542 SCIENCE PROGRESS 



even series of the Periodic Table would give organo-metallic 

 derivatives, while Zeltner, in 1908, thought that the metals of 

 the sixth group gave no indication of the formation of com- 

 pounds of this type. Considerable interest attaches, therefore, 

 to the preparation of organo-derivatives of chromium by 

 Hein {Ber., 1921, 54, 1905). Some years ago Bennett and 

 Turner {Trans. Chem. Soc, 191 4, 105, 1057) attempted to 

 prepare organo-derivatives of chromium by the action of phenyl 

 magnesium bromide on chromic chloride, but without success, 

 the main product of the reaction being diphenyl. 



2CrCl3 + 2CeH5MgBr -> CeHsX^Hs + 

 2CrCl2 + MgClg + MgBra. 



In a subsequent paper (/. Roy. Soc. New South Wales, 191 9, 

 58, 100) they pointed out that evidence had been obtained of 

 the formation of organo-metallic derivatives of chromium, 

 tungsten, and iron, but apparently did not succeed in isolating 

 any individual. Hein has been more successful, and, using 

 Bennett and Turner's method, but without heating the re- 

 action mixture, has obtained chromium pentaphenyl bromide, 

 Cr(C6H5)5Br. This compound is described as an orange-brown 

 amorphous powder difficult to purify on account of its 

 instability; the mercuri-chloride Cr(C6H5)5Br.HgCl2 can, 

 however, be obtained reasonably pure. From the crude bromide 

 there has been prepared a crystalline hydrated chromium 

 pentaphenyl hydroxide, which conductivity measurements 

 show to be a strong base. 



(2) Lead. Krause and Schmitz (Ber., 191 9, 62, 2165) 

 obtained evidence of the existence of organo-derivatives of 

 lead analogous to triphenyl methyl, in which the metal is 

 attached to but three hydrocarbon radicles. When magnesium 

 p-2-xy\y\ bromide acts upon lead dichloride, instead of lead 

 tetraxylyl, a crystalline compound is obtained which analysis and 

 molecular weight determinations indicate to be [(C8H9)3Pb]2. 

 The properties of this compound, notably the ease with 

 which it reacts with halogens at low temperatures, afford some 

 evidence that the union between the lead atoms is very feeble, 

 and that it might be regarded as lead tri-/)-2-xylyl. It reacts 

 with bromine in pyridine solution at -40° to give lead tTi-p-2- 

 xylyl bromide, which with magnesium p-2-xy\y\ bromide yields 

 lead tetra-^-2-xylyl, (CgH9)4Pb. Krause (Ber., 1921, 54, 2060) 

 has now obtained important confirmation of these views by the 

 preparation of lead tricyclohexyl, Pb(C6Hii)3. from lead di- 

 chloride and magnesium cyclohexyl bromide. Lead tricyclo- 

 hexyl, which is obtained in 50 per cent, yield, is a yellow crystal- 

 line compound decomposing at 195°. The pure substance is 



