Synthesis and Molecular Structures of Pyridine-Containing Large-Membered Cyclic Bis(alkoxy)silanes(1)

The new cyclic silanes [(C(5)H(3)N)(CH(2)O)(2)SiMe(2)](2) (1) and (C(5)H(3)N)(CH(2)CPh(2)O)(2)SiMe(2) (2) containing 16-membered and 10-membered rings, respectively, were prepared by the condensation reaction of Me(2)SiCl(2) with an appropriate pyridine diol in the presence of Et(3)N. X-ray studies show that the dimeric formulation for 1 represents a tetracoordinate cyclic silane, whereas 2 has a geometry halfway from a tetrahedron toward a trigonal bipyramid (TBP) as a result of Si-N(ax) donor action. (29)Si and (1)H NMR indicate retention of the coordination geometry for 2 in solution that undergoes rapid Si-N cleavage and ring rearrangement. In comparison with other silanes containing five- and six-membered rings that exhibit nitrogen or oxygen coordination, the presence of larger rings, as in 2 and related silanes having sulfur coordination, indicates that retention of donor action persists, thus largely ruling out ring size as a dominant factor controlling the possibility of donor action at silicon. The dimeric silane 1 crystallizes in the triclinic space group P&onemacr; with a = 6.347(3) Å, b = 12.455(4) Å, c = 14.289(5) Å, alpha = 101.63(3) degrees, beta = 102.99(3) degrees, gamma = 104.71(3) degrees, and Z = 2. The cyclic silane 2 crystallizes in the triclinic space group P&onemacr; with a = 9.733(4) Å, b = 10.938(2) Å, c = 14.312(3) Å, alpha = 89.03(2) degrees, beta = 74.59(3) degrees, gamma = 79.24(3) degrees, and Z = 2. The final conventional unweighted residuals are 0.040 (1) and 0.039 (2).