Reactivity of the Yttrium Alkyl Carbene Complex [Y(BIPM)(CH2C6H5)(THF)] (BIPM = {C(PPh2NSiMe3)2})2–: From Insertions, Substitutions, and Additions to Nontypical Transformations

Abstract

The yttrium alkyl carbene complex [Y(BIPM)(CH2Ph)(THF)] (1; BIPM = {C(PPh2NSiMe3)2})2–) was treated with a series of unsaturated organic substrates, a bulky primary amine, and a group 1 metal alkyl to gauge and compare the reactivity of the Y═Ccarbene and Y–Calkyl bonds. Treatment of 1 with tert-butyl nitrile and 1-adamantyl azide gave the 1,2-migratory insertion products [Y(BIPM){NC(But)(CH2Ph)}(THF)] (2) and [Y(BIPM){N3Ad-1,Bn-3-κ2N1,3}(THF)] (3), respectively, with no reactivity observed at the Y═C double bond even when an excess of the relevant organic substrate was added. In contrast, the heteroallenes N,N′-dicyclohexylcarbodiimide and tert-butyl isocyanate reacted at both the Y═Ccarbeneand Y–Calkyl bonds of 1 to afford [Y{C(PPh2NSiMe3)2[C(NCy)2]-κ4C,N,N′,N″}{C(NCy)2(CH2Ph)-κ2N,N′}] (4) and [Y{C(PPh2NSiMe3)2[C(O)(NBut)]-κ4C,N,N′,O}{C(O)(NBut)(CH2Ph)-κ2N,O}] (5), respectively. 4 and 5 form regardless of the molar ratio of 1 to heteroallene, with no intermediates observed; thus, it is not clear if the [2 + 2]-cycloaddition or the 1,2-migratory insertion reaction occurs first. The addition of 2 equiv of tert-butyl isothiocyanate to 1 yields dimeric [Y(BIPMH){C(S)2(NBut)-1-κS,2-κN:μ,κS′}]2 (6), benzyl nitrile, and isobutylene by desulfurization and carbene-mediated deprotonation of a tert-butyl group of 1 equiv of heteroallene. The reaction between 1 and the bulky amine DippNH2 (Dipp = C6H3Pri2) gave [Y(BIPM)(NHDipp)(THF)] (7) by alkane elimination, with no reactivity observed at the Y═Ccarbene bond. Finally, the addition of benzylpotassium to 1 afforded the yttriate polymer [Y(BIPM)(μ-η1:η6-CH2Ph)(μ-η1:η2-CH2Ph)K]∞ (8) by a formal carbopotassiation across the Y═Ccarbene bond. Complexes 2–8 have been characterized by X-ray crystallography, multielement NMR spectroscopy, FTIR spectroscopy, and CHN microanalyses.