Epimerization of Cyclic Vinylphosphirane Complexes:  The Intermediacy of Biradicals

Abstract

The phosphinidene complex Ph−P−W(CO)5 reacts with cyclopentadiene, 1,3-cyclohexadiene, 1,3-cycloheptadiene, and 1,3-cyclooctadiene to give in each case isomeric mixtures of syn- and anti-vinylphosphiranes. With longer reaction times and/or higher reaction temperatures, the anti adducts isomerize to the syn adducts. These epimerizations are likely to proceed via biradical intermediates. Only the syn-vinylphosphirane of 1,3-cyclohexadiene undergoes a [1,3]-sigmatropic shift to yield a syn-phopholene. The dichotomy of biradical and concerted mechanisms is discussed in relationship with the analogous mechanism for the vinylcyclopropane → cyclopentene rearrangement.

Linear and Branched Phospha[n]triangulanes

“…The phosphorus chemical shifts are in the narrow range of d 31 P À144 to À155 ppm with 1 J(P,W) coupling constants of 252-261 Hz. The less congested anti isomers are always formed predominantly [15] and have the more shielded 31 P NMR resonances [16] that are similar to the d À154.8 ppm reported for the parent 1-phenylphospha [2]triangulane complex 4 b. [4] The 13 C resonance of the phosphirane spiro-carbon C1 and carbon C2 are at d 25-30 (4 b 31.2) and d 15-18 ppm (4 b 19.3), respectively.…”

Addition of a Phosphinidene Complex to C=N Bonds: P-Ylides, Azaphosphiridines, and 1,3-Dipolar Cycloadditions

“…The next question is whether azaphosphiridines are intermediates in the formation of the bridged diazaphospholanes 10 a ± c. In other words, is a CPN ring indeed formed first, after which the second CN group is inserted intramolecularly, or is there a direct single-step pathway that leads to the diazaphospholanes? We ask this question because only one isomer of the bicyclic products 10 a ± c is formed at 110 8C, which is a temperature at which P-epimerization is known to occur in complexed phosphiranes, [9,10] while isomeric mixtures of 7 a ± c and 12 are obtained for the intermolecular reaction (Scheme 2 and Scheme 4).…”

“…For N(2), we assume a hydrogen position that enables hydrogen bonding to the chlorine, as the alternative position would result in an intermolecular H-bond to a carbonyl oxygen of a neighboring molecule. The sevenmembered ring has a nearly ideal chair conformation with the Cl À anion located above it on the same side as the equatorial [8]: P(1)ÀW(1) 2.503(2), P(1)À N(2) 1.674 (7), P(1)ÀC(4) 1.907(9), P(1)ÀC(1)1 1.820 (8), N(1)ÀC(1) 1.509 (10), N(1)ÀC(4) 1.521 (10), N(2)ÀC(3) 1.466(10), C(1)ÀC(2) 1.526(13), C(2)ÀC(3) 1.532 (13), C(4)ÀC(5) 1.513(11), W(1)-P(1)-N(2) 118.5(3), W(1)-P(1)-C(4) 112.2(3), W(1)-P(1)-C(11) 112.6(2), N(2)-P(1)-C(4) 105.3(4), P(1)-N(2)-C(3) 120.9(6), P(1)-C(4)-N(1) 111.6(6), C(1)-N(1)-C(4) 116.5 (7). cis phenyl groups.…”

Olefin-Cycloaddition des elektrophilen Phosphinidenkomplexes [iPr2N−P=Fe(CO)4]

“…[16] Die Kristallstruktur von 12 mit den beiden exocylischen Isopropylidengruppen zeigt interessante Eigenschaften (Abbildung 3). Das Molekül ist (5); C18-Fe-P 175.21 (11), N-P-C5 109.00 (14), N-P-C2 109.43 (13), C5-P-C2 91.63 (14), N-P-Fe 120.07 (10) annähernd C s -symmetrisch mit trigonal-bipyramidal pentakoordiniertem Fe-Atom. Das Phospholen befindet sich in der axialen Position (Fe-P 2.2798(9) ), und die C s -Symmetrie wird durch die Konformation der iPr 2 N-Gruppe mit planarer Umgebung am Stickstoffatom erhalten.…”

“…Der Phospholenring weicht leicht von der Planarität ab, wobei sich das P-Atom 0.269(5) oberhalb der C2-C3-C4-C5-Ebene in Richtung der weniger voluminösen Fe(CO) 4 -Gruppe befindet. Während die C-P-N-Winkel annähernd dem Tetraederwinkel entsprechen, deutet der C-P-C-Winkel von 91.63 (14)8 deutlich auf ein gespannenes Ringsystem hin. Als Folge davon weisen die sp 2 -Atome C2 und C5 im Ring P-C-C-Winkel von 106.68(23) bzw.…”