Platinum(II) alkyl complexes of chelating dibridgehead diphosphines P((CH2)n)3P (n=14, 18, 22); facile cis/trans isomerizations interconverting gyroscope and parachute like adducts

The gyroscope like dichloride complexes trans-Pt(Cl)(2)(P((CH2)(n))(3)P) (trans-2; n = c, 14; e, 18; g, 22) and MeLi (2 equiv.) react to yield the parachute like dimethyl complexes cis-Pt(Cl)(2)(Pt(CH2)(n))(3)P) (cis-4c,e,g, 70-91%). HCl (1 equiv.) and cis-4c react to give cis-Pt(Cl)(Me)(P((CH2)(14))(3)P) (cis-5c, 83%), which upon stirring with silica gel or crystallization affords trans-5c (89%). Similar reactions of HCl and cis-4e,g give cis/ trans-5e,g mixtures that upon stirring with silica gel yield trans-5e,g. A parallel sequence with trans-2c/EtLi gives cis-Pt(Et)(2)(P((CH2)(14))(3)P) (cis-6c, 85%) but subsequent reaction with HCl affords trans-Pt(Cl)(Et) (Pt(CH2)(14))(3)P) (trans-7c, 45%) directly. When previously reported cis-pt(Ph)(2)(P((CH2)(14))(3)P) is treated with HCl (1 equiv.), cis- and trans-Pt(Cl)(Ph)(P((CH2)(14))(3)P) are isolated (44%, 29%), with the former converting to the latter at 100 degrees C. Reactions of trans-5c and LiBr or Nal afford the halide complexes trans-Pt(X)(Me)(IN(CH2)(14))(3)P) (trans-9c, 88%; trans-10c, 87%). Thermolyses and DFT calculations that include acyclic model compounds establish trans > cis stabilities for all except the dialkyl complexes, for which energies can be closely spaced. The a donor strengths of the non-phosphine ligands are assigned key roles in the trends. The crystal structures of cis-4c, trans-5c, trans-7c, and trans-10c are determined and analyzed together with the computed structures.

Automated summary

The study investigates the reactions and products of gyroscope-like complexes, showing the formation of different compounds with different ligands and reaction conditions. The stability of the compounds is discussed, with a focus on the role of a donor strengths of the non-phosphine ligands in the trends.