The cis-isomer of di-cL-carbonyl-dicarbonyldi-rr-cyclopentadienyldi-iron has been isolated by low-temperature crystallisation and its structure determined by a single-crystal X-ray analysis. The crystals are monoclinic, a = 8.880(2), b = 12.301 (3). c = 13.1 40(3) 8, p = 108.64(1)". The space group is P2Jc with Z = 4. After leastsquares refinement with over 1500 observations R is 0.051. The i.r. spectrum of the complex has been measured in the ranges 200-1 000 and 1600-2000 cm.-l and assignments have been suggested. Study of the l H n.m.r. spectra of the cis-and trans-isomers as a function of temperature confirms that solutions of the complex contain both isomers. Mossbauer and mass-spectral data are also presented.WE describe here the preparation, spectroscopic properties, and characterisation by X-ray analysis, of the cisisomer of the dimer (I). The previous paper in this Series described an accurate redetermination of the crystal structure of the trans-isomer of the same compound (11)' originally studied by M i l k 2 The behaviour 1

Szlmmary The existence of the cis-isomer of [w-C,H,Fe (C0),l2 in the solid state has been established by i.r. and X-ray methods.THE i.r. spectrum of bis-(w-cyclopentadienyldicarbonyliron) 1

Tetrafluoropyrimidine, prepared in high yield by reaction of tetrachloropyrimidine with anhydrous potassium fluoride at elevated temperatures, is highly susceptible to attack by nucleophiles; the ease of displacement of ring fluorines decreases in the order 4-and 6-> 2-5 5-. Through use of appropriate nucleophilic reagents the following fluoro-pyrimidines have been prepared : 4-X*C4F3N2 (X = OH), 4-YC4F3N2, and4,6-Y,*C4F,N2 (Y = NH,, OMe, NHPh. NHMe. or NMe,). and 2,4,6-Z,*C4FN, (2 = OMe). The structures of these compounds were established by nuclear magnetic resonance spectroscopy. Interpretation of the orientation of nucleophilic attack on tetrafluoropyrimidine and on pentafluoropyridine is provided.

Reaction of tetrachloropyrimidine with anhydrous potassium fluoride at 530" gives tetrafluoropyrimidine, 5-chloro-2,4,6-trifluoropyrimidine, and a 90 : 8 : 2 mixture of 2,4,6-trifluoro-5-trifluoromethyl-. 2.4.5-trifluoro-6-trifluoromethyl-and 4,5,6-trifluoro-2-trifluoromethyl-pyrimidine ; the first two components of the mixture can be detected in the product of pyrolysis of tetrafluoropyrimidine at 550". Fluorination of 2,4,6-trichloro-5-nitropyrimidine with potassium fluoride a t 250" gives 2,4,6-trifluoro-5-nitropyrimidine, and similar treatment of 2,4,6-trichloro-5-cyanopyrimidine yields 5-cyano-2,4,6-trifluoro-, 4-chloro-5-cyano-2,6-difluoro-, 2,4-dichloro-5-cyano-6-fluoro-, and 4,6-d ic h I oro-5cyano -2 -f I u o ro-pyrimidine. The above 5 -substituted 2.4.6trifluoropyrimid in es a nd 2.4.6tr ifluoropyrimidine itself are readily attacked by methanol-sodium carbonate, aqueous ammonia, or propenyl-lithium with displacement of ring fluorine as fluoride; the observed orientations of attack are discussed.REACTION of tetrachloropyrimidine with anhydrous 480" for 42 hr.),2 and in an effort to obtain even higher potassium fluoride at 410" for 22 hr. gives tetrafluoro-yields a fluorination has been conducted a t 530" for 18 hr. pyrimidine and 5-chloro-2,4,6-trifluoropyrimidine in 57 Distillation of the product afforded tetrafluoropyrimidine and 25% yield, respectively.2 The yield of the former in only 44% yield, together with 5-chloro-2,4,6-triproduct can be increased substantially by using more fluoropyrimidine (7%) and a 90 : 8 : 2 mixture (6%) of drastic conditions (73% at 475" for 19 hr. ; 85y0 a t 2,4,6-trifluoro-5-trifluoromethyl-, 2,4,5-trifluoro-6-tri-

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