Neutral and Cationic Alkyl Tantalum Imido Complexes:  Synthesis and Migratory Insertion Reactions

Abstract

The synthesis and reactivity of dibenzyl cationic tantalum imido complexes is described. The trialkyl tantalum imido compounds Bn(3)Ta=NCMe(3) (1) and Np(3)Ta=NCMe(3) (2) were synthesized as starting materials for the study of dialkyl cationic tantalum imido complexes. Compound 1 undergoes insertion reactions with diisopropylcarbodiimide and 2,6-dimethylphenylisocyanide to give (bisamidinate)imido complex 5 and (bisimino-acyl)imido complex 6, respectively. Treatment of compound 1 with B(C(6)F(5))(3) gives the zwitterionic tantalum complex [Bn(2)Ta=NCMe(3)][BnB(C(6)F(5))(3)] (7) which is stabilized by eta(6)-coordination of the benzyl triaryl borate anion. Coordination of the aryl anion can be displaced by three equivalents of pyridine to give the Lewis base complex 8. Treatment of compound 1 with [Ph(3)C][B(C(6)F(5))(4)] gives the cationic tantalum imido complex [Bn(2)Ta=NCMe(3)][B(C(6)F(5))(4)] (3). This salt forms insoluble aggregates unless trapped by THF coordination or an insertion reaction with an alkyne or an alkene. Cation 3 undergoes migratory insertion reactions with diphenylacetylene, phenylacetylene, norbornene, and cis-cyclooctene to give the corresponding alkenyl or modified alkyl imido complexes. The characterization of these products and the significance of these insertion reactions with respect to Ziegler-Natta polymerizations and hydroamination reactions are described.

Early/Late Heterobimetallic Tantalum/Rhodium Species Assembled Through a Novel Bifunctional NHC‐OH Ligand

“…This suggests that the Ta–NHC association might be loose and labile, and could eventually be displaced by another metal centre with a higher affinity for the NHC moiety (see below). The metrical parameters for the Ta=N t Bu moiety (Ta‐N3‐C22 angle=173.5(4)°, TaC=N3 bond length=1.753(5) Å) are typical of tantalum–imido motifs reported in the literature . The Ta−O (1.953(3) Å) and Ta−C neopentyl (Ta−C26=2.213(6) Å, Ta−C31=2.232(5) Å) bond lengths are as expected.…”

“…The alcoholysis of the tantalum tris(neopentyl) imido complex [Ta(N t Bu)(CH 2 t Bu) 3 ] with 1 equivalent of the NHC‐alcohol ligand (HL, 2 ) in toluene at room temperature released 1 equivalent of neopentane (quantified by 1 H NMR analysis using durene as internal standard) and gave [Ta(N t Bu)(L)(CH 2 t Bu) 2 ] ( 3 ) in an isolated yield of 74 % (Scheme ). The alkylidene‐NHC complex [Ta(CH t Bu)(L)(CH 2 t Bu) 2 ] ( 4 ) was prepared in an analogous manner by the reaction of [Ta(CH t Bu)(CH 2 t Bu) 3 ] with 2 and was isolated in a yield of 84 %.…”

“…Deuterated solvents were dried over Na/benzophenone ([D 8 ]THF and C 6 D 6 ) or CaH 2 (CDCl 3 ), vacuum‐transferred to a storage flask and degassed prior to use. [Ta(N t Bu)(CH 2 t Bu) 3 ] and [Ta(CH t Bu)(CH 2 t Bu) 3 ] were prepared according to literature procedures. All other reagents were acquired from commercial sources and used as received.…”

Synthesis and Characterization of Cationic Tetramethyl Tantalum(V) Complex

“…This change planned to enter the field of predictive catalysis. Unfortunately, the drawback for tantalum with respect to tungsten is that the similar cationic Ta-complexes are scarce in literature [14][15][16], whereas there are several examples with stable cationic 2 of 9 tantalum complexes containing one or more nitrogen [17], phosphorous [18] and cyclopentadienyl containing ligands [19][20][21].…”

Suitable Approach to Prepare N‐Substituted Niobium Complexes – Study of the Factors Controlling the Process

“…Transition‐metal complexes containing nitrogen‐based ligands that can act as a reactive site, such as amido and imido ligands, continue to generate a great deal of interest on account of their crucial roles in many stoichiometric and catalytic reactions, such as olefin metathesis,, Ziegler–Natta polymerization, hydroamination reactions, and ring‐opening metathesis polymerization In addition, owing to their strong π‐donating capabilities and relative inertness, these groups have been used widely in suitable supporting ligands to stabilize high‐valent early transition‐metal complexes. The study of the organometallic chemistry of cyclopentadienyl (Cp) imido complexes of group 5 metals has been stimulated by the isoelectronic relationship between such complexes and the well‐known group 4 bent metallocenes, which are used extensively as α‐olefin polymerization catalysts …”