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Title

Synthesis, Structure, Spectroscopy, and Reactivity of Azapentadienyl-M-Phosphine Complexes (M = Co, Rh, Ir)

Date of Award

Winter 12-15-2013

Author's School

Graduate School of Arts and Sciences

Author's Department

Chemistry

Degree Name

Doctor of Philosophy (PhD)

Degree Type

Dissertation

Abstract

This dissertation focuses on the systematic synthesis of azapentadienyl–M–phosphine complexes (M = Co, Rh, Ir). The key synthetic approach involves the treatment of chloro–M–phosphine precursors with potassium tert–butylazapentadienide reagent. The reactivity of the parent azapentadienyl compounds with triflic acid and 2e− donor ligands are also investigated.

Treatment of (Cl)Co(PMe3)3 with potassium tert–butylazapentadienide produces ((1,2,3–η3)–5–tert–butylazapentadienyl)Co(PMe3)3 (1). Compound 1 undergoes ligand substitution reactions with trimethyl phosphite and carbon monoxide, generating ((1,2,3–η3)–5–tert–butylazapentadienyl)Co(PMe3)2L (2, L = P(OMe)3; 3, L = CO). Compounds 1–3 react readily with 1 equiv of triflic acid (HO3SCF3) at the azapentadienyl nitrogen, producing the corresponding η4–(tert–butylamino)butadiene–cobalt complexes (4–6). One of the key features of these monoprotonated complexes is the very long Co–C4 bond distances, indicating that η3–resonance structures are contributing to the overall bonding picture. Treatment of compound 4 with P(OMe)3 or CO leads to formation of Co(PMe3)2[P(OMe)3]3+O3SCF3− (7) or Co(PMe3)3(CO)2+O3SCF3− (8), respectively, and both cases lead to displacement of (tert–butylamino)butadiene (rather than PMe3 ligand exchange). Further addition of triflic acid to 5 leads to a second protonation at nitrogen, yielding the corresponding ammonium salt 9. Compound 9 possesses an η4–(tert–butylammonium)butadiene ligand with a strong Co–C4 interaction.

Treatment of [(cyclooctene)2Rh(μ–Cl)]2 with 4 equiv of PR3 (R = Me, Et), followed by potassium tert–butylazapentadienide, produces 16e− ((1,2,3–η3)–5–tert–butylazapentadienyl)Rh(PR3)2 (10, R = Me; 16, R = Et). Similarly, the reaction of [(cyclooctene)2Rh(μ–Cl)]2 with 6 equiv of PMe3, followed by potassium tert–butylazapentadienide, generates 18e− ((1,2,3–η3)–5–tert–butylazapentadienyl)Rh(PMe3)3 (13). These neutral compounds react cleanly with 1 equiv of triflic acid. In each case, the primary site of reactivity is the nitrogen atom, leading to the formation of monoprotonation products (11, 14, and 17). When the monoprotonated compounds are treated with additional triflic acid, the second protonation occurs at the rhodium center, producing unstable metal–hydrides. These species reductively eliminate protonated tert–butylcrotonaldimine and ultimately produce isolable octahedral Rh(III) complexes (12, 15 and 18) after addition of a third equiv of triflic acid.

The reaction of [(cyclooctene)2Ir(μ–Cl)]2 with 4 or 6 equiv of PEt3, followed by potassium tert–butylazapentadienide, leads to the formation of ((1,2,3–η3)–5–tert–butylazapentadienyl)Ir(PEt3)x (20, x = 2; 24, x = 3). Iridium compound 20 reacts with triflic acid at the metal center, producing an iridium–hydride product, 21, in which the azapentadienyl ligand coordinates in an unusual η3, η1–fashion, while iridium compound 24 reacts at nitrogen to produce the corresponding η4–butadiene product, 25. The monoprotonated iridium compounds react with additional acid at nitrogen. In the case of monoprotonated compound 21, treatment with chloride (to release N from Ir), followed by addition of acid, produces the N–protonated η3–tert–butylazapentadienyl product (23). Similarly, treatment of monoprotonated compound 25 with additional acid leads to a second protonation at nitrogen and production of the η4–(tert–butylammonium)butadiene product (26).

Language

English (en)

Chair and Committee

John R. Bleeke

Committee Members

Vladimir B. Birman, William E. Buhro, Marcus B. Foston, Liviu M. Mirica, Jay R. Turner

Comments

Permanent URL: https://doi.org/10.7936/K7J10139

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