Synthetic, reactivity, and structural studies on borylcyclopentadienyl complexes of titanium:: New CpB titanocene complexes with C-B-Cl, C-B-O, and C-B-N bridges (CpB = η5-C5H4B(C6F5)2)

The (borylcyclopentadienyl)titanium complex (Cp-B)TiCl3 (1; Cp-B = eta(5)-C5H4B(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 possesses piano stool geometry with an uncoordinated, trigonal-planar borg moiety, the -B(C6F5)(2) substituents in 2-4 act as intramolecular Lewis acids by coordinating to chloride ligands, with formation of B-Cl-Ti bridges that have relatively short B-Cl and elongated Ti-Cl bonds. The compounds are fluxional, 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)). Recrystallization 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), respectively. These complexes are based on Ti2N2 rings but show no boron-imide interactions. In contrast, the reaction of 2 with LiNHCMe3 affords (Cp-B)CpTi(mu-NHCMe3)Cl (9), which exhibits a constrained-geometry type Cp-B-N arrangement. The crystal structures of 4, 5, 8, and 9 have been determined.