Unusual Si–H Bond Activation and Formation of Cationic Scandium Amide Complexes from a Mono(amidinate)-Ligated Scandium Bis(silylamide) Complex and Their Performance in Isoprene Polymerization

Abstract

Amine elimination of scandium tris(silylamide) complex Sc[N(SiHMe 2 ) 2 ] 3 (THF) with 1 equiv of the amidine [PhC(N-2,6-i Pr 2 C 6 H 3 ) 2 ]H in toluene afforded the neutral mono(amidinate) scandium bis(silylamide) complex [PhC(N-2,6-i Pr 2 C 6 H 3 ) 2 ]Sc[N(SiHMe 2 ) 2 ] 2 (1) in 93% isolated yield. When 1 was activated with 1 equiv of [Ph 3 C][B(C 6 F 5 ) 4 ] in the presence of THF, the unexpected cationic amidinate scandium amide complex [{PhC(N-2,6-i Pr 2 C 6 H 3 ) 2 }ScN{SiHMe 2 }-{SiMe 2 N(SiHMe 2 ) 2 }(THF) 2 ][B(C 6 F 5 ) 4 ] (2) was generated. Treatment of 1 with excess AlMe 3 gave the Sc/Al heterometallic methyl complex [PhC(N-2,6-i Pr 2 C 6 H 3 ) 2 ]Sc[(μ-Me) 2 AlMe 2 ] 2 (3). All these complexes were well-characterized by elemental analysis, NMR spectroscopy, and X-ray crystallography. The combination 1/[Ph 3 C][B(C 6 F 5 ) 4 ] in toluene showed activity toward isoprene polymerization. Addition of excess AlMe 3 to the 1/[Ph 3 C][B(C 6 F 5 ) 4 ] catalyst system switched the regioselectivity of isoprene polymerization from 3,4-specific to cis-1,4-selective.

Lewis Base Mediated β-Elimination and Lewis Acid Mediated Insertion Reactions of Disilazido Zirconium Compounds

“…In addition, a recent report documents a related N(SiHMe 2 ) 2 migration from a scandium center to a β-Si upon addition of a Lewis acid, and a similar sequential hydrogen abstraction/ silazide migration sequence was proposed. 15 These similarities indicate that the reactivity pattern described in the current contribution is not simply limited to the Cp 2 Zr system.…”

“…14 Interestingly, a Si−N bond formation was recently described in the reaction of {PhC(N-2,6-(Me 2 HC) 2 C 6 H 3 ) 2 }Sc{N(SiHMe 2 ) 2 } 2 and Ph 3 C + , which gives Ph 3 CH and [Sc{N(SiHMe 2 )SiMe 2 N-(SiHMe 2 ) 2 }] + . 15 Here, we present a study of the cationic disilazidozirconium compound [Cp 2 ZrN(SiHMe 2 ) 2 ] + ([2] + ), which possesses extreme spectroscopic and structural features attributed to the side-on interaction of two SiH groups with a zirconium center. The analogy of the side-on β-Si−H⇀Zr interaction with agostic β-CH organometallic compounds is supported by pathways to form [2] + and its reactivity.…”

“…The compounds Cp 2 Zr{N(SiHMe 2 ) 2 }X (X = OTf (11), Cl(13), OMe(15), OCHMe 2(16)) react with B(C 6 F 5 ) 3 or [Ph 3 C][B(C 6 F 5 ) 4 ] in benzene to give [Cp 2 ZrN(SiHMe 2 )-(SiMe 2 -μ-X)] + (X = OTf ([12] + ), Cl ([14] + ), OMe ([17] + ), OCHMe 2 ([18] + )) (Scheme 4). In all cases, hydrogen abstraction is supported by the formation of [HB(C 6 F 5 ) 3 ] − (e.g., [12][HB(C 6 F 5 ) 3 ]: 11 B NMR −24.8 ppm, 1 J BH = 87.1 Hz) or Ph 3 CH.…”

Amido rare-earth complexes supported by an ansa bis(amidinate) ligand with a rigid 1,8-naphthalene linker: synthesis, structures and catalytic activity in rac-lactide polymerization and hydrophosphonylation of carbonyl compounds

“…Synthesis and characterization of compounds [1][2][3][4] Lanthanide amides proved to be efficient initiators for the ringopening polymerization of cyclic esters, 33,[38][39][40][41][42][43][44] components of catalyst systems for isoprene polymerization, [38][39][40][41][42][43][44] olefin hydroamination, 43,[45][46][47][48][49][50] hydrophosphination, 47 hydrophosphonylation of carbonyl compounds, [51][52][53][54][55] and aldimines. 51,56 Initially, we intended to prepare bis(amidinate) amido lanthanide complexes by the salt metathesis reactions of [1,8- and Na[N(SiMe 3 ) 2 ] 58 (THF, 60 1C, 24 h).…”

“…The borohydrides 5 and 6 had catalytic activities similar to those of amido derivatives 2-4. Thus, the addition of diethyl phosphite to 4-chloro-, 4-methyl-and 4-methoxybenzaldehyde gave the products 7a-7c in 99% yield in 15 min (Table 5, entries [28][29][30][37][38][39]. Under the same reaction conditions, when benzaldehyde and aliphatic aldehydes were used as the substrates the reaction was slower.…”