Hans-Jürgen Wessely

1,2- and 1,3-diphosphetanes from alkylidenephosphines

Abstract Alkyl- or arylbis(trimethylsilyl)phosphines as well as tris(trimethylsilyl)phosphine and the corresponding arsines react with acyl chlorides to give [1-(trimethylsiloxy)alkylidene]phosphines 1 and -arsines 2; most of their 2,2-dimethylpropylidene derivatives are thermally stable at room temperature. With the same class of phosphines as starting compounds and carbon disulfide [bis(trimethylsilylsulfano)methylidene]phosphines 3 are formed, whereas [(dialkylamino)methylidene]-4 and [diarylmethylidene]phosphines 5 or the corresponding arsines 6 and 7 can be obtained from acyl amides or ketones.1

Monomeric and dimeric (aminomethylidene)phosphines and -arsines

Abstract In (dimethylaminomethylidene)phosphines (1) [1] and -arsines (2) the internal rotation of the dimethylamino group is hindered by a barrier of 50 to 55 kJmol−1− analogous to the corresponding amidines. In order to evaluate the influence of this conjugative effect upon the P=C and (P)-C-N bond lengths, single crystal x-ray structure determinations of 1a and 2a have been carried out. For comparison, the cyclic (aminomethylidene)phosphine 1H-1,3-benzazaphosphole 5 [2] as well as the dimeric compounds 3a, 3b, and 3c [3] have been analyzed, too, while the arsenic derivative 6 was studied by others [4]. The diarsetanes 4 could not yet be isolated. The structural results indicate the E=C bonds in 1a, 2a, 5, and 6 to be scarcely elongated, the (E)-C-N bonds, however, to be shortened considerably with respect to the dimers.

Synthese und Struktur von 1,3-Dibenzyl- und 1,3-Diethyl-2,4-bis(phenylimino)-1,3-diphosphetan (Acyl- und Alkylidenphosphane ; 28)

Unter der Katalyse von wenig festem Natriumhydroxid setzen sich die aus Benzyl- oder Ethylbis(trimethylsilyl)phosphan und Phenylisocyanat gebildeten Addukte 1a und 1b bei +20°C langsam zu Hexamethyldisiloxan und oligomeren [(Phenylimino)methyliden]phosphanen um. Wahrend die Benzyl-Verbindung in unterschiedlichen Losungsmitteln nur als Gemisch aus [N,N′-(E)]- und [N,N′-(Z)]-isomerem 2,4-Bis(phenylimino)-1,3-diphosphetan 2a mit den beiden Alkylgruppen an den Phosphoratomen in trans-Stellung vorliegt, findet man bei dem in Cyclopentan gelosten Ethyl-Derivat 2b ein weiteres [N,N′-(E)/(Z)]-isomeres Dimerenpaar mit zueinander cisstandigen Substituenten sowie die beiden trimeren Formen 3b und 4b. Die aus 1,2-Dimethoxyethan oder Cyclopentan isolierten Verbindungen [N,N′-(E)]-1r,3t-Dibenzyl- (2a) und [N,N′-(E)]-1r,3t-Diethyl-2,4-bis(phenylimino)-1,3-diphosphetan 2b kristallisieren monoklin in der Raumgruppe P21/c bzw. P21/n mit folgenden, bei Mestemperaturen von +20 ± 3°C/−130 ± 3°C bestimmten Abmessungen der Elementarzelle: a = 2145,4(1)/569,3(1); b = 568,1(2)/719,1(2); c = 1960,2(2)/2042,6(4) pm; β 99,43(1)°/95,03(2)°; Z = (2+2) bzw. 2. Nach den Ergebnissen von Rontgenstrukturanalysen (RW = 0,034/0,041) weisen die Molekule Inversionszentren auf. Charakteristische gemittelte Bindungslangen (pm) und -winkel (°) sind: endocycl. P-C 185/184; C-P-C 82/81; P-C-P 98/99; exocycl. P-C 186/184; C=N 127/127; C=N-C 121/11. Catalyzed by small amounts of solid sodium hydroxide, the adducts 1a and 1b formed from benzyl- or ethylbis(trimethylsilyl)phosphine and phenylisocyanate, react at +20°C slowly to give hexamethldisiloxane and oligomeric [(phenylimino)methylidene]phosphines. In different solvents the benzyl compound was found to exist only as a mixture of [N,N′-(E)/(Z)]-isomeric 2,4-bis-(phenylimino)-1,3-diphosphetanes 2a with their alkyl groups at the phosphorus atoms in trans position, whereas in case of the ethyl derivative 2b a second pair of [N,N′-(E)/(Z)]-isomeric dimers with their substituents in cis position and two trimeric forms (3b and 4b) could be detected in cyclopentane. [N,N′-(E)]-1r,3t-dibenzyl- (2a) and [N,N′-(E)]-1r,3t-diethyl-2,4-bis(phenylimino)-1,3-diphosphetane 2b isolated from 1,2-dimethoxyethane or cyclopentane, crystallize in the monoclinic space group P21/c or P21/n, resp., with following dimensions of the unit cell determined at temperatures of measurement of +20 ± 3°C/−130 ± 3°C: a = 2145.4(1)/569.3(1); b = 568.1(2)/719.1(2); c = 1960.2(2)/2042.6(4) pm; β 99.43(1)°/95.03(2)°; Z = (2+2) and 2, resp. X-ray structure determinations (Rw = 0.034/0.041) show both molecules to be centrosymmetric. Characteristic rounded bond lengths (pm) and angles (°) are: endocyclic P-C 185/184; C-P-C 82/81; P-C-P 98/99; exocyclic P-C 186/184; C=N l27/127; C=N-C 121/11.

