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Direct Location of the Hydrido Ligands in the Dianion [H4Os10(CO)24]2 by a Neutron Diffraction Study of Its [(Ph3P)2N]+ Salt at 20 K.

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UTP (11 mg, 2mM), adjustment of the pH value, and deoxygenation with
helium, the immobilized enzymes were added (phosphoglucomutase (rabbit
muscle), 20 U ; UDP-glucose-pyrophosphorylase(bovine liver), 10 U; inorganic pyrophosphatase (yeast), 20 U ; UDP-galactose-4-epimerase (yeast), 5 U ;
galactosyltransferase (cow's milk), 2 U; pyruvate kinase (rabbit muscle), SO U).
The mixture was incubated in a shaking apparatus for two weeks at 30°C. The
enzyme, after collection by filtration and washing, could be reused. After removal of phosphate on an ion-exchange column (Dowex 1 x 8, He form), the
product was isolated by gel permeation chromatography (Fractogel TSK HW40 (S), 2 x 110 cm) (53 mg, 144 fimol, 40% yield).
3 P O z H Q
Received: March 15, 1991 [Z 4497 IE]
German version: Angew. Chem. 103 (1991) 1184
CAS Registry numbers:
1,154-17-6; 2,3573-50-0; 6,7512-17-6;7,135190-02-2; 7 heptaacetate, 13519003-3; EC, 9030-11-9.
[ll a) T. Reichstein, E. Weiss, Adv. Carbohydr. Chem. f7 (1962) 65; b) J. S .
Brimacombe, Angew. Chem. 83 (1971) 261 ; Angew. Chem. Int. Ed. Engl. 10
(1971) 236; c) J. Thiem, W. Klaffke, Top. Curr. Chem. 154 (1990) 285.
[2] a) J. Thiem, H. Karl, J. Schwentner, Synrhesis 1978, 696; b) J. Thiem, J.
Elvers, Chem. Ber. 112(1979)818;c) J. Thiem,P. Ossowski, J. Schwentner,
ibid. 113 (1980) 955; d) R. U. Lemieux, A. R. Morgan, Can. J. Chem. 43
(1965) 2190; e) K. Tatsuta, K. Fujimoto, M. Kinoshita, S. Umezawa,
Carbohydr. Res. 54 (1977) 85; f ) P. J. Garegg, B. Samuelsson, ibid. 84
(1980) C1.
[31 a) K. Bock, C. Pedersen, J. Thiem, Carbohydr. Res. 73 (1979) 85; b) R.
Preuss, R. R. Schmidt, Synthesis 1988,694; c) M. Perez, J.-M. Beau, Tetrahedron Lett. 30 (1989) 75; d) K. C. Nicolaou, T. Ladduwahetty, J. L. Randall, A. Chucholowski, J. Am. Chem. Sor. 108 (1986) 2466; e) H. Jin, R.
Tsai, K. Wiesner, Can. J. Chem. 61 (1983) 2442.
[4] T. Hayashi, T. Iwaoka, N. Takeda, E. Ohki, Chem. Pharm. Bull. 26 (1978)
1786; b) J. Thiem, H. Karl, Chem. Ber. 113 (1980) 3039.
[5] a) J. Lehmann, T. Schroter, Carbohydr. Res. 58 (1977) 65.
[6] a) H. A. Nunez, R. Barker, Biochemistry 19 (1980) 489; b) S. David, C.
Auge, Pure Appl. Chem. 59 (1987) 1501; c) M. M. Palcic, 0. P. Srivastava,
0.Hindsgaul, Carbohydr. Res. 159 (1987) 315; d) C. Augi, C. Gautheron,
H. Pora. ibid. 193 (1989) 288; e) J. Thiem, T. Wiemann, Angew. Chem. 102
(1990) 78; Angew. Chem. Inr. Ed. Engl. 29 (1990) 80.
[7] a) Product information, Riedel-de Haen, Seelze 1987; b) K. Burg, 0.
Mauz, S. Noetzel, K. Sauber, Angew. Makromol. Chem. 157 (1988) 105.
[8] a) S. L. Haynie, C.-H. Wong, G. M. Whitesides, J. Org. Chem. 47 (1982)
5416; b) C. Auge, S. David, C. Mathieu, C. Gautheron, Tetrahedron Lett.
