A Nontemplated Route to Macrocyclic Dibridgehead Diphosphorus Compounds: Crystallographic Characterization of a "Crossed-Chain" Variant of in/out Stereoisomers.

Reactions of (O=)PH(OCH2 CH3 )2 and BrMg(CH2 )m CH=CH2 (4.9-3.2 equiv; m=4 (a), 5 (b), 6 (c)) give the dialkylphosphine oxides (O=)PH[(CH2 )m CH=CH2 ]2 (2 a-c; 77-81 % after workup), which are treated with NaH and then α,ω-dibromides Br(CH2 )n Br (0.49-0.32 equiv; n=8 (a'), 10 (b'), 12 (c'), 14 (d')) to yield the bis(trialkylphosphine oxides) [H2 C=CH(CH2 )m ]2 P(=O)(CH2 )n (O=)P[(CH2 )m CH=CH2 ]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 H2 /PtO2 afford the dibridgehead diphosphine dioxides (4 bc', 4 ca'; 14-19 %, n'=2m+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, (CH2 )12 P(=O)(CH2 )12 (O=)P(CH2 )12 , as well as 3 ab' and 3 bc', are structurally characterized. The efficiencies of other routes to dibridgehead diphosphorus compounds are compared.