The mechanism of formation and the stereochemistry of mono- and bis-complexes of rhodium(III) with 1,10-phenanthroline

Abstract

The dichlorobis-(1,10-phenanthroline)rhodium(III) cation is shown by ¹H n.m.r. and vibrational (i.r. and Raman) spectroscopy to be a cis-complex. The perchlorate salt is isomorphous with cis-[Ir phen ₂Cl₂]ClO₄(phen = 1,10-phenanthroline). Mechanistic studies with the rhodium(III) bromide–1,10-phenanthroline system show that [Rh phen Br₄]^– is first formed and then reacts with further phenanthroline to afford cis-[Rh phen ₂Br₂]⁺. The role of rhodium(I) intermediates is discussed. The new complexes [phen H][Rh phen X₄](X = Cl, Br, or I) are reported. Electronic and vibrational spectroscopy suggest that the dichlorobis-(2,2′-bipyridyl)rhodium(III) cation has cis-stereochemistry as has the new complex dichlorobis(2,4,7,8-tetramethyl-1,10-phenanthroline)rhodium(III) chloride dihydrate.