Synthetic, reactivity, and structural studies on borylcyclopentadienyl complexes of titanium: New Cp-B titanocene complexes with C-B-Cl, C-B-O, and C-B-N bridges (Cp-B = eta(5)-C5H4B(C6F5)(2))
Sj. Lancaster et al., Synthetic, reactivity, and structural studies on borylcyclopentadienyl complexes of titanium: New Cp-B titanocene complexes with C-B-Cl, C-B-O, and C-B-N bridges (Cp-B = eta(5)-C5H4B(C6F5)(2)), ORGANOMETAL, 19(8), 2000, pp. 1599-1608
The (borylcyclopentadienyl)titanium complex (Cp-B)TiCl3 (1; Cp-B = eta(5)-C
5H4B(C6F5)(2)) reacts with LiC5H5 (LiCp), LiC5H4SiMe3 (LiCP'), and LiC9H7 (
LiInd) to give the titanocene complexes (Cp-B)CpTiCl2 (2), (Cp-B)Cp'TiCl2 (
3), and (Cp-B)(Ind)TiCl2 (4), respectively. In contrast to 1, which possess
es piano stool geometry with an uncoordinated, trigonal-planar borg moiety,
the -B(C6F5)(2) substituents in 2-4 act as intramolecular Lewis acids by c
oordinating to chloride ligands, with formation of B-Cl-Ti bridges that hav
e relatively short B-Cl and elongated Ti-Cl bonds. The compounds are fluxio
nal, with the -B(C6F5)(2) moiety switching rapidly from one chloride ligand
to the other (2: Delta G(double dagger) = 37 kJ mol(-1) (200 K)). Recrysta
llization of 2 in the presence of traces of moisture afforded (Cp-B)CpTi(mu
-OH)Cl (5), with a rigid B-O-Ti chelate arrangement. Treatment of 1 with 1
or 2 equiv of LiHNCMe3 gives the binuclear titanium imido complexes [(Cp-B)
TiCl(mu-NCMe3)](2) (7) and [(Cp-B)TiCl(mu-NCMe3). H2NCMe3](2) (8), respecti
vely. These complexes are based on Ti2N2 rings but show no boron-imide inte
ractions. In contrast, the reaction of 2 with LiNHCMe3 affords (Cp-B)CpTi(m
u-NHCMe3)Cl (9), which exhibits a constrained-geometry type Cp-B-N arrangem
ent. The crystal structures of 4, 5, 8, and 9 have been determined.