Synthesis, Structure and Nickel Carbonyl Complexes of Dialkylterphenyl Phosphines

The experimental and computational characterization of a series of dialkylterphenyl phosphines, PR₂ Ar' is described. The new P-donors comprise five compounds of general formula PR₂ Ar $$ (R=Me, Et, iPr, c-C₅ H₉ and c-C₆ H₁₁ ); Ar $$ = 2,6-C₆ H₃ -(3,5-C₆ H₃ -(CMe₃ )₂ )₂ ), and another five PR₂ Ar' phosphines containing the bulky alkyl groups iPr, c-C₅ H₉ or c-C₆ H₁₁ , in combination with Ar'=Ar $$ , Ar $$ , or Ar $$ (L1-L10). Steric and electronic parameters have been determined computationally and from IR and X-ray data obtained for the phosphines and for some derivatives, including tricarbonyl and dicarbonyl nickel complexes, Ni(CO)₃ (PR₂ Ar') and Ni(CO)₂ (PR₂ Ar'). In the solid state, the free phosphines PR₂ Ar' adopt one of the three possible structures formally related by rotation around the C_ipso -P bond. Details on their relative energies and on the influence of the free phosphine structure on its coordination chemistry towards Ni(CO)_n (n = 2, 3) fragments has been obtained by experimental and computational methods.