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Diphosphane-Transition Metal Complexes P2H4[Cr(CO)5]2 and P2H4[C5H5Mn(CO)2]2.

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published studies on ( 1 ) areall characterized by the following features: 1) the samples contained large proportions
of contaminants, e. y. up to 80 % of NH,; 2) the IR spectra
were so poorly reproducible that agreement could not
be reached even about the strong bands; 3) the theoretically
required number of absorptions has never been found
in the IR or UV spectra of (1 ). Thus it is hardly surprising
that the cis structure ( 1 a)['], the trans structure (1 b)I3l,
and even mixtures of
have all been deduced from
the existing spectroscopic data. Other structures, such as
( I c), were ruled out only for chemical reasons; in no
case has an unambiguous assignment of all the vibrational
frequencies of { 1 ) been possible.
H
However, unequivocal statements concerning the vibrational frequencies and the structure of ( 1 ) become possible
with the IR spectra of the p-diimine complexes
N~H2[Cr(C0)5]2 ( 2 ) , N2D2[Cr(C0)5]2 ( 3 ) , and
15N2H2[Cr(C0)5]2( 4 ) . Complex (3) is obtained from
(2) by H/D exchange with CH30D, while ( 4 ) is prepared
by the same method as (2)c51 but with "N-labeled NzH4.
H/D exchange with (2) and (3) proceeds so rapidly that
protons are repeatedly reintroduced into pure ( 3 ) .
The characteristic absorptions of the Cr(C0)5 groups,
whose assignment is established by comparison with other
compounds, appear in ( 2 ) . ( 3 ) . and ( 4 ) at the same frequencies. Their number, position, and intensity in the solid
and in T H F solution (vC0: 20055 w, I950 vs, 1923 s cm- I )
indicate an almost undistorted C4" symmetry of the
Cr(C0)5 groups and justify the assumption of local symmetry for the N2H2 ligands too. Cr(C0)5 groups show no
(typical) absorptions between 4000 and 2100, and 1800
and 700 cm- respectively; for this reason alone the bands
appearing in these regions can be attributed to the diimine
ligands. This assignment is supported by the spectra of
the isotopically labeled compounds.
Since the selection rules require that 5, 3, and 2 normal
modes of ( I a ) , ( 1 b ) , and ( 1 c), respectively, be IR active,
the number of bands observed indicate that ( 1 ) has the
cis form ( I c) in the complex ( 2 ) . Particularly Characteristic
of ( 1 a ) is the occurrence of an N=N stretching vibration
which is IR inactive in ( 1 b ) and ( 1 c). This constitutes
the first spectroscopic proof for diimine in the cis form,
corresponding to the proposed structure ( 2 a ) for the,
complex ( 2 ) .
Table I . IR frequencies ( K B r : c m - ' ) of the diimine ligands
plexes(2). (3!.and ( 4 1 .
3480
3250
1415
1352
I I05
2445
2380
1415
998
820
in
the com-
3435
3250
I370
I350
I105
observed at 1385cm-I. The other N2H2 vibrations, however, display a remarkable lack of sensitivity to changes
of the central metal and display practically the same frequency in ( 2 ) as in ( 5 ) ; they thus represent almost pure
diimine vibrations.
A close relationship betweCn the vibrational frequencies
of complexed and free diimine is clearly apparent. A series
of observationsl61 suggests that diimine most probably
forms strong hydrogen bonds with Lewis bases in the
solid state. Such a Lewis base may be diimine itself ( 1 (1)
or ( 1 e ) or, for example, NH3 (If).
Solid state IR spectra, even of pure diimine[6bl,can therefore only be expected to display frequencies that are shifted
relative to those of free diimine. Association as in ( I d ) (If') is ruled out for the diimine in (2) which can thus
be regarded to a first approximation as free ( 1 embedded
in a matrix of Cr(CO), molecules.
