Synthesis, Spectroscopy, Structure, and Reactivity of Azapentadienyl-Rhodium-Phosphine and Azapentadienyl-Iridium-Phosphine Complexes1

Abstract

We report the synthesis, spectroscopy, structure, and reactivity of (1,2,3-η3)-(5-tert-butylazapentadienyl)Rh(PMe3)x (1, x = 2; 4, x = 3) and (1,2,3-η3)-(5-tert-butylazapentadienyl)Ir(PEt3)x (7, x = 2; 12, x = 3), which are produced by reacting [(cyclooctene)2M(μ-Cl)]2 with the appropriate amount of phosphine, followed by potassium tert-butylazapentadienide. Each of these compounds reacts with 1 equivalent of triflic acid to produce a monoprotonation product. Rhodium compounds 1 and 4 react at nitrogen to produce 2 and 5, respectively. Iridium compound 7 reacts at the metal center, generating an iridium-hydride product, 8, in which the azapentadienyl ligand coordinates in an unusual η3, η1-fashion, while compound 12 reacts at nitrogen to produce 13. The monoprotonation products have been treated with additional acid, and in each case the secondary site of electrophilic addition has been determined. Rhodium compounds 2 and 5 both react with a second equivalent of triflic acid at the metal center to produce unstable metal-hydrides. These species reductively eliminate protonated tert-butylcrotonaldimine and ultimately produce isolable octahedral Rh(III) complexes 3 and 6 after addition of a third equivalent of triflic acid. In contrast, when iridium compound 8 is treated with a second equivalent of triflic acid, addition occurs at nitrogen to produce diprotonation product 9. Similarly, 13 reacts with a second equivalent of acid at nitrogen, generating a product with a diprotonated nitrogen, 14. All of the compounds reported herein have been identified by NMR, while the structures of 2, 4, 5, 6, 12, 13, and 14 have been confirmed by single-crystal X-ray diffraction.