1,3-Diphospholene-4-ylidene Chromium (Tungsten) Pentacarbonyl Complexes Formed by CO Insertion into the Ring of a 1,3-Diphosphacyclobutane-2,4-diyl-2-ide-Complexes of a Phosphanyl Carbene or a Phosphonium Ylide?

• Published in: Chemistry : a European journal 2002-05, Vol.8 (9), p.2188-2196
• Main Authors: Fuchs, André, Gudat, Dietrich, Nieger, Martin, Schmidt, Olaf, Sebastian, Manuel, Nyulaszi, Laszlo, Niecke, Edgar
• Format: Article
• Language: English
• Subjects: carbene complexes; computer chemistry; insertion; NMR spectroscopy; phosphorus heterocycles
• ISSN: 0947-6539; 1521-3765
• DOI: 10.1002/1521-3765(20020503)8:9<2188::AID-CHEM2188>3.0.CO;2-F

Reaction of the 1,3‐diphosphacyclobutane‐2,4‐diyl‐2‐ide 1 with chromium or tungsten hexacarbonyl afforded the anionic complexes [cyclo‐{P(Mes*)‐C(SiMe3)‐P(Mes*)‐C(O)‐C[M(CO)5]}]− (3 a,b: M=Cr, W) by the formal insertion of CO into the four membered ring. Computational analysis suggests that this reaction proceeds via two intermediates that can be formulated as a cyclic metal acyl and an acyclic ketenyl complex. The anionic complexes 3 a,b further reacted with electrophiles to afford the neutral complexes [cyclo‐{P(Mes*)‐C(SiMe3)‐P(Mes*)‐C(OR)‐C[M(CO)5]}] (4 a,b: M=Cr, W, R=Me; 5, 6: M=Cr, R=SiMe3, H). All products were characterized by standard spectroscopic (NMR and MS) techniques, and 4 a,b further by extensive one‐ and two‐dimensional multinuclear (1H, 13C, 31P, 183W) NMR studies. From these investigations, an unequivocal assignment of chemical shifts and coupling constants was derived, confirming unusually large shielding for the formal carbenic carbon atoms which exceed even those in complexes of imidazoyl carbenes. Single‐crystal X‐ray diffraction analyses of 3 a, 4 a,b, and 5 revealed that all of these compounds contain planar P2C3 rings. The phosphorus atoms are slightly pyramidal, and the carbon–metal distances (C−Cr 218 pm, C−W 230 pm) suggest low bond orders. Comparison of the structural parameters of 3 a with those of the O‐substitution products 4 a, 5 revealed substantial changes in endocyclic P−C bond lengths and the degree of pyramidal character of bonding at the phosphorus atoms. In line with the spectroscopic and computational results, these effects were interpreted in terms of a considerable reorganization of π electrons in the ring, which induces a substantial degree of aromatic character in the neutral complexes 4–6. Die Reaktion des 1,3‐Diphosphacyclobutan‐2,4‐diyl‐2‐ids 1 mit [Cr(CO)6] bzw. [W(CO)6] verläuft unter einer formalen Insertion von CO in den Vierring unter Ausbildung der anionischen Komplexe [cyclo‐{P(Mes*)‐C(SiMe3)‐P(Mes*)‐C(O)‐C(M(CO)5)}]− (3 a,b: M=Cr, W). Theoretischen Berechnungen zufolge sollte die Reaktion über zwei Übergangszustände, einen zyklischen Metall‐Acyl‐ und einen azyklischen Ketenylkomplex verlaufen. Die anionischen Komplexe 3 a,b bilden bei der Umsetzung mit Elektrophilen neutrale Komplexe [cyclo‐{P(Mes*)‐C(SiMe3)‐P(Mes*)‐C(OR)‐C(M(CO)5)}] (4 a,b: M=Cr, W, R=Me; 5, 6: M=Cr, R=SiMe3, H). Alle Produkte wurden durch die üblichen spektroskopischen Methoden (NMR und MS) charakterisiert. Desweiteren wurden ausg