λ ³ ‐1,3‐Diphosphacyclobutadiene‐Cobalt Complexes by Cyclodimerization of λ ³ ‐Phosphaalkynes

Abstract

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...

Aromaticity and Antiaromaticity of Four-Membered P-Heterocycles

“…The computed activation energy values for the previously described valence isomerization was considerably lower for VI (13.0 kJ mol -1 ) than that for cyclobutadiene, owning to its modest antiaromaticity [53]. The first synthesis of VI was reported in 1986 by two independent groups [89][90][91]. The dimerization of tertbutylphosphaetylene (1) was carried out in the coordination field of different metals (36), yielding different Co, Ir, and Rh complexes of VI (Scheme 14).…”

Zur Reaktion vontert-Butyl-phosphaalkin mit Molybdänkomplexen

“…Er ist nicht planar; das CO-Fragment ist um 26°aus der Ebene des P 2 C 2 -Fragmentes ausgelenkt. Wa È hrend ¹Kopf-Schwanzª-Cyclodimerisationen von Phosphaalkinen in der Koordinationsspha È re von Ûbergangsmetallen sehr ha È ufig sind [11,12], berichteten erst vor kurzem Binger et al u È ber die erste ¹Kopf-Kopfª-Cyclodimerisierung zweier tBuC≡P-Moleku È le an einem (cot)Ti-Komplexfragment unter Bildung eines 1,2-Diphosphacyclobutadienylliganden [17].…”

“…0,3014 (6) ±0,0651 (12) 0,034(6) C (5) 0,5568(11) 0,2421 (5) ±0,0954(9) 0,028(5) C (6) 0,7232(11) 0,0581(5) 0,1615(9) 0,036(5) C (7) 0,8164 (11) 0,0633 (5) 0,2332 (9) 0,027(5) C (8) 0,6391 (15) 0,0064 (6) 0,1923 (12) 0,032(5) C (9) 0,7738 (15) 0,0407 (6) 0,0740 (11) 0,024(4) C (10) 0,4802 (1) (20) 0,3954(12) 0,4725 (5) 0,1094(9) 0,033(2) C (21) 0,3485(9) 0,5188(3) 0,1019 (7) 0,038(3) C (22) 0,1662 (11) 0,3198 (5) 0,1333 (8) 0,056(4) C (23) 0,1959(11) 0,1922(5) 0,1299 (9) 0,058(4) C (24) 0,1039 (13) 0,3838 (5) 0,1329(10) 0,040(3) C(25) 0,1253 (13) 0,4173 (5) 0,0436 (9) 0,041(3) C(26) 0,1397 (15) 0,4246 (6) 0,2123 (11) 0,060(4) C (27) ±0,0231 (15) 0,3733 (7) 0,1423 (13) 0,067(4) C(28) 0,1517 (11) 0,1226 (5) 0,1351 (9) 0,029(2) C(29) 0,1224 (17) 0,1075 (7) 0,2223 (12) 0,069(4) C(30) 0,2481 (15) 0,0760 (7) 0,1027 …”

Synthesis, multinuclear NMR, and solution conformation of (η5-indenyl)CoIRfL complexes (L = CO, P-donor)

“…TIndenyl complexes are known for cobalt in formal oxidation states 111, 11, and I with the very air-sensitive Co(1) derivatives formulated as ( q 5 -i n d e n y l )~o~2 (L = ethylene (23,24), CO (25,26), PPh, (27), PMe, (28), P(OR), (29) or L, = cyclic and acyclic dienes (3,4,23) or vinylketenes (27)) being the most numerous. Fewer Co(II1) complexes have been re orted (21,27,28,30) and only one crystal P.…”