Alkyne[hydrotris(pyrazolyl)borato]tantalum Complexes – An Ethyl Group is a Better α-Agostic Donor Than a Methyl Group

Abstract

The synthesis of unprecedented alkyne hydrotris(3,5‐dimethylpyrazolyl)borato (TpMe2) tantalum(III) complexes is reported. The parent dichloro complex TpMe2TaCl2(PhC≡ CCH3) (2) is obtained from TaCl3(DME)(PhC≡CCH3) and KTpMe2. 2 reacts with methyllithium to give the dimethyl complex TpMe2Ta(CH3)2(PhC≡CCH3) (3) and with ethylmagnesium chloride to give the X‐ray characterized α‐agostic ethyl complex TpMe2Ta(Cl)(μ‐H–CHCH3)(PhC≡CCH3) (4). Reaction of 4 with methyllithium generates the mixed methyl ethyl complex TpMe2Ta(CH3)(μ‐H–CHCH3)(PhC≡CCH3) (5) in solution. Spectroscopic data indicate that 5 is α‐agostic at the ethyl group only.

Synthesis and characterization of poly(pyrazolyl)borate tantalum amide complexes and their reactivities toward oxygen

“…Although numerous studies have been conducted on polypyrazolyborate complexes of main group and transition metals, only a few studies of Ta complexes containing the ligands are known [8][9][10][11][12][13][14][15][16][17][18] . Notably, no Ta complex containing only polypyrazolyborate and amides has been reported.…”

Synthesis, Structure, and Reactivity of Niobium and Tantalum Alkyne Complexes

“…The ease with which these compounds can be synthesized, as well as the variety of different alkyne substrates supported, make them ideal starting materials for group 5 alkyne complexes; indeed, there are numerous examples in the literature ,− where 15 and 16 act as reagents for the installation of Nb­(RCCR′) or Ta­(RCCR′) units into a wide variety of ligand sets; some representative examples from work reported by the groups of Etienne − ( 17 and 18 ), Otero ( 19 ), Hill ( 20 ), and Fryzuk ( 21 ) are shown in Scheme .…”

Tantalum Complexes Incorporating Tris(pyrazolyl)Borate Ligands: Syntheses, Structures, and Ethylene Polymerization Behavior

“…The elongation of the Ta−N distance may be attributed to a more electron-donating nature of the imido group than that of the Cl atom. The extent of the trans influence of the imido auxiliary ligand is greater than that of the alkyne auxiliary ligands, Tp*TaCl 2 (η 2 -phenylpropyne) and Tp*TaEtCl(η 2 -phenylpropyne) . The average Ta−N distances for the pyrazolyl groups ( 3 : 2.29 Å; 4 : 2.31 Å) are somewhat longer than those of the reported Tp*TaCl 2 (η 2 -phenylpropyne) (average 2.25 Å), Tp*TaEtCl(η 2 -phenylpropyne) (average 2.28 Å), TpTaMe 3 Cl (average 2.27 Å), Tp*TaCl(η 2 -CH 2 NPh)(CH 2 t Bu) (average 2.27 Å), and [Tp*TaCl 3 ][TaCl 6 ] (average 2.16 Å) …”