Group VIIIB Cobalt, Rhodium, and Iridium

The passage of allene into a benzene solution of dicobalt octacarbonyl at room temperature produces air-sensitive yellow crystals of composition [(C3H4)Co(CO)3]2 (428). The spectral data indicate a 7r-allyl complex in which a CO grouping has been transferred to the 2-position of each allylic moiety. Although Co2(CO)g does not form a tt complex with tetraphenylallene, cyclopentadienyldicarbonylcobalt does react under reflux in isooctane to yield the product [C3(C6H5)4]Co(CO)(C5H5) in which the olefin appears to be a monodentate ligand (434). 

Another cobalt complex having only hydrocarbon ligands, (1,3-butadiene)cyclopentadienylcobalt, has been obtained as a volatile red solid melting at 103°-106°C by reaction of the diene with dicyclopenta-dienylcobalt or (1 -benzoyl-1,3-cyclopentadiene)cyclopentadienylcobalt (489). The compound decomposes slowly in air. 

Although butadiene reacts with Co2(CO)8 to yield the diene complexes (diene)C02(C0)e and (diene)2Co2(CO)4 (268), with alkyl- or acylcobalt tetracarbonyls it produces only the 7r-allylic species, 1-alkyl- or 1-acylmettiyl-TT-allylcobalt tricarbonyls (281). These will react, in turn, with P(C Hb)3 which displaces one CO ligand to form monotriphenyl-phospbine derivatives (281). 

Photolysis of an ethereal solution of photo-a-pyrone (157) and cyclopentadienyldicarbonylcobalt yields, in addition to the air-stable, yellow crystalline (cyclobutadiene)cyelopentadienylcobalt, a dark green, air-sensitive crystalline species melting at 121°-122°C with the empirical 

The reaction of excess 3,3-dimethyl-l-butyne with Co2(CO)g yields violet crystals of (C2HR)3Co2(CO)4 [R = 0(0113)3], which upon reaction with a OOI4 solution of bromine at 0°0 produce l,2,4-tri-ier -butylben-zene, the first benzene derivative with ortho eri-butyl substituents (368). This latter reaction, coupled with the infrared spectral and magnetic moment data, indicates structure (161) for the complex. 

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We place hydrogen as the first element in the first period, along with helium. When helium was discovered, Mendeleev put it in the second period. We put the triads of iron, cobalt, and nickel ruthenium, rhodium and palladium and osmium, iridium, and platinum in group VIIIB, in the middle of the table. Mendeleev put them in group VIII. We also have two long groups, the lanthanides and actinides, that were a headache for Mendeleev. 

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