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) Angstrom, b = 12.321(2) Angstrom, c = 14.652(2) Angstrom, alpha = 110.60(1)degrees, beta = 90.62 (1)degrees, and gamma = 103.22(1)degrees). Refinement converged at R = 0.0694 (R(w) = 0.0986) for 542 parameters using 4714 reflections with I > 2 sigma(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[5,2,1,0(5,10)] deca-1,3,5,8-tetraene-2,3,4,6-tetracarboxylate 10. This orange product crystallized in the monoclinic space group P2(1)/c (No. 14) with four molecules in the unit cell (a = 10.056(2) Angstrom, b = 14.280(1) Angstrom, c = 23.892(3) Angstrom, alpha = 90.0 degrees, beta = 94.15(1)degrees, and gamma = 90.0 degrees). Refinement converged at R = 0.0683 (R(w) = 0.0710) for 540 parameters using 3180 independent reflections with I > 3 sigma(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.