25 (1984) 1467; c) J. Thiem, W. Treder, Angew. Chem. 98 (1986) 1100;
Angew. Chem. Int. Ed. Engl. 25 (1986) 1096.
191 M. D. Percival, S. G. Withers, Can. J. Chem. 66 (1988) 1970.
[lo] T. N. Druzhinina, Y. Y. Kusov, V. N. Shibaev, N. K. Kochetkov, P. Biely,
S. Kucar, S. Bauer, Biochim. Biophys. Acta 381 (1975) 301.
[I I] T. G. Cooper, Biochemische Arbeifsmethoden, de Gruyter, Berlin 1981,
p. 53.
Scheme 2. Enzymatic glycosylation (enzymes: III, phosphoglucomutase; IV,
UDP-glucose-pyrophosphorylase; V, inorganic pyrophosphatase; VI, UDPgalactose-4-epimerase; VII, galactosyltransferase; VIIl, pyruvate kinase; all
enzymes were immobilized on activated CH-sepharose 4 B).
Table 1. Spectroscopic data for 7. 'H NMR (400 MHz, [DJacetone, [DJacetone as internal standard); 13C NMR (63 MHz, H,O, CH,CN as internal
l3CNMR (free sugar 7): 6 = 89.59 (C-1, a form), 93.93 ((2-1, B form), 99.42
(C-l'), 52.80 (C-2, a form), 55.29 (C-2, form), 32.54 (C-Z), 68.30 (C-3, a form),
71.48 (C-3, B form), 66.72 (C-3'), 77.87 (C-4, a form), 77.44 (C-4, B form), 65.73
(C-4'), 69.17 (C-5, fom), 73.79 (C-5, B form), 74.65 (C-S), 59.18 (C-6), 60.43
(C-6), 173.31(NH-CO-CH,), 20.97 (NHCO-CH3, a form), 21.25 (NHCO-CH3
B form)
'HNMR(heptaacetateof7):b = 5.77(d,JL,,, = 8.8 Hz, H-l,pform),6.06(d,
Jle.z= 3.6 Hz, H-1, a form), 7.15 (d,
= 9.4 Hz, NH, a form), 7.1 1 (d,
JNH.= 9.4 Hz, NH, B form), 4.33 (ddd, Jz, = 10.4 Hz, H-2, a form), 4.07 (m,
H-2, form), 5.23 (m, 1H, H-3), 3.95 (t, J3.4= J4, = 9.6 Hz, 1H, H-4), 3.83
= 12.2 Hz, 1H,
(ddd, J5,6*= 4.4 Hz, J5,6b= 2.2 Hz, 1 H, H-5), 4.34 (dd, J6s,6b
H-6a), 4.23 (dd, l H , H-6b), 4.83 (dd, J,.,,,.=9.6Hz, J,..,.,=2.2Hz, l H ,
= 12.5 Hz, 1H, H-Za), 1.95 (m, 1H,
H-1'). 1.76 (ddd, J2...2.r = 12.4 Hz, J2.s,3.
= 3.215.0 Hz, 1 H, H-3'), 5.23 (m, 1H, H-4),
H-Te), 5.04 (ddd, JT., 3./J3.,4.
(ddd, JC, s, = 5.6 Hz, 1H, H-S), 4.20 (dd, Js.,6'a = 3.6 Hz,
= 12.2 Hz,
1H, H-6a), 4.1 1 ppm (dd, Js.,6'b = 2.0 Hz, 1 H, H-6b)
FAB-MS (free sugar 7 ) :M e + 1 = 368, M e + Na = 390
reenter the reaction to form UDP 2-deoxyglucose. The
amount of conversion in the reaction can be quantified by
using the Fiske-Subbarov method for photometric determination of phosphate.[''] All enzymes used in the cycle are
immobilized on activated CH-sepharose and can be employed repeatedly.
