Two related oxazoline-containing cyclopentadiene ligands have been synthesized for use in catalytic studies. Bis(4,4-dimethyloxazoline) is linked to cyclopentadiene or fluorene to give 1-(cyclopentadiene)-1,1-bis(4,4-dimethyl-2-oxazolinyl)ethane (HBoMeCp) and 1-(fluorene)-1,1-bis(4,4-dimethyl-2-oxazolinyl)ethane (HBoMeFlu); coordination of these ligands to a metal center yields constrained-geometry-type piano stool compounds. Metalation of HBoMeCp is achieved by reacting the ligand with [M(μ-OMe)L]2 (M = Rh or Ir, L = C8H12, (CO)2) or by salt metathesis using the thallium salt generated by reaction with thallium ethoxide. Metalation of HBoMeFlu is achieved by in-situ generation of the potassium salt and further reaction with [M(C8H12)Cl]2. We have found that coordination in the cyclopentadienyl compound {κ0-η5-BoMeCp}RhL2 contrast that of the fluorenyl analogue {κ2-η1-BoMeFlu}RhL2. Thus, the cyclopentadienyl analogue is isolated with η5-coordination, whereas the fluorenyl analogue is isolated with κ2-η1-coordination. Conditions to substitute C8H12 with CO in BoMeCpM(C8H12) have not been found. While BoMeFluM(C8H12) can undergo substitution of CO under one atmosphere of pressure at room temperature in under thirty minutes. Cyclic voltammetry experiments for BoMeFluRh(C8H12) gives reversible voltammograms with redox potentials for the RhII and RhIII species at – 650 and 260 mV (vs Fc) respectively. BoMeCpRh(C8H12) has only yielded non-reversible voltammograms with no useful oxidation potentials. The difference in coordination between the cylopentadienyl and fluorenyl ligands appears to play a key role in the reaction of carbon monoxide displacing cyclooctadiene and their stability to provide useful, reversible electrochemical data.

Synthesis, structure, and reactivity of bis(oxazoline)-substituted cyclopentadienyl and fluorenyl rhodium and iridium complexes

249th National Meeting (2015)

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