Neutral and Cationic Group 4 Complexes Containing Bis(borylamide) Ligands, [R₂BNCH₂CH₂NBR₂]²⁻(R = 2,4,6-i-Pr₃C₆H₂, M = Zr; R = Cyclohexyl, M = Ti, Zr, Hf)

Reaction of Li 2 (TripBen)(THF) 4 ([(2,4,6-i-Pr 3 C 6 H 2 ) 2 BNCH 2 CH 2 NB(2,4,6-i-Pr 3 C 6 H 2 ) 2 ] 2 - = (TripBen) 2 - ) with ZrCl 4 (THF) 2 in toluene cleanly provides (TripBen)ZrCl 2 . (TripBen)ZrCl 2 can be alkylated with Grignard reagents to yield the dimethyl ( 2 ), diethyl ( 3 ), and dibutyl ( 4 ) derivatives, (TripBen)ZrR 2 . The structure of (TripBen)Zr(CD 3 ) 2 reveals that π bonding between boron and nitrogen results in one Trip ring on each boron being oriented over the two alkyl groups. The reaction between (TripBen)ZrMe 2 and B(C 6 F 5 ) 3 in pentane yields colorless crystals of {(TripBen)ZrMe}{MeB(C 6 F 5 ) 3 } ( 5a ). The dialkyl complexes 2 − 4 react with [HNMe 2 Ph][B(C 6 F 5 ) 4 ] in toluene to yield free dimethylaniline and species that are identical to 5a according to NMR spectra. (CyBen)M(CH 2 SiMe 3 ) 2 complexes ([(cyclohexyl) 2 BNCH 2 CH 2 NB(cyclohexyl) 2 ] 2 - = (CyBen) 2 - ) are prepared by the reaction between Li 2 (CyBen)(ether) and M(CH 2 SiMe 3 ) 2 Cl 2 (ether) x (M = Ti, Zr, or Hf). (CyBen)MI 2 complexes are formed upon treating (CyBen)M(CH 2 SiMe 3 ) 2 complexes with iodine. A variety of (CyBen)MR 2 species can be prepared, including those in which the alkyl contains β protons. The molecular structure of (CyBen)Zr(CH 2 CH 3 ) 2 shows it to be a relatively symmetric species in which one cyclohexyl ring on each boron is located directly over the two ethyl ligands. Diisobutyl complexes (CyBen)M(CH 2 CHMe 2 ) 2 react with [Ph 3 C][B(C 6 F 5 ) 4 ] in chlorobenzene at −30 °C to give the cations [(CyBen)M(CH 2 CHMe 2 )][B(C 6 F 5 ) 4 ], which are believed to be stabilized by coordination of chlorobenzene or toluene. Chlorobenzene solutions of [(CyBen)M(CH 2 CHMe 2 )(S)][B(C 6 F 5 ) 4 ] (M = Zr, Hf; S = chlorobenzene) polymerize 225 equiv of 1-hexene quantitatively at −30 °C to give regioregular poly(1-hexene) of high molecular weight ( M n = (0.4−1.3) × 10 5 g/mol) and high polydispersity (5−6).