Reactions of Trisodium Tetracarbonylmetalates(3-) of Manganese and Rhenium with Brϕnsted Acids and Other Electrophiles. Synthesis of H₂M(CO)₄^- (M = Mn and Re), (CH₃)₂Re(CO)₄^-, the First Dialkyl Derivative of a Carbonylmetalate Trianion, and Related Anionic Species

Treatment of hexamethylphosphoramide (HMPA) solutions of the trisodium tetracarbonylmetalates(3-) of manganese and rhenium with excess liquid ammonia causes precipitation of very thermally stable materials (dec ≥300 °C) that are isolated in high yields (85-95%) and represent the first available pure samples of unsolvated Na₃[M(CO)₄]. Infrared and NMR spectral studies of the protonation of Na₃[M(CO)₄] in HMPA show initial formation of the new monohydrides, HM(CO)₄^2-, which are then converted quantitatively to the dihydrides, H₂M(CO)₄^-. The new manganese dihydride, which is isoelectronic with the first known carbonyl hydride, H₂Fe(CO)₄, and the previously established rhenium complex are isolated in high yields (75-80%) as the pure salts, [Ph₄As] [cis-H₂M(CO)₄]. The monohydride dianions, HM(CO)₄^2-, also react with Ph₃SnCl to provide cis-H(Ph₃Sn)M(CO)₄^-, which can be isolated as the Et₄N⁺ salt for rhenium. The initial successful alkylation reactions of carbonylmetalates(3-) are also reported. Treatment of Na₃[Re(CO)₄] with methyl p-toluenesulfonate (MeOTs) in HMPA first provides MeRe(CO)₄^2- (identified by IR), which can be protonated or further methylated to give cis-H(Me)Re(CO)₄^- or cis-(Me)₂Re(CO)₄^-, both of which are isolated in good yields (70-80%) as Ph₄E⁺ (E = P, As) salts. These represent the first isolated alkyl derivatives of metal carbonyl trianions. IR, ¹H, and ¹³C NMR spectra also confirm that Na₃[Re(CO)₄] reacts with 1,4-butaneditosylate to provide solutions of the somewhat thermally unstable rhenacyclopentane CH₂CH₂C-H₂CH₂Re(CO)₄^-, the initial example of an anionic 18-electron metallacycloalkane. Infrared, ¹H, and ¹³C NMR spectral data have been obtained for many of these compounds and are compared with those of analogous previously known iron and osmium species.