A Nontemplated Route to Macrocyclic Dibridgehead Diphosphorus Compounds: Crystallographic Characterization of a “Crossed‐Chain” Variant of <i>in</i>/<i>out</i> Stereoisomers

Abstract

Abstract Reactions of (O=)PH(OCH 2 CH 3 ) 2 and BrMg(CH 2 ) m CH=CH 2 (4.9–3.2 equiv; m =4 ( a ), 5 ( b ), 6 ( c )) give the dialkylphosphine oxides (O=)PH[(CH 2 ) m CH=CH 2 ] 2 ( 2 a – c ; 77–81 % after workup), which are treated with NaH and then α,ω‐dibromides Br(CH 2 ) n Br (0.49–0.32 equiv; n =8 ( a′ ), 10 ( b′ ), 12 ( c′ ), 14 ( d′ )) to yield the bis(trialkylphosphine oxides) [H 2 C=CH(CH 2 ) m ] 2 P(=O)(CH 2 ) n (O=)P[(CH 2 ) m CH=CH 2 ] 2 ( 3 ab′ , 3 bc′ , 3 cd′ , 3 ca′ ; 79–84 %). Reactions of 3 bc′ and 3 ca′ with Grubbs’ first‐generation catalyst and then H 2 /PtO 2 afford the dibridgehead diphosphine dioxides ( 4 bc′ , 4 ca′ ; 14–19 %, n′ =2 m +2); 31 P 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 of in , out ‐ 4 ca′ that features crossed chains, such that the (O=)P vectors appear out , out . Whereas 4 bc′ resists crystallization, a byproduct derived from an alternative metathesis mode, ( CH 2 ) 12 P (=O)(CH 2 ) 12 (O=) P(C H 2 ) 12 , as well as 3 ab′ and 3 bc′ , are structurally characterized. The efficiencies of other routes to dibridgehead diphosphorus compounds are compared.