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The dimeric tetraacetato bridged Rh2(0COCH3) has been obtained by the interaction of ammonium chlororhodate(II1) or rhodium(II1) hydroxide with acetic a~i d , l -~ Other (carboxylato)rhodium(II) compounds were prepared directly in a similar way or from the acetate by e x~h a n g e .~?~ Halo carboxylates (RCOO-, R = CC13, CF3, CH2C1, etc.) were prepared also by interaction of rhodium trichloride with the appropriate sodium salt in ethan01.~ The carboxylatcs are normally first isolated as a solvent adduct, e.g., [Rh(OCOR) z.CzH50H]2 but are easily converted to the unsolvated complex. The acetate is readily prepared in a modification of this last procedure. A similar method is satisfactory for the preparation of other lower carboxylates as well as halo carboxylates. ProcedureCommercial rhodium trichloride trihydrate (5.0 g.) and sodium acetate trihydrate (10.0 g.) in glacial acetic acid (100 ml.) and absolute ethanol (100 ml.) were gently refluxed under nitrogen for an hour.The initial red solution rapidly becomes green, and a green solid is deposited. After cooling t o room temperature the green

lutidine with triethylalane have been reported as calorimetrically determined in «-decane.24 For (C2-Hó)3A1• NC5H5, AH, = -21.2 kcal/mole, and for (02 6)3 1• 06 3(0 3)2, AH¡ = -18.0 kcal/mole.These enthalpy values do not include a correction for the enthalpy of dimerization of triethylalane. This value has been reported as -16.93 ± 0.23 kcal/mole in hexadecane.26 Since triethylalane is about 10-11% dissociated in a hydrocarbon solvent at ambient temperatures, one can only calculate the maximum enthalpy value by making the correction based on 100% dimerization of the triethylalane. Corrected in this way, these enthalpies become -29.7 kcal/mole for pyridine and -26.5 kcal/mole for 2,6-lutidine. These are surprising results since it is expected that triethylalane would have significantly larger frontal interaction than trimethylalane. The pyridines are generally weaker donors toward trimethylalane than the methylamines or ammonia but are comparable to (26) W.