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Cooperative ligand design for late transition metal coordination compounds

University of British Columbia

This thesis describes several cyclopentyl linked enamide phosphine ligands. Reactivity and mechanistic studies using coordination compounds featuring these ligands enable exploration of ligand cooperativity. Despite complex behavior in solution due to tautomerization, coordination of (NPN)DMP/DIPPH₂ to Rh generates RhCl{(NPN)DMP/DIPPH₂}(COE). Synthesis of RhCl{(NPN)DMP/DIPPH₂}(CO) and RhHCl₂{(NPN)DMP/DIPPH₂} is possible. NMR spectroscopy and in certain cases X-ray analysis establishes the diimine tautomer of the ligand coordinates to Rh in each case. Enamide phosphine complexes, Ir{(NP)DIPP}(COD) and Ir{(NP)DMP}(COD) are synthesized from simple imine phosphine ligands. Ir{(NP)DIPP}(COD) reacts with H₂ or PriOH to form [IrH₃{(NP)DIPPH}]₂. The imine tautomer of the ligand coordinates to Ir. Treating [IrH₃{(NP)DIPPH}]₂ with CO generates Ir{(NP)DIPP}(CO)₂. A proton from the imine ligand of [IrH₃{(NP)DIPPH}]₂ combines with an Ir hydride to release H₂. Observation of three intermediates, involved in conversion of [IrH₃{(NP)DIPPH}]₂ to Ir{(NP)DIPP}(CO)₂, suggests that tautomerization of the dissociated arm is involved in cooperative H₂ loss. Four imine phosphine ligands (R(NP)R'H), where the N-aryl groups (R) and the groups attached to P(R') are varied, are synthesized. Combining each ligand with RuHCl(PPri₃)₂(CO) and KOBut generates four enamide phosphine complexes: RuH{R(NP)R'}(PPri₃)(CO). Reacting RuH{R(NP)R'}(PPri₃)(CO) with H₂ generates RuH₂{R(NP)R'H}(PPri₃)(CO). The imine tautomeric form of the ligand coordinates to Ru in all four cases. The R' groups influence the rate of reaction and percent conversion to RuH₂{R(NP)R'H}(PPri₃)(CO). The mechanism for H₂ activation is explored using RuH{Pri(NP)Pri}(PPri₃)(CO). An intermediate is identified as RuH₂(H₂){Pri(NP)PriH}(PPri₃)(CO). The T₁,min value of a ¹H NMR resonance at δ -7.2 is 22 ms at 238 K (measured to 400 MHz), consistent with a Ru dihydrogen dihydride complex. The N donor of the enamine tautomeric form of the ligand is protonated by H₂ or D₂ and has dissociated from Ru. Tautomerization of the dissociated arm is involved in formation of the final product. Certain factors inhibit alcohol dehydrogenation catalysis for Ir{(NP)DIPP}(COD) and RuH{Pri(NP)Pri}(PPri₃)(CO). Two tridentate enamide phosphine ligands are developed in an effort to generate a catalyst. These ligands enable synthesis of RuH{(PNN)But}(CO) and RuH{(PNN)Pri}(CO). Exposing RuH{(PNN)But}(CO) to 1000 equivalents of benzyl alcohol yields a TON of 13 and TOF of 0.6 h-¹ after 22 hours. Nearly identical results are obtained for RuH{(PNN)Pri}(CO).

Text

2016-01-31

Attribution-NonCommercial-NoDerivs 2.5 Canada

http://hdl.handle.net/2429/52014

Chemistry

University of British Columbia

UBCV

http://creativecommons.org/licenses/by-nc-nd/2.5/ca/