A COMPARATIVE SYNTHETIC AND STRUCTURAL STUDY OF TRIPHENYLMETHOXIDE AND TRIPHENYLSILOXIDE COMPLEXES OF THE EARLY LANTHANIDES, INCLUDING X-RAY CRYSTAL-STRUCTURES OF LA2(OCPH3)6 AND CE2(OSIPH3)6

La[N(SiMe3)2]3 reacts with 3 equiv of triphenylmethanol in toluene to form the dimer [La(OCPh3)2(mu-OCPh3)]2 (1) in 90% yield. 1 crystallizes in the triclinic space group P1BAR with a = 12.019 (3) angstrom, b = 14.287 (2) angstrom, c = 16.375 (3) angstrom, alpha = 73.99 (1)-degrees, beta = 85.39 (2)-degrees, gamma = 76.07 (2)-degrees, V = 2622.8 (8) angstrom 3, and D(calcd) = 1.34 Mg/m3 for Z = 1. Least-squares refinement on the basis of 10950 observed reflections led to a final R(F) = 3.7%. Each lanthanum atom in 1 is surrounded by two terminal and two unsymmetrically bridging alkoxide ligands such that the four oxygen donor atoms nearly describe a tetrahedron. The bridging La-O distances are 2.389 (2) and 2.483 (2) angstrom, and the terminal La-O distances average 2.180 (5) angstrom. The cerium analogue [Ce(OCPh3)2(mu-OCPh3)]2 (2) can be prepared similarly, and a single-crystal analysis shows it to be isomorphous with 1. Triphenylsilanol reacts with Ln[N(SiMe3)2]3 (Ln = La, Ce) in toluene to form the analogous Ph3SiO complexes [Ln(OSiPh3)2(mu-OSiPh3)]2 (Ln = La (3), Ce (4)). Complex 4 crystallizes from toluene in the triclinic space group P1BAR with a = 13.766 (2) angstrom, b = 14.376 (1) angstrom, c = 14.603 (2) angstrom, alpha = 73.34 (1)-degrees, beta = 70.45 (1)-degrees, gamma = 75.87 (1)-degrees, V = 2573.4 (5) angstrom 3, and D(calcd) = 1.37 Mg/m3 for Z = 1. Least-squares refinement on the basis of 5599 observed reflections led to a final R(F) = 6.3%. The structure of 4 is similar to that of 1 except that the four oxygen atoms surrounding each metal center approximate a square-pyramidal geometry which has a carbon atom of one of the arene rings in one basal position. By single-crystal analysis, complex 3 is isomorphous with 4. Complexes 3 and 4 dissolve in THF to form the previously characterized Ln(OSiPh3)3(THF)3 complexes. Compounds 1 and 2 are less soluble than 3 and 4 but dissolve in hot THF to form the more soluble THF adducts, Ln(OCPh3)3(THF)x.