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

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.