2,4-Bis(phenylimino)-1,3-diphosphetane aus Thiocarbamoyl- und Carbamoyltrimethylsilylphosphanen (Acyl- und Alkylidenphosphane ; 26)

Die Bis(trimethylsilyl)phosphane R-P[-Si(CH3)3]2 1 (R = H3C a, H5C6 b, (H3C)3C c, H11C9 d) reagieren mit Phenylisothiocyanat zu Insertionsverbindungen, die sowohl in Losung als auch im Festkorper [2] als [(N-Phenyl-Derivat 3-2b eliminiert in Gegenwart geringer Mengen an festem Natriumhydroxid, die tert-Butyl- 3-2c bzw. Mesityl-Verbindung 3-2d auch in Abwesenheit des Katalysators Bis(trimethylsilyl] sulfan; die zunachst gebildeten, instabilen [(Phenylimino)-methyliden]phosphane 6 dimerisieren rasch zu den in Losung E/Z-isomeren 2,4-Bis(phenylimino)-1,3-diphosphetanen 7. Diese cyclischen Phosphane 7 sind uber die NaOH-katalysierte Abspaltung von Hexamethyldisiloxan auch aus den Addukten 2 des Phenylisocyanats an Bis(trimethylsilyl)-phosphane 1 zuganglich. Die Temperaturabhangigkeit der NMR-Spektren wird am Beispiel des thermisch hinreichend stabilen tert-Butyl-Derivates 7c eingehend untersucht. Bis(trimethylsilyl)phosphines R-P[-Si(CH3)3]2 1 (R = H3C a, H5C6 b, (H3C)3C c, H11C9 d) and phenyl isothiocyanate give insertion compounds which were identified as [CN-phenyl, N-trimethylsilyl)thiocarbamoyl]trimethylsilylphosphines 3-2 in solution as well as in the solid state [2]. In the presence of small amounts of solid sodium hydroxide the phenyl derivative 3-2b eliminates bis(trimethylsilyl) sulfane, whereas the tert-butyl 3-2c and the mesityl compound 3-2d show the same reaction even without a catalyst. The unstable [(phenylimino)methylidene]phosphines 6 formed first, dimerize rapidly to give 2,4-bis(phenylimino)-1,3-diphosphetanes 7 which in solution exist as mixtures of the E and Z isomers. Via a NaOH-catalyzed elimination of hexamethyldisiloxane these cyclic phosphines 7 can also be obtained from the adducts of phenyl isocyanate and bis(trimethylsilyl)phosphines 1. Taking the thermally sufficiently stable tert-butyl derivative 7c as an example, the temperature dependence of n.m.r. spectra is discussed in detail.

(Dimethylaminomethyliden)-phenylarsan, ein acyclisches Alkylidenarsan (Acyl- und Alkylidenarsane ; 5)

In the absence of a catalyst phenyl-bis(trimethylsilyl)arsine reacts only very slowly with excess dimethylformamide (4) to give (dimethylaminomethylidene)-phenylarsine and hexamethyldisiloxane. In the presence of small amounts of solid sodium hydroxide, however, the reaction is already finished after four days at + 20° C. Similarly, lithium phenyltrimethylsilylarsenide · DME, which can easily be obtained from 1 a and methyllithium in 1,2·dimethoxyethane (DME), and dimethylformamide also form the alkylidenearsine (8a) and lithium trimethylsilanoIate. The NMR spectra of 3a show the rotation of the dimethylamino group to be hindered with a barrier of about 63 kJ · mol-1.