1970
G. WILKINSON, P. L. PAUSON AND F.
A\.
COTTON
[CO.VTRIBUTIOS F R O ~ LTHE DEPARTMENT OF CHEMISTRY, HARVARD UNIVERSITY]
Bis-cyclopentadienyl Compounds of Nickel and Cobalt BY C . ~YILKINSON,P. L. PAUSON’ AND F. A. COTTON RECEIVED SEPTEMBER 2, 1953 The preparation and properties of bis-cyclopentadienyInickel( 11) and bis-cyclopentadienyInickel(111) salts are described. The heat of formatioii of bis-cyclopentadienylnickel(I1) from the elements is 62.8 i 0.5 kcal. S e w preparations of biscyclopentadienylcobaIt(I1) and -iron( 11) are reported. The electronic structures of bis-cyclopentadienyl compounds are discussed.
T h e structure suggested? for bis-cyclopentadienyliron (II), in which the iron atom is symmetrically placed between two cyclopentadienyl rings has been confirmed b y X-ray crystal structure measurements.2b,4 The formation of bis-cyclopentadienyl compounds having this “sandwich” structure appears to be a general property of transitional elements which have two vacant or singly occupied d orbitals t h a t can be used in bonding, and various derivatives of t i t a n i ~ m v, ~a n a d i ~ m cobalt,6,8 ,~ nicke1,j.’ zirconium,; r u t h e n i ~ m ,rhodium1” ~ and iridiurnlo have been noted. Bis-cyclopentadienylcobalt(I1), which was briefly describedn in a preliminary communication whilst the present work was in progress, is here made by the direct vapor phase reaction of cyclopentadiene with cobalt octacarbonyl, a method previously used in the preparation of bis-cyclopentadienylchrornium(I1) . I 1 The preparation of bis-cyclopentadienylnickel(II), first reported in a preliminary conimunication,5 involves a method analogous to t h a t employed for the preparation of bis-cyclopentadienylruthenium(I1).9 Fischer and Jira’ have subsequently described the preparation b y a different method. Bis-cyclopentadienylnickel(I1) has the same structure as bis-cyclopentadienyliron(I1) and may be represented as a molecular “sandwich.” This is clearly evident from a comparison of the infrared absorption spectra shown in Fig. 1; the differences between the two compounds in the region near 1700 c n ~ . are - ~ better illustrated in Fig. 2. The similarity of the structure of (CjHjjZCo and of (CjHs)&i to t h a t of (C5Hs12Fehas been confirmed b y X-ray diffraction The ultraviolet spectra of (CjHj)S?\ii in cyclohexane and in carbon tetrachloride are shown in Fig. 3 (1) Chemistry Department, T h e Universit),, Sheffield, England. 12) fa) G. ivilkinson, M. Rosenblum, hI. C. Whiting and K. H Woodward, THISJ O C R N A L , 74, 2125 d9.52); i h ) E 0. Fj5her and a: Pfab, Z S u l u l : i o r s c h i L i z y , IB,377 ( l Y . 5 2 ) . 18) ( a ) T J Kealy and P I,. Paiiron, . V a / u r r . 168, 1039 (1951); Z hliller. J . A . ’l‘ehhttth and J. F Tremaine. J i’h?m. Sur , ( 3 2 a ) I’ 1:. I