Received. September 17. 1973 17 929c IF]
Germao version: Angew. Chem. H i . 1122 I 1973)
[ I ] Reactions ofComplexed Ligands, Part 12. This work was supported
by the Deutsche Forschungsgemeinschaft.-Part
I 1 : D S d / t n m ~ ~1.
.
B r m d l , and R . E i d d l . Angew. Chem. X i , l 1 ? 1 (1973): Angcw. Chem.
internat. Edit. 12, 1019 (1973).
[2] t.J . HUIIand B. F . Ho(hhrinirr. 1. Chem Phys. 41. I174 (1964).
[3] 4. Trombrrfi, Can. J. Phys. 46. I005 (1968); J. Chem. Soc. A 1971,
1086.
[4] K . Roserigrrri and G C Pimrntrl. J. Chcrn Phys. 4 3 . 506 (1965).
[5] D. Srllrnrrnn. A . Brondl. a n d R . Endrii, J. Organometal. Chem. 4Y,
C 2 2 (1973).
[6] Cf.: a) S. Hiinig, H . R. Mirller, and W Thirr, Angew. Chem. 77,
368 (1965): Angew. Chem. internat. Edit. 4. 271 (1965): b ) N. Wihrrg,
H . Bac.hhirhrr. and G. Fisther, rbid. 84. 889 (1972): 11. X29 (1972).
[7] T h e spectra are illustrated in a review: D Scdlniunn, Angew Chem.,
in press; Angew. Chem. internat. Edit., in press.
Diphosphane-TransitionMetal Complexes:
P2H4[Cr(C0)5]2 and P2H4[CsHsMn(C0)2]2[ ' I
By Dieter Sellmunn[*l
The frequencies observed['' for the diimine ligands in ( 2 ) ,
(3), and ( 4 ) are listed in Table 1.
Thus, contrary to previous observation^[^-^^, the NH
stretching vibrations have values to be expected for NH
compounds, and particularly for those in which the N
atom participates in multiple bonds. Surprisingly. the isotopic shifts agree fairly accurately with the values calculated
for freediimine; nevertheless, the N=N and Cr-N stretching vibrations are probably coupled, since the (N=N)
vibration in N2H2[W(C0)5]2 (5), an analog of ( 2 ) , is
1020
Spontaneous combustion in air, thermolability, extreme
sensitivity to light, and toxicity make disphosphane, P2H4,
a substance that can be handled only when special safety
precautions are enforced. However, for studying the reactivity of complexed molecules such properties-apart from
toxicity-are often highly desirable. They favor reactions
under conditions which are mild enough to prevent breakage of the metal-ligand bond.
~~
p]
Dr. D. Sellmann
Anorganisch-chemisches Lahoratorium der Technischen Universitit
8 Miinchen 2, Arcisstrasse 21 (Germany)
Anyew. Chrin. infernat. Edit. J Vol. I 2 (1973)
J No. 12
It has now become possible, for the first time, to complex
P,H, with a transition metal. Compared to the instability
of the free molecule, the diphosphane complexes are surprisingly stable.
Reaction of P2H4121according to eq. (I),
removal of the solvent at - 30 C/10- torr, and threefold
recrystallization of the residue from tetrahydrofuran (THF)
at -78 C affords the T H F adduct of the P2H4-bridged
complex ( 2 ) as colorless crystalline needles, which on
drying (20 C/10-3 torr) decompose to a yellow powder,
the analytically pure diphosphanebis(pentacarbony1chromium) (2).
( 2 ) is soluble in THF and in acetone, but insoluble in
non-polar solvents; in the solid state it is converted into
brown or green decomposition products, only after several
hours exposure t o light or air respectively. lt?tvr triitr,
(OC)SC'rPH, (3)l41 could be detected in the brown products. ( 2 ) melts at 165-168 C with decomposition to
a black liquid, which, on further heating, solidifies with
evolution of gas and formation of Cr(CO)6. An attempt
to prepare the mononuclear manganese complex
CsHjMn(C0)2P2H4( 4 ) according to eq. (2) and using
an excess of PzH4 proved unsuccessful. Contrary to expectation a dinuclear complex is formed.
