Cyclic hydroborate complexes of metallocenes.: IV.: Weak unsupported single hydrogen bridges in Cp2Zr{(μ-H)B(X)CH2Ph}{(μ-H)2BX} (X = C5H10, C4H8)

The compounds Cp2Zr{(mu-H)(BC5H10)CH2Ph}{(mu-H)(2)BC5H10}, 1, and Cp2Zr{(mu-H)(BC4H8)CH2Ph}{(mu-H)(2)BC4H8}, 2, were prepared in yields of 59% and 51%, respectively, from the reactions of Cp2ZrCl{(mu-H)(2)BX} (X = C5H10, C4H8) with PhCH2MgCl. Single-crystal X-ray diffraction analyses indicate the presence of an unsupported Zr-H-B bond in these complexes. In solution at low temperature H-1 NMR spectra are consistent with the presence of the unsupported Zr-H-B bridge in complexes 1 and 2. However, NMR spectra at room temperature indicate that the hydrogen bridge is dissociated into Cp2ZrH{(mu-H)(2)BC5H10} and B(C5H10)CH2Ph in the case of complex 1, and Cp2ZrH{(mu-H)(2)BC4H8} and B(C4H8)CH2Ph in the case of complex 2. It is possible to pump away the B(C4H8)CH2Ph from solid 2 at room temperature, leaving behind Cp2ZrH{(mu-H)(2)BC4H8}. These results suggest that the Zr-H bond acts as an electron pair donor to trivalent boron in the formation of 1 and 2. Crystal data for Cp2Zr{(mu-H)(BC5H10)CH2Ph}{(mu-H)(2)BC5H10} monoclinic, P2(1)/m (No. 11), a = 9.392(5) Angstrom, b = 13.250(4) Angstrom, c = 9.841(6) Angstrom, beta = 95.70(4)degrees, Z = 2. Crystal data for Cp2Zr{(mu-H)(BC4H8)CH2Ph}-{(mu-H)(2)BC4H8}: orthorhombic, Pbca (No. 61), a=18.1630(10) Angstrom, b=19.0497(10) Angstrom, c=13.0393(10) Angstrom, Z = 8.