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

Reactions of the hydrazinedildo complexes [M((N2Npy)-N-TBS)(NNPh2)(py)] (M = Zr (1a), Hf (1b)) with (hetero)allenes result in a variety of [2 + 2] cycloaddition products of the general type [M((N2Npy)-N-TBS) (kappa N-2,E-(E(=E'R)NNPh2)(py)] (E = CH2, S; E' = CH, N; R = alkyl, aryl). The reaction of [Zr((N2Npy)-N-TBS)(NNPh2)(py)] (1a) with 1 molar equiv of phenyl or mesityl isothiocyanate at room temperature yields [Zr((N2Npy)-N-TBS)(kappa N-2,S-SC(=NAr)NNPh2)(py)] (Ar = phenyl (2a), mesityl (2b)). Reacting the hydrazinediides [M((N2Npy)-N-TBS)(NNPh2)(py)] (M = Zr (1a), HE (1b)) with allenes results in the formation of the metallaazacyclobutanes [M((N2Npy)-N-TBS)(kappa N-2,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(N(2)(TBS)Npy)(kappa N-2,S-SC(=NAr)NNPh2)(py)] (2a) forms the isomerization product [Zr((N2Npy)-N-TBS)(kappa N-2,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(kappa N-4,N,N,N-(N2NpyNC)-N-TBS(Me)=CHCy)(NPh2)] (M = Zr (7a), Hf (7b)), [Zr((N2Npy)-N-TBS)(kappa N-2,C-(Ph)NC6H4C(Me)=C(Ph)NH)] (8) and [Zr(kappa N-4,N,N,N-(N2NpyNC)-N-TBS(Me)=CHPh)(NPh2)] (9).