Ruthenium Complexes of a Triphosphorus-Coordinating Pincer Ligand: Ru–P Ligand-Substituent Exchange Reactions Driven by Large Variations of Bond Energies

Abstract

The reaction of [(p-cymene)RuCl 2 ] 2 with the triphosphine ligand bis(2di-tert-butylphosphinophenyl)phosphine ( tBu P H PP) results in an unusual exchange reaction in which a chloride ligand and a phosphorus-bound H atom are exchanged ("H−P/Ru−Cl exchange") to give the (chlorophosphine)ruthenium hydride complex ( tBu P Cl PP)RuHCl [1 Cl -HCl; tBu P Cl PP = bis(2-di-tert-butylphosphinophenyl)chlorophosphine]. Density functional theory calculations indicate that the presumed initial product of metalation, ( tBu P H PP)RuCl 2 (1 H -Cl2), undergoes an H−P/Ru−Cl exchange via sequential P-to-Ru α-H migration to give the intermediate ( tBu PPP)RuHCl 2 , followed by Ru-to-P α-Cl migration to give the observed product 1 Cl -HCl (crystallographically characterized). Dehydrochlorination of 1 Cl -HCl under a H 2 atmosphere gives ( tBu P Cl PP)RuH 4 (1 Cl -H4), which then can undergo a second dehydrochlorination and addition of H 2 to give ( tBu P H PP)RuH 4 (1 H -H4). This reaction may proceed via the reverse of the intramolecular exchange by 1 H -Cl2, i.e., loss of H 2 from 1 Cl -H4 to give 1 Cl -H2, which could undergo Cl−P/Ru−H exchange to give ( tBu P H PP)RuHCl (1 H -HCl). Accordingly, the thermodynamics of Cl−P/Ru−H exchange are found to be highly dependent on the nature of the ancillary anionic ligand (H or Cl), which is not directly involved in the exchange. The origin of this thermodynamic dependence can be explained in terms of the high stability of complexes ( R P X PP)RuHCl (X = H, Cl; R = Me, t Bu), in which the hydride is approximately trans to a vacant coordination site and the central phosphine group is approximately trans to the weak-trans-influence chloride ligand. This conclusion has general implications for five-coordinate d 6 complexes, both pincer-and nonpincer-ligated.

Pincer-Ligated Iridium Complexes with Low-Field Ancillary Ligands: Complexes of (iPrPCP)IrCl2 and Comparison with (iPrPCP)IrHCl

“…This result is consistent with chemistry of other hydride/halide pincer metal complexes, including those that we have recently reported of ruthenium complexes (PPP)RuXY (XY = H 2 , HCl, Cl 2 ). 79 In all of these cases, we attribute the favorability of the pincer hydridohalides (5-or 6-coordinate) to the coordination of two strong-trans-influence ligands (hydride and the metalbound carbon or phosphorus in the case of PCP and PPP respectively) positioned mutually cis, and trans to weak-transinfluence ligands (H 2 O or chloride) or to a vacant coordination site. In contrast, having three (or more) strongtrans-influence ligands coordinated in the same plane inevitably leads to unfavorable trans interactions between at least two of these ligands.…”

“…From the relative thermodynamics of the hydrogenolysis reactions of Figures and , it follows that the comproportionation reactions shown in Figure are extremely favorable. This result is consistent with chemistry of other hydride/halide pincer metal complexes, including those that we have recently reported of ruthenium complexes (PPP)­RuXY (XY = H 2 , HCl, Cl 2 ) . In all of these cases, we attribute the favorability of the pincer hydridohalides (5- or 6-coordinate) to the coordination of two strong-trans-influence ligands (hydride and the metal-bound carbon or phosphorus in the case of PCP and PPP respectively) positioned mutually cis , and trans to weak- trans -influence ligands (H 2 O or chloride) or to a vacant coordination site.…”

Pincer-ligated Iridium Complexes with Low-Field Ancillary Ligands: Complexes of (iPrPCP)IrCl2 and Comparison with (iPrPCP)IrHCl

“…This result is consistent with chemistry of other hydride/halide pincer metal complexes, including those that we have recently reported of ruthenium complexes (PPP)RuXY (XY = H2, HCl, Cl2). 77 In all these cases we attribute the favorability of the pincer hydridohalides (5-or 6-coordinate) to the coordination of two strong-trans-influence ligands (hydride and the metal-bound carbon or phosphorus in the case of PCP and PPP respectively) positioned mutually cis, and trans to weak trans-influence ligands (H2O or chloride) or to a vacant coordination site. to this solution yielded 1-Cl2(H2O) and addition of CO then yielded 1-Cl2(CO).…”