Preparation, properties, and reactions of metal-containing heterocycles .92. Steric and solvent effects of the different reaction patterns of activated alkynes with diphosphamanganacyclopropanes

The product pattern of the reaction of the alkynes ZC drop CZ (4-11) [Z = CO(2)R: R = Me (4), Et (5), nPr (6), iPr (7), nBu (8), nPent (9), neo-Pent (10), cyc-Hex (11)] with the diphosphamanganacyclopropanes (OC)(4)Mn-P(1)P1/2-P(2)R(2) (1-3) depends on the polarity of the employed solvent. Whereas in n-hexane the diphosphamanganabicyclo[3.3.0]octadienones 12a-q, the diphosphamanganocyclopentenes 13a-h, and the triphosphamanganabicyclo[3.2.0]heptenone 14a-h are formed, in THF only the five-membered heterocycles 13 occur. Compound 14d is easily oxidized to the corresponding oxide 15d. According to X-ray structural analyses, both 14d and 15d crystallize in the space group P (1) over bar. The Lewis basic properties of the phosphorus atom P-2 in the heterocycle 1 were corroborated by reaction of 1 with THFCr(CO)(5) leading to the adduct (OC)(4)Mn-P(1)R1/2-P-2(R(2))Cr(CO)(5) (16). Quantitative P-31{H-1}-NMR investigations in CDCl3 enable the determination of the product ratio 13/12 as a function of the steric encumbrance of the ester substituents. An increase of the steric hindrance leads to the preferential formation of the monocyclic compounds 13. If the steric demand at the phosphorus atom P-2 is released, only the bicyclic compounds 12i-q are formed.