Metalmetal multiple bonds : IV. The chemistry of bis(cyclopentadienyldicarbonyl-molybdenum) ( Mo Mo)

Abstract

The synthesis and chemistry of Cp 2Mo 2(CO) 4 (I) a coplex containing a reaction Mo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 Cp 2Mo 2(CO) 6 precursor. Numerous soft nucleophiles add to I to give complexes, e.g., trans-(CpMo(CO) 2L) 2 (L = Ph 3P, P(OMe) 3), (μ-RC 2R′)Cp 2Mo 2(CO) 4, and (μ-SR) 2Cp 2Mo 2(CO) 4. (Et 4N)(Cp 2Mo 2(CO) 4CN) may be isolated from the reaction of cyanide ion with I. Iodine and hydrogen chloride react to give Cp 2Mo 2(CO) 4I 2 and (μ-H)(μ-Cl)Cp 2Mo 2(CO) 4, respectively. Silver and mercuric ions are reduced to the metal by I, but Ph 2Hg 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 L 4Pt (L = Ph 3P) and forms the triangulo-cluster, (μ-L 2Pt)Cp 2Mo 2(CO) 4. With Na 2Fe(CO) 4, Cp 2Mo 2(CO) 4I 2 forms the analogous cluster, (μ-Fe(CO) 4)Cp 2Mo 2(CO) 4. By electron counting rules, these clusters should contain MoMo double bonds. Evidence is presented which indicates I and Co 2(CO) 8 form an unstable tetrahedrane cluster. At 100°C in toluene, I may reversibly dimerize to give a tetrahedrane Mo 4-cluster, as shown by scrambling experiments. Complex I reacts slowly with Mn 2(CO) 10 to give CpMo(CO) 3Mn(CO) 5 as the only isolable mixed-metal product.