An approach to 1,3,4-dioxaphospholane complexes through an acid-induced ring expansion of an oxaphosphirane complex: the problem of construction and deconstruction of O,P-heterocycles.

Treatment of oxaphosphirane complex 1, triflic acid (TfOH), and various aldehydes yielded 1,3,4-dioxaphospholane complexes 5a,b-7a,b after deprotonation with NEt(3). In addition to NMR spectroscopy, IR spectroscopy, and MS data, the X-ray structures of complexes 5a and 7a were determined. (31)P NMR spectroscopic monitoring and DFT calculations provided insight into the reaction course and revealed the transient TfOH 1,3,4-dioxaphospholanium association complex TfOH-5a,b and/or TfOH-5a,b' as key reactive intermediates.

First examples of oxaphosphirane pentacarbonylchromium(0) and -molybdenum(0) complexes: synthesis, structures and reactions.

Synthesis of the first oxaphosphirane chromium(0) and molybdenum(0) complexes of the type [{(R(1)PCH(R(2))-O}M(CO)(5)] (R(1) = C(5)Me(5)) (8a-e, 15a-e) and (R(1) = CH(SiMe(3))(2)) (9a-e, 16a-e) via reaction of dichloro(organo)- (1, 2, 10, 11) and chloro(organo)phosphane complexes (3,4,12) with lithium bases and aldehydes 7a-e is reported. Furthermore, bicyclic 1,3-oxaphospholane complexes 17 and 18 have been obtained via O-protonation of oxaphosphirane complexes 8a and 15a with HCl. All complexes were characterized by NMR, IR spectroscopic, mass spectrometric investigations and, in addition, single-crystal X-ray structures of complexes 8a-e, 9a,c, 15a,b,e, 16a-c, 17, 18 are presented and discussed.

Developing click reactions of a 3-ferrocenyl-2H-azaphosphirene complex.

Atom efficient reactions of 3-ferrocenyl-2H-azaphosphirene complex 1 using a newly developed acid/base ring expansion protocol are presented. Consecutive reaction of 1 in the presence of dimethyl cyanamide with triflic acid and triethylamine yielded the selective formation of 2H-1,4,2-diazaphosphole complex 3. The same protocol using acetone, benzaldehyde and ferrocenyl aldehyde afforded 1,3,5-oxazaphosphol-3-ene complexes 4, 5a,b and 6a,b, the latter as mixtures of diastereomers, which could be separated.

Competing ring cleavage of transient O-protonated oxaphosphirane complexes: 1,3-oxaphospholane and η2-Wittig ylide complex formation.

O-Protonation and ring cleavage of oxaphosphirane complexes 1a,b enabled the synthesis of novel compounds such as the bicyclic 1,3-oxaphospholane complex 5 and the η(2)-Wittig ylide complex 7, which demonstrate the emerging chemistry of this new reactive intermediate. Whereas P-O bond cleavage occurred, in the first case, thus revealing the superior ability of the P-bonded Cp* group to stabilize cationic charge, in the second case competing C-O and P-O bond cleavages occurred, thus leading to a mixture of complexes 3, 4 and 7.