R.M. Medina

Alkynyl cobalt complexes. An electrochemical study

Abstract The preparation and characterisation of the complexes Co2(CO)5(PMe3)(μ-η2-Me3SiC2CCSiMe3) (2) and Co2(CO)4(PMe3)2(μ-η2-Me3SiC2CCSiMe3) (3) are described. A comparative electrochemical study of the complexes Co2(CO)6−nLn(μ-η2-Me3SiC2CCSiMe3) (n=0 (1); n=1, L=PMe3 (2); n=2, L=PMe3 (3), PPh2Me (4), dppa (5), dppm (6)) is presented by means of the cyclic and square-wave voltammetry techniques. Substitution of CO by phosphine ligands transforms the Co2C2 redox centre from a readily reducible to an easily oxidisable centre and contributes to the stabilisation of the Co–Co bond increasing the lifetime of the radical cations and anions.

SYNTHESIS AND CHARACTERIZATION OF NEW TRANSITION METAL DIYNYL COMPLEXES

The reaction of (η 5 -C 5 H 5 )Mo(CO)(dppe)Cl with LiCCCCSiMe 3 yielded (η 5 -C 5 H 5 )(CO)(dppe)MoCCCCSiMe 3 ( 1b ) and, as a by-product (η 5 -C 5 H 5 )Mo(CO)(dppe)Br ( 1a ). Treatment of 1b with 0.2 equivalents of tetrabutylammonium fluoride or (η 5 -C 5 H 5 )Mo(CO)(dppe)Cl with HCCCCH gave the terminal butadiyne complex (η 5 -C 5 H 5 )(CO)(dppe)MoCCCCH ( 2 ). Complex 2 was deprotonated with sec -BuLi or lithium diisopropylamide, and the resulting anion (η 5 -C 5 H 5 )(CO)(dppe)MoCCCCLi ( 3 ) was trapped with Me 3 SiCl to regenerate 1b . The synthesis of Co 2 (CO) 4 L 2 (μ-η 2 -Me 3 SiC 2 CCSiMe 3 ) (L 2 =dppa 4 , 2PPh 2 Me 5 ) compounds can be achieved by two methods: from Co 2 (CO) 6 (μ-dppa) by reaction with Me 3 SiCCCCSiMe 3 in 1:1 ratio to yield 4 , or from Co 2 (CO) 6 (μ-η 2 -Me 3 SiC 2 CCSiMe 3 ) by reaction with dppa (1:1 ratio) and PPh 2 Me (1:2 ratio) to yield 4 and 5 , respectively. When the Co 2 (CO) 4 (μ-dppa)(μ-η 2 -Me 3 SiC 2 CCSiMe 3 ) complex was treated with more Co 2 (CO) 6 (μ-dppa) the green di-substituted complex [Co 2 (CO) 4 (μ-dppa)] 2 (μ-η 2 :μ-η 2 -Me 3 SiC 2 C 2 SiMe 3 ) ( 6 ) was obtained. Desilylation of 4 with Bu 4 NF gave Co 2 (CO) 4 (μ-dppa)(μ-η 2 -Me 3 SiC 2 CCH) ( 7 ). All compounds synthesized have been characterized by analytical and spectroscopic data (IR, 1 H-, 31 P-, 13 C-NMR, MS). In addition, compounds 1a and 4 were characterized by X-ray structure analysis.

Mono-μ-hydrido complexes of pentamethylcyclopentadienylcobalt

Abstract The complex (η5-C5Me5)Co(CO)2 reacts with Cl2 and with Br2 to give [(η5-C5Me5)CoCl(μ-Cl)]2 and (η5-C5Me5)Co(CO)Br2, respectively. The latter was converted into the dimeric species [(η5-C5Me5CoBr(μ-Br)]2. The reaction of dimeric pentamethylcyclopentadienylcobalt complexes [(η5-C5Me5)CoX(μ-X)]2 (X = Cl, Br, I) with potassium hydroxide gives the mono-μ-hydrido complexes [(η5-C5Me5)CoX]2(μ-H)(μ-X).

Syntheses and reactions of [η5-CH3C5H4Cr(CO)3]2

The complexes [η5-CH3C5H4Cr(CO)3]2 have been prepared, and their reactions with trivalent phosphorus ligands L (L = Ph3P, (MeO)3P, (EtO)3P) shown to give [η5-CH3C5H4Cr(CO)2L]2 complexes.