Metal---metal multiple bonds : IV. The chemistry of bis(cyclopentadienyldicarbonyl-molybdenum) (Mo[triple bond]Mo)

Abstract

The synthesis and chemistry of Cp2Mo2(CO)4 (I) a coplex containing a reaction Mo[triple bond]Mo triple bond, are described. The formation of I in refluxing xylene is shown to occur via odd-electron intermediates from homolysis of the Mo---Mo bond in the Cp2Mo2(CO)6 precursor. Numerous soft nucleophiles add to I to give complexes, e.g., trans-(CpMo(CO)2L)2 (L = Ph3P, P(OMe)3), ([mu]-RC2R')Cp2Mo2(CO)4, and ([mu]-SR)2Cp2Mo2(CO)4. (Et4N)(Cp2Mo2(CO)4CN) may be isolated from the reaction of cyanide ion with I. Iodine and hydrogen chloride react to give Cp2Mo2(CO)4I2 and ([mu]-H)([mu]-Cl)Cp2Mo2(CO)4, respectively. Silver and mercuric ions are reduced to the metal by I, but Ph2Hg gives (CpMo(CO)3)2Hg in addition to metallic mercury. With tetracyanoethylene, I forms [CpMo(CO)4]+[TCNE]-. Complex I mimics the reaction of acetylenes with L4Pt (L = Ph3P) and forms the triangulo-cluster, ([mu]-L2Pt)Cp2Mo2(CO)4. With Na2Fe(CO)4, Cp2Mo2(CO)4I2 forms the analogous cluster, ([mu]-Fe(CO)4)Cp2Mo2(CO)4. By electron counting rules, these clusters should contain Mo=Mo double bonds. Evidence is presented which indicates I and Co2(CO)8 form an unstable tetrahedrane cluster. At 100[deg]C in toluene, I may reversibly dimerize to give a tetrahedrane Mo4-cluster, as shown by scrambling experiments. Complex I reacts slowly with Mn2(CO)10 to give CpMo(CO)3Mn(CO)5 as the only isolable mixed-metal product.