ZIRCONOCENE-MEDIATED CYCLIZATION OF ALKYNYL DIBORYLMETHANES TO 1,3-DIBOROLANES

The carbon-carbon triple bond in bis[(di-alkylamino)(phenylethynyl)bor yl]methanes 2a,b can be easily cyclized using zirconocene to give deri vatives 3a,b of the new pentalene-like 6,8-dibora-3-zirconabicyclo[3.3 .0]octa-1,4-diene, containing a zirconacyclopentadiene ring attached t o a 1,3-diboracyclopentane unit. These heterocycles are characterized by NMR methods and by an X-ray structure determination of 3b. Compound 3b crystallizes from pentane in the monoclinic space group C2/c with a = 23.11(2) angstrom, b = 8.123(1) angstrom, c = 40.08(3) angstrom, b eta = 97.63(6)degrees, V = 7458(8) angstrom3, and rho(calc) = 1.175 Mg /m3 for M = 659.7 g/mol and Z = 8.