Experimental Procedure
The reaction was carried out in Tris buffer (100 mM, pH 7.5,9 mL). The buffer
contained MgCI, (10 mM), MnCI, (5 mM), KCI (40 mM), NaN, (0.02%), and
bovine serum albumin (0.5 %). After addition of 2-deoxy-D-arabino-hexose6phosphate (2, NHF salt, 100 mg, 40 mM), N-acetylglucosamine (6, 120 mg,
60 mM), PEP (82 mg, 44 mM), glucose 1,6-diphosphate(0.1 mg, catalytic), and
1 164 0 VCH &rlagsgeseIlschafi mbH, W-6940 Weinheim. 1991
Direct Location of the Hydrido Ligands in the
Dianion [H40s,,(CO)24]2- by a
Neutron Diffraction Study of Its [(Ph,P),N] + Salt
at 20 K**
By Alan Bashall, Lutz H . Gade, Jack Lewis,*
Brian F G . Johnson, Garry J. McIntyre,*
and Mary McPartlin *
Large hydrido carbonyl clusters of transition metals
provide ideal model systems for the study of the chemisorp[*] Prof. M. McPartlin, A. Bashall
School of Chemistry, The Polytechnic of North London
Holloway Road, GB-London N7 8DB (UK)
Prof. Lord Lewis, L. H. Gade, Dr. B. F. G. Johnson
University Chemical Laboratory
Lensfield Road, GB-Cambridge CB2 IEW (UK)
Dr. G. J. McIntyre
Institut Laue-Langevin
156X, F-38042 Grenoble Cedex (France)
[**I We acknowledge financial support from the Science and Engineering Research Council (M.McP.) and the Foreign and Commonwealth Office
(Kurt Hahn Scholarship for L.H . G.). We thank Professor J. W Lauher
(Stony Brook, USA) for his molecular graphics programme CHEM-RAY
0570-0833/91/0909-1164S 3 . 5 0 i .2S/0
Angew. Chem. In(. Ed. Engl. 30 (1991) No. 9
tion of a'bynthesis gas" on the surface of bulk metals or
colloidal particles.['] Several decanuclear hydrido clusters of
osmium and ruthenium have been structurally characterized
by X-ray diffraction:' -41 and most exhibit tetracapped octahedral metal cores with what appear to be closed-packed
arrays of carbonyl ligands approximately perpendicular to
the four six-metal atom surfaces of the core. None of these
clusters shows the marked displacement of carbonyl ligands
invariably associated with surface-bonded hydride ligands in
smaller clusters,[5- 'I and it has therefore been thought, until
now, that the hydride ligands were probably all located in
interstitial sites. A neutron diffraction study of one of these
give the 134 cluster valence electrons required for the observed tetracapped octahedral geometry," 5 , 'I and the presence of hydrido ligands was confirmed by 'H NMR spectroscopy. The close similarity of the carbonyl distribution in
1 to that of the non-hydrido dianion 5 was consistent with an
interstitial location of the four hydrogen ligands. The cluster
also showed significant lengthening of a number of metalmetal distances which were attributed to the cavity expansion produced by internal hydrides. Variable-temperature
l H and 13C NMR studies showed a high degree of ligand
fluctionality in solution at ambient temperatures (CD,CI, ,
295 K). On cooling to 198 K the single broad hydride reso-
decametal clusters, the dianion 1, has now established that
all four hydride ligands are located on the surface of the
metal framework.
Single crystal X-ray studies do not allow direct location of
H atoms in polynuclear carbonyls of the third-row transition
metals, but they often lead to successful deduction of hydrogen sites using indirect methods based on detecting 'gaps' in
the carbonyl ligand~,[~-']
or on determination of potential
energy minima.[') For example, a p3 site on the surface of the
octahedral cluster monoanion 2 was deduced from the surface ligand distribution observed in the X-ray analysis,I6]and
was later confirmed by neutron diffraction studies.["] The
first interstitial H atom to be reported in a carbonyl cluster
was sited in the octahedral cavity of 3, the ruthenium analogue of 2.I"I The unexpected location was originally deduced indirectly from the extremely compact arrangement of
the carbonyl ligands which left no space for a surface H atom
and from the NMR data. This structural assignment initially
proved controversial,["] but was vindicated by later neutron
diffraction studies." 31 A similar octahedral hydride environment was revealed in neutron diffraction studies of the hexacobalt cluster [HCo,(CO),,] - .[14]
Analogous observations in X-ray studies of the decanuclear monoanion 4['] were also consistent with an interstitial
location for the H atom, because they showed a complete
coverage of the metal core by carbonyl ligands very similar
to that of the corresponding non-hydrido dianion 5.''
