André Fuchs

Valence Isomerization of a 1,3‐Diphosphacyclobutane‐2,4‐diyl: Photochemical Ring Closure to 2,4‐diphosphabicyclo[1.1.0]butane and Its Thermal Ring Opening to gauche‐1,4‐Diphosphabutadiene

The bond stretch isomer 1,3-diphosphacyclobutane-2,4-diyl 1 was transformed photochemically to give the previously unknown 2,4-diphosphabicyclo[1.1.0]butane 2, which itself can be converted thermally into gauche-1,4-diphosphabutadiene 3. The crystal structures of these three energy-rich valence isomers of 1,2-diphosphete have been determined. R=SiMe(3); Mes*=2,4,6-tBu(3)C(6)H(2).

VALENCE ISOMERIZATION IN THE SOLID STATE : FROM 1,3-DIPHOSPHACYCLOBUTANE-2,4-DIYL TO 1,2-DIHYDRO-1,2-DIPHOSPHETE

The butadiene-like phosphanylcarbene 2 is, according to ab initio calculations, the intermediate in the conversion of 1 into 3 in the solid state [Eq. (a)]; it is only 1.3 kJ mol-1 higher in energy than 1. For this conversion, only minor changes in the endocyclic bonds are required throughout the entire reaction. R2 N=2,2,6,6-Me4 C5 H6 N.

1,3-Diphosphacyclobutane-2,4-diyl-2-ylidenide: A Unique Carbene and Its Trimethylalane Complex.

A unique bonding situation is displayed by the lithium 1,3-diphosphacyclobutane-2,4-diyl-2-ylidenide 2 small middle dot[Li(thf)(n)](+) (Ar=2,4,6-tBu(3)C(6)H(2)) obtained by deprotonation of 1. According to ab initio calculations, the anion 2 can viewed as a cyclic bis(phosphanyl)carbene. Reaction with trimethylaluminum gives the complex 3 small middle dot[Li(thf)(4)](+), whose crystal structure is presented.

Valenzisomerisierung im Festkörper: vom 1,3-Diphosphacyclobutan-2,4-diyl zum 1,2-Dihydro-1,2-diphosphet

Das butadienanaloge Phosphanylcarben 2 ist Ab-initio-Rechnungen zufolge das Intermediat der Umlagerung von 1 zu 3 im Feststoff [Gl. (a)]. Seine Energieliegt nur 1.3 kJ mol−1 hoher als die von 1, und es sind bei dieser Umlagerung wahrend der gesamten Reaktion lediglich kleine Anderungen bezuglich der endocyclischen Bindungen erforderlich. R2N = 2,2,6,6-Me4C5H6N.

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?

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(SiMe(3))-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(SiMe(3))-P(Mes*)-C(OR)-C[M(CO)(5)])] (4 a,b: M=Cr, W, R=Me; 5, 6: M=Cr, R=SiMe(3), H). All products were characterized by standard spectroscopic (NMR and MS) techniques, and 4 a,b further by extensive one- and two-dimensional multinuclear ((1)H, (13)C, (31)P, (183)W) 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 P(2)C(3) 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 pi electrons in the ring, which induces a substantial degree of aromatic character in the neutral complexes 4-6.

FROM 1,3-DIPHOSPHETANE-2,4-DIYLS TO CYCLIC ANIONS AND CATIONS

The interest in diradicals has grown by the increasing number of stable diradicals which have been synthesized during the last few years. The diphosphacyclobutane-diyles have a diradicaloid molecular structure and they were the first diradicals to be prepared in the gramme scale. The combination of stability and high yield synthesis creates the opportunity both to change the substitution pattern or to prepare different valence isomers. Current experimental and computational studies reveal that electron transfer reactions of maintain the cyclic system. In the contribution, the oxidation reaction of 1 to the radical cation 2 and the cyclic diphosphaallyl cation 3 will be reported. Additionally, the remarkable mechanism of the reaction of 1 at first to the radical anion 4 but particularly to the diphosphacyclobutadiene dianion 5 under reductive conditions will be presented in detail.

1,3-Diphosphetane-2,4-diyles--Cryptocarbenes?

1,3-Diphosphetane-2,4-diyles ( A ) possess a diradical molecular structure. Experimental studies reveal interconversions of different valence isomers of the diradicals. As a consequence of the facile thermal ring opening of 1,3-diphosphetane-2.4-diyles A , we obtained crypto-phosphinocarbenes ( B ), confirmed by the results of intramolecular rearrangements as well as reactions with multiple bonded systems. A new range of five- and six-membered phosphorus heterocycles are isolated, including transition-metal complexes. The mechanism for the ring-expansion are predicted by quantum chemical calculations.

DIPHOSPHETANE-DIYLES : DIRADICAL OR HUCKEL-AROMATIC? FROM ORBITAL AND STRUCTURAL ISOMERISM TO RADICAL CATIONS AND ANIONIC CARBENES

The synthesis, crystal structure and bonding properties of various diphosphetane-diyles are discussed and compared with those of other valence isomers. Experimental studies revealed that interconversion of different isomers are possible. Furthermore, it will be shown that diphosphetane-diyles can serve as building blocks in organo phosphorus as well as metal organic chemistry.

Novel aspects in the synthesis of carbenoids containing P/C-p pi-bonds

Abstract The synthesis and x-ray structure analysis of a novel type of carbenoids, aryl-P(=E)=C(Cl)Li(thf)3 (E=N-aryl, C(SiMe3)2), as well as the first example of a 1,3-diphosphetane-2,4-diyl, (aryl-PCCl)2, is reported and on the basis of quantum chemical calculations its bonding situation is discussed. Furthermore, selected examples for the varying reaction behavior of both types of compounds are presented.