Acetylenic derivatives of mixed metal carbonyl clusters have so far received little attention [1]. Confining to the case of mixed iron and cobalt species HFeCo 3(CO) 9(C 2Ph 2) 2 [1],FeCo 3(CO) 10 C 2Ph − 2 and FeCO 3(CO) 8C 2Ph 2 [2] havebeen reported, but not fully characterized. We have studied the reactions of aliphatic acetylenes with iron and cobalt carbonyls by reacting in acetone the alkyne either with a preformed iron and cobalt cluster, HFeCo 3(CO) 12, or with a mixture of Fe(CO) 5 and Co 2(CO) 8. The products are substantially the same from both reactions, but they are obtained in different yields. For the alkyne being 3-hexyne the following complexes have been obtained: Co 4(CO) 10C 2Et 2, Co 2(CO) 6C 2Et 2, Co( 2(CO) 6EtC 2COMe, Co 2(CO) 6EtC 2CHOHMe, FeCo 2(CO) 9C 2Et 2, FeCo(CO) 6 EtC 2CHMe. The known cobalt derivatives have been fully characterized by m.s., i.r., 1H and 13C-n.m.r. The activation of one of the methylene groups α to the triple bond has also been observed in the products of the reaction with 4-octyne. The results of the reactions of HFeCo 3(CO) 12 with 3-hexyne in various solvents suggest that water is the source of the oxygen. The single crystal X-ray analysis of FeCo 2(CO) 9C 2Et 2 shows that the complex is made of an iron and cobalt triangle with three terminal CO's bonded to each metal atom. The organic ligand is σ bonded to each cobalt atom and π coordinated to the iron one, acting as a four electron donor. The binuclear iron and cobalt derivative is obtained in low yield from the above reactions, but the yield is increased to 50% by reacting Fe(CO) 5 with Co 2(CO) 6EtC 2CHOHMe. Similarly from the reaction of iron pentacarbonyl with Co 2(CO) 6C 2(CH 2OH) 2, FeCo(CO) 6CH 2OHC 2CH 2 is obtained: in this reaction also complete dehydroxylation of the ligand occurs with transfer of the ligand from cobalt to iron to give the known Fe 2(CO) 6CH 2C 2CH 2 complex [3]. On this evidence and on the basis of the spectroscopic data we suggest for the FeCo(CO) 6RC 2CHR′ derivatives a structure in which the ligand is σ bonded to the iron atom ( via the carbon atom previously bearing the hydroxy group) and π coordinated to the iron and cobalt atoms. The stereochemical non rigidity of the novel complexes and of FeCo 3(CO) − 12 will be discussed and compared with that of other iron and cobalt mixed clusters [4].
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Apr 29, 2013
Sławomir Dyjak + 4
Open Access