Rearrangement of a W(CO)₅-Complexed 7-Phosphanorbornadiene Analyzed by ab Initio MO Calculations

Abstract

The rearrangement of W(CO) 5 -complexed 7-phosphanorbornadiene 1 to the 7-phosphatricyclo-[3.2.0 4,6 ]hept-2-ene complex 2 is investigated experimentally and with the aid of ab initio theory at MP2(fc)/6-31G*. Photochemical concerted and thermal biradical pathways are considered. Calculations on the uncomplexed parent system indicate that a thermal rearrangement is unlikely because of its 6.4 kcal/mol endothermicity. The relationship of the 1 f 2 rearrangement with the CuCl-catalyzed, thermal decomposition of 1 to generate the incipient phosphinidene complex PhPW(CO) 5 is discussed.Phosphinidenes gain rapidly in popularity as versatile reagents in the syntheses of low-coordination organophosphorus compounds. 1,2 Through transition metal complexation, the otherwise triplet species 3 are stabilized to singlets. 4 Nucleophilic phosphinidenes, tailored after the Schrock complexes, use Ta and Zr in, for example, the phospha-Wittig reaction. 5 The best known electrophilic phosphinidenes, developed a decade ago by Marinetti and Mathey, 6 are stabilized by a W(CO) 5 group. They are generated in situ from the 7-phosphanorbornadiene precursor complex 1. 7 In contrast to the uncomplexed triplet PhP 3a and the nucleophilic RPdM (M ) Ta, Zr complex), 5 the electrophilic RPW(CO) 5 has not been characterized spectroscopically. It is assumed that 1 undergoes a thermal retrocycloaddition to give the tetrasubstituted benzene and the coordinated phosphinidene, which immediately adds, for example, to olefins to give phosphiranes (eq 1). [6][7][8][9][10] This phosphinidene-olefin cycloaddition is a first-order process in the thermal decomposition of 1 at ∼90-110 °C, which can be catalyzed by CuCl to occur at ∼55 °C. 6 In analogy with the chemistry of carbenes, generated from diazirines, 11 there is the lingering question whether RPW(CO) 5 phosphinidenes are formed from 1 in a concerted or a stepwise process. The possible existence of biradical intermediates surfaced in our recent observation that W(CO) 5 -complexed vinylphosphiranes P-epimerize under mild reaction conditions (eq 2). 12 Mathey 1a argued that if 1 were to give a biradical thermally it would rearrange to a cyclophosphaheptatriene (phosphepine), which has never been observed * To whom correspondence should be addressed at Vrije Universiteit.

Environmental and food analysis by desorption atmospheric pressure photoionization‐mass spectrometry

“…Gleiches gilt für die Monophosphorverbindung 7‐Phosphanorbornadien 1 A , die auf dem MP2/6‐31G*‐Niveau 22.5 kcal mol −1 stabiler ist als das Quadricyclanisomer 2 A (Abbildung 2). 3b…”

“… Vergleich des auf dem G3(MP2)‐Niveau berechneten Energieunterschieds zwischen 6 A und 8 A mit den Energieunterschieden zwischen 13 und 14 (experimentell14) sowie zwischen 1 A und 2 A (MP2/6‐31G3b). …”

Norbornadiene–Quadricyclane Valence Isomerism for a Tetraphosphorus Derivative The Netherlands Organization for Scientific Research (NOW/CW) is acknowledged for partial support (A.L.S., M.L., K.L.), as are the NSERC of Canada for a scholarship (S.B.C.), and EPSRC for funding phosphaorganometallic chemistry at Sussex University (J.F.N.). Dr. H. Zappey is thanked for the HR-MS spectra and J. C. Slootweg for his initiative.

“…Likewise, the parent 7‐phosphanorbornadiene 1 A is energetically preferred over its quadricyclane isomer 2 A by 22.5 kcal mol −1 at the MP2/6‐31G* level (Figure 2). 3b…”

“… G3(MP2) computed energy difference between 6 A and 8 A , compared to the energy difference between 13 and 14 (experimental)14 and 1 A and 2 A (MP2/6‐31G) 3b…”

1,4-Addition eines terminalen Phosphiniden-Komplexes an [5]Metacyclophan

“…Günstige Faktoren für diesen Reaktionsweg sind: 1) die hohen Koeffizienten des HOMO-1 an C8 und C11; 2) die Bootform des aromatischen Rings von 1 sowie die Pyramidalisierung an C8 und vor allem an C11, welche die für die Cycloaddition erforderliche Strukturänderung minimieren; 3) die Erhöhung der Elektronendichte an der konkaven Seite des Bootes von 1, welche die Überlappung mit 3 verbessert; 4) der Energiegewinn, der im Modell (Schema 2) bei der Bildung von 9 noch 9.2 kJ mol À1 gröûer ist als bei 10. Dies steht im Gegensatz zu der Addition des Phosphinidens HP : an (ebenes) Benzol, wobei das 1,2-Addukt 11 stabiler ist als das 1,4-Addukt 7 (Schema 2; ADF: 65.8 kJ mol À1 ; MP2(fc)/6 ± 31G*: 53.1 kJ mol À1 [9] …”