
The structure of ( 1 ) depicted in Figure 1 corresponds to
the proposed formulation, and exhibits the following features:
1) The arsenic has trigonal-planar coordination. Compound
( I ) is thus the first example of As' having this coordination
geometry.
2) The arsenic-chromium bonds having an average iength
of 238 pm clearly contain a significant x-bonding component.
They are considerably shorter than the A s - C r single bond
in (OC),Cr-As(CH,),-Mn(CO)s~ which contains a tetrahedrally coordinated dimethylarsenido bridge hgdnd with ii
Cr-As bond length of 252 pni['l. Even complexes having terminally bonded arsane ligands, in which the Cr-As bond
length should experience considerable shortening by dx-da
back bonding, display significantly longer Cr-As bond
lengthsI4*'I.
3 ) The observed torsional angles of the substituents Cr(CO),
and CbHs about the As-Cr and As<
bonds correspond
to a particularly favorable steric arrangement: the plane of
the phenyl substituent is rotated through 42" relative to the
coordination plane of the arsenic. The coordination of the
chromium atoms is pseudo-octahedral (maximum deviation
of the bond angle from 90 or 180" is 2"); those equatorial
axes of the chromium octahedra which lie closest to the coordination plane of the arsenic are displaced by 27" in opposite
directions relative to this plane.
The trigonal-planar coordination of the arsenic and the
short Cr-As bond lengths indicate that the electron deficiency
of the sextet ligand CbHs-AS: is compensated by chromiumdn-arsenic-prc back bonding in ( 1 ).
The Cr-As-Cr
grouping can therefore be approximately
described by a model of a three-center 4x system, which
can also serve as a basis for qualitative interpretation of
the unusual UV spectrum of ( 1 ) (Fig. 2).
Electronic spectrum of C,H,As ICrlCOI,lI
Since this novel structure could not be proved by spectroscopic studies we have carried out a structural analysis of (I)[*].
20000
10000
Fig. 2. Electronic spectrum of C6HsAs[CrlCO).
Fig. 1. Structure of ( 1 ) . a complex with arsenic(1) in trigonal-planar coordination.
I*]DOT Dr. Ci. Huttner. J . von
Seyerl. M . Marsili. and H.-G. Schniid
Anorganisch-chemisches Laboratorium
Fachbereich Chemie der Technischen Universitat
8 Munchen 2. Arcisstrasse 21 (Germany)
[**I
This work was supported by the Deutsche Forschungsgemeinschaft
and the Fonds der Chemischen Industrie.
434
f / i
At 16070cm - ', in a region where other pentacarbonylchromium ligand complexes show no absorption (see comparison
spectrum of (OC)5CrAs(C(,Hs)H2in Fig. 21, the spectrum
of ( I ) contains a very intense absorption band
( E = 20000 1 mol- ' cm ')I6]. The new band can be assigned
to an electronic transition from the ground state to the first
excited state of the three-center 47c system Cr-As-Cr (see
Fig. 2). The character of this transition corresponds to a
charge-transfer from the metal atoms to the ligand, since
although the p-orbital of arsenic participates in the lowest
~
unoccupied molecular orbital it is not Involved in the highest
occupied molecular orbital. Support for this interpretation
comes from the high molar extinction of the observed band.
The arsinidene complex ( I ) is the first representative of
a new class of compounds in which arsanediyl groups R-As:
are stabilized by metal-dx-arsenic-px multiple bonds.
Received: March 19, 1975 [Z 215b IE]
German version: Angew. Chem. 87,455 (1975)
CAS Registry numbers:
i l l . 55590-56-2: (OC),CrAs(C,H,)H,.
[I]
[2]
131
[4]
[5]
[6]
55590-60-8
G. Hutrner and H . 4 . Schmirl. Angew. Chem. N7. 454 (1975): Angew.
Chem. internat. Edit. 14,433 (1975).
R , =0.058; the structure was solved usmg a Syntex P 2 i diffractometer
with the Syntex XTL structure-solving system.
H . Vuhrmkump, Chem. Ber. 105, 1486 (1972).
C . B. Roberrson, P. 0.W b i m p , R. Colron, and C . J . R i x . Chem. Commun.
IY71. 573.
1. W Nowell and J . Trotrrr, J. C. S. Dalton 1972. 2378.
Since the solutions of the substance decompose during measurement,
the value given represents a lower limit.