As the only octahedral site in 4 is occupied by the carbido
atom, the possible location of a hydrido ligand in a slightly
enlarged tetrahedral cavity of the cluster was proposed, and
the 18'Os satellite pattern associated with the hydride signal
in the 'H NMR spectrum was consistent with this assignment." 6l
Carbide formation during formation of these high nuclearity clusters is suppressed by thermolyzing the Os, precursors
in high boiling protic solvents. The X-ray study of 1,13]originally obtained in low yield from the reaction of Os,(CO),,
with iBuOH,["] again showed an overall structure almost
indistinguishable from that of the carbido dianion 5 but
without the central C atom. It was formulated as
[H4Os,,(CO),,f2- because the hydrides were essential to
Angen. Chem. Int. Ed. Engl. 30 (1991) No. 9
Fig. I . Perspective views of the structures of the two isomers of the tetrahydrido dianion 1, showing the surface location of the hydrogen ligands; for clarity
only the numbers of the osmium atoms are shown: Top: isomer 1 a which has
a virtual C, axis through Os6 and Os4; bottom: isomer l b which has no
symmetry. Principal bond lengths [A] and angles ["I: (estimated standard deviations in parantheses): Osl-Os2 2.801(8); Osl-Os3 2.772(8); Osl-Os4 2.745(9);
0 ~ 2 - 0 2.868(7);
0 ~ 2 - 0 2.816(8);
0 ~ 2 - 0 2.862(8);
0 ~ 2 - 0 2.900(8);
Oslo 2.805(9); 0 ~ 3 - 0 ~2.755(8);
0 ~ 3 - 0 2.881(8);
0 ~ 3 - 0 ~2.733(8);
0 ~ 2.815(9);
0 ~ 4 - 0 ~2.798(8);
0 ~ 4 - 0 ~2.739(9);
0 ~ 4 - O s l o2.789(8); 0 ~ 5
0 ~ 62.793(7); 0 ~ 5 - O s l o2.778(8); 0 ~ 6 - 0 ~2.779(7);
0 ~ 6 - 0 ~2.910(8);
0 ~ 6 - 0 ~ 12.858(8);
0 ~ 7 - 0 2.855(8);
0 ~ 8 - 0 2.888(8);
Os8-Oslo 2.894(7);
0 ~ 9 - O s l o2.754(8); Os2-H2 1.87(2); Os2-H3 1.82(3); Os3-H2 1.89(2); Os5-H3
1.81(4); Os6-Hl 1.88(3); Os6-H2 1.85(3); Os7-H4a 1.80(5); Os8-H1 1.82(2);
Os8-H4a 1.70(4); Os8-H4b 1.77(6); Os9-H4b 1.82(5); Oslo-H1 1.89(2); 0 ~ 6
Hl-OsS 104(2); 0 ~ 1 0 - H 1 - 0 ~
6 0 ~ 1 0 - H 1 - 0 ~103(1);
Os6-H2-0s2 103(1); 0 ~ 6 . H 2 - 0 ~lOl(1);
Os5-H3-0s2 104(2); OsS-H4a-Os7
109(2); 0 ~ 9 - H 4 b - 0 ~107(3).
Verlagsgesellschaft mbH, W-6940 Weinheim, 1991
nance at 6 = - 16.48 split into two signals of equal intensity
at - 14.70 and - 19.08.['9] This signal pattern could not be
be explained in terms of a model in which the four hydride
ligands occupy interstitial sites (four tetrahedral, one octahedral) within the cluster; therefore their location on the cluster surface, though not apparent from the X-ray study could
not be ruled out. Despite persistent attempts to grow crystals
of a decanuclear hydrido species suitable for neutron studies
using a range of different counterions, none has been obtained until now.
In the present neutron study of the [(Ph,P),N)]+ salt of 1
at 20 K, the hydrido H atoms were directly located in a
difference-Fourier synthesis, and were found to be on the
cluster surface, two in p3 and two in 11, sites.[201The four
hydride ligands gave rise to five negative peaks, three of
approximately equal height and two of half height. These
were attributed to two isomers of the tetrahydrido dianion
1 a and 1 b, differing in the position of the fourth H ligand,
and distributed randomly through the crystal. The first isomer 1a has virtual C, symmetry (Fig. 1 top) and the fourth
H ligand, H4a, bridges the edge Os7-Os8; in isomer 1 b the
corresponding hydride, H4b, bridges Os8 -0s9 (Fig. 1 bottom). Significantly, two alternative orientations for a carbony1 ligand on Os8 were resolved and the two components,
C082a and C082b, were assigned to isomers 1 a and 1 b,
respectively.[211The bridged 0s-0s distances show the characteristic lengthening associated with hydrogen ligands
(range for H-bridged 2.855 to 2.910(8); for unbridged 2.733
to 2.816 8,). The results from this study demonstrate an essential role for neutron diffraction in full characterization of
large hydrido metal clusters.[221Preliminary results with neutron data collected for 1 at 295 K show a similar hydride
distribution to that in the low-temperature study.
