Comparison of the donor properties of dimethylcyanamide and acetonitrile

Abstract

The disilicides of Nd-Dy have relatively small c values (0.750 > X S~/ X~I > 0.725), so that the other two axes must increase, which is achieved by the formation of vacancies in one of the Si chains and by increase of the axis dependent on it. The structure of these silicides is therefore orthorhombic and nonstoichiometric.In the digermanides of La-Ce, a large metal and a nonmetal are present (0.750 > R G~/ R N > 0.725). The value of c is large, and, in order to maintain the value for the cell volume, one of the other two axes must de-crease. This is achieved, as can be seen from the orthorhombic structure, by the incomplete filling of one of the nonmetal chains by Ge atoms, so that these digermanides will be orthorhombic.In the digermanides of Pr-Sm the length of c is of an intermediate value (0.760 > Rc~/R,\I > 0.750). The nonmetal chains--depending also on the c axis-are not large enough to accommodate all of the Ge atoms, and vacancies appear in both the a-and b-dependent chains, resulting in nonstoichiometric tetragonal structures.Thermodynamic and spectrochemical data on the donor properties of dimethylcyanamide, ( C H I )~N C S , toward chargetransfer types of acids, conventional Lewis acids, and nickel(I1) are reported. Evidence from changes in the infrared and nmr spectra upon coordination is interpreted to indicate that the nitrile nitrogen is the donor atom. The C'I-H coupling constants are very informative in elucidating the properties of this donor and the structure of these adducts. The donor properties of N,N-dimethylcyanamide are compared with those of acetonitrile and the differences are discussed.

Urea–Boron Trihalide Adducts. I. The Boron Trifluoride Adduct of Tetramethylurea

“…(ii) 13C-'H Coupling in N-Methyl Groups Henneike and Drago have used changes in 1 3 C -'~ coupling constants of N-methyl groups on complexation with BF, as an empirical test for the donor site in dimethylcyanamide (18). Complexation direct to the nitrogen of the N-methyl group was shown to cause large increases in J13,_ , , (8-1 1 Hz in aliphatic amines), whereas complexation at a site two bonds farther removed, as in dimethylacetamide, causes much smaller increases (< 1 Hz).…”

“…It appears to be somewhat more consistent with nitrogen donation than with oxygen donation, since a rapid chemical exchange of BF, between the two nitrogens could average a change in J13,-1H of 6.4 Hz to the observed value. However, the criterion of changes in J13c.1E, has been applied to only a limited number of compounds (18) and may have limited applicability. Thus the 13C-'H coupling constant data do not exclude oxygen donation in TMU.BF,.…”

N−CN Bond Cleavage of Cyanamides by a Transition-Metal Complex

“…Coordination of cyanamide to the 16e Fe species, Cp(CO)Fe(SiEt 3 ), through the amino nitrogen, may reduce the activity of the iron complex toward R 2 N−CN bond cleavage. Derivation of cyanamide into the borane adduct at the amino nitrogen, R 2 N(BX 3 )CN (X = H, F), might engender more effective R 2 N−CN bond cleavage because of masking of the lone pair electrons on the amino nitrogen. The results (Table , entries 7−9) showed that the introduction of borane into cyanamide did not facilitate R 2 N−CN bond cleavage; instead, it reduced the activity, presumably because of steric hindrance.…”

Strong bond cleavage promoted by silyl group migration in a coordination sphere

“…Derivation of cyanamide into the borane adduct at the amino nitrogen, R 2 N(BX 3 )CN (X = H, F) [29], might engender more effective R 2 N-CN bond cleavage because of masking of the lone pair electrons on the amino nitrogen. The results (entries 7-9) showed that the introduction of borane into cyanamide did not facilitate R 2 N-CN bond cleavage; instead, it reduced the activity, presumably because of steric hindrance.…”