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.
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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-C6H4O(CH2)mCHCH2)3 [3; m = 4 (a), 5 (b), 6 (c), and 7 (d)], [Rh(COD)(-Cl)]2, and CO gives square-planar trans-Rh(CO)(Cl)[P(p-C6H4O(CH2)mCHCH2)3]2 (4a-4d). Reactions of 4b-4d with Grubbs' catalyst (first generation) and then H2 (catalyst PtO2) yield the title compounds trans-Rh(CO)(Cl)[P(p-C6H4O(CH2)nO-p-C6H4)3P] (n = 2m + 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 (CH2)n segments. Steric interactions with the PC6H4O linkages are analyzed. LiCCAr displaces the chloride ligand from 6b to give RhCCAr adducts (Ar = C6H5/p-C6H4CH3, 7b/8b). The ArCC-Rh-CO rotator of 7b rapidly rotates on the NMR time scale (-70 C), but with 8b, the longer p-CH3C6H4CC group is confined between two (CH2)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-C6H4O(CH2)6CHCH2)3]2 (X = Cl/Br), and metathesis/hydrogenation sequences yield mer,trans-Re(CO)3(X)[P(p-C6H4O(CH2)14O-p-C6H4)3P]. Reactions of 6c and 6d and excess PMe3 give the free diphosphines P(p-C6H4O(CH2)nO-p-C6H4)3P (14c and 14d, 83-75%). The addition of 14d to [Rh(CO)2(-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 (C6D5Br, 140 C) effect phosphorus inversion to give in,out isomers.
