Two Tris(imino)tin(II) and -lead(II) Cage Complexes. Syntheses and Structures of E[.mu.-N:C(tBu)Ph]3Li.cntdot.THF (E = Sn, Pb)

Abstract

The reactions of CpzPb and Cp2p. with LiN=C('Bu)Ph (1:l; 2 or 3 equiv) in THF produce the isostructural complexes Pb[p.-N=C('Bu)Ph]3Li*THF (1) and Sn[p-N=C('Bu)Ph]3Li-THF (2), respectively. Complex 2 can also be prepared by the facile ligand-exchange reaction of 1 and Cp2Sn in THF. The crystal structures of both complexes have been obtained at 153 K. Crystal data: 1, orthorhombic, space group P21212, a = 16.912(2) A, b = 19.214(2) A, c = 11.212(3) A, Z = 4; 2, monoclinic, space group P21/n, a = 10.679(2) A, b = 33.036(7) A, c = 10.683(2) A, (? = 106.84(3)", Z = 4. Both complexes havemonomeric trigonal bipyramidal EN3Licagestructures (E = Pb, Sn) in which there are sharp (ca. 80") angles at the bridging imino-N centers and close intermolecular E--Li contacts which are slightly greater than the sum of the covalent radii of the metals [2.85(3) in 1 and 2.776(4)A in 21. Model semiempirical (MNDO) calculations suggest that there is no significant E-Li bonding in either complex and that the observed core geometries mainly reflect the optimal bridging angle of the imino ligands. Monomer molecules of 1 exhibit extreme angular distortions within the PbN3Li core, resulting from two such molecules pairing up in the lattice. Their phenyl groups intermesh, and long-range (ca. 3.26 A) (ortho)C-H-Pb contacts are established. In contrast, molecules of 2 have a largely symmetrical core and do not associate in the manner of those of 1 in the solid state. This unexpected structural difference between 1 and 2 may suggest that the (ortho)C-H-.Pb contacts observed in 1 are more than simply van der Waals interactions.