REACTIONS OF GROUP-6 FISCHER CARBENE COMPLEXES WITH ALKYNES - EFFECT OF THE METAL ON THE PRODUCT DISTRIBUTION AND THE ISOLATION OF A NONTAUTOMERIZED CYCLOHEXADIENONE COMPLEX

The first comparative study on the effect of the nature of the metal on the reactions of unsaturated group 6 Fischer carbene complexes with alkynes is reported. The scope of the study includes both aryl- and alkenylcarbene complexes of chromium, molybdenum, and tungsten for both internal and terminal alkynes. Twenty-one different organic structural types have been isolated and characterized from these reactions, but in most instances phenols and indene (cyclopentadiene) products are the two most frequently observed. The general observation made is that phenol formation is favored over indene (cyclopentadiene) formation in the order chromium > tungsten > molybdenum. The effect of the concentration of the alkyne on the distribution between phenol and indene (cyclopentadiene) was also examined and was found to be most prevalent in the order molybdenum > chromium > tungsten. The bis(alkyne)(eta4-cyclohexadienone)molybdenum complex 107 has been isolated in which the final tautomerization to the phenol product has not occurred. This complex has been characterized by X-ray diffraction and provides support for the previous interpretations of the concentration effects for the reactions of chromium complexes. This complex is the first example of the long-proposed ultimate intermediate in these reactions. Crystal data for 107: space group P2(1)/c, Z = 4, a = 19.088(4) angstrom, b = 10.101(1) angstrom c = 14.578(3) angstrom, a = 90.0-degrees, beta = 109.917(13)-degrees, gamma = 90.0-degrees, R = 0.0598, and R(w) = 0.0788 for the 2405 reflections observed.