X-ray structures of triphenylphosphine and 1,2,5-triphenylphosphole products with dimethyl acetylenedicarboxylate tetramer

A tetramer of dimethyl acetylenedicarboxylate, tetramethyl 4-methoxy-5-[1,2,3-tris(methoxycarbonyl)-2-cyclopropen-1-yl]-7-oxabicyclo[2.2.1]hepta-2,5-diene-1,2,3,6-tetracarboxylate 3, was recovered from old stocks of the monomer, and was also prepared thermally from the monomer by a variation of a previous method. NMR data and an X-ray crystal structure were determined for a red 1:1 adduct of this ester with triphenylphosphine. This red adduct, tetramethyl 4-methoxy-5-[1,2,3-tris(carbomethoxy)-3-triphenylphosphoranylidenepropen-1-yl]-7-oxabicyclo[2.2.1]hepta-2,5-diene-1,2,3,6-tetracarboxylate 5, crystallized in the triclinic space group P1 (No. 2) with two molecules in the unit cell (a = 12.315(2) Å, b = 12.321(2) Å, c = 14.652(2) Å, α = 110.60(1)°, β = 90.62 (1)°, and γ = 103.22(1)°). Refinement converged at R = 0.0694 (Rw = 0.0986) for 542 parameters using 4714 reflections with I > 2σ(I). Triphenylphosphine oxide did not react with tetramer 3. Reaction of the tetramer of dimethyl acetylenedicarboxylate 3 with 1,2,5-triphenylphosphole gave an orange product with concomitant loss of a furan triester. NMR data confirmed that this was not a simple adduct, and examination of a crystal by X-ray established the structure as the dichloromethane complex of tetramethyl 1,9,10-triphenyl-1-phospha(V)tricyclo[5,2,1,05,10] deca-1,3,5,8-tetraene-2,3,4,6-tetracarboxylate 10. This orange product crystallized in the monoclinic space group P21/c (No. 14) with four molecules in the unit cell (a = 10.056(2) Å, b = 14.280(1) Å, c = 23.892(3) Å, α = 90.0°, β = 94.15(1)°, and γ = 90.0°). Refinement converged at R = 0.0683 (Rw = 0.0710) for 540 parameters using 3180 independent reflections with I > 3σ(I). The tetramer 3 did not react with 1,2,5-triphenylphosphole-1-oxide quickly, but after 9 months gave a white, probably polymeric, product.