The two p 3 sites occupied by the H ligands in 1 are the first
examples of cluster hydrides located in the center of a large
planar array of surface metal atoms. Their very congested
locations correspond to potential energy minima which are
an order of magnitude greater than that associated with the
p3 H site in the hexanuclear cluster 2 (calculated using the
HYDEX programme written by Orpedgl).Computed space
filling models[231(Fig. 2) show that the H atoms are partially
Fig. 2. Computed space-fillingmodels of the two isomers viewed perpendicular
to the faces at the front of the views in Fig. 1, that is onto the H1 p, site defined
by Os6,Os8, and Oslo: (a) isomer l a showing the p2 H atom H4a; (b) isomer
1b showing the p, H atom H4 b.
submerged under the van der Waals spheres of the three
nearest CO ligands in a completely different arrangement
from that observed on the surface of smaller clusters.[6. lo]
The nearly close-packed distribution of the carbonyl ligands
round the p 3 H atoms in 1 gives rise to some remarkably
short C ...H contact distances (2.23 to 2.35 A), compared to
a range of 2.48 to 2.70 8, for the three shortest C ... H con'
1166 0 VCH
Verlagsgesellschafi mbH, W-6940 Weinheim. 1991
tacts in the neutron study of [HOs,(CO),,]- at 20 K.['O1
Incipient C... H interaction between the CO ligands and the
H atoms on the faces may be deduced from the concerted
slight displacement of the oxygen atoms of the carbonyl
ligands away from the occupied p3 sites which can be seen in
Figure 2; this feature is absent in the two unbridged faces of
the cluster. These results provide the best molecular model so
far for chemisorption at high density of carbon monoxide
and hydrogen on (111) or (001) surfaces of metals.
Reveived: April 5,1991 [Z 4555 IE]
German version: Angew. Chem. 103 (1991) 1186
CAS Registry number:
[l] Representative references are: E. L. Muetterties, Angew. Chem. 90 (1978)
577; Angew. Chem. Int. Ed. Engl. 17 (1978) 545; E. L. Muetterties, T. N.
Rhodin, E. Band, C. F. Brucker, W. R. Pretzer, Chem. Rev. 79 (1979) 91;
G. Ertl, Gazz. Chrm. Ilaliana 109 (1979) 217.
[2] P. F. Jackson, B. F. G. Johnson, J. Lewis, M.-C. Malatesta, M. McPartlin,
W. J. H. Nelson, J. Chem. SOC.Chem. Commun. 1982.49.
[ 3 ] D. Braga, B. F. G. Johnson, J. Lewis, M. McPartlin, W. J. H . Nelson,
M. D. Vargas, J. Chem. Soe. Chem. Commun. f983, 241.
[4] P. J. Bailey, B. F. G. Johnson, J. Lewis, M. McPartlin, H. R. Powell, J.
Organomet. Chem. 377 (1989) C17.
[5] M. R. Churchill, J. Wormald, J. Am. Chem. SOC.93 (1971) 5670.
[6] M. McPratlin, C. R. Eady, B. F. G. Johnson, J. Lewis, J. Chem. Soc Chem.
Commun. 1976, 883.
[7] D. Braga, K. Henrick, B. F. G. Johnson, J. Lewis, M. McPartlin, W. J. H.
Nelson, M. D. Vargas, J. Chem. SOC.Chem. Commun. 1982,419; J. Chem.
SOC.Dalton Trans. 1984, 2151.
[8] K. Henrick, M. McPartlin, J. Morris, Angew. Chem. 97(1986) 843; Angew.
Chem. Int. Ed. Engl. 2S (1986) 853.
191 A. G. Orpen, J. Chem. Soc. Dalton Trans. 1980, 2509.
[lo] A. G. Orpen, T. F. Koetzle, Aera Crystallogr. C43 (1987) 2084.
[Ill C. R. Eady, B. F. G. Johnson, J. Lewis, M.-C. Malatesta, P. Machin, M.