Fig. 1. Projection of ( I ) perpendicular to the S4 axis: hydrogen bonds
(---).The most important bond lengths are N(21)-C(I) 1.364(4),N(21)-C("'
1.384(4), C(I)-C(2) 1.396(5), C(2)-C(3) 1.402(5), C(3)-C(4) 1.401(5), C(4)C(5) 1.441(5). C(5)-0(5) 1.232(5).&.
Structure of Octaethylxanthoporphinogen
Dihydrate [***I
By William S. Sheldrick and Jurgen-Hinrich Fuhrhop"]
Xanthoporphinogens (Greek xanthos = yellow, porphinogen
= porph(yr)in producer) were first obtained by Fischvr and
Treibs in 1927 by oxidation of porphyrins with lead dioxide,
the yield being almost quantitative[']. The stimulus to this
surprisingly successful experiment came from dehydrogenation
experiments on indigo whose structural relation to the porphyrins was at that time considered possible. It was only
40 years later that the structure of these easily crystallizable
compounds was elucidated as tetraoxoporphinogens, e. g. (I),
S, symmetry (see Fig. 1). The oxygen atoms of the bonded
water molecules lie on the S, symmetry axis above and below
the porphinogen. The atoms bound to a bridging carbon
atom. e. 9. C(5), form dihedral angles of -8.9 or 41.6 with
the planes of the neighboring pyrrole rings.
W
Fig. 2. Projection of ( I J (without the ethyl-carbon atoms) perpendicular
to [OIO].
by Inhoffiw et ul. who used spectroscopic methods[*]. It was
then noted that two molecules of water of crystallization
could not be removed even by heating in a high vacuum
at 150°C; such stable hydrates have never been observed
among porphyrins.
( 1 ) forms otetragonal crystals, I4'/a, with a = 13.801(1),
c=18.575(6) A ; Z = 4 ; dca,c,=l.19g cm-3. The structure was
solved by direct methods[31and refined for 11 15 independent
reflections (four-circle diffractometer, F 2 2.5 o ( F )to R =0.075,
Rti=0.073. All the hydrogen atoms could be located in a
difference Fourier synthesis and were therefore included logether with individual isotropic temperature factors in the last
cycles of refinement. All the other atoms were assigned anisotropic temperature factors. The molecule has crystallographic
[*] Dr. W. S. Sheldrick [ +] and Doz. Dr. J.-H. Fuhrhop
[**I
Gesellschaft fur Molekularbiologische Forschung mbH
33 Braunschweig-Stockheim. Mascheroder Weg 1 (Germany)
[ + ] T o whom correspondence should be addressed.
[**I lnstitut f u r Organische Chemie A der Technischen
Universitit
33 Braunschweig. Schleinitzstrasse (Germany)
[***) This work was supported by the Ministerium fur Forschung und
Technologie as part of the Technology Program, by the Deutsche Forschungsgemeinschaft, and by the Fonds der Chemischen Industrie.
The protons on the two opposing nitrogen atoms N(21)
and N(23) lie 0.071 8, above the imaginary plane of the molecule, whilst the protons on N(22) and N(24) lie the same
distance below the plane. One water molecule lies exactly
perpendicularly 2.216A above the center of this plane, and
a second similarly below it, the oxygen atoms of these water
molecules being each linked by hydrogen bridge bonds to two
NH protons (separations NH...O 3.016, N-H
0.92,
O...H=2.138,) . Weattribute the twisting of the chromophore
mainly to formation of these four hydrogen bridges. The
appearance of these bridge bonds which, as mentioned above,
are not observed in the related porphyrins, can be explained
as being due to the relatively high acidity of a-acyl-substituted
pyrroles.
A second effect of the water of crystallization-one that
to the best of our knowledge has never been observed beforeis the formation of a clathrate-like crystal structure (Fig. 3).
The protons of the water molecules form hydrogen bonds
to the carbonyl-oxygen atoms of the bridges in the chromophore (I). In this way each of the four hydrogen atoms
of the two water molecules interacts with a different ketoneoxygen atom of a neighboring molecule, so that each xanthoporphinogen dihydrate is linked to four other similar molecules. Each chromophore molecule thus fixes two porphinogen
435
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arsinidene, structure, spectrum, electronica, c6h5as, complexes
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