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The diphosphine complexes cis - or trans -PtCl 2 (P((CH 2 ) n ) 3 P) ( n = b/12, c/14, d/16, e/18) are demetalated by MCX nucleophiles to give the title compounds (P((CH 2 ) n ) 3 )P (3b–e, 91–71%). These “empty cages” react with PdCl 2 or PtCl 2 sources to afford trans -MCl 2 (P((CH 2 ) n ) 3 P). Low temperature 31 P NMR spectra of 3b and c show two rapidly equilibrating species (3b, 86 : 14; 3c, 97 : 3), assigned based upon computational data to in , in (major) and out , out isomers. These interconvert by homeomorphic isomerizations, akin to turning articles of clothing inside out (3b/c: Δ H ‡ 7.3/8.2 kcal mol −1 , Δ S ‡ −19.4/−11.8 eu, minor to major). At 150 °C, 3b, c, e epimerize to (60–51) : (40–49) mixtures of ( in , in / out , out ) :  in , out isomers, which are separated via the bis(borane) adducts 3b, c, e·2BH 3 . The configurational stabilities of in , out -3b, c, e preclude phosphorus inversion in the interconversion of in , in and out , out isomers. Low temperature 31 P NMR spectra of in , out -3b, c reveal degenerate in , out / out , in homeomorphic isomerizations (Δ G ‡Tc 12.1, 8.5 kcal mol −1 ). When ( in , in / out , out )-3b, c, e are crystallized, out , out isomers are obtained, despite the preference for in , in isomers in solution. The lattice structures are analyzed, and the D 3 symmetry of out , out -3c enables a particularly favorable packing motif. Similarly, ( in , in / out , out )-3c, e·2BH 3 crystallize in out , out conformations, the former with a cycloalkane solvent guest inside. 

The three secondary phosphine oxides [CH₂=CH(CH₂)₄]₂HPO (1), [CH₂=CH(CH₂)₅]₂HPO (2), and [CH₂=CH(CH₂)₆]₂HPO (3), and two diphosphine dioxides, {[CH₂=CH(CH₂)₆]₂PO(CH₂)₇}₂(4) and {[CH₂=CH(CH₂)₆]₂PO(CH₂)₄}₂(5), incorporating long methylene chains, are described. The single crystal X‐ray structures of1,2, and5have been determined. The phosphine oxides3,4, and5have been adsorbed on silica in submonolayer quantities to give3 a–5 a. The¹H,¹³C, and³¹P solid‐state NMR spectra of polycrystalline3–5have been analyzed and compared with those of3 a–5 a. The changes of the solid‐state NMR characteristics upon adsorption and the surface mobilities of the phosphine oxides are discussed.

 

Reactions of (O=)PH(OCH₂CH₃)₂and BrMg(CH₂)_mCH=CH₂(4.9–3.2 equiv;m=4 (a), 5 (b), 6 (c)) give the dialkylphosphine oxides (O=)PH[(CH₂)_mCH=CH₂]₂(2 a–c; 77–81 % after workup), which are treated with NaH and then α,ω‐dibromides Br(CH₂)_nBr (0.49–0.32 equiv;n=8 (a′), 10 (b′), 12 (c′), 14 (d′)) to yield the bis(trialkylphosphine oxides) [H₂C=CH(CH₂)_m]₂P(=O)(CH₂)_n(O=)P[(CH₂)_mCH=CH₂]₂(3 ab′,3 bc′,3 cd′,3 ca′; 79–84 %). Reactions of3 bc′and3 ca′with Grubbs’ first‐generation catalyst and then H₂/PtO₂afford the dibridgehead diphosphine dioxides(4 bc′,4 ca′; 14–19 %,n′=2m+2);³¹P NMR spectra show two stereoisomeric species (ca. 70:30). Crystal structures of two isomers of the latter are obtained,out,out‐4 ca′and a conformer ofin,out‐4 ca′that features crossed chains, such that the (O=)P vectors appearout,out. Whereas4 bc′resists crystallization, a byproduct derived from an alternative metathesis mode, (CH₂)₁₂P(=O)(CH₂)₁₂(O=)P(CH₂)₁₂, as well as3 ab′and3 bc′, are structurally characterized. The efficiencies of other routes to dibridgehead diphosphorus compounds are compared.