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 trans -spanning di(triaryl)phosphine ligands. Toward this end, a combination of P( p -C 6 H 4 O(CH 2 ) m CH═CH 2 ) 3 [ 3 ; m = 4 ( a ), 5 ( b ), 6 ( c ), and 7 ( d )], [Rh(COD)(μ-Cl)] 2 , and CO gives square-planar trans -Rh(CO)(Cl)[P( p -C 6 H 4 O(CH 2 ) m CH═CH 2 ) 3 ] 2 ( 4a - 4d ). Reactions of 4b - 4d with Grubbs' catalyst (first generation) and then H 2 (catalyst PtO 2 ) yield the title compounds trans -Rh(CO)(Cl)[P( p -C 6 H 4 O(CH 2 ) n O- p -C 6 H 4 ) 3 P] ( n = 2 m + 2, 6b - 6d ; 26-41% from 4b - 4d ). 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 2 ) n segments. Steric interactions with the PC 6 H 4 O linkages are analyzed. LiC≡CAr displaces the chloride ligand from 6b to give RhC≡CAr adducts (Ar = C 6 H 5 / p -C 6 H 4 CH 3 , 7b / 8b ). The ArC≡C-Rh-CO rotator of 7b rapidly rotates on the NMR time scale (-70 °C), but with 8b , the longer p -CH 3 C 6 H 4 C≡C group is confined between two (CH 2 ) 12 bridges, even at 120 °C. Reactions of Re(CO) 5 (X) and 3c (140 °C) give octahedral mer , trans -Re(CO) 3 (X)[P( p -C 6 H 4 O(CH 2 ) 6 CH═CH 2 ) 3 ] 2 (X = Cl/Br), and metathesis/hydrogenation sequences yield mer , trans -Re(CO) 3 (X)[P( p -C 6 H 4 O(CH 2 ) 14 O- p -C 6 H 4 ) 3 P]. Reactions of 6c and 6d and excess PMe 3 give the free diphosphines P( p -C 6 H 4 O(CH 2 ) n O- p -C 6 H 4 ) 3 P ( 14c and 14d , 83-75%). The addition of 14d to [Rh(CO) 2 (μ-Cl)] 2 reconstitutes 6d (87%). Both in , in and out , out isomers of 14c and 14d are possible, but low-temperature NMR spectra show one set of signals, consistent with rapid homeomorphic isomerizations that turn the molecules inside out. Thermolyses (C 6 D 5 Br, 140 °C) effect phosphorus inversion to give in , out isomers.