New Lanthanide Alkynylamidinates and Diiminophosphinates

Reactivity of N-Phosphinoguanidines of the Formula (HNR)(Ph2PNR)C(NAr) toward Main Group Metal Alkyls: Facile Ligand Rearrangement from N-Phosphinoguanidinates to Phosphinimine-Amidinates

We report the reactivity of N-phosphinoguanidines of the formula (HNR)(Ph₂PNR)C(NAr) (R = ⁱPr and Ar = 2,6-ⁱPr₂C₆H₃ [Dipp] for 1a, R = ⁱPr and Ar = 2,4,6-Me₃C₆H₂ [Mes] for 1b, and R = Cy and Ar = Dipp for 1c), prepared in high yields from the corresponding trisubstituted guanidines, toward main group metal alkyls AlMe₃, ZnEt₂, MgⁿBu₂, and ⁿBuLi to obtain novel phosphinoguanidinato and phosphinimine-amidinato compounds. Reactions of 1a-c with AlMe₃ at room temperature led to the kinetic phosphinoguanidinato products [Al{κ²-N,N'-(NR)C(NAr)(NRPPh₂)}Me₂] (2a-c), whereas the mild heating (60-80 °C) of solutions of 2a-c give the thermodynamic phosphinimine-amidinato products [Al{κ²-N,N'-(NR)C(NAr)(PPh₂NR)}Me₂] (3a-c) after ligand rearrangement. The reactions of equimolar amounts of 1a-c and ZnEt₂ initially give solutions containing unstable phosphinoguanidinato compounds [Zn{κ²-N,P-(NR)C(NAr)(NRPPh₂)}Et] (4a-c), which rearrange upon mild heating to the phosphinimine-amidinato derivatives [Zn{κ²-N,N'-(NR)C(NAr)(PPh₂NR)}Et] (6a-c). Bis(phosphinoguanidinato) compounds [Zn{κ²-N,P-(NR)C(NAr)(NRPPh₂)}₂] (5a-c) can be obtained under mild conditions (<45 °C) in THF, whereas bis(phosphinimine-amidinato) compounds [Zn{κ²-N,N'-(NR)C(NAr)(PPh₂NR)}₂] (7a-c) are also accessible under more forcing conditions (55-100 °C) from (i) ZnEt₂ and 1b,c (2 equiv), (ii) 6a and 1a, or (iii) 5b,c. Equimolar mixtures of MgⁿBu₂ and 1a-c in THF at room temperature give unstable phosphinimine-amidinato monoalkyl products [Mg{κ²-N,N'-(NR)C(NAr)(PPh₂NR)}ⁿBu(THF)₂] (8a-c), whereas 2 equiv of 1a,b are required to reach the bischelate compounds [Mg{κ²-N,N'-(NⁱPr)C(NAr)(PPh₂NⁱPr)}₂] (9a,b). Finally, phosphinoguanidinato compounds [Li{κ²-N,P-(NR)C(NDipp)(NRPPh₂)}(THF)₂] (10a,c) were obtained in the reactions of 1a,c with ⁿBuLi in THF under ambient conditions. The removal of the solvent from solutions of 10a,c under partial vacuum leads to the dinuclear compounds [Li₂{μ-κ²-N,N':κ¹-N-(NR)C(NDipp)(NRPPh₂)}₂(THF)₂] (11a,c) after the decoordination of one of the THF molecules in 10a,c and dimerization. Heating solutions of 10a,c at 60 °C triggers ligand rearrangement to give phosphinimine-amidinato compounds [Li{κ²-N,N'-(NR)C(NDipp)(PPh₂NR)}(THF)₂] (12a,c). We also propose a mechanism for the ligand rearrangement reaction from 10a to give 12a, supported by DFT calculations, which fits nicely with our experimental results. It essentially involves a carbodiimide deinsertion reaction followed by a [3 + 2] cycloaddition between the resulting lithium phosphino-amide and the carbodiimide.

Simple ZnEt2as a catalyst in carbodiimide hydroalkynylation: structural and mechanistic studies

Simple ZnEt₂is an efficient catalyst for the addition of terminal alkynes to carbodiimides, through amidinate complexes, and consecutive isocyanate addition and intramolecular cyclohydroamination.