| Abstrakt: |
The reaction of 1,2-{Cp*RuH}2B3H7 (1), Cp* = η5-C5Me5, with Co2(CO)8 in hexane yields two major ruthenaborane products, nido-1,2-{Cp*RuH}2-3-Co(CO)4B3H4 (2) and arachno-{Cp*RuH}(CO)B3H7 (3), as well as two other ruthenaboranes in low yield. In toluene, benzene, and THF one of these minor ruthenaborane products is found with an enhanced yield intermediate between those of 2 and 3. This compound has been isolated and characterized in solution and the solid state as the 8 skeletal electron pair (sep) arachno 1,2-{Cp*Ru}2(CO)2B3H7 (4) and shown to convert into a second isomeric form of similar stability. One isomer constitutes a diruthenium analogue of 8-sep pentaborane(11), whereas the other mimics the geometry of a known metal cluster with 8 sep. The variation in product concentrations in benzene, including [Cp*Ru(CO)2]2, {Cp*Ru(CO)2}Co(CO)4, and HCo(CO)4, as a function of time and Co2(CO)8/1 ratio has been determined by 1H and 11B NMR spectroscopy and interpreted in terms of a reaction pathway featuring competitive Co(CO)4 radical addition to ruthenium to yield 2 plus 3 and to boron to yield 4. The apparent solvent dependence of product distribution is attributed to impurity-initiated decomposition of the boron-based radical in hexane. |
