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The reaction of the (diisopropy1amino)phosphaethyne (1) with diazo compounds of the type R1R2C=N2 (2a-2c) unexpectedly leads in high yields (SO-SO%) to the l-aza-3,4-diphospholene derivatives 3a-3c, a new class of heterocycles.NMR investigations of the analogous reaction of 1 with diazocyclopentadiene 2d show that the multi-step formation of 3a-3c proceeds via the l-aza-3,4-diphospholes 6a-6d as intermediates.Phosphaalkynes RC=P exhibit a pronounced reactivity towards 1,3-dipoles and, therefore, undergo [3 + 21 cycloaddition with diazo compounds R1(H)C=N2 or R1R2C=N2 yielding regiospecifically 1 H-l,2,4-or 3 H-l,2,4-diazaphospholes[2]. Scheme 1In order to examine the cycloaddition potential of aminosubstituted phosphaalkynes R2N-C=P['s3I in comparison with the alkyl compounds RC=P we studied reactions of iPr2N-C=P (1) with diazomethane derivatives. With the reactants R'(H)C=N2 the 1,3-dipolar cycloaddition of 1 proceeds as in the case of the alkyl-substituted phosphaalkynes [eq. (la)] affording 1 H-l,2,4-dia~aphospholes[~], however, with loss of regioselectivity. Hence formation of the regioisomeric 1 H-l,2,3-diazaphospholes as side products is observed. Using R1R2C=N2 (2a-2c) as 1,3-dipolar reagents, we found a surprising substituent effect for 1 leading to the novel phosphaheterocycles 3a-3c according to Scheme 2 and not to the expected 3H-or 4H-1,2,4-diazaphospholes [eq. (1 b)].The reactions of 1 with 2a-2c take place at 25 "C in toluene solution with evolution of N2 and elimination of iPr2N-C=N which is collected in a cold trap (-196°C) [ and detected by GC-MS spectroscopy. During this process the color of the reaction mixture changes from red to brown. 31P-NMR control measurements indicate complete consumption of 1 together with an almost quantitative generation of 3a-3c after 3 to 5 hours. While 3a and 3c are stable at room temperature, even in organic solvents, the mixture of the diastereomers 3b undergoes a slow decomposition in toluene solution giving rise to the formation of a series of unidentified phosphorus-containing compounds. The molecular structures of 3a-3c were deduced from spectroscopic investigations and conclusively ascertained by an X-ray diffraction study of single crystals of 3c. The mass spectra (70 eV) of 3a and 3c show the molecular peaks M+(3a) = 520 and M+(3c) = 516 with relative intensities of 52 and 22%, respectively. The 31P resonances of 3a-3c result from an AB spin system and appear in the high-field region (lip = -109.6 to -128.6) with lJ(PA,PB) couplings of 190-203 Hz. Chemical shifts and coupling constants are characteristic of diph~sphjranes [~], especially for spirocyclic derivativesL61. Due to the chirality of the P atoms in 3a-3c

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2‐(Diisopropylamino)‐phosphaethin iPr2N‐CP (2) reagiert mit den Ni(0)‐Komplexen [Ni(1,5‐Cyclooctadien)2] bzw. [Ni(CO)3(1‐Azabicyclo[2.2.2]octan)] zu dem neuen Komplex [{η4‐(iPr2NCP)2}Ni{η2‐(iPr2NCP)}] (5), der zwei Moleküle 2 in Form des 1,3‐Diphosphacyclobutadiensystems und ein Molekül 2 „side‐on”︁ koordiniert als π‐Liganden enthält. Die Molekülstruktur von 5, ermittelt durch Röntgenbeugung an Einkristallen, bestätigt die aus den NMR‐Daten (1H‐, 13C‐, 31P) abgeleiteten Spinsysteme und Rotationsbarrieren. Die PC‐Abstände des Vierrings sind mit 1,817(2) bzw. 1,818(2) Å erwartungsgemäß erheblich länger als die PC‐Bindung des η2‐koordinierten Phosphaalkins 2 [1,671(2) Å]. Bei den Umsetzungen von 2 mit [(Ph3P)2Pt(C2H4)] bzw. [Co2(CO)8] entspricht das koordinative Verhalten dem von Alkinen; sie liefern die Komplexe [(Ph3P)2Pt{η2‐(iPr2NCP)}] (7) mit side‐on gebundenem 2 bzw. [Co2(CO)6{η2‐η2‐(iPr2NCP)}] mit 2 als 4e‐Donorbrücke in quantitativer Ausbeute. Bei dem Versuch, aus 2 und CuCl bzw. CuI Kupfer(I)‐Komplexe des Aminophosphaalkins darzustellen, bildet sich unter Einwirkung von Luft und Feuchtigkeit als einziges isolierbares Produkt das 1λ3, 3λ5‐Diphospheten (iPr2N) (10) in beträchtlicher Menge (Reinausbeute: ca. 20%). Für 10 ergibt sich aus der Kristallstrukturanalyse eine enge Beziehung zu dem Diamino‐2‐phosphaallyl‐Kation [Me(iPr2N)]+ (12), dem 1,3‐Diphosphacyclobutadien‐Liganden (iPr2NCP)2 im Zweikernkomplex [{η1‐μ2‐(iPr2NCP)2}Ni2(CO)6] (3a) sowie zu den von Becker et al. [11 b, 35] dargestellten Heterocyclen (dme)2LiOE2′ (E′ = S, 11a; E′ = Se, 11b).