Reactions of Terphenyl-Substituted Digallene (ArGaGaAriPr4)-Ga-iPr4 (Ar-iPr4 = C6H3-2,6-(C6H3-2,6-Pr-i(2))(2)) with Transition Metal Carbonyls and Theoretical Investigation of the Mechanism of Addition

摘要

The neutral digallene (ArGaGaAriPr4)-Ga-iPr4 (Ar-iPr4 = C6H3-2,6-(C6H3-2,6-Pr-i(2))(2)) was shown to react at ca. 25 degrees C in pentane solution with group 6 transition metal carbonyl complexes M(CO)(6) (M = Cr, Mo, W) under UV irradiation to afford compounds of the general formula trans[M(GaAriPr4)(2)(CO)(4)] in modest yields. The bis(gallanediyl) complexes were characterized spectroscopically and by X-ray crystallography, which demonstrated that they were isostructural. In each complex, the gallium atom is two-coordinate with essentially linear geometry, which is relatively rare for gallanediyl-substituted transition metal species. The experimental data show that the gallanediyl ligand :GaAriPr4 behaves as a good sigma-donor but a poor pi-acceptor, in agreement with prior theoretical analyses on related systems. In addition, the monogallanediyl complex Mo(GaAriPr4)(CO)(8) was synthesized by reacting (ArGaGaAriPr4)-Ga-iPr4 with two equivalents of Mo(CO)(5)NMe3 in THE solution. The mechanism of the reaction between (ArGaGaAriPr4)-Ga-iPr4 and Cr(CO)(6) was probed computationally using density functional theory. The results suggest that the reaction proceeds via an intermediate monogallanediyl complex, Cr(GaAriPr4)(CO)(5), that can be generated via two pathways, one of which involves the dimeric (ArGaGaAriPr4)-Ga-iPr4, that are possibly competing. (ArGaGaAriPr4)-Ga-iPr4 was also shown to react readily under ambient conditions with Co-2(CO)(8) to give the monosubstituted dicobalt complex Co-2(mu-GaAriPr4)(y-CO)(CO)(6) by X-ray crystallography. The :GaAriPr4 unit bridges the Co-Co bond unsymmetrically in the solid state. No evidence was found for incorporation of more than one :GaAriPr4 unit into the dicobalt complex.