Redox Chemistry of Bis(oxazolinyl)cyclopentadienyl and -fluorenyl Rhodium and Iridium Organometallic Compounds

Abstract

Rhodium and iridium compounds supported by 1-cyclopentadienyl-1,1-bis(4,4-dimethyl-2-oxazolinyl)ethane (MeC(Ox Me2 ) 2 (C 5 H 4 ); Bo M Cp) form the 18-electron piano-stool compounds {Bo M Cp}ML 2 (L = C 2 H 4 , C 8 H 12 , CO) containing two noncoordinated oxazolines. Bromination of {Bo M Cp}Rh(C 2 H 4 ) 2 gives {Bo M Cp}RhBr 2 . A single-crystal X-ray diffraction study reveals that only one oxazoline is coordinated in the solid-state structure of {Bo M Cp}RhBr 2 . The oxazolines exchange rapidly on the 1 H NMR time scale at room temperature but slowly at −10 °C. In contrast, the fluorenyl derivative MeC(Ox Me2 ) 2 (C 13 H 8 ) (Bo M Flu) forms 16-electron square-planar rhodium(I) and iridium(I) complexes containing bidentate {C,N-Bo M Flu}M coordination that features a M−C single bond (i.e., monohapto-fluorenyl bonding). {Bo M Flu}Rh(η 4 -C 8 H 12 ) undergoes two electrochemically and chemically reversible one-electron redox events with E 1/2 at −640 and 220 mV. One-electron chemical oxidation provides the long-lived rhodium(II) hydrocarbyl species [{Bo M Flu}Rh(C 8 H 12 )] + , which reacts to give the monovalent species [{Bo M Flu-H}Rh(η 4 -C 8 H 12 )] + . Alternatively, one-electron oxidation of {Bo M Flu}Ir(η 4 -C 8 H 12 ) provides a transient diamagnetic iridium hydride, detected by 1 H NMR spectroscopy, that ultimately rearranges into [{Bo M Flu-H}Ir(η 4 -C 8 H 12 )] + . This process can be prevented for both congeners by employing the allylic H-free dibenzo[a,e]cyclooctatetraene (C 16 H 12 ) ligand. Oxidation of {Bo M Flu}M(η 4 -C 16 H 12 ) (M = Rh, Ir) provides [{Bo M Flu}M(η 4 -C 16 H 12 )] + with lifetimes of greater than 1 day.

Rhodium(I) Complexes with a η1-Fluorenyl-P-phosphanylphosphorane Ligand

“…Much later, Lavigne and César 3 described B , with a N-heterocyclic carbene ligand coordinated in κ 2 -C,C fashion while Iwai and Sawamura 4 studied triarylmethane–monophosphanes and reported C , bearing a fluorenyl-phosphane coordinated in a κ 2 -C,P fashion. Finally, Sadow 5 described Rh complexes with bis(oxazolinyl)fluorenylphosphane, coordinated in a κ 2 -C,N fashion, such as D . In this contribution we describe rhodium(I) complexes C1 – C4 , with an unprecedented cyclometalated phosphanylphosphorane ligand L2 , a P(III)-P(V) species ( Figure 1 , middle).…”