Synthetic, Reactivity, and Structural Studies on Borylcyclopentadienyl Complexes of Titanium: New CpBTitanocene Complexes with C−B−Cl, C−B−O, and C−B−N Bridges (CpB= η5-C5H4B(C6F5)2)

The (borylcyclopentadienyl)titanium complex (Cp B )TiCl 3 ( 1; Cp B = η 5 -C 5 H 4 B(C 6 F 5 ) 2 ) reacts with LiC 5 H 5 (LiCp), LiC 5 H 4 SiMe 3 (LiCp‘), and LiC 9 H 7 (LiInd) to give the titanocene complexes (Cp B )CpTiCl 2 ( 2 ), (Cp B )Cp‘TiCl 2 ( 3 ), and (Cp B )(Ind)TiCl 2 ( 4 ), respectively. In contrast to 1, which possesses piano stool geometry with an uncoordinated, trigonal-planar boryl moiety, the −B(C 6 F 5 ) 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(C 6 F 5 ) 2 moiety switching rapidly from one chloride ligand to the other ( 2: Δ G ⧧ = 37 kJ mol - 1 (200 K)). Recrystallization of 2 in the presence of traces of moisture afforded (Cp B )CpTi(μ-OH)Cl ( 5 ), with a rigid B−O−Ti chelate arrangement. Treatment of 1 with 1 or 2 equiv of LiHNCMe 3 gives the binuclear titanium imido complexes [(Cp B )TiCl(μ-NCMe 3 )] 2 ( 7 ) and [(Cp B )TiCl(μ-NCMe 3 )·H 2 NCMe 3 ] 2 ( 8 ), respectively. These complexes are based on Ti 2 N 2 rings but show no boron−imide interactions. In contrast, the reaction of 2 with LiNHCMe 3 affords (Cp B )CpTi(μ-NHCMe 3 )Cl ( 9 ), which exhibits a constrained-geometry type Cp−B−N arrangement. The crystal structures of 4, 5, 8, and 9 have been determined.