摘要:
C hem ical Communications NUMBER 10/1965 26 MAY An Iron Complex with a Bridging Isonitrile Group By K. K. JOSHI, 0. S. MILLS, P. L. PAUSON, B. W. SHAW, and W. H. S ~ u s s s (Department of Pure and Applied Chemistry, The University of Strathclyde, Glasgow, C. 1, and Department of Chemistry, The University of Manchester, Manchester, 13) MANY isonitrile complexes of transition metals are analogous to the corresponding metal carbonylsl in composition and structure. Examples have recently been described2-4 showing that this simi- larity of isonitriles and carbon monoxide extends to their cyclopentadienylmetal derivatives. How- cvcr, no compounds have been reported in which isonitriles can act as bridging groups. In a pre- liminary communication2 we tentatively assigned an unbridged structure to bis [cyclopentadienyl- (phenyl isocyanide) nickel].This assignment was based on the appearance of a maximum a t 2174 cm.-l in infrared spectra taken in carbon tetrachloride or dichloroethane. It is now known that the compound decomposes in these solvents. A potassium chloride disc of a freshly prepared sample showed only a peak a t 1785 cm.-l. This is more compatible with a bridged structure analogous to that of bis (carbonylcyclopentadienyl- nickel). The ability of isonitriles to act as bridging groups has now been demonstrated by the preparation of the iron complex (I). Indeed, this example suggests that phenyl isocyanide has a greater tendency to be bridging than carbon monoxide. When iodocarbonyl (phenyl isocyanide) cyclopenta- dienyliron3 (11) was reduced with an excess of sodium borohydride in refluxing tetrahydrofuran, the product, on chromatography, gave ferrocene (16y0), bis(dicarbonylcyclopentadieny1iron) (8.4y0), and the bridged isonitrile (I) (53y').A further fraction had an infrared spectrum consistent with the presence of bis [carbonylcyclopentadienyl- (phenyl isocyanide) iron] but was obtained in in- sufficient quantity for complete purification. The structure of the isonitrile complex (I) was suggested by its infrared spectrum which showed strong bands a t 2004, 1949, 1795, and 1704 cm.-l (KI disc). All terminal isonitrile ligands examined to date have frequencies higher than 2100 cm.-l. We therefore assign the peak at 1704 cm.-l to a bridging phenyl isocyanide group. That a t 1795 cm.-l may be assigned to the bridging carbonyl and the other two peaks t o the terminal carbonyl groups.The structure (I) has been fully confirmed by X-ray-crystallographic examination. The analysis, based on 1300 reflexions (R = lly"), shows that the metal atoms are 2.53 apart and bridged by one carbonyl and one isocyanide group. There is 1 J . Chatt, P. L. Pauson, and L. Venanzi in 'Organometallic Chemistry,' ed. H. Zeiss, Reinhold, New York, 1960; 2 P. L. Pauson and W. H. Stubbs, Angem. Chem., 1962, 74, 466, (Internat. Ed. 1962, 1, 333). 3 K. K. Joshi, P. L. Pauson, and W. H. Stubbs, J . Organometallic Chem., 1963, 1, 51. 4C. E. Coffey, J . Inorg. Nuclear Chem., 1963, 25, 179. L. Malatesta in 'Progress in Inorganic Chemistry,' Vol. I, ed. F. A. Cotton, Interscience, New York, 1959.182 CHEMICAL COMMUNICATIONS no significant difference between the bridging Fe-C distances (1.91 to carbonyl, 1.90 A to isocyanide) .The angle subtended at the bridging carbon atoms is 84" in both cases. In the com- pound the isocyanide group is no longer linear but CNPh I N (111) 0. S. Mills, Acta Cryst., 1968, 11, 620. bent, through an angle of 131", a t the nitrogen atom. At the same time the phenyl group is rotated out of the plane (111) by 50'. The rotation, away from the adjacent cyclopentadienyl group, prevents short nonbonded approaches between this group and the phenyl group. The cyclo- pentadienyl groups (and terminal carbonyls) are arranged cis. If we neglect the phenyl group the remainder of the molecule contains an approxi- mate plane of mirror symmetry (non-crystallo- graphic), i.e. normal to the Fe-Fe vector and passing through the mid-point of this bond. This is in contrast to the trans-arrangement founds in crystalline bis(dicarbony1cyclopentadienyliron) where this mid-point is a crystallographic centre of symmetry, and as a consequence the two carbons of the bridging carbonyls and the two iron atoms are strictly coplanar. Although the coinci- dence of crystal symmetry and molecular sym- metry cannot arise in the less-symmetrical (I), nevertheless, deviation of this four-atom arrange- ment from coplanarity, though real, is compara- tively small; the observed dihedral angle, the fold about the Fe-Fe vector, of 166" is much larger than those found in Fe,(CO), and Co,(CO),. (Received, April 7th, 1965.)
ISSN:0009-241X
DOI:10.1039/C19650000181
出版商:RSC
年代:1965
数据来源: RSC