Iridium complexes cyanides

Rhodium and iridium complexes effect the dehydrogenation of the alkane chain in 1,6-bisdiphenylphosphinohexane to form (after treatment with cyanide ion) 1,6-(bisdiphenylphosphino)-frara-hex-3-ene.81... 

Cobalt, like iron, yields complex cyanide derivatives known respectively as cobalto-eyanides,M4Co(CN)(),andcobalti-cyanides, M3Co(CN)s. Of these, the latter alone are important. Rhodium and iridium in a similar manner yield rhodi-cyanides, M3Rh(CN)6, and iridi-cyanides, M3Ir(CN]6. 

Quite in contrast to, e.g., [CoCp2]+, borabenzene metal cations show a pronounced affinity toward hard nucleophiles such as amines, OH-, and to some extent even F- and H20. Qualitatively this affinity increases in the order CoCp2]+ 36 < 1 < 61 (69). [CoCp(C5H5BPh)]+ (1) adds tertiary amines at boron. With pyridine, the pyridinioboratacyclohexadienyl complex 70 is formed (K = 174 5 liters mol-1, in MeCN, 20°C), which can be isolated from CH2C12 as PF6- salt (69). The similar rhodium and iridium cations 36 and 37 form the stable cyanide adducts 71 and 72 (69). 

The more important simple derivatives of cobalt are divalent, the metal only yielding stable trivalent salts in conjunction with other metallic derivatives, as, for example, the cobalti-nitrites and eobalii-cyanides, or in the complex ammino derivatives. Rhodium and iridium function almost exclusively as trivalent metals in their salts. 

Proton magnetic resonance studies have also shown the presence of metal-hydrogen species in cyanide solutions of rhodium, platinum, and iridium (Table IX). In particular, the addition of CN- to a boiled aqueous solution of rhodium trichloride, followed by reduction with sodium boro-hydride, yields a solution that contains an Rh—H complex in moderately high concentrations and is stable in the absence of oxygen for several years (108). The observed coupling of the proton with the Rh10 nucleus (spin ) confirms the presence of an Rh—H bond (108). 

In aqueous solution, the complexes of most metal cations exist in dynamic equilibrium with their components. If we disturb this equilibrium, another one is instantly formed. It is quite otherwise with robust complexes which persist for hours (or even days) under conditions favourable to their decomposition any biological properties that they may have are strikingly different from those of their components. Robust complexes are formed where metal ions have 3,4 (low spin), 5, or 6 d electrons provided that formation of the complex involves large values of ligand-field stabilization energy. Metals most prone to form robust complexes are the transition metals platinum, iridium, osmium, palladium, rhodium, ruthenium, also (but not so frequently) nickel, cobalt, and iron. The halide and, particularly, the cyanide anions most readily form robust complexes with these transi-... 

Singer H, WiUdnson G (1968) Oxidative addition of hydrogen cyanide, hydrogen sulphide, and other acids to triphenylphosphine complexes of iridium(I) and ihodium(I). J Chem Soc A... 

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