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These data show that I from the second method has two NMe proton peaks in a ratio of 1:2 a t 6 = 4.28 and 4.90 upfield from benzene. All the other spectra contain these two peaks in the same ratio, but other peaks are also present. In the spectra of crude products and in the 90 and 100 OC sublimate from both methods, another pair of peaks is located a t approxiinately 6 = 4.25 and 4.78 upfield from benzene and in the ratio of 1:2. These two closely spaced pairs suggest the presence of two forms of Be(NNIe2)2 of similar structure.If Be(N&11e~)~ were a cyclic trimer as suggested by Coates ( I ) , there should be two types of NhIe protons in a ratio of 1:1, that is, there should be 18 methyl protons bonded to terminal NMez groups and 18 protons on the bridging NA' Ie2 groups. Since the ratio of the two types of NMe protons is 1:2, a trimeric structure of the type is indicated to achieve a maxiinuin coordination for beryllium. The other form of Be(NMez)z may be another configuration of this trimer; for example, there may exist cis and trans forms for the terminal NMez groups.Only I of the second method appears to be a pure compound; hence, the molecular weight of this substance was the only one measured. The values 308 and 311 (calcd. 291.3 for Be(NMe2)z trirner) indicate this material is trimeric in freezing benzene; therefore, the form of Be(NMe2)2 obtained by sublimation a t 65 OC is more accurately represented by the structure shown above than by the cyclic form.

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