NEW ROUTES TO BIS[(CYCLOPENTADIENYL)COBAL T]-MU-(ETA(5)-2,3-DIHYDRO-1,3-DIBOROLYL) TRIPLE-DECKER COMPLEXES BY HYDROGEN SHIFT REACTIONS IN DERIVATIVES OF 4,5-DIISOPROPYLIDENE-1,3-DIBOROLANE, 2,4,5-TRIISOPROPYLIDENE-1,3-DIBOROLANE, AND BENZO-1,3-DIBORAFULVENE

The 31 VE dicobalt triple-decker complexes 6, 7a, 7b, c, 8a, b, and 9a , b with bridging 2,3-dihydro-1,3-diborolyl ligands are prepared. The reaction of the 1,3-diborole 1 with [(C5Me5)-Co(C2H4)2] leads to the s andwich complex 5, which is treated with [(C5H5)Co(C2H4)2] to yield un symmetrical 6. The 4,5-di-isopropylidenetrimethyl-1,3-diborolane 3 und ergoes a metal-induced 1,5-hydrogen shift and reacts with [(C5H5)Co(C2 H4)2] to form the triple-decker 7a. The reaction of the 2,4,5-triisopr opylidene-1,3-diborolane 4 with [(C5H5)Co(C2H4)2] leads to a mixture o f the triple-deckers 7b/c, formed by intermolecular hydrogen shift. Th e benzo-1,3-diborafulvene derivatives 2b and 2c also react with [(C5H5 )Co(C2H4)2] to give the triple-decker 8b and a mixture of 9a, b. In ad dition, the trinuclear complex 8c is obtained in low yield. The new pa ramagnetic triple-decker complexes have been analyzed by NMR and ESR s pectroscopic measurements as well as by electochemistry. The constitut ions of 7b/c, 8b, 8c, and 9a/b have been confirmed by X-ray structure analyses. The complexes are isostructural, the Co-Co distances range f rom 3.277(1) (7b/c) to 3.316(1) angstrom for 8c.