Chem. Commun. 1976,945; C. R. Eady, B. F. G.
McPartlin, J. Chem. SOC.
Johnson, J. Lewis, M.-C. Malatesta, M. McPartlin, W. J. H. Nelson, J.
Chem. SOC.Dalron Trans. 1980, 383.
[I21 P. Chini, G. Longoni, S. Martinengo, A. Ceriotti, Adv. Chem. Ser. 167
(1978) 1 .
[13] P. F. Jackson, B. E G. Johnson, J. Lewis, P. Raithby, M. McPartlin,
W. J. H. Nelson, K. D. Rouse, J. Allibon, S. Mason, J. Chem. SOC.Chem.
Commun. 1980,295.
1141 D. W Hart, R. G. Teller, C. Y Wei, R. Bau, G. Longoni, S. Campanella,
P. Chini, T. F. Koetzle, Angew. Chem. 9f (1979) 86; Angew. Chern. Inr. Ed.
Engl. 18 (1979) 80.
[IS] P. F. Jackson, B. F. G. Johnson, J. Lewis, M. McPartlin, W
. J. H. Nelson,
J. Chem. SOC.Chem. Commun. 1980,224; J. Chem. SOC.Dalton Trans. 1982,
[16] E. C. Constable. B. F. G. Johnson. J. Lewis. G. N. Pain. M. J. Tavlor. J.
Chem. Soc. Chem. Commun. 1982, 754.
More efficient routes to 1, giving substantially higher yields of the cluster
( 120 %), have recently been developed and involve the thermolysis of
derivatives of Os,(CO),, in alcohols: A. J. Arnoroso, L. H. Gade, B. E G.
Johnson, J. Lewis, unpublished.
K. Wade, Adv. Inorg. Chem. Radiochem. 18 (1976) 1; R. Mason, K. M.
Thomas, D. M. P. Mingos, J. Am. Chem. Soc. 95 (1973) 3802.
The I3C NMR spectrum of 1 recorded in CD,CI, at 295 K consists of two
(exchange-broadened) carbonyl resonance signals at 6 = 175.8 and 192.9
which coalesce at 230 K. Below that temperature the spectra display a
complicated pattern of exchange processes which have to date not been
fully understood. It proved impossible to obtain a low temperature limit
spectrum even at 170 K.
Crystal data for [(PPh,),N]-1 (neutron, 20 K): C,,H,,N,O,,P,Os,,,
M,= 3655.5, triclinic, space group Pi (No. 2). a = 26.641(1), b =
17.234(1), c = 10.428(1) A, OL = 96.701(2), = 100.672(3), y = 86.148(3)",
2 = 2, V = 4667.75 A', @..,cd (20 K) = 2.600 gcm-', L = 1.3150(2) 8,
(Ge(115) monochromatic thermal neutrons), T = 20 K (Displex cryorefrigerator), p = 1.25 cm-'. Crystal size ca. 0.15 x 0.20 x 0.35 cm; fourcircle neutron diffractometer D19, equipped with a position-sensitive detector. A total of 8125 data were recorded, of which 4875 were unique.
4131 absorption corrected data (I/u(l) > 2.01 were used in full-matrix refinement of the atomic parameters obtained previously from X-ray data [2]
together with those located from this study ( R = 0.0897: R, = 0.0941).
Further details of the crystal structure investigation are available on request from the Director of the Cambridge Crystallographic Data Centre,
05?0-0833/91/0909-1166 8 3.SO-k .2S/O
Angew. Chem. Inl. Ed. Engl. 30 (1991) No. 9
University Chemical Laboratory, Lensfield road, GB-Cambridge
CB2 1EW (UK), on quoting the full journal citation.
After inclusion of the hydrido H atoms in the model, the highest residual
peak was positive (of height approximately 0.2 that of a C atom) and very
close to the center of the Os, octahedron. The I3CNMR spectra of 1 from
the batch used in the neutron study indicated the presence of ca. 20% of
the carbido dianion, (5) (known to be isomorphous with 1 as its
[(Ph,P),N]+ salt). The residual density was therefore interpreted as due to
a random 20% occmation of the cluster site bv the virtuallv isostructural
carbido dianion. The parameters of the carbido C atom (occupancy 0.2)
refined satisfactorily, and the hydrido H atoms and the disordered carbony1 ligand C082 were therefore assigned overall 0.8 total occupancy.
