Reactions of the nitridocarbonyl cluster anion [Rh6N(CO)15]– with strong bases: synthesis and crystal structure of the hydridic dianion [Rh6(µ-H)N(CO)14]2–

Abstract

The reaction of the nitridocarbonyl anion [Rh₆N(CO)₁₅]^–, as its K⁺ salt, in water or alcoholic solution with alkali metal hydroxides afforded the novel hydridic species [Rh₆(µ-H)N(CO)₁₄]^2–, isolated as the caesium (2a) and the bis(triphenylphosphine)iminium (2b) salts. Both species have been investigated by X-ray structural analysis. Compound 2a crystallizes in the hexagonal system, space group P6₃/mmc(no. 194), with a=b= 11.089(2), c= 12.308(4)Å, Z= 2. Compound 2b gives monoclinic crystals, space group C2/c(no. 15), with a= 26.896(3), b= 17.143(6), c= 20.250(2)Å, β= 118.80(1)°, Z= 4. The structures were refined on the basis of 355 (2a) and 2170 (2b) significant independent reflections to final R values of 0.0427 and 0.0491 for 2a and 2b, respectively. The anion contains a trigonal prismatic cluster centred by the nitrido ligand. The hydrido ligand bridges an interbasal Rh–Rh edge replacing a bridging CO group of the parent anion [Rh₆N(CO)₁₅]^–. This substitution causes some stereochemical effects which are discussed for 2b; in 2a the anion has essentially the same stereochemistry but the interbasal ligands (two CO and one H) are disordered, due to the presence of a three-fold crystallographic axis.