Platinum(II) alkyl complexes of chelating dibridgehead diphosphines P((CH))P ( = 14, 18, 22); facile / isomerizations interconverting gyroscope and parachute like adducts.

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