| Summary: | We report a comprehensive combined experimental and DFT investigation of the synthesis, molecular and electronic structures, and reactivity of terminal hydrazido complexes with CO2, CS2, isocyanates, and isothiocyanates. Reaction of Cp*Ti{MeC(NiPr) 2}(NtBu) with hydrazines R1R 2NNH2 gave the structurally characterized series of hydrazides Cp*Ti{MeC(NiPr)2}(NNR1R 2) (R1 = Ph, R2 = Ph (13), Me (14); R 1 = R2 = Me (15)). The energetics of this imide/hydrazine exchange reaction, as well as the electronic and molecular structures of 13-15, have been evaluated by DFT and compared with those of their methyl and phenyl imido counterparts. Reaction of 13-15 with CO2 or CS2 gave Ti=Nα cycloaddition products of the type Cp* Ti{MeC(NiPr)2}{N(NR2)C(E)E} (R = Ph, Me; E = O, S) and, in the case of CO2, cycloaddition-insertion products Cp*Ti{MeC(NiPr)2}{OC(O)N(NR2)C(O)O}, in which 2 equivs of CO2 had effectively inserted into Ti=N α. Reaction of 13 with isocyanates and isothiocyanates also gave stable cycloaddition products. Cp*Ti{MeC(NiPr) 2}{N(NPh2)C(NTol)O} reacted further with CO2 to give a mixed cycloaddition-insertion product. The tBuNCO moiety in Cp*Ti{MeC(NiPr)2}{N(NPh2)C(N tBu)O} could be displaced by CO2 or TolNCO. In contrast, the reactions of 15 are dominated by cycloaddition-elimination reactions. Reaction with tBuNCO or Ar′NCO (2 equivs) gave tBuNCNNMe2 or the heterocycle 1,2,4-N(Me) 2NC(NAr′)N(Ar′)C(O), respectively, along with [Cp*Ti{MeC(NiPr)2}(μ-O)]2. With TolNCO (2 equivs), Cp*Ti{MeC(NiPr)2}{OC(NNMe 2)N(Tol)C(NTol)O} was formed via a series of cycloaddition- elimination and cycloaddition-insertion steps. The energetics and mechanisms of the cycloaddition, cycloaddition-insertion, and cycloaddition-extrusion processes of various model imido and hydrazido complexes have been investigated using DFT. In the latter (metathesis) reactions, the reaction outcomes depend on a delicate balance of the relative affinities of NR or NNR2 for the metal center or the organic fragment (CO, CS, or RNC). © 2011 American Chemical Society.
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