COUPLING OF CO TO HC-EQUIVALENT-TO-COET IN DIMANGANESE CARBONYL-COMPLEXES

Three new compounds (OC)4Mn[C(OEt)=C(H)C(=O)]Mn(CO)5, 1,Mn2(CO)8[mu-C=C(H)C-(OEt)=O], 2, and Mn2(CO)8{mu-O=C[C(H)=C(OEt)]2}, 3, were obtained in low yields when solutions of Mn2(CO)10 and HC=COEt were irradiated (UV). The yield of 3 was significantly larger in the thermal reaction of Mn2(CO)9(NCMe) with HC=COEt, but 1 was not formed. Compound 1 was characterized by a single-crystal X-ray diffraction analysis. The molecule contains a metallacyclic ring formed by the coupling of one molecule of HC=COEt to one CO ligand. The oxygen atom of the CO group is coordinated to the metal atom. Compound 3 was converted to its bis-PMe2Ph derivative Mn2(CO)6(PMe2Ph)2{mu-O=C[C(H)=C(OEt)]2},4, which was then characterized by a single-crystal X-ray diffraction analysis. Compound 4 contains two metallacyclic rings formed by the coupling of two HC=COEt alkynes to one CO ligand. The oxygen atom of the carbonyl group is coordinated as a bridge between the two metal atoms. Compound 3 added 1 equiv of CO when exposed to a CO atmosphere in the presence of AlCl3 to yield the compound Mn2(CO)9{mu-O=C[C(H)=C(OEt)]2},5, in 90% yield. An X-ray diffraction analysis of 5 showed that one of the metallacyclic rings had been opened by the cleavage of one of the Mn-O bonds and the addition of CO to one of the manganese atoms to form a Mn(CO)5 grouping. In the absence of AlCl3 and CO, 5 slowly converted back to 3 at 25-degrees-C, 96% yield, in 24 h. When 3 was treated with HCI or NaBH4, one of the manganese atoms was removed and the new compound Mn(CO)4[C(OEt)=(H)C(O)C(H)=CH(OEt)], 6 was formed in 90% yield. Compound 6 was also characterized by a single-crystal X-ray diffraction analysis. This compound is structurally similar to 5 except that the Mn(CO)5 grouping was replaced with a hydrogen atom. Crystal data: For 1, space group = P2(1)/n, a = 12.088(2) angstrom, b = 10.521(3) angstrom, c = 15.726(3) angstrom, beta = 108.14(2)-degrees, Z = 4, 1440 reflections, R = 0.027; for 4, space group = C2/c, a = 26.271(7) angstrom, b = 9.130(2) angstrom, c = 15.616(5) angstrom, beta = 113.90(2)-degrees, Z = 4, 1226 reflections, R = 0.038; for 5, space group = P2(1)/n, a = 7.565(2) angstrom, b 22.788(4) angstrom, c = 13.015(2) angstrom, beta = 92.71(2)-degrees, Z = 4, 1515 reflections, R = 0.032; for 6, space group = P1BAR, a = 9.207(1) angstrom, b = 10.428(2) angstrom, c = 8.911(1) angstrom, alpha = 105.89(1)-degrees, beta = 93.40(1)-degrees, gamma = 70.34(1)-degrees, Z = 2,1826 reflections, R = 0.032.