[2 + 2] Cycloaddition Products of Zirconium and Hafnium Hydrazinediides with Allenes and Heteroallenes and Their Thermally Induced Rearrangements

Reactions of the hydrazinediido complexes [M­(N2TBSNpy)­(NNPh2)­(py)] (M = Zr (1a), Hf (1b)) with (hetero)­allenes result in a variety of [2 + 2] cycloaddition products of the general type [M­(N2TBSNpy)­(κ2N,E-(E­(E′R)­NNPh2)­(py)] (E = CH2, S; E′ = CH, N; R = alkyl, aryl). The reaction of [Zr­(N2TBSNpy)­(NNPh2)­(py)] (1a) with 1 molar equiv of phenyl or mesityl isothiocyanate at room temperature yields [Zr­(N2TBSNpy)­(κ2N,S-SC­(NAr)­NNPh2)­(py)] (Ar = phenyl (2a), mesityl (2b)). Reacting the hydrazinediides [M­(N2TBSNpy)­(NNPh2)­(py)] (M = Zr (1a), Hf (1b)) with allenes results in the formation of the metallaazacyclobutanes [M­(N2TBSNpy)­(κ2N,C-N­(NPh2)­CH2CCH­(R))­(py)] (M = Zr, R = Ph (4a), cyclohexyl (5a), methyl (6); M = Hf, R = phenyl (4b), cyclohexyl (5b)). Subsequent heating of the cycloaddition products revealed different reactivity patterns: the complex [Zr­(N2TBSNpy)­(κ2N,S-SC­(NAr)­NNPh2)­(py)] (2a) forms the isomerization product [Zr­(N2TBSNpy)­(κ2N,S-SC­(NNPh2))­NPh] (3), retaining the N–N bond of the hydrazide. In contrast, the metallacyclobutanes 4a,b and 5a,b show a tendency toward N–N bond cleavage, resulting in the formation of the C–N- and C–C-coupled product complexes [M­(κ4N,N,N,N-N2TBSNpyNC­(Me)CHCy)­(NPh2)] (M = Zr (7a), Hf (7b)), [Zr­(N2TBSNpy)­(κ2N,C-(Ph)­NC6H4C­(Me)C­(Ph)­NH)] (8) and [Zr­(κ4N,N,N,N-N2TBSNpyNC­(Me)=CHPh)­(NPh2)] (9).