Chemistry of 2H-azaphosphirene complexes, 16 - Syntheses, structures, and reactions of C-methoxycarbonyl-functionalized small- and medium-sized P-heterocycle complexes

Thermal ring-opening of [{2-bis(trimethylsilyl)methyl-3-phenyl-2H-azaphosph irene-kappa P}pentacarbonyltungsten(0)] (8a) in the presence of dimethyl ac etylenedicarboxylate (DMAD) led to the 2,3-bifunctionalized 1H-phosphirene complex 9a and the 4-phenyl-substituted 2H-1,2-azaphosphole complex 10a, th e latter as a by-product. If a small amount of benzonitrile was added. comp lex 10a was obtained as the main product, along with a small amount of the decomplexed 2H-1,2-azaphosphole 11, which could not be isolated. Reaction o f complex 10a with elemental sulfur furnished the corresponding P-V sulfide 13, When the ring-opening of complex 8a was performed in the presence of t wo equivalents of DMAD and two equivalents of dimethyl cyanamide, we obtain ed the 4-dimethylamino-substituted 2H-1,2-azaphosphole complex 10b, togethe r with the diastereomeric Delta(3)-1,3,2-oxazaphospholene complexes 14a,b. On reaction of [{2-pentamethylcyclopentadienyl-3-phenyl-2H-azaphosphirene-k appa P}pentacarbonyltungsten(0)] (8b) and DMAD in toluene, the correspondin g 1H-phosphirene complex 9b was only formed as a transient species and the P-coordinated P,C-cage compound 15 was the final product. Using benzonitril e as solvent, the 4-phenyl-substituted 2H-1,2-azaphosphole complex inc was obtained. together with the 7-aza-1-phosphanorbornadiene complex 16, the la tter through partial decomposition of inc coupled with rearrangement and a Diels-Alder reaction; the ratio 10c/16 was found to depend strongly on the molar ratio of complex 8b to DMAD, A cycloaddition reaction of the 2,3-bifu nctionalized 1H-phosphirene complex Sa with 2,3-dimethylbutadiene furnished the bicyclic phosphirane complex 19, along with a small, amount of the non coordinated bicyclic phosphirane 20. Reaction of complex 9a with diethylami ne yielded the phosphirane complex 21 as a 1,2-addition product, the diorga nophosphane complex 22 through ring-opening of 9a, and the 3,4-functionaliz ed 1,2-dihydro-1-phosphet-2-one complex 23 through an unprecedented ring-ex pansion reaction; the products 21, 22, 23 were formed in a ratio of ca. 1:1 :1. The structures of the 1H-phosphirene complex 9a, the 4-dimethylamino-su bstituted 2H-1,2-azaphosphole complex 10b, the bicyclic phosphirane complex 19, the phosphirane complex 21, and the 1,2-dihydro-1-phosphet-2-one compl ex 23 have been determined by single-crystal X-ray diffraction analysis.