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Theoretical investigation into the mechanism of reductive elimination from bimetallic palladium complexes

Journal Article


Abstract


  • Reductive elimination of C–Cl and C–C bonds from binuclear organopalladium complexes containing Pd–Pd bonds with overall formal oxidation state +III are explored by density functional theory for dichloromethane and acetonitrile solvent environments. An X-ray crystallographically authenticated neutral complex, [(L-C,N)ClPd(μ-O2CMe)]2 (L = benzo[h]quinolinyl) (I), is examined for C–Cl coupling, and the proposed cation, [(L-C,N)PhPd1(μ-O2CMe)2Pd2(L-C,N)]+ (II), examined for C–C coupling together with (L-C,N)PhPd1(μ-O2CMe)2Pd2Cl(L-C,N) (III) as a neutral analogue of II. In both polar and nonpolar solvents, reaction from III via chloride dissociation from Pd2 to form II is predicted to be favored. Cation II undergoes Ph–C coupling at Pd1 with concomitant Pd1–Pd2 lengthening and shortening of the Pd1–O bond trans to the carbon atom of L; natural bond orbital analysis indicates that reductive coupling from II involves depopulation of the dx2–y2 orbital of Pd1 and population of the dz2 orbitals of Pd1 and Pd2 as the Pd–Pd bond lengthens. Calculations for the symmetrical dichloro complex I indicate that a similar dissociative pathway for C–Cl coupling is competitive with a direct (nondissociative) pathway in acetonitrile, but the direct pathway is favored in dichloromethane. In contrast to the dissociative mechanism, direct coupling for I involves population of the dx2–y2 orbital of Pd1 with Pd1–O1 lengthening, significantly less population occurs for the dz2 orbital of Pd1 than for the dissociative pathway, and dz2 at Pd2 is only marginally populated resulting in an intermediate that is formally a Pd1(I)-Pd2(III) species, (L-Cl-N,Cl)Pd1(μ-O2CMe)Pd2Cl(O2CMe)(L-C,N) that releases chloride from Pd2 with loss of Pd(I)–Pd(III) bonding to form a Pd(II) species. A similar process is formulated for the less competitive direct pathway for C–C coupling from III, in this case involving decreased population of the dz2 orbital of Pd2 and strengthening of the Pd(I)–Pd(III) interaction in the analogous intermediate with η2-coordination at Pd1 by L-Ph-N, C1-C2.

UOW Authors


  •   Ariafard, Alireza (external author)
  •   Hyland, Christopher
  •   Canty, Allan J. (external author)
  •   Sharma, Manab (external author)
  •   Yates, Brian F. (external author)

Publication Date


  • 2011

Citation


  • Ariafard, A., Hyland, C. J. T., Canty, A. J., Sharma, M. & Yates, B. F. (2011). Theoretical investigation into the mechanism of reductive elimination from bimetallic palladium complexes. Inorganic Chemistry: including bioinorganic chemistry, 50 (14), 6449-6457.

Scopus Eid


  • 2-s2.0-79960236707

Ro Metadata Url


  • http://ro.uow.edu.au/smhpapers/2321

Number Of Pages


  • 8

Start Page


  • 6449

End Page


  • 6457

Volume


  • 50

Issue


  • 14

Abstract


  • Reductive elimination of C–Cl and C–C bonds from binuclear organopalladium complexes containing Pd–Pd bonds with overall formal oxidation state +III are explored by density functional theory for dichloromethane and acetonitrile solvent environments. An X-ray crystallographically authenticated neutral complex, [(L-C,N)ClPd(μ-O2CMe)]2 (L = benzo[h]quinolinyl) (I), is examined for C–Cl coupling, and the proposed cation, [(L-C,N)PhPd1(μ-O2CMe)2Pd2(L-C,N)]+ (II), examined for C–C coupling together with (L-C,N)PhPd1(μ-O2CMe)2Pd2Cl(L-C,N) (III) as a neutral analogue of II. In both polar and nonpolar solvents, reaction from III via chloride dissociation from Pd2 to form II is predicted to be favored. Cation II undergoes Ph–C coupling at Pd1 with concomitant Pd1–Pd2 lengthening and shortening of the Pd1–O bond trans to the carbon atom of L; natural bond orbital analysis indicates that reductive coupling from II involves depopulation of the dx2–y2 orbital of Pd1 and population of the dz2 orbitals of Pd1 and Pd2 as the Pd–Pd bond lengthens. Calculations for the symmetrical dichloro complex I indicate that a similar dissociative pathway for C–Cl coupling is competitive with a direct (nondissociative) pathway in acetonitrile, but the direct pathway is favored in dichloromethane. In contrast to the dissociative mechanism, direct coupling for I involves population of the dx2–y2 orbital of Pd1 with Pd1–O1 lengthening, significantly less population occurs for the dz2 orbital of Pd1 than for the dissociative pathway, and dz2 at Pd2 is only marginally populated resulting in an intermediate that is formally a Pd1(I)-Pd2(III) species, (L-Cl-N,Cl)Pd1(μ-O2CMe)Pd2Cl(O2CMe)(L-C,N) that releases chloride from Pd2 with loss of Pd(I)–Pd(III) bonding to form a Pd(II) species. A similar process is formulated for the less competitive direct pathway for C–C coupling from III, in this case involving decreased population of the dz2 orbital of Pd2 and strengthening of the Pd(I)–Pd(III) interaction in the analogous intermediate with η2-coordination at Pd1 by L-Ph-N, C1-C2.

UOW Authors


  •   Ariafard, Alireza (external author)
  •   Hyland, Christopher
  •   Canty, Allan J. (external author)
  •   Sharma, Manab (external author)
  •   Yates, Brian F. (external author)

Publication Date


  • 2011

Citation


  • Ariafard, A., Hyland, C. J. T., Canty, A. J., Sharma, M. & Yates, B. F. (2011). Theoretical investigation into the mechanism of reductive elimination from bimetallic palladium complexes. Inorganic Chemistry: including bioinorganic chemistry, 50 (14), 6449-6457.

Scopus Eid


  • 2-s2.0-79960236707

Ro Metadata Url


  • http://ro.uow.edu.au/smhpapers/2321

Number Of Pages


  • 8

Start Page


  • 6449

End Page


  • 6457

Volume


  • 50

Issue


  • 14