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 ) η 5 -C 5 H 4 B(C 6 F 5 ) 2 ) Simon J. Lancaster, Sarah Al-Benna, Mark Thornton-Pett, and Manfred Bochmann* School of Chemistry, University of Leeds, Leeds, U.K. LS2 9JT Received December 8, 1999 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: ∆G q ) 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. Introduction Complexes with boron-substituted cyclopentadienyl ligands have attracted much attention recently. Whereas boryl-Cp complexes of 18-electron metallocenes are accessible by direct borylation of cyclopentadienyl ligands with BX 3 (X ) Cl, Br, I), RBI 2 , or B 2 Cl 4 , 1 this method is not applicable to group 4 metallocenes. 2 The first examples of boryl-Cp titanium complexes were reported in 1979 by Jutzi and Seufert, who prepared the series of half-sandwich compounds (C 5 H 3 RBX 2 )TiCl 3 (R ) H, Me; X ) Cl, Br, OEt, Me) by the dehalosilylation of C 5 H 3 R(BX 2 )SiMe 3 , 3 and more recently by Shapiro and co-workers. 4 Reetz et al. described a series of borylated zirconocenes of the types (R 2 BC 5 H 4 ) 2 ZrCl 2 and (R 2 - BC 5 H 4 )(C 5 H 5 )ZrCl 2 (R ) Me, Et, OEt, C 6 F 5 ). 5 Related complexes with pendant -(CH 2 ) 3 B(C 6 F 5 ) 2 moieties were made by Piers et al. by the hydroboration of allyl-Cp complexes with HB(C 6 F 5 ) 2 . 6 A number of boron-bridged ansa-titanocenes and -zirconocenes are also known. 7 As well as neutral boryl substituents on the cyclopentadi- enyl ring, there have also been examples of anionic borato-substituted complexes, formed either through the electrophilic substitution reaction of a metallocene complex 8 or introduced as a borato-substituted cyclo- pentadienyl ligand. 9 We recently described the synthesis of ((pentafluo- rophenyl)boryl)cyclopentadienyl half-sandwich com- (1) (a) McVey, S.; Morrison, I. 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