The syntheses of group 4 metal complexes containing the ((dibenzylamino)ethyl)dicarbollide ligand DcabH C(2)N (nido-7-HNBz2(CH2)2-8-R-7,8-C2B9H10; 2) are reported. Various new types of constrained-geometry complexes [{(η5-RC2B9H9)(CH2)2(η1-NBz2)}MCl2] (M = Ti (3), Zr (4); R = H (a), Me (b)) were prepared by the reaction of the potassium salt of 2 with titanium or zirconium tetrachloride. The reaction of 2 with Ti(NMe2)4 in toluene affords [{(η5-RC2B9H9)(CH2)2(η1-NBz2)}Ti(NMe2)2] (5), which readily reacts with Me3SiCl to yield the corresponding chloride complex 3. The structure of the constrained-geometry complex [{(η5-C2B9H10)(CH2)2(η1-NBz2)}Ti(NMe2)2] (5a) was established by X-ray diffraction, which showed an η5:η1 bonding mode derived from the dicarbollylamino ligand fuctional group. In contrast, the reaction of 2 with Zr(NMe2)4 produced the untethered half-metallocene complexes [{(η5-RC2B9H9)(CH2)2(NBz2)}Zr(NMe2)2(NHMe2)] (6). The identity of 6 was confirmed by single-crystal X-ray diffraction. Due to coordination of free dimethylamine to the zirconium metal center, the sterically hindered dibenzylamine sidearm leaves the coordination sphere to form the corresponding untethered complexes. Furthermore, the titanium(IV) CGC complexes 3 exhibited unusual B,N-cyclization when reacted with O2, leading to the production of novel exocyclic dicarbollides (7). The crystallographic data were consistent with the formation of an unusual five-membered exocyclic ring, presumably due to steric interactions between the dibenzyl units and the dicarbollyl group. Finally, the sterically less bulky zirconium(IV) ((benzylamino)ethyl)dicarbollyl complex [{(η5-CH3C2B9H9)(CH2)(η1-NBz)}ZrCl2(THF)] (10b), in which the pendant amine is coordinated to the metal center, was prepared by the reaction of ZrCl4 with the potassium salt of [nido-7-NH2Bz+(CH2)-8-H-7,8-C2B9H10 -] (9b) in toluene.

A series of constrained geometry group 4 metal complexes containing the (N,N′-dimethylaminomethyl) dicarbollyl ligand Dcab N H [nido-7-NHMe 2 (CH 2 )-8-R-7,8-C 2 B 9 H 10 ] (3) was prepared. New types of constrained geometry titanium complexes with the formula (Dcab N )TiCl 2 , [{(η 5 -RC 2 B 9 H 9 )(CH 2 )(η 1 -NMe 2 )}TiCl 2 ] (R ) H, 4a; Me, 4b), were produced by the reaction of the potassium salt of 3 with titanium tetrachloride. The reaction of 3 with Ti(NMe 2 ) 4 in toluene afforded (Dcab N )Ti(NMe 2 ) 2 , [{(η 5 -RC 2 B 9 H 9 )(CH 2 )(η 1 -NMe 2 )}Ti(NMe 2 ) 2 ] (5) (R ) H, a; Me, b), which readily reacted with Me 3 SiCl to yield the corresponding chloride complexes (Dcab N )TiCl 2 (4). However, the reaction of 3 with Zr(NMe 2 ) 4 in toluene afforded (Dcab N )Zr(NMe 2 ) 2 (HNMe 2 ) [{(η 5 -RC 2 B 9 H 9 )(CH 2 )(η 1 -NMe 2 )}Zr(NMe 2 ) 2 (HNMe 2 )] (6) (R ) H, a; Me, b). The structures of the diamido complexes were established by X-ray diffraction studies of 5a and 5b, which authenticated an η 5 ;η 1 -bonding mode derived from the dicarbollylamino ligand functional group. The corresponding bis-chelate complexes, (Dcab N ) 2 Ti (7), were synthesized from the reaction of 4a with an additional dicarbollyl ligand 3a. Bis-chelated complexes (Dcab N ) 2 M (M ) Ti, 7; Zr, 8; Hf, 9) were also formed upon the reaction of 3a with MX 4 (M ) Ti, Zr, Hf) in a 2:1 molar ratio. The NMR spectra revealed that intramolecular M-N coordinations were preserved in solution, resulting in the formation of bis-chelated complexes (Dcab N ) 2 M (7-9). The tetrahedral coordination of the metal center was proven by single-crystal X-ray determination of the complex (Dcab N ) 2 Zr (8). New types of titanium alkoxides, (Dcab N )Ti(O i Pr) 2 (10), were synthesized from the reaction of 3a with Ti(O i Pr) 4 . Sterically less-demanding phenols such as C 6 H 5 OH and 2-MeC 6 H 4 OH replaced the coordinated amido ligands on (Dcab N )Ti(NMe 2 ) 2 (5a) to yield the aryloxy-stabilized CGC complexes (Dcab N )Ti(OPh) 2 (Ph ) C 6 H 5 , 11; 2-Me-C 6 H 4 , 12). The NMR spectra suggested that an intramolecular Ti-N coordination was intact in solution, resulting in a stable piano-stool structure whereby two aryloxy ligands resided in the leg positions. The aryloxy coordinations were further confirmed by single-crystal X-ray diffraction studies on the complexes (Dcab N )Ti(OPh) 2 (Ph ) C 6 H 5 , 11; 2-Me-C 6 H 4 , 12).