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Keywords:

  • Rhodium;
  • Iridium;
  • Phosphane ligands;
  • Hemilabile ligands;
  • Fluxionality

Abstract

[MCl(L2)]2 (M = Ir, L2 = 1,5-cyclooctadiene; M = Rh, L2 = norbornadiene) reacts with [2-(1,3-dioxolane-2-yl)phenyl]diphenylphosphane (1) to afford [MCl(L2)(P~O)] (M = Ir, 2; M = Rh, 3), in which the ligand is P-monodentate. Complex 3 reacts with AgClO4 to give [Rh(Nbd)(PO)]ClO4 (4), in which the ligand is P,O-bidentate. Complex 2 is static at room temp., whereas 3 and 4 undergo intramolecular exchanges, which are fast at room temperature and slow at 223 K. The conformational changes in 4 are still fast at 223 K. Complexes 24 react with CO to afford trans-[MCl(CO)(P~O)2] (M = Ir, 5; M = Rh, 6) or trans-[Rh(CO)2(P~O)2]ClO4 (7). Cyclooctadiene complexes react with PPh2(o-C6H4CHO) to afford [MClH(PPh2(o-C6H4CO))(PO] (M = Ir, 8; M = Rh, 9), in which 1 is chelating. Complex 8 contains a single diastereomer, is static in the 303–213 K range and reacts with CO to form [IrClH(PPh2(o-C6H4CO))(P~O)(CO)] (10). Complex 9 contains two diastereomers 9a/9b in a 95:5 ratio that undergo interconversion, which is slow at low temperature, and reacts with CO to undergo reductive elimination of aldehyde, cleavage of the Rh–O bond and scrambling of phosphanes. A mixture of trans-[RhCl(CO)(κ1-PPh2(o-C6H4CHO))(P~O)] (11), 6 and trans-[RhCl(CO)(κ1-PPh2(o-C6H4CHO))2] is formed. Bubbling of nitrogen transforms 11 back into 9. Compound 2 reacts with hydrogen to give the fluxional [IrCl(H)2(P~O)(PO)] (12) with trans P atoms and cis H atoms, which attains coalescence at 203 K. Complex 12 reacts with mono- or bidentate ligands to afford static [IrCl(H)2(P~O)2L] (L = CO, 13; py, 14; nPrNH2, 15) or [Ir(H)2(P~O)2(en)]BPh4 (16, en = ethylenediamine). Abstraction of halide from 12 affords [Ir(H)2(PO)2]BPh4 (17), which is fluxional owing to interconversion between only two of the possible four diastereomers, for which ΔH = 54.7 ± 0.7 kJ mol–1 and ΔS = 4.7 ± 0.2 J K–1 mol–1. The X-ray structures of 8, 15 and 16 are also reported.