New Types of Constrained Geometry Group 4 Metal Complexes Derived from the Aminomethyldicarbollyl Ligand System: Synthesis and Structural Characterization of Mono-dicarbollylamino and Bis-dicarbollylamino Group 4 Metal Complexes

A series of constrained geometry group 4 metal complexes containing the (N,N‘-dimethylaminomethyl)
dicarbollyl ligand DcabNH [nido-7-NHMe2(CH2)-8-R-7,8-C2B9H10] (3) was prepared. New types of
constrained geometry titanium complexes with the formula (DcabN)TiCl2, [{(η5-RC2B9H9)(CH2)(η1-NMe2)}TiCl2] (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(NMe2)4 in toluene afforded (DcabN)Ti(NMe2)2, [{(η5-RC2B9H9)(CH2)(η1-NMe2)}Ti(NMe2)2] (5) (R = H, a; Me, b), which readily reacted with Me3SiCl to
yield the corresponding chloride complexes (DcabN)TiCl2 (4). However, the reaction of 3 with Zr(NMe2)4
in toluene afforded (DcabN)Zr(NMe2)2(HNMe2) [{(η5-RC2B9H9)(CH2)(η1-NMe2)}Zr(NMe2)2(HNMe2)] (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 η5;η1-bonding mode derived from the dicarbollylamino ligand
functional group. The corresponding bis-chelate complexes, (DcabN)2Ti (7), were synthesized from the
reaction of 4a with an additional dicarbollyl ligand 3a. Bis-chelated complexes (DcabN)2M (M = Ti, 7;
Zr, 8; Hf, 9) were also formed upon the reaction of 3a with MX4 (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 (DcabN)2M (7−9). The tetrahedral coordination of the metal
center was proven by single-crystal X-ray determination of the complex (DcabN)2Zr (8). New types of
titanium alkoxides, (DcabN)Ti(OiPr)2 (10), were synthesized from the reaction of 3a with Ti(OiPr)4.
Sterically less-demanding phenols such as C6H5OH and 2-MeC6H4OH replaced the coordinated amido
ligands on (DcabN)Ti(NMe2)2 (5a) to yield the aryloxy-stabilized CGC complexes (DcabN)Ti(OPh)2 (Ph
= C6H5, 11; 2-Me-C6H4, 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 (DcabN)Ti(OPh)2 (Ph = C6H5, 11; 2-Me-C6H4, 12).