LANTHANIDE COMPLEXES OF BULKY SILOXIDE LIGANDS INCORPORATING PENDANT AMINE DONORS - SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF A VOLATILE TRIS(SILOXIDE) COMPLEX OF YTTRIUM(III) AND A NOVEL ZWITTERIONIC TETRAKIS(SILOXIDE) OF YTTERBIUM(III)

The silanol ligands HOSi(t-Bu)3-n[(CH2)3NMe2]n(3,n = 2;4, n = 1), were prepared from the appropriate chlorosilanes, HSi(t-Bu)3-nCln, in two steps. Reaction of 3 equiv of 3 or 4 with Ln[N(SiMe3)2]3 allowed isolation of the tris(siloxide) complexes Ln{OSi(t-Bu)3-n[(CH2)3NMe2]n}3 (5, Ln = Y, n = 2; 6, Ln = Y, n =1; 7, Ln = Ce, n = 1). Complexes 6 and 7 sublimed unchanged at 115 and 135-degrees-C at 10(-4) Torr, respectively. A single-crystal X-ray diffraction study of 6 revealed a trigonal bipyramidal geometry with the equatorial sites occupied by three siloxide O and the axial sites occupied by two NMe2 groups. The third dimethylaminopropyl arm is not coordinated. [Crystal data: triclinic space group P1BAR, a = 13.738(2) angstrom, b = 15.940(3) angstrom, c = 13.363(2) angstrom, alpha = 93.80(1)-degrees, beta = 116.77(1)-degrees, gamma = 74.55(1)-degrees, V = 2513.5 angstrom3, Z = 2, R = 0.0839, and R(W) = 0.1081.] Complex 6 is fluxional in solution to -80-degrees-C; exchange of coordinated and dangling (dimethylamino)propyl arms is suggested as a possible mechanism. Reaction of 4 equiv of 4 with Ln(N(SiMe3)2]3 produced novel zwitterionic tetrakis(siloxide) complexes, Ln[OSi-(t-Bu)2(CH2)3NMe2]3[OSi(t-Bu)2(CH2)3NMe2H) (8, Ln = Y; 9, Ln = Yb). An X-ray crystallographic study of 9 revealed a tetrahedral arrangement of siloxide O about Yb. One of the four dangling NMe2 groups is protonated and hydrogen-bonded to a second NMe2 unit. [Crystal data: monoclinic space group P2(1)/n, a = 13.266(3) angstrom, b = 23.337(5) angstrom, c = 21.914(3) angstrom, beta = 93.94(1)-degrees, V = 6768.0 angstrom3, Z = 4, R = 0.0684, and R(W) = 0.0929.] Complex 8 partially dissociates into 4 and 6 in toluene solution. A variable-temperature H-1 NMR study yielded DELTAH-degrees = 40 +/- 4 kJ mol-1 and DELTAS-degrees = 124 +/- 10 J mol-1 K-1 for this equilibrium. Reaction of 8 with LiCH2SiMe3 produced Li+{Y[OSi(t-BU)2(CH2)3NMe2]4}- (10) in good yield.