h3-Phosphaalkynes P = C -R [R = tert-butyl (la) or isopropyl (1 b)] react with (qScyclopentadienyl)biS(ethene)cobalt (2) or bis-(ethene)(q5-indenyl)cobalt (3) by displacement of ethene to yield the (q4-1,3-diphosphacycIobutadiene)cobalt complexes 4a, b and 5a,b. These are the first reported syntheses of a h3-l,3-diphosphacyclobutadiene (h3-1,3-dipho~phete)14,'*. Complex 4 reacts smoothly with the lone pairs of the phosphorus atoms to give the dinuclear or trinuclear cobalt complexes 6a,b and 7a,b. The structures of the new complexes 4-7 have been elucidated by spectroscopic methods, especially l3C-NMR spectroscopy. The Xray analyses of 4a and 5a confirm these structures.The parent compound of the phosphaalkynes, phosphaacetylene (HCEP), was first generated by Gier') in 1961. It is a highly reactive compound which, like some of its simple substitution products, is stable only at low temperature*). Systematic investigations of their synthetic potential began only after phosphaalkynes with sterically bulky organic substituents, which are stable at room temperature, had been prepared on a laboratory scale'). It was found that h3-phosphaalkynes are ideal partners for reactions with 1,3-dipole^^^.'.^) or 1,3-dienes5). They thus react very similarly to alk ynes.It was therefore of interest to carry out cycloadditions with h3-phosphaalkynes on transition metal compounds. The likelihood that this idea could be realized was enhanced after it became clear that h3-phosphaalkynes are nearly always bound 'side on' in transition metal complexes. Mononuclear complexes of platinum6), dinuclear complexes of cobalt6"'), molybdenum*), and nickel9) and trinuclear metal complexes") have been described, all having 'side on' complexation, the last mentioned containing a third metal atom bonded to the free electron pair of the phosphorus atom. The only exception is found in a recently reported series of molybdenum complexes in which the phosphaalkyne is q1 bound, probably for steric reasons").In this paper we describe in detail the reactions of the phosphaalkynes P-C-R [R = tert-buty13") (la) or isop r~p y l~~) (1 b)] with (11'-cyclopentadienyl)bis(ethene)cobalt (2)' 2, or bis(et hene)( q '-inden y 1)cobalt (3)' 2~1 3), which proceed by smooth cyclodimerization of 1 to form the corresponding (h3-1,3-diphosphacyclobutadiene)cobalt complexes. Our results with l a and 2 have already been published in a short communication14), which appeared almost simultaneously with the report by an English research group of the preparation of q5-cyclopentadienyl-1,3-diphosphacyclobutadiene complexes of cobalt and rhodium from 1 "I. ResultsWhen (q '-c yclopen tadien yl)bis(et hene)cobal t (2) reacts with excess 2-tert-butyl-1-phosphaacetylene (1 a) or 2-isopropyl-1-phosphaacetylene (1 b) at -30 to -5"C, the corresponding (1,3-diphosphacyclobutadiene)cobalt complexes 4a or 4b are obtained in 67 and 80% yield, respectively. In order to achieve higher yields of 4 it is better to use an excess of 1, since the free electron pairs of both phosphorus atoms of 4 a...

The first diphosphacyclobutadiene with three‐coordinate phosphorus could be stabilized as cobalt‐complexed compound 3 by dimerization of the phosphaalkyne 1 in the presence of the cobalt complex 2. If 2 is present in excess, di‐ and tri‐nuclear cobalt complexes are also formed, by coordination of the fragment [(C5H5)(C2H4)Co] to the P atoms of 3.

for their help with the X-ray diffraction analysis. Anyew Chrm IRI Ed Engt 26 (1987) No 9 0 YCH Verlagsgesellschaft mbH, 0-6940 Wernherm. 1987 0570-0833/87/0909-0909 $ 02 50/0

zu einem iiberraschenden Ergebnis: Statt der erwarteten Reaktion beobachtete man bei 40°C die Umlagerung von la zum 5-Amino-I-p-chlorbenzyl-4-pivaloylimidazol 3a in 25% Ausbeute. 4a J I J 3a 0 c1 2a [ ' I Priv.-Doz.

Ein partiell gespaltenes 1,3,5‐Triphosphaprisman‐Derivat 1 entsteht in der Koordinationssphäre von Vanadium, wenn tBuCP mit η6‐Naphthalin(η5‐pentamethylcyclopentadienyl)vanadium in THF umgesetzt wird. Das Triphosphaprisman‐Derivat zeigt bei Raumtemperatur in Lösung dynamisches Verhalten, und es reagiert mit CO in einfacher Weise zu dem dunkelgrünen 1,3,5‐Triphospha‐Dewar‐Benzol‐Komplex 2.magnified image