Cyclic Hydroborate Complexes of Metallocenes. IV. Weak Unsupported Single Hydrogen Bridges in Cp(2)Zr{(&mgr;-H)B(X)CH(2)Ph}{(&mgr;-H)(2)BX} (X = C(5)H(10), C(4)H(8)).

The compounds Cp(2)Zr{(&mgr;-H)(BC(5)H(10))CH(2)Ph}{(&mgr;-H)(2)BC(5)H(10)}, 1, and Cp(2)Zr{(&mgr;-H)(BC(4)H(8))CH(2)Ph}{(&mgr;-H)(2)BC(4)H(8)}, 2, were prepared in yields of 59% and 51%, respectively, from the reactions of Cp(2)ZrCl{(&mgr;-H)(2)BX} (X = C(5)H(10), C(4)H(8)) with PhCH(2)MgCl. Single-crystal X-ray diffraction analyses indicate the presence of an unsupported Zr-H-B bond in these complexes. In solution at low temperature (1)H 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 Cp(2)ZrH{(&mgr;-H)(2)BC(5)H(10)} and B(C(5)H(10))CH(2)Ph in the case of complex 1, and Cp(2)ZrH{(&mgr;-H)(2)BC(4)H(8)} and B(C(4)H(8))CH(2)Ph in the case of complex 2. It is possible to pump away the B(C(4)H(8))CH(2)Ph from solid 2 at room temperature, leaving behind Cp(2)ZrH{(&mgr;-H)(2)BC(4)H(8)}. These results suggest that the Zr-H bond acts as an electron pair donor to trivalent boron in the formation of 1and 2. Crystal data for Cp(2)Zr{(&mgr;-H)(BC(5)H(10))CH(2)Ph}{(&mgr;-H)(2)BC(5)H(10)}: monoclinic, P2(1)/m (No. 11), a = 9.392(5) Å, b = 13.250(4) Å, c = 9.841(6) Å, beta = 95.70(4) degrees, Z = 2. Crystal data for Cp(2)Zr{(&mgr;-H)(BC(4)H(8))CH(2)Ph}{(&mgr;-H)(2)BC(4)H(8)}: orthorhombic, Pbca (No. 61), a = 18.1630(10) Å, b = 19.0497(10) Å, c = 13.0393(10) Å, Z = 8.