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Keywords:

  • hydrazides;
  • N[BOND]N bond cleavage;
  • reaction mechanisms;
  • titanium

Abstract

We report a range of new transformations of the diamide–amine supported Ti[DOUBLE BOND]NNPh2 functional group with a variety of unsaturated substrates, along with DFT studies of the key mechanisms. Reaction of [Ti(N2Npy)(NNPh2)(py)] (4, N2Npy=(2-NC5H4)CMe(CH2NSiMe3)2; py=pyridine) with MeCN gave the dimeric species [Ti2(N2Npy)2{μ-NC(Me)(NNPh2)}2] through a [2+2] cycloaddition process. Reaction of 4 or [Ti(N2NMe)(NNPh2)(py)] (5, N2NMe=MeN(CH2CH2NSiMe3)2) with fluorinated benzonitriles gave the terminal hydrazonamide complexes [Ti(N2NR){NC(Armath image)NNPh2}(py)] (R=py or Me; Armath image=2,6-C6H3F2 or C6F5). DFT studies showed that this proceeds through an overall [2+2] cycloaddition–reverse cycloaddition, resulting in net insertion of Armath imageCN into the Ti[DOUBLE BOND]Nα bonds of the respective hydrazides. Reaction of 4 with a mixture of MeCN and PhCCMe gave the metallacycle [Ti(N2Npy){NC(Me)C(Ph)C(Me)NNPh2}] by sequential coupling of Ti[DOUBLE BOND]NNPh2 with PhCCMe and then MeCN. A related product, [Ti(N2Npy){NC(Me)C(ArF)C(H)NNPh2}], was formed by insertion of MeCN into the Ti[BOND]C bond of the isolated azatitanacyclobutene [Ti(N2Npy){N(NPh2)C(H)C(ArF)}] (ArF=3-C6H4F). Reaction of 4 with two equivalents of B(Armath image)3 (Armath image=C6F5) formed the zwitterionic borate [Ti(N2Npy){η2-N(NPh2)B(Armath image)3}] by electrophilic attack at Nα. Compounds 4 and 5 reacted with tBuNC and/or XylNC (Xyl=2,6-C6H3Me2) to give the Nα[BOND]Nβ bond cleavage products, [Ti(N2NR)(NCNR′)(NPh2)] (R=py or Me; R′=tBu or Xyl), containing metallated carbodiimide ligands. DFT studies of these reactions found an initial addition of RNC across Ti[DOUBLE BOND]Nα followed by Nβ coordination, and finally complete Nα transfer from the NNPh2 to the RNC fragment. Reaction of 5 with Ar′NCE (E=O, S, Se; Ar′=2,6-C6H3iPr2) gave the [2+2] cycloaddition products [Ti(N2NMe){N(NPh2)C(NAr′)O}(py)] and [Ti(N2NMe){N(NPh2)C(NAr′)E}] (E=S or Se), which did not undergo further transformation of the Ti[BOND]N[BOND]NPh2 moiety.