Square-Planar and Octahedral Gyroscope-Like Metal Complexes Consisting of Dipolar Rotators Encased in Dibridgehead Di(triaryl)phosphine Stators: Syntheses, Structures, Dynamic Properties, and Reactivity.

For a variety of purposes, it is of interest to embed metals in cagelike -spanning di(triaryl)phosphine ligands. Toward this end, a combination of P(-CHO(CH)CH═CH) [; = 4 (), 5 (), 6 (), and 7 ()], [Rh(COD)(μ-Cl)], and CO gives square-planar -Rh(CO)(Cl)[P(-CHO(CH)CH═CH)] (-). Reactions of - with Grubbs' catalyst (first generation) and then H (catalyst PtO) yield the title compounds -Rh(CO)(Cl)[P(-CHO(CH)O--CH)P] ( = 2 + 2, -; 26-41% from -). Two are crystallographically characterized. The Cl-Rh-CO moieties rapidly rotate on the NMR time scale at -120 °C, per the ample clearance provided by the (CH) segments. Steric interactions with the PCHO linkages are analyzed. LiC≡CAr displaces the chloride ligand from to give RhC≡CAr adducts (Ar = CH/-CHCH, /). The ArC≡C-Rh-CO rotator of rapidly rotates on the NMR time scale (-70 °C), but with , the longer -CHCHC≡C group is confined between two (CH) bridges, even at 120 °C. Reactions of Re(CO)(X) and (140 °C) give octahedral ,-Re(CO)(X)[P(-CHO(CH)CH═CH)] (X = Cl/Br), and metathesis/hydrogenation sequences yield ,-Re(CO)(X)[P(-CHO(CH)O--CH)P]. Reactions of and and excess PMe give the free diphosphines P(-CHO(CH)O--CH)P ( and , 83-75%). The addition of to [Rh(CO)(μ-Cl)] reconstitutes (87%). Both , and , isomers of and are possible, but low-temperature NMR spectra show one set of signals, consistent with rapid homeomorphic isomerizations that turn the molecules inside out. Thermolyses (CDBr, 140 °C) effect phosphorus inversion to give , isomers.