C,HiMn(CO)2.THF[3]+3P,H,
5/
2%
P,H,[C,H,Mn(CO),],
(2)
and 'H-NMR spectra the mother liquors contained. in
addition to (j),at least one further compound containing
C5H5Mn(C0)2- and P,H,. groups which, however. has
not yet been identified.
(6) is soluble in benzene, toluene, THF, and acetone but
insoluble in petroleum ether. Like ( 2 ) the compound is
surprisingly stable towards light and air but not in solution,
whereupon it is rapidly converted into black-brown products. (6) melts with decomposition at 152--155°C.
The binuclear character of ( 2 ) . like that of ( 6 ) was
established by the mass spectra, in which the molecular
ions appear at m/tr=452 and 41X respectively.
The 'H-NMR spectrum of (2) (in [D6]-acetone, 30 C )
shows 21 doublet for the PzH4 protons at 6 = 5.07 ppm,
J,,=351
Hz. The IR spectrum (KBr)contains. alongside
the \*('O frequencies of the Cr(CO)<yotips 12070. 1950,
and 1910 cm- I), characteristic absorptions for the PzHJ
ligands at 23XOw, 2345ni (vPH), 1075m iind 750s cni
(6PH2).In the 'H-NMR spectrum of ( 6 ) (in C6D6,25 C).
two signals appear at 6=4.16 and 4.42 (intensity ratio
5:2)due to the CsH5- and P2H4-protons respectively. The
P2H, signal is split by P-H coupling into a doublet
( J p H = 3 3 4Hz). the C 5 H j signal into a pseudo-triplet
(JI~.--(..H
1.5~ Hz).
=
The IR spectrum (KBr) contains, in
addition to the CsH jMn(C0)2 bands, absorptions at
-.
73TTvw.
-.
3 3 5 m . 1075m and 75Sscni-'. which cxn be
ascribed to the P2H, ligand.
Elemental analysis and mass, IR, and 'H-NMR spectra
confirm the bridging function of diphosphane in the complexes ( 2 ) and ( 6 ) . The surprising stability of the two
complexes in the solid state might be due to matrix-like
embedding of the reactive diphosphane into the bulky
carbonylmetal groups and back-bonding effects.
(61
Received: September 17. 1Y73 [Z Y29d IF.]
German version: Angew. C'hem. X5, I123 11Y73)
+ by-products
After dropwise addition of ( 5 ) (30 mmol in 400mI THF)
to a solution of P2H4(90mmol) in T H F (30 ml) all volatile
fractions were removed by evaporation at -30 C and
the resulting residue dried for 24h at 20 C/10-3 torr.
Fivefold recrystallization of the black-brown residue
from toluene at -78 C afforded analytically pure
diphosphanebis(cyclopentadienyldicarbonylmanganese)
(6) as pale brown crystalline needles. According to IR
A n g w Chmnt. inrrrnai. Edii. ! Yo!. I 2 (19731 !N o . I2
[I]
Reactions oiComplexed Ligands, Part 13. This work was supported
by the De~itscheFors~hungsgcmeinschaFtPart 12: D. Scllriionn. 4 . Brrrnr!l.
and R . k m / d / .Angcw. [ h e m 85. I112 (lY73). Angew. C'hein internat.
Edit. 12, 1020(1973).
[2] Preparation: M . Buiidlcr and L. Scliiiiirtr. 2. Anorg. Ailg Chem.
289. 219 (1957).
131 W Sfrohmrirr. Angew. Chem. 76, 873 (1964):Angew. Chcm. internat.
Edit. 3, 730 (1964).
[4] E. 0.Fisclter, E. Loriis. W Burhr!t, and J . ,Wi;hv, Chem Ber. 102.
2547 ( 1969).
1021
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