Insertion, protonolysis and photolysis reactivity of a thorium monoalkyl amidinate complex

Abstract

The reactivity of the thorium monoalkyl complex Th(CH₂SiMe₃)(BIMA)₃ [1, BIMA = MeC(NⁱPr)₂] with various small molecules is described. While steric congestion prohibits the insertion of N,N'-diisopropylcarbodiimide into the Th-C bond in 1, the first thorium tetrakis(amidinate) complex, Th(BIMA)₄ (2), is synthesized via an alternative salt metathesis route. Insertion of p-tolyl azide leads to the triazenido complex Th[(p-tolyl)NNN(CH₂SiMe₃)-κ²N^1,2](BIMA)₃ (3), which then undergoes thermal decomposition to the amido species Th[(p-tolyl)N(SiMe₃)](BIMA)₃ (4). The reaction of 1 with 2,6-dimethylphenylisocyanide results in the thorium iminoacyl complex Th[η²-(C[double bond, length as m-dash]N)-2,6-Me₂-C₆H₃(CH₂SiMe₃)](BIMA)₃ (5), while the reaction with isoelectronic CO leads to the products Th[OC([double bond, length as m-dash]CH₂)SiMe₃](BIMA)₃ (6) and Th[OC(NⁱPr)C(CH₂SiMe₃)(C(Me)N(ⁱPr))O-κ²O,O'](BIMA)₂ (7), the latter being the result of CO coupling and insertion into an amidinate ligand. Protonolysis is achieved with several substrates, producing amido (9), aryloxide (10), phosphido (11a,b), acetylide (12), and cationic (13) complexes. Ligand exchange with 9-borabicyclo[3.3.1]nonane (9-BBN) results in formation of the thorium borohydride complex (BIMA)₃Th(μ-H)₂[B(C₈H₁₄)] (14). Complex 1 also reacts under photolytic conditions to eliminate SiMe₄ and produce Th(BIMA)₂(BIMA*) [15, BIMA* = (ⁱPr)NC(CH₂)N(ⁱPr)], featuring a rare example of a dianionic amidinate ligand. Complexes 2, 3, 5, 6, 11a, and 12-15 were characterized by ¹H and ¹³C{¹H} NMR spectroscopy, FTIR, EA, melting point and X-ray crystallography. All other complexes were identified by one or more of these spectroscopic techniques.