The experimental and computational characterization of a series of dialkylterphenyl phosphines, PR2Ar′ is described. The new P‐donors comprise five compounds of general formula PR2ArDtbp2 (R=Me, Et, iPr, c‐C5H9 and c‐C6H11); ArDtbp2 = 2,6‐C6H3‐(3,5‐C6H3‐(CMe3)2)2), and another five PR2Ar′ phosphines containing the bulky alkyl groups iPr, c‐C5H9 or c‐C6H11, in combination with Ar′=ArXyl2 , ArXyl'2 , or ArPh2 (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(PR2Ar′) and Ni(CO)2(PR2Ar′). In the solid state, the free phosphines PR2Ar′ adopt one of the three possible structures formally related by rotation around the Cipso−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.