[22] This study clearly demonstrates that negative evidence for surface location
of H ligands in large clusters is unreliable, and the question of the exact
location of all the H atoms formerly assigned to interstitial tetrahedral sites
must be re-examined. For example the X-ray evidence for the interstitial
nature of the H ligand in [HOs,,C(CO),,]- can, with hindsight, be explained by an external p 2 H and threefold disorder of the cluster anion in
the Ph,As+ salt and sixfold disorder in the Ph,PMe+ salt [2]. Significantly,
preliminary X-ray results for the dihydride [H,Os,,C(CO),,] show a similar disorder of two carbonyl ligands to that observed in 1 and have been
interpreted as indicating two p, H ligands on the surface (D. Braga, University of Bologna, personal communication).
[23] Calculated using a molecular graphics programme CHEM-RAY: J. W.
Lauher, J. Mol. Graphics 8 (1990) 34. The osmium atoms were assigned
covalent radii of 1.5 8, to give a clearer view of the surface ligands. All
other atoms have spheres of van der Waals radii [PI.
8 qN- Et
Dr. A. C. Filippou, Dr. W. Griinleitner, Dipl.-Chem. C. Volkl, Dip1.Chem. P. Kiprof
Anorganisch-Chemisches Institut der Technischen Universitat Miinchen
Lichtenbergstrasse 4, W-8046 Garching (FRG)
This work was supported by the Volkswagen-Stiftung and the LeonhardLorenz-Stiftung. We thank Prof. W: A . Herrmann and Prof. E. 0.Fischer
for support of our work and Prof. P. Hofmann for discussions.
Angew. Chem. Int. Ed. Engl. 30 (1991) No. 9
The coupling of two carbyne ligands to form an acetylene
ligand according to M(CH), -+ M(C,H,) is symmetryallowed for d4 metal centers.[lal In fact, MO calculations [Ib] on the hypothetical 38-electron d4 complexes
[W(CH),Cl,(CO),] and [W(CH),Cp(CO)]C121predict a
spontaneous rearrangement to the 16-electron acetylene
complexes [W($-HC=CH)Cl,(CO),] and [W(qZ-HC=CH)
Cp(CO)]', which may be stabilized by complexation with
further ligands. However, these calculations also indicate
that n-donor substituents on the carbyne carbon stabilize the
bis(carbyne) form relative to the alkyne complex. Mononuclear bis(carbyne) complexes are extremely rare, but are often postulated as intermediates in C-C coupling reactions
that form alkyne complexes from carbyne precursors.131
We have now prepared the first bis(carbyne) complexes of
tungsten and selectively converted them into alkyne complexes. The starting materials for the three-stage synthesis
are the q5-C5Me, tungsten complexes l a and lbt4](Scheme
1). Treatment of l a with tBuNC leads to the displacement of
the CO ligand to form 2, which is then reduced to 4 with
sodium amalgam in the presence of tBuNC. A similar reaction sequence for l b leads via 3 to the ethyl isocyanide derivative 5. The monocarbyne complexes 4 and 5 are finally
alkylated with [Et,O]BF, to yield selectively the yellow bis(carbyne) derivatives 6 and 7,respectively.
Nucleophilic reagents induce coupling of the two carbyne
ligands in 7 to form an alkyne unit. Thus reaction of 7 with
0 VCH VerlagsgesellschaflmbH,
By Alexander Constantin Filippou,* Walter Grunleitner,
Christian Volkl, and Paul Kiprof
- 2 NaBr
+ Na/Hg (ex.)
- 2 Nal
l . / K C N Et
Metal-Centered Coupling of Two Carbyne Ligands
To Form an Alkyne Ligand**
*+ NWHg (ex.)
+ t BuNC
6 7
Scheme 1. RT = room temperature, ex.
ethyl isocyanide yields the W" complex 8 (Scheme 2). A
coupling of the two carbyne ligands is also induced by oxidizing agents, as shown by the reaction of 7 with Br, which
affords the W'"-alkyne complex 9 (Scheme 2).
The bis(carbyne) complexes 6 and 7IZ1are unusually thermally stable: compound 6 decomposes only after several
CHzCl2, RT
Scheme 2.
W-6940 Weinheim, 1991
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salt, ph3p, h4os10, stud, direct, diffraction, hydride, dianion, ligand, neutron, location
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