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Dedicated to Professor Edgar Niecke on the occasion of his 60th birthdayThe chemistry of the norbornadienes (bicyclo[2.2.1]hepta-2,5-dienes) displays a variety of interesting aspects. One of these is the photochemical isomerization of norbornadienes to quadricyclanes [1] and its catalytic reversal. [2] Another is the synthesis, stability, and reactivity of heterocyclic analogues bearing a nitrogen or phosphorus atom at the 1-and/or 7-position (I ± III in Figure 1); particularly noteworthy results from this area concern the differences in stability between 7-aza- [3] and 7-phosphanorbornadienes (Type II), [4] (the latter can be stabilized and isolated by coordination of the phosphorus to a metal [5] ), and catalytic reactions [6] using 1-phosphanorbornadienes [7] (Type I) as novel ligands.

Thermal ring‐opening of [{2‐bis(trimethylsilyl)methyl‐3‐ phenyl‐2H‐azaphosphirene‐ĸP}pentacarbonyltungsten(0)] (8a) in the presence of dimethyl acetylenedicarboxylate (DMAD) led to the 2,3‐bifunctionalized 1H‐phosphirene complex 9a and the 4‐phenyl‐substituted 2H‐1,2‐azaphosphole complex 10a, the latter as a by‐product. If a small amount of benzonitrile was added, complex 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 of complex 10a with elemental sulfur furnished the corresponding PV sulfide 13. When the ring‐opening of complex 8a was performed in the presence of two equivalents of DMAD and two equivalents of dimethyl cyanamide, we obtained the 4‐dimethylamino‐substituted 2H‐1,2‐azaphosphole complex 10b, together with the diastereomeric Δ3‐1,3,2‐oxazaphospholene complexes 14a,b. On reaction of [{2‐pentamethylcyclopentadienyl‐3‐phenyl‐2H‐azaphosphirene‐ĸP}pentacarbonyltungsten(0)] (8b) and DMAD in toluene, the corresponding 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 benzonitrile as solvent, the 4‐phenyl‐substituted 2H‐1,2‐azaphosphole complex 10c was obtained, together with the 7‐aza‐1‐phosphanorbornadiene complex 16, the latter through partial decomposition of 10c 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‐bifunctionalized 1H‐phosphirene complex 9a with 2,3‐dimethylbutadiene furnished the bicyclic phosphirane complex 19, along with a small amount of the noncoordinated bicyclic phosphirane 20. Reaction of complex 9a with diethylamine yielded the phosphirane complex 21 as a 1,2‐addition product, the diorganophosphane complex 22 through ring‐opening of 9a, and the 3,4‐functionalized 1,2‐dihydro‐1‐phosphet‐2‐one complex 23 through an unprecedented ring‐expansion 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‐substituted 2H‐1,2‐azaphosphole complex 10b, the bicyclic phosphirane complex 19, the phosphirane complex 21, and the 1,2‐dihydro‐1‐phosphet‐2‐one complex 23 have been determined by single‐crystal X‐ray diffraction analysis.

New l#-diphosphirene and 2,3-dihydro-l,2,3-triphosphete tungsten complexes have been synthesized, by thermal decomposition of different 2#-azaphosphirene complexes in the presence of various phosphaalkynes. Novel phosphorus-carbon cage complexes were obtained, if a pentamethylcyclopentadienyl-substituted 2//-azaphosphirene complex and alkyl-substituted phosphaalkynes were employed.