Gyroscope-like molecules consisting of PdX2/PtX2 rotators encased in three-spoke stators: synthesis via alkene metathesis, and facile substitution and demetalation

Reactions of trans-MCl2(P((CH2)6(CH=CH2)3)2 (M = a, Pd; b, Pt) and Grubbs' catalyst, followed by hydrogenation (ClRh(PPh3)3), give the title compounds trans-MCl2(P((CH2)14)3P) (2a, 37%; 2b, 43%). These react with LiBr, NaI, and KCN to give the corresponding MBr2, MI2, and M(CN)2 species (58-99%). 13C NMR data show that the MX2 moieties rapidly rotate within the diphosphine cage on the NMR time scale, even at -120 degrees C. The reaction of 2b and KSCN gives separable Pt(SCN)2 and Pt(SCN)(NCS) species (5b, 27%; 6b, 30%), and that with Ph2Zn gives a PtPh2 species (7b, 55%). NMR data for 5b-7b show that MX2 rotation is no longer rapid. Reactions of 2b with excess NaCCH or KCN afford the free dibridgehead diphosphine P((CH2)14)3P (66-83%), presumably as an "in/in" isomer, as addition of PtCl2 regenerates 2b. The crystal structures of 2a and 7b are analyzed with respect to MX2 rotation.